Synthesis of 2-oxazolone-4-carboxylates from 3-nosyloxy- and 3-bromo-2-ketoesters.
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.
Okonya
John F
JF
Department of Chemistry and Biochemistry, North Horseshoe Drive, New Mexico State University, Las Cruces, New Mexico 88003-8001, USA.
Hoffman
Robert V
RV
Johnson
M Catherine
MC