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DOI: 10.1055/sos-SD-027-00847

Schobert, R.; Gordon, G. J.Science of Synthesis, (2004271005.

Most reactions of phosphorus ylides reflect the pronounced nucleophilicity of the α-carbon atom, the activity of which is widely tunable by varying substitution. For instance, electron-withdrawing carbonyl groups or π-stabilizing silyl groups increase the stability of ylides and, thus, lower their reactivity toward electrophiles, whereas electron-releasing residues such as metals, alkyl, or alkoxy groups act conversely. Typical electrophiles that react with ylides include alkyl halides, epoxides, compounds with carbonyl or other activated polarized multiple bonds, carbenes, and various 1,3-dipolar systems. The reactions proceed with the formation of one or several new CC single, double, or triple bonds and, in many cases, also with concomitant expulsion of either triaryl/trialkylphosphines or -phosphine oxides. The ylidic bond is also susceptible to hydrolysis, reduction, or oxidation, and may also undergo concerted thermal rearrangement and cyclic elimination processes. All these reactions, which quite often exhibit a high degree of regio- and stereoselectivity and tolerance of further functional groups, open access to key organic functionalities such as those found in alkenes, alkynes, acyclic and cyclic alkanes, and carbonyl compounds. However, by far the most important reaction of phosphorus ylides is still the Wittig alkenation of carbonyl compounds.