The Intramolecular 1,3-Dipolar Cyclisation of Mesoionic Species Generated by the Thermolysis of the Mixed Anhydrides of Acetic and N-Alkynoyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic Acids

Article abstract of DOI:10.1016/S0040-4020(01)86306-7

The intramolecular cyclisations of mesoionic intermediates formed by heating N-alkynoyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acids C-(CH2)nCO, where n = 3 or 4> with acetic anhydride, have been investigated.The final products are octahydropentaleno<2,3-a>isoquinolines and hexahydroindeno<2,3-a>isoquinolines, respectively, formed by the expulsion of carbon dioxide from the initial adducts.The behaviour of alkenes and alkynes as dienophiles in intermolecular versions of the cycloaddition reactions have also been studied.Alkynes bearing electron withdrawing groups afford pyrrolo<1,2-b>isoquinolines, but unless alkenes, such as benzylidenemalonodinitrile are used (where the first formed adduct can eliminate HCN, prior to loss of CO2), the reactions fail.