Copper Catalyzed Synthesis of 3‐Nitro‐Quinolines from Nitro‐Olefins and Anthranils: Its Application in the Synthesis of Quindoline

Synthesis of acridones via Ir(III)-catalyzed amination annulation of oxazoles with anthranils

An unprecedented Ir(III)-catalyzed C-H activation/amination/annulation of 2-phenyloxazoles with anthranils for the highly selective preparation of acridone derivatives in one-pot under controlled conditions is reported. This protocol is characterized by atom economy and high regioselectivity. A wide range of anthranils with 2-phenyloxazoles were well tolerated and afforded the desired products in moderate to good yields, in which the anthranil serves as a convenient amination reagent.

Synthesis of 4-styrylquinolines via direct oxidative C3-alkenylation of anthranils under Pd(II) catalysis

The palladium-catalyzed oxidative C3-alkenylation of anthranils (2,1-benzisoxazoles) with various styrenes has been successfully achieved. The C3-alkenylated anthranils were subsequently utilized in a [4+2]-cycloaddition with in situ generated α,β-unsaturated ketones leading to the synthesis of a diverse range of olefin-containing quinolines. Notably, this reaction exclusively yielded mono-alkenylated products with E-selectivity. The optimized catalytic conditions were compatible with a wide variety of substituted olefins and anthranils, forming various C3-alkenylated anthranils with good yields. To showcase the application of the present methodology, the C3-alkenylated anthranils have been employed as synthons to access a wide range of substituted quinolines.

Efficient Buchwald-Hartwig and nitrene-mediated five-membered ring closure approaches to the total synthesis of quindoline. Unexpected direct conversion of a nitro group into a phosphazene

Two total syntheses of quindoline, which take place through the intermediacy of 3-nitroquinoline derivatives, are reported. The general synthetic sequence involves construction of the latter by mechanochemical condensation of benzaldehydes with 2-amino-nitrostyrene, followed either by reduction of the nitro group of the heterocycle and Buchwald-Hartwig cyclization or by a nitrene-mediated cyclization under solventless conditions. Use of PPh₃ to generate the nitrene resulted in the unprecedented formation of a phosphazene in place of quindoline. This unexpected transformation was explained by means of DFT computations.

Synthesis of acridines via copper-catalyzed amination/annulation cascades between arylboronic acids and anthranils

Copper-catalyzed tandem cyclization reactions between arylboronic acids and anthranils have been established, providing new approaches for one-pot assembly of azacycle acridines. This one-pot protocol features simple operation, precious-metal-free conditions and good functional group compatibility, thus providing an efficient approach for the synthesis of a variety of acridines in moderate to good yields.

Rh(III)-Catalyzed Tandem Reaction Access to (Quinazolin-2-yl)methanone Derivatives from 2,1-Benzisoxazoles and α-Azido Ketones

A Rh(III)-catalyzed tandem reaction for the synthesis of (quinazolin-2-yl)methanone derivatives has been explored from 2,1-benzisoxazoles and α-azido ketones. The transformation involves Rh(III)-catalyzed denitrogenation of α-azido ketones, aza-[4 + 2] cycloaddition, ring opening, and dehydration aromatization processes. Notably, the aza-[4 + 2] cycloaddition of an imine rhodium complex intermediate with 2,1-benzisoxazoles is the key to this reaction.