Synthesis via ring-opening

In polyester synthesis via ring-opening polymerizations, metal catalysts are often used. For medical applications of polyesters, however, there has been concern about harmful effects of the metallic residues. Enzymatic synthesis of a metal-free polyester was demonstrated by the polymerization of l,4-dioxan-2-one using Candida antarctica lipase (lipase CA). Under appropriate reaction conditions, the high molecular weight polymer (molecular weight = 4.1 x 10" ) was obtained. 

Figure 6. DALA synthesis via ring opening of a lactam. (Adapted with permission from reference 29. Copyright 1986 Thieme.)...

The present contribution deals primarily with the polymer synthesis via ring-opening metathesis polymerization. Acyclic diene metathesis (ADMET) [20,32-38], the other metathetic route to polymers is omitted. This article intends to give a brief overview, for more details and further applications see, e.g.. Refs. [1,4,20-29]. 

The polysaccharide synthesis via ring-opening polymerization method is an attractive method leading to structurally well-defined polysaccharides which are rarely attained by direct chemical modifications of natural polysaccharides. The synthetic polysaccharides obtained are useful tools to elucidate relations between the structure and functionality of polysaccharides and to develop new types of polysaccharides with novel properties. 

Reinhoudt et al.53) have reported the first synthesis of a monocyclic thiepin stabilized by electronic effects of the substituents. This synthesis utilizes the idea described in Section 2.3.3. 3-Methyl-4-pyrrolidinothiophene (85a) was treated in deuteriochloroform at —30 °C with dimethyl acetylenedicarboxylate. H-NMR monitoring of the reaction indicated that a [2 + 2]cycloaddition proceeded slowly at this temperature giving the 2-thiabicyclo[3.2.0]heptadiene (86a) which rearranged via ring opening of the cyclobutene moiety to the 4-pyrrolydinylthiepin (87a). At the... 

In addition to solvent uses, esters of lactic acid can be used to recover pure lactic acid via hydrolysis, which in-tum is used to make optically active dilactide and subsequently polylactic acid used for drag delivery system.5 This method of recovery for certain lactic acid applications is critical in synthesis of medicinal grade polymer because only optically active polymers with low Tg are useful for drug delivery systems. Lactic acid esters themselves can also be directly converted into polymers, (Figure 1), although the commercial route proceeds via ring-opening polymerization of dilactide. 

Matsumura S. Enzymatic Synthesis of Polyesters via Ring-Opening Polymerization. Vol. 194, pp. 95-132. 

Scheme 4.44 Total synthesis of mimulaxanthin via ring-opening reduction of epoxide 169.

The polymerization of 1 mentioned above should be compared with the enzymatic synthesis of chitin reported by Kobayashi and coworkers, in which an oxazoline derivative of A, A -diacetylchitobiose, the repeating unit of chitin was polymerized in the presence of chitinase enzyme via ring-opening addition process to give an artihcial chitin (Scheme 6) [5]. The method using an enzyme, however, may not enable synthesis of nonnatural-type aminopolysaccharide because the reaction catalyzed by chitinase enzyme is limited to the formation of (1 4)-P-glycosidic linkage. 

Scheme 8.1 Synthesis of cross-linked polymer beads via ring-opening metathesis precipitation polymerization. [Mo] = Mo(N-2,6-i-Pr2-...

Bazzi HS, Sleiman HR Adenine-containing block copolymers via ring-opening metathesis polymerization synthesis and self-assembly into rod morphologies. Macromolecules 2002 35 9617-9620. 

K. Kobayashi and T. Kondo, Synthesis of a regiospecifically fluorinated polysaccharide 3-deoxy-3-fluoro-(l — 6)-o -D-glucopyranan via ring-opening polymerization, Macromolecules, 30 (1997) 6531-6535. 

Table 12. Synthesis of Fluoro Amines via Ring Opening of Aziridines...

Fukumoto et al have taken advantage of the propensity for inward rotation of an acyl group to prepare the isochroman-3-one (36), an intermediate in their synthesis of geneserine, a constituent of the calabar bean. The conversion of the benzocyclobutene (37) to (36) proceeds via ring opening to the o-quinodimethane (38) followed by cyclization and a 3,3-sigmatropic rearrangement. 

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