Development of catalysts for the Baylis–Hillman reaction: the application of tetramethylguanidine and attempts to use a supported analogue

Abstract

We show here that tetramethylguanidine (TMG) is a useful catalyst for the Baylis–Hillman reaction of aldehydes with methyl acrylate, showing good activity with a range of aldehyde substrates and, unlike many other catalysts or catalyst mixtures, it can be used to good effect with simple aliphatic aldehydes. We show that the activity of the catalyst is decreased when the reaction is run using solvents rather than solvent-free but, in the case where a solvent is necessary, dichloromethane offers the best results. Attempts to use supported or derivatised TMG complexes as catalysts for the reaction have been unsuccessful suggesting that the presence of an amine hydrogen is key to the activity of TMG. Attempts to use stabilised aliphatic phosphines as catalysts for the reaction have proven partly successful, with only modest yields of product being obtained with 2-(dicyclohexylphosphino)biphenyl and 2-(di-tert-butylphosphino)biphenyl. The Verkade superbase, P(MeNCH₂CH₂)₃N, proved inactive as a catalyst, an adduct with the acrylate being the only product formed.