Journal of Organic Chemistry p. 2025 - 2032 (1994)
Update date:2022-07-29
Topics:
Brown, Herbert C.
Dhokte, Ulhas P.
Two higher analogues of α-pinene, 2-isobutyl- and 2-isopropylapopinenes, promising chiral auxiliaries for asymmetric hydroboration, were readily synthesized from α-pinene in good chemical yield.A quantitative study was made of the rates and stoichiometry of the hydroboration of a number of representative 2-organylapopinenes (2-R-apopinenes) with representative boranes, such as BH3*SMe2 (BMS) and BH3*THF, in order to develop a convenient procedure for the synthesis of mono- and bis(2-organylapoisopinocampheyl)boranes <2-R-apoisopinylborane (RapBH2) and bis(2-R-apoisopinyl)borane (Rap2BH), respectively>, under investigation as possible improved asymmetric hydroborating reagents.It was evident that the sterically bulkier 2-R-apopinenes such as 2-phenyl- and 2-isopropylapopinenes reacted with boranes at room temperature to form essentially RapBH2 in >/=95percent yield, while a yield of >/=90percent was realized in the case of 2-isobutylapopinene.However, α-pinene, and 2-ethyl- and 2-n-propylapopinenes smoothly reacted with boranes to form a mixture of RapBH2 and Rap2BH.Under the reaction conditions employed, 2-ethyl-, 2-n-propyl-, 2-isobutyl-, 2-phenyl-, and 2-isopropylapopinenes failed to produce clean Rap2BH.The rate of hydroboration decreased significantly with increase in bulk of the organyl group at the 2-position of the apopinene.
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Doi:10.1039/c3cc49323g
(2014)Doi:10.1139/v94-019
(1994)Doi:10.1039/JR9650006570
()Doi:10.1021/jm00036a004
(1994)Doi:10.1016/S0040-4020(01)90461-2
(1994)Doi:10.1016/0022-328X(94)80221-1
(1994)