Concise Asymmetric Syntheses of (+)- and (-)-Tetraponerine-8, (+)- and (-)-Tetraponerine-7, and their Ethyl Homologues. A Correction of the Structures of Tetraponerine-3, and -7.

Article abstract of DOI:10.1016/0040-4020(94)01030-4

(+)- and (-)-T-8, (+)- and (-)-9-epi-T8, and their ethyl homologues were synthesized in six steps and 27percent overall yield from chiral acetylenic sulfoxide (+)-7a or (+)-7b, via a cycloaddition reaction with 3,4,5,6-tetrahydropyridine-1-oxide, and chromatographic separation of the resulting diastereoisomeric Δ⁴-isoxazolines.Comparison of the spectral properties of the synthetic (+)-9-epi-T-8 with those of natural (+)-T-7 and (+)-T-3 led us to correct the structures of the latter two compounds.The absolute configuration of (+)-T-4 was determined to be 5R,9S,11R, and those of (+)-T-7 and (+)-T-3 to be 5R,9R,11R by comparison of their CD curves with those of the synthetic compounds.