Total synthesis of (-)-7-deoxyloganin exploiting N-heterocyclic carbene catalysis with α,β-unsaturated enol esters

This account describes studies on the application of N-heterocyclic carbene (NHC) catalysis to the synthesis of the iridoid natural product (-)-7-deoxyloganin. The synthesis has been completed in 17 steps, while an improved formal synthesis can be achieved in 10 steps. Pivotal to both approaches is the application of NHC catalysis with ester oxidation state substrates that allows conversion of α,β-unsaturated enol esters to the corresponding dihydropyranone. Subsequent conversion of this material to the natural product is achieved by chemoselective reduction of the lactone and glycosylation using an approach originally developed by Tietze. A number of end game strategies have been examined, with the successful approach involving early installation of methyl ester functionality.