Diels-Alder Reaction Lab Report

ABSTRACT

The Diels-Alder reaction has been an area of great research interest with regards to enhancing enantioselectivity in the reaction by use of various catalysts and reaction conditions.

INTRODUCTION

In organic chemistry, a Diels-Alder reaction refers to a 4, 2 cycloaddition between a diene consisting of alternating double bonds and a substituted alkene (the dienophile) resulting in a substituted cyclohexene system. The reaction is often used to reliably control regioselective and enantioselective aspects in organic synthesis.

If specific conditions are applied, these reactions can be reversible, with the reverse reaction referred to as the retro-Diels-Alder reaction.

Mechanism, Regioselectivity and Enantioselectivity of the Diels-Alder Reaction

It is classed as a [4πS+2πS] cycloaddition; progressing via a thermally allowed 4n+2 cycloaddition involving a suprafacial/suprafacial interaction between a 4π electron system with a 2π electron system.

This can be explained using Molecular Orbital Theorem (MOT) as follows by considering the frontier molecular orbitals, FMO, of the reactants: For a ‘normal’

N-arylsulfonyl tryptophanderivatives were investigated as ligands for the reaction due to “the high π-electron-donating characterof the indole ring” (?)B-n-butyloxazaborolidine was used at 5 mol% to accelerate and control the reaction of cyclopentadiene and 2-bromoacrolein (-78 °C) in DCM. Enantioselectivity of the desired 2R adduct occurred at ca. 200:1 with a high yield. This catalyst can be used to enantioselectively produce gibberellic acid, a plant hormone, as well as the antiulcer agent, cassiol and eunicenone. (Corey and Loh,