Synthesis of β-Oxabutyrolactams Starting from 2,5-Dihydrooxazoles

Abstract

A new synthetic pathway to generate β-oxabutyrolactams starting from 2,5-dihydrooxazoles is described. This procedure is based on the addition of acid chlorides to heterocyclic imines followed by oxidation in the presence of pyridinium chlorochromate.

Key words

heterocycles - imines - β-oxabutyrolactams - oxidation - N-acyliminium ion

References

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14

In the major diastereomers, saturation of the protons of the methyl moiety at C5 generates a very small NOE for the proton at C4, indicating trans-configuration. Compared to the ROE experiments of the minor diastereomers, the saturation of the protons of the methyl moiety at C5 led to a strong NOE for the proton at C4, consequently indicating cis-configuration.

15

Saturation of the protons of the methyl group at C5 (˜1 ppm) gave a strong NOE for the proton at C4 and a moderate NOE for the proton at C2, indicating cis-configuration for the protons at C2 and C4.