Assembly of Furazan-Fused Quinolines via an Expeditious Metal-Free [2+2+1] Radical Tandem Cyclization Process

Abstract

A [2+2+1]-NO-segment-incorporating heteroannulative cascade is described. This versatile method, particularly using modular cyanoarylated ketimine substrates, allows efficient access to structurally diversified quinolines embedded with an oxadiazole core. This metal-free protocol proceeds smoothly at 30 °C, offers easy manipulation of substituents on the quinoline moiety, and tolerates a spectrum of functional groups. Density functional theory calculation revealed that the cyano moiety is crucial to facilitate the early cyclization step in this heteroannulation process and is different from the previously established late cyclization mechanistic interpretation.

Preparation of a benziodazole-type iodine(III) compound and its application as a nitrating reagent for synthesis of furazans via a copper-catalyzed cascade process

“…Differing from the existing O 2 NO-I(III) reagents that have been uniformly used as nitrooxylating reagents for introducing O 2 NO moiety, the O 2 NO-I(III) 1d described in this work can be regarded as a nitrating reagent and incorporate its NO moiety to furazan skeleton in a fully- endo pattern. Furthermore, the current method also provides an alternative approach, which is in nature different from the existing strategies 34 , 49 – 65 , to the biologically interesting furazan heterocycles.…”

“…1c , react. 5) 65 . Although all the above approaches have their respective merits in obtaining the corresponding furazan derivatives, the development of novel synthetic routes to access this unique heterocycle should still be of important synthetic value.…”

Synthetic approaches and applications of an underprivileged 1,2,5‐oxadiazole moiety: A review

“…The advantages of this approach include ease of setup, moderate conditions, quick reactions, selectivity, enhanced yields, good compound purity and low cost compared with its homogeneous catalyst (Scheme 6). Deng et al (2021) reported a method in which arylketimine 12 and nitro compound 13 were employed as starting materials in an expedient metal-free tandem cyclization reaction to create 1,2,5-oxadiazole-fused quinolines 14 (Scheme 7). Makhova and Fershtat (2018) reported another method comprising nitrosation of styrenes 15 in an acidic medium under the influence of sodium nitrite to yield 3-aryl-4-nitr o-1,2,5-oxadiazole-N-oxide 16 (Scheme 8).…”

“…Deng et al (2021) reported a method in which arylketimine 12 and nitro compound 13 were employed as starting materials in an expedient metal‐free tandem cyclization reaction to create 1,2,5‐oxadiazole‐fused quinolines 14 (Scheme 7).…”

Cascade Annulation Strategy for Expeditious Assembly of Hydroxybenzo[c]chromen-6-ones and Their Photophysical Property Studies

“…Very recently, Liu established a Brønsted acid-catalyzed tandem 1,6-addition/double annulation protocol using o -hydroxyphenyl propargylic alcohols and nitrones to give densely functionalized chromeno­[3,2- d ]­isoxazoles (Scheme b­(iv)) . In continuing our interest of investigating chromene and fused arene systems, we sought to adopt the o -AQM chemistry in a new cascade reaction between alkylaminophenols and 1-(4-ethoxy-2,4-dioxobutyl)­pyridin-1-ium bromide, for modular assembly of hydroxybenzo­[ c ]­chromen-6-one with rich diversity of substitution patterns.…”