Temperature-Dependent Double Isocyanide Insertion Reaction To Construct a Polycyclic Skeleton

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.

Temperature-Dependent Divergent Cyclopentadiene Synthesis through Cobalt-Catalyzed C-C Activation of Cyclopropenes

We report a temperature-dependent divergent approach to synthesize multisubstituted cyclopentadienes through cobalt-catalyzed carbon-carbon (C-C) bond activation of cyclopropenes and ring expansion with internal alkynes. By employing different heating procedures, two cyclopentadiene substitution isomers were efficiently and selectively constructed. This reaction does not require preactivation of the metal catalyst or additional reducing reagents. Preliminary mechanistic investigations suggest that the key steps are oxidative addition of the cyclopropene to cobalt catalyst, followed by alkyne insertion and 1,5-ester shift.

Heterocycles via SiCl4-Promoted Isocyanide Additions to Oxonitriles

SiCl4 promotes isocyanide additions to oxoalkenenitriles to selectively generate 3-acylpyrroles, 2-aminofurans, or pyrrolidinones. Cyclic oxoalkenenitriles add 2 equiv of an isocyanide that installs the two core atoms of an acylpyrrole and a nitrile substituent, whereas acyclic oxoalkenenitriles add 1 equiv of an isocyanide to afford 2-aminofurans; subsequent air oxidation generates pyrrolidinones via a furan oxygenation-cleavage-cyclization sequence. The syntheses proceed under mild conditions to rapidly access three richly decorated heterocycles.

Cascade reaction of o-enoyl arylisocyanide and o-hydroxy aromatic aldimine: diastereoselective access to a polycyclic spirobenzoxazine chromeno[4,3-b]pyrrole derivative

A series of structurally unusual spirobenzoxazine chromeno[4,3-b]pyrrole derivatives have been efficiently constructed in a single operation from readily available starting materials. This domino transformation forms successively three new rings and provides a fast and economic strategy with excellent diastereoselectivity.

Crystal structure of N-(1H-indol-2-yl-methyl-idene)-4-meth-oxy-aniline

The mol-ecule of the title compound, C16H14N2O, contains an essentially planar indole ring system and a phenyl ring. In the crystal, the mol-ecules are linked by a weak inter-molecular C-H⋯O hydrogen bond and C-H⋯π inter-actions, forming a one-dimensional column structure along the b-axis direction. These columns are linked by other C-H⋯π inter-actions, forming a two-dimensional network structure.

Nickel-promoted oxidative domino Csp3-H/N-H bond double-isocyanide insertion reaction to construct pyrrolin-2-ones

The first nickel-catalyzed oxidative domino C_sp3-H/N-H double isocyanide insertion reaction of acetamides with isocyanides has been developed for the synthesis of pyrrolin-2-one derivatives. A wide range of acetamides bearing various functional groups are compatible with this reaction system by utilizing Ni(acac)₂ as a catalyst. In this transformation, isocyanide could serve as a C1 connector and insert into the inactive C_sp3-H bond, representing an effective way to construct heterocycles.

Palladium-catalyzed double coupling reaction of terminal alkynes with isocyanides: a direct approach to symmetrical N-aryl dialkynylimines

A novel and efficient one-pot synthesis of symmetrical N-aryl dialkynylimines via palladium-catalyzed and copper-promoted isocyanide insertion, cross-coupling and elimination has been developed. This method features readily available starting materials, mild reaction conditions and high atom efficiency as well as simple one-pot operation, which make this strategy highly attractive. Moreover, 2-iodobenzo[f]quinoline derivatives can be obtained via electrophilic cyclization of N-aryl dialkynylimines.

Palladium-Catalyzed Diarylation of Isocyanides with Tetraarylleads for the Selective Synthesis of Imines and α-Diimines

Using tetraaryllead compounds (PbAr₄) as arylating reagents, isocyanides undergo selective diarylation in the presence of palladium catalysts such as Pd(OAc)₂ or Pd(PPh₃)₄ to afford imines and/or α-diimines based on the isocyanide employed. With aliphatic isocyanides, imines are obtained preferentially, whereas α-diimines are formed in the case of electron-rich aromatic isocyanides. The differences in imine/α-diimine selectivity can be attributed to the stability of imidoylpalladium intermediates formed in this catalytic reaction. Compared with other arylating reagents, tetraaryllead compounds are excellent candidates for use in the selective transformations to imines and/or α-diimines, especially in terms of inhibiting the oligomerization of isocyanides, which results in a lower product selectivity in many transition-metal-catalyzed reactions of isocyanides.

Cascade double isocyanide insertion and C-N coupling of 2-iodo-2'-isocyano-1,1'-biphenyls

A palladium-catalyzed double isocyanide insertion using 2-iodo-2'-isocyano-1,1'-biphenyls followed by copper-catalyzed intramolecular C-N coupling, delivering a unique heterocyclic structure containing both phenanthridine and carbazole scaffolds, has been developed. In this cascade process, four chemical bonds, including two C-C, one C-O, and one C-N bonds are formed consecutively without isolating an intermediate. The strategy of using a functionalized isocyanide in double insertion provides a quick approach for constructing heterocyclic systems with high bond-forming efficiency.

[1 + 2 + 3] Annulation as a General Access to Indolo[3,2- b]carbazoles: Synthesis of Malasseziazole C

A formal [1 + 2 + 3] annulation of methyleneindolinones with o-alkenyl arylisocyanides has been developed for the general and efficient synthesis of both symmetrical and unsymmetrical indolo[3,2- b]carbazoles. The chemoselectivity of this domino reaction was tuned by a tethered alkenyl group, which enables successive formation of three new bonds and two rings from readily accessible starting materials in a single operation. Furthermore, this methodology was used as a key step in the synthesis of the alkaloid malasseziazole C.

A bicyclization reaction with two molecular allenyl ketones and isocyanides: synthesis of a lactone-containing azaspirocycle derivative

A novel bicyclization reaction of two molecular allenyl ketones and isocyanides has been disclosed. This strategy allows for the construction of structurally complex spirocyclic lactam–lactone systems in an efficient manner.

Cascade cyclization and acyl migration of propargylic esters with isocyanides: rapid access to substituted furans

A novel rearrangement of ester-activated propargylic acetate with isocyanide has been disclosed. This protocol enables a quick synthesis of polysubstituted furan derivatives.

Carbon-nitrogen bond cleavage of pyridine with two molecular substituted allenoates: access to 2-arylpyrimidin-4(3H)-one

A DABCO-catalyzed annulation reaction of pyridin-2-amine and substituted allenoates has been disclosed. This strategy allows for the ring-opening of a pyridine ring system and the formation of two new rings including a pyrimidinone ring and a benzene ring in an efficient manner.

Nickle Catalysis Enables Access to Thiazolidines from Thioureas via Oxidative Double Isocyanide Insertion Reactions

An efficient synthesis of thiazolidine-2,4,5-triimine derivatives was developed via Ni-catalyzed oxidative double isocyanide insertion to thioureas under air conditions, in which thioureas play three roles as a substrate, a ligand, and overcoming isocyanide polymerization. The reaction is featured by employing a low-cost and low loading Ni(acac)₂ catalyst, without any additives, and high atom economy. This is the first example to directly apply a Ni(II) catalyst in oxidative double isocyanide insertion reactions.

A Critical Review on Advances in the Multicomponent Synthesis of Pyrroles

Nitrogen containing heterocyclic compounds are biologically significant molecules. This is especially true for pyrrole a five membered nitrogen containing aromatic molecule, which is present as a key structural motif in a large number of drugs and lead molecules. This review aims to provide an overview of the multi-component reaction (MCR) based methodologies used for the synthesis of pyrrole and its derivatives, focusing particularly on eco-friendly methods that avoid the use of hazardous reagents, solvents and catalysts are deemed especially relevant to the disciplines of medicinal chemistry and drug discovery.

Highly Regioselective Synthesis of Oxindolyl-Pyrroles and Quinolines via a One-Pot, Sequential Meyer-Schuster Rearrangement, Anti-Michael Addition/C(sp3)-H Functionalization, and Azacyclization

A one-pot, sequential Meyer-Schuster (MS) rearrangement of oxindole-derived propargyl alcohols to the corresponding α,β-unsaturated enones and their anti-Michael addition, followed by intramolecular azacyclization is described in a highly regioselective manner using Ca(OTf)₂ as the promoter. Further, we described the one-pot MS rearrangement, followed by C_(sp³)-H functionalization of 2-methyl azaarenes at α-carbon of these doubly activated alkenes. Control experiments and computational calculations were performed to propose the reaction mechanism.

When Ethyl Isocyanoacetate Meets Isatins: A 1,3-Dipolar/Inverse 1,3-Dipolar/Olefination Reaction for Access to 3-Ylideneoxindoles

A new CuI/1,10-phen-catalyzed reaction for the synthesis of 3-ylideneoxindoles from readily available isatins and ethyl isocyanoacetate, in which ethyl isocyanoacetate acts as a latent two-carbon donor like the Wittig reagent, is reported. A tandem procedure including 1,3-dipolar cycloaddition/inverse 1,3-dipolar ring opening/olefination allows the preparation of 3-ylideneoxindoles with broad functional group tolerance.

A domino reaction of 2-isocyanophenyloxyacrylate and aryne to synthesize arenes with vicinal olefin and benzoxazole

An unusual domino reaction of 2-isocyanophenyloxyacrylate and aryne has been disclosed. The present strategy experiences nucleophilic addition, Michael addition, carbon–oxygen cleavage, and cyclization, thus enabling the quick aryne vicinal difunctionalization by the installation of a benzoxazole and an olefin.

Ytterbium and silver co-catalyzed synthesis of pyrrole-fused bicyclic skeletons from enynones and isocyanides

A cascade reaction of isocyanide and enynone using Yb/Ag cooperative catalysis provided a quick access to structurally complex pyrrole-fused heterocycles.

Copper-catalyzed synthesis of arylcarboxamides from aldehydes and isocyanides: the isocyano group as an N1 synthon

For the first time, transition-metal-catalyzed isocyanide group acting as an N1 synthon rather than exhibiting the carbene-like reactivity was discovered, exploiting a new reactivity profile of isocyanides.

Direct carboxamidation of cyclic 2-diazo-1,3-diketones by Rh2(OAc)4-catalyzed isocyanide insertion–hydrolysis

A novel and efficient strategy for the synthesis of 2-hydroxy-6-oxocyclohex-1-enecarboxamides through a Rh₂(OAc)₄-catalyzed direct carboxamidation of cyclic 2-diazo-1,3-diketones has been developed.

A multicomponent bicyclization reaction of isocyanide, allenoate, imine and water to synthesize pyrrolidine-fused rings

A multicomponent bicyclization of isocyanide, allenoate, imine, and water has been disclosed. This protocol involves the formation of five chemical bonds (two C–C, two C–N, and one C–O), thus providing a new pathway to fused rings.

Palladium-Catalyzed Synthesis of 5-Iminopyrrolones through Isocyanide Double Insertion Reaction with Terminal Alkynes and Water

With the combination of Pd(dppf)Cl₂ and Cu(OAc)₂, a variety of 5-iminopyrrolones were synthesized in moderate to good yields from terminal alkynes, isocyanide, and water via isocyanide double insertion and cycloaddition reaction. A plausible reaction mechanism for this process is depicted. Furthermore, selected compounds 3c, 3e, and 3h exhibited good activities against HepG2 (human liver cancer), NCI-H460 (human lung cancer), and SK-OV-3 (human ovarian cancer) cell lines with IC₅₀ values in the range of 10.63-22.63 μmol L^-1.

Substrate-controlled switchable asymmetric annulations to access polyheterocyclic skeletons

Substrate-controlled switchable asymmetric annulations of Morita–Baylis–Hillman carbonates from isatins and α-cyano-α,β-unsaturated ketones catalysed by cinchona-derived tertiary amines, giving tetrahydrofuro[2′,3′:4,5]pyrano[2,3-b]indoles or spirooxindoles incorporating a cyclopentene motif, were disclosed.

Radical perfluoroalkylation – easy access to 2-perfluoroalkylindol-3-imines via electron catalysis

Arylisonitriles react with alkyl and perfluoroalkyl radicals to form 2-alkylated indole-3-iminesviatwo sequential additions to the isonitrile moiety followed by homolytic aromatic substitution.

Scandium triflate-catalyzed selective ring opening and rearrangement reaction of spiro-epoxyoxindole and carbonyl compounds

Scandium triflate-catalyzed reactions between spiro-epoxyoxindole and carbonyl compounds have been disclosed. Furthermore, an unprecedented rearrangement takes place to yield alkylidene oxindoles when aromatic aldehydes are used as carbonyl components.