1,3-versus 1,2-Asymmetric induction in the reduction of β-hydroxy ketones by intramolecular hydrosilylation
摘要:
The role of 1,2-asymmetric induction has been investigated in the 1,3-anti-selective reduction of beta-hydroxy ketones via intramolecular hydrosilylation. For the alpha-methyl beta-hydroxy ketones 2a, 3a, the effect of the alpha-substituent is negligible except that it appears to reinforce 1,3-asymmetric induction. For the alpha-ethyl beta-hydroxy ketones 2b, 3b, 1,3-asymmetric induction is dominant but not overwhelming. The super-acid TfOH2+ B(OTf)4- has been used as a catalyst for the hydrosilylation giving, in one case, an improved result when compared with previous methodology.
Stereoseletive Reduction of<i>β</i>-Hydroxy Ketones to 1,3-Diols with the Aid of a Terphenylboronic Acid
作者:Hiroshi Yamashita、Koichi Narasaka
DOI:10.1246/cl.1996.539
日期:1996.7
stereoselective reduction of acyclic and cyclic β-hydroxy ketones. The terphenylboronic acid 1 and acyclic β-hydroxy ketones 2 are converted to the corresponding boronates by azeotropic removal of water. The resulting boronates are treated in situ with reducing reagents to give syn 1,3-diols 3 almost exclusively. Anti α-substituted β-hydroxy ketones 8 are also reduced to give anti, anti 1,3-diol 9 stereoselectively