2-Methylene-1,3-dioxepane synthesis

Agarwal, S. (2007) Radical ring opening and vinyl copolymerization of 2,3,4,5,6 pentafluorostyrene with 5,6-benzo-2-methylene-13-dioxepane synthesis and structural characterization using ID and 2D NMR techniques. / Polym. Res., 13 (5), 403. 

FIGURE 6 Synthesis of PCL by the free radical polymerization of 2-methylene-l,3-dioxepane. (From Ref. 51.)... 

Bailey, W, J., Ni, Z., and Wu, S.-R., Synthesis of poly-e-capralactone via a free radical mechanism. Free radical ringopening polymerization of 2-methylene-l, 3-dioxepane, J. Polym. Sci., Polym. Chem. Ed.. 3021-3030, 1982. 

This indicates the possibility of making addition polymers biodegradable by the introduction of ester linkages in to the backbone. Since the free radical ring-opening polymerization of cyclic ketene acetals, such as 2-methylene-1,3-dioxepane (1, Scheme I), made possible the introduction of ester groups into the backbone of addition polymers, this appeared to be an attractive method for the synthesis of biodegradable addition polymers. 

The monomers that have been used for the synthesis include glycolide, lactide, (3-propiolactone, (3-butyro lactone, y-butyrolactone, 6-valerolactone, e-caprol-actone, l,5-dioxepan-2-one, pivalolactone, l,4-dioxane-2-one, 2-methylene-1, 3-dioxolane, 2-methylene-l, 3-dioxepane, etc. The structures of some of these monomers are given in Table 1. 

Yuan, J.Y. and Pan, C.Y. (2002) Synthesis of block copolymer from 5,6-benzo-2-methylene-13-dioxepane and methyl acrylate via atom transfer radical polymerization. Chin. J. Polym. Sci., 20 (2),... 

Synthesis and enzymatic degradation of 2 methylene-1,3-dioxepane and methyl acrylate copolymers. J. Polym. 

Srinivasan, A., Hollinger, J.O., and Matyjaszewski, K. (2008) Synthesis, characterization, and in vitro cell culture viability of degradable poly(N isopropylacrylamide-co-5,6-benzo-2-methylene-l,3-dioxepane)-based polymers and crosslinked gels. /. Biomed. Mater. Res. A, 87A (2), 345. 

Arynes have also been employed in a variety of [2+2] cycloadditions. By employing Stevens s and Bisacchi s methodology for the synthesis of benzocydobutenones [94], Santelli et al. have examined the synthesis of benzo-biscyclobutenone 173 by the [2+2] cydoaddition of a dibenzyne with 2-methylene-l,3-dioxepane (Scheme 12.50) [95]. The biscycloadduct 172 was obtained in a 20% yield and smoothly transformed to the corresponding bisketone 173 after hydrolysis. The stracture of 172 was confirmed by single-crystal X-ray analysis. 

PCL can also be obtained by free radical polymerization of 2-methylene-1,3-dioxepane initiated with AIBN. However, this reaction pathway is not of great importance except in the case of the synthesis of some copolymers. 

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