The synthesis and 5-HT2A receptor affinities of ring altered derivatives of spiro [9, 10- dihydroanthracene]-9, 3′-pyrrolidine (4), a structurally unique tetracyclic 5-HT2A receptor antagonist, are described. The characteristics of the parent compound prove to be necessary for optimal 5-HT2A receptor affinity. However, expansion of the size of the pyrrolidine and central rings produce compounds with reasonably high 5-HT2A receptor ...