Regioregular poly(3-substituted thiophene) derivative bearing pentamethyldisiloxane moiety at the 3-substituent is prepared by nickel-catalyzed polymerization reactions with dehydrobrominative or debrominative generation of the organometallic monomer. The monomer precursors 2-bromo-3-(4pentamethyldisiloxybutan-1-yl)thiophene (1a) and 2,5-dibromo-3-(4-pentamethyldisiloxybutan-1-yl)thiophene (1b) are prepared from 3-methylthiophene with 45 steps in overall good yields. Treatment of 1a with TMPMgCl¢LiCl at room temperature for 3 h forms an organometallic monomer and following the addition of a nickel catalyst affords the corresponding polythiophene bearing a disiloxane moiety in the side chain. The reaction of 1b with Grignard reagent leads to the similar monomer and addition of a catalytic amount of [NiCl 2 (dppe)] also affords polythiophene in highly regioregular manners. The obtained polythiophene is found to be dissolved in a hydrocarbon such as hexane.

Preparation of 2,2¤-bithiophene derivatives bearing ω-alkenyl groups at the 3,3¤-positions and ring-closing metathesis reactions of the obtained compound were performed. The reaction of bithiophene bearing 3-butenyl substituents 1 with 5 mol % Grubbs 1st generation catalyst underwent ring-closing metathesis (RCM) to afford the cyclized product 7 showing winding vine-shaped molecular asymmetry in up to 88% yield. Enantioselective RCM was also achieved by the use of chiral Schrock Hoveyda molybdenum-alkylidene catalyst in up to 87% ee.

Winding vine-shaped molecular asymmetry is induced by enantioselective ring-closing metathesis with a chiral molybdenum catalyst. The reaction proceeds under mild conditions through an E-selective ring-closing metathesis leading to macrocyclic bisazoles with enantioselectivities of up to 96% ee.

The chirality of winding vine-shaped heterobiaryls with molecular asymmetry is recognized by a sugar-based chiral oxidant. Kinetic resolution of (±)-bisbenzoimidazole bearing an olefin moiety takes place with Shi’s asymmetric epoxidation to observe krel value up to ca. 35 affording the corresponding epoxide. The reaction of a (±)-bithiophene derivative also recognized the chirality to give the corresponding epoxide with er of 96:4 at 39% conversion. Dynamic kinetic resolution is found to take place when unsymmetrical biaryl composed of benzoimidazole/thiophene is subjected to Shi’s epoxidation, whose conversion of the racemic substrate exceeds to 50%.

OKAYAMA, Y.; TSUJI, S.; TOYOMORI, Y.; MORI, A.; ARAE, S.; WU, W.-Y.; TAKAHASHI, T.; OGASAWARA*, M.; Angew. Chem., Int. Ed. 54 (2015) 16, 4927-4931, http://dx.doi.org/10.1002/anie.201500459 ; Dep. Chem. Sci. Eng., Fac. Eng., Kobe Univ., Nada, Kobe 657, Japan; Eng.) -Mais 32-052