Studies in the furan series. 23. Preparation of some new 5‐substituted furfurylallylarylamines. Influence of substituents on the intramolecular Diels‐Alder (IMDA) reaction

Abstract

Several new N‐allyl‐N‐(5‐substituted)‐2‐furfuryl‐p)‐toluidines IIIa‐e with Cl, Br, I, NO2 or CH3O groups in position 5 of the furan nucleus were prepared by allylation of the corresponding secondary furfurylaryl‐amines. Both, electron withdrawing and releasing substituents enhanced the yield of intramolecular [4+2] cycloaddition.

Intramolecular Diels–Alder Reactions of Cycloalkenones: Stereoselectivity, Lewis Acid Acceleration, and Halogen Substituent Effects

“…21 This effect should extend to the analogous IMDA reactions, and thus we have modeled the reaction between 2-bromocyclobutenone and a tethered diene (Figure 8). The influence of halogen substituents on dienes in Diels-Alder reactions have been studied by us and other groups, 8a,22 but the investigations of the effects of α-halogenated enones have been limited to intermolecular cases. 23 …”

“…This “halogen effect” was previously in our work on halofuran cycloaddition with Padwa. 22a Additionally, the preference of the endo transition state is increased from 0.7 kcal/mol to 2.1 kcal/mol. These changes, along with the larger asynchronicity of the bond formation, are indicative of a more polar transition structure, reminiscent of conducting the reaction in the presence of BF 3 .…”

Advances in Diels–Alder/aromatization of biomass furan derivatives towards renewable aromatic hydrocarbons

“…hindered the reaction seriously. [29][30][31][32][33][34][35][36] Therefore, precisely controlling the reactivity of the substrates and successfully achieving high efficiency are the major challenges for the process of producing aromatic hydrocarbons from furan derivatives, aiming to implement carbon-neutral sustainable technologies in the chemical industry.…”

The Origin of the Halogen Effect on Reactivity and Reversibility of Diels–Alder Cycloadditions Involving Furan

“…A number of apparently reasonable cycloadditions have been found to be unsuccessful, usually due to substrate inertness [8] or the tendency for products to undergo retrocycloadditions. [9][10][11] A celebrated example is the unattainable direct synthesis of cantharidin (6). [12] Figure 1 illustrates products of failed cycloadditions (8 and 9) as well as lowyielding cycloadditions (10 and 11).…”