The present invention relates to a series of substituted bis aryl and heteroaryl compounds of formula (I): Wherein X, Y, Z, A, B, D, Ar, R1 and R2 are as defined herein. The compounds of this invention are selective 5HT2A antagonists, and are therefore, useful in treating a variety of diseases including but not limited to a wide variety of sleep disorders as disclosed and claimed herein.