9-Borabicyclo nonane primary alcohols

Enantioselective reduction is not possible for aldehydes, since the products are primary alcohols in which the reduced carbon is not chiral, but deuterated aldehydes RCDO give a chiral product, and these have been reduced enantioselectively with B-(3-pinanyl)-9-borabicyclo[3.3.1]nonane (Alpine-Borane) with almost complete optical purity. ... 

There are a wide variety of hydroborating reagents, including BH3 complexes, pinacolborane, thexyl borane, and catechol borane. The following employs 9-borabicyclo[3.3.1]nonane (9-BBN), which places the boron on the less sterically hindered carbon with high regioselectivity however, completely removing the cyclooctane by-products can be problematic. The alkylborane can be isolated, but is typically used directly in the next reaction, in this case oxidation to the primary alcohol. 

Reduction of aldehydes labeled with deuterium or tritium leads to primary alcohols which are chiral by virtue of the label. Alternatively, the label can be introduced by the use of deuterated Alpine-Borane, which can be prepared by hydroboration with 9-borabicyclo[3.3.1]nonane-... 

Reduction of Carbonyl Groups. Rapid reduction of salts of carboxylic acids to alcohols with 2 molar equivalents of borane in tetrahydrofuran (THF) has been reported. Full details have appeared of the improved procedure for reduction of esters to primary alcohols, using borane dimethyl sulphide (6,157) in THF at reflux, which allows the dimethyl sulphide that is liberated to distil off during the reaction. Further suggested procedures for the reduction of esters to primary alcohols use lithium borohydride in diethyl ether or THF, calcium borohydride in THF, and sodium borohydride in a t-butyl alcohol-methanol mixed solvent. The reactions using lithium borohydride-diethyl ether can be catalysed by lithium 9-boratobicyclo[3.3.1]nonane (1), lithium triethylboro-hydride, or the Lewis acid 9-methoxy-9-borabicyclo[3.3.1]nonane (2). ... 

Midland, M. M. Greer, S. Tramontano, A. Zderic, S. A. Chiral Trialkylborane Reducing Agents. Preparation of 1-Deuterio Primary Alcohols of High Enantiomeric Purity. J. Am. Chem. Soc. 1979, 101, 2352-2355. Midland, M. M. McDowell, D. C. Hatch, R. L. Tramontano, A. Reduction of a,P-Acetylenic Ketones with B-3-Pinanyl-9-borabicyclo[3.3.1]nonane. High Asymmetric Induction in Aliphatic Systems /. Am. Chem. Soc. 1980,102, 867-9. 

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