Enantiopure sulfinylthiopyrans and related compounds from alkylsulfinylbuta-1,3-dienes

Uncatalyzed and LiClO4 catalyzed cycloadditions of (R-S)-1-{1-[(1S)-isoborneol-10-sulfinyl]vinyl}cyclohexene 1 and (R-S,E)-3-[(1S)-isoborneol-10-sulfinyl]-1-methoxybuta-1,3-diene 2 with di(p-toryl)- and di(p-anisyl)-thioketones 3 and 4 occur with complete regioselectivity. The lack of facial diastereoselectivity, observed in the cycloadditions of 1 with 3 or 4, appears to be a consequence of the sterical features of both diene and dienophile which, in the transition states, make the topological differentiation induced by the presence of the alkylsulfinyl group as chiral auxiliary uninfluential. No significant improvement in diastereoselectivity is observed in the LiClO4 catalyzed reactions, but the obtained enantiopure cycloadducts are easily separated by column chromatography and isolated in high yields. (C) 1999 Elsevier Science Ltd. All rights reserved.