Asymmetric Total Synthesis of the 1-epi-Aglycon of the Cripowellins A and B
摘要:
[GRAPHICS]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-epiaglycon 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.
First Enantioselective Synthesis of (-)-(2<i>S</i>,6<i>S</i>)-(6-Ethyltetrahydropyran-2-yl)formic Acid
作者:Mário L. Vasconcellos、Leandro S. M. Miranda、Bruno A. Meireles、Jerônimo S. Costa、Vera. L. Pereira
DOI:10.1055/s-2005-863744
日期:——
the first enantioselective synthesis of (-)-(2S,6S)-(6-ethyltetrahydropyran-2-yl)formic acid (2) in five steps (30% overall yield, 87% ee), from the commercial chiral template (R)-2,3-isopropylideneglyceraldehyde (4). The two stereogenic centers in 2 were controlled by diastereoselective Barbier allylation of 4 in aqueousmedia and an efficient Prins cyclization reaction between 5 with propanal.