2- nonane asymmetric reductions

Asymmetric reduction of ketones using Alpine-borane . Alpine-borane = B-isopinocampheyl-9-borabicyclo[3.3.1]nonane. 

Asymmetric reduction of ketones. Ipc BCl is somewhat superior to B-3-pin-anyl-9-borabicyclo[3.3.1]nonane (12, 397) for enantioselective reduction of alkyl aryl ketones at normal pressures to (S)-alcohols. In general, optical yields are 78-98%. It is also useful for asymmetric reduction of ketones in which one alkyl group is tertiary. Thus 3,3-dimethyl-2-butanone is reduced in 95% ee at 25°.1... 

Rates of hydroboration of (61 R = Me, Et, Pr, Bu, and Ph) with 9-borabicyclo-[3.3.1]nonane have been elucidated and found to decrease with increasing steric bulk of R no reaction was observed for R = Pr1. The products (62) are potentially valuable for the asymmetric reduction of prochiral ketones.61... 

Boranes represent a family of reagents that has proved useful for asymmetric reductions. Here the asymmetric reduction of 3 is realized with Z -(3-pinanyl)-9-borabicyclo[3.3.1]nonane (15) ((5)-Alpine... 

Acetylenic ketones are important synthetic intermediates in the synthesis of a variety of natural products. Optically active propargyl alcohols of either configuration are readily available in high optical purity by asymmetric reduction of propargyl ketones with B-3-pinanyl-9-borabicyclo(3.3.1)nonane (Eq. 31). 

Although -3-pinanyl-9-borabicyclo[3.3.1]nonane and related substances have also been developed as efficient asymmetric reducing agents for carbonyl compounds (Volume 8, Chapter 1.3), we discuss here only asymmetric reductions using chirally modified metal hydride reagents. The asymmetric hydrosilyl-ation of a carbonyl group catalyzed by a chirally modified transition metal is mentioned briefly. 

Midland, M. M McLoughlin, J. I., Gabriel, J. Asymmetric reductions of prochiral ketones with B-3-pinanyl-9-borabicyclo[3.3.1]nonane (Alpine-Borane) at elevated pressures. J. Org. Chem. 1989, 54,159-165. 

Rogic, M. M. Conformational Analysis and the Transition State in Asymmetric Reductions with Boranes Based on (+)-a-Pinene. 1. Benzaldehyde Reduction with Alpine Borane and Other B-Alkyl-9-borabicyclo[3.3.1]nonanes. ASemiempirical Study. J. Org. Chem. 1996, 61, 1341-1346. 

ASYMMETRIC REDUCTIONS 2,2 -Dihydroxy-1, l -binaphthyl-Lithium aluminum hydride. (2S,3RM+)-4-Dimethyl-amino-3-methyl-l,2-diphenyl-2-butanol. Lithium aluminum hydride-(-)-N-Methyiephedrine. B-(3)-oi-Pinanyl-9-borabicyclo[3.3.1 ]nonane. (S)-2-(2,6-Xylidinomethyl)pyrrolidine. 

Asymmetric reduction of propargyl ketones with (R) or (S) Alpine borane (B-isopinocamphenyl-9-borabicyclo, [3,3,1] nonane(A))... 

Trialkylborohydrides prepared from optically active alkenes may be used for asymmetric-reduction. For example, reaction of fcrt-butyllithium with Alpine-borane, prepared by hy-droboration of ( + )- or ( —)-a-pinene with 9-borabicyclo[3.3.1]nonane (see Section D.2.3.5.1.), provides Alpine-hydride. 1 his reagent reduces 1-phenylethanone in 17% ee72. A more effective reagent is NB-Enantride, prepared in a similar manner by treatment of the product from hydroboration of the benzyl ether of 2-(2-hydroxyethyl)-6,6-diinethylbicyclo[3.3.1]hept-2-ene (nopol. see Section D.2.3.5.1.) with toV-butyllithium73. 

Brown and coworkers [1] have found that NB-Enantrane is effective only for the reduction of a,(3-acetylenic ketones. The reduction of other ketones is too slow to be of any practical use. The retarded rate is attributed to the steric bulk at the 2 position since no internal coordination has been detected by "B NMR (6 86 ppm) [2]. On the other hand, Alpine-Borane has proven to be versatile reagent for the asymmetric reduction of variety of ketones. Consequently, two reagents B-(iso-2-ethylapopinocampheyl)-9-borabicyclo[3.3.1]nonane (Eapine-Borane) and B-(iso-2- -propylapopinocampheyl)-9-BBN (Prapine-Borane) having increasing steric requirement at the 2 position, are prepared by the hydroboration [3] of 2-ethyl- and 2-n-propylapopinene. 

Scheme 6.3 Proposed transition state made for asymmetric reduction with B-isopinocamphenyl-9-borabicyclo[3.3.I]nonane [36,40],...

R)-Propargylic alcohols have also been produced, this time in 73—100% e.e., by asymmetric reduction of a,/3-acetylenic ketones with the chiral borane prepared from (+)-a-pinene and 9-borabicyclo[3.3.1]nonane (9-BBN) (Scheme 10), a system already known to reduce aldehydes to chiral alcohols cf. 2,115). These results compare favourably with those from the LiAlH4- Darvon complex above, and the availability of both (+)-and (-)-o -pinene means that either (R)-or (5)-propargylic alcohols may be produced. 

Sih (38) has described the reduction of E-l-iodo-l-octen-3-one with Penicillium decumbens to give the desired S-alcohol. Based on optical rotation, the e.e. was about 80%, An asymmetric chemical reduction of this same ketone, using lithium aluminum hydride that had been partially decomposed by one mole each of S-2,2 -dihydroxy-l,T-binaphthol and ethanol (42), gave the desired alcohol in 97% e.e. This reagent also reduced l-octyn-3-one in 84% e.e. to the corresponding alcohol (43). A 92% e.e. could be obtained with B-3-pinanyl-9-borabicyclo[3.3.1]nonane as the reducing agent (44). 

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