Ring-closing-metathesis-based synthesis of annellated coumarins from 8-allylcoumarins

8-Allylcoumarins are conveniently accessible through a microwave-promoted tandem Claisen rearrangement/Wittig olefination/cyclization sequence. They serve as a versatile platform for the annellation of five- to seven-membered rings using ring-closing olefin metathesis (RCM). Furano-, pyrano-, oxepino- and azepinocoumarins were synthesized from the same set of precursors using Ru-catalyzed double bond isomerizations and RCM in a defined order. One class of products, pyrano[2,3-f]chromene-2,8-diones, were inaccessible through direct RCM of an acrylate, but became available from the analogous allyl ether via an assisted tandem catalytic RCM/allylic oxidation sequence.

Concise strategy for the synthesis of eleven-membered and ansa-bridged thirteen-membered lactone macrolides by ring-closing metathesis reaction

The eleven-membered macrolides and thirteen-membered ansa-bridged macrolides have been synthesized successfully by ring-closing metathesis reaction in the absence of the additive Ti(OiPr)4, which is essential for the metathesis reaction of the ester precursors.