A total synthesis of myrrhine, (±)-hippodamine, and (±)-convergine

A seven-step, stereoselective, total synthesis of the ladybug defensive substance myrrhine ( 5 ) from 2,4,6-collidine is presented. Successive alkylation and acylation of 2,4,6-collidine followed by ketalization provides 2-(3-[2-(1,3-dioxolanyl)]propyl)-6-(2-methyl-2-[1,3-dioxolanyl]methyl)-4-methylpyridine ( 14 ). Sodium-alcohol reduction gives the corresponding all-cis piperidine 17 . Hydrolysis of 17 followed by acid-catalyzed cyclization provides ketone 26 . Reduction of the carbonyl group in 26 gives myrrhine ( 5 ). Cyclization using pyrrolidine - acetic acid gives a mixture of ketones ( 26 and 31 ). Reduction of 31 gives (±)-hippodamine ( 4 ). Oxidation of (±)-hippodamine with peracid gives (±)-convergine ( 3 ).