New Strategy for the Stereoselective Synthesis of Fluorinated β-Amino Acids
摘要:
Racemic and chiral nonracemic alpha-substituted and alpha-unsubstituted beta-fluoroalkyl beta-amino acid derivatives 6 and 9 have been synthesized in two steps starting from fluorinated imidoyl chlorides 1 and ester enolates. This approach is based on the chemical reduction of previously obtained gamma-fluorinated beta-enamino esters 4 by using ZnI2/NaBH4 in a nonchelated aprotic medium (dry CH2Cl2) as the reducing agent. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction. The process takes place with high yields and with moderate to good diastereoselectivity. The best results related to diastereoselective reduction of chiral beta-enamino esters 4 were provided by the use of (-)-8-phenylmenthol as a chiral auxiliary.
New Strategy for the Stereoselective Synthesis of Fluorinated β-Amino Acids
摘要:
Racemic and chiral nonracemic alpha-substituted and alpha-unsubstituted beta-fluoroalkyl beta-amino acid derivatives 6 and 9 have been synthesized in two steps starting from fluorinated imidoyl chlorides 1 and ester enolates. This approach is based on the chemical reduction of previously obtained gamma-fluorinated beta-enamino esters 4 by using ZnI2/NaBH4 in a nonchelated aprotic medium (dry CH2Cl2) as the reducing agent. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction. The process takes place with high yields and with moderate to good diastereoselectivity. The best results related to diastereoselective reduction of chiral beta-enamino esters 4 were provided by the use of (-)-8-phenylmenthol as a chiral auxiliary.
An enantioselective palladium-catalyzed hydrogenation of β-fluoroalkyl β-amino acrylic acidderivatives has been successfully developed, providing the corresponding chiral β-fluoroalkyl β-aminoacidderivatives in good yields with excellent enantioselectivities. In addition, chiral γ-fluoroalkyl γ-amino alcohol could be synthesized by a simple reduction of the corresponding hydrogenated product. The
First Highly Diastereoselective Synthesis of <i>s</i><i>yn</i> α-Methyl β-Fluoroalkyl β-Amino Esters
作者:Santos Fustero、Belén Pina、Marta García de la Torre、Antonio Navarro、Carmen Ramírez de Arellano、Antonio Simón
DOI:10.1021/ol990774o
日期:1999.10.1
[GRAPHICS]A new two-step approach for the diastereoselective synthesis of the syn alpha-methyl beta-fluoroalkyl beta-amino esters 4 has been developed. This approach is based on the chemical reduction of the fluorinated beta-enamino esters 3, which have been previously obtained from imidoyl chlorides 1 and lithium ester enolates, with Znl(2)/NaBH4 as the reducing agent. The process takes place with high syn diastereoselectivity and good to excellent yields. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction.
New Strategy for the Stereoselective Synthesis of Fluorinated β-Amino Acids
作者:Santos Fustero、Belén Pina、Esther Salavert、Antonio Navarro、M. Carmen Ramírez de Arellano、Antonio Simón Fuentes
DOI:10.1021/jo025621k
日期:2002.7.1
Racemic and chiral nonracemic alpha-substituted and alpha-unsubstituted beta-fluoroalkyl beta-amino acid derivatives 6 and 9 have been synthesized in two steps starting from fluorinated imidoyl chlorides 1 and ester enolates. This approach is based on the chemical reduction of previously obtained gamma-fluorinated beta-enamino esters 4 by using ZnI2/NaBH4 in a nonchelated aprotic medium (dry CH2Cl2) as the reducing agent. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction. The process takes place with high yields and with moderate to good diastereoselectivity. The best results related to diastereoselective reduction of chiral beta-enamino esters 4 were provided by the use of (-)-8-phenylmenthol as a chiral auxiliary.