Photochromic thiazoles

Symmetrical and unsymmetrical thenoines, diketones, and chloro ketones 213-225 containing substituted thienyl, benzothiophene, and other moieties are versatile precursors of structures containing various heterocycles as bridges. Chloro ketones were used, for example, in the synthesis of photochromic thiazoles 226 (01IZV113) and tetrathiafulva-lenes 227 (99CL1071) (Scheme 65). 

Acyloin 213 with thioamides, thiosemicarbazides, and methyl dithio-carbazate in trifluoroacetic acid give photochromic thiazole-, thiadiazine-, and pyrazole-bridged dihetarylethenes 254,255, and 256-258, respectively (Scheme 72) (OlIZVllS, 06ZOR882). 

Fedorov, Yu., Fedorova, O., Schepel, N., Gromov, S., Alfimov, M., J. Saltiel (2004) Synthesis and multitopic complex formation of die photochromic bis-crown ether based on benzobis(thiazole), J. Phys. Org. Chem., in press. 

Diarylethenes having thiazole rings also undergo thermally irreversible photochromic reactions.8 Introduction of a trifluoromethyl group at the 4-position of the thiazole ring is effective in increasing the thermal stability of the closed-ring form. 

Raman spectroscopy has been used in the spectral analysis of several benzothiazolines <77HCA215> and some benzothiazolium photochromic styryl dyes <93SA(A)1055>. Gold (III) chloride complexes of the type of LAuCh (L = thiazole) have been studied by low frequency Raman and infrared spectroscopy <93Mi 306-03>. 

Not only lithium derivatives of thiophene and also of other heterocycles, particularly, thiazole (Scheme 30), react with perfluorocyclopentene to form photochromes. As a rule, the yields of the thiazole derivatives are significantly inferior to those for the thienyl derivatives [79-82]. 

Non-traditional photochromes 95 and 96 were synthesized by the reactions of 2-bromo-3-methyl-2-bntene and 4-bromo-5-methyl-2-phenylthiazole with BnLi and the corresponding monoflnorides [102] (Scheme 35) and new photochromic di-arleth-enes 97 bearing both the thiazole and benzene moieties that exhibit fluorescence in solution and in the PMMA film [103] are worth mentioning. 

A novel and efficient palladium-catalyzed direct diheteroarylation of 1,2-dichlorop erfluorocyclopentene with a variety of heteroarenes has recently been reported, giving rise to l,2-di(hetaryl)perfluorocyclopentene photochromic compounds 102. The reaction occurs with thiazoles, thiophenes, or furan derivatives and tolerates varions substituents [112] (Scheme 37). 

The central moiety of photochroms is usually the cyclopentene (59) or 2,2,3,3,4,4-hexafluorocyclopentene (60). Novel diatylethenes constructed with 1,3-imidazole (61), 2-cyclopentenone (62), thiazole (63), °° ° 1,2-dicyanoethylene (64), l/f-l,3,2-diazaborole (65), li -l,3,2-diazaphosphole (66), ° maleic anhydride (67), ° maleimide (68), ° ° azulene (69), ° 2,2,3,3,4,4,5,5-octafluorocyclohexene (70), all l-substituted cyclopentene (71), or other heteroaromatics (72)-(75) as the central moieties were prepared, which have potential to become good photochromic materials. In addition, diatylethenes hearing asymmetric aryl groups, which showed good photochromic properties, were developed. ... 

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