Stabilizing the Hammick intermediate.

The possible stabilization of pyridine-2-ylidene has been investigated at B3LYP/6-31+G* and B3LYP/6-311+G** levels of theory. The aromaticity of this compound is a significant contributor to its stability (ISE(c) = 24-27 kcal mol(-1), Bird index = 77, NICS(0) = -6.8 ppm, NICS(1) = -9.1 ppm; all about 80% of those for the H-shift isomer pyridine). The stabilization energy of the carbene (measured by an appropriate isodesmic reaction) can be influenced by the substitution at nitrogen with bulky groups, and at the carbon atom by amino groups. Considering possible competitive deprotonation reactions of the most likely synthetic route, 1j, 1k, and 1L are suggested as synthesizeable new stable carbenes.