Electrooxidation Based Strategy Towards the Core 3-Amino-6-Hydroxy­azepan-2-one

Abstract

We describe a practical synthesis of protected (3S,6R)-6-hydroxy-cyclolysine derivatives starting from cyclic l-lysine. ­Evaluation of the electrochemical oxidation of various protected amino-caprolactams allowed a regioselective electromethoxylation at the α-position to the lactam nitrogen. Formation of the corresponding enamide by elimination of methanol followed by a diastereoselective dihydroxylation, diacetylation and subsequent regioselective reduction afford the orthogonally protected (3S,6R)-3-amino-6-hydroxy-azepan-2-one.

Key words

bengamides - diastereoselectivity - dihydroxylation - electrooxidation - osmium

References

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11

Electromethoxylations with Et₄NOTs, Bu₄NBF₄, Bu₄NClO₄ as electrolytes were less successful.

15

We observed similar C=C reductions when endocyclic enecarbamates derived from pipecolic acid were submitted to hydroboration with borane or dihaloboranes (unpublished results).

20

The osmylation/acetylation sequence carried out with substrate 5c gave a mixture of the expected diacetate 7c contamined by a bicyclic aminal resulting from intramolecular displacement of the hemiaminal hydroxy group via the corresponding iminium ion.

23

Indeed, examination of the IR spectra showed no significant changes in the lactam carbonyl absorption between lactams 4 or 3 and enamides 2 or 5.