Cyclic oxonium ylides: building blocks for iterative synthesis of polycyclic ethers

A series of diazoketones bearing remote benzyl or allyl ethers was subjected to a variety of conditions for catalytic diazodecomposition and cyclic oxonium ylide formation as a possible method for polycyclic ether synthesis. Allyl ethers , and underwent efficient conversion to the corresponding bis(pyran) and tris(pyran) products in the presence of Cu(tfacac)2, while benzyl ether was converted to bicyclic products and with Rh2(tpa)4. Treatment of homologous substrate with Rh2(tpa)4 provided novel medium-ring cyclopropanation products in good yield.