2-AZIDO-1-METHYLINDOLE AND 3-AZIDO-1-METHYLINDOLE - SYNTHESIS, THERMAL REACTIVITY, H-1-NMR AND C-13-NMR SPECTRAL PROPERTIES, AND SEMIEMPIRICAL MNDO-PM3 STRUCTURAL CALCULATIONS

2-azido-, 1, and 3-azido-1-methylindole, 2 are prepared by azido group transfer reaction of the appropriate heteroaryllithium derivative wit h p-toluenesulphonyl azide. Mild thermal fragmentation of azide 1 in i nert solvent leads to a ring-opened ortho-quinone cyanomethide methyli mine intermediate A which, by [4+2] cyclodimerization followed by rear rangement, mainly affords alpha,beta-dicyanostyr-2-yl)-1,2-phenylenedi amine) whose molecular structure was confirmed by an X-ray crystal str ucture determination. In addition, azide 1 generally reacts with termi nal or 1,2-disubstituted E or Z alkenes to give aziridines (arising by extrusion of nitrogen and ring-contraction of former triazolines) as well as 4-cyanotetrahydroquinolines, the Diels-Alder [4+2] cycloadduct s of A; however, in the presence of 1-pyrrolidino-1-cyclopentene it on ly affords the appropriate triazoline in quantitative yields. On the o ther hand, azide 2 fails to react similarly with alkenes, but in the p resence of alkynes, viz. (trimethylsilyl)-acetylene and methyl propiol ate, affords the corresponding triazoles five times faster than the is omeric azide 1. Kinetic measurements indicated that azides 1 and 2 exh ibit first-order thermal decomposition with comparable activation para meters (E(a) = 23.0 and 22.1 kcal mol(-1), Delta S-not equal = -8.1 an d -9.8 cal mol(-1) K-1, respectively). Ground-state electron density d istributions and geometries are presented for both azides 1 and 2 as d etermined by semiempirical MNDO-PM3 calculations.