Catalytic Asymmetric Spirocyclizing Diels-Alder Reactions of Enones: Stereoselective Total and Formal Syntheses of α-Chamigrene, β-Chamigrene, Laurencenone C, Colletoic Acid, and Omphalic Acid

We disdose a general catalytic enantioselective Diels-Alder reaction of exo-enones with dienes to give spirocyclanes. The obtained products feature highly congested quaternary stereogenic spirocenters and are used in concise total and formal syntheses of several sesquiterpenes, including of alpha-chamigrene, beta-chamigrene, laurencenone C, colletoic acid, and omphalic acid. The stereo- and regioselectivities of our spirocyclizing cycloaddition are effectively controlled by strongly acidic and confined imidodiphosphorimidate catalysts. Computational studies shed light on the origin of reactivity and selectivity.

Automated summary

A catalytic enantioselective Diels-Alder reaction has been developed for the synthesis of spirocycles containing highly congested quaternary stereogenic centers. The obtained products are utilized in the concise total and formal syntheses of several sesquiterpenes. The selectivity and regioselectivity of the reaction are controlled by strongly acidic and confined imidodiphosphorimidate catalysts.