| This thesis contains three parts. Part I presents an attempted enantioselective trapping electrophilic of an electrochemically-generated benzylic radical. The aim of this work was to trap a chlorobenzyl radical intermediate with an α,β-unsaturated ester containing a rigid acyclic chiral auxiliary to form cyclopropane with a high degree of enantiomeric selectivity. 3-(Benzoyloxy)-2,2,6,6-tetramethyl-3-heptyl fumarate monoethyl ester (21) was synthesized as a chiral auxiliary. This chiral auxiliary (21) is an acyclic but strongly conformationally biased molecule. The effort was made to add chlorobenzyl radical to chiral auxiliary (21) by electrochemically reducing a mixture of Co (II) (salen), benzal chloride and chiral auxiliary (21) in DMF. Even through no desired product was formed, we learned that the radicals coupled faster than it reacted with the double bond, possibly because the double bond was too sterically hindered in the chiral auxiliary (21).;Part II presents nucleophilic trapping of an electrochemically-generated benzylic carbocation. Anodic oxidation of 1,2-bis-(trimethylsityl)-1,2-diphenylethane (38) in methanol affords a 65:35 mixture of 1,2-dimethoxy-1,2-diphenylethane (dl:meso 10:1) and diphenylacetaldehyde dimethylacetal. The unsymmetric disilane 1,2-bis(trimethylsily)-1-phenylethane (51) and related compounds were used to generate carbocations by electrochemical oxidation and to trap them with nucleophiles. Nucleophilic attack on beta-silyl carbocation can take place at two sites. The oxidation results of 1,2- bis-(trimethylsily1)-1,2-diphenylethane (38) have shown that attack at carbon (path A) is the primary mode of reaction in methanol. A different mode of reaction is observed with the unsymmetrical disilane. Controlled-potential oxidation of 1,2-bis(trimethylsily)-1-phenylethane (51) at +0.8 V afforded a 7:1 mixture of styrene and methoxysilane. The results can be interpreted in terms of nucleophilic attack on silicon (path B) as the primary mode of reaction. Gratifyingly, anodic oxidation of the bis-t -butyldimethylsilyl derivative in methanol was found to afford a >199:1 ratio of methoxysilane to styrene, in contrast to the 1:7 ratio observed with the trimethylsily1 derivative. Thus, it appears that steric effects can indeed be used to force the anodic behavior of these 1,2-disilanes into the path A channel.;Part III presents electrophilic trapping of fluoride-generated benzylic carbanions. Tetrabutylammonium triphenyldifluorosilicate (TBAT) constitutes a convenient anhydrous source of fluoride ion. It can be employed as a fluoride source to convert C-Si bonds to C-C bonds by cleavage and addition the resulting carbanions to electrophiles. 1-Phenyl-1,2-bis(trimethylsilyl)ethane was treated with TBAT in the presence of a variety of electrophiles. The corresponding carbanion coupled with electrophiles, including aldehydes, ketones, cinnamaldehyde, methyl cinnamate, dimethyl fumarate, dimethyl maleate, benzyl bromide, 1-bromo-2-butyne, and N-benzylidene aniline to generate monoadducts in good yields. |
