Merging Visible‐Light Photoredox and Lewis Acid Catalysis for the Intramolecular Aza‐Diels–Alder Reaction: Synthesis of Substituted Chromeno[4,3‐b]quinolines and [1,6]Naphthyridines

Abstract

Substituted chromeno[4,3‐b]quinolines and [1,6]naphthyridines were achieved by tandem intramolecular aza‐Diels–Alder reaction using a strategy of combination of visible‐light photoredox and Lewis‐acid‐catalysis. This intramolecular aza‐Diels–Alder cycloaddition took place between the in situ generated benzylidene anilines derived from arylamines and salicylaldehyde or 2‐aminoaryl aldehydes bearing a tethered alkene partner, followed by oxidative aromatization to give the target products. The study on the oxidative aromatization step revealed that it is much faster than the cyclization step; both the combination of imine and Lewis acid, and the combination of photocatalyst and Lewis acid under aerobic condition with the irradiation of visible light are efficient to achieve the transformation. This method provided a new access to the synthesis of important heterocycles under mild reaction conditions.

Synthesis of 1,2-Dihydroquinolines via Hydrazine-Catalyzed Ring-Closing Carbonyl-Olefin Metathesis

“…The crude material was purified by column chromatography (hexane: EtOAc: CH2Cl2 = 6:1:1) to furnish 15b as a white solid in 83% yield (649.9 mg, 1.66 mmol). 7 13 C NMR (126 MHz,CDCl3) δ 190.0,144.2,141.4,136.0,135.8,135.4,134.7,134.1,129.7,128.7,128.59,128.57,128.2,128.2,128.0,126.5,122.5,54.2,21.6. .…”

“…Prepared from N- (2-formyl-4-(trifluoromethoxy) 7,148.8,144.4,140.0,139.8,137.8,134.6,129.8,127.8,125.9,120.3 (q,J = 259.6),119.7,116.9,49.2,25.6,21.6,17.7. HRMS (ESI)…”

Domino Transformations of Ene/Yne Tethered Salicylaldehyde Derivatives: Pluripotent Platforms for the Construction of High sp3 Content and Privileged Architectures

“…5,6‐Dihydrodibenzo[ b , h ][1,6]naphthyridines ( 46 a ) and chromeno[4,3‐ b ]quinolines ( 46 b ) were synthesized by Zhang et al. by photocatalytic aerobic aza‐Diels–Alder cycloaddition . The 2‐(cinnamyloxy)benzaldehyde ( 45 a ) or N ‐cinnamyl‐ N ‐(2‐formylphenyl)‐4‐methylbenzenesulfonamide ( 45 b ) were treated with arylamines 10 using Ru(bpy) 3 (PF 6 ) 2 as the photosensitizer and BF 3 ⋅ Et 2 O as an effective Lewis acid catalyst .…”

“…[33] Owing to their significant biological activities, o-ene/yne tethered benzaldehydes were used for the construction of these scaffolds through [4+ +2] hetero-Diels-Alder reactions. [34] The 2-(cinnamyloxy)benzaldehyde( 45 a)o rN-cinnamyl-N-(2-formylphenyl)-4-methylbenzenesulfonamide (45 b)w ere treated with arylamines 10 using Ru(bpy) 3 (PF 6 ) 2 as the photosensitizer and BF 3 ·Et 2 Oa sa ne ffectiveL ewis acid catalyst. [34] The mechanism of this transformation is presented in Scheme1 1.…”

“…[34] The 2-(cinnamyloxy)benzaldehyde( 45 a)o rN-cinnamyl-N-(2-formylphenyl)-4-methylbenzenesulfonamide (45 b)w ere treated with arylamines 10 using Ru(bpy) 3 (PF 6 ) 2 as the photosensitizer and BF 3 ·Et 2 Oa sa ne ffectiveL ewis acid catalyst. [34] The mechanism of this transformation is presented in Scheme1 1. The imine In 2016, Sridharan'sg roup published an inverse electrondemanda za-Diels-Alder reaction of 2-(N-propargylamino)benzaldehydes (47)w ith arylamines 10 in the presence of cupric bromide in toluene.T his reactiond eliveredalibrary of diverse scaffolds bearing 5,6-dihydrodibenzo [b,h] [1,6]naphthyridines (46 a;S cheme 11).…”