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[reaction: see text] Highly stereoselective titanium-mediated aldol reactions 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. 相似文献
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Saul F. Teloxa Stuart C. D. Kennington Marc Camats Prof. Pedro Romea Prof. Fèlix Urpí Prof. Gabriel Aullón Dr. Mercè Font-Bardia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11540-11548
A direct and highly enantioselective reaction of N-azidoacetyl-1,3-thiazolidine-2-thione with trimethyl orthoformate catalyzed by Tol-BINAPNiCl2 in the presence of TESOTf and 2,6-lutidine is reported. The heterocyclic scaffold can be easily removed by addition of a wide array of amines to give the corresponding enantiomerically pure 2-azido-3,3-dimethoxypropanamides in high yields. Appropriate manipulation of the N-benzyl amide derivative provides an efficient access to the antiepileptic agent lacosamide through a new enantioselective C−C bond-forming process. DFT computational studies uncover clues for the understanding of the remarkable stereocontrol of the addition of a nickel(II) enolate to a putative oxocarbenium intermediate from trimethyl orthoformate. 相似文献
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[reaction: see text] Two intramolecular C[bond]H...X (X = O, S) interactions in (S)-N-acyl-4-isopropyl-1,3-thiazolidine-2-thiones are documented through crystallographic and spectroscopic evidence and high-level theoretical calculations. The key role played by the sulfur atoms has been made clear by comparison with structurally related (S)-N-acyl-4-isopropyl-1,3-oxazolidin-2-ones. 相似文献
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Larrosa I Romea P Urpí F Balsells D Vilarrasa J Font-Bardia M Solans X 《Organic letters》2002,4(26):4651-4654
[reaction: see text] Lewis acid mediated addition of chiral titanium enolates to glycals provides either alpha- or beta-1'-methyl-substituted C-glycosides. This highly stereoselective methodology permits the modular preparation of three of the four possible diastereomers. 相似文献
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Cosp A Romea P Talavera P Urpí F Vilarrasa J Font-Bardia M Solans X 《Organic letters》2001,3(4):615-617
[reaction: see text] High stereoselectivities (up to 98% de) have been achieved for the Lewis acid-mediated cross-coupling reaction of dimethyl acetals to a chiral 1,3-thiazolidine-2-thione-derived titanium enolate. The reaction affords enantiopure anti alpha-methyl-beta-alkoxy carbonyl compounds in a wide range of acetals. 相似文献
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Alternative titanium-mediated aldol procedures based on several protected beta-hydroxy ethyl ketones have been surveyed. Eventually, enolization of (S)-1-benzyloxy-2-methyl-3-pentanone (1) with (i-PrO)TiCl3/i-Pr2NEt provided a very reactive enolate that afforded the corresponding 2,4-syn-4,5-syn aldol adducts in high yields and diastereomeric ratios with a broad range of aldehydes. 相似文献
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New syntheses of densely functionalized protected derivatives of 3-amino-3,6-dideoxyaminosugars have been accomplished in an efficient and straightforward manner. The key step of such approaches involves a highly stereoselective titanium-mediated aldol addition of a chiral α-bromo ketone, easily available from lactate esters, to crotonaldehyde. Further functional group transformations, including a new regioselective Staudinger-aza-Wittig reaction of an azidodiacetate, afford in a few steps and high yield the desired carbohydrates as advanced intermediates capable of participating in subsequent glycosylation reactions. 相似文献
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A substrate-controlled synthesis of (+)-herboxidiene from two lactate-derived chiral ketones is described. Remarkably, most of the carbon backbone was constructed through highly stereoselective titanium-mediated aldol reactions and an Ireland-Claisen rearrangement. Furthermore, an oxa-Michael cyclization and a high-yield Suzuki coupling were used to assemble the pyran ring and the diene moiety respectively. 相似文献