In order to address this issue, a new type of crotonate-derived sulfur ylide was developed in recent years. Because of the introduction of allylic part, the negative carbon dipolar would tend to tautomerize to other position with the base involved as the C3 synthesizers through a domino process (Scheme 1b). Scheme 1. Recent advances in the catalytic cyclization reactions of sulfur ylides as the C1 or C3 synthesizers