Diels­Alder reactions of unsaturated boronic esters: Rational design, development, and mechanistic studies using experimental and computational methodologies

GRIMBLAT, NICOLÁS; VALLEJOS, MARGARITA M.; PELLEGRINET, SILVINA C.

Honolulu, Hawaii

Congreso; The International Chemical Congress of Pacific Basin Societies 2015 (Pacifichem); 2015

The DielsAlder (DA) reactions of unsaturated boronic esters were first described more than five decades ago. In the last years, a renewed interest insuch processes arouse, both from the experimental and theoretical viewpoints. In 2010, we reported that the DA reactions of vinylboronates occurred readily under microwave irradiation. More recently, we investigated the DA reactions of pinacol alkenylboronic esters with different substitution patterns both under thermal heating and Brønsted acid catalysis. Initial attempts to perform the DA reactions of MIDA vinylboronates and pinacol alkynylboronates under the same type of conditions were unsuccessful. In addition, in the past years, we have been devoted to developthe organocatalytic and asymmetric version of the DA reaction of alkenylboronic esters. Exploratory experiments showed that α-hydroxyacids were more efficient than binaphthols. After much experimentation, the conditions of the reaction of dibutyl vinylboronate with cyclopentadiene were optimized. Mandelic acid proved to be an excellent promoter and also an efficient catalystof the reaction, though enantioselectivities were poor. Theoreticalcal culations allowed us to rationalize the experimental results. At present, we are doing more experiments and calculations to rationally design improved catalysts and to extend the scope of the reaction.