The study of solvent-free heterocyclic synthesis reported that the solvent-free conditions are better than molecular solvents for cyclocondensation reactions; and the chemical mechanistic aspects of solvent-free reactions discussed are associated with cyclocondensation reactions. The use of solvent-free conditions in heterocyclic synthesis generally leads to similar or higher yields and a reduction in the reaction time as compared to the same reaction performed in the presence of molecular solvents. The experiments resulted that all reactions performed in MW, both domestic oven and synthesis equipment, presented better yields and shorter reaction times than those not carried out in MW. The E-factor for solvent-free reactions presented showed values in a range of 0.1-4.9 for reactions performed under solvent-free conditions considering only the synthetic steps and a range of 5.0-49.9 and 50.0-100.0 for reactions accomplished using molecular solvents.