Synthesis and properties of 4H-imidazoles. Part 2.

Abstract

The 1-(2,2-disubstituted alk-1-enyl)-5-phenyltetrazoles 2 and 4 are prepared from 1-methyl-5-phenyltetrazole and 5-phenyl-1-trimethylsilylmethyltetrazole by formation and appropriate interception of the α-lithioalkyl derivatives. Photolysis of the tetrazoles 2a and 4 gives the stable 4H-imidazoles 9 and 5, respectively. Similar photolysis of the tetrazole 2b gives the tetrazolophenanthrene 12 by an oxidative photocyclisation which is faster than nitrogen extrusion from the tetrazole ring. However, on further irradiation the tetrazolophenanthrene 12 can be transformed into the polycyclic 4H-imidazole 13. The 4H-imidazoles all undergo [1,5] alkyl or aryl shifts to carbon when heated, 5, 7, 9 and 13 giving 6, 8, 10 and 14 respectively.