Total Synthesis Of (+/-)Marmin And Related Coumarin Monoterpenes

(±)-Marmin ( 1a ) and its cis isomer ( 1b ) have been synthesized from 7-neranyloxycoumarin ( 10a ) and 7-neryloxycoumarin ( 10b ), respectively, by way of the corresponding terminal epoxides 2a and 2a . The geometrically and positionally specific route confirms the structure and, in particular, the irons double bond geometry of natural (+)-marmin and epoxide (+)- 2a . The latter, upon reaction with stannic chloride in benzene gives rise to the naturally occurring cyclic monoterpene coumarin types 3 and 6 as well as the previously unknown double-bond isomer 13 .