Absolute configuration and total synthesis of (-)-cabenegrin A-I

Article abstract of DOI:10.1016/S0040-4020(99)00490-1

The total synthesis of (-)-cabenegrin A-I [(-)-1] in five steps was achieved from (-)-6aR, 11aR-maackiain [(-)-5], which in turn was prepared by the optical resolution of racemic (±)-5 using S-(-)α-methylbenzyl isocyanate as the the chiral auxiliary. The homochirality of(-)-maackiain [(- )-5] and (-)cabenegrin A-I [(-)-1] was proved by CD measurements. Synthesis of (±)maackiain [(±)-5] is also presented, starting from the readily available phenol derivatives resorcinol and sesamol, which demonstrates the synthetic utility of the Heck-type oxyarylation process for obtaining pterocarpane derivatives on a multigram scale. A new ring-opening reaction of pterocarpanes (7 → 28) is described.