A concise enantioselective synthesis of the AB ring system of the manzamine alkaloids by ring-closing enyne metathesis

The AB ring system found in the manzamine A and related alkaloids has been prepared from (−)-quinine by a short enantioselective route. The key step in the sequence is a ruthenium-catalysed ring-closing enyne metathesis re action which delivers a bicyclic diene in good yield. The functionality required for further elaboration of the AB system has been installed by sequential regioselective hydroboration and stereoselective catalytic aminohydroxylation.