A hetero Diels-Alder concerted vs. aldol stepwise mechanism in the cyclization of silyloxyazadienes with aldehydes: A theoretical study

The Diels-Alder reaction of 3-silyloxy-2-azadiene with formaldehyde has been studied at the B3LYP/6-31G* level of theory and the role played by a Lewis acid evaluated. It is shown that the reaction is preferred when the Lewis acid coordinates to the aldehyde oxygen. This coordination allows for a concerted as well as a stepwise mechanism for the cyclization. (c) Wiley-VCH Verlag GmbH & Co.