Electrophiles rearrangement

The pronounced acidity of the bridgehead hydrogen atoms in 4 (R = H) facilitates the regio-selective introduction of electrophiles. Rearrangements of 4 (R = H, Me, CHO, C02Me) catalyzed by dicarbonyldichlororhodium(I) lead to 4-substituted 1-benzothiepins 5,10 except in the case of R = Me where a mixture (1 1.3) of 3- and 4-methyl-l-benzothiepin is obtained (total yield 98 %). In the case of the dimethyl-substituted derivative 8 (R1 = R2 = Me), however, the rhodium(I)-catalyzed isomerization reaction leads to the thiophene isomer. 

The electrophilic rearrangement of 2,3-dibromotetrafluoropropene (5) has been achieved with aluminum tribromide in high yield under mild conditions 9- the dibromide 6 is an intermediate in the synthesis of tetraflnoropropyne. 

Several electrophilic rearrangements of arsacyclohexadienes appear closely related to the direct substitution reaction. 4-Substituted-l-aryl-4-methoxycyclohexadienes 65 are smoothly converted to 4-substituted-2-aryl-arsabenzenes 68 on treatment with acid 102). Presumed intermediate 67 is, of course, analogous to the intermediates in the direct electrophilic substitution. 

The rearrangement of cyclopropylcarbene to cyclobutene was studied theoretically using B3LYP at the 6-311G(d) level.58 The results show that the rearrangement of cyclopropylcarbene to cyclobutene is an electrophilic rearrangement, very different from the traditional mechanism of nucleophilic rearrangement for carbocations. 

HFPO undergoes an electrophilic rearrangement catalyzed by Lewis acids to give hexafluoroacetone (HFA, VII), in virtual quantitative yield (Eq. 13.10). This reaction is used in a commercial process to make HFA and competes favorably with the preparation of HFA... 

Gololobov, Y.G., Galkina, M.A., Dovgan, O.V, Krasnova, LY, Petrovskii, P.V, Antipin, M.Y., bronzov, 11, Lyssenko, K.A. and Schmutzler, R., Intramolecular electrophilic rearrangements in saturated acyclic systems. Reactivity of the zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate with respect to different types of electrophiles, Russ. Chem. Bull 50 (2), 279-286 (2001). 

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