Samarium triflate

Treatment of V-acyloxazolidinone 122 with hydroxylamines using samarium triflate as a Lewis acid gives the corresponding hydroxamic acids 123 in 50-98% yields at room temperature (Scheme 61). The conversion proceeds with a high degree of chemoselectivity and without racemization of chiral centers at the a-position to the acyl group. 

The diastereoselective cycloaddition of 2-phenyl-4-dimethylamino-l-thia-3-azabuta-l,3-diene with a choice of dienophiles and in the presence of a Lewis acid provides a convenient route to 5,6-dihydro-4//-l,3-thiazines <2002TL6067, 2004T1827>. The more stable /ra r-adducts are produced exclusively. The approach using (4A)-3-acryloyl-4-benzyloxazolidin-2-one 198 provides access to the chiral 5,6-dihydro-4//-l,3-thiazine 199 <2004T1827>. The exceptional level of selectivity is only achieved when magnesium bromide is used. The chiral auxiliary was removed by reaction with lithium benzoxide to give the benzyl ester 200, and reaction with catalytic amount of samarium triflate and methanol provides the methyl ester 201 (Scheme 21). 2-Substituted-5,6-dihydro-l,3-thiazines are conveniently synthesized from nitriles or thiocyanates and 4-mercapto-2-methylbutan-2-ol to produce... 

Treatment of A-acyloxazolidinones with hydroxylamines using samarium triflate as a Lewis acid, afforded the corresponding hydroxamic acids in good yields <02OL3343>. 

Chang, G X, Lowary, T L, A glycosylation protocol based on activation of glycosyl 2-pyridyl sulfones with samarium triflate, Org. Lett., 2, 1505-1508, 2000. 

The three-coordinate 16-electron nickel complex (dtbpe)Ni=GPh2 was obtained by N2 extrusion from the diphenyldiazomethane complex (dtbpe)Ni(N,N N2GPh2), dtbpe= l,2-bis(di-/ r/-butylphosphino)ethane, in the presence of a catalytic amount of samarium triflate (Equation (10)). ... 

Fukuzawa S-I, Yahara Y, Kamiyana A, Hara M, Kikuchi S (2005) Stereoselective pinacol coupling of chiral formylferrocene using divalent samarium triflate preparation of a new chiral bisferrocenyl oxazoline ligand and its application to asymmetric Diels-Alder reactions. Org Lett 7 5809-5812... 

Evans and Wu have prepared complexes derived from PyBOx ligands and samarium or gadolinium triflates that were efficient for the Diels-Alder reaction between various quinones and dienes [102] (see Scheme 38 for an example). 

Thus, samarium(III)-triflate-promoted reactions provided O-linked disaccharides in moderate to excellent yields [308]. Szeja and Niemiec reported the use of 5-nitro-S-pirydyl glucoside as glycosyl donors in P-glucosidase-catalyzed glycosylation of alcohols [494]. 

A samarium(ll) species can also be obtained by reduction of samarium(m) bromide with lithium metal (Equation (27)) or samarium(lll) triflate with r r-butyllithium (Equation (28))4 Proportionation between 1 equiv. of samarium(O) and 2 equiv. of a samarium(m) species can also be employed for generation of a samarium(ll) species (Equations (29) and (30)). 

Samarium(ii) triflate without halide ions, Sm(OTf)2(CH3CN)i,s, can be generated by treatment of samarium with... 

Samarium(ll) triflate, a halogen-free samarium(ll), can also be prepared by disproprotionation of samarium(iii) triflate and samarium(O) in DMF in the presence of a catalytic amount of mercury. 

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. 

Samarium(II) triflate, a promising reagent for selective organic synthesis, has been prepared by treatment of a THF solution of Sm(OTf )3 with 1 equiv of an or-ganolithium (or organomagnesium) reagent at room tempeature [69,70] (Scheme 28). Generation of the samarium(II) was unsuccessful in the presence of HMPA. 

Zriba, R., Bezzenine-Lafollee, S., Guibe, R, Magnier-Bouvier, C. TL 48, 8234 (2007). Samarium(III) triflate. 

It is well known that transition metal-catalyzed carbon-carbon bond formations are extraordinarily difficult with sterically hindered, electron-rich aryl triflates.However, just such a transformation was required to install the Z-propenyl fragment necessary for the samarium-mediated cyclization. Lauren s initial attempts to achieve this goal afforded predominantly detriflated material and capricious reactions leading to loss of biaryl enantiopurity. 

Glycosylation. Samarium(III) triflate catalyzes the reaction of glycosyl 2-pyridyl sulfones with alcohols. This method is applicable to the preparation of di- and trisaccharides containing both furanose and pyranose residues. The difference in reactivity from... 

Samarium(II) triflate-nickek Alkylations. Samarium II taining catalytic amounts of H with NiF for condensation of ki... 

Alkylations. Samarium(II) triflate is prepared by reduction with Sm in DME containing catalytic amounts of Hg. The solvated product is freed of solvent and combined with Nil2 for condensation of ketones and acrylic esters to afford y-lactones. 

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