IE52338B1 - Intermediates useful in the preparation of certain chiral hydantoins,including sorbinil - Google Patents

Description

This invention is concerned with hydantoin intermediates which are useful in the preparation of certain chiral hydantoins, especially sorbinil. The use of these intermediates is described in our copending Patent Application No. 709/81, from which the present application is a divisional.

The hydantoin intermediates of the-invention have the formulae:- where X is chloro or fluoro.

The compounds of the formula (V) can be prepared according to the following reaction scheme:52338 Formation of Imine S—(-)-alpha-methylbenzylamxne (II) (III) (IV) Induction of 4S Stererochemistry HCN Addition HCN Condensation/Cyclization/Hydrolysis 1) C1SO2NCO 2) H2O+ Compound (VII) is formed during the conversion of (IV) to (V) and can, if desired, be isolated.

The starting 6-halo-4-chromanones (II, more systematically named as 6-halo-2,3-dihydro-4H-l-benzopyran4-ones) are available commercially or by literature methods (See Sarges, U.S. Patent 4,117,230).

The initial stage of the synthesis, conversion of (ID to the imine (III) is usually carried out in an inert, anhydrous solvent, such as an aromatic hydrocarbon (e.g. benzene, toluene) or an ether (tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diglyme). By inert solvent is meant one which will not react significantly with reagents or products under the conditions employed. Selection of a solvent for the reaction is otherwise noncritical. The reaction is preferably carried out under conditions wherein the water is removed from the reaction mixture-either azeotropically (e.g. from benzene, toluene or diglyme) or by the addition of a dehydrating agent such as titanium tetrachloride. The latter is the preferred dehydrating agent, since high yields of the desired imine are obtained. The temperature for the reaction is not critical, e.g. from -10°C to 70oC. The middle range of 20oC.-45°C is preferred, since the reaction proceeds at a reasonable rate, being complete in some 6 to 48 hours, with minimal degradation. The reaction is conveniently monitored by infrared spectroscopy: following disappearance of the characteristic ketone carbonyl vibration. In this manner optimal reaction time at any given temperature is readily determined. The molar ratio of ketone, amine and titanium tetrachloride is not critical. It can range from theoretical (1:1:0.5) to 1:4:0.75, with an added base such as a tertiary amine like triethylamine to neutralize the hydrogen chloride produced as a by-product in the reaction or during isolation (e.g. 4 moles of base/mole of titanium tetrachlorid^. If desired, excess of the amine reactant itself can be used as the base for neutralization of the hydrogen chloride. If reaction is incomplete after the usual reaction time (e.g. in the case where traces of water are inadvertently present), additional titanium tetrachloride can be added to force the reaction to completion.

In the second stage of the 4-stage sequence, hydrogen cyanide is added to the carbon-nitrogen double-bond of the imine (III). It is at this stage that the desired asymmetry at C.4 is induced, through preferential formation and crystallization of the S,S-diastereomer. Anhydrous conditions are employed to prevent possible hydrolysis of of the imine. Selection of a solvent is dictated by the requirement that the desired diastereomer crystallize cleanly therefrom. Ethanol is a solvent well suited for this purpose, but it is evident that simple experimentation would identify other suitable solvents, e.g. other lower alkanols. The temperature of the reaction can be over a range of temperatures, e.g. -20°C. to 35eC. Lower temperatures facilitate dissolution of the hydrogen cyanide gas. Intermediate temperatures (e.g. 10-20°C.) facilitate crystallization of the product while lower temperatures (e.g. -5°C. to 5®C.) improve the yield, since the solubility of the product decreases with temperature. The reaction time is not critical, the range of 0.5 to 6 hours being quite satisfactory. The molar ratio of hydrogen cyanide to imine can range from theoretical 1:1 up to 100:1.

Generally, an excess of hydrogen cyanide is employedd (e.g. 10:1 to 50:1) in order to improve the reaction rate, forcing it to completion in the specified time.

The third stage in the synthetic sequence is the condensation of the aminonitrile (IV) with chlorosulfonylisocyanate to form the chlorosulfonylurea derivative (VI), (VI) followed by cyclization to form certain cyclised intermediates [including the imine (VII)], (VII) and finally hydrolysis of said intermediates to form the phenalkylated hydantoin (V). This sequence represents a novel process for the formation of hydantoins, and is an important feature of the present invention where known hydantoin forming reagents do not perform satisfactorily.

The formation of the chlorosulfonylurea (VI) is typically carried out in an aprotic solvent, inert to the highly reactive chlorosulfonylisocyanate. Suitable solvents are, e.g aromatic hydrocarbons (e.g. benzene, toluene), chlorinated hydrocarbons (e.g. methylene chloride, chloroform, chlorobenzene), and ethers (e.g. tetra20 hydrofuran, dimethoxyethane). The product is usually isolated in crude form by stripping the solvent so that a low boiling solvent such as methylene chloride is particularly well suited for this reaction. The temperature of condensation is not critical (e.g. 0-50 °C.,, but the reaction is so rapid that it is conveniently carried out at room temperature for about 10 minutes. The molar ratio of aminonitrile to chlorosulfonylisocyanate is preferably, but not restricted to, the theoretical 1:1, since clean reaction products result therefrom.

The cyclization and hydrolysis to the phenalkylated hydantoin (V) is generally carried out without isolation of any cyclised intermediates. These reactions are preferably carried out in hot, aqueous hydrochloric acid, after an initial stirring period of about 10 minutes at ambient temperature. Total reaction time at about 90-105°C. is preferably about 2 hours. Since the reaction is heterogeneous, vigorous agitation is helpful in attaining complete conversion of (VI) via said cyclised intermediates [including (VII)] to (V) in the specified reaction time. If desired, the intermediate imine (VII) can be isolated.

The intermediates of the invention may be used to prepare certain chiral hydantoin end products (including sorbinil) as described in our Patent Application No. 709/81.

The present invention is illustrated by the following examples. However, it should be understood that the invention is not limited to the specific details of these examples.

EXAMPLE 1 S-2,3-Dihydro'-6-f luoro-4- (1-phenylethylimino) -4H1-benzopyran (HI, X=F) A flame dried 3 neck flask fitted with a mechanical stirrer, dropping funnel, Nj inlet, and thermometer was charged with 0.83 g (5 mmoles) of 2,3-dihydro-6-fluoro4H-l-benzopyran-4-one (Sarges, U.S. Patents 4,117,230; 4,130,174) and 30 ml of dry benzene. The solution was cooled to 0° and to it was added a solution of 1.94 ml. (15 mmoles) of S-(-)-alpha-methylbenzylamine in 15 ml of dry benzene. After 15 minutes and while keeping the temperature below 10°C,a solution of 0.275 ml. (2.5 mmoles) of TiCl^ in 10 ml of benzene was added dropwise over 20 min. The red-brown suspension was allowed to warm to room temperature and stirred for 18 hours. At this time, another 0.5 ml. of S-(-)-alpha-methylbenzylamine was added, followed after 15 minutes by another 0.1 ml. of TiCl4 in 5 ml of benzene. After stirring for an additional 3 hours at room temperature, i.r. analysis of a filtered aliquot showed no ketone carbonyl and a new strong band at 1635 cm_\ The suspension was filtered through a coarse sintered glass funnel charged with celite and the filter cake was washed twice with 50 ml. portions of benzene. The filtrate was concentrated in vacuo to a tacky residue, which was triturated several times with petroleum ether. The combined triturates were filtered and the filtrate concentrated in vacuo to yield 1.07 g. (80%) of S-2,3-dihydro-6-fluoro-4-(1-phenylethylimino)4H-l-benzopyran (oil; i.r. 1650 cm S m/e 269).

EXAMPLE 2 S-6-Chloro-2,3-dihydro-4-(l-phenylethyliinino)-4H-l-faenzo~ pyran (III, X=C1) By the same procedure as Example 1, 5 g (0.027 mol) of 6-chloro-2,3-dihydro-4H-l-benzopyran-4-one, 10.6 ml (0.082 mol) of S-(-)-alpha-methylbenzylamine, and 1.5 ml (0.0137 mole) of titanium tetrachloride in 275 ml of dry benzene gave, after a 24 hour reaction time without the addition of more reagents, 7.1 g (91%) of S-6-chloro10 2,3-dihydro-4-(1-phenylethylimino)-4H-l-benzopyran [viscous oil; m/e 287/285; nmr (CDClg-TMS) delta 1.5 (d,3H); 2.7 (t,2H), 4.2 (t,2H), 5.75 (q,lH); 6.8 (d,lH); 7.1-7.5 (m,6H); 8.2 (d,lH)J.

EXAMPLE 3 S-4-Cyano-2,3-dihydro-6-fluoro-4-(S-l-phenylethylamino)-4H-l-benzopyran (IV, X=F) A hydrogen cyanide generator (a 3 neck flask containing 15 ml. of 50% aqueous sulfuric acid, fitted with a dropping funnel containing an aqueous solution of 6.8 g. of sodium cyanide in 30 ml. of water, was connected by tubing via a calcium chloride drying tube to the inlet tube of the main reaction vessel, a 3-necked round bottom flask with a magnetic stirrer and a perfusion capillary tube which could be lowered below the solvent surface. Throughout the reaction a gentle stream of nitrogen was passed through the hydrogen cyanide generator, the reaction flask, and finally through a neutralizing trap containing 5N sodium hydroxide. The reaction flask was charged with S-2,3-dihydro-6-fluoro-(1-phenylethylimino)4H-l-benzopyran (2.7 g., 10 mmoles) in 60 ml. of absolute ethanol and cooled to -10eC. Hydrogen cyanide was generated over about 30 minutes by adding the sodium cyanide solution dropwise to the sulfuric acid. The hydrogen cyanide generator was warmed, and all remaining hydrogen cyanide flushed into the reactor with nitrogen (about 45 minutes).

The reaction mixture was warmed to room temperature. Filtration gave 2.105 g..(71%) of S-4-cyano-2,3-dihydro25 6-fluoro-4-(S-l-phenylethylamino)-4H-l-benzopyran [m.p. 130-132°C. (dec.)).

Anal. Calcd. for C18H17N2OF: C, 72.95; H, 5.78, N, 9.46. Found: C, 73.01, H, 5.88, N, 9.45.

EXAMPLE 4 S-6-chloro-4-cyano-2,3-dihydro-4-(S-l-phenylethylamino)-4H-l-benzopyran (IV, X=C1) Using the procedure of Example 3, 1.01 g. (3.53 mmol) 5 of S-6-chloro-2,3-dihydro-4-(l-phenylethylimino)-4H-benzopyran in 15 ml of ethanol was reacted with hydrogen cyanide made from 1.73 g. (35.3 mmol) of sodium cyanide in 8 ml. of water and 4 ml. of 50% sulfuric acid. The hydrogen cyanide was generated over 10 minutes. Residual 1® hydrogen cyanide was flushed into the reaction mixture by heating the generator to 80°C. for 5 minutes. The reaction mixture was warmed to 0°C. and filtered to yield 781 mg (71%) of S-6-chloro-4-cyano-2,3-dihydro-4-(S-lphenylethylamino)-4H-l-benzopyran (mp 146-8“C (dec.)].

Anal. Calcd. for C, 69.11, H, 5.48; N, 8.96.

Found: C, 69.36; H, 5.62; N, 9.05.

EXAMPLE 5 S-2,3-Dihydro-6-f luoro-31 -(S-l-phenylethyl)-spiro/4H-lbenzopyran-4,4' -imidazolidine] -21,51 -dione (V, X=F) To a solution of 0.25 g. (0.84 mmoles) of S-4-cyano5 2,3-dihydro-6-fluoro-4- (S-l-phenylethylamino) -4H-l-benzopyran in 10 ml. of methylene chloride was added 48 mg. (0.34 mmol) of chlorosulfonyl isocyanate. After stirring 10 minutes at room temperature, the solution was concentrated in vacuo to a foam. After addition of 7.5 ml. of IN hydro10 chloric acid the suspension was stirred for 10 minutes at room temperature, followed by heating on a steam bath for 1 hour. After cooling to room temperature, the precipitated solid was filtered, washed with water, and dried to give 168 mg. (50%, S-2,3-dihydro-6-fluoro-3*15 (S-l-phenylethyl)-spiro[4H-l-benzopyran-4,4’-imidazolidine]2’,5'-dione (mp 226-8°C). An analytical sample was prepared by recrystallization from ethanol-water.

Anal. Calcd. for ci9Hi7FN2°3: C, 67.05, H, 5.04, N, 8.23. Found: C, 66.79, H, 5.18, N, 8.38. 2θ By reheating the filtrate, a second crop (10-20%) is obtained. Alternatively, by heating the reaction on a steambath for 2 hours, after addition of the hydrochloric acid, yields of about 79% are obtained directly, without need to obtain second crop by further heating of the filtrate.

EXAMPLE 6 S-6-Chloro-2,3-dihydro-3'-(S-l-phenylethyl)-spiro [4H-l-benzopyran-4,4,-imi.dazolidine]-2' ,5'dione (V,X=C1) By the procedure of Example 5, 0.5 g. (1.6 mmol) of S-6-chloro-4-cyano-2,3-dihydro-4-(S-i-phenylethylamino)-4H-l-benzopyran and 0.14 ml (1.6 mmol) of chlorosulfonyl isocyanate gave 0.509 g. (89%) of S-6chloro-2,3-dihydro-3 ’ - (S-l-phenylethyl) -spiro(4H-l-benzopyran-4,4'-imidazolidinel-2',5*-dione [mp 268-70eCJ.

Anal. Calcd. for C19H17C1N2O3s C, 63.95, H, 4.80, N, 7.85. Founds C, 63.66, H, 4.98, N, 7.67.

Claims (9)

1. A compound of the formula:- wherein X is chloro or fluoro.

2. A process for preparing a compound of the formula (V) as defined in claim 1, which comprises condensing a nitrile of the formula:- where X is chloro or fluoro, with chlorosulfonyl isocyanate followed by cyclisation and hydrolysis to form the alphamethylbenzylhydantoin (V).

3. A process according to claim 2, wherein the 15 cyclisation and hydrolysis is carried out with aqueous hydrochloric acid.

4. A process for preparing a compound of the formula (V) as defined in claim 1, which comprises cyclising a chlorosulfonylurea of the formula:52338 (VI) C1SO,NH Ο 2 \ζίCH. X wherein X is chloro or fluoro, followed by hydrolysis.

5. A process for preparing a compound of the formula (VII) as defined in claim 1, which comprises 5 cyclising (with net hydrolysis and elimination of hydrogen chloride and sulfur trioxide, a compound of the formula (VI, as defined in claim 4.

6. A process for preparing a compound of the formula (V) as defined in claim 1, which comprises 10 hydrolysing a compound of the formula (VII, as defined in claim 1.

7. A compound of the formula (V) or (VII) given and defined in claim J., substantially as hereinbefore described with particular reference to the accompanying 15 Examples.

8. , A process for preparing a compound of the formula (V) or (VII) given and defined in claim 1, substantially as hereinbefore described with particular reference to the accompanying Examples.

9. A compound of the formula (V) or (VII) given and defined in claim 1, whenever prepared by a process claimed in a preceding claim.