A stereodivergent total synthesis has been executed based on the plausibly misassigned structure of the unusual marine hydrindane mucosin (1). The topological connectivity of the four contiguous all-carbon stereocenters has been examined by selective permutation on the highlighted core. Thus, capitalizing on an unprecedented stereofacial preference of the cis-fused bicycle[4.3.0]non-3-ene system when
Total synthesis based on the originally claimed structure of mucosin
作者:Harrison C. Gallantree-Smith、Simen G. Antonsen、Carl H. Görbitz、Trond V. Hansen、Jens M. J. Nolsøe、Yngve H. Stenstrøm
DOI:10.1039/c6ob01511e
日期:——
The first totalsynthesis aimed at the naturally occurring eicosanoid bicycle mucosin is reported. A practical route has been devised allowing the issues relating to the previous assignment of stereochemistry to be examined. X-ray crystallography was performed on a late stage intermediate to pinpoint the topological relationship displayed by the featured bicyclo[4.3.0]non-3-ene scaffold.
The chiral mono-thiol diester, 1 or 2, is converted to the corresponding enantiomeric cyclised products,(–)-7 and (+)-7 or (–)-9, and (+)-9, depending on whether LDA or AlCl3–Et3N is used.
It was revealed that the Dieckmann type annulation of a half-thiol diester having latent σ-symmetry did not always proceed in the regiocontrolled fashion even though the reaction yielded the desired β-keto ester. Direction of the regioselectivity dramatically differed depending on the base employed, which was demonstrated by treating an optically pure half-thiol diester with lithium diisopropylamide, dimsylsodium, and dimsylpotassium, respectively.
The chiral bicyclic β-keto ester (14), which is synthesised by our methods involving stereoselective differentiation between two identical groups in the diamide (4) of (R)-4-methoxycarbonyl-1,3-thiazolidine-2-thione and regiocontrolled Dieckmann-type cyclisation of half-thiol diester (11), has been successfully converted into (+)-carbacyclin (2).