200 Years of The Haloform Reaction: Methods and Applications

Discovered in 1822, the haloform reaction is one of the oldest synthetic organic reactions. The haloform reaction enables the synthesis of carboxylic acids, esters or amides from methyl ketones. The reaction proceeds via exhaustive α-halogenation and then substitution by a nucleophile to liberate a haloform. The methyl group therefore behaves as a masked leaving group. The reaction methodology has undergone several important developments in the last 200 years, transitioning from a diagnostic test of methyl ketones to a synthetically useful tool for accessing complex esters and amides. The success of the general approach has been exhibited through the use of the reaction in the synthesis of many different complex molecules in fields ranging from natural product synthesis, pharmaceuticals, agrochemicals, fragrants and flavourings. The reaction has not been extensively reviewed since 1934. Therefore, herein we provide details of the history and mechanism of the haloform reaction, as well as an overview of the developments in the methodology and a survey of examples, particularly in natural product synthesis, in which the haloform reaction has been used.

Electron Donor-Acceptor Complex-Assisted Photochemical Conversion of O-2-Nitrobenzyl Protected Hydroxamates to Amides

The hydroxamic acid functionality is present in various medicinal agents and has attracted special interest for synthetic transformations in both organic and medicinal chemistry. The N-O bond cleavage of hydroxamic acid derivatives provides an interesting transformation for the generation of various products. We demonstrate, herein, that O-benzyl-type protected hydroxamic acids may undergo photochemical N-O bond cleavage, in the presence or absence of a catalyst, leading to amides. Although some O-benzyl protected aromatic hydroxamates may be photochemically converted to amides in the presence of a base and anthracene as the catalyst, employing O-2-nitrobenzyl group allowed the smooth conversion of both aliphatic and aromatic hydroxamates to primary or secondary amides in good to excellent yields in the presence of an amine, bypassing the need of a catalyst. DFT and UV-Vis studies supported the effective generation of an electron donor-acceptor (EDA) complex between O-2-nitrobenzyl hydroxamates and amines, which enabled the successful product formation under these photochemical conditions. An extensive substrate scope was demonstrated, showcasing that both aliphatic and aromatic hydroxamates are compatible with this protocol, affording a wide variety of primary and secondary amides.

A general synthesis of aromatic amides via palladium-catalyzed direct aminocarbonylation of aryl chlorides

Aryl amines made easy by palladium-catalyzed aminocarbonylation of aryl chlorides.

Mild and efficient synthesis of trans-3-aryl-2-nitro-2,3-dihydrobenzofurans on water

A protocol to prepare trans-3-aryl-2-nitro-2,3-dihydrobenzofurans has been developed on water. The protocol avoids the use of toxic solvents, tedious work-up procedures, and chromatographic separation.

Multicomponent synthesis of diphenyl-1,3-thiazole-barbituric acid hybrids and their fluorescence property studies

A series of novel diphenyl-1,3-thiazole linked barbituric acid hybrids (4) were prepared by two catalyst-free methods from readily available starting materials.