We are developing the synthesis of biologically interesting condensed-heteroaromatic compounds, including natural products by the thermal electrocyclic reaction of 6 pi electron system incorporating the double bond of the principal aromatic or heteroaromatic ring. In this report, we describe three types of electrocyclic reactions as follows; 1) the synthesis of highly-substituted carbazole alkaloids based on the allene-mediated electrocyclic reaction involving an indole 2,3-bond, 2) the synthesis of beta -carboline alkaloids and isoquinoline-5,8-quinone alkaloids based on the thermal electrocyclic reaction of an 1-azahexatriene system involving an indole 2,3-bond or benzene 1,2-bond, and 3) the synthesis of new tetracyclic pyrido [2,3-b] indole, grossularines, based on the thermal electrocyclic of an 2-azahexatriene system including the indole 2,3-bond.