In the first (theoretical) part of this thesis, the different mechanistic ways for the conversion of dithiocarbamates to dialkyl thiourea derivatives have been investigated using the high-accurate DFT calculations (M06-2X/aug-cc-pvtz). The energy details of all the pathways were investigated in the gas phase and implicit and explicit solvation models (PCM, and solvent-assisted) using water as solvent. Two general mechanisms and several pathways have been considered to investigate this mechanism. The first mechanism (A) involves with the preparation of alkyl isothiocyanate, following by the addition of alkyl amine and the proton transfer. The second mechanism (B) involves with the addition of alkyl amine, proton transfer and elimination of thiol. In the experimental part of this study, first, various ?-cyano hydroxylamines have been synthesized via a 3-component reaction between aromatic aldehydes, phenylhydroxylamine and trimethylsilyl cyanide at room temperature. In this line, several solvents and catalyst were employed to obtain the more appropriate ones for the reaction. Among the employed solvents and catalysts, methanol (as solvent) and NiCl 2 (as catalyst) showed the highest performances. To complete of these experiments, the mechanistic details for it have been studied. For this purpose, the possible mechanistic pathways for both steps of this reaction in the gas phase and explicit solvent (methanol) model have been studied using DFT calculations. Moreover, the energy profiles for all possible mechanistic steps were obtained. Geometry optimizations and frequency calculations of all structures were performed. The results of these computations were in complete accordance with the experimental results, which showed the methanol is the best solvent and NiCl 2 is the most appropriate catalyst for this reaction, among the studied solvents and catalysts. In the second experimental study, A green and solvent-free method was developed for alkylation of N,N-dialkylanilines with substituted ?-nitrostyrenes using of [ChCl][ZnCl 2 ] 2 deep eutectic solvent. All products were synthesized in high yields and great regioselectivity. The synthetic protocol was expanded for alkylation of pyrrole and indole to produce pharmaceutically active compounds. The reduction of the nitro group of the product to amine was performed using Pd/C and hydrazine to produce amphetamine structure. In the third experimental study, various derivatives of ?-cyanophosphonates were synthesized by presenting a new reaction between ?-nitrostyrenes and triphenylphosphitre in [ChCl][ZnCl 2 ] 2 deep eutectic solvent. All products show high yield in mild condition. The interesting mechanism was proposed for the reaction and evaluated by detection of byproduct and NMR characterization of isolated intermediate. In the final study, a new method for synthesis of benzofurans from salicylaldehyde derivatives and nitro epoxides without using catalyst was proposed. Different derivatives were synthesized from the catalyst-free reaction using 3 mmol K 2 CO 3 as base, 1 mL DMF as solvent, 110 °C and 12 h in 60-84% yields. Among four different employed nitroepoxides, the highest yields were obtained by using 3-nitro derivative. The proposed mechanism for the reaction was confirmed by stereochemical evidences, detection of released acetate anion and isolation and structure determination of the important intermediate.