Asymmetric Diels–Alder reaction of optically active α-(2-exo-hydroxy-10-bornyl)sulfinylmaleimides and its application to optically active 5-functionalised pyrrolines via retro-Diels–Alder reaction

Abstract

Optically pure sulfinylmaleimides 1 have been synthesized. The Diets–Alder reactions of the sulfoxides 1 with various dienes showed high diastereoselectivity. Regioselective reduction of the adducts 4c and 6c followed by desulfinylation afforded the γ-hydroxy lactams 17 and 27, respectively. N-Acyliminium additions using compounds 17 and 27 proceeded diastereoselectively to give γ-alkyl lactams 23 and 29 by virtue of its conformationally rigid, bicyclo [2.2.1]- and 7-oxabicyclo [2.2.1]- heptene moiety, respectively. The use of compound 29 allows a simple preparation of chirally 5functionalised Δ³-pyrrolin-2-ones of high optical purity such as compound 25via retro-Diels–Alder reaction, whereas the thermal cycloreversion of adduct 23 required such forcing conditions as flash vacuum pyrolysis.