Solution-Phase Microwave-Assisted Synthesis of Unsubstituted and Modified α-Quinque- and Sexithiophenes

Abstract

The facile synthesis of poorly soluble unsubstituted and modified alpha-quinque- and sexithiophenes under microwave irradiation in the liquid phase is described. The use of microwave irradiation allowed these compounds to be prepared in a few minutes and at high yields by means of the Suzuki cross-coupling reaction. Unsubstituted sexithiophene was obtained in 10 min via the one-pot borylation/Suzuki reaction, purified according to a very simple procedure, and isolated in 84% yield. The efficient synthesis of two new methylated quinque- and sexithiophenes displaying liquid crystalline properties is reported. A new microwave-assisted methodology for the conversion of aldehyde-terminated quinque- and sexithiophenes into the corresponding cyano derivatives is also described. The use of microwaves was extended to the Sonogashira coupling reaction and found to be very effective in the preparation of a quinquethiophene containing acetylenic spacers. The electronic and optical characterization of this compound is reported and discussed in relation to that of unsubstituted quinquethiophene.

Controlled Microwave Heating in Modern Organic Synthesis

“…Several research groups have reported other high-speed microwave-assisted transition-metal-catalyzed transforma-tions, such as Suzuki, [279] Heck, [280] Sonogashira, [281] Negishi, [282] and Liebeskind-Srogl reactions, [283] BuchwaldHartwig aminations, [284] and related reactions. [285] Bahn and Adolfsson have demonstrated that functionalized 2,5-dihydropyrroles can be obtained by microwavemediated ruthenium-catalyzed ring-closing metathesis (RCM).…”

Synthesis of Organic Dyes with Linkers Between 9,9-Dimethylfluorenyl Terminal and α-Cyanoacrylic Acid Anchor, Effect of the Linkers on UV-Vis Absorption Spectra, and Photovoltaic Properties in Dye-Sensitized Solar Cells

“…9 Palladium-catalyzed Suzuki coupling of iodide 8 with 2-thiopheneboronic acid (9) afforded the intermediate 10 in 58% yield. 10 And formylation at C-2 position of thiophene by n-BuLi and DMF (68%) 11 and condensation of the resulting aldehyde with cyanoacetic acid in the presence of piperidine (78%) provided the organic dye 1. 12 Synthesis of organic dye 2 was summarized in Scheme 2.…”

“…zeneboronic acid (11) and then 2-thiopheneboronic acid (9) in 52% and 71% yield provided the intermediate 12.…”

“…10 Formylation at C-2 position of thiophene (68%) 11 and condensation of the aldehyde with cyanoacetic acid (65%) as in Scheme 1 provided the organic dye 2. 12 Preparation of organic dye 3 was initiated from the commercially available 4-bromobenzaldehyde (13) (Scheme 3).…”

“…Reagents and Conditions: (a) 4-bromophenylboronic acid (11) (1.1 eq), Pd(PPh3)2Cl2 (0.09 eq), 2 M Na2CO3-DME-H2O (5 : 9 : 1), reflux, 12 hr, 52%. (b) Pd(PPh3)2Cl2 (0.09 eq), 2-thiopheneboronic acid (9) (1.4eq), 2 M Na2CO3-DME-H2O (5 : 9 : 1), reflux, 12 hr, 71%.…”