Synthesis of Fused-β-Lactams through Selective Gold-Catalyzed Oxycyclization of Dioxolane-Tethered Enynes

The gold-catalyzed preparation of 2-azetidinone-fused oxacycles was accomplished from β-lactam-linked enynes through heterocyclization reaction taking advantage of the acetonide pendant group. While the synthesis of fused tetrahydrofuran-β-lactams from 1,3-enynes could be considered as an unusual metal-catalyzed cyclization of enynols, α-alkoxy dioxolane-tethered 1,3-enynes exclusively undergo bis-oxycyclization to afford tricyclic bridged acetals.借助丙酮叉悬挂基团，通过杂环化反应，以β-内酰胺连接的烯炔为起始原料，成功实现了金催化制备2-氮杂环丁酮并氧杂环（2-azetidinone-fused oxacycles）的过程。尽管由1,3-烯炔合成并四氢呋喃-β-内酰胺（fused tetrahydrofuran-β-lactams）可被视为一种非常规的烯炔醇金属催化环化反应，但带有α-烷氧基二氧戊环侧链的1,3-烯炔仅发生双氧环化反应，进而得到三环桥缩醛（tricyclic bridged acetals）产物。