Reversal of Stereoselectivity in [5 + 2] Pyrone−Alkene Cycloadditions Using a Sulfoxide-to-Sulfoximine Switch. Enantiodivergent Synthesis of 8-Oxabicyclo[3.2.1]octane Systems
作者:Fernando López、Luis Castedo、José L. Mascareñas
DOI:10.1021/ol007061m
日期:2001.2.1
[reaction: see text] Switching from a sulfinyl to a sulfonimidoyl group allows the reversal of the sense of asymmetricinduction in thermal [5C + 2C] intramolecular pyrone-alkene cycloadditions. Removal of the sulfoximine unit from the resulting cycloadducts yields optically active oxabicyclic systems that are enantiomeric to those obtained using the sulfinyl chiral auxiliary.
those obtained from the sulfinyl precursors. Cleavage of the oxa-bridge on the desulfurated adducts yields highlyfunctionalized seven-membered carbocyclic derivatives in enantiopure form. Alternative cleavage of the seven-membered carbocycle provides enantiomerically enriched tetrahydrofurans. We have exploited this reaction pathway for the synthesis of the naturally occurring enantiomer of nemorensic