213013-06-0Relevant academic research and scientific papers
N-Mesityl-C-acylketenimines: 1,5-Sigmatropic Shifts and Electrocyclization to Quinolines
Rao, V. V. Ramana,Fulloon, Belinda E.,Bernhardt, Paul V.,Koch, Rainer,Wentrup, Curt
, p. 5779 - 5786 (2007/10/03)
Flash vacuum thermolysis (FVT) of triazoles 6a- c generates α-oxoketenimines 10, the ester 10a being isolable. FVT of pyrroledione 8 generates the isomeric imidoylketene 9a. Ketenes 9 and ketenimines 10 undergo thermal interconversion by 1,3-shifts of methoxy and dimethylamino groups under mild FVT conditions (ca. 350-400°C). Both 9 and 10 are directly observable by IR spectroscopy at either 77 K or on Ar matrix isolation at 12 K. On FVT at temperatures above ca. 400°C, the ketenimines 10 undergo a 1,5-H shift to o-quinoid imines 12/13, followed by electrocyclization to dihydroquinolines 14 (unobserved) and 15 (observed by NMR). The latter are easily oxidized to alkylquinoline-3-carboxylates or quinoline-3-carboxamides 16 by atmospheric oxygen. Ab initio calculations on model compounds 18-23 predict an energy barrier of ca. 38 kcal mol-1 (161 kJ mol-1) for the 1,5-H shift in N-(o-methylphenyl)ketenimines via the transition state TS19 followed by an electrocyclization barrier to dihydroquinoline 23a via TS22a of ca. 16 kcal mol-1.
