X= Y-ZH Systems as Potential 1, 3-Dipoles. Part 45. 1, 2 Proton Sponge Effects on the 1, 2-Prototropic Formation of Azomethine Ylides from Arylidene Benzylamines
A strong rate enhancing effect of an ortho-methoxy or an ortho-dimethylamino group on the 1, 2-prototropic generation of azomethine ylides from arylidene arylmethylamines is demonstrated. In the absence of such functionality azomethine ylide formation fails to occur in boiling xylene. The reactions generate the E, E-or syn-azomethine ylide stereoselectively if a single ortho-OMe or-NMe2 group is present or stereospecifically if either bifurcated H- ...