ASYMMETRIC PROTONATIONS OF ENOL DERIVATIVES

Described herein are two methods of asymmetric protonation of enol der ivatives under acidic and basic conditions. The process under basic co nditions is protonation of prochiral simple enolates with (S,S)-imide 1 which possesses an asymmetric 2-oxazoline ring. Various lithium enol ates derived from the corresponding alpha-monoalkylated cycloalkanones have been protonated by 1 and (R,R)imide 2 with 97-68% ee. The cataly tic enantioselective protonation of lithium enolate has been realized using a catalytic amount of (S,S)-imide 1 and stoichiometric amount of an achiral proton source. Diastereoselective protonation of lithium e nolate of (-)-menthone has also been achieved stoichiometrically and c atalytically. The process under acidic conditions is protonation of si lyl enol ethers and ketene bis(trialkylsilyl) acetals with Lewis acid assisted chiral Bronsted acid (LBA) which is prepared from optically a ctive binaphthol and tin tetrachloride. The catalytic process has been realized using a catalytic amount of optically active 2-hydroxy-2'-me thoxy-1,1'-binaphthyl and a stoichiometric amount of 2,6-dimethylpheno l in the presence of tin tetrachloride.