No abstract

Tetrabutylammonium triphenyldifluorosilicate (TBAT) can be employed as a fluoride source to cleave silicon-carbon bonds thus generating in situ carbanions that coupled with a variety of electrophiles, including aldehydes and ketones, in moderate to high yields. Among the examples reported is the first instance of fluoride-induced intermolecular coupling between allyltrimethylsilane and imine derivatives. Also, of particular note is the TBAT-initiated coupling of primary alkyl halides with allyltrimethylsilane. TBAT is an easily handled crystalline solid that has several advantages over tetrabutylammonium fluoride (TBAF) as a fluoride source; it is anhydrous, nonhygroscopic, soluble in most commonly used organic solvents, and less basic than TBAF.

Hypervalent azido- and cyanosilicate derivatives, prepared in situ by the reaction of trimethylsilyl azide or trimethylsilyl cyanide, respectively, with tetrabutylammonium fluoride, are effective sources of nucleophilic azide or cyanide. Primary and secondary alkyl halides and sulfonates undergo rapid and efficient azide or cyanide displacement in the absence of phase transfer catalysts with the silicate derivatives. Application of these reagents to the stereoselective synthesis of glycosyl azide derivatives is reported.

Palladium-catalyzed cross-coupling of phenyl, vinyl, and allyl siloxane derivatives proceeded in good to excellent yield with aryl iodides, electron-deficient aryl bromides, and allylic benzoates. Methyl and 2,2,2-trifluoroethyl siloxane derivatives can be employed in the coupling reaction. Electron-donating and -withdrawing groups are tolerated on the aryl halide without affecting the coupling. The scope and limitations of this alternative to Stille and Suzuki couplings is outlined.

The Mitsunobu reaction occurs typically with inversion of configuration in secondary alcohol derivatives. In this paper, a mechanistic explanation for lactonizations of hindered alcohols under Mitsunobu conditions with retention is proposed. This involves the intermediacy of an acyloxyphosphonium salt followed by acyl transfer to the alcohol.