Spirocyclic Tetramates by Sequential Knoevenagel and [1,5]-Prototropic Shift

Highly
functionalized spirocyclic tetramates were prepared via
a sequential Knoevenagel reaction and [1,5]-prototropic shift (T-reaction)
of bicyclic tetramates. While these compounds isomerize in solution,
stable analogues can be prepared via an appropriate choice of substituents.
Further modification of these compounds allows for the introduction
of aromatic groups, making them suitable as skeletons for application
in medicinal chemistry.