Chemistry of Heterocyclic Ketene Aminals: Construction of Imidazo(pyrido)[1,2-a]pyridines and Imidazo(pyrido)[3,2,1-ij][1,8]naphthyridines via DABCO-Catalyzed Tandem Annulations

Abstract

2-(2-Chloroaroyl)methyleneimidazolidines with four reactive sites show fascinating structural features and could be used as a new strategy for the synthesis of novel heterocycles. This paper presents our new findings in the reaction of 2-(2-chloroaroyl)methyleneimidazolidines with allenic esters affording functionalized imidazo(pyrido)[1,2-a]pyridines via DABCO-catalyzed tandem annulations. Of particular significance is the incorporation of an o-halo group into the aryl ring of 2-benzoylmethylene-imidazolidines to set up a convenient and general way for constructing unusual imidazo(pyrido)[3,2,1-ij][1,8]naphthyridines.

Synthesis of Bicyclic ortho-Aminocarbonitrile Derivatives Catalyzed by 1,4-Diazabicyclo[2.2.2]octane

“…[13] For example, reactions of 2-(2-chloroaroyl)methyleneimidazolidines with allenic esters catalyzed by DABCO have been realized and afforded imidazo(pyrido) [1,2-a]pyridines with good yields. [14] In 2012, functionalized chromen-5-ones and pyrano[3,2-c]chromen-5-ones were prepared from the reaction of α-oxoketene-N,S-arylaminoacetals, aromatic aldehydes, and dimedone/4-hydroxycoumarinin the presence of DABCO. [15] Recently, a [4 ＋ 2] cyclo-addition reaction catalyzed by DABCO was reported by Meng and co-workers.…”

Reactions of 3‐Acylchromones with Heterocyclic Ketene Aminals: One‐Pot Synthesis and Phosphatase Inhibitory Activity of Fused Pyridine Derivatives

“…Heterocyclic ketene aminals (HKAs) are highly reactive reagents that contain three nucleophilic centers. They have been used as building blocks in domino and multicomponent reactions, for the synthesis of indoles, quinolines, naphthyridines, 1,2,3‐triazoles, coumarins, pyridines, and pyrimidines . However, the reaction of HKAs with chromones has scarcely been reported to date , .…”

Selective Synthesis of Highly Functionalized Bicyclic Pyridinone and 1,3‐Oxazinane Derivatives

“…Synthetic methods based on heterocyclic ketene aminal (HKA) building blocks have received wide attention . To date, different substrates, such as diethyl 2,3‐diiodofumarate,[19a] ethyl propiolate, β‐keto ester enol tosylates, itaconic anhydride, alkylidene Meldrum's acid, allenic esters, ethyl 3‐(4‐nitrophenyl)propiolate, 4,4,4‐trifluoro‐3‐oxobutanoate,[25a] and others, have been used to synthesize bicyclic pyridinones. It is still important, however, to explore efficient methods for the preparation of highly functionalized bicyclic pyridinones to meet present drug discovery and high‐throughput screening needs.…”