Methyl sorbate, asymmetric polymerization

In 1960, Natta reported the first direct synthesis of an optically active polymer from an achiral monomer, where methyl sorbate was polymerized using (R)-2-pentyllithium [95]. Ozonolysis of the polymer (under conditions possibly allowing epimerization) produced (S)-methyl succinic acid in 5% ee, which provides evidence of asymmetric induction and absolute configuration of the polymer main chain. Since this initial report, a remarkable void in the Hterature exists concerning the synthesis of main-chain chiral polymers from achiral monomers using anionic initiators. Okamoto and Oishi have polymerized N-substituted maleimides with chiral anionic initiators (Scheme 14) [96,97]. The polymer is assumed to have predominantly a frans-diisotactic microstructuxe, which adopts a secondary helical structure. The absolute configuration of the main chain has... 

Natta carried out the anionic polymerization of methyl sorbate, a 1,3-diene, with an optically active initiator and obtained an optically active homopolymer with main-chain chirality. The high molecular weight crystalline polymer produced with (P)-2-methylbutyllithium had a tritactic (di-iso-rra/w-tactic) structure. This was probably the first metal-catalyzed asymmetric polymerization 134). Polymerization of other dienes was attempted by using various asymmetric methods 135). 

In the case of the polymerization of methyl and butyl sorbates optical purity varies by varying the type of asymmetric complex used as catalyst. In non-systematic runs carried out with catalysts prepared from lithium-butyl and (—)-menthyl-ethyl-ether, [M]n increases... 

In fact sorbic acid (XXXIII) has been transformed in menthyl-sorbate and the ester (XXXIV) has been polymerized (36) by butyl-lithium (Scheme 6) the prevalence of asymmetric carbon atoms having one of the possible configurations in the main chain of the polysorbic acid (XXXV), not isolated by the authors, has been proved by oxidizing the polymer and measuring the optical activity of the obtained methyl succinic acid, which actually was optically active and had an optical purity of 6% (36). 

Diene Polymers Polymerization of a 1,3-diene yields a polymer having true asymmetric centers in the main chain and ozonolysis of the polymer gives a chiral diacid compound (12) whose analysis of optical purity discloses the extent of chiral induction in the polymerization (Scheme 11.2) [12,35-39], The polymerization of methyl and butyl sorbates methyl and butyl styrylacrylates and methyl, ethyl, butyl, and /-butyl 1,3-butadiene-1-carboxylates using (+)-2-methylbutyllithium, butyllithium/(-)-menthyl ethyl ether, butyllithium/menthoxy-Na, butyllithium/bomeoxy-Na, butyllithium/Ti((-)-menthoxy)4, and butyllithium/bomyl ethyl ether initiators [35-37] and that of 1,3-pentadiene in the presence of... 

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