Enyne metathesis

from Wikipedia, the free encyclopedia

The enyne metathesis is a reaction in organic chemistry in which a conjugated 1,3- diene is formed from an alkene and an alkyne using a carbene complex catalyst . It belongs to the olefin metathesis and is mechanistically and formally closely linked to alkene metathesis and alkyne metathesis .

General

If the enyne metathesis takes place intermolecularly between an alkene and an alkyne, it is called a cross-enyne metathesis. If both functional groups are present in one molecule ( enyne ), the reaction takes place intramolecularly and is called enyne ring-closing metathesis. The driving force of such reactions is the formation of a thermodynamically stable conjugated double bond system in the product. Therefore, unlike alkene metathesis, the reaction is irreversible. Furthermore, the reaction is atom-economical .

The enyne ring-closing metathesis is more relevant than the enyne cross-metathesis and is particularly useful in the synthesis of heterocycles and natural products .

Cross enyne metathesis

In the cross-enyne metathesis, an alkene reacts with an alkyne at the respective multiple bonds . In the product there is a single bond in the place of the former triple bond:

Cross enine metathesis overview

The reaction is usually not stereoselective , so that (E) and (Z) isomers are formed.

Enyne ring-closing metathesis

In the enyne ring-closing metathesis, the alkyne group of an enyne reacts with the alkene group to form rings. The alkene group must be terminal. The reaction can produce two products which differ in their ring size by one carbon atom. Here, too, there is a single bond in the product in place of the former triple bond. An exemplary ring-closing metathesis with five- and six-membered rings can be seen in the reaction scheme.

Overview of ring-closing metathesis V4.svg

If there are several double and triple bonds in an acyclic molecule, several enyne ring-closing metatheses can occur, in which case a polycyclic product is formed. This special case is also called tandem enyne metathesis.

Individual evidence

  1. ↑ a b c d e Steven T. Diver & Anthony J. Giessert: Enyne Metathesis (Enyne Bond Reorganization). In: Chemical Reviews 2004, Vol. 104 (3), pp. 1317-1382. doi : 10.1021 / cr020009e .
  2. ↑ a b c Entry on enyne metathesis. In: Römpp Online . Georg Thieme Verlag, accessed on September 3, 2019.
  3. ^ A b Steven T. Diver & Justin R. Griffiths: Ene-Yne Metathesis . In: Karol Grela (Ed.): Olefin Metathesis - Theory and Practice . Hoboken Wiley, 2014, ISBN 978-1-118-20794-9 , chap. 4 , p. 153-185 .
  4. ^ Hélène Villar, Marcus Frings & Carsten Bolm: Ring closing enyne metathesis: A powerful tool for the synthesis of heterocycles . In: Chemical Society Reviews . tape 36 , 2007, p. 55-66 , doi : 10.1039 / b508899m .
  5. ↑ Tim Vorfalt: Olefin Metathesis - Synthesis and Mechanism of Ruthenium-NHC Complexes. Technische Universität Darmstadt, 2010. Online at: / PDF .