Versatile base-catalyzed route to polycyclic heteroaromatic compounds by intramolecular Aza-Michael addition

A catalytic new synthetic approach to 3,4-dihydropyrazino[ 1,2-a]indol-1 (2H) -ones by intramolecular 1,4-dddition of readily available alpha,beta-unsaturated esters, is described. Here, the use of a range of organic as well as inorganic bases (5-10 mol-%) allowed a fast (30 min) and regioselective ring-closing reaction to be performed in high yields under simpleoperational conditions. Moreover, the protocol was effectively employed, as the key step, in the synthesis of the dibromopyrrolo alkaloid derivative N-Bn-longamide b. ((c) Wiley-VCH Verlag GmbH & Co.