Smart cleavage reactions: the synthesis of an array of ureas from polymer-bound carbamates. 
The solid-phase synthesis of a library of di-, tri-, and tetrasubstituted ureas is described.  In this approach, an array of polymer-bound carbamates was synthesized.  These polymer-bound primary and secondary amine carbamates were then treated under "smart" diversity-building cleavage conditions using a series of aluminum amide complexes to form the corresponding urea cleavage products.  The crude cleavage products from this study were isolated in excellent yield and purity.  To show the applicability of this strategy, a series of biaryl ureas were synthesized using sequential solid-phase Suzuki coupling and urea formation reactions.