Pyrolysis of annelated hexa- and heptamethylene-tetrazoles: Formation of 9- and 10-membered cyclic carbodiimides

•Flash vacuum pyrolysis of 8- and 9-membered polymethylenetetrazoles is reinterpreted.•The products are 9- and 10-membered cyclic carbodiimides rather than cyanamides.•FVP of tetrazolo[1,5-a]azocine yields transient 9-membered cyclic carbodiimide.•FVP of tetrazolo[1,5-a]azonine yields transient 10-membered cyclic carbodiimide.

A reinterpretation of the spectroscopic data for the products of flash vacuum pyrolysis (FVP) of 8- and 9-membered polymethylenetetrazoles 1, 3, 5, and 7 with annelated benzene rings indicates that these are not cyanamides 2, 4, 6, and 8, but 9- and 10-membered cyclic carbodiimides 9, 10, 11, and 12. FVP of the corresponding tetrazolo[1,5-a]azocine and tetrazolo[1,5-a]azonine derivatives 13 and 17 was investigated by isolation of the products in cryogenic matrices and by matrix photolysis and found to yield 9- and 10-membered cyclic carbodiimides 14 and 18 as transient intermediates en route to indolo[2,3-b]quinoline 15 and dibenzo[b,f]naphthyridine 19.