Silver acetate catalysed cycloadditions of isocyanoacetates

C-H functionalization enabled by multiple isocyanides

Past decades have witnessed significant advance of isocyanides as a class of versatile organic synthons as well as their broad applications in multi-component reactions (MCRs) and other tandem reactions. Reactions involving multiple isocyanides allow the construction of molecules with further diversification and complexity, while C-H functionalization emphasizes the advantages of high atom economy, broad substrate availability and great synthetic efficiency. This promising synergistic strategy of C-H functionalization involving multiple isocyanides provides a variety of valuable synthetic methods for organic chemists' toolbox and offers considerable potential in pharmaceutical chemistry and materials science as well. The present review outlines in detail various reaction types of C-H functionalization enabled by multiple isocyanides, and the relevant mechanistic rationale is discussed.

General Approach to Amides through Decarboxylative Radical Cross-Coupling of Carboxylic Acids and Isocyanides

Herein, we report a silver-catalyzed protocol for decarboxylative cross-coupling between carboxylic acids and isocyanides, leading to linear amide products through a free-radical mechanism. The disclosed approach provides a general entry to a variety of decorated amides, accommodating a diverse array of radical precursors, including aryl, heteroaryl, alkynyl, alkenyl, and alkyl carboxylic acids. Notably, the protocol proved to be efficient for decarboxylative late-stage functionalization of several elaborate pharmaceuticals, demonstrating its potential applications.

Silver-promoted dearomative [3+4] cycloaddition of anthranils with α-isocyanoacetates: access to benzodiazepines

The first example of silver-promoted [3+4] cycloaddition of α-isocyanoacetates with anthranils as aromatic Michael accepters, offering access to benzo[d][1,3]diazepinones, has been developed. Mechanistic studies revealed that an "oxygen migration" rearrangement process was involved in this dearomative cycloaddition reaction. Additionally, benzo[d][1,3]diazepinones were obtained efficiently as well under catalytic conditions. Broad functional groups were well tolerated under mild reaction conditions.

Rh(I)-catalysed imine-directed C-H functionalization via the oxidative [3 + 2] cycloaddition of benzylamine derivatives with maleimides

The Rh(I)-catalysed imine-directed oxidative [3 + 2] cycloaddition of benzylamines with maleimides is reported. A wide range of both benzylamines and maleimides is applicable to the reaction. A one-pot three component strategy using benzylamines, 2-pyridinecarboxaldehyde, and maleimides is successfully achieved. Mechanistic studies including deuterium labelling experiments suggest that a zwitterionic intermediate is formed and is a key intermediate through the Rh-catalysed activation of a benzylic C(sp³)-H bond of the imine.

Catalytic Metal-Enabled Romance of Isocyanides for Use as “C1N1” Synthons in Cyclization: Beyond Radical Chemistry

Cyclizative reactions have attracted considerable attentions in organic synthesis with regard to the high atom economy and synthetic efficiency towards cyclic architectures. Especially, isocyanide-based cyclizations have proven to be a...

Asmic Isocyanide [3 + 2] Cascade to Dihydrooxazoles and Dihydroimidazoles

The versatile isocyanide building block Asmic, anisylsulfanylmethylisocyanide, reacts with aldehydes and ketones in a BF₃·OEt₂-mediated condensation to afford thioimidoyl-substituted 2,5-dihydrooxazoles. The condensation is distinguished from related base and transition-metal-catalyzed [3 + 2] processes in proceeding via the condensation of aldehydes and ketones with 2 equiv of an isocyanide followed by a molecular rearrangement that installs four new bonds. BF₃·OEt₂ mediates an analogous condensation of Asmic with imines to generate N-substituted dihydroimidazoles. Mechanistically, BF₃·OEt₂ activates the isocyanide to facilitate deprotonation evolving to a zwitterion that traps π-electrophiles in a formal [3 + 2] process. A second deprotonation-condensation with Asmic initiates a structural rearrangement involving a sulfanyl elimination-addition transposition sequence. The resulting dihydrooxazoles and dihydroimidazoles contain a thioimidate that serves as a diversification point for further elaboration.

NaH Promoted One-Pot Tandem Reactions of 3-(1-Alkynyl) Chromones to Form 2-Nitrogen-Substituted Xanthones

A silver-catalyzed dimerization of ethyl isocyanoacetates could trigger the tandem reaction of 3-(1-alkynyl) chromones under the basic condition in a one-pot reaction to afford xanthone skeletons with 2-imidazolyl substitution in an efficient manner. With the control experiment in hand, a mechanism including dimerization of isocyanoacetate/deprotonation/Michael addition/ring-opening/cyclization 1,2-elimination was deduced. Further investigation for the base was carried out, resulting in NaH as an optimal base to avoid the dimerization of 3-(1-alkynyl) chromones. The scope of this methodology was extended on the different substituents of 3-(1-alkynyl)-chromones and the potential of other N-heterocycle glycine ester anions to give the novel functional 2-nitrogen-derived xanthones.

Rhodium-catalyzed homodimerization–cyclization reaction of two vinyl isocyanides: a general route to 2-(isoquinolin-1-yl)oxazoles

A novel rhodium-catalyzed homodimerization–cyclization reaction of two vinyl isocyanides has been developed for the synthesis of 2-(isoquinolin-1-yl)oxazoles by formation of three new bonds and two rings in a single step.

Domino synthesis of fully substituted pyridines by silver-catalyzed chemoselective hetero-dimerization of isocyanides

A silver-catalyzed hetero-dimerization of various vinyl isocyanides with isocyanoacetamides has been developed for the efficient and practical synthesis of fully substituted pyridines in a single operation.

To each his own: isonitriles for all flavors. Functionalized isocyanides as valuable tools in organic synthesis

The term functionalized isocyanides refers to all those isocyanides in which a neighbouring functional group can finely tune the reactivity of the isocyano group or can be exploited in post-functionalization processes. In this manuscript, we have reviewed all the isocyanides in which the pendant functional group causes either deviation from or reinforces the normal reactivity of the isocyano group and categorized them to highlight their common features and differences. An analysis of their synthetic potential and the possible unexplored directions for future research studies is also addressed.

Azomethine-isocyanide [3+2] cycloaddition to imidazoles promoted by silver and DBU

A new silver-promoted [3+2] cycloaddition of azomethine ylides with isocyanides has been described to construct a variety of 1,2,4-trisubstituted imidazoles of vital bioactive molecules.

Cu(i)-catalyzed Michael addition of ketiminoesters to β-trifluoromethyl β,β-disubstituted enones: rapid access to 1-pyrrolines bearing a quaternary all-carbon stereocenter

Chiral pyrrolines with two contiguous stereocenters, including a trifluoromethylated quaternary all-carbon stereocenter, were provided from β-trifluoromethyl β,β-disubstituted enones and glycine ketoimino ester.

Silver-Catalyzed Isocyanide-Isocyanide [3+2] Cross-Cycloaddition Involving 1,2-Group Migration: Efficient Synthesis of Trisubstituted lmidazoles

Imidazole ring is an important five-membered aromatic heterocycle that is widely present in natural products and synthetic molecules. The isocyanide-isocyanide [3+2] cross-cycloaddition reaction constitutes a straightforward method to access imidazoles starting from the easily available chemicals. So far, only three successive reports are known and all lead to the formation of 1,4-disubstituted imidazoles. Here, we report the first isocyanide-isocyanide [3+2] cross-cycloaddition reaction allowing for the formation of 1,4,5-trisubstituted imidazoles under silver catalysis. An unexpected 1,2-migration of sulfonyl, alkoxycaybonyl, and carbamoyl groups took place during the cyclization process that is responsible for the formation of trisubstituted imidazoles. This report displayed a mechanistically novel synthetic method toward a variety of imidazole derivatives, which are otherwise difficult to access by conventional methods.

Catalytic σ-activation of carbon–carbon triple bonds: reactions of propargylic alcohols and alkynes

A variety of organic transformations have been developed based on conceptually novel catalytic σ-activation of CC bonds of alkynes.

Synthesis of Functionalized Chromeno[2,3-b]pyrrol-4(1H)-ones by Silver-Catalyzed Cascade Reactions of Chromones/Thiochromones and Isocyanoacetates

A novel and convenient approach to the synthesis of chromeno[2,3-b]pyrrol-4(1H)-ones has been developed. Furthermore, the method involves a facile silver-catalyzed cascade cyclization reaction including an intramolecular C-O bond formation. The silver salt acts as a key promoter.

A multicomponent pathway-inspired regioselective synthesis of 2,3,4-trisubstituted 1H-pyrroles via [3+2] cycloaddition reaction

An operationally simple, functional group tolerant and highly efficient domino protocol for the synthesis of pyrroles has been developed.

Nano-copper catalysed highly regioselective synthesis of 2,4-disubstituted pyrroles from terminal alkynes and isocyanides

Nano-copper(0) stabilized on alumina prepared from Cu–Al hydrotalcite has been reported for completely regioselective synthesis of 2,4-disubstituted pyrroles from unactivated terminal aromatic/aliphatic alkynes and isocyanides.

A general and practical route to 4,5-disubstituted oxazoles using acid chlorides and isocyanides

An efficient and mild method for the synthesis of 4,5-di-substituted oxazolesvia[3 + 2] cycloaddition reaction of isocyanides and acid chlorides is reported.

Ag(I)-catalyzed tandem [6+3] annulation/isomerization of isocyanoacetates with fulvenes: an expedient approach to synthesize fused dihydropyridines

An unprecedented Ag(i)-catalyzed tandem [6+3] cycloaddition/isomerization of isocyanoacetates with fulvenes has been developed, affording the fused dihydropyridine derivatives in good yields with exclusive regioselectivities.