Palladium-catalyzed functionalization was presently performed
on
two building blocks: 4-oxazolin-2-ones and 4-methylene-2-oxazolidinones.
Direct Heck arylation of 4-oxazolin-2-ones led to a series of 5-aryl-4-oxazolin-2-ones,
including analogues with N-chiral auxiliary, in an almost quantitative
yield. The Pd(II)-catalyzed homocoupling reaction of 4-oxazolin-2-ones
provided novel heterocyclic across-ring dienes. Meanwhile, the intramolecular
cross-coupling of N-aryl-4-methylene-2-oxazolidinones
furnished a series of oxazolo[3,4-a]indol-3-ones.
Further functionalization of 4-methylene-2-oxazolidinones afforded
substituted indoles and heterocyclic-fused indoles with aryl, bromo,
carbinol, formyl, and vinyl groups. A computational study was carried
out to account for the behavior of the formylated derivatives. The
currently developed methodology was applied to a new formal total
synthesis of ellipticine.
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