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An efficient environmentally benign route for the synthesis of benzimidazo[2,1-a]isoquinoline has been developed by reacting 2-ethynylbenzaldehyde and related substituted alkynylbenzaldehydes with variously substituted ortho-phenylenediamines and aliphatic amines in ethanol. This method provides a convenient, room temperature, atom-economical, and catalyst-free access to diversely substituted isoquinoline fused benzimidazoles. Regioselectivity of the reaction, as referred to o-phenylenediamines, was confirmed by X-ray crystallography. The reaction was found to occur in three major steps (imine formations, cyclization, and aromatization) and a mechanism has been proposed.

The oxidative cleavage of styrenes to benzaldehydes by an environmentally benign heterogeneous catalytic method is described. The commercially available, inexpensive KSF montmorillonite was applied as a catalyst for the cleavage reaction at moderate temperatures using air as a sustainable oxidant in aqueous medium. The approach has been thoroughly optimized by testing several commercially available heterogeneous catalysts, including supported Pd and Rh catalysts, acidic montmorillonites and other common oxides such as silica or alumina. A broad variety of reaction conditions were assessed, including catalyst/reactant/solvent ratios, temperature, solvent and reaction time. The optimized conditions yielded benzaldehyde from styrene with high yield and exclusive selectivity. The scope of the reaction has also been investigated by using substituted styrenes as substrates. The data indicate that KSF is an excellent and at the same time sustainable catalyst for the oxidative cleavage. When also considering the simplicity of this method, it makes for a good alternative that can serve as a green replacement for the traditional ozonolysis reaction.

The chemoselective reduction of a broad variety of functional groups by a Pd/C–Al–H2O system is described. The reduction is based on the reaction of Al with the solvent water that in situ produces hydrogen that is utilized by the supported Pd catalyst toward the hydrogenation of the target functional groups. The hydrogenations are carried out under mild conditions and provided the products in high yields and selectivity. The reduction system appeared to be effective for a broad range of functional groups, including C–C, C–N, C–O and N–O multiple bonds, aromatic rings, hydrogenolysis of C–O, C–N and C–Halogen bonds. The appropriate selection of the reaction conditions allowed the selective preparation of different products from the same substrate. The simplicity, cost, tunability and the environmentally benign character of the catalytic system offer numerous advantages over the currently available methods.

The application of ultrasonic irradiation for the activation of chemical reactions, commonly known as sonochemistry, has contributed to the development of a number of processes that are considered to be environmentally benign. The use of ultrasonic waves to activate synthetic processes usually results in shorter reaction times and higher yields and selectivities, namely, cleaner products. This work aims to provide an overview of recent applications that illustrate the use of sonochemistry in the field of green or sustainable synthesis. In the first part of the chapter, organic synthetic processes are surveyed, including applications in aqueous, nonaqueous, or biphasic systems as well as homogeneous and heterogeneous catalytic reactions. In the second part of the work, the focus will be on an emerging field, the preparation of nanoparticles.