Abstract
The first total and stereoselective synthesis of (±)-tecomanine (1), one of the monoterpene alkaloids, was accomplished starting from ethyl 1, 6-dihydro-3 (2H)-oxopyridine-1-carboxylate (2a). The allylic alcohol (8), obtained as a major product on treatment of 2a with methylmagnesium iodide, was subjected to the Claisen rearrangement using ethyl (1-propenyl) ether to afford the aldehyde (30) which was converted to the methyl ketone (32). The acetal (33) was stereoselectively hydrated by a hydroboration-oxidation process to give the alcohol (34) in an excellent yield. To prevent formation of the furan (38), the product (34) was initially hydrolyzed and then oxidized to afford the diketone (36). Although 36 is a mixture of two diastereoisomers due to the configuration of the side-chain methyl group, each isomer, 36a and 36b, provided solely the desired product (40) upon base-catalyzed intramolecular aldol reaction. The urethane (40) was easily converted into (±)-tecomanine (1) by LiAIH4 reduction and subsequent PCC oxidation.
