Lithium halides epoxide rearrangement

Solid complexes of defined stoichiometry have been prepared for all the lithium halides with HMPA. For LiBr, both [LiBr(HMPA)2] and [LiBr(HMPA)4] have been obtained as solids of defined m.p., but the 1 1 complex, the kinetically active species for epoxide rearrangement, has not been isolated. The rate of epoxide loss and solubility of LiBr increased proportionately with added solubilizer (HMPA), to a maximum rate at a 1 1 ratio of addend LiBr. Additional HMPA beyond this ratio caused the rate to decrease even though all the LiBr remained in solution. At an addend LiBr ratio of 2 1, the reaction effectively ceased. These observations allow the conclusions that [LiBr(HMPA)2] is more stable than the reactive 1 1 complex in benzene, and that only the latter is kinetically competent. 

Lithium derivatives of allyl silanes react in the y-position with alkyl halides, epoxides, and carbonyl compounds. The lithium derivative 110 of allyl silane 109 gives only the y-adduct 111 with ketones.31 Vinyl silanes such as 111 are usually converted into carbonyl compounds via epoxides which rearrange with Lewis acid catalysis and loss of silicon to give protected versions of ketones or aldehydes 112. 

TT-ALLYLNICKEL HALIDES METHALLYLBENZENE, 52, 115 Rearrangement of epoxides to allylic alcohols, 53, 17 Reduction, by controlled-po-tential electrolysis, 52, 22 by lithium aluminum hydride of exo-3,4-dichlorobicyclo [3.2.l]oct-2-ene to 3-chlorobicyclo[3.2.l]oct-2-ene, 51, 61... 

Allylic alcohols are reduced with lithium or sodium in ammonia, or low molecular weight amines either with or without alcohols. The thermodynamically more stable product is often formed, leading to rearrangement in some cases (equation 71). Methyl and cyclic ethers are similarly reduced (equations 72 and 73), as are allylic acetates, halides and epoxides (equation 74 and 75). 7.i08 Benzylic and allylic sulfides and sulfones are readily reduced to hydrocarbons using lithium or sodium in alcoholic solvents or in amines. " Allylic sulfones are reduced in a similar manner (Scheme 11)," either with or without migration of the double bond, depending on the reaction conditions used. 

Reactions of phenylthiocyclopropyl lithium with alkyl halides and epoxides have also been reported to deliver products opened to a variety of carbonyl derivatives jS-(l-Phenylthio)cyclopropyl enones have been prepared by using lithium salts of a-hydroxymethylene ketones as electrophiles and dehydrating with acid (equation 110). Rearrangement to cyclobutanones occurs with trifluoroacetic acid, whereas thermal vinylcyclopropane-cyclopentene expansion sometimes gives mixtures of regioisomers . 

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