Rearrangement, butyllithium induced

The stereoisomers of ds-ds-ds-cycloheptatriene 103 and 104 have been postulated as intermediates in the thermal rearrangement of the homobenz-valene 102 to ds-bicyclo[3.2.0]hepta-2,6-diene (105a) (120). The cis-trans-cycloheptadiene derivative 107 is considered to be the intermediate in the butyllithium-induced rearrangement of the /1-bromocyclopropyloxirane 106 to ds-bicyclo[3.2.0]hept-6-en-2-ol (108) (121). Evidence of the intermediacy of 107 was obtained by trapping with 1,3-diphenylbenzoisofuran. 

Methyl (2E,4E)Senoates. The dianion (2) of 1 can be prepared by treatment with I.DA and then sec-butyllithium in THF at —78°. The dianion is alkylated selectively at the a-allylic position to give 3 as the major product. Treatment of 3 with LDA induces a [2,3]sigmatropic rearrangement to 4. Remaining steps to the diunsaturated ester (6) are methylation, oxidation, and dchydrosulfcnylation.1... 

With phenylsilylated salts, the same type of /V,/V-d i m e t h y I b e n z y I a m i n e s are formed accompanied by /V,/V-d i meth yi -2-1ri meth y I s i I yi meth y I benzyi am i ne. A mechanism involving silylated and non-silylated intermediate ylid has been proposed. Using LAH in place of sodium amide induces cleavage of the silyl group, especially in the triphenylsilyl case. With w-butyllithium, the same two products are obtained in equal amounts accompanied with a Stevens rearrangement product as a minor compound. 

Additions to Electron-deficient Species. Diazomethane will also add to highly electrophilic species such as sulfenes or im-minium salts to give the corresponding three-memheredring heterocycles. When the reaction is performed on sulfenes, the products are episulfones which are intermediates in the Ramherg-Backlund rearrangement, and are therefore precursors for the s)mthesis of alkenes via chelotropic extrusion of SO2. The sulfenes are typically prepared in situ by treatment of a sulfonyl chloride with a mild base, such as Triethylamine (eq 47). Similarly, the addition of diazomethane to imminium salts has been used to methyle-nate carbonyls. In this case, the intermediate aziridinium salt is treated with a strong base, such as Butyllithium, in order to induce elimination (eq 48). 

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