Several years ago the photoinduced reaction of mixed phosphonium-iodonium ylides (1) with acetylenes (2) to give λ 5 -phosphinolines (3) and substituted furans (4) was described. This reaction is one-pot, metal-free synthesis of heterocycles 3 and 4 with the yields of 40% to 80%. The reaction proceeds only in dichloromethane (DCM) at the high ylide concentrations (>0.01 mol/L). The product analysis by 31 P NMR, electrospray ionization mass spectrometry, UVvis spectrophotometry, and the dynamic light scattering study of the self-aggregation of the ylide in DCM showed a dual role of the solvent in the photoinduced reactions of mixed phosphonium-iodonium ylide: (i) at the low ylide concentrations (<0.01 mol/L), the conjugated photoinitiation of the chain reaction in DCM results in the formation of chlorine-containing products and (ii) at the high ylide concentrations (>0.01 mol/L), the photolysis mechanism is determined by self-organization of the ylide molecules to give large stable aggregates in DCM, in which the target heterocycles are synthesized. Two important issues follow from the study. First, the annulation reaction between mixed phosphonium-iodonium ylide and acetylenes occurs only when the reactive intermediates are in close proximity to one other, and, second, DCM is not inert reagent in reactions occurring with participation of radicals and in one form or another can participate in photoinduced radical reactions of various solutes.KEYWORDS annulation with acetylenes, dichloromethane, phosphonium-iodonium ylides, radical reactions, selfassembly This article is dedicated with respect and affection to the memory of the late Prof. Nikolay S. Zefirov.

Novel hetarylazo dyes containing tetrazole and tetra- or dihydroquinoline moieties were synthesized and their spectral properties in solvents of different polarities and H-bonding abilities were examined. The dyes exhibit solvatochromism dramatically depending on the proton accepting ability of solvents: (DMSO > HO > MeOH > ACN > CHCl) and the dye concentration. Upon dilution the absorption maximum of the visible band shows a blue shift and the absorption coefficient of the maximum decreases. This was accounted for by complex formation either between the dye molecules or between the dye and solvent molecules. The H-bond with partial proton transfer is formed between the acidic NH group of the tetrazole moiety of a dye molecule and the basic NH group of the hydroquinoline moiety of the other dye molecule or with a solvent with proton accepting ability. Upon dilution the equilibrium shifts to the complex with a solvent. The coexistence of several forms of the dye molecules with different absorption spectra was demonstrated in pulse photolysis upon excitation by light with different wavelengths. Three forms of cis-isomers were registered. The photogenerated cis-isomers decay with lifetimes from 200 μs to 5 ms. The fast cis-trans dark isomerization determines the photostability of the dyes.

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