Synthesis and Characterization of Nonsymmetric Cyclopentene-Based Dithienylethenes

Abstract

Nonsymmetric cyclopentene-based dithienylethenes, containing both thienyl and benzothienyl units, have been synthesized for the first time, employing intramolecular McMurry reaction as a key transformation to target compounds 10 and 16. Photochromic properties of these compounds were examined in toluene and acetonitrile solutions, PMMA layers, solid films, and crystal phase. To explain an unprecedented single-crystalline photochromism phenomena of 10, X-ray crystallographic analysis was performed, revealing a significant influence of strong S···S interatomic interactions on the intramolecular distance between two photochemical reaction centers in the molecule. Compound 16 could be further synthetically modified in a step-by-step manner, thus serving as potential key intermediate to various complex bifunctional photochromic molecules.

Synthesis and studies of symmetric dibenzothienylcyclopentenes

“…Previously, we showed that the halide insertion into nonsymmetric dithienylethenes did not crucially influence the absorption spectra of the compounds. 23 In turn, symmetric photochromes fully confirmed this observation displaying basically no distinction in the absorption spectra: both the wavelengths of absorption band maxima for cyclic forms and values of absorption density for either unsubstituted or halidesubstituted compounds looked analogous, showing no dependence of these parameters on the halide origin.…”

“…23 Besides, as was shown, bromides in dithienylethenes remained intact under McMurry conditions. Acylation of benzothiophene 7 with glutaryl dichloride was rather straightforward and afforded diketone 8, which was subsequently converted to the target dibromide 6 by McMurry reaction in excellent overall yield.…”

“…23 This time we decided to show applicability of Pd (0) catalysis to the coupling of symmetric dibromide 6 with simple amines: n-amylamine and pyrrolidine, as primary and secondary amines, correspondingly (Table 3). Both reactions proceeded smoothly providing symmetric diamines after 7 h of stirring at 85 o C. Lower yield of 18 could be explained by the visually observed air sensitivity of the product, besides, to minimize its decomposition Al 2 O 3 was used during the purification of 18 instead of the traditionally employed silica gel.…”

“…Considering that inclusion of benzothiophene units in perfluorocyclopentenebridged analogs led to high quantum yield, rapid response, remarkable fatigue resistance and excellent thermal stability of the photochromic molecules, 6,18 it would be logical to investigate benzothiophene-substituted cyclopentenes, in turn. However, despite the synthesis of the first symmetric unsubstituted analog described years ago, 19 only a handful of functionalized molecules of this type were reported since, which comprised compounds of both symmetric [20][21][22] and nonsymmetric 23,24 structures. Recent review on synthetic methods used for construction of dithienylcyclopentenes nicely summarized known approaches.…”

Facile synthesis of photoactive diaryl(hetaryl)cyclopentenes by ionic hydrogenation

“…2,21-24 Another approach involves the Pd-catalyzed cross-coupling of 1,2dibromocyclopentene (pathway II in Scheme 1). 4, 11,12,25,26 These methods are quite suitable for thiophene and benzothiophene derivatives, including unsymmetric, 23 but they are generally limited to azole compounds (oxazole, imidazole, thiazole) because the starting compounds are difficult to access and the reaction requires harsh conditions. In addition, an alternative synthesis was used for the preparation of diarylcyclopentene derivatives by the reduction of the carbonyl group in diarylcyclopentenones.…”