The synthesis of N-benzo-heterocycles, such as benzimidazoles, benzodiazepines and quinoxalines by a microwave assisted solvent-free solid acid catalyzed method is described. The commercially available and inexpensive K-10 montmorillonite is an excellent catalyst for the synthesis of the target compounds, many of which are unknown. The reactions have been carried out using a wide variety of o-functionalized aniline derivatives, along with ketones, aldehydes and some bifunctional reagents such as keto-esters and diketones. The cyclization reactions have been initiated by microwave irradiation and provided the products in very high yields (up to 98%) and excellent selectivities in very short reaction times (1-18 min). The effective combination of solid acid catalysis, solvent-free conditions and microwave irradiation provides an attractive highly eco-friendly approach for the synthesis of these important heterocycles. Beyond these, the ease of product isolation, catalyst stability and handling make this process an attractive, environmentally benign alternative for the synthesis of the target compounds.