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Sulfonium, oxosulfonium and thiocarbonyl ylides

Deprotonation of sulfonium and oxosulfonium salts affords ylides, of structure R S −C −R′ and R S(O) −C −R′. While sulfonium ylides, for instance in the Johnson–Corey–Chaykovsky reaction used to synthesize epoxides, are sometimes drawn with a C=S double bond, e.g., R S=CR′, the ylidic carbon–sulfur bond is highly polarized and is better described as being ionic. Sulfonium ylides are key intermediates in the synthetically useful Stevens rearrangement. Thiocarbonyl ylides (RR′C=S −C −RR′) can form by ring-opening of thiiranes, photocyclization of aryl vinyl sulfides, as well as by other processes.