The treatment of pain continues to be the subject of considerable pharmaceutical and clinical research. α2 Adrenoceptor agonists are intriguing because they produce clinically effective analgesia that is devoid of opioid-related side effects. The α2 adrenergic agonist clonidine (1) is prescribed for the epidural treatment of severe pain, and the α2 agonist dexmedetomidine (2) is used in veterinary practice and for humans in several countries outside the United States. The primary site of antinociceptive action for α2 adrenergic analgesia is in the dorsal horn of the spinal cord. α2 Adrenergic receptors are localized largely in the presynaptic membrane, and activation of these receptors inhibits the release of pain-inducing neurotransmitters such as substance P, glutamic acid, and CGRP. We have recently reported the potent α2 adrenergic receptor affinity and analgesic activity associated with (imidazomethyl)oxazoles and -thiazoles, such as 3 (RWJ-37210). In addition, we have investigated a large number of (imidazomethyl)thiophenes, such as 4, that have a similar biological profile. Analyzing the preferred conformations of 4 by molecular modeling revealed significant torsional freedom for rotation of the two single bonds between the imidazole and thiophene. To restrict the rotation of this molecule, we extended and combined the 2-ethyl substituent with the bridging carbon atom to obtain the (imidazo)thianaphthene chemical series (e.g. 8 and 9, Scheme 1). These compounds are potent α2 adrenergic receptor ligands, and certain members of the series are very active in animal models of antinociception. 4-(4-Imidazo)-6,7-dihydrothianaphthene (14) has a favorable biological profile in vivo and is a prototype for this class of analgesic agents. The (imidazo)thianaphthenes are a new class of α2 adrenergic agents that display potent receptor binding affinity and are active in animal models of analgesia. 4-(4-Imidazo)-1,3-dimethyl-6,7-dihydrothianaphthene (22) is an exceedingly potent ligand for the α2D adrenergic receptor (Ki = 0.0086 nM) and is >10 000 fold selective relative to the α1 adrenergic receptor. This compound is more potent than dexmedetomidine at α2D and is a useful pharmacological tool drug for studies involving the α2D adrenergic receptor.