HYDROBORATION ISOPINOCAMPHEOL

HYDROBORATION OF OLEFINS (+)-ISOPINOCAMPHEOL, 52, 59 Hydroboration-oxidation of olefins, 53, 83... 

Isopinocampheol has been prepared by hydrogenation of irams-pinocarveol with a neutral nickel catalyst at 70-100°. The hydroboration reaction provides a convenient procedure for the conversion of olefins to alcohols without rearrangement and with a predictable stereochemistry. The reaction has been applied to a large number of olefins of widely different structures. The results obtained support the proposed generaliza-tit)ii that hydroboration involves an anborane from the less hindered side of the double bond. ... 

The stereochemical outcome of hydroboration, syn steroselectivity, was originally based on the stereochemistry of alcohols isolated after hydroboration-oxida-tion.349,350 Thus, for example, (+)-a-pinene yields (—)-isopinocampheol after the oxidation of (—)-diisopinocampheylborane (36) ... 

Among the pinene-derived mono-alcohols, only (-)-isopinocampheol [(— )-33] has been used as an auxiliary. Its enantiomer ( + )-33 is commercially available or is readily prepared by a hydroboration/oxidation sequence from (+)-a-pinene (for a detailed procedure, see ref 34). The phenyl ether of (—)-33 has been used as a starting material for cyclic enol ethers 35. obtained by Birch reduction of the phenyl group3s, which are used as chiral dienes in Diels-Alder reactions (Section D.1.6.1.1.1.), although no description of the synthesis of the ether has been given. The alcohol has also been used for the synthesis of di(isopinocampheyloxy)-2-propenylborane 3433 (Section D.2.3.5.). 

R. L. Blankespoor and K. Piers,/. Chem. Educ., 68, 693 (1991), Hydroboration-Oxidation of (lR)-( + )-a-Pinene to Isopinocampheol A Microscale Experiment that Displays Regio-and Stereochemistry Using NMR Spectroscopy and Molecular Mechanics Calculations. 

After the asymmetric hydroboration-oxidation sequence is completed, the desired product is separated via its silver(I) complex from (+)-isopinocampheol. The desired product can also be isolated by column chromatography. 

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