A new sequence for the synthesis of 3-(poly)enoyltetramic acids

Metal-Catalyzed and Metal-Mediated Approaches to the Synthesis and Functionalization of Tetramic Acids

“…Moreover, the synthesis of N-acyl tetramic acids may require an additional step due to deprotection of the nitrogen from the sodium ethoxide. However, some great enantioselective syntheses exist, such as the synthesis of Fuligorubin A 4 by Ley (Scheme 2; Part C) [57,58] and the synthesis of 3-polyenoyltetramic acids by Jones [59]. The key modification was the use of a milder base (TBAF or tBuOK) for a short time.…”

One-pot Synthesis of Optically Active Tetramic Acids from Amino Acids Mediated by 1-Hydroxybenzotriazole

“…On the other hand, Moloney et al 10 provided a N-acyloxazolidine derived from L-serine as a suitable precursor for the construction of chiral substituted tetramic acids with high enantiomeric excess. Other methodologies based on the enantioselective Lacey-Dieckmann cyclization, requiring strongly basic conditions 11,12 have also been reported.…”

Explorations of an intramolecular route to pyrrolo[3,4-b]isoxazoles: an unexpected retro-Claisen reaction

“…7 The results were inconsistent, with product 1 H NMR spectra sometimes showing loss of the tert-butyloxycarbonyl group and sometimes not. Samples retaining the tertbutyloxycarbonyl group had 1 H NMR spectra that implied acylation of the oxime N-atom rather than the amine function, with a signal for the proton NHBoc being observed at δ 4.62 (1H, d, J 9.6 Hz). More surprisingly, the NMR spectra suggested the reduced structure 5a, having an unexpected additional CH 2 N signal (δ 4.11-4.24, 2H, m; δ C 65.6) and no oxime sp 2 -CHN The capricious behaviour in the thermolysis led us to switch to the corresponding N-benzyloxycarbonyl aldoxime 4b, prepared from Nbenzyloxycarbonyl-S-valine methyl ester as outlined above for the tert-butyloxycarbonyl compound 4a.…”

“…C (100 MHz) NMR spectra were recorded on Bruker AC-250 or AC-400 spectrometers in CDCl 3 solutions with Me 4 Si or (CD 3 ) 2 SO as internal standard unless otherwise specified. Chemical shifts δ are given in parts per million (ppm) and 1 H coupling constants J in Hz, with multiplicities: s (singlet), d (doublet), t (triplet) and m (multiplet). Mass spectra were recorded on a JEOL SX102 spectrometer, or carried out by the EPSRC National Mass Spectrometry Service Centre (Swansea) or on a ZQ2000 spectrometer with Waters 600 series liquid handling system, dual wavelength UV and ELS detectors at Novartis, Horsham UK.…”

“…1 These metabolites show a range of biological activities, ranging through antibiotic, antitumour, antifungal and antiviral; 2 they also have a relationship to the inducers of bacterial quorum sensing. 3 Over recent years we have focussed on pyrroloisoxazoles 2 and 3 as providing masked forms of the polar enol functionality in the acyltetramic acids.…”