Epoxides rearrangement mechanism

A considerable amount of work was required to optimize the leaving group and avoid racem-ization through a Payne rearrangement mechanism.12 Of course, the Sharpless epoxidation of allyl alcohols is well-known to access these 3-functionalized epoxides. 

Epoxide-carbaayl rearrangement. Lithium bromide effects facile rearrangement of epoxides to aldehydes and/or ketones in benzene solution. The salt is insoluble in benzene but addition of 1 mole of HMPT or tri- -bulylphosphine oxide per mole of lithium bromide affords a soluble complex which effects the epoxide rearrangement. Evidence suggests a mechanism involving the salt of the bromohydrin as an intermediate. 

Hart and coworkers used trifluoroacetic acid to catalyze some deep-seated epoxide rearrangements, illustrated by the examples in equations (15) and (16). An unusual mechanism involving scission of the epoxide C— bond was suggested for the conversion of (38) to (39), in order to accommodate deuterium-labeling results. 

As discussed by Ruckel et al., (14) the catalytic cationic polymerizations of a-plnene oxide and B-plnene oxide both Involve the concomitant opening of the epoxide and cyclobutane rings In the propagation step. This rearrangement mechanism also clearly operates In the radlatlon-lnduced polymerization of these monomers, and Is depicted below for a-plnene oxide (Scheme ). 

The phosphite esters function in this formulation as primary heat stabilizers by replacing labile chlorides on PVC via the Arbuzov rearrangement mechanism. When phosphites are used at optimized levels in combination with catalytic amounts of zinc and normal levels of epoxidized soybean oil, they provide excellent early color and adequate long-term stability to flexible PVC compounds. Their use also helps in lowering stabilization cost, elimination of toxic metals, elimination of plate out, poor printability, viscosity drift in plastisols, haze, bloom, water blush, and staining. 

The reductive elimination of a variety of )3-substituted sulfones for the preparation of di-and tri-substituted olefins (e.g. 75 to 76) and the use of allyl sulfones as synthetic equivalents of the allyl dianion CH=CH—CHj , has prompted considerable interest in the [1,3]rearrangements of allylic sulfones ". Kocienski has thus reported that while epoxidation of allylic sulfone 74 with MCPBA in CH2CI2 at room temperature afforded the expected product 75, epoxidation in the presence of two equivalents of NaHCOj afforded the isomeric j ,y-epoxysulfone 77. Similar results were obtained with other a-mono- or di-substituted sulfones. On the other hand, the reaction of y-substituted allylic sulfones results in the isomerization of the double bond, only. The following addition-elimination free radical chain mechanism has been suggested (equations 45, 46). In a closely related and simultaneously published investigation, Whitham and coworkers reported the 1,3-rearrangement of a number of acyclic and cyclic allylic p-tolyl sulfones on treatment with either benzoyl peroxide in CCI4 under reflux or with... 

Mechanisms for nucleophilic aliphatic substitution at glycosides, 41, 277 Mechanisms of hydrolysis and rearrangements of epoxides, 40, 247 Mechanisms of oxygenations in zeolites, 42, 225 Mechanisms, nitrosation, 19, 381... 

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