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4H-Thienopyrrole (4) was synthesised from the azide (8) by intramolecular 1,3-dipolar cycloaddition followed by acid-catalysed 1,3-dipolar cycloreversion of the dihydrotriazole intermediate (9); the crystal structure of one of the products formed on trapping (4) with N-phenylmaleimide has been determined.

The benzene and quinoxaline fused Δ2-1,2,3-triazolines 1a and 1b were synthesized in good yields using Knoevenagel condensation and intramolecular 1,3-dipolar cycloaddition as two of the key reactions. Photolysis (254 nm) of Δ2-1,2,3-triazoline 1a or 1b in acetonitrile led to the homolytic cleavage of nitrogen that generated diethyl diazomalonate 7, highly reactive intermediates aziridines 8a,b, and isoindoles B. The latter two species subsequently underwent rearrangement to give the nitrogen extrusion products 9a,b, and polymers. Furthermore, the reactive intermediates were trapped by dienophiles to give the corresponding cycloadducts. Subsequent rearrangement of the N-bridged cycloadducts gave N-substituted pyrrolo[3,4-b]quinoxalines 12b and 15b in 6% and 9% yields, respectively. Irradiation of 1a in the presence of fumaronitrile led to the isolation of cycloadduct 16a with retention of stereochemistry. Thermal reaction of 1b gave more nitrogen extruded product 9b (58-63% yield) than that by photolysis (5-23% yield), which implied that zwitterionic intermediate might be involved in the former.

The photochemical or thermal decomposition of ethyl diazomalonate (1) or ethyl 3,3-diazirinedi-carboxylate in methanol solutions yields the O-H insertion product 6, while products of the Wolff rearrangement were not detected in both cases. The analysis of temperature-dependent 13C NMR spectra and the results of DFT B3LYP/6-311+G(3df,2p) and MP2/aug-cc-pVTZ//B3LYP/6-311+G(3df,2p) calculations allow us to conclude that diazodiester 1 predominantly exists in the Z,Z-conformation. In contrast, photolysis of the cyclic isopropylidene diazomalonate (3), which also has a Z,Z-configuration of the diazodicarbonyl moiety, results in a clean Wolff rearrangement. These observations allow us to conclude that the direction of the photodecomposition of diazomalonates is not controlled by the ground-state conformation. The quantum-mechanical analysis of the potential energy surfaces for the dediazotization of 1 and 3 suggests that the formation of a carbene as a discrete intermediate is controlled by the ability of the latter to adopt a conformation in which carbonyl groups are almost orthogonal to the carbene plane. The outcome of the photolysis of ethyl diazomalonate depends on the wavelength of irradiation. Irradiation with 254 nm light results in the loss of nitrogen and the formation of dicarboethoxycarbene (5, Φ254 = 0.31), while at longer wavelengths, diazirine 2 becomes an important byproduct (Φ350 = 0.09). This observation suggests that the formation of carbene 5 and isomerization to diazirine proceed from different electronically excited states of ethyl diazomalonate.

The electrochemical reduction of nitrophenyl azide in DMF, acetonitrile, and butyronitrile is initially a one-electron process that affords the corresponding anion radical as a transient intermediate.Although p-O2NC6H4N3 radical anion is too short-lived t

2H-Pyrrolopyridine (1) and 2H-pyrrolopyridine (2) were prepared and reacted with N-phenylmaleimide to give Diels-Alder adducts.

The 2,4-dihydropyrroloindole ring system, readily prepared from 1--2-methyl-3-formylindole, underwent Diels-Alder reaction with highly reactive dienophiles, e.g. benzyne and N-phenylmaleimide, to give cycloadducts in exc