Alkyne metathesis

Alkyne metathesis is an

Metal-catalyzed alkyne metathesis was first described in 1968 by Bailey, et al. The Bailey system utilized a mixture of tungsten and silicon oxides at temperatures as high as 450 °C. In 1974 Mortreux reported the use of a homogeneous catalyst—molybdenum hexacarbonyl at 160 °C—to observe an alkyne scrambling phenomenon, in which an unsymmetrical alkyne equilibrates with its two symmetrical derivatives.^[4] The Mortreux system consists of the

Molybdenum catalyst with aniline-derived ligands are highly effective catalysts.^[6]

• Catalysts for alkyne metathesis
• 
• 
  "canopy catalysts"
• 
  Air stable low-valent d2 rhenium alkylidyne
• 
  various Schrock-based alkyne metathesis catalysts

The so-called "canopy catalysts" containing tripodal ligands are particularly active and easy to prepare.^[7]

Catalyst degradation

Typical degradation pathways for these catalysts include hydrolysis and oxidation.

In practice,

The same two-step procedure was used in the synthesis of the naturally occurring cyclophane turriane.

Trisamidomolybdenum(VI) alkylidyne complexes catalyze alkyne metathesis.^[12]

Natural product synthesis

RCAM can also be used as strategic step in

Another example shows a highly functionalized enyne, which displays a rare thiazolidinone unit, can be metathesized under Mo(III) catalyst, neither this unusual sulfur-containing heterocycle nor the elimination-prone tertiary glycoside posed any problem in the ring-closing step.^[15]

The total synthesis of spirastrellolide F employs alkyne metathesis in one step.

Nitrile-alkyne cross-metathesis

By replacing a tungsten alkylidyne by a tungsten nitride and introducing a nitrile Nitrile-Alkyne Cross-Metathesis or NACM couples two nitrile groups together to a new alkyne. Nitrogen is collected by use of a sacrificial alkyne (elemental N₂ is not formed):^[17][18]

See also

• Olefin metathesis, redistribution of alkene bonds
• Alkane metathesis, redistribution of alkane bonds

References