Calcium isopropoxide

Calcium isopropoxide complexed to the simplest Ph-BOX ligand serves as a Bronsted base and chiral catalyst for rendering glycine t-butyl ester into a nucleophile toward acrylic esters. 

Kobayashi et al. developed catalytic asymmetric 1,4-additions using chiral calcium species prepared from calcium isopropoxide and chiral bisoxazoline ligands 39, 166 and 168. They found that calcium pyBOX catalysts could effectively mediate catalytic asymmetric additions of 1,3-dicarbonyl compounds 4 to nitroalkenes 86, N-Boc-imines 138 or unsaturated amides 49 giving products 165,167 and 170, respectively. Neutral coordinative ligands worked well in these reactions, giving a noticeably faster rate of reaction... 

While calcium isopropoxide, Ca(0 Pr)2 has been employed successfully in the preparation of chiral catalysts, it was also found that calcium amide (e.g., Ca (HMDS)2) worked well in these reactions as a catalyst. Calcium amides have a stronger Brpnsted basicity and a higher solubility in many solvents compared with calcium alkoxides. Interestingly, it was reported that chiral calcium amide catalysts prepared from Ca(HMDS)2 could be employed successfully in [3+2] cycloaddition reactions (Scheme 4) [48]. 

Aluminium isopropoxide can be obtained as a fine powder from technical sources. When the bottle has once been opened however, the stopper should be firmly replaced and covered with wax more conveniently, the stoppered bottle can be kept in an atmospheric desiccator over calcium chloride or sodium hydroxide, preferably in the dark. 

Commercial tert.-butyl alcohol dried over calcium oxide is suitable for this preparation. Aluminum isopropoxide or ethoxide 2 may be used in place of the aluminum /er/.-butoxide to remove traces of water. The grade of metal known as fast cutting rods has proved most satisfactory. The checkers used turnings made from aluminum cast from melted-down kitchen utensils. Aluminum ferf.-butoxide has also been prepared successfully in another laboratory from commercially pure aluminum (2S) and from rods of the alloy 17ST (communication from L. F. Fieser). The checkers were able to obtain considerably higher yields of the butoxide from pure aluminum than from a copper-bearing alloy. 

It was noticed as early as 1925 that alkoxides of calcium, magnesium and particularly aluminum could catalyze the reduction of aldehydes by ethanol as shown in equation (65).242,243 Removal of very volatile acetaldehyde is easily achieved to drive the reaction to the right. In 1926, Ponndorf devised a method in which both aldehydes and ketones could be reduced to alcohols by adding excess alcohol and aluminum isopropoxide.244 Such reductions are today referred to as Meerwein-Ponndorf-Verley reactions. Although alkoxides of a number of metals, e.g. sodium, boron, tin, titanium and zirconium, have been used for these reactions, those of aluminum are by far the best. 

Ignition on contact with furfuryl alcohol powdered metals (e.g., magnesium iron) wood. Violent reaction with aluminum isopropoxide -f- heavy metal salts charcoal coal dimethylphenylphosphine hydrogen selenide lithium tetrahydroaluminate metals (e.g., potassium, sodium, lithium) metal oxides (e.g., cobalt oxide, iron oxide, lead oxide, lead hydroxide, manganese oxide, mercur oxide, nickel oxide) metal salts (e.g., calcium permanganate) methanol + phosphoric acid 4-methyl-2,4,6-triazatricyclo [5.2.2.0 ] undeca-8-ene-3,5-dione + potassium hydroxide a-phenylselenoketones phosphorus phosphorus (V) oxide tin(II) chloride unsaturated organic compounds. 

Alkaline-earth alkoxides are insoluble and involatile in contrast to the double alkoxides formed by dissolving the alkaline earth metal in a solution of niobium or tantalum isopropoxide in propan-2-ol. With the exception of the magnesium derivative which decomposes on heating, they can be sublimed in vacuo, thermal stability diminishing in the order Ba > Sr > Ca. The calcium and strontium derivatives are monomeric in refluxing benzene, the others are insoluble. Attempts to elucidate structures by n.m.r. spectroscopy were foiled by the rapid exchange of geminal dimethyl protons (see also p. 66). 

Enantioselective addition of (C2Hs)2Zn to RCHO. Of a variety of chiral N-sulfonylamino alcohols, 1 was found to be the most effective ligand for asymmetric addition of dicthylzinc to aldehydes catalyzed by titanium(IV) isopropoxide in methylene chloride. Addition of calcium hydride or 4 A molecular sieves docs not affect the enantioselectivity but can increase the yield. 

Piperonyl alcohol 328 2-Propanol is rendered anhydrous by 4 hours boiling with calcium oxide, distillation, further boiling with aluminum isopropoxide, and renewed distillation. 50 g of piperonal in 500 ml of this alcohol are treated with 10 g of aluminum isopropoxide, and the whole is heated in an oil-bath at 95° under a Widmer column attached to a descending condenser. At the end of this time, 200 ml of distillate have passed over (b.p. 77-81°) and acetone is no longer detectable in a sample by means of 2,4-dinitrophenylhydrazine in N-hydro-chloric acid. The residue is treated with water, made just acid with hydrochloric acid, and extracted with ether. The extract is dried and evaporated, and the residue is distilled in a vacuum, giving 45 g of a product of b.p. 151°/13 mm. This solidifies to crystals melting at 51°. 

To increase the mixing effects and interaction with the hydroxyl groups, the PEG polymer may be replaced by its monomer, ethylene glycol (EG, 0H(CH2)0H). The EG method also has the advantage of the use of alcohol soluble source chemical such as titanium isopropoxide. Nano-sized titania, calcium titanate [17,18] and barium titanate [9] have been synthesized by the EG method at relatively low organic weight percentages. 

Kinetic resolution of secondary allylic alcohols by Sharpless asymmetric epoxidation using fert-butylhydroperoxide in the presence of a chiral titanium-tartrate catalyst has been widely used in the synthesis of chiral natural products. As an extension of this synthetic procedure, the kinetic resolution of a-(2-furfuryl)alkylamides with a modified Sharpless reagent has been used . Thus treatment of racemic A-p-toluenesulphonyl-a-(2-furfuryl)ethylamine [( )-74] with fert-butylhydroperoxide, titanium isopropoxide [Ti(OPr-/)4], calcium hydride (CaHa), silica gel and L-(+)-diisopropyl tartrate [l-(+)-DIPT] gave (S)-Al-p-toluenesulphonyl-a-(2-furfuryl)ethylamine [(S)-74] in high chemical yield and enantiomeric excess . Similarly prepared were the (S)-Al-p-toluenesulphonyl-a-(2-furfuryl)-n-propylamine and other homologues of (S)-74 using l-(+)-D1PT. When D-(—)-DIPT was used, the enantiomers were formed . ... 

Although commercially available and highly active in ROP of e-CL and l-LA, calcium methoxide is of limited interest because of its low solubility and aggregation (87). Feijen and co-workers used however successfully the strategy implemented for lanthanide alkoxides. The (THF)2Ca[N(SiMe3)2]2 precursor was indeed reacted with isopropanol with in situ formation of Ca isopropoxide. ROP of e-CL and l-LA is then controlled at room temperature as testified by the agreement between theoretical and experimental Mn and low Mw/Mn(<1.3). Poly(e-CL)-6-poly(L-LA) was also synthesized with success, racemization was not observed during ROP of l-LA, and the kinetics was second order in monomer (88). 

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