A transition metal-free [3 + 2] cycloaddition approach for the efficient synthesis of trisubstituted pyrrole derivatives from β-chlorovinyl aldehydes

A transition metal-free, Cs2CO3-promoted approach has been devised for the efficient synthesis of nitrile-substituted novel pyrrole derivatives from β-chlorovinyl aldehydes. Interestingly, the strategy was also found to be applicable to the synthesis of chromenone-fused pyrrole derivatives. The reaction proceeded through [3 + 2] cycloaddition between diversely substituted aryl propiolonitriles and toluenesulphonylmethyl isocyanide in DMF at ambient temperature. This approach offers several advantages including the use of inexpensive and readily available starting materials, wide substrate scope, operational simplicity, short reaction times (15 min-1.5 h), high atom economy, sustainable reaction conditions and high product yields. The strategy has been found to be amenable for gram-scale synthesis, and the scope of the strategy has been demonstrated for the synthesis of a diverse library of novel pyrrole derivatives with yields of up to 91%. The generated pyrrole derivatives are amenable for late-stage functionalisation and functional group interconversion.

SnCl2-mediated heterocyclization approach for the synthesis of benzisoxazole/quinoline-embedded β-carboline scaffolds

A Sn(II)-mediated facile entry towards construction of C-C/C-O and C-C/C-N bonds was devised. The developed reductive heterocyclization method is described for the synthesis of a diverse range of novel β-carboline C-1- and C-3-linked vinyl benzisoxazole analogues from the corresponding 2-nitro chalcones. In addition, the synthesis of β-carboline C-1-substituted quinolines (Nitramarine analogues) was achieved. The protocol was extended towards the formation of quinoline C-3-substituted benzisoxazole derivatives in good yields utilizing 2-alkynyl-3-formyl quinolines and 2-nitroacetophenone as templates. The scope of our strategy was demonstrated with the synthesis of a library of 56 novel molecules. The synthesized benzisoxazole derivatives had light-emitting properties to deliver a fluorescence quantum yield up to 33%.

Synthesis of polysubstituted pyrroles via isocyanide-based multicomponent reactions as an efficient synthesis tool

The present review covers all synthetic methods based on isocyanide-based multicomponent reactions for the preparation of polysubstituted pyrroles as the parent cores of many essential drugs, biologically active compounds, and compounds with wide application in materials science.