Computational investigation of rearrangements in huisgen cycloadducts of azolium N-dicyanomethanide 1,3-dipoles with alkynes: a mechanistic panoply.
The reaction surfaces leading to rearrangements and ring expansions of azapentalene cycloadducts of imidazolo- and triazolodicyanomethanide 1,3-dipoles with alkynes are studied with the B3LYP DFT method using the 6-31G(d) and 6-311+G(2d,p) basis sets. The surprisingly complex surface involves (1) consecutive but not combined pericyclic steps, a coarctate TS, and pseudopericyclic mechanisms, (2) anchimerically assisted H-atom transfer competing effectively with concerted symmetry-allowed sigmatropic steps, and (3) azolium methanide zwitterions and ketenimines as key intermediates. The azolium methanide is identified as the intermediate detected previously in a variable-temperature NMR experiment that converted the unstable cycloadduct to product imine.
Burke
Luke A
LA
Chemistry Department, Rutgers University, Camden, New Jersey 08102, USA. burke@camden.rutgers.edu
Butler
Richard N
RN