Concise Four-Step Total Synthesis of (±)-Carpanone

Key words

(±)-carpanone - oxidative phenolic coupling - hetero-Diels–Alder reaction - biomimetic synthesis - ortho-quinone methide

Significance

Isolated from the bark of the carpano tree, (±)-carpanone possesses significant structural complexity in the form of five contiguous stereocenters and six rings. Inspired by the proposed biosynthesis (G. C. Brophy et al. Tetrahedron Lett. 1969, 10, 5159), Chapman et al. established that the target can be formed in a single step by oxidation of the simple and achiral precursor D.

Comment

Known 6-allylsesamol (C), accessible from sesamol in two steps, was transformed into phenol D by double bond migration under basic conditions. Treatment with PdCl₂ effected oxidative phenolic coupling, followed by an intramolecular inverse-electron-demand hetero-Diels–Alder reaction to set all five contiguous stereocenters and furnish the target structure.