Stereocontrol of intramolecular Diels-Alder reactions by an allylic diphenylcyclopropyl group.

Intramolecular Diels-Alder reactions of ester-linked 1,3,8-nonatrienes carrying a diphenylcyclopropyl substituent attached to C1 proceed with high levels of stereoselectivity. The stereochemical outcomes of these reactions are explained by reference to B3LYP/6-31G(d) transition structures. Experimentally, the diphenylcyclopropane rings remain intact through these IMDA reactions, notwithstanding their predicted extremely high degree of asynchronicity (the B3LYP-computed lengths in the IMDA transition structures differ by as much as 1.

Enhanced stereocontrol in Diels-Alder reactions of chiral dienols.

This combined experimental-computational investigation demonstrates that the presence of a removable bromine substituent on a diene leads to complete pi-diastereofacial and endo/exo stereoselection in both intermolecular and intramolecular Diels-Alder reactions. The influence of the bromine upon stereoselectivity is dramatic: the cycloaddition of nonbrominated precursor 18E, for example, gives four diastereomeric products in a 55:13:16:16 ratio; the bromine-containing analogue gives one stereoisomer within the limits of detection. The examination of B3LYP/6-31+G(d) transition structures allows an interpretation of these experimental findings.

Intramolecular Diels-Alder reactions of ester-linked 1,3,8-nonatrienes.

[structures: see text] Penta-1,3-dienyl acrylates undergo kinetically controlled intramolecular Diels-Alder (IMDA) reactions and DFT calculations (B3LYP/6-31+G(d)) predict stereoselectivities that are in very good agreement with the experimental values. The nature of the diene C1 substituent has virtually no influence upon reactivity or trans/cis-stereoselectivity whereas terminal C9 dienophile substituents have a substantial effect on both the reactivity and stereoselectivity of these IMDA reactions. The TSs highlight contributions from strain in the developing tether-containing ring, and steric and electronic effects between tether and dienophile substituents, thus providing insight into the origins of IMDA reactivity and stereoselectivity.

On the Diels-Alder reactions of pentadienyl maleates and citraconates.

Reactions between conjugated dienols and maleic anhydride provide either cis-fused or trans-fused bicyclic products as major products, depending upon how the reaction is carried out. Simply mixing the two reactants together generally leads to cis-fused lactone acids in thermal reactions which proceed viaintermolecular Diels-Alder reaction followed by intramolecular esterification. Pre-forming the maleate half ester derivative followed by heating affords predominantly trans-fused lactone acids in good yields by way of an intramolecular Diels-Alder (IMDA) reaction.

Optimising stereoselectivity in intramolecular Diels-Alder reactions of pentadienyl acrylates: synthetic and computational investigations into the "steric directing group" approach.

Experimental conditions for the intramolecular cycloaddition of four related pentadienyl acrylates 3, 4, 5 and 6 are reported. In contrast with several previous reports, pentadienyl acrylates do undergo synthetically useful intramolecular Diels-Alder reactions: 3, 4, 5 and 6 cyclise at reasonable rates at temperatures of 132-180 degrees C at atmospheric pressure in moderate to good yields. The stereochemical outcome of each of these reactions was accurately measured and the results are in good agreement with transition structure populations predicted using B3LYP/6-31+G(d) theory.