A wide range of new oxime-based photochromic diarylethenes of the cyclopentenone series have been synthesized. Their spectral properties have been investigated in detail upon UV/vis light irradiation in acetonitrile solution, and distinct correlations between photochromic characteristics and substance structures are revealed. It was found that the introduction of an oxime group into the cyclopentene ring has a significant influence on the switching characteristics-primarily on the thermal stability, and a series of thermally stable oxime-based photochromic diarylcyclopentenones have been prepared. The results obtained suggest that the modifications of the ethene "bridge" are a promising way to tune the spectral parameters of diarylethenes in an accurate manner and thus to synthesize the photochromic compounds with desired properties.

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The bromination of 2,3-diarylcyclopent-2-en-1-ones under various conditions has been studied. It was found that depending on the brominating reagent and nature of solvent the bromine atom can be introduced at the 4- or 5-position of the ethene "bridge", as well as into the aryl moieties. Aryl group bromination is accomplished with such reagents as molecular bromine, N-bromosuccinimide, or tetrabutylammonium tribromide. 5-Bromocyclopentenones with very high efficiency can be obtained by the reaction with copper(II) bromide in methanol, while 4-bromoketones are prepared in n-propyl acetate. The developed methods can be highly useful for the synthesis of bromo-substituted 2-cyclopenten-1-ones and their close analogues, which are important synthons in organic synthesis and for the preparation of a variety of useful substances.

C Acylation of Meldrum´s acid by (het)arylacetic acids in ethanol in the presence of 1,1' carbonyldiimidazole leads to ethyl 4 (het)aryl 3 oxobutanoates in high yields.