Chirality induction in cyclopolymerization: 4. Using three diastereomeric templates, methyl, 4,6-O-isopropylidene-α-d

Add time:08/02/2019    Source:sciencedirect.com

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]43523, c = 1.0 in CHCl3) 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.

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