Photooxygenation of the Helimers of (−)-Isocolchicine: Regio- and Facial Selectivity of the [4 + 2] Cycloaddition with Singlet Oxygen and Surprising Endoperoxide Transformations
作者:René Brecht、Frank Büttner、Markus Böhm、Gunther Seitz、Gerlinde Frenzen、Astrid Pilz、Werner Massa
DOI:10.1021/jo991171t
日期:2001.5.1
Photooxygenation of the helimeric mixture of (-)-(M,7S)/(P,7S)-isocolchicine (6) with the superdienophile singletoxygen has been studied. Cycloaddition occurred with high regioselectivity at the 7a,11-positions of the alkaloid and predominantly at the diene face anti to the amidic substituent at the stereogenic center C-7, leading to two endoperoxides 7 (syn) and 8 (anti) with an 1:7 ratio. The structure