Scope and limitations of the use of partially unsaturated sultams as dienophiles and dienes in [4+2] Diels-Alder reaction

This study explores the reactivity of five- and six-membered sultams as both dienes and dienophiles in Diels-Alder reactions. As dienes in [4+2] cycloaddition, vinyl sultam bearing an additional endocyclic C=C double bond reacted with highly electron-poor alkenes, namely with maleimide, revealing that successful cycloadduct formation occurred only under aqueous reflux conditions. Alternative conditions, including organic solvents and Lewis acid catalysis, were unsuccessful in promoting the reaction. Other dienophiles, such as acrylates and acetylene carboxylates, were ineffective, with sultam undergoing self-cycloaddition in moderate yields. As a dienophile, the partially unsaturated sultam reacted selectively only with electron-enriched Danishefsky’s diene, forming a fused sultam with an enone moiety. Other dienes, ranging from electron-enriched to electron-poor derivatives, did not react under the applied conditions, leaving the starting material unaltered. These results demonstrate the highly selective reactivity of sultams, influenced by their electronic properties, and provide valuable insights into their utility in synthetic organic chemistry