A radical cyclisation strategy to α-spiro-β-methylene-γ-butyrolactones. Total synthesis of (±)-norbakkenolide-A
Abstract
The 5-exo-dig radical cyclisation reaction of the bromoacetals 9, obtained from the enol ethers 8, and treatment of the resulting hemiacetal 10 with Jones′ reagent transforms the cyclic ketones 7 and 12 into α-spiro-β-methylene-γ-butyrolactones 11 and norbakkenolide-A 2.