Access to quinolinones via DMAP-catalysed cascade reaction of 2-substituted benzoic acids with organic azides

Abstract

Herein, we report a DMAP-catalysed Curtius rearrangement and intramolecular cyclisation cascade reaction of 2-substituted aryl carboxylic acids with organic azides for the first time. This protocol features simple operation, broad...

Carbonylative Synthesis of Fused Quinoxalinones via Palladium-Catalyzed Cascade Cyclization of 2-Heteroaryl Iodobenzene and NaN3

“…First, the treatment of 2-(1H-pyrrol-1-yl)aniline 1a′ with bis(trichloromethyl) carbonate in the presence of base could produce pyrrolo [1,2-a]quinoxalinone 2a in 64% yield via an isocyanate intermediate (Scheme 3a). In combination with the isocyanate formation by a Curtius rearrangement reported previously, 6,9,10 we speculated that an isocyanate intermediate was involved in the current transformation. In addition, from the replacement of iodide in substrate 1a with other halogen substituents, such as F, Cl, or Br, the reaction was totally inhibited and no desired product 2a could be detected, indicating the necessity of the iodide group in the starting pyrrole substrate (Scheme 3b).…”

“…Very recently, Hu, Gao, and co-workers developed a 4dimethylaminopyridine (DMAP)-catalyzed cascade reaction of 2-pyrrolyl-substituted benzoic acids with organic azides for the synthesis of pyrrolo [1,2-a]quinoxalinones in moderate to good yields (Scheme 1c), 6 in which acyl azide was formed and underwent a Curtius rearrangement to generate the isocyanate intermediate. Despite notable achievements being obtained, some of the above strategies usually suffer from the tedious synthesis of reaction substrates and the relatively narrow reaction scope.…”

“…Another mainstream synthetic pathway is the insertion of a carbonyl unit into 2-pyrrolylanilines using different reactive carbonyl candidates, including the traditionally used triphosgene, dioxazolone or phenyl isocyanate, and CO or CO 2 (Scheme b). , Noteworthy is that N–H and C–H bond [5 + 1] carbonylative annulation is involved in these transformations. Very recently, Hu, Gao, and co-workers developed a 4-dimethylaminopyridine (DMAP)-catalyzed cascade reaction of 2-pyrrolyl-substituted benzoic acids with organic azides for the synthesis of pyrrolo­[1,2- a ]­quinoxalinones in moderate to good yields (Scheme c), in which acyl azide was formed and underwent a Curtius rearrangement to generate the isocyanate intermediate. Despite notable achievements being obtained, some of the above strategies usually suffer from the tedious synthesis of reaction substrates and the relatively narrow reaction scope.…”

“…On the basis of the preliminary mechanistic studies and the precedent reports, , a tentative reaction was proposed, as depicted in Scheme c. Initially, the oxidative addition of Pd(0) species to the C–I bond of substrate 1a afforded Pd­(II) complex A , which underwent the coordination and insertion of carbon monoxide to lead to the acyl-palladium intermediate B .…”

DMAP Catalyzed One-Pot Curtius Rearrangement Using 1,1-Dimethyl-2,2,2-trichloroethoxycarbonyl Azide

“…These methods generally use stoichiometric and possibly hazardous reagents to activate the carboxylic acids, require the isolation of active intermediates, and can form multiple side products, thus reducing the step and atom efficiency and narrowing the tolerance of functional groups. Curtius–Yamada rearrangement is the most straightforward and widely used method discovered by Yamada et al in 1972 (Scheme A), which converts carboxylic acids to isocyanates directly in one pot by using diphenylphosphoryl azide (DPPA) as the carboxylic acid activation reagent and the source of azido anion . It generally requires a two-step process: the formation of acyl azides with the aid of a stoichiometric quantity of a base, followed by a Curtius rearrangement under thermal conditions.…”