Synthesis and spectral properties of fluorescent photochromic diarylethenes with 6,6a-dihydropentalene-2(1H)-one ethene “bridge”

• A new method for the preparation of pentalene-2-one derivatives was proposed.
• The main products yields on the cyclization stage depend on alkali concentration.
• The spectral characteristics of the synthesized compounds were studied.
• The pentalenone derivatives exhibit photochromic and fluorescence properties.

An alternative synthetic strategy for the preparation of 6,6a-dihydropentalene-2(1H)-one derivatives comprising the stage of the regioselective α-bromination of cyclopentenone system has been proposed. The method along with the bromination process includes the alkylation of ethyl 4-aryl-3-oxobutanoate with bromocyclopentenones and intramolecular carbocyclization reaction of alkylated product. The cyclization reaction has been studied in detail and it was found that the yields of the main and side products depend strongly on alkali concentration, and the method can be also used to design 8,8a-dihydrocyclopenta[a]inden-2(1H)-one unit. The spectral properties of the compounds obtained have been studied, and it was found that pentalenone derivatives as well as starting cyclopentenones, exhibit photochromic properties; in addition, the former, unlike the latter, are also fluorescent.

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