Studies in polypropionate synthesis: High π-face selectivity in syn and anti aldol reactions of chiral boron enolates of lactate-derived ketones
摘要:
Use of (c)Hex(2)BCl/Me(2)NEt in the aldol reactions of the alpha'-benzoyloxy ketone 7 with aldehydes leads to high stereoselectivity (97-99.5% ds) for the crystalline anti adducts 11. Under similar conditions, the corresponding benzyl ether 6 favours formation of the syn adducts 9.
Highly Stereoselective Aldol Reactions of Titanium Enolates from Lactate-Derived Chiral Ketones
作者:Joan G. Solsona、Pedro Romea、Fèlix Urpí、Jaume Vilarrasa
DOI:10.1021/ol0274054
日期:2003.2.1
[reaction: see text] Highly stereoselective titanium-mediated aldolreactions based on lactate-derived ketones are reported. The stereochemical outcome of the process depends on the protecting group (PMB or Bn) and the Lewis acid (i-PrOTiCl(3) or TiCl(4)) used in the enolization step, the corresponding anti-syn or syn-syn aldols being prepared in high yields and with diastereomeric ratios up to 99:1
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)