Lithium borohydride hydroboration

Liquid injection molding, for silicone rubbers, 3, 674—675 Liquid ligands, in metal vapor synthesis, 1, 229 Liquid-phase catalysis, supported, for green olefin hydroformylation, 12, 855 Lithiacarbaboranes, preparation, 3, 114 Lithiation, arene chromium tricarbonyls, 5, 236 Lithium aluminum amides, reactions, 3, 282 Lithium aluminum hydride, for alcohol reductions, 3, 279 Lithium borohydride, in hydroborations, 9, 158 Lithium gallium hydride, in reduction reactions, 9, 738 Lithium indium hydride, in carbonyl reductions, 9, 713—714... 

Gp2TiCl2/NaBH4 mixtures have been studied as a convenient system for the hydroboration of alkenes. Mechanistic studies for these reactions are reported. These processes provide different regioselectivities and are catalyzed by the isolated Cp2Ti(/x-H)2BEl2 species. Lithium borohydride appears to be involved in the formation of the true catalytically active complex. Extensive nB NMR experiments indicated that the predominant products in the hydroboration reaction of Ph-CH=CH2 are a regiomeric mixture of tetraalkylborates, with minor amounts of trialkylborohydrides.1624,1625... 

The reduction of epoxides withborane is noteworthy as it gives rise to the less substituted alcohol as the major product (7.96), in contrast to reduction with complex hydrides (compare with Scheme 7.71). The reaction is catalysed by small amounts of sodium or lithium borohydride and high yields of the alcohol are obtained. With 1-alkylcycloalkene epoxides, the 2-alkylcycloalkanols produced are entirely cis, and this reaction thus complements the hydroboration-oxidation of cycloalkenes described in Section 5.1, which leads to trans products. Reaction with borane in the presence of boron trifluoride has also been used for the reduction of epoxides and for the conversion of lactones and some esters into ethers. 

Borohydrides, 13 613-621 lithium, 13 620-621 potassium, 13 620 sodium, 13 614—620 in uranium systems, 25 440 Boron (B), 4 132-138. See also Boranes Hydroboration MgB2 entries addition to aluminum wrought alloys, 2 327... 

An improved method for the preparation of methyl 2-oxo-5-vinyl-cyclopen-tanecarboxylate (389) by treatment of dimethyl ( )-2-hexenedioate (390), with the cuprate made from vinyllithium and copper(I) cyanide (77-85%), led to a short synthesis of mitsugashiwalactone (391) (Scheme 34), another noriridoid isolated from Boschniaka rossica Borohydride reduction and dehydration gave methyl 5-vinyl-l-cyclopentenecarboxylate (392), and this could be cyclized by hydroboration and extended treatment with hydrogen peroxide—conditions for the highest yield in the cyclization seem to be with hydroboration in base— then a separate acid-catalyzed cyclization. The methyl group was added with lithium dimethyl cuprate. ... 

Chiral 9-alkyl-9-borabicyclo[3.3.1]nonanes, available by hydroboration of <7.s,<7.5-1,5-cyclooc-tadiene with monoalkylboranes generated from lithium monoalkyl borohydrides, can alkylate a-halogenated ketones, esters and nitriles in the presence of alkali metal rm-butoxide in tetrahydrofuran22. 

In 1956 Herbert C. Brown (b. 1912) discovered that in ethereal solution diborane (B2H5) dissociates into borane (BH3), which can add to an alkene. The organoborane formed can be converted to an alcohol by treatment with hydrogen peroxide, and the overall result of this hydroboration reaction is the anti-Markovnikoff addition to the double bond. Brown was also responsible for the introduction into organic chemistry of the reducing agents sodium borohydride (sodium tetrahydridoborate(lll)) and lithium aluminium hydride (lithium tetrahydridoaluminate(lll)). 

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