Calcium-catalyzed formal [3 + 2] annulation of C,N-diacyliminium ions with nucleophilic phenols: a diversity oriented synthesis of 3-aminofurans

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.

Arylation and Aryne Insertion into C-Acylimines: A Simple, Flexible, and Divergent Synthesis of C2-Aryl Indoles

We reveal a direct strategy for the flexible synthesis of C2-aryl/heteroaryl indoles without transition metal catalysts. The synthesis involves a one-pot, four-component reaction of readily available starting materials to offer diversity around the indole moiety with a broad substrate scope and high yields. The reaction proceeds via the Friedel-Crafts C-arylation of C-acylimine formed in situ, followed by N-arylation with aryne, a formal [3+2] cycloaddition, and a subsequent aromatization cascade.