Boron isopropoxide

Z)-x,p- Unsaturated nitriles.2 The lithio derivative of 1 reacts with aldehydes to form a mixture of (Z)- and (E)-a,/J-unsaturated nitriles with some preference for the former isomer. The stereoselectivity in favor of the (Z)-isomer in reactions with aliphatic aldehydes is markedly improved by use of the boron derivative, obtained by treatment of the lithium reagent with boron isopropoxide. Addition of HMPT also favors the (Z)-isomer. 

Boron isopropoxide. See Triisopropyl borate Boron methoxide. See Trimethyl borate Boron, (N-methylmethanamine) trihydro-, (T-4)-. See Dimethylamine borane... 

Synonyms Boric acid, triisopropyl ester Boric acid, tris (1-methylethyl) ester Boron isopropoxide Boron triisopropoxide Isopropyl borate... 

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. 

Using aluminum isopropoxide as the reducing agent under thermodynamically controlled conditions (84.5 °C, 22 h), 2-(l-cyclohexenyl)butanone is converted to the more stable tram-2-(l-cyclohexenyl)cyclobutanol whereas the d.v-alcohol (80%) is obtained using the sterically more demanding boron reagent, potassium [hydrido-tris(l-methylpropyl)boranate]142. 

After exchanging boron trifluoride etherate against titanium(IV) isopropoxide to promote the aza-Michael step, the enantiomericaUy pure N-sulfinyl amine 199 could be coupled to methyl vinyl ketone as well to give a mixture of the pyrrolidines 200 and 201 in nearly quantitative yield with remarkable substrate-induced diastereoselectivity (Scheme 2.70) [40b]. 

The process of reducing carbonyl compounds (aldehydes or ketones) to alcohols is therefore known as the Meerwein-Ponndorf-Verley reaction. Although alkoxides of a number of metal(loid)s such as sodium, magnesium, titanium, zirconium, iron, boron, aluminium, tin, and antimony have been used for these reactions, those of aluminium are by far preferred, since they tend to give the minimum degree of side reactions. The use of aluminium isopropoxide over other alkoxides was also preferred by Young et al as well as by Adkins and Cox. ... 

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