Ethylene Glycol: A Powerful Catalyst‐Free Medium for CC Bond‐Forming Reactions

Catalyst-free and additive-free reactions enabling C-C bond formation: a journey towards a sustainable future

This review focuses on the catalyst- and additive-free C-C bond forming reactions reported mostly from the year 2005 to date. C-C bond forming reactions are highly important as large and complex organic molecules can be derived from simpler ones via these reactions. On the other hand, catalyst- and additive-free reactions are economical, environmentally friendly and less sensitive to air/moisture, allow easy separation of products and are operationally simple. Hence, a large number of research articles have been published in this area. Though a few reviews are available on the catalyst-free organic reactions, most of them were published a few years ago. The current review excludes catalysts as well as additives and is specific to only C-C bond formation. Besides many organic name reactions, catalyst/additive-free C-H functionalizations, coupling reactions and UV-visible-light-promoted reactions are also discussed. Undoubtedly, the contents of this review will motivate readers to do more novel work in this area which will accelerate the journey towards a sustainable future.

Hypervalent iodine mediated synthesis of imidazo[1,2-a]pyridine ethers: consecutive methylene linkage and insertion of ethylene glycol

Hypervalent iodine mediated selective synthesis of imidazo[1,2-a]pyridine ethers using ethylene glycol as a methoxy ethanol source as well as solvent under metal-free conditions is described.

Lithium triethylborohydride-promoted generation of α,α-difluoroenolates from 2-iodo-2,2-difluoroacetophenones: an unprecedented utilization of lithium triethylborohydride

Lithium triethylborohydride was found to promote the generation of α,α-difluoroenolates from 2-iodo-2,2-difluoroacetophenones, and applied to the synthesis of polyfluorinated β-hydroxy ketones via self-condensation or aldol reaction.

Organocatalytic enantioselective Mukaiyama–Mannich reaction of fluorinated enol silyl ethers and cyclic N-sulfonyl ketimines

The first catalytic asymmetric Mukaiyama–Mannich reaction of fluorinated silyl enol ethers and ketimines is developed, allowing highly enantioselective synthesis of benzosultam based β-fluorinated C^α-tetrasubstituted α-amino acid derivatives.

Catalyst-free synthesis of α1-oxindole-α-hydroxyphosphonates via phospha-aldol reaction of isatins employing N-heterocyclic phosphine (NHP)-thiourea

A catalyst-free phospha-aldol reaction of isatins with NHP-thiourea has been developed and the critical role of the Brønsted acid in this transformation is unveiled.

Asymmetric synthesis of (3S,1'S)-3-(1-amino-2,2,2-trifluoroethyl)-1-(alkyl)-indolin-2-one derivatives by addition of (S)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine to 1-(alkyl)-indolin-2-ones

This paper presents the first study of the addition reactions between amide-derived nucleophiles and chiral CF3-containing N-sulfinyl-imines. We demonstrate that enolates of 1-(alkyl)-indolin-2-ones cleanly react with (S)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine affording 3-(1-amino-2,2,2-trifluoroethyl)-1-(alkyl)-indolin-2-ones of (3S,1'S) absolute configuration as the major reaction products with synthetically meaningful diastereoselectivity and chemical yields. The reactions were shown to be of general practical application for preparation of various oxindole derivatives in a diastereomerically pure form.

An efficient catalyst-free Mukaiyama-aldol reaction of fluorinated enol silyl ethers with tryptanthrin

We report an efficient Mukaiyama-aldol reaction of tryptanthrin with fluorinated enol silyl ethers, which is carried out in methanol without the use of any catalyst. This represents the first modification of tryptanthrin by a fluoroalkyl group, which is applied to the total synthesis of the difluoro analogues of the natural product Phaitanthrin B.

Palladium-catalyzed intermolecular oxidative cyclization of N-aryl enamines with isocyanides through double sp2 C–H bonds cleavage: facile synthesis of 4-aminoquinoline derivatives

An efficient method for the synthesis of 4-aminoquinolines via palladium-catalyzed intermolecular oxidative cyclization of N-aryl enamines and isocyanides through double sp² C–H bonds cleavage has been developed.

Recent advances in the application of deep eutectic solvents as sustainable media as well as catalysts in organic reactions

This review highlights the recent advances using deep eutectic solvents (DESs), deep eutectic ionic liquids (DEILs), low-melting mixtures (LMMs) or low transition temperature mixtures (LTTMs) as green media as well as catalysts in organic reactions.

Metal free stereoselective synthesis of functionalized enamides

An efficient and expeditious DABCO-mediated synthesis of functionalized enamides from alkenes is delineated. The reaction proceeds through an unprecedented cascade involving an Aza-Michael addition/α-bromination/elimination and a Morita-Baylis-Hillman type reaction to generate functionalized enamides in a regio- & stereoselective fashion.