5.3.2 Homologations

Diazomethane reacts with aldehydes to afford methyl ketones and ketones can be converted into higher homologues (Scheme 8). In both the cases the yields are moderate due to the formation of epoxides as by-product.

Scheme 8

Mechanism

The addition of diazomethane to the carbonyl group of the aldehydes or ketone can give betain, which could lose nitrogen and lead rearrangement to yield higher ketone or can cyclize to afford epoxides (Scheme 9).

Scheme 9

Example:

Y. Auberson, R. Mampuya, Bimwala, P. Vogel, Tetrahedron Lett. 1991 , 32 , 1637.

 

Arndt-Eistert Homologation Reaction

The reaction of acid chloride with diazomethane gives a -diazoketone, which rearranges with loss of nitrogen to provide ketene in the presence of colloidal silver. The ketene is subsequently transformed into carboxylic acid (Scheme 10). It is called Arndt-Eistert Homologation reaction.

Scheme 10