- Conjugate addition of lithium N-tert-butyldimethylsilyloxy-N-(α-methylbenzyl)amide: asymmetric synthesis of β2,2,3-trisubstituted amino acids
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Conjugate addition of the homochiral ammonia equivalent lithium N-tert-butyldimethylsilyloxy-N-(α-methylbenzyl)amide to a range of α,β-unsaturated esters gives the corresponding β-amino esters in moderate to good levels of diastereoselectivity. O-Desilylation and cyclisation furnishes homochiral isoxazolidin-5-ones in >99:1 dr after purification. Sequential alkylation of these templates proceeds to give the corresponding 3,4-anti-disubstituted and 3,4,4-trisubstituted derivatives as single diastereoisomers after purification. The first alkylation occurs with high levels of diastereoselectivity on the face of the enolate anti to the C(3)-substituent, whereas the facial selectivity of the second alkylation is governed by a chiral relay effect, which depends upon the relative steric bulk of both the C(3)- and C(4)-substituents. Subsequent hydrogenolysis promotes cleavage of both the N-α-methylbenzyl group and the N-O bond within the isoxazolidin-5-one ring in one pot to give the corresponding β2,2,3-trisubstituted amino acids directly.
- Bentley, Scott A.,Davies, Stephen G.,Lee, James A.,Roberts, Paul M.,Russell, Angela J.,Thomson, James E.,Toms, Steven M.
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scheme or table
p. 4604 - 4620
(2010/07/05)
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- An improved process for the synthesis and isolation of (S)-N-(1- phenylettiyl)hydroxylamine
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A three-step, single-solvent telescoped process amenable to the large-scale manufacture of (S)-N-(1-phenylethyl)hydroxylamine p-toluenesulfonic acid salt is reported. This synthetic protocol has been applied to the preparation of other chiral hydroxylamin
- Patel, Ian,Smith, Neil A.,Tyler, Simon N. G.
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experimental part
p. 49 - 53
(2010/04/22)
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- Chemical process
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A process for preparing a salt of compound of formula (I) wherein R1 and R2 are independently selected from an organic group other than hydrogen, said process comprising reacting a compound of formula (II) with water and an organic a
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Page/Page column 3
(2008/06/13)
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- A novel transformation of primary amines to N-monoalkylhydroxylamines
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A novel transformation of primary amines to the corresponding N-monoalkylhydroxylamines is described. The three-step protocol involves selective mono-cyanomethylation of primary amines, regioselective formation of nitrones by m-CPBA oxidation, and hydroxylaminolysis of the nitrones with hydroxylamine hydrochloride. The method is applicable for a wide range of primary amines, including alkyl, benzyl, and chiral.
- Tokuyama,Kuboyama,Amano,Yamashita,Fukuyama
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p. 1299 - 1304
(2007/10/03)
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