This thesis focuses on NHC-catalyzed annulation of nitroalkenes, enals and , -unsaturated carboxylic acids. (1) NHCs were found to be efficient catalysts for the [4+2] annulation of -substituted nitroalkenes. The scope of Rauhut-Currier reaction was successfully extended to the most challenging -substituted alkenes by this method; (2) Enals were successfully used for [4+2] annulations with azodicarboxylates catalyzed by NHC via -addition. Highly enantiopure tetrahydropyridazinones and -amino acid derivatives could be easily prepared by subsequent transformations of the resulting dihydropyridazinones. (4) The readily available , -unsaturated carboxylic acids were first successfully employed to generate the , -unsaturated acyl azolium intermediates by using NHC for the enantioselective [3+2] and [3+3] annulations.