Pinacol coupling

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The pinacol coupling is a chemical reaction from the field of organic chemistry .

It was described in 1859 by Wilhelm Rudolph Fittig for the synthesis of pinacols . Through this reaction, ketones or aldehydes are coupled to 1,2-diols by reaction with metals (e.g. magnesium ) and a new carbon-carbon bond is formed . These diols are versatile intermediates in organic synthesis. These can be implemented, for example, in the pinacol rearrangement .

Reaction mechanism

During the reaction there is a one-electron transfer from the metal to the carbonyl compound ( acetone in the example ) 1 . This reduction forms a ketyl radical anion . If two such radical anions combine to form a dianion, the vicinal diol ( pinacol ) 2 is obtained after subsequent acid hydrolysis  :

Pinacol coupling reaction mechanism

The coupling can lead to the formation of two neighboring stereocenters if an asymmetrical ketone or an aldehyde (except formaldehyde ) is used as the starting material instead of acetone .

Whether the reductive coupling of two carbonyl compounds leads to 1,2-diols or to further deoxygenation depends on the oxygen affinity of the metal used. In the case of deoxygenation, the pinacolate then forms an alkene .

The McMurry reaction is also suitable for the pinacol synthesis and, depending on the reaction conditions, leads to very high yields.

literature

  • Organic Synthetic Highlights III. Wiley-VCH, Weinheim 1998, pp. 113-118.
  • KPC Vollhardt , NE Schore Organic Chemistry. , 4th edition, Wiley-VCH, Weinheim 2005, pp. 885-886.
  • Organikum author collective 22nd edition, Wiley-VCH, Weinheim, 2004, ISBN 3-527-31148-3 .
  • FA Carey, RJ Sundberg Organic Chemistry - An Advanced Textbook. , Wiley-VCH, Weinheim 1995, pp. 1006-1007.
  • B. Bogdanovic ', A. Bolte, J. Organomet. Chem. 1995, 502, 109-121.
  • A. Fürstner , B. Bogdanovic, Angew. Chem., Int. Ed. Engl., 1996, 35, 2442.

See also

Individual evidence

  1. ↑ R. Fittig: About some metamorphoses of the acetone of acetic acid . In: Annals of Chemistry and Pharmacy . tape 110 , no. 1 , 1859, p. 23 , doi : 10.1002 / jlac.18591100104 ( archive.org ).
  2. ↑ Jonathan Clayden, Nick Greeves, Stuart Warren: Organische Chemie , Springer Spectrum, 2013, 2nd edition, pp. 1074-1077, ISBN 978-3-642-34715-3 .