Pyrrolizidine alkaloid analogues. Synthesis of 11-membered macrocyclic diesters of (±)-synthanecine A

Abstract
Treatment of (±)-synthanecine A (4) with various glutaric anhydride derivatives [(5a–f) and (7)] yielded the corresponding 6-monoesters of (±)-synthanecine A. Lactonisation of these monoesters was carried out by the Corey–Nicolaou method to give a range of 11 -membered macrocyclic diesters [(6a–f), (8), and (9)] of synthanecine A. The macrocyclic nature of these new pyrrolizidine alkaloid analogues was established by spectroscopic data and by comparison of their 1H n.m.r. and mass spectra with those of macrocyclic pyrrolizidine alkaloids.

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