Stereoselective titanium-mediated syn -aldol reaction from a lactate-derived chiral ethyl ketone
作者:Joan G Solsona、Pedro Romea、Fèlix Urpı́
DOI:10.1016/j.tetlet.2004.05.077
日期:2004.7
TiCl4 has given access to the corresponding 2,4-anti-4,5-syn aldol adducts with the highest diastereomeric ratios. The excellent stereocontrol exerted by the aforementioned ketone has been demonstrated in double asymmetric reactions involving chiral α-methyl-β-OTBDPS aldehydes.
Stereoselectivity of TiCl4-mediatedaldolreactionsfrom (S)-2-benzyloxy-3-pentanone is dramatically improved when the reaction is carried out in the presence of 1.1 equiv of tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME). The resultant 2,4-syn-4,5-syn adducts are then obtained in diastereomeric ratios up to 97:3, which proves that the appropriate choice of the Lewis acid (TiCl4−THF or DME vs Ti(i-PrO)Cl3)