Much effort has been devoted to solving the so-called "sigma (σ) enigma" since the term "σ receptor" was introduced in 1976. While many ligands with high affinity for σ sites have been discovered, little is known about the biochemical and molecular nature of these sites. A major problem in σ receptor research is the lack of specific ligands, as most agents bind to other receptor systems (e.g., serotonin 5-HT2, dopamine D2), making it unclear if their pharmacological properties are due to σ site interaction. Selective ligands are crucial for characterizing σ sites and developing therapeutic agents. Spirotetralines 1 are potent σ ligands but may have affinity for other receptors. To improve affinity for σ1 receptors and discriminate among σ sites and other systems, we synthesized 1′-benzyl-3,4-dihydrospiro[2H-1-benzothiopyran-2,4′-piperidine] (2, spipethiane) and its corresponding sulfoxide (3) and sulfone (4); 1′-benzyl-3,4-dihydrospiro[2H-1-benzopyran-2,4′-piperidine] (5) was included to verify the role of the sulfur atom in 2. We evaluated the in vitro activity of compounds 1-5 on σ1, σ2, serotonin 5-HT2, dopamine D2, muscarinic, opioid, PCP, and α1-adrenoreceptors, as well as σ3 binding sites and tyrosine hydroxylase (TH) activity. Results show that replacing the carbonyl group of 1 with sulfur (2) or oxygen (5) increases σ1 affinity, while 2 (spipethiane) exhibits superpotent affinity and high selectivity for σ1 receptors, with no significant affinity for other receptor systems. Oxidation of 2 to sulfoxide 3 or sulfone 4 causes a 40-50-fold decrease in σ1 affinity. Spipethiane (2) has low affinity for σ3 binding sites (IC50 = 632 ± 18 nM) and no effect on TH activity up to 0.1 μM. It is markedly more selective for σ1 receptors than 5. Thus, spipethiane is a potent and highly selective σ1 ligand.