Diisopinocampheylborane, IpC

The hydroboration of acetylenes (3) with diisopinocampheylborane (IpC)2BH in THF led after refunctionalisation and transesterification to the olefins (4a, b, c) isolated in good yields. Monooxidation with mCpBA led to the sulfoxide (4d) whereas the sulfone (4e) was obtained with two equivalents of mCpBA. The same sulfone (4e) could also be obtained in an excellent overall yield by radical addition of phenylsulfonyl iodide to the pinacol ester of vinylboronic acid followed by a dehydroiodination in the presence of Et2N (87 % overall yield). The carboxylic ester (4a) could be transformed into the corresponding carboxylic acid (4f) (79 % yield) 11 which led to the acid chloride (4g) by treatment with freshly distilled thionyl chloride at 0°C (91 % yield), p-keto vinylboronates are easily accessible by oxidation of the corresponding protected allylic alcohol according to the following scheme ... 

Monoisopinocampheylborane [(IPC)BH2], see diisopinocampheylborane, 1, 266-268 4, 161-162. The laboratories of Pelter and of Brown have succeeded in the preparation of monoisopinocampheylborane by hydroboration of a-pinene. In one method, equimolar proportions of ( + )-a-pinene and BHs-THF are mixed in THF and the solution is allowed to stand for 96 hours, after which time it contains about 90% (IPOBH2, 4.75% (IPO2BH, and 4.75% BH3 THF. The last material is precipitated as TMEDA-2BH3, and the solution is used for hydroboration. Alternatively, addition of TMEDA precipitates TMEDA-2(IPC)BH2 as a white soiid, m.p. 139-140°. This is dissolved in THF, and then BF3 etherate is added to generate (IPOBH2. 

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