Silylation of N,O-Diacylhydroxylamines:  NMR Spectra and Structure of the Products

Abstract

Silylation of N, O-diacylhydroxylamines with N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide produces only O-silylated products and no N-silylated derivative. Steric interactions of the substituents on the nitrogen atom with the O-N oxygen atom control the configuration on the CdN bond in the product: a Z isomer is formed almost exclusively from N-benzoylhydroxylamines, and a mixture of E and Z isomers is produced from N-acetyl derivatives. The relative stability of all isomers in various conformations was confirmed by calculations at the B3LYP/6-31G(d,p) level. The tert-butyldimethylsilyl derivatives have been fully characterized by their 1 H, 13 C, 15 N, and 29 Si NMR spectra.

15N NMR Spectroscopy in Structural Analysis: An Update (2001 - 2005)

“…For each substrate the initial reaction occurs at the 5position to give a -adduct. Oxidation by peroxide in acetic acid or m-chloroperbenzoic acid leads to 15 N NMR spectra of silylated benzhydroxamic acids [266] and silylation products of N, O-diacetyl-hydroxylamines [267] have also been studied by Schraml and coworkers. 1 H NMR measurements on 4-nitrobenzofuroxan labeled with 15 N provide evidence, based on the absolute values of n J( 15 N, 1 H) coupling constants, that the rearrangement involves an intramolecular Boulton-Katritzky mechanism.…”

N,O-diacylhydroxylamines—structures in crystals and solutions

“…The relevance of the 15 N chemical shift is apparent from a comparison with the shifts −64/−82 and −69/−76 observed in E/Z pairs of tert-butyldimethylsilylated derivatives of 1B and 3B, respectively. 6 The line-widths of the 1 H, 15 N and 13 C NMR signals from the C(O)-NH-O-C(O) moiety depend on the concentration of the solute and on the molecular structure (Table 4). The variations in line-widths together with our failure to resolve the large one-bond coupling (approx.…”

“…Such a case was observed recently during silylation of N,O-diacylhydroxylamines 1-4 (Scheme 1): the ratio of the two products formed was considerably different in aliphatic and aromatic derivatives. 6 This led us to extend our studies to the parent compounds using additional experimental methods. between aromatic and aliphatic derivatives which is important for our purpose.…”