Journal of Organic Chemistry 2010-05-07

A ring contraction strategy toward a diastereoselective total synthesis of (+)-bakkenolide A.

Vânia M T Carneiro, Helena M C Ferraz, Tiago O Vieira, Eloisa E Ishikawa, Luiz F Silva

Index: J. Org. Chem. 75(9) , 2877-82, (2010)

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Abstract

A diastereoselective route to (+)-bakkenolide A is presented from the readily available optically active Wieland-Miescher ketone. This novel synthesis of this sesquiterpene lactone features the following as key stereoselective transformations: (i) the ring contraction reaction of a octalone mediated by thallium(III) nitrate (TTN); (ii) a hydrogenation to create the cis-fused junction; and (iii) the formation of the C7 quaternary center through an enolate intermediate. Furthermore, during this work, the absolute configuration of a trinorsesquiterpene isolated from Senecio humillimus was assigned.