Tandem Cyclopropanation/Ring-Closing Metathesis of Dienynes

Certain dienynes give cyclorearrangement by tandem cyclopropanation/ring-closing alkene metathesis, triggered by either a ruthenium carbene or noncarbene ruthenium(II) precatalyst. The process represents a variation of enyne metathesis where presumed cyclopropyl carbene intermediates undergo a consecutive ring-closing metathesis. A mechanistic proposal is offered, and sequential use of catalysts provided a tandem ring-closing enyne/alkene metathesis product.