Oscar R. Suárez-Castillo

Visible-Light-Promoted Au(I) to Au(III) Oxidation in Triazol-5-ylidene Complexes.

Reaction of triazolium precursors [MIC(CH2 )n - H+ ]I- (n=1-3) with potassium hexamethyldisilazane (KHMDS) and AuCl(SMe2 ) generates the gold(I) complexes of the type MIC(CH2 )n ⋅AuI. Visible light exposure of the latter complexes promotes a spontaneous disproportionation process rendering gold(III) complexes of the type [{MIC(CH2 )n }2 ⋅AuI2 ]+ I- . Both the AuI and AuIII complex series were tested in the catalytic hydrohydrazination of terminal alkynes using hydrazine as nitrogen source.

MICROWAVE-ASSISTED SYNTHESIS OF 3,1-BENZOXAZIN-2-ONES FROM 3-HYDROXYOXINDOLES

A general protocol for the synthesis of 3,l-benzoxazin-2-ones 18 from 3-liydroxyoxindoles 16 in a two steps sequence through phenylsuccinates or phenylpropionates 17 is described. Best reaction conditions for ring opening of 16 to succinates or propionates 17 were achieved using alcohol/silica gel, while cyclization of 17 to benzoxazinones 18 was easily done with HCl/alcohol. It was also found that 17 and 18 can be transesterified using HCl/alcohol. Most transformations were carried out by traditional heating and by microwave (MW) irradiation to accelerate reaction rates.

Stereospecific 5JHortho,OMe couplings in methoxyindoles, methoxycoumarins, and methoxyflavones

Long‐range coupling constants 5JHortho,OMe were measured in series of methoxyindoles, methoxycoumarins, and methoxyflavones by the modified J doubling in the frequency domain method. The COSY and NOESY spectra revealed the coupling of the –OMe group with a specific proton at the ortho position and its preferred conformation. Homonuclear 1H–1H couplings were confirmed by irradiation of the –OMe signal. Density functional theory calculations of 5JHortho,OMe using the modified aug‐cc‐pVTZ basis set evidenced that the Fermi contact term shows good agreement with the experimental J values. Accurate chemical shift and coupling constant values followed after iterative quantum mechanical spectral analysis using the PERCH software. Copyright

Cascade [1,3]-sigmatropic rearrangements of ketene O,O-acetals: kinetic and DFT level mechanistic studies.

The regioisomeric alpha-cyano ketene-O,O-dialkyl acetals 2a-e and 4a-e, sequential intermediates in the diazomethane induced conversion of indole alpha-cyano-gamma-lactones 1a-e to 2-indolyl cyanomalonates 5a-e, were isolated and characterized. Formation of the steady-state intermediate cycloprop[b]indoles 3a-e was evidenced by means of NMR and confirmed by the X-ray structure of 3c, demonstrating that the formation of 5a-e from 2a-e proceeds through two consecutive and one parallel unimolecular steps, with intermediates 3a-e formed in reversible processes. Evidence that the reversible reactions proceed via [1,3]-rearrangements is presented. The steady-state kinetic approach applied to intermediate 3 allowed a minimal two consecutive step 2 --> 4--> 5 kinetic model, in which the steric bulkiness of the alkyl substituent affects strongly the associated rate constants, k(1) and k(2), inverting the rate-determining step. The solvation effects enhanced the feasibility of these skeletal rearrangements as they stabilized the transition states to a great extent. The experimental determined thermodynamic parameters and DFT calculations suggest that these cascade rearrangements occur through [1,3]-sigmatropic mechanisms, in which asynchronous bond reorganization processes via four membered pseudopericyclic transition states are highly favorable.

The absolute configuration of cuauhtemone and related compounds

Abstract The absolute configuration of cuauhtemone, a eudesmane-type sesquiterpene isolated from Pluchea species (Asteraceae), has been revised from 1 to 2 by chemical correlation with (R)-(+)-2-methyl-1,2-butanediol 3 through the naturally occurring 2,3-epoxy-2-methylbutanoate derivative 4. The relative stereochemistry of 4 was confirmed by X-ray diffraction analysis. The obtained data are also useful for reconsideration of the absolute configurations of a relevant group of natural products, which were elucidated according to the stereochemistry of cuauhtemone.

Regioselective Synthesis of 3-Indolyl(alkoxy)acetates

The regioselective synthesis of N-carbomethoxy-2-alkoxyindolenines and a-alkoxyindoles is reported. Brornination of indole 5 with NBSlAIBNlCC14 gave a-bromoindole 6 which after treatment with ROHI3A molecular Sieves afforded (Z-) and (E)-2-alkoxyindolenines 8a-d as the main products, together with minor amounts of a-alkosyindoles 9a-d. The reversed regioselectivity was achieved in the absence of molecular Sieves to give a-alkoxyindoles 9a-d as the main products, while no traces of Z- or E-8a-d were detected.

Structure elucidation of configurational isomers of nitrile-substituted spirocyclopropyloxindoles by NMR spectroscopy, molecular modeling, and X-ray crystallography.

Keywords: NMR; 1H-NMR; 13C-NMR; spirooxindoles; cyclopropanes; anisotropy; X-ray crystallography; DFT calculations

Unimolecular rearrangements of ketene‐O,O‐acetals and fragmentations occurring in the gas phase

Gas phase skeletal rearrangements of regioisomeric 3-cyano-2-methoxy-3a-alkylfuro[2,3-b]- and [3,2-b]indoles were evidenced by product ions [M-32](+•), consistent with loss of methanol, on electron ionization in their mass spectra. The rearranged products occurring in gas phase were demonstrated to have elemental composition and fragmentation properties identical to those of authentic samples of 2-indolyl cyanomalonates. Isotopic labeling experiments support the formation mechanism of the [M-32](+•) ion. Additional thermal gas-phase reaction products were characterized by comparison with an authentic sample.

Expedient Synthesis of Highly Functionalized Abnormal Carbenegold(I) Complexes

The reaction of 4-substituted imidazol-2-ylidenes with various electrophiles produces a series of 2,4-functionalized imidazolium salts. Subsequent metalation of these precursors using AuCl(SMe2) provides the first examples of highly functionalized abnormal carbenegold(I) complexes. The present protocol introduces a new strategy for the synthesis of metallic abnormal carbenes featuring diverse functional groups.

Complete 1H NMR assignment of 3-formylindole derivatives.

3-Formylindoles including indolylglyoxylate esters and indolylglyoxylamides are widely found in nature as alkaloids, and are important building blocks or synthetic intermediates for drug discovery, and for the synthesis of natural products. A careful inspection of the H NMR data of these molecules reveals that multiplicities for H4 and H7 are reported as broad doublets, as doublet of doublets-like, as a combination of doublet of doublets and multiplets, or simply as doublets. In the case of H5 and H6, they are reported as triplet of doublets, as triplets, or as doublet of triplets despite the fact that in most cases, their chemical shifts are claimed to be unambiguously assigned. In addition, incorrect coupling constant values for the incorrect multiplicities for H4–H7 are also reported. A prudent signal description of the H4–H7 system is rarely given asmultiples without reporting coupling constant values. Consequently, we describe herein complete and accurate chemical shift and coupling constant assignments for H4–H7 in representative series, using compounds 1–10, which followed after spectral analysis using the PERCH software and selective proton irradiations.