1,3-Dipolar Cycloaddition of Nitrile Oxides to 8-Azaheptafulvenes
作者:Remo Gandolfi、Anna Gamba、Paolo Grünanger
DOI:10.3987/com-94-s50
日期:——
Azaheptafulvenes (2) reacted readily with nitrile oxides (1) to give, as a rule, only adducts derived from a reaction involving the C=N moiety of 2. The adducts consisted of a mixture of rapidly equilibrating ''spiro'' and ''condensed'' isomers, i.e. 6 reversible arrow 8, whose ratio was found to be dependent on substituents, temperature and solvent. The zwitterion (7) is an an appealing intermediate both for cycloaddition and isomerisation. Decomposition of the adducts to benzene, R(1)CN and R(2)NCO provided evidence in favor of the presence of the ''norcaradiene'' derivatives (14) (undetectable by nmr) in equilibrium with 6 and 8. Only products arising from the ''spiro'' isomer (6) were obtained in high yields in the catalytic hydrogenation of 6/8.