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27.24.2.1 Synthesis of Product Subclass 2

DOI: 10.1055/sos-SD-027-00847

Schobert, R.; Gordon, G. J.Science of Synthesis, (200427987.

The most general method of ylide generation is the formation of a quaternary phosphonium salt by the reaction of a phosphine with an alkyl halide, followed by removal of an α-proton by a base.[‌135‌] The ylide can also be liberated from the salt by electrolysis (Section 27.24.2.1.2.4) and pyrolytic elimination (Section 27.24.2.1.2.2). Other important methods of preparation[‌136‌,‌137‌] are the replacement of α-hydrogens in preformed ylides with carbon residues (Sections 27.24.2.1.1.1 and 27.24.2.1.1.2), and the addition of tertiary phosphines to electron-deficient alkenes and alkynes, to epoxides, or to a carbene generated in situ from a diazoalkane (Section 27.24.2.1.3.1). Normally phosphorus ylides are prepared from triphenylphosphine, however the use of other triarylphosphines and trialkylphosphines[‌138‌‌140‌] is not uncommon.

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