An efficient HCl promoted Petasis reaction of 2-pyridinecarbaldehydes,amines and 1,2-oxborol-2(5H)-ols

A Petasis reaction of 2-pyridinecarbaldehydes with various amines and 4-substituted 1,2-oxaborol-2(5H)-ols was developed. In the presence of HCl, the reaction proceeded smoothly under very mild conditions and the corresponding desired products were obtained in medium to excellent yields. This method allows the access a wide range of highly functionalized allylic alcohols, which might be useful compounds in medicinal and material chemistry.     

A green protocol for the one-pot multicomponent Petasis boronic Mannich reaction using ball milling

Solvent-free reactions of salicylaldehyde with various boronic acids and amines were accomplished under ball-milling conditions to achieve the corresponding alkyl- and arylaminophenols in good to excellent yields. This simple protocol offers advantages such as high yields, shorter reaction times, simple workup procedure and eco-friendliness.     

An improved protocol for the selective hydroaminomethylation of arylethylenes

The hydroaminomethylation of arylethylenes with anilines proceeds under mild conditions in the presence of [Rh(cod)₂BF₄] and dppf as catalyst system to give the corresponding branched amphetamine derivatives in good selectivity and yield.     

对Niementowski反应的改进

在三氯氧磷存在下,以甲酰胺和邻氨基苯甲酸类化合物为原料,用改进的Niementowski反应合成了5种喹唑啉酮化合物：6-X-4(3H)-喹唑啉酮(X=NO2,Cl,Br,I)和1-(呋喃-2-甲基)-6-磺酰胺基-7-氯-4(1H)-喹唑啉酮,并对该反应的历程进行了初步探讨。     

An improved microwave assisted protocol for Yonemitsu-type trimolecular condensation

Due to the presence of the indole ring in a number of bioactive compounds, novel methods for the preparation of polyfunctionalized indole derivatives are of great interest. The combined use of Lewis acid catalysis and microwave irradiation furnished satisfactory results in the Yonemitsu-type trimolecular condensation of indoles with aldehydes and 1,3-dicarbonyl compounds, such as malonates and acetoacetates.     

An efficient catalytic protocol for the Pauson-Khand reaction

New experimental conditions have been developed for an efficient catalytic Pauson-Khand reaction. These are based on the use of a mixture of molecular sieves and tert-butanol as inducers of the process. This mixture, with the appearance of a paste, is able to adsorb CO, thus improving the conversion and making it possible to effect the reactions in the absence of a CO atmosphere. The protocol is applied to known and unknown substrates and compared to previously described conditions, showing good results with intra- and intermolecular examples.     

An improved protocol for ligandless Suzuki-Miyaura coupling in water

Using a reverse order of addition of reagents, PdCl₂ and Pd(OAc)₂ are efficient catalysts for the Suzuki-Miyaura reactions in water. The ligandless and mild conditions, the high stability of the catalytic system, short reaction time and good to excellent yields are important features of this protocol.     

On the use of boronates in the Petasis reaction

Alcohols are solvents of choice to react boronates, aldehydes and either primary or secondary amines. Thus, while the reaction proceeds sluggishly, or not at all, in aprotic solvents, the desired aminoacids are in most cases obtained in high yields when conducted in methanol or hexafluoro-iso-propanol. In the case of secondary amines, microwave activation is shown to strongly accelerate the process without altering the yields.     

An improved potential energy surface for the F+H2 reaction

A new ground state potential energy surface has been developed for the F+H₂ reaction. Using the UCCSD(T) method, ab initio calculations were performed for 786 geometries located mainly in the exit channel of the reaction. The new data was used to correct exit channel errors that have become apparent in the potential energy surface of Stark and Werner [J. Chem. Phys. 104 (1996) 6515]. While the entrance channel and saddlepoint properties of the Stark–Werner surface are unchanged on the new potential, the exit channel behavior is more satisfactory. The exothermicity on the new surface is much closer to the experimental value. The new surface also greatly diminishes the exit channel van der Waals well that was too pronounced on the Stark–Werner surface. Several preliminary dynamical scattering calculations were carried out using the new surface for total angular momentum equal to zero for F+H₂ and F+HD. It is found that gross features of the reaction dynamics are quite similar to those predicted by the Stark–Werner surface, in particular the reactive resonance for F+HD and F+H₂ survive. However, the most of the exit channel van der Waals resonances disappear on the new surface. It is predicted that the differential cross-sections at low collision energy for the F+H₂ reaction may be drastically modified from the predictions based on the Stark–Werner surface.     

An improved reaction valve for flow injection analysis

Summary A new type reaction valve for flow injection analysis has been developed. In a FIA system with this valve the injected sample is once passed into a loop of the valve, thereafter the valve is rotated to the next position. Therefore, the sample is retained in the loop in a stop-state for a long time and the next sample is introduced into another loop in the next position. When the valve is rotated for one round, the stopped sample in the fist loop is again passed into the detector flow cell. Thus, an analysis, which needs a long reaction time, can be performed with this valve with high precision.

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Verbessertes Reaktionsventil für die Flie\injektionsanalyse

     

A copper-catalyzed Petasis reaction for the synthesis of tertiary amines and amino esters

We have developed a copper-catalyzed process for the coupling of aldehydes, amines, and boronic acids. This allows greater reactivity with simple aryl boronic acids and allows coupling reactions to proceed that previously failed. Initial mechanistic studies support a process involving transmetalation from boron to copper.     

An improved protocol for the RuO4-catalyzed dihydroxylation of olefins

[reaction: see text] Dihydroxylation under ruthenium catalysis provides an easy access to syn-diols, although overoxidation is a common side reaction. Furthermore, the high catalyst loadings offset the lower price of ruthenium compared to osmium. In this paper, we present an improved protocol for the RuO(4)-catalyzed syn-dihydroxylation using only 0.5 mol % catalyst under acidic conditions. A variety of olefins can be hydroxylated in good to excellent yields with only minor formation of side products.     

An improved protocol for the Prins desymmetrisation of cyclohexa-1,4-dienes

Improved conditions are reported for the Prins-pinacol rearrangement of cyclohexa-1,4-diene-derived acetals. The use of triflic acid gives particularly clean reaction, resulting in a mixture of regioisomers in an approximately 10:1 ratio. A tethered version of this reaction is also reported, giving a tricyclic compound with the same stereochemistry as the core of the cladiellin diterpenes.     

An improved protocol for synthesis of N-arylamides and benzoxazoles by the copper-catalyzed reaction of aryl halides with nitriles

An improved protocol for the synthesis of N-arylamides and benzoxazoles by the copper-catalyzed reaction of aryl halides with nitriles has been developed. Use of acetaldoxime as the hydrolysis reagent instead of H₂O facilitates the operation of the reaction. The significantly decreased amount of nitriles, along with use of weak base K₂CO₃ instead of strong base KOH, makes this transformation atom-efficient and environmentally benign. A variety of N-arylamides and benzoxazole derivatives can be synthesized according to this approach.     

An improved Ullmann-Ukita-Buchwald-Li conditions for CuI-catalyzed coupling reaction of 2-pyridones with aryl halides

An effective CuI-trans-N,N′-dimethylcyclohexane-1,2-diamine (DMCDA)-K₂CO₃-catalyzed coupling reaction of 2-pyridones with aryl halides is described. Under our conditions, DMCDA was found to be an effective catalyst that facilitates the coupling reactions even in toluene, a common industrial solvent. In addition, 3-bromopyridine could also be coupled effectively under these conditions, indicating that the catalytic reactivity of this system is high. The reaction could be applied for polymer modification and iterative oligo-pyridone synthesis.     

An improved calculation of the transition state for the F + H2 reaction

Using a large, balanced one-electron basis set, fully optimized reaction space (FORS) calculations to optimize the orbitals and to estimate the internal correlation energy, multi-reference configuration interaction calculations including all single and double excitations out of the FORS reference space to estimate a fraction of the external correlation energy, and the method of scaled external correlation (SEC), we calculate the interaction energy of F with H₂ in the vicinity of the saddle point for the reaction F + H₂ → HF + H. Our calculated barrier height, 1.6 kcal/mol, is considerably lower than values obtained in recent ab initio calculations, and the saddle point geometry is about 0.3 a₀ looser. This indicates that the part of the external correlation energy omitted from MR CISD calculations because of the incompleteness of the one-electron basis set and the truncation of the CI expansion, as estimated by the SEC method, has a significant effect on both the saddle point energy and its geometry.     

A direct synthesis of allenes by a traceless Petasis reaction

A one-pot synthesis of allenes by the 2-nitrobenzenesulfonylhydrazide-mediated coupling of hydroxyaldehydes or ketones with alkynyl trifluoroborate salts is reported. This mild process involves in situ formation of a sulfonylhydrazone that reacts with alkynyl trifluoroborates to generate a transient propargylic hydrazide species. Decomposition of this unstable hydrazide via an intermediate monoalkyldiazine produces the allene products through an alkene walk mechanism.     

Carbon-carbon bond formation via a tandem cationic 2-aza-Cope rearrangement-Lewis acid promoted Petasis reaction

Potassium alkynyltrifluoroborates and potassium (2-phenyl)vinyltrifluoroborates react with N-3-butenyl-(2,2-dichloro-1-propylidene)amine in the presence of BF₃·Et₂O as a Lewis acid to synthesize rearranged Mannich products. The reaction starts with a cationic 2-aza-Cope rearrangement of the imine, followed by the Lewis acid promoted borono-Mannich-type reaction on the rearranged imine to result in a new class of functionalized N-homoallylamines.     

An improved protocol for the Pd-catalyzed alpha-arylation of aldehydes with aryl halides

An improved protocol for the Pd-catalyzed alpha-arylation of aldehydes with aryl halides has been developed. The new catalytic system allows for the coupling of an array of substrates including challenging electron-rich aryl bromides and less reactive aryl chlorides. The utility of this method has been demonstrated in a new total synthesis of (+/-)-sporochnol.     

A new and efficient one-pot synthesis of 2-hydroxy-1,4-dihydrobenzoxazines via a three-component Petasis reaction

The secondary amines synthesized by the reaction between 2-aminophenols and aromatic aldehydes, via the reduction of the corresponding imines, were employed in the synthesis of new 2-hydroxy-2H-1,4-benzoxazine derivatives through a one-pot Petasis multicomponent reaction in good to excellent yields.