文摘
A highly enantioselective synthesis of spirocycles and bridged rings has been developed through a formal [4 + 2] cycloaddition reaction between enones and N-sulfonylimines. The unprecedented strategy has been realized utilizing N-sulfonylimine as a novel dienophile through enamine鈥搃minium tautomerism of N-sulfonylimine. In addition, a 纬,蔚-regioselective cycloaddition reaction proceeded by employing methylene chromene species as dienophiles.