Lewis Base Switched [3+3] and [4+2] Annulation Reaction 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 biaryl 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 sulfamoyloxy group depending on the reaction conditions.