Nucleophile-Controlled Regiodivergent Domino Reactions of Enetriones with γ-Bromocrotonates: Access to 1,3-Dienic Esters and Tetrasubstituted Pyrans

Herein, we developed an efficient nucleophile-controlled regiodivergent domino reaction between enetriones and γ-bromocrotonates. This method allowed for the rapid synthesis of a range of 1,3-dienic esters and tetrasubstituted pyrans under metal-free conditions. In the presence of pyridine, a S_N2 substitution/Michael addition/elimination sequence formed 1,3-dienic esters in satisfactory yields with high E-stereoselectivities. Alternatively, a S_N2 substitution/Michael addition/cyclization/cyclopropanation/cyclopropane ring-opening process forged tetrasubstituted pyrans in good yields with the help of Et₃N. It is interesting to note that the site-selective reactions of γ-bromocrotonates at the α- or γ-position were readily realized by modulating pyridine and Et₃N. Furthermore, the simple pyridine and Et₃N act as both nucleophiles in S_N2 substitution reactions and Lewis bases in deprotonation processes.