N-Isopropenylazoles: I. Direct N-Isopropenylation of Azoles with Propyne and Allene

A number of previously unknown N-isopropenyl-substituted pyrroles, indoles, and di- and -triazoles were synthesized in 20-86% yield by reaction of the corresponding azole with an equilibrium mixture of propyne with allene or pure propyne and allene in the system KOH-DMSO (105-145°C, 5-15 h, atmospheric or elevated pressure). The reaction is regioselective. The electronic and steric structure and the degree of conjugation between the exocyclic double bond and the azole ring are discussed on the basis of the ¹H and ¹³C NMR spectra. Almost complete absence of p- conjugation in ,'-disubstituted N-isopropenylazoles have been found.     

N-Isopropenylazoles: II. Fragmentation of N-Isopropenylazoles under Electron Impact

Fragmentation under electron impact of all N-isopropenylazoles, except for N-isopropenyl-2- phenylpyrrole, involves elimination of propyne or allene with formation of the corresponding NH azoles. N-Isopropenylpyrrole, N-isopropenyl-4,5,6,7-tetrahydroindole, and N-isopropenylindole give rise to rearrangement of the molecular ion into azepine structure, while the fragmentation of N-isopropenyl-2-phenylpyrrole is accompanied by transfromation into 5-methyl-5,6-dihydropyrrolo[2,1-a]isoquinoline. Retrodiene decom- position is the main fragmentation pathway of the molecular ions derived from N-isopropenyl-4,5,6,7-tetrahydroindole and its 2-methyl-substituted analog. In the decomposition of 2,3-di- and 2,3,5-trimethyl-N-isopropenylpyrrole, the major fragment ions are formed from the [M - H]⁺ ion having a pyridinium structure rather than from the molecular ion. N-Isopropenyldi- and -triazoles undergo fragmentation along competing pathways involving cleavage of the heteroring.