Synthesis of 2-Oxazolone-4-carboxylates from 3-Nosyloxy- and 3-Bromo-2-ketoesters
摘要:
New methods for the synthesis of 2-oxazolone-4-carboxylates from 3-nosyloxy- and 3-bromo-2-ketoesters are described. Condensation of 3-nosyloxy-2-ketoesters with methyl carbamate in refluxing toluene in the presence of p-TSA provided 2-oxazolone-4-carboxylates in good yields (41-80%). Alternatively, bromination of alpha-ketoesters with CuBr2 provided 3-bromo-2-ketoesters which condensed with methyl carbamate in the presence of p-TSA and AgOTf under similar conditions to provide 2-oxazolone-4-carboxylates in comparable yields (30-79%). The 2-oxazolone-4-carboxylates bear functionality that can be elaborated to a variety of potentially useful compounds. For example, some of these heterocycles were readily N-acylated, reduced to alcohols, or saponified and coupled with amino acids.
Convergent Synthesis of 2-Oxazolone-4-carboxylates Esters by Reaction of Aldehydes with Ambivalent <i>N</i>-Cbz-α-Tosylglycinate Ester
作者:Masahiro Abe、Baptiste Picard、Michaël De Paolis
DOI:10.1021/acs.orglett.0c01703
日期:2020.6.19
N-Cbz-α-tosylglycinate ester was combined with aldehydes in a redox-neutral sequence leading to 2-oxazolone-4-carboxylates with high functional group tolerance. While the scope of the method was delineated to primary and secondary aliphatic aldehydes as well as aromatics, no racemization occurred with chiral aldehydes such as Garner’s. Hitherto unknown, this process relies on the ambivalent role of
N -Cbz-α-甲苯磺酰基甘氨酸酯与醛以氧化还原中性顺序结合,产生具有高官能团耐受性的2-恶唑酮-4-羧酸酯。尽管该方法的范围被限定为伯和仲脂族醛以及芳族化合物,但手性醛(如Garner's)未发生外消旋作用。迄今为止未知,该过程依赖于N -Cbz-α-甲苯磺酰基甘氨酸酯作为亲核试剂的矛盾作用。
Oxidation of didehydro-α-amino acids as a route to β-hydroxy-or β-amino-pyruvic derivatives and to α-acylglycinates
Oxidation of protected didehydro-alpha-amino acids with N-bromosuccinimide or lead tetraacetate affords imines of beta-bromo- or beta-acetoxy-pyruvates. The hydrolysis of brominated imines proceeds through addition of water followed by intramolecular displacement of bromine, According to experimental procedures, intermediate hydroxyaziridines, hydroxyoxazolines or aminoepoxides have to be considered. Two pathways are examined for hydrolysis of beta-acetoxyimines: cyclisation to oxazolones or conversion to acylglycinates when imines are converted to the isomeric enamines prior to deprotection.
Synthesis of 4-carboethoxy-4-oxazolin-2-ones from 3-nosyloxy-2-ketoesters
作者:Robert V. Hoffman、M.Catherine Johnson、John F. Okonya
DOI:10.1016/s0040-4039(97)10854-1
日期:1998.3
3-Nosyloxy-2-ketoesters, available from 2-ketoesters, react efficiently with methyl carbamate and tosic acid in refluxing toluene to provide 4-carboalkoxy-4-oxazolin-2-ones in good yields (41-84%). (C) 1998 Elsevier Science Ltd. All rights reserved.