Oxidation scandium triflate

The methoxymethyl ether protecting groups of 33 were then cleaved using triphenylphosphine and carbon tetrabromide. The resulting hydroquinone function was oxidized by palladium on carbon under an atmosphere of air to afford the quinone 52 (70 %). A two-step procedure was implemented to install the diazo function. First, the ketone function of 52 was condensed with N,N -bis( tert-butyldimethylsilyl)hydrazine in the presence of scandium triflate, which formed the Af-tert-butyldimethylsilyl hydrazone 53. The hydrazone (53) was then oxidized using difluoroiodobenzene to afford kinamycin C (3) in 35 % yield. 

Elsewhere, Faita et al. (438) bound the Evans chiral auxiliary to Wang or Merrifield resin for use as a dipolarophile in cycloadditions with C,N-diphenyl-nitrone. Yields on both resins are significantly reduced in comparison to the solution phase reaction (43-20% compared to 95%) but are unaffected by addition of magnesium perchlorate or scandium triflate catalyst. A one-pot process has been reported by Hinzen and Ley (439) that oxidizes secondary hydroxylamines to the... 

Several catalysts have been found for the ring opening of epoxides. For instance, cyclohexene oxide gave an excellent yield of the trans-fi-amino alcohol when treated with either aromatic or aliphatic amines in the presence of a scandium triflate catalyst.21 Aromatic epoxides react in a regiospeciflc reaction at the benzylic carbon when treated with aromatic amines and scandium triflate but at the least substituted carbon of the epoxide ring when aliphatic amines react. Electronic effects are more important in the reactions of the aromatic epoxides whereas steric factors control the reaction with aliphatic epoxides. 

SC2395>. Reaction of o-phenylenediamine and an aryl aldehyde in the presence of a catalytic amount of scandium triflate Sc(OTf)3 gives 2-(aryl)benzimidazoles in moderate to good yields. In this transformation, oxygen serves as the oxidant (Scheme 302) <2004H(63)2769>. 

It was only in 1995 that the first structure of a hydrated salt of scandium containing only water molecules in its coordination sphere was reported. Refluxing scandium oxide with triflic acid leads to the isolation of hydrated scandium triflate Sc(03SCF3)3 9H20. It is isomorphous with the hydrated lanthanide triflates, containing tricapped trigonally prismatic coordinate scandium in the [Sc(H20)g] ions, with Sc—O (vertices) = 2.171(9) A and Sc—O (face capped) 2.47(2) A. 

Figure 5.27 summarizes our synthesis of (/ )-(+)-143, the opposite enantiomer of the naturally occurring (-)-nocardione B. Commercially available 5-methoxy-l-tetralone (A) was treated with lithium hexam-ethyldisilazide (LiHMDS), followed by (S )-propylene oxide (B) in the presence of scandium triflate in dry toluene to give hydroxy ketone C. The hydroxy group of C was protected as 2,2,2-trichloroethoxycarbonate to give D, and its alicyclic ring was oxidized with selenium dioxide to give E. 

Important variants for the synthesis of benzimidazoles allow the use of aldehydes, rather than acids ytterbium triflate (best for aliphatic aldehydes) or scandium triflate catalyse the condensation and the subsequent air oxidation of the dihydrobenzimidazole immediate product. Incorporating nitrobenzene in the reaction mixture as the oxidant can also be used. orf/to-Nitroanilines can be used by incorporating a reducing agent in the reaction mixture - e.g. hydrogen over palladium or sodium dithionite - for in situ generation of the orffto-phenylenediamine. 2-Aryl-benzothiazoles can be made from 2-aminobenzenethiol, aromatic aldehydes and air, in the presence of activated carbon. ... 

Preparative Methods scandium triflate is commercially available. On the other hand, it can also be prepared from the corresponding oxide (SC2O3) and aqueous trifluoromethanesulfonic acid (TfOH). After filtration and concentration of the clear aqueous solution in vacuo, the resulting hydrated salt is dried in vacuo (< 1 mmHg) at 200 °C for 40 h to afford the anhydrous triflate, which is stored over P2O5. 

Alkylation Using Alkanes. Direct alkylation of pyridines and quinolines using simple alkanes and terf-butyl peroxide as oxidant was developed. This C-C bond forming reaction was carried out by using Sc(OTf)3 as a Lewis acid to increase the reactivity of pyridine and quinoline derivatives (eq 37). Scandium triflate demonstrated the best catalytic activity among the Lewis acids tested. While bis-alkylation product was obtained using quinoline, only mono-alkylation products were afforded when isoquinoline was used. Cycloheptane, cyclohexane, and norbornane were determined to be suitable reaction partners. 

In 2012, Chi et al. disclosed an oxidative y-addition of enals to tri-fluoroacetophenone for the synthesis of unsaturated 5-lactones 114 under NHC catalysis. Scandium triflate/magnesium triflate as relatively strong Lewis acid cocatalysts were found to be effective for enantiocontrol involving the relatively remote enal y-carbon (Scheme 20.49). 

Reddy VP, Kumar V, Rao KR (2010) Copper oxide nanoparticles catalyzed vinylation of imidazoles with vinyl halides under ligand-free conditions. Tet Lett 51 3181-3185 Dandia A, Parewa V, Rathore KS (2012) Synthesis and characterization of CdS and Mn doped CdS nanoparticles and their catalytic application for chemoselective synthesis of benzimidazoles and benzothiazoles in aqueous medium. Catal Comm 28 90-94 Itoh T, Nagata K, Ishikawa H, Ohsawa A (2004) Synthesis of 2-arylbenzothiazoles and imidazoles using scandium triflate as a catalyst for both a ring closing and an oxidation steps. Heterocycles 63 2769-2783... 

Table 8.3 Oxidation of sulfides in the presence of catalytic amounts of scandium triflate.

Catalytic amounts of scandium triflate [Sc(OTf)3] were found to greatly increase the rate of oxidation of sulfides by 60% H2O2 [30] The reaction is run at room temperature in methylene chloride containing 10% ethanol. The reaction shows quite a high selectivity for sulfoxide with sulfones being formed in only 2-4%. 

Related to the nitrile oxide cycloadditions presented in Scheme 6.206 are 1,3-dipolar cycloaddition reactions of nitrones with alkenes leading to isoxazolidines. The group of Comes-Franchini has described cycloadditions of (Z)-a-phenyl-N-methylnitrone with allylic fluorides leading to enantiopure fluorine-containing isoxazolidines, and ultimately to amino polyols (Scheme 6.207) [374]. The reactions were carried out under solvent-free conditions in the presence of 5 mol% of either scandium(III) or indium(III) triflate. In the racemic series, an optimized 74% yield of an exo/endo mixture of cycloadducts was obtained within 15 min at 100 °C. In the case of the enantiopure allyl fluoride, a similar product distribution was achieved after 25 min at 100 °C. Reduction of the isoxazolidine cycloadducts with lithium aluminum hydride provided fluorinated enantiopure polyols of pharmaceutical interest possessing four stereocenters. 

It is a commonplace to say that there has been explosive growth in the use of lanthanides in organic chemistry. For many years, the use of cerium(iv) compounds as oxidants was widespread, but more recently a whole range of other compounds have made their appearance. Thus samarium(ii) compounds are now routinely used as one-electron reducing agents and the use of trifluoromethanesulfonate ( triflate ) salts of scandium and the lanthanides as water-soluble Lewis acid catalysts is widespread. Beta-diketonate complexes and alkoxides have also come into use there are even applications of mischmetal in organic synthesis. 

Dibromobiphenyl 210 and the amine 209 were prepared in five and ten steps, respectively. The double Buchwald-Hartwig coupling of 209 and 210 using 0.2 equiv. of tris(dibenzylideneacetone)dipalladium, 0.6 equiv. of 2-dicyclohexyl-phosphino-2, 4, 6 -triisopropylbiphenyl (X-Phos), and 3 equiv. of sodium ferf-but-oxide in toluene at 130°C in a sealed tube afforded the carbazole 213 in 59% yield (Scheme 50) [206]. Subsequent treatment with scandium(III) triflate resulted in removal of the MOM group, cleavage of the ketal, and subsequent Friedel-Crafts-... 

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