AbstractTreatment of [Ru]C=CPh (1, [Ru] = (η5‐C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) with PhN=C=S at room temperature affords the [2 + 2] cycloaddition product (2) which contains a four‐membered‐ring heterocycle. A series of cationic S‐alkylated ruthenium vinylidene complexes [Ru]=C=C(Ph)C(=NPh)SCH2R+(3a, R = CONH2;3b, R = CH=CH2;3c, R =p‐C6H4CF3) and N‐alkylated ruthenium vinylidene complexes [Ru]=C=C(Ph)C(=S)N(Ph)CH2R+(4b, R = CH=CH2;4c, R =p‐C6H4CF3) are prepared from2with organic halides at room temperature with high yields. Deprotonation of3aand3cbyn‐Bu4NOH in acetone induces novel cyclization reactionsviaC‐C bond formation and yields neutral five‐membered‐ring heterocyclic complexes (5a, R = CONH2;5c, R =p‐C6H4CF3). In a similar manner, deprotonation of4band4cby NaOMe in CH2Cl2also induces another cyclization to yield the pyrrole‐2‐thione complexes (6b, R = CH=CH2;6c, R =p‐C6H4CF3). At room temperature,5cisomerizes to the 2‐aminothi