Intramolecular [2+2+1] Cycloadditions with (Cyclobutadiene)tricarbonyliron

Abstract

Highly functionalized strained rings are prepared through the cycloaddition of cyclobutadiene to alkynes. An intramolecular [2+2+1] cycloaddition is optimized for a variety of (cyclobutadiene)tricarbonyliron substrates with tethered alkynyl units (see scheme; CAN=cerium(IV) ammonium nitrate). The nature of the tether between the reactive functional groups in this transformation is found to have a significant influence on the outcome.