Takahiro Uesaka

Chirality induction in cyclopolymerization : 4. Using three diastereomeric templates, methyl 4,6-O-isopropylidene-α-D-gluco-, manno- and altropyranoside in the cyclopolymerization of bis(4-vinylbenzoate) with styrene

Abstract Three distyryl monomers, methyl 4,6- O -isopropylidine-,2,3-bis- O -(4-vinylbenzoyl)-α- d -gluco- ( 1a ), altro- ( 1b ) and mannopyranoside ( 1c ), were prepared. These monomers possess the same configuration except for the torsion angle between the two (4-vinylbenzoyl) groups, which is 60°, −60° and 180° for 1a, 1b and 1c respectively. Their cyclocopolymerizations with styrene ( 2 ) were carried out using α,α′-azobisisobutyronitrile in toluene at 60°C. The resulting copolymers were hydrolysed using potassium hydroxide in methanol/tetrahydrofuran under reflux and then treated with diazomethane to yield poly(methyl 4-vinylbenzoate- co -styrene)s ( 4a, 4b and 4c ). The copolymer 4a showed optical activity with a maximum specific rotation ([ α ] 435 23 , c = 1.0 in CHCl 3 ) of −6.0°. Copolymers 4b and 4c had optical rotations of −1.9° and −2.0° respectively, which were smaller than that of 4a . The chirality was negative for 1a and positive for 1b , and was positive for 4a and 4b . On the other hand, 1c showed a very weak Cotton effect, and the chirality was positive for 4c .

(2S,4S)-2,4-Pentanediol as the acyclic template for asymmetric induction in cyclocopolymerization

Abstract The copolymerizations of (2S,4S)-2,4-pentanedyl bis(4-vinylbenzoate), a monomer having a chiral acyclic template, with styrene (St) were carried out using azobisisobutyronitrile in toluene at 60°C. The copolymers obtained (4) essentially consisted of the cyclic repeating and St units, because characteristic absorption at 5.3 and 5.8 ppm due to the vinyl protons disappeared in the 1H nuclear magnetic resonance spectra. The specific rotation ([α]43523, c 1.0, CHCl3) of 4 changed from +319.3° to +395.2°. The removal of the chiral template from 4 was carried out in aqueous MeOH using KOH, and the resulting hydrolysed copolymers were then converted into poly(methyl 4-vinylbenzoate-co-styrene) (5) by reacting with diazomethane. The specific rotation ([α]43523, c 1.0, CHCl3) of 5 was −9.4°C to −46.3°. The circular dichroic (c.d.) spectrum of 5 showed a splitting Cotton effect with a negative Cotton effect at 255.2 nm and a positive one at 237.2 nm. According to the c.d. excition chirality method, copolymer 5 had a negative chirality in which two 4-vinylbenzoyl groups twisted counterclockwise, i.e. an (R,R)-configuration of the vicinal (methyl 4-vinylbenzoate) units in the main chain.