Regio- and Diastereoselective [3 + 2]-Spiroannulation of Benzoxazines with Chalcones: A Rh(III)-Catalyzed Redox-Neutral Approach to α-Aroyl Spiro-Indanamines.

We report an atom-economic Rh(III)-catalyzed [3 + 2]-spiroannulation reaction between cyclic ketimines and α,ß-unsaturated carbonyl compounds, allowing the synthesis of novel spirocycles with concomitant generation of three stereogenic centers in one pot. The reaction does not require any silver additives or external oxidants and is believed to proceed in a redox-neutral manner. A broad substrate scope with good functional group tolerance permitted the synthesis of a vast spectrum of spirocyclic 1,4-benzoxazine derivatives containing polysubstituted α-aroyl-indanamines in good to excellent yields with high diastereoselectivity.

Straightforward Access to Anthrone Functionalized Benzylic Amines via Organocatalytic 1,2-Addition of Anthrones to Imines at Ambient Temperature.

Activation of anthrone via benzylic deprotonation in the presence of triethylamine paves the way for the 1,2-addition reaction with imines to provide the desired functionalized anthrones in good to excellent yields under mild and operationally simple reaction conditions with a broad range of substrate scopes without using any external additives or toxic stoichiometric reagents.

Iridium-catalyzed direct C-H arylation of cyclic N-sulfonyl ketimines with arylsiloxanes at ambient temperature.

An iridium-catalyzed ortho-selective C-H arylation of cyclic N-sulfonyl ketimines has been achieved with environmentally benign aryl siloxanes. The reaction is highly efficient and proceeds at ambient temperature which is the key feature of the methodology considering the weak coordination nature of the substrate as well as the sluggish reactivity of siloxanes. A wide array of pharmaceutically relevant novel biaryls has been synthesized under operationally simple conditions.

Ir(III)/MPAA-Catalyzed Mild and Selective C-H Amidation of N-Sulfonyl Ketimines: Access To Benzosultam-Fused Quinazolines/Quinazolinones.

Ir(III)-catalyzed unprecedented mild C-H amidation for weakly coordinating cyclic N-sulfonyl ketimines, accelerated by a mono protected l-amino acid, has been developed. The method uses 1,4,2-dioxazol-5-ones as the robust amidating reagent in conjunction with a catalytic amount of silver triflate. It is highly selective and does not require a stoichiometric amount of oxidants or additives. A series of mechanistic experiments was performed to gain some insights into the reaction mechanism. The strategy provides easy access to novel benzosultam-quinazoline and benzosultam-quinazolinone hybrid scaffolds endowed with pharmaceutically relevant features.

Rhodium-Catalyzed sp2 C-H Acetoxylation of N-Aryl Azaindoles/N-Heteroaryl Indolines.

A silver- and copper-free rhodium-catalyzed C-H acetoxylation reaction of azaindoles has been achieved at near ambient temperature employing PIDA as a nonmetallic acetoxy source. The method is highly selective, efficient, and scalable and requires acetic anhydride as the sole additive. The scope of the reaction has been successfully tested with a wide array of medicinally important heterocyclic scaffolds with diverse functional group tolerance. A series of kinetic experiments was conducted to gain detailed insight into the reaction mechanism. The methodology developed could be successfully expanded for C7-acetoxylation of indoline derivatives using pyrimidine as a detachable directing group for the synthesis of 7-hydroxyindole.

Ruthenium-Catalyzed Direct and Selective C-H Cyanation of N-(Hetero)aryl-7-azaindoles.

An efficient, highly regioselective, and scalable ruthenium-catalyzed o-aryl C-H mono-cyanation of N-aryl-7-azaindoles to form N-(2-cyanoaryl)-7-azaindoles has been developed through N-directed ortho C-H activation using N-cyano-N-phenyl-p-toluenesulfonamide as cyanating reagent in the presence of AgOTf and NaOAc in DCE. A range of substrates has furnished cyanated azaindoles in good to excellent yields under the simple reaction conditions. Involvement of C-H metalation has been supported by a kinetic study. This methodology provides easy access to a class of pharmaceutically significant molecules and their precursors.

Electrochemical C(sp3)-C(sp3) cross-dehydrogenative coupling: enabling access to 9-substituted fluorescent acridanes.

A straightforward strategy for direct access of C9-functionalized N-alkyl-acridanes in good to excellent yields has been established via a metal- and external oxidant-free sustainable electrochemical C(sp3)-C(sp3) cross-dehydrogenative coupling reaction between acridanes and benzo fused lactones at ambient temperature. A broad substrate scope with superior functional-group tolerance via anodic oxidation of acridanes permitted the synthesis of a vast spectrum of fluorescence-active acridanes with high quantum yields.

[3+2] Cascade Ring-Closing/Ring-Opening Strategy: Access to N-Indene-Tethered Amino Alcohols.

An unprecedented atom-economic redox neutral regioselective Rh(III)-catalyzed cascade [3+2] annulation of 2-aryl oxazoline with α,ß-unsaturated nitro olefins has been accomplished, furnishing a novel set of nitro-functionalized indene-tethered amino alcohols through a synergistic ring-closing/ring-opening strategy via the formation of two new C-C bonds and the regioselective cleavage of the C2-O bond of oxazoline under silver free mild reaction conditions with a broad substrate scope.

Synthesis of indene-fused spiro-dibenz(ox)azepines via Rh(III)-catalyzed cascade regioselective C-H activation/annulation.

We report an unprecedented atom-economic one-pot Cp*Rh(III)-catalyzed regioselective [3+2]-spiroannulation reaction between dibenz(ox)azepines and ynones, allowing the synthesis of biologically relevant novel spirocyclic dibenz(ox)azepines under operationally simple and mild reaction conditions. The reaction proceeds without any silver additive or external oxidant implementing a redox-neutral pathway. A broad substrate scope with diverse functional group tolerance permitted the regioselective synthesis of a wide spectrum of indene-containing spirocyclic dibenz(ox)azepines in good to excellent yields. Also, we showcased detailed mechanistic studies to justify the formation of spirocycles. In addition, the synthetic utility of this process was also demonstrated by the modular synthesis of various steroid conjugates.

A condition-tuned unorthodox approach to indole-3-carboxylic acids and anthranilic acids via carbon atom translocation.

We describe a robust one-pot cascade method for the synthesis of indole-3-carboxylic acids using isatins and DMSO via a one-carbon translocation involving in situ generation of α,ß-unsaturated methylvinylsulfoxide followed by amide bond cleavage and ring closure. The methodology has been extended to afford anthranilic acid derivatives by tuning the reaction conditions in the presence of molecular oxygen. Importantly, easy access to commercially available drugs, including tropisetron, is demonstrated.

Palladium-catalyzed aerobic oxidative cyclization of N-aryl imines: indole synthesis from anilines and ketones.

We report here an operationally simple, palladium-catalyzed cyclization reaction of N-aryl imines, affording indoles via the oxidative linkage of two C-H bonds under mild conditions using molecular oxygen as the sole oxidant. The process allows quick and atom-economical assembly of indole rings from inexpensive and readily available anilines and ketones and tolerates a broad range of functional groups.

A radical-radical cross-coupling reaction of xanthene with sulfonyl hydrazides: facile access to xanthen-9-sulfone derivatives.

A straightforward strategy for direct incorporation of sulfonyl units into a xanthene moiety for accessing xanthen-9-sulfone derivatives in good to excellent yields has been established via metal-free radical-radical cross-coupling reaction of xanthenes and sulfonyl hydrazides. Using easily accessible starting materials, this methodology proceeds efficiently with a high degree of functional group compatibility and with a wide scope of both xanthenes and sulfonyl hydrazides under operationally simple reaction conditions. Mechanistic investigations revealed that sulfonyl radicals could be generated from sulfonyl hydrazides in the presence of TBHP under an oxygen atmosphere.

Redox-neutral indole annulation cascades.

Aminobenzaldehydes react with indoles in an unprecedented cascade reaction. This acid-catalyzed redox-neutral annulation proceeds via a condensation/1,5-hydride shift/ring-closure sequence. Polycyclic azepinoindoles and related compounds are obtained in a single step with good to excellent yields.

Copper-Catalyzed Direct sp2 C-H Silylation of Arylamides Using Disilanes.

A copper-catalyzed method for direct intermolecular ortho-silylation of benzamides has been developed that affords organosilane products in moderate to high yields. The key features include: (i) use of commercially available disilanes as a silicon source with 8-aminoquinoline as a bidentate directing group, (ii) use of earth-abundant first-row transition metal, (iii) operationally simple conditions without the need of an inert atmosphere, and (iv) tolerance of a wide range of functional groups. The practicality and effectiveness of this method have been demonstrated by a gram-scale experiment. This strategy, therefore, constitutes a convenient way of constructing C-Si bonds useful for synthetic organic chemistry.

Diastereoselective Spirocyclization of Benzoxazines with Nitroalkenes via Rhodium-Catalyzed C-H Functionalization/Annulation Cascade under Mild Conditions.

A Rh(III)-catalyzed [3 + 2] annulation of benzoxazines with nitroolefins that proceeds via redox-neutral C-H functionalization has been demonstrated, leading to the novel class of spirocycles in a single step. The construction of three continuous stereogenic centers has been achieved starting from easily accessible achiral substrates in an atom-efficient manner under mild reaction conditions. A broad range of pharmaceutically relevant nitro substituted spirocyclic 2,3-dihydro-1,4-benzoxazine derivatives has been synthesized in good to excellent yields with high diastereoselectivity.

Catalytic enantioselective intramolecular redox reactions: ring-fused tetrahydroquinolines.

The first example of a catalytic enantioselective intramolecular hydride shift/ring closure reaction is reported. This redox neutral reaction cascade allows for the efficient formation of ring-fused tetrahydroquinolines in high enantioselectivities.

Diastereoselective Spirocyclization of Cyclic N-Sulfonyl Ketimines with Nitroalkenes via Iridium-Catalyzed Redox-Neutral Cascade Reaction.

An Ir(III)-catalyzed [3 + 2] annulation of weakly coordinating N-sulfonyl ketimines with challenging α, ß-unsaturated nitro olefins has been achieved via redox-neutral C-H functionalization in the presence of a catalytic amount of silver hexafluoroantimonate. The generation of three consecutive stereogenic centers in a single step via direct C-H functionalization is the prime feature of this methodology. A wide array of pharmaceutically relevant nitro-substituted spirocyclic benzosultams was synthesized with good to excellent diastereoselectivity as well as in high yield starting from easily accessible substrates.

Hydroxyalkylation of conjugated nitroalkenes with activated nonenolizable carbonyl compounds.

[reaction: see text] The Morita-Baylis-Hillman reaction of a variety of conjugated nitroalkenes with activated nonenolizable carbonyl compounds such as glyoxylate, trifluoropyruvate, pyruvaldehyde, and ninhydrin in the presence of 40-100 mol % of DMAP in acetonitrile or 100 mol % of imidazole in CHCl(3) or THF provided the adducts in decent to good yields. In most cases, the reactions catalyzed by DMAP in acetonitrile were faster and provided the desired MBH adducts in higher yields as compared to the imidazole catalyzed reactions.

Phenanthridine synthesis through iron-catalyzed intramolecular N-arylation of O-acetyl oxime.

O-Acetyl oximes derived from 2'-arylacetophenones undergo N-O bond cleavage/intramolecular N-arylation in the presence of a catalytic amount of iron(III) acetylacetonate in acetic acid. In combination with the conventional cross-coupling or directed C-H arylation, the reaction offers a convenient route to substituted phenanthridines.

Facile Access to Ring-Fused Aminals via Direct α-Amination of Secondary Amines with ortho-Aminobenzaldehydes. Synthesis of Vasicine, Deoxyvasicine, Deoxyvasicinone, Mackinazolinone and Ruteacarpine.

Secondary amines undergo redox-neutral reactions with aminobenzaldehydes under conventional and microwave heating to furnish polycyclic aminals via amine α-amination/N-alkylation. This unique α-functionalization reaction proceeds without the involvement of transition metals or other additives. The resulting aminal products are precursors for various quinazolinone alkaloids and their analogues.