Protection isopropoxide

Deuterium oxide (7.5 ml) is added dropwise to aluminum isopropoxide (25 g.) The mixture is shaken for about 5 min and then warmed to 70° for 10 min to complete the reaction. The resulting deuterioisopropanol is distilled at room temperature and 1 mm pressure into a liquid nitrogen-cooled trap. Redistillation at atmospheric pressure yields pure isopropanol-OD (9.5 g bp 82-83°). All operations must be protected from moisture. 

DeCamp et al.t19l synthesized the lactone intermediate of the 1-hydroxyethylene isostere with high yields and stereoselectivity. As summarized in Scheme 10 (Section 10.6.2), the titanium homoenolate is prepared from ethyl 3-iodopropionate. The iodide is metalated with zinc/copper couple to give the iodozinc homoenolate species. The alkyltitanium homoenolate is then generated by transmetalation of the iodozinc precursor with one of the several chlorotitanium isopropoxide species. The resulting titanium homoenolate reacts with a N-protected a-amino aldehyde, leading to a mixture of 45-diastereomers. In the last step, the product is lactonized. 

High yields and enantiopurity have been realized by a highly diastereoselective MPV reduction of protected a-amino aromatic ketones using catalytic amounts of aluminium isopropoxide. The high anti selectivity resulted from the chelation of the (g) nitrogen anion to the aluminium. In contrast, high syn selectivity was obtained with a-alkoxy ketones and other compounds via Felkin-Ahn control.354... 

Miura and co-workers reported the protection of phenols by allyl alcohols in the presence of catalytic amounts of palladium(II) acetate and titanium(IV) isopropoxide. The reaction is remarkably general however, it fails in the case of 3,5-dimethoxyphenol because of the exclusive formation of a C-allylated product. 

Zirconium support modification of alumina was performed by adding zirconium, in the form of zirconium isopropoxide, under an inert atmosphere to isopropanol. Alumina was added to this solution, and the mixture stirred at 60 "C for 1 hour. The solvent was removed under a vacuum of 3kPa (a) with a jacket temperature of 95 °C. The resultant modified support was subsequently calcined at 600 C for 2 hours to obtain a protected modified catalyst support. The amount of precursor was found to be 0.1 Zr atoms/nm fresh support. 

The ability of zeolites to adsorb and retain small molecules such as water forms the basis of their use in the noncatalytic synthesis of fine chemicals (Van Bekkum and Kouwenhoven, 1988, 1989). One of the best recent examples is the use of NaA zeolite in the Sharpless asymmetrical epoxidation of ally lie alcohols (see Chapter 10) (Gao et al., 1987 Antonioletti et al 1992). In this Ti(IV)-catalyzed epoxidation by t-butyl hydroperoxide in the presence of diethyl tartrate (reaction 6.4), it has been demonstrated that the inclusion of zeolites (3 A or 4 A) leads to high conversion (>95%) and high enantioselectivity (90-95% ee). The effect of the zeolite is quite dramatic. It is believed that the role of the zeolite is to protect the titanium isopropoxide catalyst from water, perhaps generated during the reaction. 

In 2010 Bertus and coworkers developed an optimised multigram-scale synthesis of aminocyclopropanecarbojg lic aeid derivatives in which the key step is the titanium-eatalysed cyclopropanation of a Boc-protected cyanohydrin. The cyclopropanation reaction was carried out using 20 mol% of titanium(iv) isopropoxide in the presence of 2.1 equivalents of ethylmagne-sium bromide to afford a titanacyclopropane, which is the catalytically active species, giving the JV-Boc-protected 1-aminocyclopropanol in 65% yield that can be oxidised to the carboxylic acid in quantitative yield. 

Despite the typical behavior of five-membered cycUc carbonates to result in polyether carbonates upon polymerization at higher temperatures (T> 150°C), five-membered cyclic carbonates derived from methyl-4,6-0-benzylidene-glucopy-ranoside (39) [79] and 1,2-O-isopropylidene-D-xylofuranose (40) [80] were polymerized at temperatures below 70 °C, without any eUmination of carbon dioxide, to produce polycarbonates. The polymerization of 39 was carried out with 1,8 diaz-abicyclo [5.4.0]undec-7-ene (DBU) or potassium tert-butoxide, while that of 40 was performed with potassium tert-butoxide or yttrium isopropoxide as initiator. After removal of the protection groups, the carbohydrate polymers with carbonate main-chain linkages were obtained. 

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