Diastereoselective Synthesis of Diquinanes and Triquinanes Bearing Vicinal Quaternary Carbon Stereocenters from Acyclic Allene-based Precursors via a Cascade Reaction

A cascade benzenethiol-mediated intramolecular
[3 + 2] cycloaddition
reaction between an allene and an α,β-unsaturated aldehyde
or ester is developed for the diastereoselective synthesis of [3.3.0]
bicyclic system bearing two quaternary atoms at their bridgehead positions.
Notably, these structurally complex systems can be found in a wide
range of natural products.