STABILIZED ZWITTERIONIC DERIVATIVES FROM THE REACTION OF 16-CHLORO-1-DEHYDROVINCADIFFORMINE WITH SODIUM ALKOXIDES

Treatment of 16-chloro-1-dehydrovincadifformine 2a and 16-chloro-1-deh ydrotabersonine 2b with sodium methoxide respectively yielded the 16-m ethoxyindolenines 11a vs 11b, and the two betaines 12a vs 12b and 14a vs 14b. Sodium ethoxide gave similar results, except for the absence o f the 16-ethoxyindolenines. The structures of all derivatives were asc ertained by their spectroscopic data, by chemical correlations, and by transformations to compound 26, whose racemate was prepared by total synthesis. In contrast with previously described reactions of 2a,b in alcohols, the formation of the internally bolted zwitterionic derivati ves 12-15 under the influence of alkoxides appears here to govern the reaction pathways. (C) 1998 Elsevier Science Ltd. All rights reserved.