Oxidations of Deformyl-3-Isogeissoschizine

The conversions of deformyl-3-isogeissoschizine into its indole-inverted isomer by an oxidation-reduction sequence and into its oxindole equivalent by an oxidation scheme are described.     

A [3+2] dipolar cycloaddition route to 3-hydroxy-3-alkyl oxindoles: an approach to pyrrolidinoindoline alkaloids

A [3 + 2] cycloaddition approach to the 3-hydroxy-3-alkyl oxindole scaffold is described. Isoxazolines obtained by cycloaddition of nitrile oxide 3 with 3-methylene oxindoles were elaborated to 3-hydroxy-3-cyanomethyl oxindoles employing a one-pot protocol en route to the pyrrolidinoindoline moiety which is found in many natural products. The total syntheses of alkaloids (±)-alline and (±)-CPC-1 were achieved using this methodology.     

Bicyclic guanidine-catalyzed asymmetric Michael additions of 3-benzyl-substituted oxindoles to N-maleimides

A bicyclic guanidine-catalyzed Michael addition of 3-benzyl substituted oxindoles to N-maleimides has been developed to produce oxindole derivatives with a quaternary carbon chiral center at the 3-position in excellent yields and enantio- and diastereoselectivities. This is the first incorporation of N-benzylic α-branched succinimides into 3,3-disubstituted oxindoles.     

Organocatalytic stereoselective conjugate addition of 3-substituted oxindoles with in situ generated ortho-quinone methides

A novel method for the stereoselective conjugate addition of 3-substituted oxindoles to in situ generated o-QMs was described. This process was catalyzed efficiently by a cinchonidine-derived squaramide catalyst in oil-water phase, furnishing the corresponding 3,3-disubsituted oxindole derivatives in moderate to high yields (up to 98%) with high stereoselectivities (up to 95%?ee, 15.4:1?dr). The utility of this reaction was also investigated by the gram-scale synthesis and derivatization of one of the products.     

Pd-catalyzed synthesis of 3-(diarylmethylene)-2-oxindoles and 3-(arylmethylene)-2-oxindoles

An efficient method for the stereoselective synthesis of 3-(diarylmethylene)-2-oxindoles and 3-(arylmethylene)-2-oxindoles via carbopalladation is described. In this approach, an Ugi-4-component reaction (4-CR) adduct was used as the starting material. A one-pot sequence involving intermolecular carbopalladation C-H activation/C-C bond formation efficiently afforded the oxindole derivatives.     

Organocatalytic asymmetric conjugate addition of 3-monosubstituted oxindoles to (E)-1,4-diaryl-2-buten-1,4-diones: a strategy for the indirect enantioselective furanylation and pyrrolylation of 3-alkyloxindoles

An asymmetric conjugate addition of 3-monosubstituted oxindoles to a range of (E)-1,4-diaryl-2-buten-1,4-diones, catalyzed by commercially available cinchonine, is described. This organocatalytic asymmetric reaction affords a broad range of 3,3'-disubstituted oxindoles that contain a 1,4-dicarbonyl moiety and vicinal quaternary and tertiary stereogenic centers in high-to-excellent yields (up to 98%), with excellent diastereomeric and moderate-to-high enantiomeric ratios (up to 99:1 and 95:5, respectively). Subsequently, cyclization of the 1,4-dicarbonyl moiety in the resultant Michael adducts under different Paal-Knorr conditions results in two new kinds of 3,3'-disubstituted oxindoles--3-furanyl- and 3-pyrrolyl-3-alkyl-oxindoles--in high yields and good enantioselectivities. Notably, the studies presented here sufficiently confirm that this two-step strategy of sequential conjugate addition/Paal-Knorr cyclization is not only an attractive method for the indirect enantioselective heteroarylation of 3-alkyloxindoles, but also opens up new avenues toward asymmetric synthesis of structurally diverse 3,3'-disubstituted oxindole derivatives.     

DBU-Catalyzed, facile and efficient method for synthesis of spirocyclic 2-oxindole derivatives with incorporated 6-amino-4H-pyridazines and fused derivatives via [3+3] atom combination

3-Cyanomethylidene oxindole derivatives were prepared in excellent yields utilizing DBU-promoted Knoevenagel condensation of isatin derivatives with active methylene reagents. The isolated products were then reacted with azaenamines via a DBU-promoted Michael addition to yield spirocyclic 2-oxindole derivatives with incorporated 6-amino-4H-pyridazines and their fused derivatives.     

Iridium catalysed C-3 alkylation of oxindole with alcohols under solvent free thermal or microwave conditions

Ir-catalysed alkylation of oxindole and N-methyl oxindole with a range of substituted benzyl and heteroaryl alcohols under solvent free thermal or microwave conditions afforded the corresponding C-3-monoalkylated products in high to excellent yield.     

An Organocatalytic Mannich/Denitration Reaction for the Asymmetric Synthesis of 3‐Ethylacetate‐Substitued 3‐Amino‐2‐Oxindoles: Formal Synthesis of AG‐041R

The highly enantioselective organocatalytic addition of ethyl nitroacetate to isatin‐derived N‐Boc ketimines (Boc=tert‐butoxycarbonyl), followed by the removal of the nitro group, is described. The scalable reaction sequence leads to the title compounds as important intermediates of pyrroloindoline alkaloids and related drugs in excellent yields and enantioselectivities. The synthesis of the hexahydrofurano[2,3‐b]indole skeleton, the spirocarbamate oxindole unit, and the formal synthesis of AG‐041R have been carried out to demonstrate the synthetic utility of this protocol.     

An Imidazoline–Aminophenol (IAP) Nickel Catalyst: Structure and Catalytic Activity in the Enantioselective 1,4‐Addition of 3′‐Indolyl‐3‐Oxindoles to Nitroethylene

The structure of a nickel complex of imidazoline–aminophenol (IAP) prepared from IAP with Ni(OAc)₂ was elucidated as cis‐bis(imidazolineaminophenoxide) [Ni(IAP)₂]. The [Ni(IAP)₂] complex smoothly promoted catalytic asymmetric 1,4‐addition of 3′‐indolyl‐3‐oxindole to nitroethylene to provide chiral mixed 3,3′‐bisindoles with high enantioselectivities. Mechanistic studies using ESI‐MS analyses suggest that one IAP ligand dissociated from [Ni(IAP)₂] to generate the Ni–enolate of 3′‐indolyl‐3‐oxindole. From the optically active 3,3′‐mixed indole adduct, biologically important 3′‐indolyl‐3‐pyrrolidinoindoline was successfully synthesized in a three‐step reaction sequence.     

新型3,3′-吡咯双螺环氧化吲哚类化合物的有机催化不对称合成

以3-异硫氰氧化吲哚(1)与3-烯氧化吲哚(2),经济易得的有机奎宁作为有机催化剂,在二氯甲烷溶剂中发生Michael加成环化反应,合成了12个未见文献报道的3,3′-吡咯双螺环氧化吲哚类化合物3a^3l,产率81%~92%,ee值86%~>99%,dr值7/1~>20/1,其结构经1H NMR,13C NMR和HR-MS(ESI-TOF)表征。通过培养3c(CCDC:1961579)和3j(CCDC:1961580)单晶,确定其绝对构型为(2′R,3′S,4′R)。     

多相CeO2催化剂上氧化吲哚与醛的选择性C3烯基化反应

本文报道了将市售CeO2作为一种高活性和可重复使用的催化剂用于无溶剂条件下氧化吲哚与醛的C3选择性烷基化反应.这种催化方法一般适用于不同的芳香族和脂肪族醛,得到3-烷基二烯-辛醇,产率高(87%–99%),立体选择性高(79%–93%为E-异构体).这是从氧化吲哚与各种脂肪族醛催化合成3-烯基氧化吲哚的首例.采用原位红外光谱研究了CeO2上Lewis酸位点与苯甲醛之间的Lewis酸-碱相互作用.不同粒径CeO2催化剂的构效关系研究表明,无缺陷CeO2表面是该反应的活性中心.     

Catalytic Enantioselective Carboannulation with Allylsilanes

The first catalytic asymmetric carboannulation with allylsilanes is presented. The enantioselective [3+2] annulation is catalyzed using a scandium(III)/indapybox complex with tetrakis‐[3,5‐bis(trifluoromethyl)phenyl]‐borate (BArF) to enhance catalytic activity and control stereoselectivity. Functionalized cyclopentanes containing a quaternary carbon center are derived from alkylidene oxindole, coumarin, and malonate substrates with high stereoselectivity. The enantioselective 1,4‐conjugate addition and enantioselective lactone formation (by trapping of the β‐silyl carbocation) is also described.     

An expedient synthesis of 3-alkylideneoxindoles by Ti(OPr)4/pyridine-mediated Knoevenagel condensation

3-Alkylideneoxindoles have been prepared in excellent yields from oxindole and carbonyl compounds via an in situ generated titanium enolate of oxindole. (Z)-3-Alkylideneoxindoles could be synthesized selectively as major products from unsymmetrical ketones.     

An atypical easy reductive cleavage of the conjugated CC bond in 1,1′-disubstituted isoindigos under the action of aqueous hydrazine hydrate

The reaction of diverse symmetrically-substituted isoindigo derivatives with 80% aqueous hydrazine hydrate is described. The influence of the structure of the substituent on either oxindole or isatin-3-hydrazone formation is discussed.     

2,4‐Dinitrophenol‐Catalyzed α‐C(sp3)−H and C(sp)−H Bond Functionalization of Cyclic Amines and Alkynes: Highly Regio‐/Diastereoselective Synthesis of α‐Alkynyl‐3‐Amino‐2‐Oxindoles

A transition‐metal‐ and oxidant‐free DNP (2,4‐dinitrophenol)‐catalyzed atom‐economical regio‐ and diastereoselective synthesis of monofunctionalized α‐alkynyl‐3‐amino‐2‐oxindole derivatives by C?H bond functionalization of cyclic amines and alkynes with indoline‐2,3‐diones has been developed. This cascade event sequentially involves the reductive amination of indoline‐2,3‐dione by imine formation and cross coupling between C(sp³)?H and C(sp)?H of the cyclic amines and alkynes. This reaction offers an efficient and attractive pathway to different types of α‐alkynyl‐3‐amino‐2‐oxindole derivatives in good yields with a wide tolerance of functional groups. The salient feature of this methodology is that it completely suppresses the homocoupling of alkynes. To the best of our knowledge, this is the first example of a DNP‐catalyzed metal‐free direct C(sp³)?H and C(sp)?H bond functionalization providing biologically active α‐alkynyl‐3‐amino‐2‐oxindole scaffolds.     

Organocatalytic Asymmetric Conjugate Addition of 3‐Monosubstituted Oxindoles to (E)‐1,4‐Diaryl‐2‐buten‐1,4‐diones: A Strategy for the Indirect Enantioselective Furanylation and Pyrrolylation of 3‐Alkyloxindoles

An asymmetric conjugate addition of 3‐monosubstituted oxindoles to a range of (E)‐1,4‐diaryl‐2‐buten‐1,4‐diones, catalyzed by commercially available cinchonine, is described. This organocatalytic asymmetric reaction affords a broad range of 3,3′‐disubstituted oxindoles that contain a 1,4‐dicarbonyl moiety and vicinal quaternary and tertiary stereogenic centers in high‐to‐excellent yields (up to 98 %), with excellent diastereomeric and moderate‐to‐high enantiomeric ratios (up to 99:1 and 95:5, respectively). Subsequently, cyclization of the 1,4‐dicarbonyl moiety in the resultant Michael adducts under different Paal–Knorr conditions results in two new kinds of 3,3′‐disubstituted oxindoles—3‐furanyl‐ and 3‐pyrrolyl‐3‐alkyl‐oxindoles—in high yields and good enantioselectivities. Notably, the studies presented here sufficiently confirm that this two‐step strategy of sequential conjugate addition/Paal–Knorr cyclization is not only an attractive method for the indirect enantioselective heteroarylation of 3‐alkyloxindoles, but also opens up new avenues toward asymmetric synthesis of structurally diverse 3,3′‐disubstituted oxindole derivatives.     

An efficient one-pot synthesis of spiro dihydrofuran oxindole and spiro 2-hydroxytetrahydrofuran oxindole derivatives via (3+2) oxidative cycloaddition mediated by CAN

Spiro dihydrofuran oxindole derivatives were prepared via a (3+2) oxidative cycloaddition of 1,3-dicarbonyl compounds to 3-(phenyl-2-oxoethylidene)-1-methyloxindole and 3-benzylidene-1-methyloxindole derivatives mediated by ceric ammonium nitrate. In the case of the reaction of 3-(phenyl-2-oxoethylidene)-1-methyloxindole derivatives with acyclic 1,3-dicarbonyl compounds, spiro 2-hydroxytetrahydrofuran oxindole derivatives were obtained.     

Spiroquinazoline support studies: methods for the preparation of imidazoloindolines from oxindoles

Two methods for the annulation of glycine to the 1 and 2 positions of oxindoles are described. The first method involves introduction of an α-azidoacetyl group on the oxindole nitrogen followed by an intramolecular Staudinger reaction to complete the annulation. The second method involves acylation of the oxindole nitrogen with an N-Cbz-glycine derivative followed by reduction of the oxindole carbonyl group and subsequent cyclization to provide an imidazoloindoline.     

Efficient asymmetric synthesis of novel gastrin receptor antagonist AG-041R via highly stereoselective alkylation of oxindole enolates

An efficient method for asymmetric synthesis of the potent Gastrin/CCK-B receptor antagonist AG-041R was developed. Core oxindole stereochemistry was established by asymmetric alkylation of oxindole enolates with bromoacetic acid esters, using l-menthol as a chiral auxiliary. The key alkylation reaction of the oxindole enolates generated tetrasubstituted chiral intermediates with high diastereoselectivity. The stereoselective alkylation reactions are described in detail.