Remote 1,5-stereoinduction in boron aldol reactions of methyl ketones: application to the convergent assembly of the 1,3-polyol sequence of (+)-roxaticin
摘要:
By exploiting 1,5-anti stereoinduction in the boron aldol coupling of the beta -alkoxy methyl ketones 6 and 8 with aldehydes 7 and 9, the convergent synthesis of 2, corresponding to the fully protected polyol sequence of the 30-membered macrolide, (+)-roxaticin (1), was achieved in an efficient manner (15 steps and 24.0% yield from ketone 15). (C) 2001 Elsevier Science Ltd. All rights reserved.
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)
Aldol-like reactions of titanium enolates derived from α-OH, α-OBn, and α-OTBS ketones with a series of aldehydes have been studied. In sharp contrast to the O-benzyl derivatives, the TBS-protected ketones lead to excellent yields and selectivities ( ratios from 30:1 to >95:1) even for the lactate-derived substrate (2-tert-butyldimethylsilyloxy-3-pentanone).
Manipulation of the aldol adducts from lactate-derived ketones. A versatile chiral auxiliary for the asymmetric synthesis of β-hydroxy carbonyl compounds
作者:Ian Paterson、Debra J. Wallace
DOI:10.1016/0040-4039(94)88435-8
日期:1994.11
The ketones 1 and 2 can be transformed into a wide range of enantiomerically-pure anti and syn α-methyl-β-hydroxy ketones and aldehydes. The α′-methyl group in 5 and 11 may be retained, demonstrating the use of the lactate-derived group as an optional chiral auxiliary.