TFA catalyst

The major diastereomer seen with each of the rhodium(II) catalysts surveyed was 36a, leading to 41a (Tab. 16.7). For the TFA catalyst (entry 5) a significant proportion... 

Alkanes also undergo carboxylation with CO, as shown in Scheme 2. Carboxylation of alkanes to carboxylic acids is one of the interesting and important functionalization processes. The first example of carboxylation of alkanes was performed on cyclohexane using a Pd(0Ac)2/K2S208/TFA catalyst system [2]. This carboxylation reaction was extended to gaseous alkanes, for example methane, ethane, and propane. Thus, acetic acid (AcOH) was synthesized from methane and CO in the presence of a Pd catalyst but with a low conversion yield [3]. Recently, the acetic acid synthesis was much improved by using vanadium catalysts such as VO(acac)2 and afforded AcOH almost quantitatively [4],... 

There are two values of surface area and volume of nitrogen adsorbed (BJH method), obtained with the parent H-Y zeolite and the H-Y/TFA sample (Table 1) the first corresponds to the zeolite-type micropores and the other, to the mesopores. Figure 1 shows the pore size distribution of the H-Y/TFA catalyst there is a sharp peak (not shown here) in the micropore region and another peak at 4nm in the mesopore region. Such a bimodal pore size distribution was also observed with the parent zeolite. 

Figure 1 Pore size distribution (mesopore region) of the H-Y/TFA catalyst. V (Volume of nitrogen adsorbed) and D (pore diameter) are expressed in cc/g and nm (10 9 m), respectively.

The reaction of tripyrranes with pyrrolecarboxaldehyde in the presence of TFA catalyst followed by oxidation with chloranil results in a simultaneous oxidative coupling and condensation to generate a meso-free corrole <02OL4233>. A fluorescence receptor based on triaza-18-crown-6 ether combined with two /V-guanidinium groups (and one A-anthracen-9-ylmethyl moiety) could bind several biologically important amino acids in aqueous methanol... 

Reagents and conditions i) NHa, CHjCl2 ii) potassium phthalimide, DMF iii) A/-(hydroxymethyl)- or N-(chioromethyl) phthalimide, GHjClj, TFA, catalyst (HF, CFaSOsH, SnClj, FeCIa) iv) A/-(hydroxymethyl)-trifluoracetamide v) NHaNHj HjO, EtOH vi) KOH, EtOH... 

The bifunetional amine la TFA catalyst was further recognised to affect the intramoleeular aldol reaction of tricarbonyl substrates, yielding bi-cyclo[4.3.0]nonane derivatives with high enantioselectivities (Scheme 9.4). ... 

Alkanes such as methane, ethane, propane, and cyclohexane also undergo carboxylation with CO. The first example of carboxylation of alkanes was performed on cyclohexane using a Pd(0Ac)2/K2S208/TFA catalyst system (Scheme... 

The ROP of TMC initiated with several alcohols was examined by Endo s group.It was found that the reactions proceeded without acidic catalyst in low conversions. However, when the polymerization was carried out in the presence of alcohol/trifluoroacetic acid (ROH/TFA) catalyst system the corresponding PCs with Mn = 2500-6800 were formed. The molecular weights increased with an increase of the monomer conversion. Mechanistic aspects studied by NMR spectroscopy indicated that carbonate rings are activated by TEA. The signals of the methylene protons shifted to lower fields by 0.06-0.11 ppm in the NMR spectra after the addition of TEA. Downfield shifts of the carbonyl carbon atom signals in TMC were observed by 3.94-4.15 ppm in the C NMR spectra. 

A series of chiral boron catalysts prepared from, e.g., N-sulfonyl a-amino acids has also been developed and used in a variety of cycloaddition reactions [18]. Corey et al. have applied the chiral (S)-tryptophan-derived oxazaborolidine-boron catalyst 11 and used it for the conversion of, e.g., benzaldehyde la to the cycloaddition product 3a by reaction with Danishefsky s diene 2a [18h]. This reaction la affords mainly the Mukaiyama aldol product 10, which, after isolation, was converted to 3a by treatment with TFA (Scheme 4.11). It was observed that no cycloaddition product was produced in the initial step, providing evidence for the two-step process. 

HPLC High Performance Liquid Chromatography LHRH Lutenizing Hormone Releasing Hormone PTC Phase transfer catalyst SPPS Solid Phase Peptide Synthesis TFA Trifluoro acetic acid... 

We initially tested Candida antarctica lipase using imidazolium salt as solvent because CAL was found to be the best enzyme to resolve our model substrate 5-phenyl-l-penten-3-ol (la) the acylation rate was strongly dependent on the anionic part of the solvents. The best results were recorded when [bmim][BF4] was employed as the solvent, and the reaction rate was nearly equal to that of the reference reaction in diisopropyl ether. The second choice of solvent was [bmim][PFg]. On the contrary, a significant drop in the reaction rate was obtained when the reaction was carried out in TFA salt or OTf salt. From these results, we concluded that BF4 salt and PFg salt were suitable solvents for the present lipase-catalyzed reaction. Acylation of la was accomplished by these four enzymes Candida antarctica lipase, lipase QL from Alcaligenes, Lipase PS from Burkholderia cepacia and Candida rugosa lipase. In contrast, no reaction took place when PPL or PLE was used as catalyst in this solvent system. These results were established in March 2000 but we encountered a serious problem in that the results were significantly dependent on the lot of the ILs that we prepared ourselves. The problem was very serious because sometimes the reaction did not proceed at all. So we attempted to purify the ILs and established a very successful procedure (Fig. 3) the salt was first washed with a mixed solvent of hexane and ethyl acetate (2 1 or 4 1), treated with activated charcoal and passed into activated alumina neutral type I as an acetone solution. It was evaporated and dried under reduced... 

Treatment of a mixture of alcohol 10 and chiral imidate 67 with catalytic TfOH only afforded a 1.2 to 1.3 1 mixture of 18 19 in a combined HPLC assay yield of 91%. Clearly, under these conditions, the reaction was proceeding under an SN1 reaction pathway. The use of other acid catalysts (TMSOTf, HC1, H2S04, TFA, MsOH) in a variety of solvent systems and under a number of reaction conditions did not improve the diastereomeric ratio of 18 19 (typically 1.2 1), or simply resulted in no reaction. 

Other electrophilic substitution reactions on aromatic and heteroaromatic systems are summarized in Scheme 6.143. Friedel-Crafts alkylation of N,N-dimethyl-aniline with squaric acid dichloride was accomplished by heating the two components in dichloromethane at 120 °C in the absence of a Lewis acid catalyst to provide a 23% yield of the 2-aryl-l-chlorocydobut-l-ene-3,4-dione product (Scheme 6.143 a) [281]. Hydrolysis of the monochloride provided a 2-aryl-l-hydroxycyclobut-l-ene-3,4-dione, an inhibitor of protein tyrosine phosphatases [281], Formylation of 4-chloro-3-nitrophenol with hexamethylenetetramine and trifluoroacetic acid (TFA) at 115 °C for 5 h furnished the corresponding benzaldehyde in 43% yield, which was further manipulated into a benzofuran derivative (Scheme 6.143b) [282]. 4-Chloro-5-bromo-pyrazolopyrimidine is an important intermediate in the synthesis of pyrazolopyrimi-dine derivatives showing activity against multiple kinase subfamilies (see also Scheme 6.20) and can be rapidly prepared from 4-chloropyrazolopyrimidine and N-bromosuccinimide (NBS) by microwave irradiation in acetonitrile (Scheme... 

Hydroarylations of alkynes are catalyzed by gold complexes and these bear some resemblance to the Fujiwara Pd-catalyzed reaction. In general, when using gold chemistry, better Z/E selectivities are observed compared with palladium, lower catalyst loadings and milder conditions (neutral not TFA) are used. The mechanism involves the attack of ArH on the Au-coordinated alkyne. Flowever, electron-poor acetylenes only appear to work with palladium chemistry (Equations (75) and (76)).72... 

The intermolecular reaction of phenols with propiolic esters occurs in the presence of a Pd(OAc)2 catalyst to afford coumarin derivatives directly.48,48a An exclusive formation of 5,6,7-trimethoxy-4-phenylcoumarin is observed in the Pd(OAc)2-catalyzed reaction of 3,4,5-trimethoxyphenol with ethyl phenylpropiolate in TFA (Equation (46)). Coumarin derivatives are obtained in high yields in the cases of electron-rich phenols, such as 3,4-methylenedioxyphenol, 3-methoxyphenol, 2-naphthol, and 3,5-dimethylphenol. A similar direct route to coumarin derivatives is accomplished by the reaction of phenols with propiolic acids (Equation (47)).49 A similar reaction proceeds in formic acid at room temperature for the synthesis of coumarins.50,50a Interestingly, Pd(0), rather than Pd(n), is involved in this reaction. 

Interestingly, Co(OAc)2 has been found to be an efficient catalyst for the carboxylation of propane.105,105a For example, the reaction of propane (1 atm) with CO (30 atm) in the presence of Co(OAc)2 (0.1 mmol) and K2S2Og (10 mmol) in TFA gave butyric acids in 58% yields based on propane (Equation (80)). 

The Pd-catalyzed reaction of simple arenes and nitriles provides a useful synthesis of aromatic ketones.120 The reaction of toluene and benzonitrile in the presence of Pd(OAc)2 as a catalyst in DMSO and TFA gives diarylketones (Equation (92)). The presence of DMSO is essential in this reaction. 

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