Collective synthesis of humulanolides using a metathesis cascade reaction

A new method has been developed for the concise and asymmetric synthesis of seven humulanolides in 5-7 steps without the need for protecting groups. Notably, the challenging 11-membered ring and bridged butenolide moieties in asteriscunolide D and 6,7,9,10-tetrahydroasteriscunolide were introduced in one step using a ring-opening/ring-closing metathesis cascade reaction. Asteriscunolide D was used as a versatile synthetic precursor to prepare asteriscunolides A-C via a photoinduced isomerization reaction, asteriscanolide via a unique transannular Michael reaction, and 6,7,9,10-tetradehydroasteriscanolide via a transannular Morita-Baylis-Hillman-type reaction. The unique bicyclo[6.3.0]undecane core was introduced diastereoselectively.