Abstract
The unusual [5.3.2]-bicyclic structure of the insecticidal Amaryllidaceae alkaloids cripowellin A (1) and B (2) has been synthesized for the first time via a sequence of Sharpless dihydroxylation, ring-closing metathesis, and intramolecular Heck reaction. The asymmetric synthesis of the 1-epi-aglycon 82 proceeds with virtually complete diastereo- and enantioselectivity (de, ee ≥ 98%) in 13 steps and an overall yield of 5.6%. In addition, three alternative approaches toward the aglycon 3 are also described focusing on (1) the alkylation of the 2-benzazepinedithianes 35 and 36 with the electrophile 11, (2) a radical cyclization of the precursor (R/S,S,S)-39, and (3) an intramolecular arylation reaction of the aryl ketone 47.
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