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Seyferth–Gilbert Homologation
The Seyferth–Gilbert homologation is a chemical reaction of an aryl ketone 1 (or aldehyde) with dimethyl (diazomethyl)phosphonate 2 and potassium tert-butoxide to give substituted alkynes 3. Dimethyl (diazomethyl)phosphonate 2 is often called the Seyferth–Gilbert reagent. This reaction is called a ''Homologation reactions, homologation'' because the product has exactly one additional carbon more than the starting material. Reaction mechanism Deprotonation of the Seyferth–Gilbert reagent A gives an anion B, which reacts with the ketone to form the oxaphosphetane D. Elimination of dimethylphosphate E gives the vinyl group, vinyl diazo-intermediate Fa and Fb. The generation of nitrogen gas gives a vinyl group, vinyl carbene G, which via a 1,2-rearrangement, 1,2-migration forms the desired alkyne H. Bestmann modification The dimethyl (diazomethyl)phosphonate carbanion can be generated ''in situ'' from dimethyl-1-diazo-2-oxopropylphosphonate (also called the Ohira-Bestmann ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diazo
In organic chemistry, the diazo group is an organic moiety consisting of two linked nitrogen atoms at the terminal position. Overall charge-neutral organic compounds containing the diazo group bound to a carbon atom are called diazo compounds or diazoalkanes and are described by the general structural formula . The simplest example of a diazo compound is diazomethane, . Diazo compounds () should not be confused with azo compounds () or with diazonium compounds (). Structure The electronic structure of diazo compounds is characterized by π electron density delocalized over the α-carbon and two nitrogen atoms, along with an orthogonal π system with electron density delocalized over only the terminal nitrogen atoms. Because all octet rule-satisfying resonance forms of diazo compounds have formal charges, they are members of a class of compounds known as 1,3-dipoles. Some of the most stable diazo compounds are α-diazo-β-diketones and α-diazo-β-diesters, in which the e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
