Synthesis of novel substituted (4H-furo[2,3-h]chromen-9-yl)-acetic acids via multicomponent reaction of flavones, arylglyoxals and Meldrum’s acid

Calcium-Catalyzed Synthesis of Fused Furo[2,3-b]furans and Substituted Furans from 2-Oxo Aldehydes and Cyclic Enols

We report here an atom-economical, syn-diastereoselective synthesis of naphtho-fused furo[2,3-b]furans along with naphthofurans at room temperature using readily available 2-naphthols and 2-oxo aldehydes using an alkaline earth catalyst [Ca(OTf)2]. 2-Oxo aldehydes having both aryl and alkyl substitutions reacted well. A good number of arenols responded to give fused furans, but selected arenols gave only furofurans. Synthetic applications and gram-scale synthesis were also demonstrated to strengthen this strategy.

Aryl glyoxal: a prime synthetic equivalent for multicomponent reactions in the designing of oxygen heterocycles

The category of bifunctional building blocks overrides many others because of their fascinating wide applicability in synthetic chemistry. Aryl glyoxal is one of the key molecules that has been extensively used in heterocyclic chemistry to afford nearly all types of five- and six-membered heterocycles, which are the structural constituents of many natural products. The multicomponent reaction is a practical strategy to utilize this wonderful moiety with different types of starting materials to obtain numerous diverse oxygen heterocycles. This review covers the advancement of aryl glyoxal as a prime synthetic equivalent in recent years for the synthesis of oxygen heterocycles.

Photoinduced assembly of the 3,4,4a,7a-tetrahydro-1H-cyclopenta[b]pyridine-2,7-dione core on the basis of allomaltol derivatives

A novel photochemical method for the construction of previously unknown substituted 4a,7a-dihydroxy-5-methyl-3,4,4a,7a-tetrahydro-1H-cyclopenta[b]pyridine-2,7-diones based on readily available allomaltol derivatives containing an amide group was established. The proposed approach includes the photoinduced contraction of an allomaltol ring and the subsequent intramolecular cyclization of an unstable α-hydroxy-1,2-diketone intermediate. For the first time we have shown the use of a side chain amide function as a trapping element for the final cyclization of photogenerated α-hydroxy-1,2-diketones. The structures of two synthesized photoproducts were determined by X-ray diffraction.