Green strategies in Bronsted and Lewis acid catalysis

Catalysis is a key point among the 12 principles of Green Chemistry. The employment of a catalyst in a chemical process involves reduction of time, energy consumption and cost. A coherent approach to green catalysis is the research for non-toxic, easily available and renewable catalysts. One of the strategies to achieve this goal relies on Lewis acid-assisted BrØnsted acid catalysis. In particular, Fe2(SO4)3·nH2O in acetic acid proved to be an efficient and regioselective catalyst for the hydration of both terminal and internal alkynes. In the latter case, complete regioselectivity and yields close to 90% were obtained in mild acidic conditions, which also proved to be useful for the conversion of TMS-substituted internal arylalkynes into acetyl derivatives. To another issue, in the domain of organocatalysis, the principles of green chemistry often find a natural way of explication. However, this may not happen when organic molecules with engineered structures are used as catalysts. In the case of BINOL-type phosphoric acids, multi-step synthesis of the catalyst includes non-atom economic reactions and Pd-catalyzed Suzuki coupling, leading to critical issues due to toxicity, cost and waste disposal. Our strategy to overcome this difficulty with a green mindset is the design of a new generation of chiral phosphoric acids, starting from natural products and waste material from processing of naturally occurring soy lecithin. The new potential catalysts will be then tested on model reactions to compare their catalytic efficiency to those of BINOL-engineered phosphporic acids.