The formation and characterisation of redox active and luminescent materials from the electrooxidation of indolizine.

Indolizine has been synthesised on the small scale with enhanced yield using a novel Flash Vacuum Pyrolysis method. Electrooxidation of indolizine results in the formation of a redox-active film on the electrode surface. Excellent agreement is found between calculated and experimental indolizine oxidation potentials; a combination of fluorescence and electrochemical studies are consistent with the computational prediction that electroxidation results in the formation of three specific and redox active indolizine dimers. The insoluble redox active film is considered to be polymeric and to arise from the further oxidation of these dimers at the electrode. This combination of methods can be used for the characterisation of products formed from the electrooxidation of novel luminescent heteroaromatics synthesised on a small scale and particularly those of interest as redox active species for electrochemical processes and devices.

Reactions of 2-(pyrrol-1-yl)benzyl radicals and related species under flash vacuum pyrolysis conditions.

2-(Pyrrol-1-yl)phenoxyl, aminyl, thiophenoxyl and benzyl radicals 2a-2d, respectively, were generated in the gas-phase under flash vacuum pyrolysis conditions. In all cases except the phenoxyl, cyclisation took place providing acceptable synthetic routes to the fused heterocycles 11, 14 and 15, respectively. Only sigmatropic rearrangement products were isolated, in low yields, from the phenoxyl 2a. The pyrrolo[1,2-a]benzimidazole 11 adopts the 1H-tautomer exclusively in chloroform solution. Electrophilic substitution reactions of pyrrolo[2,1-b]benzothiophene 14 were studied, including protonation, deuterium exchange, Vilsmeier formylation and reaction with dimethyl acetylenedicarboxylate. 2-(2,5-Diarylpyrrol-1-yl)thiophenoxyl, phenoxyl and aminyl radicals 23a-f, were also generated in the gas-phase under similar conditions. The thiophenoxyls 23a/b gave extremely complex pyrolysate mixtures in which primary cyclisation products were formed by attack of the radical at the pyrrrole ring and attack at the ipso-, ortho- and meta- positions of the aryl ring. Secondary pyrolysis products were obtained by specific sigmatropic shifts of the N-aryl group. The 2,5-di(thien-2-yl)thiophenoxyl radical 23c gave the pyrrolobenzothiazole 31c as the only cyclisation product in low yield. FVP of the phenoxyl and aminyl radical generators 26d and 26f, respectively, gave 3-arylpyrrolo[1,2-f]phenanthridines 46d and 46f, respectively, by a hydrogen transfer-cyclisation mechanism.