Executive Summary : | Although the concept of “organocatalysis” was introduced in the beginning of 20th century, apart from phase-transfer catalysis, the potential of organocatalysts has been realized after the seminal contributions by the 2021 Nobel laureates Prof. Benjamin List and Prof. David McMillan. One of the recent addition in this broad area is “carbocation” catalysis, which is often referred as “organic Lewis acid catalysis”. The main objective of this proposal is to explore the Lewis acidity of triaryl-cyclopropenium cations in catalytic organic transformations. The important thing is that, although these triaryl-cyclopropenium cations are known in the literature for more than a century, they have not been explored as organic Lewis acid catalyst in organic transformations so far. These cations can be easily prepared in a single step through Friedel-Crafts reaction of the respective arenes with commercially available tetrachlorocyclopropene in the presence of stoichiometric amounts of AgOTf. In fact, we have already made a few triaryl-cyclopropenium cations and tested their catalytic utility in a couple of organic transformations such as Nazarov cyclization and 1,6-conjugate addition reactions of p-quinone methides. We found that, in both the reactions, these cations act as a catalyst and the respective products were obtained in more than 90% yields. Since our hypothesis is already tested, we wish to utilize these cations as organic Lewis acids in other synthetic transformations such as nucleophilic addition reactions to carbonyl compounds and imines, ring-opening of epoxides, activation of alkynes, etc. Later, we are planning to prepare a couple of enantiomerically pure triaryl-cyclopropenium cations and explore them in some important enantioselective reactions (conjugate addition reactions, ring-opening of epoxides and aziridines, nucleophilic addition reactions of carbonyl compounds, rearrangement reactions, etc.). Similarly, as a part of this proposal, we also wish to prepare a few unprecedented tropylium based chiral carbocations substituted with (-)-menthol and/or borneol. These catalysts will be tested in some fundamental enantioselective transformations. Since this research area is relatively new and unexplored, it may become one of the new sub-areas in organocatalysis. Therefore, we feel, the successful outcomes of this proposal would attract the international scientific community and also scientists working in industry. This will give an opportunity for a possible industrial and/or international collaborations. |