B-Methoxydiisopinocampheylborane1

(+)

[85134-98-1]  · C21H37BO  · B-Methoxydiisopinocampheylborane  · (MW 316.39) (-)

[99438-28-5]

(intermediate for the synthesis of B-allyl- and B-crotyldiisopinocampheylboranes;2 reacts with potassium hydride to form an asymmetric reducing agent3)

Physical Data: mp >110 °C.

Form Supplied in: white solid; commercially available; typical impurities include the disproportionation products IpcB(OMe)2 and B(OMe)3.

Analysis of Reagent Purity: 11B NMR (d +52).

Preparative Methods: prepared in two steps from either (+)- or (-)-a-pinene (eq 1).

Preparation of B-Allyldiisopinocampheylborane and Related Reagents.

Addition of allylic Grignard or potassium reagents to B-methoxydiisopinocampheylborane (Ipc2BOMe) provides the corresponding allylic boranes (eqs 2 and 3).2 Note that (-)-Ipc2BOMe, derived from (+)-a-pinene, produces (+)-Ipc2BAll and Ipc2BCrt reagents, and (+)-Ipc2BOMe gives the corresponding (-)-allylic boranes. These allyl and crotyl boranes condense with aldehydes to provide secondary homoallylic alcohols with high levels of enantioselection (see also B-Allyldiisopinocampheylborane and B-Crotyldiisopinocampheylborane).

Acetylide Coupling.

B-Methoxydiisopinocampheylborane reacts with Lithium (Trimethylsilyl)acetylide to provide, after iodine-promoted rearrangement and desilylation, a-chiral monosubstituted alkynes in excellent yield (eq 4).4

B-Methoxydiisopinocampheylborohydrides.

Treatment of Ipc2BOMe with an excess of Potassium Hydride produces the corresponding potassium B-methoxydiisopinocampheylborohydride.3 The reduction of ketones with this reagent proceeds in high yield but with modest enantioselection (eq 5).


1. Brown, H. C.; Ramachandran, P. V. PAC 1991, 63, 307.
2. (a) Jadhav, P. K.; Bhat, K. S.; Perumal, P. T.; Brown, H. C. JOC 1986, 51, 432. (b) Racherla, U. S.; Brown, H. C. JOC 1991, 56, 401. (c) Brown, H. C.; Bhat, K. S. JACS 1986, 108, 5919.
3. Cho, B. T. Bull. Korean Chem. Soc. 1991, 12, 662.
4. Brown, H. C.; Mahindroo, V. K.; Bhat, N. G.; Singaram, B. JOC 1991, 56, 1500.

Mark T. Goulet

Merck Research Laboratories, Rahway, NJ, USA



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