Gold-Catalyzed Synthesis of 3-Arylindoles via Annulation of Nitrosoarenes and Alkynes

Nitroso-azomethine(ene) reaction enabled annulations of nitrosoarenes, azomethines and alkenes

An unprecedented example of a nitroso-azomethine(ene) reaction is reported. Nitroso-azomethine(ene) reaction-mediated unprecedented annulation of nitrosoarenes, azomethines, and alkenes to furnish arylquinolines via arene functionalization of nitrosoarene has been developed. DFT studies provided mechanistic insights into the newly developed nitroso-azomethine(ene) reaction.

Silver-catalyzed nitrosation and nitration of aromatic amides using NOBF4

Divergent aromatic ring nitrosation and nitration of aromatic amides are reported using NOBF4 as the electrophile under silver-catalyzed conditions. The reactions proceed efficiently with a wide range of compatible functionalities providing ortho-position nitrosation products, deacylation nitrosation products, and nitration products from different tertiary and secondary aromatic amides.

Lewis acid catalyzed reactivity switch: pseudo three-component annulation of nitrosoarenes and (epoxy)styrenes

A Lewis acid catalyzed annulation reaction via arene functionalization of nitrosoarenes and C-C cleavage of (epoxy)styrene to provide arylquinolines is reported. The Lewis acid catalyst altered the annulation pattern providing arylquinolines instead of oxazolidines. The reaction with styrene resulted in a mixture of 2,4-diarylquinoline and 4-arylquinoline, while only 3-arylquinoline was formed from the reaction of epoxystyrene.

Acid mediated coupling of aliphatic amines and nitrosoarenes to indoles

Traditionally, amines react with nitrosoarenes to provide the corresponding imines or azo compounds. Herein, we report an acid mediated annulation reaction of aliphatic amines and nitrosoarenes to provide indole derivatives. The elusive direct annulation of aliphatic amines and nitrosoarenes via simultaneous C-C and C-N bond formation was achieved under metal free conditions. This conceptually novel method for indole synthesis does not require pre-functionalization steps for the new C-C and C-N bond formation. The method has been applied for an elegant synthesis of nor-neocryptolepine and neocryptolepine.

Step and redox efficient nitroarene to indole synthesis

A step and redox efficient nitroarene to indole synthesis was herein developed, in sharp contrast to the rich literature on the construction of indoles. Elemental Zinc was found to be best terminal reductant.

Radical chemistry of nitrosoarenes: concepts, synthetic applications and directions

The radical chemistry of nitrosoarenes has recently emerged as an attractive and important topic in organic chemistry.

Gold-Catalyzed Aromatizations of 3-Ene-5-siloxy-1,6-diynes with Nitrosoarenes To Enable 1,4-N,O-Functionalizations: One-Pot Construction of 4-Hydroxy-3-aminobenzaldehyde Cores

This work describes gold-catalyzed aromatizations of 3-ene-5-siloxy-1,6-diynes with nitrosoarenes to form 4-hydroxy-3-aminobenzaldehyde derivatives, manifesting the use of nitrosoarenes as 1,4-N,O-functionalization sources. Various 3-ene-5-siloxy-1,6-diynes in benzoid and nonbenzoid types are applicable substrates. A series of ¹⁸O- and ²H-labeling experiments have been conducted to exclude gold-π-alkyne intermediates. We postulate a mechanism of dual gold catalysis involving initial formation of gold-π-alkynylgold species that activates a 1,5-hydrogen shift to form reactive 1,6-dipoles, thus furnishing intramolecular Michael-type reactions with nitrosonium electrophiles.

A novel synthesis of N-hydroxy-3-aroylindoles and 3-aroylindoles

A straightforward indole synthesis via annulation of C-nitrosoaromatics with conjugated terminal alkynones was realised achieving a simple, highly regioselective, atom- and step economical access to 3-aroylindoles in moderate to good yields. Further functionalizations of indole scaffolds were investigated and an easy way to JWH-018, a synthetic cannabinoid, was achieved.

Synthesis of topologically constrained naphthalimide appended palladium(ii)–N-heterocyclic carbene complexes – insights into additive controlled product selectivity

Pd(ii)–NHC catalyzed regioselective heteroannulation of o-haloanilines and arylethynyl-trimethylsilane to yield indoles and additive controlled switchable product selectivity has been demonstrated.

Metal free direct C(sp2)–H arylaminations using nitrosoarenes to 2-hydroxy-di(het)aryl amines as multifunctional Aβ-aggregation modulators

A direct C(sp²)–H arylamination of 2-hydroxyarenes using nitrosoarenes was achieved under metal free conditions without the aid of additional reagents/steps for N–O bond cleavage.

Electronic effect of substituents on anilines favors 1,4-addition totrans-β-nitrostyrenes: access toN-substituted 3-arylindoles and 3-arylindoles

A simple and an efficient method for the regioselective synthesis ofN-alkyl/aryl/H 3-arylindole derivatives fromN-substituted anilines andtrans-β-nitrostyrenes has been described using 10 mol% of bismuth(iii) triflate as a catalyst in acetonitrile at 80 °C.

Metal-Free Sequential C(sp2)-H/OH and C(sp3)-H Aminations of Nitrosoarenes and N-Heterocycles to Ring-Fused Imidazoles

Hydrogen bond assisted ortho-selective C(sp²)-H amination of nitrosoarenes and subsequent α-C(sp³)-H functionalization of aliphatic amines is achieved under metal-free conditions. The annulation of nitrosoarenes and 2-hydroxy-C-nitroso compounds with N-heterocycles provides a facile excess to a wide range of biologically relevant ring-fused benzimidazoles and structurally novel polycyclic imidazoles, respectively. Nucleophilic aromatic hydrogen substitution (S_NArH) was found to be preferred over classical S_NAr reaction during the C(sp²)-H amination of halogenated nitrosoarenes.

O, Bao X. Computational insights into the mechanisms of Au(i)-catalysed intramolecular addition of the hydroxylamine group onto alkynes

Computational studies were carried out to understand the reaction mechanisms and the origin of the substrate-dependent chemo- and regio-selectivities of the Au(i)-catalysed intramolecular addition of the hydroxylamine group onto alkynes.

Synthesis of 3-arylindole derivatives from nitroalkane precursors

3-Arylindole derivatives were synthesized by Cu(i) catalysed intramolecular Ullmann coupling of 2-bromoarylaminoalkanes.

Fe-catalyzed synthesis of substituted N-aryl oxazolidines

An unprecedented Fe-catalyzed oxazolidine formation was observed from the reaction of allyl alcohols with arylhydroxylamines in presence of formaldehyde or its equivalents.

Divergent reactivity in palladium-catalyzed annulation with diarylamines and α,β-unsaturated acids: direct access to substituted 2-quinolinones and indoles

A palladium-catalyzed CH activation strategy has been successfully employed for exclusive synthesis of a variety of 3-substituted indoles. A [3+3] annulation for synthesizing substituted 2-quinolinones was recently developed by reaction of α,β-unsaturated carboxylic acids with diarylamines under acidic conditions. In the present work, an analogous [3+2] annulation is achieved from the same set of starting materials under basic conditions to generate 1,3-disubstituted indoles exclusively. Mechanistic studies revealed an ortho-palladation-π-coordination-β-migratory insertion-β-hydride elimination reaction sequence to be operative under the reaction conditions.

Synthesis of substituted quinolines via allylic amination and intramolecular Heck-coupling

A new catalytic approach for the synthesis of substituted quinolines via C-N and C-C bond formation using 2-haloaryl hydroxylamines and allylic C-H substrates is described. Fe-catalyzed allylic C-H amination followed by Pd-catalyzed intramolecular Heck-coupling and aerobic dehydrogenation deliver the valuable quinoline and naphthyridine heterocycles in good to excellent overall yields. In this process, Pd(OAc)2 plays a dual role in catalyzing Heck coupling as well as aerobic dehydrogenation of dihydroquinolines.

Gold-catalyzed 1,2-iminonitronation of electron-deficient alkynes with nitrosoarenes to afford α-imidoyl nitrones

Gold-catalyzed 1,2-iminonitronation of diverse propiolate derivatives with nitrosoarenes to give α-imidoyl nitrones is described.

Gold-catalyzed isomerization of unactivated allenes into 1,3-dienes under ambient conditions

We have developed a gold-catalyzed isomerization of unactivated allenes into 1,3-dienes with nitrosobenzene as an additive. This reaction proceeded almost exclusively at room temperature for highly substituted allenes. The utility of this reaction is manifested by the development of one-pot [4+2]-cycloaddition of allenes and reactive alkenes.

Gold-catalyzed formal [3 + 3] and [4 + 2] cycloaddition reactions of nitrosobenzenes with alkenylgold carbenoids

We report two new formal cycloaddition reactions between nitrosobenzenes and alkenylgold carbenoids. We obtained quinoline oxides 3 in satisfactory yields from the gold-catalyzed [3 + 3]-cycloadditions between nitrosobenzenes and alkenyldiazo esters 1. For propargyl esters 5, its resulting gold carbenes react with nitrosobenzene to give alkenylimine 8, followed by a [4 + 2]-cycloaddition with nitrosobenzene.