Dibutyl vinyl boronate

Scheme9.9 Bromotrichloromethane addition to dibutyl vinyl-boronate.

The addition of ethyl diazoacetate and diphenyldiazomethane to dibutyl vinyl-boronate was first reported over forty years ago [87]. This initial study was completed later to establish the scope and limitations of these reactions and the exact nature of the intermediates involved [88]. The regioselective cydoaddition step was immediately followed by a spontaneous 1,3-migration of boron to give a N-boronyl 2-pyrazo-line, which can be trapped, after hydrolysis, with phenylisocyanate (Scheme 9.41). 

The polymerization of cydic disulfides to polydisulfides has been reported in the 1940s and 1950s. In some cases the polymerizations occur spontaneously. Tobolsky et reported that l-oxa-4,5-dithiacycloheptane and l,3-dioxa-6,7-dithiacyclononane are polymerized by cationic initiators such as sulfuric acid or boron trifluoride. Davis and Fettes repotted the anionic polymerization of various cyclic disulfides. In the same period it was also described that cyclic disulfides can copolymetize with vinyl monomers such as styrene and butyl acrylate with AIBN as initiator. That the incorporation of the disulfide was due to copolymerization and not by chain transfer was established by comparing the thermal polymerization of styrene in the presence of dibutyl disulfide and in the presence of l-oxa-4,5-dithiacycloheptane. In the first case, the polymer contained 2 sulfur atoms per macromolecule as a result of transfer reactions and in the second case 4-20 sulfur atoms depending on the ratio of monomers. 

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