In work previously earned out by this group, 3a, 6a-diaryl hexahydropryrrolotnazoles underwent photoinduced disrotatory nng expansion to the new 2,5,6,7-tetrahydro- 1,2,3,5 tetrazocines. The aim the current work was to introduce a fifth nitrogen atom to this system to form the previously unknown pentazocines. To achieve the addition of a fifth nitrogen atom to the nng system, the 1,3-dipolar cycloadditions of tnazohum- 1-imides with nitrogen-containing dipolarophiles were investigated. Previously the only nitrogen containing dipolarophiles that had been successfully used in addition to tnazohum-1-imides were isocyanates and isothiocyanates. The reaction of tnazohum- 1-imides with isocyanates and isothiocyanates was extended, giving a range of imidazo-1,2,3-tnazoles with an unsaturated C-5 position. A new range of imidazo-1,2,3-tnazoles was synthesised by the cycloaddition of tnazohum- 1-imides with N-sulfonyl imines, giving for the first time imidazo-1,2,3- tnazoles with a saturated C-5 position Subsequent detosylation and decarboxylation gave an N-4-C-5 double bond. Reduction of this double bond returned C-5 to the saturated state Novel oxazolo-1,2,3-tnazoles were identified as side products of the cycloaddition reaction. The photochemical rearrangements of these cycloadducts were found to depend on the degree of saturation at C-5 and also on the substituent group at the C-5 position The first step m the photochemical reactions of all the imidazo-1,2,3-tnazoles is likely to be disrotatory nng-opemng to give the pentazocines as intermediates However these nng systems appear to be unstable and undergo subsequent reactions Irradiation of the saturated compounds with no substituents gave the tetrahydro-1,2,3,5,7-pentazocines as intermediates, but it is believed that these were oxidised to the dihydro pentazocines. Transannular nng contraction and rearrangement led to the fragmentation of the molecule Irradiation of the saturated compounds and those with electron-withdrawing substituents also led to nng opening, but again, transannular nng contraction, followed by fragmentation of the molecule led to the formation of substituted 1,2,4-tnazoles