Synthesis of conformationally constrained spirohydantoins with a dibenzo[a,d]heptadiene ring

Conformationally constrained dibenzo[a,d]cycloheptadiene-based spirohydanto ins were prepared from dibenzosuberone via the transformation of the a-hydr oxy ester to the azido ester, followed by its reduction to the amino ester, and cyclization of the carbomethoxy N,N'-asymmetric ureas, derived from th e amino ester with triphosgene and a variety of amines. A novel ring expans ion reaction was also observed in the process.