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Bioinspired Diastereoconvergent Synthesis of the Tricyclic Core of Palodesangrens via Diels–Alder Reaction, LiAlH4-Mediated Isomerization, and Acid-Mediated Cyclization

Author:
Songthammawat, Poramate, Wangngae, Sirilak, Matsumoto, Koki, Duangkamol, Chuthamat, Ruchirawat, Somsak, Ploypradith, Poonsakdi
Source:
Journal of organic chemistry 2018 v.83 no.9 pp. 5225-5241
ISSN:
1520-6904
Subject:
alcohols, biomimetics, chalcones, cyclohexenes, isomerization, isomers, moieties, organic chemistry, stereochemistry
Abstract:
The cyclohexene moiety of the tricyclic 6,7-diaryl-tetrahydro-6H-benzo[c]chromene core of palodesangrens could be assembled in a biomimetic and step-economical fashion by the Diels–Alder reaction between the electron-rich (E)-1,3-butadienylarenes as the diene and the electron-deficient chalcones as the dienophile. During the reduction of ketone to the corresponding alcohol by LiAlH₄, the mixture of endo and exo isomers underwent a novel diastereoconvergent LiAlH₄-mediated isomerization to install the desired stereochemistry at C10a. Subsequent pyran ring closure under acidic conditions installed the stereochemistry at the remaining C6. Overall, the tricyclic core of palodesangrens could be prepared in three steps and up to 38% yield.
Agid:
6047270