Multicomponent reactions promoted by mechanical energy are critically reviewed.

Cheap and readily available aqueous formaldehyde was used as a formylating reagent in a homologation reaction with nonstabilized diazo compounds, enabled by UV photolysis of bench-stable oxadiazolines in a flow photoreactor. Various aliphatic aldehydes were synthesized along with the corresponding derivatized alcohols and benzimidazoles. No transition-metal catalyst or additive was required to affect the reaction, which proceeded at room temperature in 80 min.

Pyrrole is one of the most important one-ring heterocycles because of its widespread presence in natural products and unnatural bioactive compounds and drugs in clinical use. The preparation of pyrroles by reaction between primary amines, β-dicarbonyl compounds, and α-halo ketones, known as the Hantzsch pyrrole synthesis, is reviewed here for the first time. In spite of its age and its named reaction status, this method has received little attention in the literature. Recent work involving the use of non-conventional conditions has rejuvenated this classical reaction and this is emphasized in this review. Some applications of the Hantzsch reaction in target-oriented synthesis are also discussed.1 Introduction2 The Conventional Hantzsch Pyrrole Synthesis3 Hantzsch Pyrrole Synthesis under Non-conventional Conditions4 Applications of the Hantzsch Pyrrole Synthesis5 Conclusions

The combination of a three-component, solvent-free pyrrole synthesis performed under mechanochemical conditions with a TMSOTf-catalyzed oxonium-mediated cyclization gave general access to pyrrolo[2,1-a]isoquinoline derivatives under very mild conditions. The structural diversity generated by this method was extended by the preparation of six additional unusual polyheterocyclic frameworks.