Silver-catalyzed P-centered anion nucleophilic addition to isocyanide: access to 2-phosphinoyl indoles/indol-3-ols

A silver-catalyzed chemoselective cascade nucleophilic addition of a P-centered anion to isocyanides and cyclization reaction was developed for the efficient and practical synthesis of a wide range of 2-phosphinoyl indole and indol-3-ol derivatives. Unlike the well-documented synthesis of phosphorus-functionalized heterocycles via a P-centered radical, an anionic reactivity profile of phosphine oxides is most likely involved in this domino transformation.

Modular Synthesis of Tetrasubstituted Pyrroles via an Annulative Migration Reaction of Allenyl Ketones and p-Toluenesulfonylmethyl Isocyanide

The metal-free cyclization of allenyl ketones and p-toluenesulfonylmethyl isocyanide (TosMIC), promoted by Cs₂CO₃, provides a convenient access to tetrasubstituted pyrroles in which an acyl group undergoes 1,2-migration. This tandem Michael addition/annulative migration synthetic strategy is general and high-yielding for various substituted allenyl ketones. Moreover, a phosphoryl or ester moiety is also a suitable functionality to enable such migration.

Dinucleophilic Reactivity of Isocyanoacetate: Base-Catalyzed One-Pot Access to 4-Azafluorenes and 4-Azafluorenones

A base-catalyzed double annulation of isocyanoacetates with various enynones has been developed for the expeditious synthesis of 4-azafluorene and 4-azafluorenone derivatives. Against the well-known 1,3-dipolar reactivities, the active methylene and isocyano groups of isocyanoacetate serve as nucleophiles in this domino transformation.

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.

A transition metal-free approach towards the regioselective synthesis of β-carboline tethered pyrroles and 2,3-dihydro-1H-pyrroles

A transition metal-free one-pot sequential approach has been unfolded for the synthesis of β-carboline tethered pyrroles and 2,3-dihydro-1H-pyrroles by using highly diverse 1-formyl-9H-β-carbolines as a template.

Synthesis of Highly Functionalized Indoles and Indolones via Selectivity-Switchable Olefinations

Highly functionalized indoles and indolones were prepared via selectivity-switchable mono- or diolefinations. The Julia olefination of the products followed by a Brønsted acid-prompted cyclization afforded indolones, whereas the indoles were obtained by a sequential Wittig olefination and electrocyclization. This method opens divergent access to highly functionalized nitrogen-containing bicyclic or tricyclic heterocycles.

Asymmetric [4 + 2] cycloadditions with 3-furfural derivatives and α-cyano-α,β-unsaturated ketones

An asymmetric [4 + 2] cycloaddition reaction with 2-benzyl-3-furfurals and α-cyano-chalcones was developed to afford chiral tetrahydrobenzofurans having dense substitutions.

Nitrile-assisted oxidation over oxidative-annulation: Pd-catalyzed α,β-dehydrogenation of α-cinnamyl β-keto nitriles

A palladium-catalyzed oxidation reaction is disclosed where the nitrile functionality on the substrate simply changes the course of the reaction. Our previous finding showed that using the Pd(ii)-catalyst in the presence of benzoquinone as an oxidant, 2-cinnamyl-1,3-dicarbonyls provides functionalized furans via oxidative cyclization. When a nitrile group is replaced with one of the carbonyl functionalities of the same substrate, the oxidative cyclization was completely suppressed; instead, the oxidation at the α,β-position occurred to provide α,β,γ,δ-diene containing β-keto nitriles.

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.

Isocyanide-based multicomponent reactions in the synthesis of heterocycles

In this review, we update our previous presentation, underscoring the recent applications of isocyanides as privileged synthons in the synthesis of various heterocyclic compounds, especially focused on those synthesizedviamulticomponent reactions.

Tandem cycloaddition–decarboxylation of α-keto acid and isocyanide under oxidant-free conditions towards monosubstituted oxazoles

An efficient method, tandem [3 + 2] cycloaddition–decarboxylation of α-keto acid and isocyanide promoted by copper salt, has been developed for constructing monosubstituted oxazole. The elegant approach ingeniously avoids consuming excess oxidants.

Arylsulfonylmethyl isocyanides: a novel paradigm in organic synthesis

p-Tosylmethyl isocyanide (TosMIC), an α-acidic isocyanide has emerged as a privileged reagent to access biologically relevant fused heterocycles and some natural products like (−)-ushikulide A, variolin B, porphobilinogen and mansouramycin B.

Silver-catalyzed cascade reaction of tosylmethyl isocyanide (TosMIC) with propargylic alcohols to (E)-vinyl sulfones: dual roles of TosMIC

An silver-catalyzed cascade reaction of tosylmethyl isocyanide (TosMIC) with propargylic alcohols for the synthesis of (E)-vinyl sulfones has been developed where TosMIC plays a dual role as both the reactant in the allenylation of propargylic alcohols and the sulfonyl source.

Catalytic Isonitrile Insertions and Condensations Initiated by RNC-X Complexation

Isonitriles are delicately poised chemical entities capable of being coaxed to react as nucleophiles or electrophiles. Directing this tunable reactivity with metal and non-metal catalysts provides rapid access to a large array of complex nitrogenous structures ideally functionalized for medicinal applications. Isonitrile insertion into transition metal complexes has featured in numerous synthetic and mechanistic studies, leading to rapid deployment of isonitriles in numerous catalytic processes, including multicomponent reactions (MCR). Covering the literature from 1990-2014, the present review collates reaction types to highlight reactivity trends and allow catalyst comparison.