Seyferth-Gilbert homologation

What is Seyferth-Gilbert homologation?

The Seyferth-Gilbert homologation, also known as the Seyferth-Gilbert reaction, was first reported by Seyferth in 1970, and subsequently extended by Gilbert et al. in 1979. It is a reaction that transforms aldehydes or ketones into alkynes with an additional carbon atom through the use of dimethyl (diazomethyl)phosphonate and potassium t-butoxide KO-t-Bu.

Seyferth-Gilbert homologation - general reaction scheme
Seyferth-Gilbert homologation
  • R = alkyl, aryl
  • R’ = H, alkyl, aryl

This reaction has several names, including the Gilbert-Seyferth homologation, Gilbert-Seyferth reaction, Seyferth-Gilbert reaction, and Seyferth-Gilbert homologation.

Dimethyl (diazomethyl)phosphonate (MeO)2P(O)CHN2 is also known by various names, including the Seyferth-Gilbert reagent, Seyferth reagentSeyferth-Gilbert diazophosphonate reagent, Gilbert-Seyferth diazo phosphonic reagent, and Gilbert-Seyferth reagent.


  • Seyferth, D. and Marmor, R., Tetrahedron Lett., 1970, 2493
  • Gilbert, J. C. and Weerasooriya, U., J. Org. Chem., 1979, 44, 4997