Studies on the Reactions of Heterocyclic Compounds. VIII. 1, 3-Dipolar Cycloaddition Reaction of Isoquinolinium Cyano (methoxycarbonyl)-methylide with Dimethyl Acetylenedicarboxylate : Structure and Reaction of the Adduct

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1, 3-Dipolar cycloaddition of isoquinolinium cyano (methoxycarbonyl) methylide (V) and dimethyl acetylenedicarboxylate gave only one (VI) of the two possible primary adducts. Examination of the pyrolysis of this adduct revealed the structure of VI to have 10bhydrogen and 3-ester group in cis configuration. Heating of VI afforded 2, 3-dihydropyrroloisoquinoline (VIII), while its treatment with hydrogen chloride in benzene, followed by neutralization with potassium carbonate afforded the adduct (XIII) of two diastereoisomers (VIII and XIV). VIII was found to be unstable to acid and base, resulting in immediate hydrolysis of the ester group in its 3-position and decarboxylation to the diester (X). From the consideration of its reaction mechanism, the ester group in the 2- and 3-positions of VIII was determined to have a cis configuration and those in XIV, a trans configuration.