Studies Towards the Synthesis of Salvinorin A

Salvinorin A 1, a psychoactive neoclerodane diterpenoid from the Mexican sage S. divinorum, has gained inter-est as a selective κ-opioid receptor agonist. Non-racemic 3-furylamines 9a and 9b have been prepared from (+)-pseudoephedrine and (−)-ephedrine for application in the stereoselective synthesis of the ketone ring of 1. Diels–Alder reaction of 9b with methyl acrylate in aqueous media, followed by selective ether bridge cleavage, has allowed access to the cyclohexenone 17 with preservation of stereochemistry at C2. A model route to the lactone ring has also been achieved through a one-pot deconjugation/esterification procedure of 2-bromocrotonyl chloride 20 to the furyl alcohol 19 followed by Reformatski-mediated ring closure