US3147280A - Preparation of benzofuran derivatives - Google Patents

Description

United States Patent PREPARATIQN OF BENZOFURAN DERIVATIVES This application is a division of application Serial No. 293,564, filed July 8, 1963.

A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sub-licences for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to and has among its objects the provision of novel methods for preparing benzofuran derivatives and the provision of new compounds so prepared. A particular object of the invention is the synthesis of benzofuran derivatives by oxidation of fiavylium salts. Another object of the invention is the provision of methods for preparing coumestrol and related compounds from benzofurans.

Further objects and advantages of the invention will be evident from the following description wherein parts and percentages are by weight unless otherwise specified.

In accordance with the invention, benzofuran derivatives are prepared by oxidizing flavylium salts. By this technique many different types of benzofuran compounds can be prepared in a single step and with yields at least as high as 50% of the theoretical. The reaction may be exemplified by the following formulas which depict the synthesis of 2-(4-hydroxyphenyl)-3 acetylbenzofuran from 3-methyl-4'-hydroxyflavylium chloride, i.e.

C-CHa The process of the invention is by no means limited to the example above but can be applied to fiavyliurn salts of all kinds and generically the synthesis may be represented by the formulas wherein each R and R are radicals which are inert in the It is evident from the above formulas that the oxidation has the end result of rearranging the benzopyrylium ring into a benzofuran ring and conversion of the ring carbon atom at position 3 into a side-chain carbonyl Otherwise stated, the synthesis may be considered to involve (a) opening of the benzopyrylium ring between the 2 and 3 positions, (12) reclosing of the ring between the 2 and 4 positions, and (c) oxidation of the ring carbon atom originally at position 3 to a side-chain carbonyl radical. This sequence is depicted below merely to explain the end resultwhich has been definitely determined-but without delimiting the invention to the particular mechanisms shown:

A significant advantage of the process of the invention is its versatility in that many different kinds of benzofuran derivatives may be prepared simply by selecting the appropriate flavylium salt starting material. As evident from the preceding formulas, the various substituents (R and R) are unaltered in the synthesis and thus are present in the benzofuran product. Indeed, all the substituen-ts designated by R maintain their same relativeposition. In the case of the substituent at position 3, that is, R, the rearrangement of the benzopyrylium ring to a benzofuran ring and formation of the carbonyl side group give rise to a new side-chain at the corresponding position of the *benzofuran nucleus. Specifically, the substituent R present on the flavylium salt is converted into a substituent O in This unique transformation permits one to create many dilferent types of substituents at position 3 on the benzofuran product. For example, if R is a hydrocarbon group or a substituted hydrocarbon group, a ketone group is formed, e.g., a -CH group is converted into a group, a C H -OH group is converted into i-CBH4OH a -C H OCH group is converted into a group, etc. If R is an ether radical, an ester group is formed, e.g., an -OCH group is converted into i -COOH an OC H,;OCH group is converted into etc. Such ester formation is particularly advantageous where it is desired to synthesize benzofuran derivatives having a carboxyl group (-COOH) at position 3. In such case, the oxidation is applied to a fiavylium salt having an ether group in the 3 position, for example, a methoxy, ethoxy, phenoxy, or benzoxy group. This then yields the benzofuran derivative having an ester group at position 3. Thus, the above stated examples yield the carbomethoxy, carboethoxy, carbophenoxy, and carbobenzoxy groups, respectively, at position 3 in the benzofuran products. These ester groups or any otherscan then be readily converted to carboxyl by contacting the product with aqueous alkali. The significance of all this is that the process of the invention provides a technique by which one can synthesize benzofurans containing particular substituents at position 3, which compounds either cannot be prepared by conventional syntheses or which would require elaborate multi-step syntheses with very poor yields if they could be synthesized.

As noted hereinabove, the process of the invention is of a very versatile character and may be applied to all types of flavylium salts where in R and R are radicals which are not affected by the oxidation reaction. Typical of such substituents are those set forth below by way of illustration but not limitation:

The radicals represented by the Rs may typically be such radicals as hydrogen; hydroxy; lower alkyl, e.g., methyl, ethyl, propyl, isopropyl, butyl; lower alkoxy, e.g., methoxy, ethoxy, propoxy, isopropoxy, butoxy; benzoxy; phenoxy; etc. The radical represented by R may typically be such radicals as lower alkyl, e.g., methyl, ethyl, propyl, isopropyl, butyl; lower alkoxy, e.g., methoxy, ethoxy, propoxy, isopropoxy, butoxy; phenyl; lower alkylphenyl; lower alkoxyphenyl; phenoxy; lower alkylphenoxy; lower alkoxyphenoxy; benzyl; lower alkylbenzyl; lower alkoxybenzyl; benzoxy; lower alkylbenzoxy; lower alkoxybenzoxy; carboxy-lower alkyl; carboxy-lower alkoxy; carboxyphenyl; carboxyphenoxy; carboxybenzyl; carboxybenzoxy, etc. The radical represented by X is usually the chloride ion but may be the anion of other acids, e.g., the bromide, sulphate, bisulphate, benzenesulphonate, paratoluenesulphonate, etc. ion.

The oxidation in accordance with the invention basically involves contacting the flavylium salt with an oxidizing agent which contains a peroxide linkage, such compounds being commonly referred to as peroxygen oxidizing agents. Typical of these are hydrogen peroxide, sodium peroxide, acetyl peroxide, benzoyl peroxide, tertiary butyl hydroperoxide, alkali metal salts of tertiary butyl peroxide, ascaridole, urea peroxide, alkali metal salts of per-acids such as peracetic, persulphuric, perbenzoic, and the like. Generally, the reaction is carried out in an inert solvent such as methanol, ethanol, isopropanol, ter- 7 tiary butyl alcohol, or the like. To assist in dissolving the flavylium compound it is often necessary to add water to the solvent and more preferable than plain water is a conventional buffer solution having a pH of about four to six. Generally, it is preferred to heat the aqueousalcohol system to assist in dissolving the fiavylium salt and it may be heated to as high as its boiling point which may be as high as about 100 C. in appropriate cases. The temperature at which the reaction is carried out is not critical and may range from 100 C. down to room temperatures or even below room temperature although it is obvious that the speed of reaction will be slower at the lower temperatures. A convenient plan of operation is to dissolve the flavylium salt in the alcohol-water or alcohol-buffer system, applying heat to bring the system to about 70-100 C., and then add the oxidizing agent and allow the system to stand without applying any more heating. The reaction proceeds quite rapidly under such conditions and the product is formed in a matter of a few minutes to an hour at the outside. The amount of oxidizing agent used is generally in excess of the stoichiometric amount. The product is easily recovered from the system by diluting it with water. The precipitated product can then be collected and recrystallized in conventional manner from aqueous methanol or methanol-acetone mixtures.

The benzofuran derivatives, which are the subject of this invention, form a class of compounds which exhibit estrogenic properties directly or which can be readily converted into compounds which are estrogenic. Particularly effective in this regard are the compounds which contain hydroxy and/or methoxy groups on the fused benzene nucleus and on the side-chain phenyl nucleus. Because of this estrogenic activity, the products of the invention may be employed in animal husbandry in the same manner as conventional with diethylstilbestrol and other known estrogenic agents-for the purpose of increasing weight gain and increasing efiiciency of feed utilization. To this end, the compounds of the invention may be administered to animals by incorporating them in conventional feeds; by addition to water or other fluid; by addition to grit fed to birds; by administration in capsules, pellets, or by injection; by implantation of pellets, and so forth. The amount of the compounds to be administered will, of course, vary depending on the type of animal, the body weight thereof, the physiological response desired, and the mode of administration. For example, where the benzofuran derivatives are administered in admixture with a feed, dosage may be that physiologically equivalent to about from 0.01 to 8 milligrams of diethylstilbestrol per lbs. of body weight per day. Generally, it is preferred to administer them by incorporation in a conventional feed. Thus the feed may consist mainly of vegetable material such as corn, wheat, barley, milo, hay, dehydrated alfalfa or other forage material, soybean meal, cottonseed meal, distillers grains, peanut meal, oat hulls, bran, corn stalks, corn cobs, sorghum, beet pulp, or the like. For a high-energy diet a major proportion of grain or oil-seed meal is preferred. In addition to the main vegetable portion, the feed may contain the usual supplements such as mineral salts, vitamin preparations, fish meal, fish oil, linseed oil, antibiotic supplements, and so forth. In general, the feed may contain on the order of 0.001 to 1 lb. of the benzofuran derivative per ton of feed. The benzofuran derivatives may be applied, for example, to chickens, turkeys, geese, ducks, swine, sheep, cattle, horses, and so forth. Thereby, im portant practical effects are gain, including increased rate of gain and increased efficiency of feed utilization. As noted above, the invention is of particularly practical value as applied to animals, such as steers, which are grown primarily for meat. Thus, by application of the teachings of the invention, the animals are caused to gain weight more rapidly and produce more flesh per unit weight of feed with resulting economic benefits.

Another phase of the present invention concerns the preparation of coumestrol and related compounds from benzofurans. Coumestrol is an estrogenic coumarinocoumarone which has been isolated from alfalfa and a variety of clover speciesBickotf and Booth, US. Patent 2,890,116. Coumestrol has also been synthesized (Emerson and Bickolf, US. Patent 2,884,427) and various derivatives thereof such as the esters and ethers have also been synthesized (Bickoff and Booth, U. S. Patents 2,929,713 and 2,987,398) and shown to have estrogenic properties.

By applying the principles described herein, coumestrol and various other coumarino-coumarones are synthesized by a procedure which is simple and which affords high yields. Basically, the synthesis involves the following steps: By oxidation of the appropriate flavylium salt, as described above, there is prepared a benzofuran containing an ester group at the 3 position and containing a hydroxy group on the phenyl ring in ortho position. This benzofuran is then contacted with acid whereby lactonization occurs and a coumarino-coumarone is formed. The

synthesis of coumestrol from 2',4',7-trihydroxy-3-meth0xy flavylium chloride is shown by the following formulas:

2,4,7-trihydroxy-3methoxy fiavylium chloride l oxidation I2- (2,4-dihydroxypheny1) -3-carbomethoxy-6-hydroxy beuzofuran l iactonization it i Flavylium salt l oxidation Benzofuran l laetionization R R I Coumarino-coumarone wherein the radicals represented by R and X are as described hereinabove and R" represents a hydrocarbon or a substituted hydrocarbon radical as, for example, lower alkyl, phenyl, benzyl, lower alkylphenyl, lower alkylbenzyl, lower alkoxyphenyl, lower alkoxybenzyl, etc. It is to be noted that the particular configuration of the radical represented by R is of no importance as it does not appear in the final product; it merely serves as a blocking 6 group during the oxidation. Accordingly, regarding the lactonization reaction, the radical may be any esterified carboxyl radical. It may also be observed that the 2' and 6 positions on the phenyl ring are equivalent and the same product is obtained whether the ortho hydroxy group is considered as being at the 2' position or the 6' position. In the event that both the 2' and the 6' positions are occupied by hydroxy, a single coumarino-coumarone is produced if the phenyl ring is substituted symmetrically; where the substitution is unsymmetrical, a mixture of two isomeric products will be produced. This distinction is further demonstrated by the following formulas:

l R on -OR B C Ii 0 (A) Symmetrical substitution on phenyl ring R OH | C-O R I] 0 Single product OH 1'; Q

| B OH C-OR R H O (B) Unsymmetrical substitution on phenyl ring )1 \..J I? OH R If (|)H I C-O OO R 11 R ll 0 0 Isometric products In preparing the cournarino-cournarones, the synthesis may be carried out by first producing the benzofur an derivative, isolating it, and then applying lactonization. However, isolation of the intermediate benzofuran is not necessary and ordinarily the lactonization is applied to the system containing the benzofuran as produced by the oxidation step. The lactonization step is carried out by exposing the benzofuran to acidic hydrolysis so that the ester group at position 3 is hydrolyzed and can then lactonize with the ortho hydroxy group on the phenyl ring. The acidic hydrolytic conditions are established as conventional in other lactonization procedures, by con tasting the benzofuran in an aqueous system with a strong acid, for example, hydrochloric, sulphuric, or benzenesulphonic, or the like. Heating, for example, up to a temperature of about 75-100 C., may be applied to hasten the lactonization. The coumarino-coumarones, particularly those which contain hydroxy and/ or metho-xy 7 v groups on the coumarine or the coumarone moieties, exhibit estrogenic activity and can be used for the same purposes as described above for the benzofurans, i.e., in animal feeding, to attain increased rate of gain and increased efiiciency of feed utilization.

The flavylium salts employed as starting materials in the preparation of the benzofurans or cournarino-coumarones are most readily prepared by the Robinson method (see, for example, D. D. Pratt and R. Robinson, J. Chem. Soc., 1923, page 74-5 et seq.) which involves condensation of (1) orthohydroxy benzaldehyde or its substituted derivatives with (2) acetophenone or the substituted derivatives thereof. By selection of the substituents on the respective reactants, any desired fiavylium derivative may be produced. Typical applications of this synthesis are also disclosed in my copending patent application, Serial No. 254,030 filed January 25, 1963.

EXAMPLES The invention is further demonstrated by the following illustrative examples.

The benzofuran products of Examples I to XIII have the following structure:

Example I PREPARATION OF 2-(4-HYDROXYPHENYL)-3-ACETYL BENZOFURAN o 'l StructurcFormula v1; 3: 41-011., 6:11, 7:11, 4'=OH 4'-hydroxyfiavylium chloride (30 g.) was mixed into boiling methanol (300 ml.) and then there was added buffer solution (300 ml.) and 30% aqueous H 0 ml). After mixing these components, heating was stopped and the solution allowed to cool to room temperature. It was observed that in a minute pale yellow crystals were forming in the system. After standing for one hour, water was added to bring the total volume to one liter and the precipitate was separated and recrystallized from acetone-methanol. The benzofuran product (15 g.) had a melting point of 173173.5 C. and displayed the following ultraviolet absorption characteristics: In ethanol: peaks at 234 and 313 and inflection at 260 m In ethanol plus sodium ethylate (0.02 N): peaks at 249, 268, and 365 mg.

The product was converted into various derivatives:

The acetate 60 t t Formula VI:3= -CCH3, 6 11, 7:11, 4=OCCH3 by reaction with acetic anhydride and sodium acetate; the 05 benzyl ether 0 (FormulaVI: 3: CCH [3:H, 7:11, 4: O-CH C H by reaction with benzyl chloride and alkali; and the methyl ether 0 1 (Formula VI: 3: &Cll;, 0:11, 7:11, 1: 0 CH by reaction with methyl iodide and alkali. The properties of these derivatives are as follows:

PREPARATION OF 2 (4-HYDROXYPHENYL) -3-ACETYL' 7-l\IETHOXYBENZOFURAN Structure-Formula VI: 3:-&CII3, 6:11, 7: OCII3, 4: OII

To boiling methanol (600 ml.) was added 3-methyl-8- methoxy-4'-hydroxy fiavylium chloride (60 g.), buffer solution (600 ml.), and 30% aqueous H 0 ml.). After mixing these components, heating was discontinued and the mixture allowed to come to room temperature. After standing for one hour, water was added to bring the total volume to about 2 liters and the precipitate collected and recrystallized from methanol-acetone. The benzofuran product (32 g.) was in the form of long colorless felted crystals, M.P. 222 C. and displayed the following UV absorption information: In ethanol: peak at 311, inflection at 263 m In ethanol plus NaOH: peaks at 252 and 362, inflection at 273 nm.

The product was converted into various derivatives: The acetate by reaction with acetic anhydride and sodium acetate; the benzoate O II (Formula VI: 3: --OCI I;, 6:I{, 7:0 CH9, 4: 0 i l C ll) by reaction with benzoyl chloride; the benzyl ether 0 II (Formula v1: 3: -e-orn, 0:11, 7: --0 CH3, 4': 0 01120.11,

by reaction with benzyl chloride and alkali; the methyl ether 0 II (Formula VI: 3: CC1I 6:11, 7:0 011;, 4: -0 CH by reaction with methyl iodide and alkali; the oxime of the methyl ether ifiIOH Formula VI: 3: C--CH 6:11, 7: -OGH 4': OCH

by reaction of the methyl ether with hydroxylarnine. Melting points of these derivatives were found to be:

M.P., C. Acetate 117 Benzoate Benzyl ether 153-154 Methyl ether 98 Oxime of methyl ether 158 Example III PREPARATION OF 2-PHENYL-3-ACETYL-7- METHOXYBENZOFURAN StructureFormula VI: 3=CCH 6:11, 7:OCH;, 4=II A. o-Vanillin (15.2 g.) and propiophenone (13.4 g.) were dissolved in a mixture of ethyl acetate (50 ml.) and ethanol (10 ml.). The solution was saturated with HCl gas and allowed to stand overnight. Then the long orange needles of 3-methy1-8-methoxyl fiavylium chloride which had formed were separated from the solution.

B. To boiling methanol (200 ml.) was added the fiavylium salt prepared above, buffer solution (50 ml.), and

aqueous 30% H (30 ml.). Then additional butler (50 and methanol (50 ml.) were added to keep the fiavylium salt in solution. Heating was discontinued and the system allowed to come to room temperatures. After standing for 20 minutes, excess water was added and the precipitated material was collected and recrystallized from methanol-acetone. The benzofuran product (9.2 g.) was 1n the form of long colorless needles, M.P. 107 C., and displayed (in ethanol) a peak at 289 mp. The oxime derivative IIIOH Formula VI: 3=(d-OH 61H, 7=OC'Hs, 4=I-I) and the benzal derivative Formula VI: 3=OCH=CHC6H5, 62H, 7=O CH3, 4=H of this product had melting points of 154 and 139-140 C., respectively.

Example IV PREPARATION OF 2-PHENYL-3-ACETYL-6- HYDROXYBENZOFURAN To boiling methanol (50 ml.) was added 3-methyl-7- hydroxyfiavylium chloride (4 g.), buffer solution (50 ml.) and 30% aqueous H 0 (8 ml.). After mixing these components, heating was discontinued and the system allowed to cool. After standing about 4 hours the system was diluted with water and the precipitated material collected and recrystallized from methanol-acetone. The benzofuran product was in the form of colorless crystals, M.P. 159-160 C. The acetate 0 (Formula VI: 3= (i!OH 6=-Oi 3--OH 7:11, 4 H) had a melting point of 72 C., the benzoate 0 (Formula VI: 3=("3OH3, 6=-Oid-CaH 7=H, 4=H had a melting point at 134 C.

Example V PREPARATION OF 2- l-METHOXYPHENYL) -3 ACETYL- 6-HYDROXYBENZOFURAN StructureFormula VI: 3=( i-CH 6:011, 7:151, 4=OOI-I3 To boiling methanol (40 ml.) was added 3-methyl-7- hydroxy-4'-methoXy-flavylium chloride (2 g.), 40 ml. buffer solution, and aqueous 30% H 0 (2 ml.). After mixing these ingredients, heating was discontinued and the system was allowed to cool. After standing about 2 hours the mixture was diluted with water and the precipitatcd material collected and recrystallized from wet methanol. The benzofuran product was in the form of flat, slightly yellow needles, M.P. ISO-151 C.

The acetate (Formula VI: 3: (dCH3, 6=OOCH3, 7=H, 4'=-o CH had a melting point of 93 C. and exhibited a peak at 311 m (in ethanol).

Example VI PREPARATION OF 2-(l-HYDROXYPHENYL)-3-ACETYL- 6-HYDROXYBENZOFURAN O I Structure-Formula VI: 3=(JCH 6:011, 7=H, 4=OH To-boilingmethanol (40 ml.) was added 3-methyl-7- hydroxy-4'-hydroxy fiavylium chloride (4 grams) and buffer solution (60 ml.). The solution was heated to boiling to completely dissolve the fiavylium salt. Then, aqueous 30% H 0 (8 ml.) was added and heating was discontinued. After standing for about 1% hours the sysn u u (Formula VI: 3=-COH3, 6:O C 06115, 7=H, 4=O C CuH5 the benzyl ether .1 (Formula VI: 3 0-011 6=0 011 0 11 7=H, 4=-0OH,0 H, the methyl ether 0 (Formula VI: 3=i JCH 6=-OCH3, 7:H, 4=OCH;) the benzal derivative 0 (Formula VI: 3=- JOH=oH-C H 6=OH, 7=H, 4'=oH) and the acetate of the benzal derivative 0 6=oiiOH 7=H, 4'=o-( ior,) Properties of these compounds were found to be:

Melting UV absorption, m point, C.

112 Peaks at 236 and 307.

Benzoate 143-14 Benzyl ether. 141-142 Peaks at 239 and 327. Methyl ether Benzal derivative 225 Acetate of benzal derivative 118 Example VII PREPARATION OF 2-(4METHOXYPHENYL)-3 CARBOPHENOXYBENZOFURAN ll Structure-Formula VI: 3=O-O C011 6:11, 7=H, 4=O CH3 A. 3-phenoxy-4-methoxy fiavylium chloride was prepared by condensing equimolar proportions of salicyl aldehyde and 4-methoxy-u-phenoxyacetophenone in ethyl acetate saturated with HCl gas.

B. To 200 ml. of boiling methanol were added 10 g. of the aforesaid fiavylium salt, 25 ml. of buffer solution and 25 ml. of aqueous 30% H 0 An additional 50 ml. of methanol and 25 ml. of buffer solution were added to clear the solution, then heating was discontinued and the system allowed to cool. After standing about an hour, excess water was added and the precipitated crystals were collected and recrystallized from wet methanol. The benzofuran product (4 g.) had a melting point of 92 C. and exhibited peaks at 229 and 319 m (in ethanol).

A portion of the product was treated with alkali to hydrolyze the carbophenoxy group at position 3 to a carboxyl group. The resulting compound (Formula VI: 3=COOH, 6=H, 7=H, 4=OCH had a melting point of 217 C. and exhibited a peak at 311 m (in ethanol). The carboxylic derivative was esterified with methanol to form the methyl ester 0 u (Formula VI: 3=COOH 6:11, 7:11, 4=-OCH;

This compound had a melting point of 81 C. and exhibited a peak at 311 me (in ethanol).

Example VIII PREPARATION OF 3-(CARBO-fZ-HETHOXY-PHENOXY)- 4METHOXYBENZOFURAN Structure-Formula VI:

OCH

A. 3-(o-methoxyphenoxy)-4--methoxy flavylium chloride was prepared by condensing equimolar proportions of salicyl aldehyde and 4-methoxy a (2 methoxyphenoxy)-acetophenone in ethyl acetate saturated with HCl gas.

B. To boiling methanol (20 ml.) were added 1 gram of the above fiavylium salt, 5 ml. of buffer solution and aqueous 30% H (2 ml.). Heating was discontinued and the system allowed to cool. It was noted that decolorization of the solution occurred very rapidly. After standing about minutes the system was diluted with water, the precipitated material collected and recrystallized from acetone-methanol. The product (0.45 g.) was in the form of colorless prisms, M.P. 126 C. A sample of the product hydrolyzed with alkali forms the carboxyl derivative (Formula VI: 3 COOH, 6 H, 7 H, 4=OCH having a melting point of 217 C., peak at 311 mu. A sample of the carboxyl derivative was converted to the methyl ester M.P. 81 C.

Example IX Preparation of benzofuran derivative having the strucproduct (0.97 g.) was in the form of cream-colored glistening needles, M.P. about 264 C., peak at 327 mg (in ethanol).

A sample of the product was methylated to produce the methyl ether-methyl ester. This compound had a M.P. of 119 C., peak at 322 m A sample of the product treated with aqueous alkali gave the carboxyl derivative (Formula VI: 3=COOH, 6=H, 7=H, 4'==OH), M.P. 224 C., peak at 316 m Example X Preparation of benzofuran derivative of the structure:

Q-on 01 A. 3-(4-methoxyphenoxy) 4-hydroxy flavylium chloride was prepared by condensing equimolar proportions OCH of salicyl aldehyde and 4-hydroxy-a-( l-methoxyphenoxy) acetophenone in ethyl acetate saturated with HCI gas.

B. To 40 ml. of hot methanol were added 2 grams of the above fiavylium salt, 15 ml. of butter solution, and 5 ml. of 30% H 0 solution. Heating was discontinued and the solution allowed to stand about 5 minutes. The reaction mixture was diluted with water, the precipitate collected and recrystallized from wet acetone-methanol. The benzoturan derivative (1.15 g.) was obtained as cream-colored glistening needles, M.P. 195 C., peak at 322 m The acetate had a melting point of 161 C., peak at 307 m Example XI PREPARATION OF 2-(4-\[ETHOXYPHENYL)-3-CARBO- PHENOXY-T-METHOXYBENZOFURAN A. 3-phenoxy-8,4-dimethoxyfiavylium chloride was prepared by condensing equimolar proportions of 2-hydroxy-B-methoxy benzaldehyde and 4-methoxy-a-phenoxy acetophenone in ethyl acetate-glacial acetic acid saturated with HCl gas.

B. To ml. of hot methanol were added 2 grams of the above fiavylium salt, 5 ml. of buffer solution, and 5 ml. of 30% H 0 solution. After allowing the mixture to stand about 5 minutes without heating, it was diluted With water and the precipitated solid collected and recrystallized from acetone-methanol. The benzofuran product (0.65 g.) had a melting point of 161 C. and peak at 317 m A sample of the product treated with aqueous alkali gave the carboxy derivative (Formula VI: 3=-COOH, 6=H, 7=OCH 4=OCH M.P. 203-204 0, peaks at 309 and 260 m Example XII PREPARATION OF 2-(4-HYDROXYPHENYL)-3- CARBOMETHOXYBENZOFURAN Strueture-Formula VI: 3=-i J-OCH 6:11, 7:11, 4' 011 A. 3-methoxy-4'-hydroxyfiavyliurn chloride was prepared by condensing equimolar proportions of salicyl aldehyde and 4-hydroxy-a-methoxy acetophenone in ethyl acetate saturated with HCl gas.

B. To 40 ml. of hot methanol were added 2 grams of the above fiavylium salt, 30 ml. of buffer solution, and 4 ml. of 30% H 0 solution. The reaction system was allowed to stand 10 minutes without heating, then it was diluted with water. The precipitate was collected and recrystallized from aqueous methanol. The product (1 g.) was in the form of colorless needles, M.P. 187 C., peak at 316 III/1.. The acetate had a melting point of C. peaks at 303 and 224 mp.

Example XIII PREPARATION OF 2-(4-METHOXYPHENYL)-3- CARBOMETHOXYBENZOFURAN To 20 ml. of hot methanol were added 1 gram of 3,4'- dimethoxyflavylium chloride, 10 ml. buffer solution, and 2 ml. of 30% H 0 solution. After standing for 10 minutes without applying heat, water was added, the precipitated material was collected and recrystallized from methanol. The benzofuran product (.46 g.) was in the form of cream-colored needles, M.P. 81 C.

Example XIV PREPARATION OF COUMESTROL A. Preparation of flavylium chloride intermediate.- Equimolar proportions of 2,4-dihydroxybenzaldehyde and n-methoxy-2,4-dibenzyloxyacetophenone were condensed in ethereal HCl to give 3-methoXy-7-hydroXy-2,4'-dibenzyloxy-fiavylium chloride. This compound was dcbenzylated in acetic acid-concentrated hydrochloric acid to prochloride (Formula III, above).

lie vide the compound 3-methoxy-2',4,7-trihydroxy flavylium Properties of this compound were carrnine-red needles recrystallized from aqueous methanolic HCl, A max.=508, 282, 263, 240 my. (in ethanol, 0.5% H01).

B. Oxidation and lactonization of flavylium chloride intermediate.-A suspension of the flavylium chloride (10 g.) in warm (about 60 C.) methanol (200 ml.) was diluted with water (100 ml.) and 20 ml. of 30% hydrogen peroxide added. After 10 minutes the yellow-brown solution of the benzofuran (Formula IV, above) was acidified with concentrated sulphuric acid (40 ml.) heated for 15 minutes on the steam bath, and allowed to cool to room temperature. Coumestrol (Formula V, above) precipitated as a fawn-colored, crystalline powder (4.18 g.). It migrated as a single, blue fluorescent (in UV light) spot on silicic acid chromatostrips and Was essentially pure. Recrystallized for analysis from acetone or purified through its diacetate, coumestrol was obtained as a yellow, crystalline powder, M.P. 350 C. It was chromatographically, estrogenically, and spectrally identical with an authenic specimen of the natural estrogen.

Example XV Two grams of 2,4'-dihydroxy-3,7-dimethoxy flavylium chloride was dissolved in 50 ml. of warm methanol and butter solution (10 ml.) and 30% H solution (4 ml.) were added. The system was allowed to stand for minutes, then concentrated sulphuric acid (8 ml.) and water (10 ml.) were added and the system heated on the steam bath for 20 minutes. The reaction mixture was allowed to cool and slightly pink crystals separated out (0.6 g.). This product was recrystallized from acetone-methanol, forming white needles, M.P. 338339 C., 7\ max. in ethanol, 342, 303, 292, 242 m The product had the structure The acetate was prepared by reacting it with acetic anhydride and sodium acetate and crystallized from acetic acid-methanol: Colorless neeedles, M.P. 240-241 C., A max. 337, 243 mu.

Example XVI The procedure of Example XV was repeated but using a different starting material, namely, 2,4'-dihydroxy- 3,8-dimethoxy flavylium chloride. The product, obtained in 45% yield, had the structure 0 orno- Methyl ether: M.P. 195 C., l\ max. (in ethanol) 344,

Example XVII One-half gram of 2',7-dihydroxy-3,4-dimethoxy flavylium chloride was mixed with warm (about 60 C.) ethanol (10 ml.), Water (5 ml), 30% H 0 solution (1 m1.) and allowed to stand 10 minutes. The system was then diluted with water to a volume of 50 ml. and the benzofuran product, 2-(2-hydroxy-4-methoxyphenyl)- 3-carbornethoxy-6-hydroxy-benz0furan, was extracted with ether (three SO-ml. portions). The ether extract was washed with water, dried over Na SO filtered, and evaporated. The residue was dissolved in 5 ml. glacial acetic acid; a solution of 2 ml. conc. H in 3 ml. H O was added and the system heated on the steam bath 20 minutes. Crystals of a slightly orange color separated (0.2 g.). This product was recrystallized from acetonemethanol, forming cream needles, M.P. 276-278 C. Structure of the product was- The acetate of this compound had a MP. 205-206 C. Having thus described the invention, What is claimed is: 1. A method for synthesizing a coumarino-coumarone which comprises reacting a benzofuran of the formula-- wherein each R represents a radical of the group consisting of hydrogen, hydroxyl, lower alkyl, lower alkoxy, benzoxy, and phenoxy and where R" represents an esterified carboxyl group, with a strong acid in the presence of water to cause hydrolysis and lactonization to produce a compound of the formula- R R R R /O -R R it | o-o R ll 0 No references cited.

Claims (1)

1. 3. A METHOD FOR PREPARING COUMESTROL WHICH COMPRISES REACTING 3-METHYOXY-2'',4'',7-TRIHYDROXY FLAVYLIUM CHLORIDE WITH HYDROGEN PEROXIDE TO PRODUCE 2-(2,4-DIHYDROXYPHENYL)-3-CARBOMETHOXY-6-HYDROXY BENZOFURAN, AND REACTING SAID BENZOFURAN WITH A STRONG ACID IN THE PRESENCE OF WATER TO PRODUCE COUMESTROL.