[2+2] Photodimerization of Stilbazoles Promoted by Oxalic Acid in Suspension

Abstract

In this study, a very simple technique to perform efficiently photodimerization of some vinylpyridines is reported. By irradiating a stirred mixture of several stilbazoles with solid oxalic acid dihydrate dispersed in a nonpolar (i.e., cyclohexane) or moderately polar (benzene, dichloromethane, dioxane) solvent, the corresponding dimeric cyclobutane adducts were obtained in high yields and excellent regio‐ and stereoselectivities. The strategy could also be applied successfully to oily, waxy, or even insoluble stilbazoles. Moreover, the oxalic acid loading could be lowered to substoichiometric amounts. When further optimizations were needed, our strategy was found to be highly flexible to identify other oligocarboxylic acids as alternative additives to improve, or even overturn, the regioselectivity. Oxalic acid and other oligocarboxylic acids were found to be capable of orienting more than 50 stilbazoles toward photodimerization under these conditions.

Halogen-Bond Mediated [2+2] Photodimerizations: À la Carte Access to Unsymmetrical Cyclobutanes in the Solid State

“…Analytical data: 1 H NMR (400 MHz, DMSO- d 6 ): δ 8.33 (ddd, J = 4.8, 1.7, 0.9 Hz, 2H a ), 8.31 (dd, J = 4.5, 1.5 Hz, 4H b ), 7.50 (app td, J = 7.7, 1.8 Hz, 2H c ), 7.21 (dd, J = 4.5, 1.6 Hz, 4H d ), 7.12 (d, J = 7.8 Hz, 2H e ), 7.02 (ddd, J = 7.5, 4.9, 1.0 Hz, 2H f ), 4.89 (d, J = 6.4 Hz, 2H g ), 4.69 (d, J = 6.3 Hz, 2H h ). Spectral data were consistent with those previously reported [ 20 ] for the same compound.…”

“…The alkene C=C bonds of ( 1,3-di-I-tFb )∙( 2,4-bpe ) are photoactive. When ( 1,3-di-I-tFb )∙( 2,4-bpe ) was subjected to UV-irradiation (broadband Hg lamp, 80 h), 2,4’-bpe underwent a photodimerization to generate hh -2,4-tpcb stereospecifically, regiospecifically, and in quantitative conversion [ 20 ] ( Scheme 2 , Table 4 ). The formation of the photoproduct was evidenced by the complete disappearance of the pair of olefinic doublets ( δ H = 7.65, 7.59 ppm) with concomitant emergence of a pair of cyclobutane resonances ( δ H = 4.89, 4.69 ppm) in the 1 H NMR spectrum ( Figure S3 of the ESI).…”

Sulfur‐Catalyzed Oxidative Condensation of Aryl Alkyl Ketones with o‐Phenylenediamines: Access to Quinoxalines

“…Treatment of of 1 a and 2 a in DMSO (0.5 mL) in the presence of S (1 eq) at 100 °C for 16 h afforded 2‐phenylquinoxaline ( 3 aa ) in 31% isolated yield (entry 1). The presence of an acid additive such as oxalic acid dihydrate, [16] TsOH ⋅ H 2 O, TFA was found to favor the reaction by accelerating the condensation of the ketone function of 1 a with the amino groups of 2 a leading to 3 aa in 45% (entries 2–4). While the best yield was achieved at 110 °C (entry 5), the reaction performed at other temperatures resulted in lower yields of 3 aa (entries 6–8), possibly due to degradation of o ‐phenylenediamine 1 a via uncontrollable reactions with DMSO at higher temperature (entry 6) or incomplete conversion at lower temperatures (entries 7–8).…”

Stabilized photoemission from organic molecules in zero-dimensional hybrid Zn and Cd halides

“…(E)-4-Styrylpyridine was synthesized by condensation of 4-picoline with benzaldehyde in acetic anhydride using literature procedures. 36,37 (E)-4-Styrylpyridinium chloride (RCl) was obtained by dissolving (E)-4-styrylpyridine in a sufficient amount of aqueous hydrochloric acid, then allowing evaporation to occur until long needles formed, which were collected by filtration and allowed to dry (Fig. S1 †) 38,39 Synthesis of RMCl 4 (M = Zn, Cd)…”