Synthesis and molecular structures of (1S)-cis,cis-iridolactones

Abstract

Two cis,cis-iridolactones (1) and (2) with a natural (S)-configuration at C(1) have been synthesized and their crystal and molecular structures determined by direct methods and refined by least-squares to R 0.109 and 0.064. As in the natural trans,cis-isomers (iridomirmecines), (5) and (6), the heterocyclic ring has a boat conformation which allows the C(8) methyl group to assume an equatorial position. Spectroscopic measurements indicate that this type of geometry, which has the lowest strain-energy as calculated by molecular mechanics (GEMO program),is also present in solution.