Stereoselective Cyclization Routes to Fused Pyrrole-Pyrazine-Oxazoles

Significance

A stereoselective synthesis of tricyclic pyrrole-pyrazine-oxazole derivatives is reported. Upon treatment under Vilsmeier-Haack conditions, pyrroles, derived from amino acid esters, undergo formylation and then the formylated products are treated with norephedrine to form pyrrole-pyrazine-oxazole-fused derivatives in high yields. The stereochemical outcome is exclusively determined by the absolute stereochemistry of norephedrine. This result makes it possible to combine amino acid esters and enantiomers of norephedrine with stereochemical control to get a wide range of enantiomeric fused pyrrole-pyrazine-oxazole derivatives.