Application Of Nbcl₅ As A Lewis Acid Catalyst In Organic Synthesis

Since G. N. Lewis laid the foundation for this important theory in the 1920's, Lewis acid catalysts have developed quickly. Lewis acids can make many organic reactions which can not or difficult to be carried out, have successfully performed under moderate conditions. So they contributed to the development of synthetic organic chemistry to a large extent. This work researches about new applications of NbCl5 in organic reaction on the basis of works of predecessors.First of all, the recent development and application of niobium pentachloride as a catalyst in organic reactions including the formation and cleavage of common protecting groups, reduction, cyclization, addition, substitution and rearrangement were summarized.The hydroxyl is a very actively functional group. It is easy to be acylated, oxidated, alkylated and dehydrated. One of protection hydroxyl's methods formed the trimethylsilyl ethers. The trimethylsilyl ethers have many virtues, such as not easy to be oxidized, high stabilization, low viscosity and easy to be prepared. The hexamethyldisilazane (HMDS) is a nontixic and inexpensive reagent. It has been commonly used in the protection of hydroxyl group. We discovered that the reaction of alcohols or phenols with HMDS can obtains the corresponding trimethylsilyl ethers in CH2Cl2 or in absence of solvent at room temperature in high yield.The quinoxaline derivatives are important heterocyclic compounds, which exhibit a diverse rang of biological properties, such as antitumor, cytotoxic, antiviral, antibacterial, antiinflammatory and kinase inhibitor properties. They have also been used as dyes, efficient electron luminescent material, organic semiconductors, DNA cleaving agents, photoinitiators in UV-cured coatings, and donor materials. We discovered that the reactions of 1,2-phenylenediamines and 1,2-diketones catalyzed by NbCl5 can be carried out smoothly at room temperature.α-Aminophosphonates are biological and pharmacological activity, such as inhibitors of enzymes, antibiotic, haptens of catalytic antibodies, antibiotics. They are also intermediates for the preparation of medicinal compounds. Movever,α-aminophosphonates have the merit of low toxicity to mammals. We discovered the reactions of aldehydes, anilines and diethyl phosphite catalyzed by NbCl5 can be carried out smoothly in short time at 60oC under solvent-free conditions.The synthesis of triarylmethanes is an old but still active research area in organic synthesis. Triarylmethanes are a very important class of synthetic dyes used to colour silk, wool, jute, leather, cotton and paper. These dyes are famous for their excellent intensity of color, their brilliant shades of red, blue and green, and low lightfastness on many substrates. We discovered the reactions of aldehydes and N,N-dimethylaniline or N,N-diethylaniline catalyzed by NbCl5 can be carried out smoothly at 60oC under solvent-free conditions.In conclusion, NbCl5 has played an important role in organic reactions and been used extensively. Reactions catalyzed by NbCl5 have many advantages, such as mild reaction conditions, short reaction times, high yield, low catalyst loading and easy to be operated and so on. So we believe NbCl5 will be used much extensively with deep researches for chemists.