Complexity-enhancing acid-promoted rearrangement of tricyclic products of tandem Ugi 4CC/intramolecular Diels-Alder reaction.

The unexpected rearrangement of 2,3,7,7a-tetrahydro-3a,6-epoxyisoindol-1-one products of the tandem Ugi 4CC/intramolecular Diels-Alder reaction in 85% H3PO4 was discovered to provide diastereomerically pure tricyclic bislactam lactone-containing natural product-like products in high yield. Mechanistic rationale for the observed rearrangement was proposed and has been tentatively confirmed by additional experiments.