Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D263/00—Heterocyclic compounds containing 1,3-oxazole or hydrogenated 1,3-oxazole rings
  • C07D263/52—Heterocyclic compounds containing 1,3-oxazole or hydrogenated 1,3-oxazole rings condensed with carbocyclic rings or ring systems
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07B—GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR
  • C07B41/00—Formation or introduction of functional groups containing oxygen
  • C07B41/06—Formation or introduction of functional groups containing oxygen of carbonyl groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07B—GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR
  • C07B41/00—Formation or introduction of functional groups containing oxygen
  • C07B41/08—Formation or introduction of functional groups containing oxygen of carboxyl groups or salts, halides or anhydrides thereof
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
  • C07C45/30—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with halogen containing compounds, e.g. hypohalogenation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/29—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with halogen-containing compounds which may be formed in situ

Definitions

• Oxidation is one of the most fundamental transformations in organic synthesis and there are numerous methods reported in the literature. (Hudlicky, M. "Oxidations in Organic Chemistry” ACS Monograph 186, 1990.) However, direct conversion of primary alcohols to the corresponding carboxylic acids is still a challenge especially in the presence of other functional groups. There are only a few commonly used methods for this transformation including Cr0 3 /H 2 S0 4 (Bowden; Heilbron; Jones; Weedon /. Chem. Soc, 1946, 39; Bowers; H.; Jones; L. J. Chem. Soc, 1953, 2548; Millar, J. G.; Oehlschlager, A. C; Wong, J. W.
• This chromium catalyzed oxidation method avoids the chromium disposal issues associated with running a typical Jones oxidation reaction, reduces the epimerization of any -chiral centers, oxidizes secondary alcohols to the corresponding ketones in quantitative yield, and is a one step procedure.
• the reaction is mild, rapid, high yielding and only requires 1-2 mol % of Cr0 3 .
• the present invention discloses a process for preparing a compound of Formula I:
• R 1 ⁇ R 2 I comprising reacting a compound of Formula II
• the present invention discloses a process for preparing a compound of Formula I:
• Rl is: a) OH
• C1-C8 alkoxy, C1-C8 alkyl, or C3-C8 cycloalkyl are unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH,
• CO2R 4 Br, Cl, F, I, CF3, N(R5)2, C1-C8 alkoxy, C3-C8 cycloalkyl, aryl, heteroaryl, heterocyclyl, CO(CH2)nCH3, and CO(CH2)nCH2N(R5) 2 ,
• aryl is defined as phenyl or naphthyl , which is unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH, CO2R 4 , Br, Cl, F, I, CF3, N(R5)2, C1-C8 alkoxy, C1-C8 alkyl, C3-C8 cycloalkyl, CO(CH2) n CH3, CO(CH2) n CH2N(R5)2, or when aryl is substituted on adjacent carbons they can form a 5- or 6- membered fused ring having one, two or three heteroatoms selected from O, N, and S, this ring is unsubstituted or substituted on carbon or nitrogen with one, two or three substituents selected from the group consisting of: OH, CO2R 4 , Br, Cl, F, I, CF3, N(R7)2, C1-C8 alkoxy, Cl-C ⁇ alkyl, C3-C8 cycloalkyl
• heteroaryl is defined as a 5- or 6-membered aromatic ring containing 1, 2 or 3 heteroatoms selected from O, N and S , which is unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH,
• heterocyclyl is defined as a 5- or 6-membered, non-aromatic ring containing 1, 2 or 3 heteroatoms selected from O, N and S , which may contain one or two double bonds and which is unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH, CO2R 4 , Br, Cl, F, I, CF3, N(R5) 2 , C1-C8 alkoxy, Cl-C ⁇ alkyl, C3-C8 cycloalkyl, CO(CH2) n CH3, CO(CH2) n CH2N(R5)2, and additionally the 5- or 6- membered ring can be benzofused and unsustituted or subtituted with one, two or three substituents as described above;
• R2 is: a) C1-C8 alkyl, b) C3-C7 cycloalkyl, c) aryl, d) heteroaryl, or e) heterocyclyl;
• n is: : 0 to 5;
• t 0, 1 or 2;
• R 4 is: H, or Cl-C ⁇ alkyl
• R 5 is: H, or C1-C8 alkyl, or aryl
• R7 is: H, C1-C8 alkyl, aryl, when two R ⁇ substutients are on the same nitrogen they can join to form a ring of 3 to 6 atoms; comprising reacting a compound of Formula II in a solvent,
• V-OH R 2 II with a solution of periodic acid, a catalytic amount of a chromium reagent in a solvent to oxidize to the compound of Formula I.
• the present invention discloses a process for preparing a compound of Formula I:
• Rl is a) OH, b) H, c) C1-C8 alkyl, d) Cl-C8 alkoxy 1, e) C3-C7 cycloalkyl, f) aryl, g) heteroaryl, or h) heterocyclyl;
• Cl-C ⁇ alkoxy, C1-C8 alkyl, or C3-C8 cycloalkyl are unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH, CO2R 4 , Br, Cl, F, I, CF3, N(R5)2, Cl-C ⁇ alkoxy, C3-C8 cycloalkyl, aryl, heteroaryl, heterocyclyl, CO(CH2)nCH3, and CO(CH2)nCH2N(R5) 2
• aryl is defined as phenyl or naphthyl , which is unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH, CO2R 4 , Br, Cl, F, I, CF3, N(R5)2, C1-C8 alkoxy, C1-C8 alkyl, C3-C8 cycloalkyl, CO(CH2) n CH3, CO(CH2) n CH2N
• CO2R 4 Br, Cl, F, I, CF3, N(R7)2, -C8 alkoxy, -C8 alkyl, C3-C8 cycloalkyl, CO(CH2) n CH3, and CO(CH2)nCH2N(R5) 2 ;
• heteroaryl is defined as a 5- or 6-membered aromatic ring containing 1, 2 or 3 heteroatoms selected from O, N and S , which is unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH, CO2R 4 , Br, Cl, F, I, CF3, N(R5)2, C1-C8 alkoxy, C1-C8 alkyl, C3-C8 cycloalkyl, CO(CH2) n CH3, CO(CH2)nCH2N(R5)2, and additionally the 5- or 6- membered aromatic ring can be benzofused and unsustituted or subtituted with one, two or three substituents as described above;
• heterocyclyl is defined as a 5- or 6-membered, non-aromatic ring containing 1 , 2 or 3 heteroatoms selected from O, N and S , which may contain one or two double bonds and which is unsubstituted or substituted with one, two or three substituents selected from the group consisting of: OH, CO2R 4 , Br, Cl, F, I, CF3, N(R5)2, C1-C8 alkoxy, C1-C8 alkyl, C3-C8 cycloalkyl, CO(CH2)nCH3,
• R 2 is: a) C1-C8 alkyl, b) C3-C7 cycloalkyl, c) aryl, d) heteroaryl, or e) heterocyclyl;
• n 0 to 5;
• t 0, 1 or 2;
• R 4 is: H, or C1-C8 alkyl
• R 5 is: H, or C1-C8 alkyl, or aryl
• R7 is: H, Cl-C ⁇ alkyl, aryl, when two R ⁇ substutients are on the same nitrogen they can join to form a ring of 3 to 6 atoms;
• V-OH R 2 II with a solution of periodic acid, a catalytic amount of a chromium reagent in a solvent at a temperature range of about -20°C to about 40°C for about 15 minutes to about 24 hours to oxidize to the compound of Formula I.
• the solvent is selected from the group consisting of: acetonitrile, tetrahydrofuran, diethyl ether, MTBE (methyl t-butyl ether), DME (dimethoxy ethane), DIGLYME (2-methoxyethyl ether), TRIGLYME (triethylene glycol
• the periodic acid H 5 I0 6
• the periodic acid is utilized in about 2.0 to about 4.0 equivalents, preferably about 2.5 equivalents.
• a minimum of two equivalents of periodic acid are needed to carry out the oxidation from a primary alcohol to a carboxylic acid.
• an additional equivalent of periodic acid for each basic functional group will be needed to carry out the oxidation.
• the chromium reagent is selected from the group consisting of: Cr0 3 , Na ⁇ O ? , K 2 Cr 2 0 7 , CrX 3 , where X is Cl, Br, F, N0 2 , OAc, or C10 4 .
• the process as recited above, wherein the chromium reagent is utilized in about 0.1 to about 10 mole percent, preferably about 1.0 to about 2.0 mole percent.
• the temperature range is about -20°C to about 30°C, and preferably about -10°C to about 0°C.
• the reaction time is about 15 minutes to about 24 hours and preferably between about 45 minutes and about 1.5 hours.
• alkyl substituents recited above denote straight and branched chain hydrocarbons of the length specified such as methyl, ethyl, isopropyl, isobutyl, tert-butyl, neopentyl, isopentyl, etc.
• alkenyl-substituents denote alkyl groups as described above which are modified so that each contains a carbon to carbon double bond such as vinyl, allyl and 2-butenyl.
• Cycloalkyl denotes rings composed of 3 to 8 methylene groups, each of which may be substituted or unsubstituted with other hydrocarbon substituents, and include for example cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and 4-methylcyclohexyl.
• the alkoxy substituent represents an alkyl group as described above attached through an oxygen bridge.
• the aryl substituent represents phenyl and 1 -naphthyl or 2- naphthyl, including aryl substituted with a 5- or 6-membered fused ring, such as an unsubstituted and substituted methylenedioxy, oxazolyl, imidazolyl, or thiazolyl ring.
• the heteroaryl substituent represents a carbazolyl, furanyl, thienyl, pyrrolyl, imidazolyl, isoxazolyl, isothiazolyl, thiazolyl, oxazolyl, triazolyl, pyrazolyl, pyrazinyl, pyridyl, pyrimidyl, purinyl.
• the heterocyclyl substituent represents, oxazolidinyl, thiazolidinyl, imidazolidinyl, thiazolidinyl, oxadiazolyl, thiadiazolyl, morpholinyl, piperidinyl, piperazinyl, or pyrrolidinyl.
• the best yields can be obtained by adding a solution of H 5 I0 6 /Cr0 3 (2.5 equiv./l.l mol %) in wet MeCN (0.75 v % water) to the alcohols at 0-5 °C.
• the reactions were typically complete within one hour.
• a stock solution of H 5 I0 6 /Cr0 3 was prepared by dissolving H 5 I0 6 (11.4 g, 50 mmol) and Cr0 3 (23 mg, 1.2 mol %) in wet MeCN (0.75 v % water) to a volume of 114 mL (complete dissolution typically required 1-2 hours).
• the H 5 I0 6 /Cr0 3 solution (11.4 mL) was then added to a solution of the alcohol 1 (2.0 mmol) in wet acetonitrile (10 mL, 0.75 v % water) in 30-60 minutes while maintaining the reaction temperature at 0-5 °C.
• the mixture was aged at 0 °C for 0.5 h and the completion of the reaction was confirmed by HPLC assay.
• the reaction was quenched by adding an aqueous solution of Na 2 HP0 4 (0.60 g in 10 mL H 2 0). Toluene (15 mL) was added and organic layer was separated and washed with 1/1 brine/water mixture (2 x 10 mL) then a mixture of aqueous NaHS0 3 (0.22 in 5 mL water) and brine (5 mL). The organic layer was then concentrated to give the crude carboxylic acid 2. Most of the crude products were quite pure based on ⁇ NMR analysis and HPLC assay.
• the reaction must be controlled with intermittent cooling and by careful monitoring of the addition rate.
• the mixture is aged for 30 min at 20- 25°C.
• Boron trifluoride etherate (36.9 g) is added over a period of 30 min at 30-35°C.
• Ethyl acetate (500 mL) is added and the layers are separated. The organic layer is washed with water (100 mL) and then transfered to a 1L round bottom flask equipped for distillation. The solution was concentrated and charged with fresh ethyl acetate. This is repeated until a solution with a volume of 200 mL has KF ⁇ 200 ⁇ g/mL. The solvent is then switched to DMF to give the final volume of 200 mL with a KF ⁇ 200 ⁇ g/mL.
• the addition funnel is charged with water (400 mL) which is added dropwise to the reaction mixture over a period of 30 min. while maintaining the temperture ⁇ 15°C.
• the temperature is controlled by cooling and monitoring the rate of addition.
• the initial addition of water is highly exothermic. Using large excess of thionyl chloride results in a more exothermic quench. If the quench temperture is not controlled, hydrolysis of the benzyl chloride back to the alcohol may result.
• the resulting thick white slurry is aged for 1 h at 0-5°C.
• the benzyl chloride is isolated by filtration. The cake is washed with (1: 1) DMF:H 2 0 (lOOmL) and then water (200 mL). The solid is dried in vacuo to give 93 g of the benzyl chloride( 94% yield, 96 A%).
• Methoxypropene (140 mL) is charged to an addition funnel and added over 30 minutes at a temperature of 50°C.
• reaction slurry is aged for 1-2 hours at 50°C. HPLC assay at this point shows ⁇ 0.5A% of the amide remaining. The amide is not removed in the isolation so it is important to push the reaction to completion.
• the reaction slurry is cooled to 0-5 °C and quenched by addition of 5% aqueous sodium carbonate solution (1 L) and heptane (1 L). The layers are stirred and separated and the organic is washed with water (300 mL).
• a THF solution (2L, KF ⁇ 200 ⁇ g/mL) of the acetonide (252 g) and the benzyl chloride (255 g) is cooled to -10°C.
• Lithium bis(trimethylsilyl)amide (1.45 L) is added dropwise over 5 h at 0-2°C. The mixture is then aged for 1.5 h and assayed by HPLC.
• the reaction is quenched by adding aqueous saturated ammonium chloride solution (1 L).
• the initial addition of the ammonium chloride should be slow in order to control the foaming.
• the rate can be increased when the foaming subsides.
• the quenched reaction is then transfered into a mixture of aqueous ammonium chloride (1.5 L), water (0.5 L), and ethyl acetate (3 L). The mixture is then agitated for 15 min and the layers are separated. The organic layer is washed with water (1 L) and brine (0.5 L). The ethyl acetate solution is concentrated to a low volume and
• the dioxane solution of the coupled product is charged to a 12 L round bottom flask and 6 M HC1 (1.5 L) is charged. The mixture is heated to reflux and monitored by HPLC.
• the mixture is cooled to 20°C and MTBE (3 L) is added.
• the mixture is agitated for 15 min and the layers are separated.
• the organic layer is washed with water (1 L).
• the MTBE solution of the crude acid is extracted with 0.6 M sodium hydroxide (2 L).
• the aqueous solution of the sodium salt of the acid is combined with MTBE (2.5 L) and cooled to 10°C.
• the two phase mixture is acidified with 5.4 M sulfuric acid (250 mL), agitated for 15 min, settled and the layers separated.
• the MTBE solution of the acid is washed with water (0.5 L).
• the MTBE solution of the acid is dried by distilation and then solvent switched to THF.
• the final volume of the THF is 2 L with a KF ⁇ 250 ⁇ g/mL.
• THF solution (2 L) of the acid is added to the sodium borohydride slurry over 1 h while maintaining the temperature at 20-25°C.
• reaction is controlled with a cooling bath and by carefully monitoring the addition rate. A nitrogen sweep and proper venting of the hydrogen is also important.
• the mixture is aged for 30 min at 20-25 °C.
• Boron trifluoride etherate (152 g) is added over 1 h at 30-35 °C. The addition produces a delayed exotherm and should be carefully monitored in order to control the reaction temperature.
• the resulting milky white slurry is aged for 1 h at 30 °C and sampled for HPLC assay.
• the reaction mixture is cooled to 15 °C and carefully quenched in a cold (10°C) ammonium chloride solution (1.5 L) while maintaing the temperature at 25 °C.
• the rate of hydrogen evolution is controlled by the rate of the addition of the mixture into the ammonium chloride.
• the quenched mixture is distilled in vacuo to remove the THF.
• the aqueous layer is extracted with MTBE (1.5 L) and the organic layer is dried by flushing with additional MTBE.
• the MTBE solution is then solvent switched to hexanes and adjusted to a volume of 350 mL and seeded.
• the slurry is aged for 2 h at 20 °C and then cooled to 0-5 °C aged for 1 h and filtered.
• the cake is washed with cold hexanes (200 mL).
• the solid is dried under a nitrogen sweep.
• the isolated solid (164 g) is > 99A% by HPLC and > 99%ee.
• the alcohol was prepared following the general procedure recited in Example 1.
• the enantiomeric purity of product (2d) was determined by chiral HPLC after reducing it to the alcohol (Id) with BH 3 THF.
• HPLC conditions column CHIRALCEL OD-H; hexane/i- PrOH (97/3, 1.00 mL/min); UV detection at 220nm. Retention times: (R)-isomer, 23.6 min; (S)-isomer, 29.2 min.

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