Glaser coupling

The Glaser coupling is a type of coupling reaction. It is by far the oldest acetylenic coupling and is based on cuprous salts like copper(I) chloride or copper(I) bromide and an additional oxidant like oxygen. The base in its original scope is ammonia. The solvent is water or an alcohol. The reaction was first reported by Carl Andreas Glaser [de] in 1869.^[1][2] He suggested the following process for his way to diphenylbutadiyne:

CuCl + PhC₂H + NH₃ → PhC₂Cu + NH₄Cl

4 PhC₂Cu + O₂ → 2PhC₂C₂Ph + 2Cu₂O

Modifications

Eglinton reaction

In the related Eglinton reaction two terminal alkynes are coupled by a copper(II) salt such as

The oxidative coupling of alkynes has been used to synthesize a number of fungal antibiotics. The stoichiometry is represented by this highly simplified scheme:[4]

Such reactions proceed via

This methodology was used in the synthesis of cyclooctadecanonaene.^[5] Another example is the synthesis of diphenylbutadiyne from phenylacetylene.^[6]

Hay coupling

The Hay coupling is variant of the Glaser coupling. It relies on the

In 1882 Adolf von Baeyer used the method to prepare 1,4-bis(2-nitrophenyl)butadiyne, en route to indigo dye.^[9][10]

Shortly afterwards, Baeyer reported a different route to indigo, now known as the

See also

• Cadiot–Chodkiewicz coupling - Another alkyne coupling reaction catalysed by copper(I).
• Sonogashira coupling - Pd/Cu catalysed coupling of an alkyne and an aryl or vinyl halide
• Castro–Stephens coupling - A cross-coupling reaction between a copper(I) acetylide and an aryl halide
• Fritsch–Buttenberg–Wiechell rearrangement - can also form diynes

References