Reactivity, Selectivity and Scope of Diels-Alder Reactions of Boron-substituted Furans

FEDERICO DEZOTTI; NOELIA S. MEDRÁN; SILVINA C. PELLEGRINET

Congreso; Empowering Women in Organic Chemistry 2021; 2021

EWOC

The Diels-Alder reactions of unsaturated organoboron compounds have been known for many decades. However, new variants continue to appear in the literature. The first examples with simple alkynyl- and alkenylboronic esters progressively evolved into a wide range of reactions. In 2019, we reported an experimental and theoretical study of the Diels-Alder reactions of boron-substituted furans with maleic anhydride. Within the analogues with boron substituents at C-3, the potassium trifluoroborate emerged as a highly reactive and exo selective diene. On the other hand, the reactions for the C-2 derivatives were unsuccessful. Herein, we describe the results of the [4+2] cycloadditions with other electron deficient dienophiles. The reactions of N-phenylmaleimide with the boron substituted furans at C-3 occurred very efficiently and showed variable endo/exo selectivities. Gratifyingly, when the potassium furan-2-trifluoroborate was reacted with 3 the exo cycloadduct was obtained exclusively with high yield. Other dienophiles such as dimethyl fumarate and methyl acrylate were evaluated but the reactions were less favorable. In addition, we have explored different alternatives to convert the 7-oxabicyclo[2.2.l]hept-2-ene products into a variety more functionalized and diverse compounds. Theoretical calculations to rationalize the experimental results are underway.