(R)- and (S)-3-hydroxy-4,4-dimethyl-1-phenyl-2-pyrrolidinone as chiral auxiliaries in Diels-Alder reactions

A study of the Dials-Alder reactions of the esters derived from acrylic, me thacrylic, trans-crotonic and trans-cinnamic acid and the chiral auxiliarie s (R)- and/or (S)-3-hydroxy-4,4-dimethyl-1-phenyl-2-pyrrolidinone (4, 17, 2 5 and 26, respectively) with different dienes [cyclopentadiene 5, isoprene 8, 11,12-dimethylene-9,10-dihydro-9,10-ethanoanthracene 9 and anthracene 10 ], catalyzed by titanium tetrachloride, is described. Cyclopentadiene gave adducts with esters (R)- or (S)-4 and (R)-25 with high endo- and facial-dia stereoselectivities. Diene 5 reacted with (+/-)-17 without endo-diastereose lectivity and failed to give a cycloadduct with (+/-)-26. Isoprene reacted only with ester (S)-4 with high facial-diastereoselectivity. The reaction o f 9 with (R)-4 failed, because the diene was not stable under the acid reac tion conditions. Adducts derived from 10 and esters (S)-4 and (R)-17 could be obtained with high facial-diastereoselectivity. LiOH-hydrolysis of the a dducts derived from esters (R)- or (S)-4 and (R)-25 gave the corresponding enantiopure acids, the chiral auxiliaries being completely recovered unchan ged. However, hydrolysis of the adduct derived from 10 and (R)-17, required more drastic basic conditions which partially epimerized the chiral auxili ary. X-Ray diffraction analysis of the adducts derived from 10 and esters ( S)-4 and (R)-17, let us establish their relative configurations and, taking into account the absolute configuration of the starring chiral auxiliary, their absolute configurations. (C) 1999 Elsevier Science Ltd. All rights re served.