三氟甲磺酸銀/苯乙炔促進乙酸烯炔酯的取代反應及其產物之後續環化

Abstract

烯炔化合物為良好的分子內環化反應前驅物，本研究提供溫和條件使乙酸烯炔酯1進行取代反應，以三氟甲磺酸銀 (silver triflate, AgOTf) 及苯乙炔 (phenylacetylene) 作為催化劑，促進乙酸烯炔酯1中的乙酸根離子 (acetate ion, OAc-) 離去，產生共軛穩定的烯炔陽離子，並與不同親核試劑如乙醯胺 (acetamide)、三甲基烯丙基矽烷 (allyltrimethylsilane) 與烯醇矽醚 (silyl enol ether) 進行取代反應，分別得到N-烯炔基乙醯胺2、3,7-二烯-1-辛炔3與1-苯基-4-烯-6-炔-1-庚酮4，都得到良好的產率，也成功進行碳-碳鍵的生成，使烯炔分子的骨架有更多樣化的延伸。 本研究也進一步將N-烯炔基乙醯胺2在鹼性條件下以鈀金屬活化三鍵進行分子內環化得到2-甲基乙醯吡咯5，以及將3,7-二烯-1-辛炔3在亞金離子的催化下進行分子內環化得到雙環[4.2.0]辛-1,7-二烯6，此雙環[4.2.0]辛-1,7-二烯6可在氧化劑的幫助下脫氫形成雙環[4.2.0]辛-1,3,5-三烯7。

Enyne compounds are excellent precursors for intramolecular cyclization reactions. This study provides mild conditions for the substitution reactions of enynyl acetate 1. Using silver triflate and phenylacetylene as the catalysts, the acetoxy group in enynyl acetate 1 was removed to generate a conjugated and stabilized enynyl cation, which underwent reactions with various nucleophiles such as acetamide, allyltrimethylsilane, and silyl enol ether to yield N-enynylacetamides 2, 3,7-diene-1-octynes 3, and 1-phenyl-4-ene-6-yne-1-heptanones 4, respectively, with good yields. These reactions offer efficient ways to construct carbon-carbon bonds for diversifying the framework of the enyne molecules. Furthermore, N-enynylacetamides 2 underwent intramolecular cyclization with palladium activation under basic conditions to produce 2-methylacylpyrroles 5. Similarly, 3,7-diene-1-octyne 3 undergoes Au(I)-catalyzed intramolecular cyclization to form bicyclo[4.2.0]octa-1,7-dienes 6, which was further oxidized with the help of an oxidizing agent to form bicyclo[4.2.0]octa-1,3,5-trienes 7.