Multiselective Diels–Alder Reaction of α-Arylacroleins Catalyzed by Boron Tribromide-Assisted Chiral Phosphoric Acids

Abstract

A multiselective Diels−Alder (DA) reaction of α-arylacroleins with cyclopentadiene using BBr 3 -assisted chiral BINOL-derived phosphoric acid catalysts has been developed. This unusual exo-and enantioselective DA reaction can be multicontrolled by the chiral cavity of the in situ-formed acid−base cooperative catalysts, in particular, suppressing the competitive hetero Diels−Alder (HDA) reaction effectively.

Photochemical Isomerization of Cyclohept-1-ene-1-carbaldehyde: Strain-Release Cycloadditions and Ene Reactions

“…UV–vis (CH 2 Cl 2 ) λ max (ε) = 239 nm (3879 M –1 cm –1 ). The data obtained matched those reported in the literature …”

“…The data obtained matched those reported in the literature. 22 General Procedure for the Photoinduced Reactions. A solution of the α,β-unsaturated carbaldehyde in dry CH 2 Cl 2 (1.5 mL) was transferred to a Duran phototube.…”

“…IR (ATR) [cm −1 ] = 2922 (s), 2853 (m), 1721 (s), 1592 (w). MS (EI, 70 eV) m/z (%) = 81 (22), 149 (100), 205 (5)…”

“…Carbonyl groups are known to serve as potential handles for Lewis acid-catalyzed photochemistry, but a given Lewis acid should not induce a reaction of 2a in the dark. Because strong Lewis acids promote Diels–Alder reactions of compound 1 or α-arylacroleins, we tested the reactivity of aldehyde 2a with 1,3-dienes in the presence of Lewis acids. We observed rapid consumption of 2a in the presence of cyclopenta-1,3-diene and ethylaluminum dichloride as Lewis acids, even at −78 °C.…”

Diastereodivergentcis- andtrans-fused [4 + 2] annulations of cyclic 1,3-dienes and 1-azadienesvialigand-controlled palladium catalysis

“…The application of cyclic alkenes as dienophile partners in a Diels–Alder cycloaddition reaction provides a very straight-forward strategy to access fused skeletons; however, cis -fused products are usually obtained due to the inherent concerted reaction mechanism. 9 As illustrated in Scheme 1b , exclusive endo -selectivity was observed in the uncatalysed inverse-electron-demand Diels–Alder reaction between 1,3-cyclohexadiene 1a and aurone-derived 1-azadiene 2a, 10 resulting in the formation of cis -fused polycyclic product 3a in a moderate yield after heating the reaction mixture at 80 °C for 36 h. Recently, our group demonstrated that Pd 0 could act as a π-Lewis base catalyst to increase the highest occupied molecular orbital (HOMO) energy of linear 1,3-dienes through η 2 -coordination, thus promoting asymmetric Friedel–Crafts-type vinylogous addition to N -sulfonylimines enantioselectively. 11 We envisaged that the Pd 0 -π-Lewis base catalysis would facilitate the asymmetric assembly of 1,3-cyclohexadiene 1a and 1-azadiene 2a by generating the high-HOMO-energy complex I.…”