Magnesium triflate. catalyst

Magnesium triflate and zinc triflate are outstanding catalysts for the intro duction of the thioketal group for the protection of the ketone function [126] The reaction of a variety of ketones with ethane 1,2-dithiol in the presence of these triflates proceeds under mild conditions to form the corresponding thioketals in high yield (equation 62)... 

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... 

Takacs, J.M., Lawson, E.C., Reno, M.J., Youngman, M.A. and Quincy, D.A. (1997) Enantioselective Diels—Alder reactions Room temperature bis(oxazoline)-zinc, magnesium, and copper triflate catalysts. Tetrahedron Asymmetry, 8, 3073—3078. 

Since the addition of dimethylpyrazole to an isocyanate is reversible by heating at 60°C, the product (10) is known as a blocked isocyanate . Now, it has been shown that magnesium triflate, Mg(OTf)2, is highly active as a catalyst in the reaction at 60 °C between an acid and a blocked isocyanate to give an amide. Thus blocked hexyl isocyanate (10) and heptanoic acid (11) when heated in equimolar quantities in CHCI3 at reflux for 1 h in the presence of 1 mol% Mg(OTf)2 gave a quantitative yield of IV-heptyloctamide (12) with evolution of CO2.6... 

Thioketalization.1 Zinc (or magnesium) triflate is an efficient catalyst for thioke-talization with 1,2-ethanedithiol, particularly in the cases of acid-sensitive ketones and highly hindered ketones (e.g., camphor ethane dithioketal, 99% yield). A4-Cholestenone is converted into the corresponding dithioketal cleanly with zinc triflate, but into a 4 1 mixture of the A4- and A5-cholestenone dithioketals with magnesium triflate. In general, zinc triflate is more effective than magnesium triflate. 

Simple imines undergo Diels-Alder reactions in the presence of suitable catalysts. Lanthanide triflates, which are stable in water, are especially effective. Thus in the presence of 10 mol% of ytterbium or scandium triflate, Danishefsky s diene 4 reacts with benzylideneaniline in acetonitrile at 0 °C to give the dihydropyridone 76 quantitatively (equation 50) analogous products are obtained from 4 and furylideneaniline, benzyli-denebenzylamine and pentyIidenebenzylamine. In a one-pot version of the reaction, a mixture of an aldehyde, an amine and the diene 4 in acetonitrile containing magnesium sulfate is treated with 10 mol% ytterbium triflate to afford the dihydropyridone in ca 80% yield. Even phenylglyoxal monohydrate can be employed. ... 

In the example in Scheme 1.170, the TJ-alkene is formed from the -alkenyl halide. Likewise, the Z-alkene is formed selectively from the Z-alkenyl halide. Alkenyl tri-llates are also good substrates for alkylation with organocuprate reagents. Treatment of the alkenyl triflate 170 with methyl magnesium bromide and copper(I) iodide as catalyst, gave the alkylated product 171, used in a synthesis of paeonilactone A (1.171). 27... 

In 2009, Seidel and co-workers reported a Lewis acid-catalyzed [l,5]-hydride transfer reaction for the synthesis of polycyclic tetrahydroquinolines. It was found that the gadolinium triflate could efficiently accelerate the reaction (Scheme 4.4a). Preliminary attempts to realize asymmetric catalysis revealed that when a chiral magnesium bisoxazoline was utilized as the catalyst, the desired product 6a could be obtained in 74% yield and 30% ee, which was the first example of a catalytic asymmetric [l,5]-hydride transfer reaction by a chiral Lewis acid (Scheme 4.4b). The reason for the relatively low enanti-oselectivity was attributed to the reversibility of the ring-closure step in the presence of a strong Lewis acid catalyst. 

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