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■ Tandem Radical Cyclization Reactions, Initiated at Nitrogen, as an Approach to the CDE-Tricyclic Cores of Certain Post-secodine Alkaloids

Martin G. Banwell* and David W. Lupton

*Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia

Abstract

The nitrogen-radical precursors (10-15) have been prepared and subjected to reaction conditions expected to promote tandem radical cyclization sequences leading to the CDE-tricyclic frameworks associated with alkaloids such as vindoline (1) and ibophyllidine (2). In the event, each of precursors (10, 11, 12 and 13) participated in the desired processes and thus providing products, (28, 29, 30 and 31) respectively, embodying ring systems related to ibophyllidine (2). In contrast, the higher homologue (14), of PTOC-carbamate (12) decomposed upon exposure to radical chain initiation conditions while the N-chloro-analogue (15) simply underwent reductive dechlorination to give compound (27). As such the title processes appear unlikely to offer a useful approach to the CDE-tricyclic ring system associated with vindoline-type alkaloids.