Morita-Baylis-Hillman Reactions with Nitroalkenes: A Case Study

We report on the use of a highly reactive super-DMAP catalyst in Morita-Baylis-Hillman (MBH) reactions of nitroalkenes with ethyl glyoxylate, which result in excellent conversions and short reaction times with, importantly, very low catalyst loading. An extensive study of this particular reaction is presented, which examines all mechanistic and experimental details. Several critical points were hence uncovered that include the correlation between reaction efficiency and Lewis basicity of the catalyst; the double role played by the promoter, primarily as a nucleophilic activator towards the nitroalkene, and as a Bronsted base that triggers glyoxylate depolymerisation. More generally, the limitations in the choice of electrophiles that can engage efficiently in MBH-type transformations are rationalized by the competition between a productive pathway and a nitroalkene polymerization process. Other aspects of this transformation, used as a case study, are presented in the light of physical organic chemistry.