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Procedure: 10 mL 1-neck flask, stirbar, septum, N2
inlet Dissolved
0.100 g of aldehyde I in 5.0 mL of
absolute MeOH. Stirred at rt. Added 0.029 g of powdered NaBH4. Vigorous gas evolution was
observed. After 10 min, TLC (10:90
EtOAc-hexanes, PMA) showed product spot at Rf 0.15. The reaction was quenched with sat. aq. NH4Cl and
extracted with Et2O.
The organic layer was dried over MgSO4, filtered and the
solvent was removed by rotary evaporation. The product was isolated by flash chromatography on silica
gel using 20:80 EtOAc-hexanes as eluant.
The product was a clear, colorless oil. notes The reduction of aldehydes with
NaBH4 is thought to be a concerted process whereby an O-B bond is
formed as addition of hydride to the carbonyl proceeds. All four hydrides from BH4
are available for addition and this complicates the reaction mechanism which is
depicted below for a single hydride transfer. After addition, solvolysis with MeOH liberates the free
hydroxyl and completes the reaction.
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