Methylations catalyst

Oxirane, 2-lithio-2-triphenylsilyl-, 7, 25 Oxirane, methyl-catalyst... 

Thiazolium chloride, 3-benzyl-5-(2-hydroxyethyl)-4-methyl-catalyst... 

The B-methyl catalysts were prepared by reacting the aminoalcohol with trimethyl-boroxine, followed by an azeotropic distillation with toluene. 

Some chiral quaternary ammonium salts are also effective in Michael addition reactions. The Merck catalysts 7 (R=4-CF3, X=Br) and 9 (R=4-CF3, X=Br, 10,11-dihydro) were used tor the Michael additions of 59,61, and 64 to vinyl ketones to give the adducts 60,62, and 65 (isolated as 66), respectively,148,491 with excellent enantioselectivity, as shown in Scheme 19. The Michael addition of the O Donnell imine 23 to the a,(3-unsaturated carbonyl compounds also efficiently proceeded by use of the N-anthracenyl-methyl catalyst 12 (R=allyl, X=Br), giving the Michael adducts 67 (Scheme 20).1251... 

Researchers at Sepracor later disclosed the use of a new class of chiral oxazaborolidines derived from r/. v-aminoindanol in the enantioselective borane reduction of a-haloketones.6,7 The 5-hydrogen oxazaborolidine ligand 10 was prepared in situ from d,v-aminoindanol 1 and BH3 THF.8 Stock solutions of 5-methyl oxazaborolidine 11-16 were obtained by reaction of the corresponding N-alkyl aminoindanol with trimethyl boroxine.6,7 5-Methyl catalyst 11 was found to be more selective (94% ee at 0°C) than the 5-hydrogen catalyst 10 (89% ee at 0°C), and enantioselectivities with 11 increased at lower temperatures (96% ee at -20°C). The catalyst structure was modified by introduction of A-a I kyI substituents. As a general trend, reactivities and selectivities decreased as the steric bulk or the chelating ability of the A -alkyl substituent increased (Scheme 17.4). 

Borane reduction of a variety of aromatic ketones using 5-10 mol% of 5-methyl catalyst 11 proceeded in >95% yield and in 80-97% ee. a-Haloketones were generally more reactive (90-97% ee) than simple ketones, which required higher temperatures (0°C compared to -20°C) to react to completion and led to lower enantioselectivities (80-90% ee).118 A complementary study by Umani-Ronchi and co-workers37 described the borane reduction of cyclic and acyclic ketones using catalyst 10. All products were obtained in >89% yield and >85% ee. Cyclic and hindered ketones led to the highest enantioselectivities (up to 96% ee) at room temperature. 

The reaction is relatively mild and proceeds readily with the use of 0.2-0.3% sodium methylate catalyst at an operating temperature of 70-75°C and at atmospheric pressure. 

The asymmetric total synthesis of prostaglandin Ei utilizing a two-component coupling process was achieved in the laboratory of B.W. Spur. The hydroxylated side-chain of the target was prepared via the catalytic asymmetric reduction of a y-iodo vinyl ketone with catecholborane in the presence of Corey s CBS catalyst. The reduction proceeded in 95% yield and >96% ee. The best results were obtained at low temperature and with the use of the B-n-butyl catalyst. The 6-methyl catalyst afforded lower enantiomeric excess and at higher temperatures the ee dropped due to competing non-catalyzed reduction. 

To 1341b of an aqueous solution of sorbitol (contains 5% water) in an autoclave is added 225 gm sodium methylate catalyst and the mixture is heated to 70°C. 

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