Antifertility agents: synthesis of yuehchukene analogues: 6β-(indol-3-yl)-9,12-dimethyl-6,7,10,11-tetrahydro-7,11-methano-5H-[b]indole and 6β-(indol-3-yl)-9,12-dimethyl-6,7,8,11-tetrahydro-7,11-methano-5H-cyclo-oct[b]indole

Abstract

Diels–Alder reactions between (E)-3-(3-methylbuta-1,3-dienyl)-1-tosylindole (3) and β-substituted acrylic acid derivatives are described. Reaction of (3) with maleic anhydride afforded the adduct (14). The latter compound in the presence of aluminium trichloride underwent intramolecular acylation with rearrangement to give 9-methyl-6-oxo-5-tosyl-6,7,8,11-tetrahydro-7,11-methano-5H-cyclo-oct[b]indole-12-carboxylic acid (16) and its double bond isomer (17) possessing a skeleton with a close resemblance to that of yuehchukene (1), an antifertility agent. Compounds (16) and (17) were stereoselectively converted into the title compounds (28) and (29). The structures of two precursors, (24) and (25), of compounds (28) and (29) have been determined by X-ray crystallography.