Polycyclic Ring Formation Using Bis-diazolactams for Cascade Stitching

The
chemoselective reaction of donor/acceptor (D/A) and acceptor/acceptor
(A/A) diazo moieties in the same molecule was examined using 3-diazo-1-(ethyl
2-diazomalonyl)­indolin-2-one under rhodium­(II) catalysis. The metallo
carbenoid derived from the D/A diazo group is preferentially formed
and undergoes selective CH, NH, and OH insertion reactions, cyclopropanation,
cyclopropenation, sulfur ylide formation/2,3-sigmatropic rearrangement,
as well as nitrogen ylide formation followed by azetidine ring expansion.
The initial reaction can be paired with a subsequent tandem cascade
sequence involving dipole formation/cycloaddition in either an intra-
or intermolecular sense to generate polycyclic N-heterocycles
in one pot, with the formation up to three new rings in a single operation.
Excellent diastereoselectivity was observed in the intramolecular
cycloaddition reaction producing 5 to 7-membered rings.