Reactivity, Selectivity and Scope of Diels-Alder Reactions of Boronsubstituted Furans

DEZOTTI FEDERICO; MEDRAN NOELIA S.; PELLEGRINET SILVINA, C.

Philadelphia

Congreso; Empowering Women in Organic Chemistry; 2021

The Diels-Alder reactions of unsaturated organoboron compounds have been known formany decades. However, new variants continue to appear in the literature. The firstexamples with simple alkynyl and alkenylboronic esters progressively evolved into a widerange of reactions. In 2019, we reported an experimental and theoretical study of the DielsAlder reactions of boron-substituted furans (1) with maleic anhydride (2). Within theanalogues with boron substituents at C-3, the potassium trifluoroborate emerged as a highlyreactive and exo selective diene. On the other hand, the reactions for the C-2 derivatives wereunsuccessful. Herein, we describe the results of the [4+2] cycloadditions with other electrondeficient dienophiles. The reactions of N-phenylmaleimide (3) with the boron-substitutedfurans at C-3 occurred very efficiently and showed variable endo/exo selectivities.Gratifyingly, when the potassium furan-2-trifluoroborate was reacted with 3 the exocycloadduct was obtained exclusively with high yield. Other dienophiles such as dimethylfumarate (4) and methyl acrylate (5) were evaluated but the reactions were less favorable. Inaddition, we have explored different alternatives to convert the 7-oxabicyclo[2.2.l]hept-2-eneproducts 6 into a variety more functionalized and diverse compounds. Theoreticalcalculations to rationalize the experimental results are underway.