Total synthesis of (-)-morphine.

We have developed an efficient total synthesis of (-)-morphine in 5% overall yield with the longest linear sequence consisting of 17 steps from 2-cyclohexen-1-one. The cyclohexenol unit was prepared by means of an enzymatic resolution and a Suzuki-Miyaura coupling as key steps. Construction of the morphinan core features an intramolecular aldol reaction and an intramolecular 1,6-addition. Furthermore, mild deprotection conditions to remove the 2,4-dinitrobenzenesulfonyl (DNs) group enabled the facile construction of the morphinan skeleton. We have also established an efficient synthetic route to a cyclohexenol unit containing an N-methyl-DNs-amide moiety.