Facile Rearrangements of Alkynylamino Heterocycles with Noble Metal Cations

A number of 2-(alkynylamino)-substituted heterocycles have been synthesized. These heterocycles rearrange in the presence of silver(I) and gold(I) salts to give novel 2 H -pyrimido[2,1- b ]benzoxazoles, 2 H -pyrimido[2,1- b ]benzothiazoles, and a 2 H -pyrimido[2,1- b ]benzoselenazole. Two of the the 2 H -pyrimido[2,1- b ]benzoxazoles were isolated in good yield. The kinetics of the silver tetrafluoroborate-catalyzed rearrangements of selected (alkynylamino)benzoxazoles and benzothiazoles have been examined by 1 H NMR in CD 3 CN. Factors affecting the electron densities of the triple bond and of the nitrogen atom in the heterocycle are important in influencing the rate of rearrangement.