Shapiro reaction
The Shapiro reaction is a chemical reaction that the synthesis of alkenes from ketones is by means of a Arylsulfonhydrazids. Lithium alkyls serve as the base . Furthermore, the Shapiro reaction enables the synthesis of lithiated alkenes. Mechanistically , the Shapiro reaction is closely related to the Bamford-Stevens reaction . The reaction is named after its developer Robert H. Shapiro .
mechanism
First, an arylsulfonhydrazide condenses on the ketone used. This is then deprotonated by two molecules of a lithium alkyl ( e.g. methyl lithium or butyl lithium ) . The resulting dianion then stabilizes with elimination of the aryl sulfinate. The elimination of molecular nitrogen leads to the formation of the lithiated alkene. When the reaction solution is worked up in water, it is protonated with formation of an alkene.
If the reaction mixture is not worked up in water, the lithiated alkene can also be used as a nucleophile . This enables, for example, the coupling of the alkene to metal centers, for example for the production of cuprates . It can also be alkylated at this position by adding electrophiles (for example haloalkanes ) .
literature
- Reinhard Brückner: reaction mechanisms . 3rd edition, Spektrum Akademischer Verlag, Munich 2004, ISBN 3-8274-1579-9 .
Individual evidence
- ^ Shapiro RH, Lipton MF, Kolonko KJ, Buswell RL, Capuano LA: Tosylhydrazones and alkyllithium reagents: More on the regiospecificity of the reaction and the trapping of three intermediates . In: Tetrahedron Letters . tape 16 , no. 22-23 , 1975, pp. 1811-1814 , doi : 10.1016 / S0040-4039 (00) 75263-4 .
- ↑ RH Shapiro: Alkenes from Tosylhydrazones . In: Organic Reactions . tape 23 , 1976, p. 405 , doi : 10.1002 / 0471264180.or023.03 .