Photoreactions of (3-aziridinylacrylonitriles and acrylates with alkenes: formation of head-to-head adducts and application to the preparation of pyrrolizidine alkaloid

摘要

The photochemical C,C-bond cleavage of N-benzyl beta-aziridinylacrylonitrile 1 and acrylate 2 and the subsequent [3+2] cycloaddition with electron-deficient alkenes afforded head-to-head adducts selectively and efficiently. Irradiation of N-phenyl aziridine 3 with acrylonitrile gave adducts, but photoreaction of N-benzoyl aziridine 4 and thermal reactions of 3 and 4 with alkenes yielded C(gamma),N-cleaved products instead of cycloadducts. N-trityl aziridine 5 also reacted with electron-deficient alkenes, affording 2,3-cis-pyrrolidine derivatives exclusively. A formal synthesis of a pyrrolizidine alkaloid, isoretronecanol (27), starting from 5 was achieved in a convenient manner. (C) 2004 Elsevier Ltd. All rights reserved.