Based on our experimental results and previous related studies, 11b,12 a possible mechanism for this type of [4+3] annulation reactions was proposed (Scheme 4). Firstly, deprotonation of Scheme 3. Scope of the Seven-membered Carbocycles a a Reaction conditions: 4 (0.10 mmol, 1.0 eq), 2 (0.12 mmol, 1.2 eq), Cs2CO3 (0.2 mmol, 2.0 eq), CHCl3 (0.5 mL), r.t, 4 h. crotonate-derived sulfur ylides 2a results in a carbanion allylic ylide intermediate A in the presence of a base (such as Cs2CO3, NaH). Carbanion allylic ylide intermediates B is formed by tautomerism from sulfur ylide intermediate A. Then, an intermolecular Michael addition of carbanion allylic ylide intermediate B as C3 synthons to functional diene as the start step. Followed by the nucleophilic site of diene attacks the carbanion allylic ylide to implement a closed cycle process and one equivalent of SMe2 was separated from the system to complete the whole domino process. Finally, the highly functional none-fused cycles including nitrogen-heterocycles or carbocycles are obtained.