Abstract  Mild and efficient AuCl3/AgOTf-catalyzed Pictet-Spengler reactions were developed to afford in good yields a variety of tetrahydroisoquinoline and tetrahydro-beta-carboline ring systems, which constitute important motifs in biologically active natural and synthetic organic compounds.

Abstract  Reaction of [Cp*TiMe3] with O(SiPh2OH)2 yields the titanium siloxide derivative [Cp*TiMe{(OSiPh2)2O}]. Complex reacts with H2O to yield the corresponding oxo-titanium derivative [(Cp*Ti{(OSiPh2)2O})2(micro-O)]. The molecular structure of complex has been established by X-ray diffraction. Complex reacts with triphenylsilanol to give the asymmetric titanium siloxide [Cp*Ti(OSiPh3){(OSiPh2)2O}]. Treatment of the dinuclear titanium compound [(Cp*TiCl2)2(micro-O)] with an equimolar amount of O(SiPh2OH)2 yields complex [(Cp*TiCl)2{micro-(OSiPh2)2O}(micro-O)] in which the disiloxide moiety is bridging two titanium atoms. The structure of has been determined by X-ray diffraction. Reaction of [Cp*TiMe3] with HOSiPh3 yields the titanium triphenylsiloxide [Cp*TiMe2(OSiPh3)]. Complex reacts with water to yield [{Cp*TiMe(OSiPh3)}2(micro-O)]. The triflate compound [Cp*Ti(OSiPh3)2(OTf)] can be prepared by reaction of with HOTf and triphenylsilanol. We have tested the catalytic activity of some of the complexes in the epoxidation of cyclohexene.

Abstract  Indanones and coumarins are important intermediates for the convenient synthesis of many pharmaceutical and biologically active compounds. Fluoroorganics play a vital role in the design of very effective therapeutics due to significant enhancenment in their lipophilicity, bioavailability, and fast uptake by the presence of fluorine in these molecules. Herein, we report an efficient one-pot synthesis of trifluoromethylated arylpropanoic acids, indanones, and dihydrocoumarins using Friedel-Crafts alkylation or tandem Friedel-Crafts alkylation-cycloacylation of arenes/phenols with 2-(trifluoromethyl)acrylic acid under superacidic conditions using trifluoromethanesulfonic acid. The results have been rationalized by the structure energy calculations of the involved reaction intermediates using ab initio theoretical methods.

Abstract  Silicon-functionalized SynPhase Lanterns are useful for the combinatorial synthesis of small-molecule libraries. Lanterns bearing an alkyl tethered diisopropylarylsilane are first activated with triflic acid to afford the corresponding diisopropylsilyl triflate, which is then reacted with a library scaffold bearing a free alcohol. Once the scaffold has been loaded onto the solid phase, a variety of transformations can be run, including amine cappings, cross-coupling reactions and amide bond formation. These reactions can yield a variety of products when run sequentially using split-pool synthesis strategies. Upon completion of the solid-phase transformations, the small-molecules are released from the Lanterns using HF/pyridine. Using the techniques described within, libraries can be made ranging from a few compounds to >10,000 members in a highly efficient manner.

Abstract  The borate-insoluble chitin-protein complex, CB-I, from prepupal sarcophagid larvae was cleaved with chymotrypsin and trifluoromethanesulfonic acid releasing a polypeptide fragment of Mr 68 000. The intact glycoprotein was blocked at the C terminus; the N-terminal sequence of Asp-Val-Ala-His-Tyr was not homologous with seven of the borate-soluble nonglycosylated structural proteins. Bityrosine was identified as a component of the primary chain, both half-residues occupied in peptide linkages. Sclerotization initiated a decline in bityrosine coincident with the addition of soluble proteins to the tanned matrix. The chitin-protein complex also included bound peroxidase, propolyphenol oxidase, and an o-diphenol subject to oxidation on activation of the zymogen. In the course of the oxidation N termini declined in accordance with the formation of 1,4 quinonoid cross-links.

Abstract  The mechanism of the Brønsted acid-catalyzed aza-Darzens reaction is explored by charting the stereochemical outcome of the triflic acid-promoted conversion of trans-triazolines to cis-aziridines. These experiments are consistent with the intermediacy of an α-diazonium-β-amino ester intermediate.

Abstract  The xylylene moiety (ortho, meta, and para) was employed as a rigid tether in the spacer-mediated synthesis of difructose dianhydrides (DFAs), a unique class of bis-spiroacetal derivatives present in food products. The synthetic methodology exploits the suitability of triflic acid to promote spirocyclization in organic solvents under irreversible reaction conditions, using anomeric isopropylidene fructose derivatives as precursors. Advantage was taken of the strong dependence of the conformational properties of DFAs on the relative configuration of the spiroketal centers. Highly stereoselective syntheses of the contra-thermodynamic difructofuranose and difructopyranose diastereomers, namely the C2-symmetric derivatives having the beta-configuration at both anomeric centers, have been accomplished by judicious choice of the xylylene positional isomer and of the linking position to the fructose building blocks. Interestingly, the rigid spacer concept has also been implemented to favor intermolecular processes leading to higher macrocyclic architectures that incorporate the bis-spiro fructodisaccharide subunit.

Abstract  A variety of aminoalkynes and related heterocycles are reacted in the Bronsted superacid CF(3)SO(3)H (triflic acid), and products are obtained in generally good yields (69-99%) from Friedel-Crafts-type reactions. The reactions are consistent with the formation of novel dicationic intermediates having a vinyl cationic site and an adjacent protonated N-heterocycle or ammonium cation.

Abstract  The hybrid imine/amine palladium(II) coordination complexes [PdX2(kappa2-N(imino),N(amino))](X = Cl, AcO; kappa2-N(imino),N(amino)= 4ClC6H4CHNCH2(CH2)nN(CH3)2, n= 1, 2) have been prepared in different isomeric forms which include E/Z arrangement around the C[double bond]N bond of the hybrid ligand and {Pd(kappa(2)-N(imino),N(amino))} ring conformation. The crystal structures of four of them, E-1AcO, Z-1AcO, E-2AcO and E-2Cl, have been determined and the solution behaviour in acetic acid, the common cyclometallating solvent, for all these systems studied. The complexes in acetic acid solution are shown to maintain the structure determined by X-ray crystallography, as they do in deuterated chloroform. Nevertheless, a partial opening equilibrium of the {Pd(kappa2-N(imino),N(amino))} ring is observed by NMR experiments. When the complexes are held in solution for longer periods the corresponding cyclometallated derivatives, 1AcO-CM, 2AcO-CM, 1Cl-CM and 2Cl-CM, containing the {Pd(kappa2-C,N(imino))} palladacycle are obtained, as characterized by 1H NMR spectroscopy. In these compounds the total opening of the N(amino) moiety of the ligand has occurred. The C-H bond activation process has been studied kinetico-mechanistically at different temperatures, pressures and acid concentrations; the results agree with the need of an opening of the chelate ring in [PdX2(kappa2-N(imino),N(amino))] prior to the proper cyclometallation reaction. The values of the enthalpies of activation are higher than those observed for known N-monodentated cyclometallating ligands, as should correspond to the contribution of a ligand dechelation pre-equilibrium. The entropies and volumes of activation are also indicative of this predissociation that include an important amount of contractive ordering. The presence of small amounts of triflic acid in the reaction medium accelerates the reaction to the value observed for N(imino)-monodentate systems, indicating that the full opening of the chelate ring has taken place. For the badly oriented isomeric forms of the ligand in the chelated complex (Z), the cyclometallation process is even more slow and corresponds directly to the reorganization of the ligand to its cyclopalladation-active (E) conformation.

Abstract  [reaction: see text] Reaction of para-substituted anilines with styrene derivatives at elevated temperatures, when catalyzed by CF3SO3H, results in highly chemoselective ortho-alkylation of the aniline. When R = H, dialkylation can be achieved by varying the ratio of styrene to aniline. Several different substituted anilines and styrenes were examined, and good yields (42-87%) were obtained, except in the case where electron-withdrawing substituents are present on the styrene.

Abstract  Homoallylic phosphine boranes undergo intramolecular hydroboration upon activation by triflic acid. The reaction occurs via an intermediate B-trifluorosulfonyloxyborane complex such as 15, followed by S(N)1-like or S(N)2-like displacement of the triflate leaving group, apparently leading to the formation of a four-center transition state. In the case of trisubstituted double bonds, as in the substrates 29 and 32, ionic hydrogenation of the alkene competes with internal hydroboration.

Abstract  Direct liquid-phase sulfonation of methane to methanesulfonic acid (MSA) with SO2 has been achieved in triflic acid using K2S2O8 as the oxidant and a small amount of a Ca salt as the promoter. The effects of reaction conditions on the conversion of SO2 to MSA were examined. Included were the influence of solvent acidity, reaction duration, reaction temperature, amount of K2S2O8, and composition and amount of promoters.

Abstract  The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of ligands 2-4 and 6 allows for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. With use of Xantphos 5, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkylamine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions.

Abstract  The reaction of 3,5-di-O-benzyl-2-deoxy-d-ribofuranose with various alkynyllithium reagents afforded diastereomeric mixtures of the corresponding ring-opened alkynyldiols. The resulting diastereomeric mixtures were successively treated with Co(2)(CO)(8), a catalytic amount of TfOH, Et(3)N, and iodine in one pot to give alkynyl C-3,5-di-O-benzyl-2-deoxy-beta-d-ribofuranosides with high beta-selectivities. The cobalt-mediated cyclization (intramolecular Nicholas reaction) is reversible; thus, thermodynamically more stable beta-anomers were obtained preferentially. The alkynyl C-deoxyribofuranosides were converted to a variety of C-deoxyribofuranoside derivatives.

Abstract  The infrared spectra of 2,2,2-trifluoroethyl trifluoromethanesulfonate (CF3SO2OCH2CF3) were obtained in the gaseous, liquid and solid states as well as the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory were used to predict the most stable geometry and conformation of the studied molecule. Subsequently, the harmonic vibrational frequencies and force field were calculated. An assignment of the observed spectral features made after comparison with the related molecules and with the predicted frequencies was used as the basis of a scaling of the original force field in order to reproduce as well as possible the experimental frequencies. With this purpose a set of scale factors was calculated by a least square procedure, leading to a final root mean square deviation (RMSD) of 9.7 cm(-1).

Abstract  In the Brønsted superacid CF(3)SO(3)H (triflic acid), amides are able to form reactive, dicationic electrophiles. It is shown that these dicationic intermediates participate in two distinctly different types of electrophilic reactions. The protonated amide increases the reactivity of an adjacent electrophilic group, and the protonated amide group itself shows enhanced reactivity arising from an adjacent cationic charge. In the latter case, several types of amides are even capable of reacting with benzene by Friedel-Crafts acylation. [reaction--see text]

Abstract  Both pivaloyl cation in the presence of hydride donors and protonated pivalaldehyde in superacid media (both aprotic and protic) rearrange to protonated methyl isopropyl ketone involving gitionic dicationic intermediates. In our earlier studies we have found that the rearrangement of pivaladehyde to methyl isopropyl ketone occurs quantitatively in the presence of various superacidic media such as anhydrous HF, triflic acid, boron trifluoride-2,2,2-trifluoroethanol complex (BF(3).2CF(3)CH(2)OH) etc. Our present study with environmentally more benign and stable amine:HF complexes, namely pyridinium poly(hydrogen fluoride) (PPHF) (5), poly(4-vinylpyridinium) poly(hydrogen fluoride) (6), and poly(ethyleniminium) poly(hydrogen fluoride) (PEIHF) (7) shows that these modified HF equivalents can carry sufficient amount of immobilized HF and provide ample acidity for complete isomerization of pivalaldehyde to methyl isopropyl ketone. Calculations on protioformyl, acetyl and pivaloyl dications at the B3LYP/6-311 ++ G(d,p) and CCSD(T)/6-311 ++ G(d,p)//B3LYP/6-311 ++ G(d,p) levels have been performed to compare the nature of protosolvation of formyl, acetyl, pivaloyl cations and protonated pivaladehyde in superacid media. These studies further suggest protosolvation of protonated pivalaldehyde leading to gitionic dications at high acidities resulting in the carbocatioinic rearrangement. The reported carbocationic rearrangement under superacidic activation represents a novel solution chemistry equivalent of the well known gas-phase McLafferty rearrangement.

Abstract  An acidic O-specific polysaccharide was obtained by mild acid degradation of the lipopolysaccharide of Proteus vulgaris O15 and studied by sugar and methylation analyses along with 1H and 13C NMR spectroscopy, including 2D COSY, TOCSY, ROESY, and H-detected 1H,(13)C HMQC experiments. The polysaccharide was found to contain an ether of GlcNAc with lactic acid, and the following structure of the repeating unit was established:-->3)-alpha-D-GlcpNAc4(R-Lac)6Ac-(1-->2)-beta-D-GlcpA-(1-->3)-alpha-L-6dTalp2Ac-(1-->3)-beta-D-GlcpNAc-(1-->where L-6dTal and D-GlcNAc4(R-Lac) are 6-deoxy-L-talose and 2-acetamido-4-O-[(R)-1-carboxyethyl]-2-deoxy-D-glucose, respectively. The latter sugar, which to our knowledge has not been hitherto found in nature, was isolated from the polysaccharide by solvolysis with anhydrous triflic acid and identified by comparison with the authentic synthetic compound. Serological studies with the Smith-degraded polysaccharide showed an importance of 2-substituted GlcA for manifesting of the immunospecificity of P. vulgaris O15.

Abstract  Reactions of metal-metal bonded homobimetallic (Pd(2)) and heterobimetallic (PtPd) complexes, supported by a P,P'-bridging-bis(P,N-chelating) coordination mode of the potentially hexadentate ligand 1,1-bis[di(o-N,N-dimethylanilinyl)phosphino]methane (dmapm), with CO, diethylacetylenedicarboxylate (DEAD), and thiols (RSH) in CH(2)Cl(2) are described. At room temperature, rac-Pd(2)Cl(2)(mu-N,P:P',N'-dmapm) gives the stable complexes Pd(2)Cl(2)(mu-CO)(2)(mu-P:P'-dmapm) and PdCl(eta2-DEAD)(mu-P:P',N-dmapm)PdCl (which is fluxional in solution), while rac-PtPdCl(2)(mu-N,P:P',N'-dmapm) disproportionates to PtCl(2)(P,P'-dmapm) and Pd metal, although at low temperature intermediate carbonyl species are detected in the CO reaction. The reactions with thiols in the presence of triflic acid (HOTf) generate rac-[MPdCl(2)(mu-SR)(mu-N,P:P',N'-dmapm)][OTf] and H(2) for both M = Pt and Pd. In CH(2)Cl(2), PdX(2)(dmapm) species (X = halide or CN) exist as equilibrium mixtures of P,P'- and P,N-ligated forms. For X = Cl, the P,P'-P,N equilibrium is governed by DeltaH degrees = -5.5 +/- 0.5 kJ mol(-1) and DeltaS degrees = 10 +/- 1 J mol(-1) K(-1), and the ring-strain energy within the P,P'-isomer is approximately 32 kJ mol(-1); the equilibrium increasingly favors the P,N-form with X = CN > I > Br > Cl. The solid-state structures of rac-[PtPdCl(2)(mu-SEt)(mu-N,P:P',N'-dmapm)][OTf] and PdCl(2)(P,N-dmapm) are presented; the latter contains both bound and free N- and P-atoms of identical types in the same molecule and permits an assessment of sigma- and pi-bonding between these atoms and Pd.

Abstract  Experiments show that 1,1'-bi-2-naphthol (BINOL) undergoes facile C1-C1' bond cleavage under action of triflic acid at temperatures above 0 °C to give mainly 2-naphthol along with oligomeric material. CASSCF and MRMP//CASSCF computations have demonstrated unambiguously that this unusual mode of scission of the biaryl bond can occur in the C1,C1'-diprotonated form of BINOL via a mechanism involving homolytic cleavage prompted by the intramolecular electrostatic repulsion. These findings also provide insights into the mechanism of a comparatively easy thermal cleavage of BINOL, implying the intermediacy of its neutral diketo form.

Abstract  The 6-O-mesyl derivative of phenyl 1-thio-beta-D-glucopyranoside was prepared from D-glucose as a synthetic equivalent of a 6-deoxy-hexosyl donor. Racemic methyl 11-hydroxytetradecanoate (methyl convolvulinolate) was synthesized by Grignard reaction of propylmagnesium bromide with 10-undecenal followed by hydroboration. Both intermediates were coupled by NIS-TfOH-promoted glycosidation to give a mixture of two diasteromeric glucopyranosides, which were separated on a preparative scale by medium pressure chromatography. One of the products was identified as having the natural (S)-configuration by comparison of its 1H NMR spectrum with an authentic sample prepared from the corresponding chiral hydroxyfatty acid.

Abstract  Triflic acid catalyzed cascade stereoselective reaction of glycals with styrenes delivers complex oxabicyclic scaffolds such as cis-oxadecalins or cis-cyclopentanofurans simply by tweaking the solvent. In the presence of participating solvents like benzene/toluene, cascade Ferrier C-glycosylation and double Friedel-Crafts reaction leads to densely chiral benzo-fused oxadecalins, whereas in DCM, an unprecedented ring-opening, ring-closing sequence generated cis-cyclopentanofurans. An attempt has been made to explain the above cascade sequences via intermediate trapping, kinetic experiments, and Baldwin's rules.

Abstract  Sulfonyl azides have been widely used as sulfonamido, diazo, and azido donors, as well as all-nitrogen 1,3-dipoles donors in synthetic chemistry. Here, the sulfonyl azides were used as efficient sulfonyl donors, which is very unusual. Trifluoromethanesulfonic acid-induced formation of the sulfonyl cation reactive species from sulfonyl azides was developed and used for the first time to couple various inactivated arenes to prepare sulfones at ambient temperature.

Abstract  Addition of 2 equiv of Ce(4+) to the dimeric ruthenium mu-oxo ion cis,cis-[(bpy)(2)Ru(OH(2))](2)O(4+) (formal oxidation state III-III, subsequently denoted [3,3]) or addition of 1 equiv of Ce(4+) to the corresponding [3,4] ion gave near-quantitative conversion to the [4,4] ion, confirming our recent assignment of this oxidation state as an accumulating intermediate during water oxidation by the cis,cis-[(bpy)(2)Ru(O)](2)O(4+) ([5,5]) ion. The rates of water exchange at the cis-aqua positions in the [3,3] and [3,4] ions were investigated by incubating H(2)(18)O-enriched samples in normal water for predetermined times, then oxidizing them to the [5,5] state and measuring by resonance Raman (RR) spectroscopy changes in the magnitudes of the O-isotope sensitive bands at 780 and 818 cm(-1). These bands have been assigned to Ru=(18)O and Ru=(16)O stretching modes, respectively, for ruthenyl bonds formed by deprotonation of the aqua ligands upon oxidation to the [5,5] state. An intermediate accumulated during the course of the isotope exchange reaction that gave a [5,5] ion possessing both approximately 782 and approximately 812 cm(-1) bands; this spectrum was assigned to the mixed-isotope species, (bpy)(2)Ru((16)O)(16)ORu((18)O)(bpy)(2)(4+). Kinetic analysis of solutions at various levels of oxidation indicated that only the [3,3] ion underwent substitution; the exchange rate constant obtained in 0.5 M trifluoromethanesulfonic acid, 23 degrees C, was 7 x 10(-3) s(-1), which is (10(3)-10(5))-fold larger than rate constants measured for anation of monomeric (bpy)(2)Ru(III)X(H(2)O)(3+) ions bearing simple sigma-donor ligands (X).