A general, efficient, convenient synthesis of chiral bis(terpenyl)haloborane reagents, valuable for asymmetric synthesis via organoboranes

• Published in: Tetrahedron letters Vol. 37; no. 46; pp. 8345 - 8348
• Main Authors: Dhokte, Ulhas P., Soundararajan, Raman, Ramachandran, P.Veeraraghavan, Brown, Herbert C.
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 11.11.1996; Elsevier
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; KETONES; ALPHA-PINENE; HYDROBORATION; 2-ORGANYLAPOISOPINOCAMPHEYLBORANES; 2-ORGANYLAPOPINENES; SELECTIVE REDUCTIONS; REPRESENTATIVE ALKENES; HIGH OPTICAL PURITY
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/0040-4039(96)01908-9

The chiral, sterically-varied bis(terpenyl)haloboranes (Ter 2BX; X = Cl, Br, and I), potentially important reagents for asymmetric synthesis, are conveniently prepared in essentially quantitative yield by the in situ tandem reduction-hydroboration under mild conditions of boron trihalide, trialkylsilane, and representative terpenes (Ter). Use of ethyl ether (EE) as solvent accelerates the formation of the sterically bulkier Ter 2BCl derivatives. Typically the reaction is over in less than 2 h in comparison with the literature procedure requiring 36 h at room temperature. The chiral, sterically-varied bis(terpenyl)haloboranes (Ter 2BX; X = Cl, Br, I), potentially important reagents for asymmetric synthesis, are conveniently prepared in essentially quantitative yield by the in situ tandem reduction-hydroboration under mild conditions of boron trihalide, trialkylsilane, and representative terpenes (Ter). Use of ethyl ether (EE) as solvent accelerates the formation of the sterically bulkier Ter 2BCl derivatives. The reaction is over in less than 2 h in contrast to the literature procedure (36 h at rt).