Alkoxides preparation

The alkoxides and aryloxides, particularly of yttrium have excited recent interest. This is because of their potential use in the production of electronic and ceramic materials,in particular high temperature superconductors, by the deposition of pure oxides (metallo-organic chemical vapour deposition, MOCVD). They are moisture sensitive but mostly polymeric and involatile and so attempts have been made to inhibit polymerization and produce the required volatility by using bulky alkoxide ligands. M(OR)3, R = 2,6-di-terr-butyl-4-methylphenoxide, are indeed 3-coordinate (pyramidal) monomers but still not sufficiently volatile. More success has been achieved with fluorinated alkoxides, prepared by reacting the parent alcohols with the metal tris-(bis-trimethylsilylamides) ... 

Disubstituted dihydrofurans and dihydropyrans were prepared via allylic etherification [68] in a similar manner to dihydropyrroles (cf Section 9.4.6). Thus, diaste-reoisomeric ethers were generated by the reaction of cinnamyl tert-butyl carbonate with the copper alkoxide prepared from (Rj-l-octen-3-ol, depending on which enantiomer of the phosphoramidite ligand was used (Scheme 9.39). Good yields and excellent selectivities were obtained. RCM in a standard manner gave cis- and trans-dihydrofuran derivatives in good yield, and the same method was used for the preparation of dihydropyrans. 

Firstly, we examined the asymmetric hydrocyanation of 3-phenylpropanal. When 3-phenylpropanal was treated with cyanotrimethylsilane using the chiral titanium alkoxide prepared from dichlorodiisopropoxytitanium and the chiral 1,4-diol 17b in toluene at room temperature, only a trace amount of the... 

The diethylzinc-alcohol (1 2) system was also extensively studied by Tsuruta and his co workers (85,86). Amorphous zinc dialkoxide was concluded to be an active species, because crystalline zinc alkoxide prepared from zinc chloride and lithium alkoxide proved to have only a very small catalytic activity. Based on kinetic studies of the polymerization of propylene oxide with the ZnEt2-CH3OH (1 2) catalyst system, the catalytically active species was concluded to be the complex formed by coordination of one molecule of monomer to the catalyst. In the polymerization of propylene oxide with the catalyst system, it was concluded that the monomer was polymerized by ring opening brought about by cleaving the CH2-0 bond (87). 

Figure 16 FTIR spectra obtained ex situ (external reflectance mode) from Li surfaces prepared and stored in ethers of the glyme family. Reference spectra of Li alkoxides prepared as thin layers on Li surfaces are also presented [149]. (With copyrights from Elsevier Science Ltd., 1998.) (a) Diglyme (DG, CH3OCH2CH2OCH2CH2OCH3) (upper solid line) DG + Li (dashed line) CE OCE CE OLi on Li spectra of CH3OLi and (LiOCH2)2 on Li are also presented (as indicated), (b) Ethyl glyme (EG, CH3, CH2OCH2CH2OCH2CH3) (upper solid line) EG + Li (dashed line) CHjCE OLi on Li (lower solid line) (LiOCH2)2 on Li.

The sodium alkoxides prepared from primary and secondary alcohols and sodium hydride in a mixture of THF and DMF or DMSO react with p-methoxy-benzyl chloride at room temperature to give the p-methoxybenzyl ethers in good yield. Use of THF alone is not so satisfactory. p-Methoxybenzyl chloride (nip -1 °C bp 117 C/L9 kPa) is moisture sensitive and deteriorates on standing so it should be freshly distilled in vacuo before use. In sluggish reactions, the rate can be increased by the addition of a catalytic amount of tetrabutylam-... 

The sodium or potassium alkoxides prepared from primary and secondary alcohols and sodium hydride or potassium hydride in THF react with chloromethyl methyl ether to give the MOM ethers in good yield [Scheme 4.253].383 469 An... 

The sodium or potassium alkoxide prepared from primary and secondary alcohols and sodium hydride or potassium hydride in THF reacts with 2-(trimethyl-silyi)ethoxymethyl chloride (SEMCl, bp 57-59 PC/1 kPa, HAZARD carcinogenic) to give the SEM ethers in good yield [Scheme 4.304]481 Alternatively, the alcohol can be alkylated with SEMC1 in the presence of f-PrjNEt in dichloro-methane at 4013 C [Scheme 4.305].257,525,555 Conversion of the SEMCl to the corresponding iodide in situ using tetrabutylammonium iodide accelerates the reaction ... 

Section 1.1.3.3 Formation of 1-vinyl-2-alkylcyclohexanes from 1,7-dienes. Narasaka demonstrated that the chiral titanium alkoxide prepared from TiCl2(OPr )2 and (213) catalyzes the asynunetric intramolecular ene reaction of oxazolidinone (212) in Freon 113 at 0 °C to give 63% of ene adduct (214) in >98% enantiomeric excess and 25% of the hetero Diels-Alder adduct. ... 

Komiya, S., Taneichi, S., Yamamoto, A., Yamamoto, T. Transition metal alkoxides. Preparation and properties of bis(aryloxy)iron(ll) and bis(alkoxy)iron(ll) complexes having 2,2 -bipyridine ligands. Bull. Chem. Soc. Jpn. 1980, 53, 673-679. 

Trialkyltin alkoxides prepared by evacuation of methanol from a mixture of an alcohol and trialkyltin methoxide are easily oxidized by bromine in the presence of trialkyltin alkoxide as HBr scavenger, producing the desired aldehyde and ketone efficiently [324]. This oxidation is more feasible on organotin alkoxides derived from secondary alcohols than those from primary alcohols, and enables regioselective oxidation of polyols [325]. The regioselectivity in oxidation of vicinal secondary alcohols was also examined [326], and the empirical informative results were invoked for access to namenamicin A-C disaccbarides (Scheme 12.177) [327]. 

Various triakylaluminum reagents can be obtained on an industrial scale. However, their utilization in asymmetric alkylation is limited, for example, an enantioselective allylation of aldehydes by allyldialkylaluminum [53]. Recently, Chan et al. reported the first example of a catalytic alkylation of aldehyde using triethylaluminum [54]. Asymmetric ethylations of various aromatic aldehydes proceed in very high yields and ees in the presence of a chiral titanium alkoxide prepared from Ti(0-f-Pr)4 and chiral 5,5, 6,6, 7,7, 8,8 -octahydro-l,T-bi-2-naph-thol (Hg-BINOL) (Scheme 19). It is noteworthy that Hg-BINOL is a more efficient chiral catalyst than BINOL. High enantioselectivity can be attained only in the... 

Chirally modified lanthanide alkoxides [prepared in situ from Ln(0-/-Bu)3 and chiral ligands] give higher asymmetric induction in the reduction of acetophenone (for La. 32%ee) than the normally used aluminum or alkali metal alkoxides208. However, the decrease of ee values with increasing reaction time shows that kinetic control is not maintained with 2-propanol as the reducing agent. 

The isopropoxide is crystalline, subliming in a vacuum at 170°, but other alkoxides, prepared from the isopropyl compound by alcohol exchange, are non-volatile and presumably polymerized by Ce—O(R)—Ce bridges. 

It is now reasonably well established that metal dialkylamides/bis(trimethylsilyl)-amides are valuable starting materials when the more conventional methods for metal alkoxide preparation fail. 

Table 2.22 Electronic spectral data (cm ) for chromium(lll) alkoxides prepared by different routes ...

Williams P.A, Jones A.C., Bickley J.F., Steiner A., Davies H.O., Leedham T.J., Impey SA., Garcia J., Allen S., Rougier A., Blyr A. Synthesis and crystal structures ofdimethylaminoethanol adducts of Ni(ll) acetate and Ni(II) acetylacetonate. Precursors for the sol-gel deposition of electrochromic nickel oxide thin films, J. Mater. Chem. 2001, 11 2329 Yanovskaya M.L, Kotova N.M., Golubko N.V., Turova N.Ya. Reactions of magnesium and titanium alkoxides. Preparation and characterization of alkoxy-derived magnesium titanate powders and ceramics, J. Sol-Gel Sci. Tech. 1998 11 23... 

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