Novel steroid mimics directed towards the estradiol skeleton

A series of non-sym. tri- and tetra-substituted ureas, e.g. I (R = H, Me) were prepd. to mimic the rigid tetracyclic core of estradiol. Tetra-substituted ureas were prepd. by a five-step protocol, involving activation and displacement of a carbonyldiimidazole adduct in 48-67% overall yield. This method was unsuccessful for tri-substituted ureas, which were prepd. in 42-74% yields by an alternative four-step method, which included a one-pot 4-nitrophenyl carbamate formation/displacement sequence.