Efficient synthesis of functionalized dihydroquinolines, quinolines and dihydrobenzo[b]azepine via an iron(iii) chloride-catalyzed intramolecular alkyne–carbonyl metathesis of alkyne tethered 2-amino benzaldehyde/acetophenone derivatives

Abstract

In this study we have developed an efficient synthesis of 1,2-dihydroquinoline and dihydrobenzo[b]azepine derivatives involving the iron(III) chloride intramolecular alkyne-carbonyl metathesis reaction for the first time. Various functionalized 1,2-dihydroquinolines and dihydrobenzo[b]azepines were prepared from easily accessible substrates in the presence of environmentally friendly and inexpensive iron(III) chloride (10 mol%) under mild conditions. The method is applicable to a wide range of substrates containing different functional groups and furnishing products in good to excellent yields. This methodology was further extended to the one-pot synthesis of 3-acyl quinolines via alkyne-carbonyl metathesis/detosylation/aromatization of N-propargyl-2-aminobenzaldehyde/acetophenone derivatives by the addition of NaOH/EtOH. While many Lewis acid and Brønsted acid catalysts were investigated, anhydrous iron(III) chloride turned out to be the best catalyst for this transformation.

One‐Pot Synthesis of Naphtho[1′,2′:4,5]imidazo[1,2‐a]pyridin‐5‐yl(aryl)methanones through Sequential Sonogashira Coupling/Alkyne–Carbonyl Metathesis

“…Intramolecular ACM version is attractive because it generates a variety of complex carbonyl and heterocycles from simple starting materials. Generally, these reactions are catalyzed by Lewis acids, strong Brønsted acids or transition‐metal catalysts …”

I2‐Promoted Intramolecular Oxidative Cyclization of Butenyl Anilines: A Facile Route to Benzo[b]azepines

“…Recent years, a series of [ m + n ] cycloadditions have emerged as versatile methods to access various benzo[ b ]azepines [9] . Besides these methods, benzo[ b ]azepine skeletons could be assembled through intramolecular cross‐coupling reactions, [10a–d] photocatalytic radical reactions, [10e] ring expansion reactions, [10f–g] and others [10h–k] . For instance, Wang [11] developed a method for the construction of benzo[ b ]azepines via copper‐catalyzed oxidative C( sp 3 )−H/C( sp 2 )−H cross‐coupling (Scheme 1a).…”

Recent Trends in Iron‐Catalyzed Reactions towards the Synthesis of Nitrogen‐Containing Heterocycles

“…A synthetic protocol for 1,2‐dihydroquinolines, quinolines and benzo[ b ]azepines through intramolecular alkyne–carbonyl metathesis reactions was reported using environmentally friendly and economical iron(III) chloride (10 mol%) under mild conditions (Scheme ) . This protocol was found to be applicable to a wide collection of substrates bearing different functional groups affording interesting products in good to excellent yields.…”