Imidoylketene dimerization and rearrangement

Abstract

FVT of pyrroledione 10 affords the NH-imidoylketene 11, which is characterized by its matrix isolation IR spectrum (2117 cm⁻¹). On warming above 170 K, 11 dimerizes to the oxazinone 13, the X-ray crystal structure of which is reported. Imidoylketene 11 also undergoes a (reversible) 1,3-phenyl shift to afford the detectable α-oxoketenimine 16 (2062 cm⁻¹) which at FVT temperatures above 400 °C, isomerizes to 2-cyano-2-phenylacetophenone 18 (optimally at 700 °C). Moreover, imidoylketene 11 can cyclize to azetinone 19, detectable at FVT temperatures up to 570 °C, which undergoes cycloreversion to diphenylacetylene 20 and isocyanic acid (HNCO) 21. Energy profiles calculated at the B3LYP/6-31G** level for the unsubstituted imidoylketene, the diphenylimidoylketene 11 and the N-tert-butylimidoylketene are also reported.