Synthesis and reactions of 2-substituted ethyl N-alkylmalonylhydroxamic acids.

Alkylation of O-silylated N-alkylmalonylhydroxamic acids provides a method for the synthesis of 2-substituted N-alkylmalonyl hydroxamic acids. The substituent at C-2 does not materially change the chemistry of the alpha-lactam intermediates produced from them. They can be converted to unsymmetric ureas and hydantoins in high yields. The addition of unsaturated substituents at C-2 is used to produce cyclic ureas containing medium rings via RCM reactions.

Origins of regioselectivity in the reactions of alpha-lactams with nucleophiles. Two distinct acid-catalyzed pathways involving O- and N-protonation.

Sterically stabilized alpha-lactams react by two distinct acid-catalyzed pathways. Protonation on oxygen results in nucleophilic attack at the acyl carbon and gives C-2 products. Protonation on nitrogen leads to nucleophilic attack at the C-3 carbon and yields C-3 products. The mechanism thus developed is very useful for understanding the changes in rates and product distributions in the reactions of sterically stabilized alpha-lactams with nucleophiles. It can also be extrapolated to other alpha-lactams so that a more coherent picture of alpha-lactam reactivity can be developed.

Highly stereoselective syntheses of syn- and anti-1,2-amino alcohols.

The reduction of N-protected amino ketones can be carried stereoselectively to produce either the syn- or anti-amino alcohol diastereomer. Carbamate-protected amino ketones can be reduced predictably and selectively to anti-amino alcohols with LiAlH(O-t-Bu)3 in ethanol at -78 degrees C. N-Trityl-protected amino ketones can be reduced selectively to syn-amino alcohols with LiAlH(O-t-Bu)3 in THF at -5 degrees C.

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.

A Stereocontrolled Synthesis of Monofluoro Ketomethylene Dipeptide Isosteres.

A simple, stereocontrolled synthesis of monofluoro ketomethylene dipeptide isosteres has been developed. N-Tritylated ketomethylene dipeptide isosteres, prepared from N-tritylated amino acids, are converted to their Z-TMS enol ethers and fluorinated with Selectfluor. There is cooperative stereocontrol between the N-tritylamine group and the alkyl group at C-2. The method is short (six steps), diastereoselective (85 --> 95%), and enantioselective (>95%).

Synthesis and Reactions of 3-(Nosyloxy)-2-keto Esters.

A series of 3-(nosyloxy)-2-keto esters 7a-j were prepared from the corresponding alpha-keto esters by conversion to the trimethylsilyl enol ether and reaction with p-nitrobenzenesulfonyl peroxide. Conversion of these materials to 1,2,3-trifunctionalized compounds is described, and comparison of their properties with isomeric 2-(nosyloxy)-3-keto esters is discussed.