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Esters Alpine borane

Alpine-Borane,prepared by hydroborationofa-pinenewith9-borabicyclo[3.3. Ijnonane (9-BBN), reduces aldehydes, a-keto esters and acetylenic ketones with excellent enantioselectivity. The reduction proceeds via a cyclic process similar to the MPV reaction. [Pg.125]

The use of alpine-borane (3) has also been extended to include the reduction of acyl cyanides (14) to optically active p-amino alcohols (15),10 as well as the reduction of a-keto esters (16) into the corresponding a-hydroxy esters (17). ... [Pg.42]

Hydroxy-esters. - Once again, most contributions to this area involve the synthesis of chiral hydroxy-esters. Almost complete enantioselectivity is achieved in the reduction of a-keto-esters to a-hydroxy-esters using Alpine-Borane (B-(3-pinanyl)-9-BBN) derived from either (+)- or (-)-a-pinene when the reactions are carried out at relatively high concentrations (>2M). Many other types of prochiral ketones are also reduced with excellent asymmetric inductions although 3-keto-esters may not be particularly suitable substrates as ethyl acetoacetate is reduced to ethyl 3-hydroxybutanoate with an enantiomeric excess of only... [Pg.96]

The reaction is extended [3] to the reduction of a-ketoesters, another class of ketones, possessing powerful electron-withdrawing ester group. The reduction of a-ketoesters with 40% excess of neat Alpine-Borane proceeds rapidly at 25 °C (Eq. 26.4 Table 26.9) [3,4b]. [Pg.442]

However, unlike Eapine-Borane and Alpine-Borane Prapine-Borane fails to provide improved asymmetric induction in the reduction of a-keto esters (Table 26.19) [1]. [Pg.458]

In the asymmetric reduction of a-ketoesters, the asymmetric induction depends on the steric inequality of two moieties attached to the carbonyl group [9]. The reduction of hindered a-ketoesters yields the corresponding a-hy-droxyesters with optical purities approaching 100% ee (Eq. 26.28). This contrasts strongly with the 11% ee realized in the reduction of 7 (R= i-Pr) with neat Alpine-Borane [9b]. Alpine-Borane (from (-t)-pinene) yields (S)-alcohols in the reduction of both alkylaromatic ketones and a-ketoesters. On the other hand K-glucoride yields (R)-alcohols with aralkylketones and (S)-alcohols with a-keto esters (Table 26.27) [7]. [Pg.467]


See other pages where Esters Alpine borane is mentioned: [Pg.247]    [Pg.1102]    [Pg.603]    [Pg.603]    [Pg.236]    [Pg.479]    [Pg.1102]    [Pg.301]    [Pg.83]    [Pg.407]    [Pg.603]    [Pg.25]    [Pg.158]   
See also in sourсe #XX -- [ Pg.603 ]

See also in sourсe #XX -- [ Pg.603 ]

See also in sourсe #XX -- [ Pg.603 ]




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Alpine borane

Alpine boranes

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