First enantioselective synthesis of isagarin, a natural product isolated from Pentas longiflora Oliv.

For the first time, an enantioselective synthesis of both 1R,4S-isagarin 1a and 1S,4R-isagarin 1b was achieved starting from 1,4-dimethoxy-2-vinylnaphthalene 2. The key steps involve a Sharpless asymmetric dihydroxylation and reaction with an acetonylating pyridinium ylid. The different optical rotations and melting points of the enantiopure 1R,4S-isagarin 1a and 1S,4R-isagarin 1b with respect to the isolated natural product will be addressed.