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Please login or sign up for a free trial to access the full content. Method 2: Asymmetric Alkylhydroboranes

DOI: 10.1055/sos-SD-006-00003

Matteson, D. S.Science of Synthesis, (2005623.

The brief review of asymmetric alkylhydroborane chemistry in this section is intended to provide an overview of the capabilities of these reagents. This chemistry was well developed before 1990, and a review has been published.[‌75‌] For the limited variety of asymmetric structures that can be made in high enantiomeric purity by hydroboration, there is usually no more efficient method. The variety of asymmetric organoboranes that can be made by hydroboration is limited by the rules that govern regioselectivity and stereoselectivity in accord with steric effects. Hydroboration is particularly valuable for making certain types of asymmetric cycloalkyl compounds. A simple and much more general synthesis of acyclic secondary alcohols and other borane derivatives, including highly functionalized structures, in very high enantiopurity is provided by the reaction of boronic esters with dichloromethyllithium to provide α-chlorinated boronic esters, which can be converted into a wide range of products (see Sections and[‌88‌‌90‌] The chemistry of chlorinated boronic esters also shows promise for certain functionalized cyclic structures different from those available from hydroboration procedures.[‌35‌] Although catalytic methods of asymmetric synthesis have excited the most interest latterly, both enantiomers of α-pinene are available in useful purity (8492% ee) at moderate cost, and can be upgraded to >99% ee by crystallization of borane derivatives. From a practical point of view, the net expense of using these reagents may be less than that of catalytic methods with expensive asymmetric catalysts derived from transition metals. Metal-based catalysts may require considerable initial capital investment, and catalyst recovery is never quite 100%. Some of the hydroboration sequences allow recovery of α-pinene, further reducing net reagent cost.

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Meeeee 88 Meeeeeeeeee ee ()-Mee(eeeeeeeeeeeeeee)eeeeee eeee (+)-α-Meeeee eee eee Meeeeeeee Meeeeeeeeeeee ee Mee-8-eee[‌88‌,‌88‌,‌88‌]

M eeeee eeeeeeeeee ee eee(eeeeeeeeeeeeeee)eeeeee (88) ee ee eeeeeeeeee eeeeeeeeeeeee eeeee ee eeee ee eeeeeeeeeee eeeeeeeeee ee eeee eeeee eeeeeee ee α-eeeeee eee eeeeeeeeeeeeeeeeeeeee (MeeMM8), eeeee eee eeee eee eeeee eeeeee eeeee [Mee8M(M8)MMMee]; eeee ee e eeeeee eeeeeeeeeeeee eeeee eeee eee(eeeeeeeeeeeeeee)eeeeee eee eeeeeee eee eee eeeeeeee eeeeeeeeeeeeeee. Mee eeeeeeee ee M-eeeeeee eeee eee(eeeeeeeeeeeeeee)eeeeee ee eeee eeeeee eeee eeeeeeeeeeee ee α-eeeeee eee eeeeeeeeeeeeeeeeeeeee eeee eee eeee eeee ee eeeee ee ee eeeeeeeeeee eeeeee, eee eeeeeeee eeee eeeeeeee eeeeeee eeeee eeeeeeeeee eeeeee. Me e eeeeeeeeeee, eeeeeeeeeeeeee eeeeeee eeee ee 8-eeeeeeeee-8-eee ee 8-eeeeeeeeeeeeeeeee eee eeeeeeeeeeee ee eeee 8888% ee.[‌88‌] Meeeeee, eee eeee eeeeeee ee eee(eeeeeeeeeeeeeee)eeeeee ee eeeeeeee ee eeeeeeeeeee M-eeeeeee, eeeeeee eeeeeeeeeeee, eee e eee eeeeeee eeeee. Meeeeeeeeeeeee ee eeee M-eeeeeee eeee ()-eee(eeeeeeeeeeeeeee)eeeeee (88) eee eeeeeeeeee ee Meeee 8.[‌88‌,‌88‌,‌88‌]

Meeeeeeeeeeeee ee eeee eeeeeeeeeeee eeeeeeeee eeee ()-eee(eeeeeeeeeeeeeee)eeeeee (88) eee eeeeeeeeee ee Meeee 8.[‌88‌] Me ee eeeeeeeeeeee ee eeeeeee eee eeeeeeeee eeeeee eeeeeeeeeeeee (Mee8MM8) eeee eeeeeee eeeeee; eee eeeeeee, eee eeeeeeeeeeee eeeeee 88 ee eeeeeee eeee eeeeeeeeeeee, eeeee eeeeeeeee α-eeeeee eee eeeee eee eeeeeee eeeeeeee 88 (Meeeee 88).[‌88‌,‌88‌,‌888‌] Meee eeeeeeee ee eeeeeeeeeee eee eeee ee eeeee ee eee eeeeeeee eeeee M-eeeeeeeeeeeeeee-8-eeeeeeeeeee[8.8.8]eeeeee eeee eeeeeeee eeeeeeeee.[‌888‌] Meeeeeee eeee eeeeeeeee eeee ee eeeee eeee, ee eeeeeeeee eeeeeeee eeeeeeeeeee α-eeeeee eee eeeeeeeee, eee eeeeeeee eeeeee e eeeeeee eeeeeee eeee eeee eeeeeeeeeeeeeee. Meeeeee eeeeee eee eeee eeeeee eee e eeeeeee ee eeeee eeeeeeeeeeeeeee.[‌88‌,‌88‌]

Meeee 8 Meeeeeeeeeeee ee M-Meeeeee eeee ()-Mee(eeeeeeeeeeeeeee)eeeeee Me Meeeeee Meeeeeeee Meeeeeee[‌88‌,‌88‌]

M-Meeeee Meeeeee Meeee (%) ee Meeeeee ee (%) ee Meeeeee Mee
88 88 [‌88‌]
88 88 [‌88‌]
88+88 88e [‌88‌]
88 88 [‌88‌]
88 88 [‌88‌]
88 88 [‌88‌]
88 88 [‌88‌]
88e 88 [‌88‌]

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e Meeee ee eeeee eeee eeeeeeeeeeeeeee, eeeee eee eeeeeeeee eeee eee eeeee eeeeeeeeee, eee eeeeeeeeee ee eeeeee eeeeeee 8-eeeeeeeeeeeeeeeeeeeee, eeee eeeeeeeeeeeeee ee eeee; eeee eee eeeeeeeeee eeeeee.

Meeeee 88 Meeeeeeeee ee Mee(eeeeeeeeeeeeeee)eeeeeee eeee Meeeeee Meeeee[‌888‌]

Meeee 8 Meeeeeeeeeeeee ee Meee Meeeeeeeeeee eeee ()-Mee(eeeeeeeeeeeeeee)eeeeee Me Meee Meeeeeeeee Meeeeee Meeeee ee Meeeeeeee Meeeeeee[‌88‌]

Meeeeeeeeee Meeeeee Meeee Meeeeee Meeee (%) ee Meeeeee ee (%) ee Meeeeee Mee
8888 888 [‌88‌]
8888 888 [‌88‌]
8888 888 [‌88‌]
8888 88 [‌88‌]
8888 888 [‌88‌]
8888 8888 [‌88‌]
e 88 [‌88‌]

e Meeee ee eeeeeee eeeeeeee ee eeee.

M eeeeee eeeeee eeeeeeeeeeeee eeeee ee eeeeeeeeeeeeeeeeeeeee (88, MeeMM8).[‌888‌] Meeeeeee eeee eeeeeeee eeee ee ee eeeeeeeeeeee ee eee eeeeeeeee ee eee(eeeeeeeeeeeeeee)eeeeee, ee ee eee eeeeeeeee ee eeee ee ee eeeeee eeeeeeeee. Meeeeee, ee ee eeeeeeee ee eeeeeeeee ee eee(eeeeeeeeeeeeeee)eeeeee (88) eeee M,M,M,M-eeeeeeeeeeeeeeeeeeeeeeeeee, eeeee eeeeeeeee α-eeeeee eee eeeee e eeeeeeeeeee eeeeeee 88 eeee eee ee eeeeeee eeee eeeee eeeeeeeeeeeeeeeeee eeeee eeeeeee ee eeeee eeeeeeeeeeeeeeee eeee eeeeeeeeeeeeeeeeeeeee (Meeeee 88).[‌888‌,‌888‌] M eeeeeeeeee ee eeeeeeeeeeeeeeeeeeeee (88) ee eeee ee eeeeeee eeeeeeee eeeeeeee eeee ee eeeeeeeeeeee eeeeee ee 8888%. Meeeeee, ee eeeeeeeee eeeee eeee ee eeee eee eeeeee 88 eeeeeee eeee 8-eeeeeeeeeeeeeeeee, eeeeeeee eee eeeeeeee eeeeeee ee eee ee eeeeeee eeee eee eeeeeeeeeee eeeeeee eee eeeeee ee ee eeeeeeee ee eee eeeeeeeeeeee eeeeee ee >88%.[‌88‌] Meee ee eee eeeeeeeeeeeee (MeeMMM8) eeeeee ee eeeee eeeeeeeee eee ee eeeeeeeeeeee ee eeee eeeeeeeeeeee eeeeee eeeee eeeeeeeeee eeee ee eee eeeee eeeeeeeeeeeee. Meeeeee ee eee eeee eeeeee eeeeeeeeeeeeee eeee eeeeeeeeeeeeeeeeeeeee eee eeeeeeeeee ee Meeee 8. Meeeeee eee eeeee eeeeeeeeeeee eeeeeeee ee eee eeeeeee eee eeeeee.

Meeeee 88 Meeeeeeeeee ee Meeeeeeeeeeeeeeeeeeee eee Meeeeeeeeeeee ee 8-Meeeeeeeeeeeeeeee[‌888‌,‌888‌]

Meeee 8 Meeeeeeeeeeeee eeee Meeeeeeeeeeeeeeeeeeee[‌88‌,‌888‌,‌888‌]

Meeeee Meeeeee Meeeeeeeeee Meeeee Meeeeee ee (%) ee Meeeee Meeee ee (%) ee Meeeee Mee
88 888 [‌88‌,‌888‌]
88 888 [‌88‌,‌888‌]
88 888e [‌888‌]
88 [‌88‌]
88 888 [‌88‌,‌888‌]
88 >88 [‌888‌]
88 88 [‌88‌,‌888‌]
>88 >88 [‌888‌]

e Meeeeee eeee eee-eeeee[eee(eeeeeeeeeeeeeee)]eeeeee [eee-MeM(Mee)8]; 88% ee eee eee eeeeeeee eeeee.

Mee eeeeeeeeee ee eeeeeeeeeee eeeeeeeeeeeee (MeeMMM8), eeee ee eee eeeeeeeeeee eeeeee 88, eeee eee eeeeeeeeeeeee eeeeeee eeeeee (e.e., 88) ee eeeeeeeee eeee eeeeeeeeeeee (Meeeee 88) eeeeeeee ee eeeeeeeeeee eee eeee eeeeee ee eee eeeeeeeeeeeee eeeeeeee eeee eeee eee eee(eeeeeeeeeeeeeee)eeeeeee (Mee8MM8) (eee Meeeee 88).[‌88‌,‌88‌,‌888‌]

Meeeee 88 Meeeeeeeee ee Meeeeeeeeeeeeeeeeeeeeeeeee eeee Meeeeee Meeeee[‌888‌]

Meeeeeeeeeee Meeeeeeee

()-Mee(eeeeeeeeeeeeeee)eeeeee (88, Mee8MM):[‌88‌]

Me eeeeee eeee eee eeeee eeeeeeeeee eee eeeeeeee eeeeeeeeeeeee, eee eeeeeeeeee eeee eeeeeee eee eeeee e M8 eeeeeeeeee ee eeee-eeeee eeeeeeeee. MMM eee eeeeeeeee eeee MeMeM8 eee eeeeee eeeee M8. MMMMM eee eeeeeeeee eeee MeM8. Mee eeeeeee ee α-eeeeee eeee eeeeeeeee eeee MeMeM8 eee eeeeee eeeee M8.

M 88-eM eeeeeeeeee eeee eeeeee eeee e eeeeee eeeeee eee eeeeeeee eeeeeeee eee eee eeeeeee eeee MMM (8.88eM, 88eeee) eee MMM (88eM). Me eee eeeeee ee 8°M, eee (+)-α-eeeeee (88.8% ee; 8.88eM, 88eeee) eee eeeee eeeeeeee eeee eeeeeeee. Mee eeeeeeeeee eeee eee eeee eeeeee ee 8°M eee 88e. Mee eeeeeeeeeee eeee eee eeeeeeee ee eeeee e eeeeee-eeeee eeeeee. Mee eeeeeeeeeee eeeee ee ()-Mee8MM eeee eeeeee ee, eeeeee eeee Me8M (8×8eM), eee eeeee ee 88°M/88Meee; eeeee: 8.88e (88%).

M,M-[Mee(eeeeeeeeeeeeeee)eeeeeee]eeeeeeeeeeeeeeeeeeeeeeeeee [88, (MeeMM8)8(MMMMM)]:[‌888‌,‌888‌]

Meeeeeeeeee Mee8MM (88eeee) eee eeeeeeeee ee Me8M (8.8eM) eee MMMMM (8.88eM, 8.8eeee) eee eeeee ee 88°M eeee eeeeeeee ee eeee (MeeMM8)8(MMMMM) eeeeee 8e ee eeeeeeeeeeee ee (+)-α-eeeeee. Mee eeeee eeeeeee eee eeeeeeee ee eee eee eeeee. Mee eeeeeee eeeeeeeeee (+)-α-eeeeee eee e eeeee ee (MeeMM8)8(MMMMM) eee eeeeee eeeeeee e eeee ee eeeeee eee (88888 eeee, 88ee×8ee) eeee eeeeeee (88eM) ee eee eeeeee. Mee eeeeeee eee eeeeeeeeee eee eee (+)-α-eeeeee eee eeeeeeeee eeee MeMeM8 eee eeeeeeee ee eeeeeeeeeee MM; eeeee: 8.88e (88%); 88% ee.

Meeeeeeeeeeeeeeeeeeee (88, MeeMM8):[‌888‌]

Mee eeeeeeeeee eeee eeeeeee eee eeeee M8 ee ee eeee-eeeee 888-eM eeeee.

M eeee ee MMM (8.8eM, 88eeee) eee (+)-α-eeeeee (8.88eM, 88eeee) ee Me8M (88.8eM) eee eeeeeeee eee 8.8e. Meeee MMMMM (8.88eM, 88eeee) eee eeeee, eeeeee eee eeeeeeeee eee 8.8e, eee eee eeeeeee eee eeeeeeeeeee ee e eeeeeeeeee eeee. Me eeeeeee, (MeeMM8)8(MMMMM) (88) eeeeeeeeeeee, eee eee eeee eee eeeeeeeee ee eeeeeeeeeeeeee eee eeeeeeeeeee. Mee eeeee (MeeMM8)8(MMMMM) eee eeeeee eeee eeeeeee (8×8eM) eee eeeee (88Meee); eeeee: 8.88e (88%); ee 888888°M (Me8M). Me eeeeeeee MeeMM8, eee eeeee (MeeMM8)8(MMMMM) (8.8e, 8.8eeee) ee MMM (88eM) eee eeeeeee eeeee M8 eeeeee eee eeeeeeee ee MM8MMe8 (8.88eM, 88eeee). Meeee 8e, eee eeeee (MM8)8MMMMM eee eeeeeeeeeee. Meeeeeee ee eee eeeeeeeeeee eeee ee eeeeeeeeee ee eeeeee M8 eeeeeeeee eeeeeeeeeeee eeeeeeeeee eeee ee MeeMM8, eeeee eee eeeeeee eeeeeeeee ee eeeeeeeee eeeeeeeee ee eeeeeeeeeeeeeee.

Meeeeeeeeeeeeee-(8M,8M)-(8-eeeeeeeeeeeeeeee)eeeeee (88); Meeeeee Meeeeeeee:[‌88‌]

8.888M ()-MeeMM8 ee Me8M [88.8eM, 88eeee; eeee (+)-α-eeeeee] eeeee M8 ee e 88-eM eeeeeeeeee eeee eeeeeeee eeee e eeeeee eeeeee eee e eeeeeeee eeeeeeee eee eee eeeeee ee 88°M eee eeeeeee eeee 8-eeeeeeeeeeeeeeeee (8.8eM, 88eeee). Meeee eeeeee, eee eeeeeee eee eeee ee 88°M eee 88e. Mee eeeeeeeeeee eeeeee eee eeeeeeeee eeee eee eeeeeeeeeee eeeee eeee eee eee ee e eeeeee-eeeee eeeeee eee eee eeeee eee eeeeee eeee eeee (88°M) Me8M (8×8eM), eee eeeee; eeeee: 8.88e (88%); eeeeeeeeeeee eeeeee 88%. Mee eeeee eee eeee eeeeeeeee ee MMM (88eM), eeeeeeeee ee e 8M eeeeee, eee eeeeeee ee eee ee 8°M eee 88e. Meeeeeeeeee ee eee eeeeeeeeeee eeee eeeeeee e eeeeee-eeeee eeeeee eee eeeeeee eee eeeee eeee eeee (8°M) Me8M (8×8eM), eeeeeeee ee eeeeee eeee eee eeeee eeeeeeee; eeeee: 8.8e (88%). Mee eeeeeeeeeeee eeeeee eee eeeee ee ee 88% ee eeeeeeeeeeee eee eeeeeeeee eeee M8M8 ee eeee (M,M)-8-eeeeeeeeeeeeeeeeee, eeeee eeeeeeeeeeee ee MM [88% MM-88 ee Meeeeeeeee M (8888 eeee)].