Borane, di-3-pinanyl

The reduction of monocyclic ketones with disiamylborane and di-3-pinanyl-borane takes place from the less hindered side to yield predominantly the less stable of the two possible isomers. In contrast, 9-BBN exerts little influence on the direction taken by the reduction. With 3-methyl- and 4-tert-butylcyclohex-anones, the products are predominantly the more stable of the two possible isomers. Reduction of bicyclic ketones such as norcamphor and camphor proceeds with preferential attack of the 9-BBN from the less hindered side, yielding the less stable of the two possible isomers (Eq. 25.1). 

Addition of alane and borane to alkenes affords a host of alkylated alanes and boranes with various reducing properties (and sometimes bizarre names) diisobutylalane (Dibal-H ) [104], 9-borabicyclo[3.3.1]nonane (9-BBN) (prepared from borane and 1,5-cyclooctadiene) [705], mono- [106,107] and diiso-pinocampheylborane (B-di-3-pinanylborane) (both prepared from borane and optically active a-pinene) [108], isopinocampheyl-9-borabicyclo[3.3.1 Jnonane alias B-3-pinanyl-9-borabicyclo[3.3.1]nonane (3-pinanyl-9-BBN) (prepared from 9-borabicyclo [3.3.1]nonane and a-pinene) [709], NB-Enanthrane prepared from 9-borabicyclo[3.3.1]nonane and nopol benzyl ether) [770] and others. ... 

C. AByrmetvic hydroboration tuith (+)-di-3-pinanylboTvme to form methyl (lR,SR)-5-hydroxy-2-cyclopentene-l-aeetate (Note 4). The (+)-d1-3-pinanyl-borane is prepared from (-)-a-plnene by a modification5,6 of the method of Brown (Note 14). 

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