Cerium triflate

Selective oxidation of methyl pyrroles 65 possessing an a-carboxylic ester and sensitive p-substituents can be accomplished using cerium triflate in methanol <96TL315>. Moreover, the resultant a-methoxymethylpyrroles 66 may be converted to dipyrrylmethanes 67 in a "one-pot" sequence by treatment with 48% HBr. The dipyrrylmethanes, in turn, can be further oxidized to dipyrryl ketones by ceric ammonium nitrate <96JHC221>. 

In another example, a catalytic amount of cerium triflate hydrate was dispersed and isolated in [BMIMJPFg for the direct formation of tetrahydropyranol derivatives. The reaction involves a simple homoallyl alcohol and an aldehyde. When an organic solvent such as chloroform was employed, an undesired ether derivative formed as the major product. In the ionic liquid, however, the desired tetrahydropyranol was exclusive. Although the yield was moderate, this example constitutes the first relatively facile and direct formation of the synthetically useful pyranol derivative the only effective catalyst reported is the ionic liquid (168). 

In subsequent studies, methyl vinyl ketone (2.0 mmole) was chosen as the dienophile so as to determine the combined effect of the ionic liquid (2 mL) and the Lewis acids (0.2 and 0.5 wt%) upon the yield and selectivity. Without the Lewis acid catalyst, this system demonstrated a 52% conversion of the cyclopentadiene (2.2 mmol) in 1 h with the endojexo selectivity being 85/15. The cerium triflate-catalyzed reaction was quantitative in 5 min and the endo. exo selectivity was very good for this experiment as well (94 6, endo. exo). Also with the scandium or yttrium salts tested, reactions came to completion in a short time with high stereo-selection. Cerium, scandium and yttrium triflates are strong Lewis acids known to be quite effective catalysts in the cycloadditions of cyclopentadiene with acyclic aldehydes, ketones, quinones and cycloalkenones. These compounds are expected to act as strong Lewis acids because of their hard character and the electron-withdrawing triflate group. On the other hand, reaction times of 1 hour were required for... 

Cerium(IV) trifluoromethanesulfonate [cerium triflate, Ce(0S02CF3)4 H2O, Ce(OTf)4 H2O] [698999-65-4] M 736.4 (anhydrous), slowly decomposes above 120 to give trivalent cerium species. 

Tetrahydropyranol derivatives in ionic liquid were prepared by the reaction of homoallyl alcohols and an aldel de (Scheme 11.50) in the presence of the catalyst cerium triflate [108],... 

The [(Me3C)2C5H5]3Ce analog (Sofield and Andersen 1995) has been obtained from cerium triflate and [(Me3C)2C5H3]2Mg (in ratio 1 1.5). The same reaction with... 

Dalpozzo R, De Nino A, Maiuolo L, Procopio A, Tagarelli A, Sindona G, Bartoli G (2002) Simple and efficient chemoselective mild deprotection of acetals and ketals using cerium(III) triflate. J Org Chem 67 9093-9095... 

Yamashiro et al. 1972), boron trifluoride etherate in acetic acid (Schnabel et al. 1971), trimethylsylil triflate (Schmidt et al. 1987), trimethylsilyl perchlorate (Vorbrueggen Krolikiewicz 1975), and, most frequently, trifluoroacetic acid (Farowicki Kocienski 1995 and references therein). Deprotection of the /-HOC group under neutral conditions was not described until recently, yet it is highly desirable. Now it has been found that the tert-butoxycarbonyl protecting group for amines, alcohols, or thiols is removed efficiently (90-99% yield) with use of 0.2 equivalent of cerium ammonium nitrate in acetonitrile at 80°C (Hwu et al. 1996) ... 

With this end in view, phenyldimcthylsilyl tri-n-butylstannane was added under the influence of zero-valent palladium compound with high regioselectivity and in excellent yield to the acetylene 386 to give the metallated olefin 387 (Scheme 56). The vinyl lithium carbanion 388 generated therefrom, was then converted by reaction with cerium(lll) chloride into an equilibrium mixture (1 1) of the cerium salts 389 and 390 respectively. However, the 1,2-addition of 389 to the caibonyl of 391, which in principle would have eventually led to ( )-pretazettine, did not occur due to steric reasons — instead, only deprotonation of 391 was observed. On the other hand, 390 did function as a suitable nucleophile to provide the olefinic product 392. Exposure of 392 to copper(II) triflate induced its transformation via the nine membered enol (Scheme 55) to the requisite C-silyl hydroindole 393. On treatment with tetrafluoroboric acid diethyl ether complex in dichloromethane, compound 393 suffered... 

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. 

Table 7 Reaction of thiiranes with NuH cerium(iv) triflate...

Addition of zinc(II) chloride to the lithium compound 4 gave the zinc derivative 6, which is stable even at 50 °C in tetrahydrofuran. The palladium-catalyzed coupling reaction of the zinc salt with vinyl iodides, vinyl triflates and aryl iodides produced vinyl and aryl derivatives 7 and 8 (Table 1, entries 11-16). Cerium derivatives of cyclopropenone acetals were prepared by addition of the lithium salt 4 to a suspension of anhydrous cerium(III) chloride in tetrahydrofuran at — 70 C. The resulting organocerium reagent coupled with oc-aminoaldehydes (Table 1, entry 17). ° ... 

All the lanthanide(m) triflates are commercially available from the Aldrich Chemical Co. bar Promethium (radioactive) and Cerium (available in its 44 oxidation state). 

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