CYCLOADDITION REACTION OF 3-CYANOINDOLIZINES WITH DIMETHYL ACETYLENEDICARBOXYLATE —FORMATION OF CYCL[3.2.2]AZINES AND 1:2 ADDUCTS
3-Cyano- and 3-cyano-6,8-dimethylindolizines (1a) and (1b) react with dimethyl acetylenedicarboxylate in refluxing toluene in the presence of Pd–C to give the cycl[3.2.2]azines (4a) and (4b), respectively, while 3-cyano-7-methyl- and 3-cyano-7-benzylindolizines (1c) and (1d) affording the 1:2 adducts (6c) and (6d) along with cycl[3.2.2]azine (4d).