Lewis Base-Switched [3 + 3] and [4 + 2] Annulation Reactions of δ-Acetoxy Allenoates with Cyclic N-Sulfonyl Imines: Divergent Synthesis of Functionalized α-Pyridyl Acetates and Teraryl Scaffolds.

Under metal-free conditions, δ-acetoxy allenoates react with cyclic N-sulfonyl imines (sulfamidate imines/sulfonyl imines) to afford functionalized 2-pyridinyl acetates (α-pyridyl acetates) or teraryl motifs by a simple Lewis base switch. Thus, while DBU/Na2CO3 combination-directed [3 + 3] annulation involves sulfonyl elimination via O-S or C-S bond cleavage, affording 2-pyridinyl acetates, Ph3P-catalyzed [4 + 2] annulation leads to functionalized teraryls via Mannich coupling and C-N bond cleavage with retention or cleavage of the sulfamoyloxy group depending on the reaction conditions.