Copper(I)-Catalyzed Direct Oxidative Annulation of 1,3-Dicarbonyl Compounds with Maleimides: Access to Polysubstituted Dihydrofuran Derivatives

Abstract

An efficient annulation method for the synthesis of polysubstituted dihydrofurans from 1,3-dicarbonyl compounds and maleimides is described. The reactions can afford furo­[2,3-c]­pyrrole derivatives with satisfactory yields. The developed strategy realizes the direct oxidative double C­(sp3)–H functionalization in the presence of copper­(I) salts and 2-(tert-butylperoxy)-2-methylpropane. Meanwhile, this protocol features a mild reaction condition and simple catalytic system. A reaction mechanism involving a single electron oxidation is also proposed.

Modular Access to 2-(Trifluoromethyl)pyrazolo[1,5-a]pyridines and Their Benzo Analogues through a Copper(I)-Catalyzed Radical Annulation

“…Based on our experimental observations and the previously reported literature, a plausible mechanism for this copper­(I)-catalyzed annulation of 2-pyridyl derivatives with CF 3 CN (generated in situ) was proposed (Scheme ). The t BuO radical, which is readily generated from the Cu­(I) complex and DTBP, undergoes hydrogen abstraction from substrate 1 to give benzylic carbon-centered radical I .…”

Gold-catalyzed formal (3 + 2) and (4 + 2) cycloaddition reactions using propiolates: assembly of 2,3-dihydrofurans and 3,4-dihydropyrans via a multistep cascade process

“…5 For 2,3-dihydrofurans, one of the most common cycloaddition approaches is the (4 + 1) reactions between α,β-unsaturated carbonyl compounds and 1,1-dipole equivalents such as diazo compounds and ylides (Scheme 2b). 6 Additionally, various (3 + 2) cycloaddition reactions were developed, such as the oxidative couplings between carbonyl compounds and alkenes, 7 the double alkylation of carbonyl compounds with biselectrophiles, 8 and the redox-neutral cycloadditions between alkenes and carbene equivalents such as diazo ketones, sulfonium ylides, and iodonium ylides, 9 between polarized alkynes and epoxides 10 or allylic cyanohydrins, 11 between carbonyl compounds and allenylsilanes, allenoates, or Morita–Baylis–Hillman adducts 12 and so on. It is worth noting that both dihydrofurans and dihydropyrans could be synthesized in a cycloaddition fashion using polarized alkynes as dipolarophiles and epoxides as 1,3-dipoles or oxetanes as 1,4-dipoles.…”