¤@¡BFlash vacuum pyrolysis (FVP) of 2-dimethylaminostilbene and its derivatives via elimination of methyl radical followed by cyclization gave quinoline and 1-methylindole and 3-phenylquinoline and 3-phenylindole. On the other hand, Photolysis of 2-dimethylaminostilbene and its derivatives via electrocyclization gave 1-dimethylaminophenanthrene, phenanthrene, 2-(4-methoxy-phenyl)-1-methyl-1H- quinolin-4-one and 1-methyl-1H-indol-2-yl)phenylmethanone. Photolysis of 2,4'-dimethoxystilbene in acidic sulotion gave 1,6-dimethoxypheanthrene and 1-methoxypheanthrene and ketone compound via electrocyclization followed by [1,9] hydrogen shift. ¤G¡BFVP of 2-(2-chlorostyryl)pyridine gave benzo[f]quinolin, benzo[h]quinolin, on the other hand, FVP of 4-(2-chlorostyryl)pyridine gave different benzo[h]quinolin.

¤@.Pyrolysis of 2-(N,N-dimethylamino)styrylarenes (29a-e) and 2-(N,N- benzylmethylamino)styrylarenes (30a-f) both gave 2-(ar-2-yl)- benzo[b]arenes 35a-f, 39a-e, their isomers 36a-e, 40a-e and the other products. On the other hand, photolysis of 29a-e gave electrocyclic products 2, 57b-e and 22a-e, respectively. However photolysis of 30a-f only gave the complicated and unknown compounds. ¤G.Pyrolysis of benzoic 1,3-dimethyl-2-indolyl anhydride (54) gave (1,3-dimethylindol-2-yl)phenylmethanone (63), 1,3-dimethylindole (65) and bis(1,3-dimethylindol-2-yl)methanone (66) as the main products.

The formation of iminyl radicals from a range of precursors, including hydrazone imines and oxime ethers, under FVP conditions is well documented in the literature.1 Once formed, the iminyl radical can undergo cyclisation onto various aromatic ring systems including phenyl rings, thiophenes and furans to form new fused aromatics.2 The aim of this thesis was to expand the scope of cyclisation of iminyl radical onto pyrrole-type rings and 2-azole rings, generating novel heterocyclic cores via pyrolysis of the corresponding oxime ether precursors. In addition, the cyclisation of iminyl radicals onto C-C double bonds was investigated and afforded isoquinolines shown in Scheme II, providing a new way to synthesise these heterocyclic cores. Mechanistic predictions were supported by DFT calculations in which the thermodynamics and kinetics of the systems were established and the products of iminyl cyclisation reactions were characterised using a range of 2D NMR experiments.

Routes to N-amino heterocycles were reviewed and findings applied to generate flash vacuum pyrolysis (FVP) precursors of two types - ketene generators and azol-1-yl radical generators. N-Amino heterocycles can be used as nitrogen radical generators, the N-N bond being homolytically cleaved at furnace temperatures of approximately 850 °C. A number of 2-substituted benzimidazoles were synthesised and subsequently Naminated. The 2-arylbenzimidazole precursors 1-amino-2-(2-methylphenyl)-1Hbenzimidazole and 1-amino-2-(2-ethylphenyl)-1H-benzimidazole were synthesised and subjected to FVP. The hydrogen transfer processes of the resulting azol-1-yl radicals were investigated. Pyrolysis of 1-amino-2-(2-methylphenyl)-1Hbenzimidazole resulted in three products; 2-(2-methylphenyl)-1H-benzimdazole, 11H-benzo[4,5]imidazo[1,2-a]isoindole and 1-(2-methylphenyl)-1Hbenzo[ d]imidazol-2-amine. Pyrolysis of 1-amino-2-(2-ethylphenyl)-1Hbenzimidazole resulted in five products, four of which have been successfully isolated and identified as 2-(2-ethylphenyl)-1H-benzimidazole, 5,6- dihydrobenzo[4,5]imidazo[2,1-a]isoquinoline, 1-(2-ethylphenyl)-1Hbenzo[ d]imidazol-2-amine and 11-methyl-11H-benzo[4,5]imidazo[2,1-a]isoindole. The mechanism of formation of most products is initiated by hydrogen atom transfer to the azol-1-yl radical position. N-Aminopyrazole was reacted with 5-methoxymethylene-2,2-dimethyl-1,3-dioxane- 4,6-dione to form the corresponding 5-(N-aminopyrazolyl)methylene derivative, which, when subjected to FVP, eliminates acetone and carbon dioxide to form a methyleneketene. This subsequently undergoes a [1,3]-hydrogen shift giving an imidoylketene which can collapse onto the neighbouring nitrogen atom forming pyrazolo[1,2-a][1,2,3]triazin-5-ium-4-olate (a novel heterocyclic mesomeric betaine system) or cyclise onto the adjacent carbon atom to yield a pyrazolopyridazinone. On variation of the furnace temperature it was apparent the former forms at relatively moderate temperatures (~500 °C) whereas the latter begins to predominate as the furnace temperature increases (~700 °C). The relationship between these kinetic and thermodynamic products was modelled using DFT calculations. By using substituted pyrazole precursors, substituents could be incorporated into all three available positions around the pyrazole ring. Using substituted acrylic esters as alternative imidoylketene generators, substituents could also be incorporated into both available positions in the pyridazinone ring. All corresponding betaine and pyrazolopyridazinone products were isolated and characterised.

3-(o-(Methylthio)phenyl)-1-phenylprop-2-en-1-one (48) ¡B1-(o-(methylthio)-phenyl)-3-phenylprop-2-en-1-one (49) and 1-(o-(methylthio)phenyl)-3-phenylprop-2-yn-1-one (50) had been studied by means of pyrolysis and photolysis. Under pyrolytic conditions, compound 48 gave phenanthrene (2) as the major product. Both compounds 49 and 50 gave thioflavone (53) as the major product. Under photolytic conditions, compounds 48-50 gave the expected products 2-benzoylbenzo[b]thiophene (51)¡B 2-benzylidenebenzo[b]thiophen-3-one (52) and thioflavone (53), respectively.

1-(o-(Dimethylamino)phenyl)-3-phenylprop-2-en-1-one (62), 3-(o-(dimethylamino)phenyl)-1-phenylpropenone (63) and 1-(o-(dimethyl- amino)phenyl)-3-phenylprop-2-yn-1-one (64) were synthesized and their pyrolytic and photolytic chemistry were studied. Flash vacuum pyrolysis (FVP) of 62 and 64 gave 11H-benzo[a]carbazole (72) and benzo[c]carba-zole (73), FVP of 63 gave phenanthrene (2) and 1-methylquinolin-2(1H)-one (84). Under photolytic conditions, 62 and 64 gave the expected photocyclic products 1-methyl-2-phenylquinolin-4-one (65), while 63 gave the expected photocyclic products (1-methyl-1H-indol-2-yl)phenyl-methanone (66).

1. Generation of nitrenes by means of photolysis of arylmethylazides and its derivatives have been studies. Pyrolysis of 2-azidomethylthiophene¡]44a¡^ gave 2-thiophenecarboxaldehyde¡]77a¡^and (2-thienylmethylidene)-2-thienylamine¡]45a¡^, and pyrolysis of 2-azidomethylbenzo[b]thiophene¡]44b¡^gave the corresponding products. Pyrolysis of 2-azido-1-(2-thienyl)ethanone¡]52a¡^gave 2-thiophenecarboxaldehyde¡]77a¡^, 2-acetylthiophene¡]80a¡^and 2-(thiophene-2-carbonyl)amino-1-(2-thienyl)ethanone¡]83a¡^, and pyrolysis of 2-azido-1-(2-benzo[b]thienyl)ethanone¡]52b¡^gave the corresponding products. 2. Pyrolysis of 3-cyclohexeno[b]furylmethyl benzoate¡]35¡^gave cyclohexeno-4-methylenecyclobuten-3-one¡]25¡^via highly reactive carbene intermediate. At high temperature, compound 25 can continue the reaction of elimination and ring opening to give benzene¡]43¡^, fulvene¡]46¡^, 2-ethylnylcyclohex-1-ene carbaldehyde¡]44¡^ and 4,5-dimethylenecyclopent-2-enone¡]45¡^.

¤@. Photolysis of 2-azido-1-(2- pyridyl)ethanone (68),2-azido-1-(3-pyridyl)ethanone) (69),2-azido-1-(1-methyl-2-pyrryl)ethanone (53) and 2-azido-1-(1-methyl-3-indo yl)ethanone gave Norrish products (71, 7 3-76), (84-86, 89), (92-94) and (93, 95-98). ¤G. Pyrolysis of 2-(azidomethyl)pyridine (9) and 4-(azidomethyl)pyr idine (10) gave the expected products 1,3,5-tri-2-pyridyl-2,4-diaza-1,4-pentadiene (13) and 1,3,5-tri-4-pyridyl-2,4-diaza-1,4-pentadiene (21). ¤T. Pyrolysis of 2-cyclohexeno[b]furylmethyl benzoate (31) gave 2-methylbenzo[b]- furan (40) and benzene products.

¤@¡BPyrolysis of 2-azido-1-(4-methoxyphenyl)ethanone (69) and 2-(2-azidoethyl)furan (85) gave nitrene intermediate to study. There is 2-(4-methoxybenzoyl)-4-(4- methoxyphenyl)imidazole (81) ¡B2-(4-methoxybenzoyl)-5-(4-methoxyphenyl) imidazole] (81¡¦)¡B2,3-di(4-methoxybenzoyl)-5-(4-methoxyphenyl) pyrazine] (82) and 3,5-di(2-furyl) pyridine (92) for pyrolysis products. ¤G¡BPyrolysis of3-methyl-2-cyclohexen[b] furylmethyl benzoate) (50) gave carbene intermediate to study. There is 2,3-dimethylene cyclohexen[b]furan (59) for pyrolysis products.

1. FVP of arylmethylazides (33b¡B34b) via 3,3-sigmatropic rearrangement gave nitrogen-containing heterocyclic compounds (2b¡B4b). FVP of 35 gave 3-benzyl-2-thiophenecarbaldehyde (65) by 1,2 H shift of nitrene 32 followed by hydrolysis. 2. FVP of benzoic 3-(1-propenyl)-2-thiophenecarboxylic anhydride (67) gave 7-hydroxybenzo[b]thiophene (70) and cyclopenteno[b]thiophene (71). Compound 71 is difficult to synthesize by normal organic synthetic methods. The formation of 7-hydroxybenzo[b]thiophene (70) suggesting the existence of 68. 3. FVP of arylimine gave phenanthridine (3)¡B3-methylpyrrolo[2,3-c] quinoline (69) and thieno[2,3-c]quinoline (134). Such a method can synthesize tricyclic products in one step. On the other hand, photolytic study of arylimine gave compounds 156¡B184¡B164¡B180¡B185 and 186.