Selective Reduction of Cyclic Conjugate Enones with NaBH4 in the Presence of Cyclodextrins

Article abstract of DOI:10.1021/jo00360a023

The NaBH4 reduction of 2-cyclohexenone (1a), 3-methyl-2-cyclohexenone (1b), and 3,5,5-trimethyl-2-cyclohexenone (1c) to the corresponding cyclohexanols (2) and cyclohexenols (3) has been investigated in aqueous alkaline media, in the absence and in the presence of α- and β-cyclodextrins (CD) and two modified β-CDs.Changes in the <2>/<3> ratios are induced by substrate inclusion in the CD's cavities.The reduction (1b) is accelerated in the presence of β-CD.The strength and mode of substrate insertion into the CD's cavities have been inferred from a 1H NMR spectroscopy investigation.The formation of a ternary complex made of CD, substrate, and boron hydride species is suggested to account for the observed selectivities.