Efavirenz has been obtained by two related ways: 1) The acylation of 4-chloroaniline (I) with pivaloyl chloride (II) by means of Na2CO3 in toluene gives the expected anilide (III), which is acylated with ethyl trifluoroacetate by means of butyllithium in THF yielding, after hydrolysis with HCl, 2'-amino-5'-chloro-2,2,2-trifluoroacetophenone (IV). The benzylation of (IV) with 4-methoxybenzyl chloride (V) in basic alumina affords the protected acetophenone (VI), which is regioselectively condensed with cyclopropylacetylene (VII) [obtained by cyclization of 5-chloro-1-pentyne (VIII) by means of butyllithium in cyclohexane] by means of butyllithium in THF in the presence of (1R,2S)-1-phenyl-2-(1-pyrrolidinyl)-1-propanol (IX) giving the (S)-isomer of the tertiary alcohol (X) exclusively. The cyclization of (X) with phosgene and triethylamine or K2CO3 in toluene/THF yields the benzoxazinone (XI), which is finally deprotected with ceric ammonium nitrate in acetonitrile/water. 2) The condensation of 2'-amino-5'-chloro-2,2,2-trifluoroacetophenone (IV) with cyclopropylacetylene (VIII) by means of butyllithium or ethylmagnesium bromide in THF gives (?-2-(2-amino-5-chlorophenyl)-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-ol (XII). The cyclization of (XII) with carbonyldiimidazole (XIII) in hot THF yields the racemic benzoxazinone (XIV). Compound (XIV) is submitted to optical resolution by condensation with (S)-(-)-camphanoyl chloride by means of dimethylaminopyridine (DMAP) in dichloromethane to give the acyl derivative (XVI) as a diastereomeric mixture that is resolved by crystallization and finally decomposed with HCl in ethanol or butanol.
A new enantioselective synthesis of efavirenz starting from 2-[5-chloro-2-(4-methoxybenzylamino)phenyl]-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2(S)-ol (I), a previously described intermediate [see Drugs Fut 1998 23(2):133], has been reported: The oxidative cyclization of butynol (I) with dichlorodicyanobenzoquinone (DDQ) in toluene gives the benzoxazine (II) which, without isolation, is treated with NaOH and NaBH4 in methanol yielding the aminoalcohol (III). The acylation of (III) with methyl chloroformate (IV) and NaHCO3 in water affords the carbamate (V). Finally, this compound is cyclized by means of lithium tert-butoxide in tert-butyl methyl ether, or KOH in tert-butyl methyl ether/water.
A new enantioselective synthesis of efavirenz starting from 2-[5-chloro-2-(4-methoxybenzylamino)phenyl]-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2(S)-ol (I), a previously described intermediate [see Drugs Fut 1998 23(2):133], has been reported: The oxidative cyclization of butynol (I) with dichlorodicyanobenzoquinone (DDQ) in toluene gives the benzoxazine (II) which, without isolation, is treated with NaOH and NaBH4 in methanol yielding the aminoalcohol (III). The acylation of (III) with p-nitrophenyl chloroformate (IV) and NaHCO3 in water affords the carbamate (V). Finally, this compound is cyclized by means of lithium tert-butoxide in tert-butyl methyl ether, or KOH in tert-butyl methyl ether/water.