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Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
A ring contraction strategy toward a diastereoselective total synthesis of (+)-bakkenolide A
Vânia M T Carneiro1, Helena M C Ferraz, Tiago O Vieira
1Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, CP 26077, CEP 05513-970 São Paulo SP, Brazil.
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.
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