Abstract
For the purpose of the synthesis of indole alkaloids having alkyl substituents at the benzene portion of the indole, two novel procedures are developed for synthesizing 4, 5, 6 and/or 7-alkylindole derivatives from pyrrole derivatives. One is a stannic chloride or ptoluenesulfonic acid catalyzed cyclization reaction of compounds 20 and 24, which are synthesized by a stannous chloride mediated reaction of 1-trimethylsily-1, 3-butadiene derivatives 23 on the endoperoxide of 1-methoxycarbonylpyrrole 13. Another is a sulfuric acid catalyzed ring cyclization of 1-tosylpyrrole derivatives 74 to afford 4, 6 and 7-alkyl substituted indoles. These results are applied to the synthesis of (±)-α-cyclopiazonic acid 5, a mycotoxin isolated first from Penicillium cyclopium, teleocidin A-1 8a and A-2 8b, tumor promoters, and N-alkylergolines and their D-nor or D-homo derivatives, 81, 82, and 83.
