Silyl halides, regioselective reaction with

Cathodic substitution stands for C,C bond or C, heteroatom bond formation with cathodically generated anions. The question of regioselectivity is encountered in the reaction of such anions with allyl halides (path a) or in the reaction of allyl anions generated in an ECE process from allyl halides (path b). Cathodic reductive silylation of an allyl halide proceeds regioselectively at the less substituted position (Fig. 15) [91]. From the reduction potentials of the halides it is proposed that the reaction follows path b. 

Titanocene dichloride also catalyzes a regioselective carbomagnesiation of alkenes 187 (equation 115) and dienes 188 (equation 116). The reaction proceeds at 0°C in THF in the presence of Cp2TiCl2, an organic halide and n-BuMgCl which leads to the catalytic species, affording benzyl, allyl or a-silyl alkylmagnesium halides, which are trapped with electrophiles (equation 117) . ... 

Mori has employed transmetallation, well documented in other organozirco-nium reactions [59], to form y-allylated a-silyl allyl amines (Eq. 19) [40,41] and substituted pyrroles (Eq. 20) [60] after the insertion of alkynes into the Zr-C bond of zirconaaziridines. The reaction sequence in Eq. 19 uses stoichiometric quantities of Zr, but catalytic amounts of Cu, and both the insertion and allylation steps proceed with high regioselectivity. Using an acyl halide instead of allyl chloride gives tetra- and pentasubstituted pyrroles, in a one-pot reaction (Eq. 20). 

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