these reactions. Enhanced preference for the more sterically demanding Michael adducts is obtained with Bu(2)Sn(OTf)(2), SnCl(4), and Et(3)SiClO(4) in the former reaction while TiCl(4) gives the highest selectivity for the less sterically demanding products in the latter case. These results are interpreted in terms of alternative reaction mechanisms. The reaction of less bulky ketene silyl acetals are
Solvent-Dependent Diastereoselectivities in Reductions of β-Hydroxyketones by SmI<sub>2</sub>
作者:Pramod R. Chopade、Todd A. Davis、Edamana Prasad、Robert A. Flowers
DOI:10.1021/ol049129u
日期:2004.8.1
The reductions of a series of beta-hydroxyketones by Sml(2) were examined in THF, DME, and CH3CN using methanol as a proton source. Reductions in THF and DME typically lead to the syn diastereomer with DME providing higher diastereoselectivities. Reductions in CH3CN provided the anti diastereomer predominantly. This study reveals that solvation plays an important role in substrate reduction by Sml(2).
Reduction of β-Hydroxyketones by SmI<sub>2</sub>/H<sub>2</sub>O/Et<sub>3</sub>N
作者:Todd A. Davis、Pramod R. Chopade、Göran Hilmersson、Robert A. Flowers
DOI:10.1021/ol047835p
日期:2005.1.1
Reduction of a series of beta-hydroxyketones by SmI2/H2O/Et3N provided 1,3-diols in quantitative yields. The reactions were exceedingly clean with no byproduct formation, negating the need for further purification. Most reactions provided moderate to excellent diastereoselectivity with syn-diols as the major isomer in most instances.
Conformational effects of alkyl groups on the .pi. .far. .pi.* transitions of .alpha.-enones