Collective synthesis of several 2,7′-cyclolignans and their correlation by chemical transformations

Abstract

Collective synthesis of anti-malarial 2,7′-cyclolignans has been stereoselectively achieved employing (±)-cyclogalgravin (2) as a linchpin through a series of functional group conversions, including redox reactions. Interestingly, 2 can be correlated with the neolignan (±)-kadangustin J (1) isolated from a different plant source, through a highly efficient dehydrative cyclization reaction with excellent diastereotopic differentiation of the veratryl group and concomitant construction of the C1–C7 bond. It is noteworthy that the first total synthesis of stereodivergent (±)-8,8′-epi-aristoligone (5), (±)-8′-epi-aristoligone (7), (±)-8′-epi-8-OH-aristoligone (8) and (±)-8′-epi-aristoligol (9) was demonstrated.