Oxidative transformation of azides to aryl nitriles using DIB/TBHP: scope and mechanistic insights

Bis(tert-butylperoxy)iodobenzene, generated in situ by the reaction between diacetoxyl iodobenzene (DIB) and tert-butyl hydroperoxide (TBHP), was used in the oxidative transformation of primary azides to nitriles, and secondary azides to ketones.     

可溶性聚合物支持的二醋酸碘苯在合成吡唑啉衍生物中的应用

聚乙二醇支持的二醋酸碘苯作为可溶性聚合物试剂可在温和的反应条件下将醛的苯基腙氧化成为腈亚胺中间体，该中间体进而可与丙烯酸甲酯发生1，3-偶极环回成反应，以良好的产率和完全的区域选择性生成吡唑啉衍生物。     

Efficient oxidative ipso-fluorination of para-substituted phenols using pyridinium polyhydrogen fluoride in combination with hypervalent iodine(III) reagents

Diacetoxyiodobenzene (PIDA) and bis(trifluoroacetoxy)iodobenzene (PIFA) in the presence of pyridinium polyhydrogen fluoride (PPHF) are effective for the fluorination of para-substituted phenols to give a variety of 4-fluorocyclohexa-2,5-dienones in a good yield. (R,S)-1,1′-Bi-5,6,7,8-tetrahydro-2-naphthol (and its monoacetate) yields atropoisomeric fluorocyclohexadienones. The 4-substituted carbamate open-chain phenols were readily converted to fluorohydroindolenone and fluorohydroquinolenone derivatives by intramolecular conjugate addition.     

A convenient phosphoryloxylactonization of pentenoic acids with catalytic hypervalent iodine(III) reagent

A novel and convenient catalytic method for phosphoryloxylactonization of pentenoic acids is available: the cyclization of 4-pentenoic acids with phosphates using iodobenzene as a recyclable catalyst in combination with m-chloroperbenzoic acid as the terminal oxidant was easily carried out in CF₃CH₂OH at room temperature, giving phosphoryloxylactons in good yields, some of them had two diastereoisomers.     

Stereoselective synthesis of δ-heteroaryl substituted β-hydroxy-γ,δ-unsaturated α-amino acids

Enantiomerically pure δ-heteroaryl substituted β-hydroxy-γ,δ-unsaturated α-amino acids were stereoselectively synthesized starting from (2R)-(+)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine (Schöllkopf’s reagent) and suitable β-heteroaryl-α,β-unsaturated aldehydes. The stereocontrolled addition gave a mixture of two diastereoisomers whose configurations were assigned on the basis of spectroscopic data and the accepted model for aldol condensation of the Schöllkopf’s reagent. Upon controlled hydrolysis the adducts were transformed into the corresponding methyl esters of δ-heteroaryl substituted β-hydroxy-γ,δ-unsaturated α-amino acids.     

Trichloroacetonitrile–hydrogen peroxide: a simple and efficient system for the selective oxidation of tertiary and secondary amines

A variety of tertiary and secondary amines were efficiently oxidized to their corresponding N-oxides and nitrones, respectively, using the trichloroacetonitrile–hydrogen peroxide system. The in situ generated trichloromethylperoxyimidic acid is the active reagent for the oxidation processes.     

Hypervalent Iodine in Synthesis. 90. A Mild and Efficient Method for the Iodination of Pyrazoles

Abstract

The combined reagent of iodobenzene diacetate (or polymer-supported iodobenzene diacetate) with iodine was used as an effective iodinating agent of pyrazoles to the corresponding 4-iodopyrazole derivatives at room temperature with high yields.     

2,4,6-Tris(4-iodophenoxy)-1,3,5-triazine as a new recyclable “iodoarene” for in situ generation of hypervalent iodine(III) reagent for α-tosyloxylation of enolizable ketones

The synthesis of 2,4,6-tris[(4-iodo)phenoxy)]-1,3,5-triazine 6, as a new recyclable nonpolymeric analogue of iodobenzene is achieved using the reaction of 2,4,6-trichloro-1,3,5-triazine with 4-iodophenol in the presence of KOH. The application of 6 as a recyclable ‘iodoarene’ is demonstrated for α-tosyloxylation of enolizable ketones via in situ generation of hypervalent iodine(III) species using PTSA and MCPBA as the terminal oxidant. The recyclability of the reagent 6 was possible owing to the facile recovery and reuse from the reaction mixture due to its near insolubility in methanol.     

Oxidative rearrangement of alkenes using in situ generated hypervalent iodine(III)

A novel protocol for the oxidative rearrangement of alkenes using in situ generated hypervalent iodine(III) was developed. This approach uses inexpensive, readily available, and stable chemicals (PhI, mCPBA, and TsOH) giving rearrangement products in yields comparable to those obtained using the more expensive commercially available [hydroxy(tosyloxy)iodo]benzene [HTIB or Koser’s reagent]. Additionally, an alternative protocol for the synthesis of 1-methyl-2-tetralone through the one-step epoxidation/rearrangement of 4-methyl-1,2-dihydronaphthalene using mCPBA and TsOH was developed.     

Cross—Coupling of Aryl Iodides with Malononitrile Catalyzed by Palladium N—Heterocyclic Carbene Complex System

Eight N-heterocyclic carbenes (NHC),generated in situ from their imidazolium salts,as ligands of palladium complexes were used for the catalytic coupling of iodobenzene with malononi-trile anion,It was found that 1,3-bis(2,4,6-trimethylphenyl)-imidazolium chloride (IMesHCl)-Pd2(dba)3 catalytic system has the highest activity to obtain phenyl malononitrile among the imidazolium salts.The substituted iodoarenes reacted with malononitrile anions by using the catalytic system to give cross-coupling products in yields from 50% to 96%.     

An unexpected oxidation of unactivated methylene C-H using DIB/TBHP protocol

An in situ generated hypervalent iodine species, bis(tert-butylperoxy)iodobenzene, was used as a peroxy radical source for the oxidation of unreactive, remote, and isolated alkyl (cyclic or aliphatic) esters and amides to the corresponding keto compounds under very mild conditions.     

Separations of a-hexachlorocyclohexane (a-HCH) and pentachlorocyclohexene (PCCH) enantiomers on a cyclodextrin-phase (Cyclodex-B) by HRGC/ECD

The separation of a-hexachlorocyclohexane and of all eight possible pentachlorocyclohexene isomers into their enantiomers by high-resolution gas chromatography and electron capture detection was achieved by using permethylated β-cyclodextrin in DB 1701 (Cyclodex-B, J & W) as chiral stationary phase. The first step in the metabolism of 1,2,3,4,5,6-hexachlorocyclohexane (HCH) is the formation of 1,3,4,5,6-pentachlorocyclohexene-1 (PCCH). Various degradation experiments were carried out with α-, β-, γ-, and δ-HCH. Whereas β-HCH gave no degradation products, the isomers α-, γ-, and δ-HCH degraded into various PCCHs and trichlorobenzenes, when using pyridine as dehydrochlorination reagent in xylene at 60°C. Isomerization into other HCH isomers was observed only for δ-HCH. Enantioselective dehydrochlorination was observed for a- and γ-HCH using the alkaloid (?)-brucine, R-(+)- or S-(?)-a-phenylethylamine as chiral base.     

A convenient method for the preparation of oxazaborolidine catalyst in situ using (S)-α,α-diphenylpyrrolidinemethanol,tetrabutylammonium borohydride,and methyl iodide for the asymmetric reduction of prochiral ketones

An oxazaborolidine catalyst is readily prepared in situ at 25 °C in THF using (S)-α,α-diphenylpyrrolidinemethanol and borane generated from tetrabutylammonium borohydride/CH₃I reagent system. The oxazaborolidine/BH₃ reagent system prepared in this way is useful for the reduction of prochiral ketones to the corresponding alcohols with up to 99% ee.     

Pinene-derived iminodiacetic acid (PIDA): a powerful ligand for stereoselective synthesis and iterative cross-coupling of C(sp3) boronate building blocks

Efficient access to chiral C(sp(3)) boronates in stereochemically pure form is critical for realizing the substantial potential of such building blocks in complex-molecule synthesis. We herein report that a pinene-derived iminodiacetic acid (PIDA) ligand enables the highly diastereoselective synthesis of a wide range of oxiranyl C(sp(3)) boronates from the corresponding olefins. These oxiranyl PIDA boronates, in turn, can be readily transformed into unprecedented stable α-boryl aldehydes via a novel 1,2-migration of the boronate group that proceeds with complete maintenance of stereochemical purity. B-Protected haloboronic acids containing dual sp(3)-hybridized C centers are readily accessible via this platform, and the herein demonstrated capacity for stereocontrolled iterative C(sp(3)) cross-coupling with this novel type of bifunctional reagent to access a medicinally important chiral small-molecule target in highly enantioenriched form represents a substantial advance for the building-block-based approach to synthesis.     

Hypervalent Iodine Catalyzed Cyclization of Aryl‐Substituted Alkanoic Acids

A novel and efficient procedure was developed for direct preparation of aryl‐substituted lactones from corresponding aryl‐substituted alkanoic acids, catalyzed by the in situ generated hypervalent iodine intermediate from iodobenzene (PhI). In this protocol, aryl‐substituted alkanoic acids were treated with m‐chloroperbenzoic acid (mCPBA) and KBr in the presence of a catalytic amount of PhI in 2,2,2‐trifluoroethanol at room temperature for 24 h, resulting in corresponding aryl lactones in moderate‐to‐good yields.     

Efficient phenolic oxidations using μ-oxo-bridged phenyliodine trifluoroacetate

The excellent oxidizing behavior of the μ-oxo-bridged phenyliodine trifluoroacetate 1 is revealed during the phenolic oxidations mediated by hypervalent iodine(III) reagents. The use of the μ-oxo-bridged compound 1 instead of PhI(OAc)₂ (PIDA) and PhI(OCOCF₃)₂ (PIFA) during the oxidative cyclization of phenols involving carbon-oxygen, carbon-nitrogen, and carbon-carbon bond formations could produce spirocyclized cyclohexadienones in comparable or somewhat better yields. Thus, we have concluded that the unique reagent 1 is a promising alternative to PIDA and PIFA, and the use of reagent 1 as a reasonable choice is recommended for the hypervalent iodine(III)-mediated phenolic oxidations as well as other transformations.     

Cross-metathesis of C-allyl iminosugars with alkenyl oxazolidines as a key step in the synthesis of C-iminoglycosyl alpha-amino acids. A route to iminosugar containing C-glycopeptides

[structures: see text] A general access to a novel class of sugar alpha-amino acids composed of iminofuranose and iminopyranose residues anomerically linked to the glycinyl group through an alkyl chain is described. A set of eight compounds was prepared by the same reaction sequence involving as an initial step the Grubbs Ru-carbene-catalyzed cross-metathesis (CM) of various N-Cbz-protected allyl C-iminoglycosides with N-Boc-vinyl- and N-Boc-allyloxazolidine. The isolated yields of the CM products (mixtures of E- and Z-alkenes) varied in the range 40-70%. Each mixture was elaborated by first reducing the carbon-carbon double bond using in situ generated diimide and then unveiling the N-Boc glycinyl group [CH(BocNH)CO2H] by oxidative cleavage of the oxazolidine ring by the Jones reagent. All amino acids were characterized as their methyl esters. The insertion of a model C-iminoglycosyl-2-aminopentanoic acid into a tripeptide via sequential carboxylic and amino group coupling with L-phenylalanine derivatives was carried out as a demonstration of the potential of these sugar amino acids in designed glycopeptide synthesis.     

Selective and sensitive determination of peptides using 3,4-dihydroxyphenylacetic acid as a fluorogenic reagent

A novel fluorescence (FL) reaction for N-terminal Gly-containing peptides has been developed using 3,4-dihydroxyphenylacetic acid (3,4-DHPAA). The reaction of the peptides with 3,4-DHPAA was carried out in borate buffer (pH 8.0) in the presence of sodium periodate at 37 °C for 10 min, and the FL was measured with a spectrofluorimeter at the excitation and emission wavelengths of 370 nm and 465 nm, respectively. The 3,4-DHPAA reagent generated particularly strong FL for peptides containing Gly at their N-termini. When various other bio-substances, such as amino acids, sugars, nucleic bases, nucleotides, and proteins, were reacted with 3,4-DHPAA, no FL was observed. Under optimized reaction conditions, the lower detection limit of 0.25 μmol L⁻¹ was obtained for the N-terminal Gly-containing peptides of Gly-Pro (GP) and Gly-Pro-Pro (GPP), which gave 3 times greater FL intensity than that observed for the reagent blank. The proposed reaction with 3,4-DHPAA as a fluorogenic reagent is selective and sensitive for the detection of N-terminal Gly-containing peptides, and therefore, this method could be a useful tool for the determination of these particular oligopeptides.     

Direct arylation of benzoxazole C-H bonds with iodobenzene diacetates

A Pd (OAc)₂-catalyzed direct arylation of benzoxazole C-H bonds has been achieved with iodobenzene diacetates as the arylation reagent in moderate to good yields. The procedure tolerates a series of functional groups, such as methoxy, nitro, cyano, chloro, and bromo groups.     

Facile evolution of asymmetric organocatalysts in water assisted by surfactant Brønsted acids

Simple mixing of chiral amines and surfactant Brønsted acids such as p-dodecyl benzenesulfonic acid (DBSA) leads to highly effective and selective organocatalysts in water. The in situ generated catalysts catalyze highly stereoselective desymmetrization of prochiral ketones via direct aldol reactions (up to >16:1 dr, >99% ee) in water using micelle as reaction media. The current strategy was also applied in asymmetric Michael addition leading to a catalytic system with good activity and stereoselectivity.