Concise formal synthesis of (-)-7-deoxyloganin via n-heterocyclic carbene catalysed rearrangement of alpha,beta-unsaturated enol esters

NHC catalysed rearrangement of alpha,beta-unsaturated enol esters derived from formyl acetates and cyclopentyl annulated alpha,beta-unsaturated acids provides the cyclopentapyranone core of (-)-7-deoxyloganin (1) with diastereo- and chemoselectivity in 6 steps starting from (-)-citronellal. The elaboration to the natural product has been investigated using two new approaches. The most successful intercepts our previous work on (-)-7-deoxyloganin (1) allowing completion of a formal total synthesis in 10-steps.