Zinc Bromide Links

Reaction of the benzotriazole-linked phenothiazine 444 with 2,3-dihydrofuran and zinc bromide yields the peri-fused furopyridophenothiazine 445 (Equation 193) <1999JHC473>. 

In interesting contrast to the above, 2,3,4,6-tetra-0-benzyl-/)-glucose, converted to a (1-imidazolylcarbonyl derivative, gave modest yields of mainly a-linked disaccharides when treated with one molar equivalent of alcohol and zinc bromide (Scheme 19). ... 

Silver imidazolate together with mercury(II) chloride or zinc(II) chloride has proved to an efficient promoting system for glycosidations. For example, l,2-(ra/w-linked aryl glucosides have been prepared from fully acetylated glycopyranosyl bromides in almost quantitative yield (equation 6).7(5... 

The ene reaction where both partners are simple alkenes is quite useful when the partners are linked so as to provide for an intramolecular ene reaction. There is a preference for the formation of cw-disubstituted cyclopentane and frans-disubstituted cyclohexane systems resulting from thermally induced, intramolecular ene reactions. For example, levels of transjcis control of 92 8 to > 99 1 were found for the intramolecular cyclization of methyl 2-cyano-9-methyl-3,8-decadienoate23 24. Furthermore, the same tran. -stereochemical relationship was obtained when the reaction was carried out at room temperature in the presence of zinc(II) bromide with control consistently at the 99 1 level for R and R2 either methoxycarbonyl or cyano groups24, This preference for trans fusion does not appear to be greatly altered by added substituents on the chain connecting the reacting partners (vide infra). 

Carbon suboxide is related in structure and properties to ketene, CH2 = CO, since both compounds contain a CO group linked by a double bond to carbon. Ketene is formed when the vapor of bromoacetyl bromide is heated with zinc —... 

Using allyl bromide as a model system it was found that on reaction with zinc oxide in a polyisobutene medium at usual cure temperatures, no allyl bromide, which would be expected from the first mechanism, was detected. (Feniak et ai, 1974). The very good thermal stability is also consistent with carbon-carbon-links which would be produced by the second mechanism. 

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