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).