A biomimetic approach for bicyclic alkaloids using acetal pro-nucleophile: total synthesis of (±)-epilupinine and formal syntheses of (±)-laburnine, (±)-isoretronecanol, (±)-tashiromine

A direct Mannich type diastereoselective biomimetic cyclization using acetal as a pro-nucleophile leading to the hydroxymethyl substituted bicyclic framework of various bicyclic alkaloids is presented. Following this protocol, total synthesis of (±)-epilupinine and formal syntheses of (±)-laburnine, (±)-isoretronecanol and (±)-tashiromine are described.