AbstractThe stereochemistry of the α‐sulfinyl carbanion has been studied. It has been elucidated that a 2‐pyridylmethyl substituent on the sulfinyl sulfur chelates onto the counter cation in an ion pair to fix the conformation of the anion at a particular orientation. Then, the steric bulk of the other substituent plays a role to control the reacting face. A soft electrophile such as methyl iodide attacks the anion from the more open side. On the other hand, a hard electrophile such as a proton is initially trapped by the polar part of the ion pair and no steric effect oper