Synthesis of the 5,6-dihydroxymorpholin-3-one fragment of monanchocidin A.

Monanchocidin A is a recently isolated pentacyclic guanidinium alkaloid that contains an unusual highly oxidized morpholinone fragment. Herein we report a rapid synthesis of this heterocyclic scaffold and confirm its structure. The key reaction involves an acid promoted hemiketalization/hemiaminalization of an α-hydroxyamide and α-ketoaldehyde that proceeds with exclusive regioselectivity and high diastereoselectivity to form the natural scaffold in moderate to high yield.