Bamford-Stevens reaction

The Bamford-Stevens reaction - also Bamford-Stevens-Shapiro olefination - is a reaction from the field of organic chemistry . It is used to synthesize alkenes from ketones with the same number of carbon atoms in the starting material and the product. The name reaction is named after its discoverers William Randall Bamford and Thomas Stevens Stevens .

Overview

The Bamford-Stevens reaction allows a ketone to be converted into an isomeric mixture of cis and trans alkenes:

The Bamford-Stevens reaction can be carried out in different ways: Sodium alcoholates serve as the base or, as in the Shapiro reaction, lithium alkyls . Depending on the base in protic or aprotic solvent. Mixtures of (Z) / (E) isomers are formed in the protic solvent , whereas (Z) -alkenes [ cis -alkenes] are preferably formed in the aprotic solvent .

Reaction mechanism

The following illustrations show a plausible course of the reaction based on the literature. The mechanism is shown using butanone and methanolate as the base. Ar denotes an aryl group such as a phenyl group . First, the butanone ( 1 ) is reacted with an arylsulfonhydrazide to form sulfonylhydrazone 2 . This is deprotonated by the methanolate :

The diazo compound 3 is formed with elimination of the aryl sulfinate . The decisive factor for the further course of the reaction is whether the process is carried out in protic or aprotic solvents.

Second reaction in protic solvent

In protic solvents, a proton is abstracted from the solvent molecule in the next step . This creates the diazonium salt 4 :

The carbocation 5 is formed therefrom with the splitting off of molecular nitrogen . Deprotonation then leads to the alkene. The elimination to the double bond is unselective depending on the stability of the carbocation. Mixtures of ( E ) isomer 6a and ( Z ) isomer 6b are formed .

Second reaction in aprotic solvent

If the reaction is carried out in aprotic solvents, the carbene 7 is formed from the diazo compound 3 with elimination of molecular nitrogen :

7 reacts by a hydride shift preferentially to form the ( Z ) -alkene 6b .

Practical meaning

The Bamford-Stevens reaction is a purely laboratory process. Because of the formation of stoichiometric amounts of several waste materials , the atom economy of the Bamford-Stevens reaction is so bad that nobody realizes a technical synthesis for alkenes based on this reaction.

literature

Thomas Laue, Andreas Plagens: Name and keyword reactions in organic chemistry. 5th edition, Vieweg + Teubner, 2006, ISBN 3-8351-0091-2 , p. 26 ( limited preview in the Google book search).
László Kürti , Barbara Czakó: Strategic Applications of Named Reactions in Organic Synthesis. Elsevier Academic Press, Burlington / San Diego / London 2005, ISBN 0-12-369483-3 .

Individual evidence

^ WR Bamford, TS Stevens: The decomposition of toluene-p-sulphonylhydrazones by alkali. In: Journal of the Chemical Society (Resumed). 1952, pp. 4735-4740, doi : 10.1039 / JR9520004735 .
↑ L. Kürti , B. Czakó: Stratigic Applications of Named Reactions in Organic Synthesis. Elsevier Academic Press, Amsterdam 2005, ISBN 978-0-12-429785-2 , p. 36.
↑ T. Laue, A. Plagens: Name and keyword reactions. 5th edition, BG Teubner / GWV Fachverlage, Wiesbaden 2006, ISBN 978-3-8351-0091-6 , pp. 26-27.

Web links

Commons : Bamford-Stevens reaction - Collection of images, videos and audio files

organic-chemie.ch: Bamford-Stevens reaction

[1] WR Bamford, TS Stevens: The decomposition of toluene-p-sulphonylhydrazones by alkali. In: Journal of the Chemical Society (Resumed). 1952, pp. 4735-4740, doi : 10.1039 / JR9520004735 .

[Kürti_36-2] L. Kürti , B. Czakó: Stratigic Applications of Named Reactions in Organic Synthesis. Elsevier Academic Press, Amsterdam 2005, ISBN 978-0-12-429785-2 , p. 36.

[Laue_26-27-3] T. Laue, A. Plagens: Name and keyword reactions. 5th edition, BG Teubner / GWV Fachverlage, Wiesbaden 2006, ISBN 978-3-8351-0091-6 , pp. 26-27.