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Studies toward the Total Synthesis of the Oxindole Alkaloid Gelsedine:  An Efficient Allene-Terminated N-Acyliminium Ion Cyclization

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journal contribution
posted on 12.12.1997, 00:00 by Winfred G. Beyersbergen van Henegouwen, Henk Hiemstra
This paper reports the synthesis of the advanced intermediate 26 in a projected synthesis of enantiopure ent-gelsedine (5). The route starts from (S)-malic acid and features the creation of four new stereocenters with complete control of stereochemistry. The key step is a novel allene-terminated N-acyliminium ion cyclization that leads to the required 7-azabicyclo[4.2.1]nonane-4,8-dione skeleton. Additional functionalities including the C-8 ethyl and the C-9 hydroxymethyl are introduced in an efficient manner.