2-diazo-2H-indoles

2-Diazo-2H-indoles were prepared by diazotization of the corresponding 1H-i ndol-2-amines and subsequent neutralization. On the basis of NMR data and a b initio, and semiempirical calculations, we suggest that the zwitterionic form A is the most representative structure for 2-diazo-2H-indoles. In fact , spectral data are compatible with a IH-indole structure, and the fully op timized molecules gave distances in agreement with those reported for the a nion obtained from 1H-indole. The calculated charges are compatible with a zwitterionic structure in which the negative charge is mainly located at th e ring N-atom at variance with the case of diazopyrroles and 3-diazo-3H-ind oles where the negative charge is essentially located on the ipso C-atom.