An unusual rearrangement in the boron-trifluoride-promoted reaction of tetracyclo[6.3.0.04,11.05,9]undecane-2,7-dione monoethylene acetal with ethyl diazoacetate

Abstract

is composed of six fused five-membered rings with three recognizable norbornane moieties, a seven-membered heterocyclic ring in a twist-chair conformation and an extended side chain. The fivemembered rings of the norbornane moieties are twisted from the normal envelope conformation toward half-chair. There is an intermolecular hydrogen bond involving the disordered side chain. Molecular-mechanics calculations estimate the angle and torsional strains to be 163.1 and 121.4 kJ mol-1, respectively.