1451070-61-3Relevant academic research and scientific papers
Isocyanide cyclization reactions: 4-methylene-4H-benzo[d][1,3]oxazine, 3-benzyl-4-methylene-3,4-dihydroquinazolines and 3-(4-benzyl)-3H-quinazolin-4- ones - Experiment and theory
Neue, Benedikt,Reiermann, Ralph,Froehlich, Roland,Wibbeling, Birgit,Bergander, Klaus,Wuerthwein, Ernst-Ulrich
, p. 4944 - 4952 (2013/08/23)
2-Isocyanoacetophenone (3a) was found to be an easily accessible starting material for the unexpected formation of various heterocyclic systems. Thus, a hitherto unknown rather unstable 4-methylene-4H-benzoxazine derivative 4, which could be characterized by NMR spectroscopy, was formed in situ by the reaction of 3a in the presence of weak acids. In the presence of benzylamines, a new class of 3,4-dihydroquinazoline derivatives 6 and their oxidation products, quinazolin-4-ones 9, were obtained. The starting materials and products were completely characterized by spectroscopic and X-ray analysis. The scope and limitations of these cyclization reactions were investigated under various reaction conditions. High-level quantum chemical calculations were carried out to elucidate the mechanisms leading to scaffolds 4 and 6. The calculations suggest that the formation of 4 and 6 involves the generation of an unusual six-membered N-heterocyclic carbene or its C-protonated form as a reaction intermediate, followed by tautomerisation. This mechanism might also be applicable to other isocyanide cyclization reactions. Copyright
