Reaction of 2-hydroxy-1,2,2-triphenylethyl propionate with non-activated ketones and enones: Stereoselective aldol and Michael addition

The TiCl4-mediated Mukaiyama-type reaction of the silyl ketene acetal 2, de rived from (R)-propionate 1, with the ketones 3a-d occurs in a stereoselect ive manner. The aldol product 4c is obtained from the enone 3c, whereas the homologous compound 3d undergoes a 1,4 addition and leads to the keto este r 5. The configurations of the deprotected aldol adduct 6 (obtained from 3c ) and the Michael product 5 are determined by crystal structure analyses. T he diastereomerically and enantiomerically pure esters 4a-c, 5, and 6, as w ell as the carboxylic acid 7 and the diol 8, containing two or three contig uous stereogenic carbon centers, are prepared. The enantiomerically pure co mpounds 9 and 8 result from the cleavage of the chiral auxiliary reagent 1, 1,2-triphenyl-1,2-ethanediol, which can be recovered.