Azomethine ylides such as 1 and 4 in which the nitrogen atom is incorporated in a six-membered heterocyclic ring undergo regiospecific [3+2] cycloadditions with the phosphaalkynes 2a and b at 130–140 °C to furnish the phosphaindolizines 3 and 5a–c after elimination of ethyl formate or hydrogen cyanide, respectively. In contrast, dipoles of the type 6 react unspecifically with the phosphaalkyne 2a to
Cycloaddition reactions of cycloimmonium ylides with triphenylcyclopropene
作者:Kiyoshi Matsumoto、Takane Uchida
DOI:10.1039/p19810000073
日期:——
course of the reaction is discussed qualitatively. The pyrazinium dicyanomethylide (16) with TPP produces the 7-azaindolizine (19), whereas pyridazinium (17) and phthalazinium (18) dicyanomethylides give the primary adducts (20) and (21), respectively. Reaction of pyridinium bis(alkoxycarbonyl)methylides (22) with TPP gives, however, generally poor or no yield of the indolizines.
Cyclooctyne smoothly underwent 1,3-dipolar cycloaddition with pyridinium dicyanomethylides to afford the corresponding indolizines (8-cyario-7-azatricyclo[7.6.0.02,7]pentadeca-1,3,5,8-tetraenes) in excellent yields.