Oxiranes, reactions

It seems that the initiation step of the copolymerisation most likely involves the oxirane reaction [according to scheme (3)]. Zinc alcoholate species formed in this reaction can easily propagate the copolymer chain, coordinating and enchaining both the oxirane [scheme (3)] and the cyclic carbonate [scheme (15)] comonomers. However, in the case of the cyclic carbonate, its enchainment may also proceed according to scheme (14), leading to decarboxylation. Thus, the obtained poly(ether-carbonate)s are characterised by a lower content of carbonate units with respect to the ether units [82,146]. 

Different competitive processes are dependent on the diazo compound, on the unsaturated system, and on the solvent. With 1,1,1-trifluorobutan-2-one and diazomethane, the corresponding oxirane is formed almost exclusively. While methyl trifluoropyruvatc reacts with diazomethane to provide a mixture of the oxiranes, reaction of the pyruvate with ethyl diazoacetate provides a stable [3-1-2] cycloadduct.Chiral fluoroalkyl-substituted /i-oxo sulfoxide (e.g., 1) readily react with diazomethane to provide the corresponding chiral epoxides. Use of methanol as solvent favors oxirane formation over the competitive enol ether formation. 

The activated THF reacts with the same nucleophilic species from the reaction system, similarly to the activated oxirane (reaction 7.24). 

Nucleophilic Ring-opening Reactions of Oxirans.—Reactions with Oxygen and Nitrogen Nucleophiles. A series of papers have appeared that deal with the reactions of lower aliphatic alcohols (R OH) with (120 = Me) to yield (121 ... 

Another broad class of oxirane reactions are viewed as heterocychc interconversions, as they transform the epoxide system into another heterocychc entity. This is illustrated by the following examples, in which epoxides are transformed... 

These reactions are rapid and the sulfide is efficiently oxidized to sulfoxide as the only product with no over-oxidation to sulfone. The oxirane reaction [Eq. (1)] is thought to proceed via a direct oxygen transfer from the oxirane to the sulfide. In a recent mechanistic study [9] it was found that a hypervalent sulfurane is an intermediate in the oxidation of sulfides by dioxiranes. This intermediate is in equih-brium with the electrophilic zwitterionic intermediate formed as a result of electrophilic attack by the peroxide on the sulfide. 

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