從香葉醇到二萜類天然物Galanal A和Galanal B之全合成

Abstract

本論文的第一章節由天然物galanal A和B的第一個全合成研究所構成，合成路徑從自然界中含量豐富的香葉醇原料開始。關鍵步驟分別是路易士酸輔助手性布忍斯特酸複合體所調控的陽離子多烯環化反應以及鈦陽離子調控的自由基環化反應分別來建構不對稱的AB雙環結構以及在BC雙環連接點位置上的全碳原子連結之四級碳原子中心。 本論文的第二章節由不對稱多烯環化反應的文獻回顧以及將氫原子引發的不對稱多烯環化反應用在galanal A和B全合成路徑中的雙烯基質之研究探討所組成。經過配位基和路易士酸的篩選之後，R型苄基單取代聯萘酚與四氯化錫所組成的路易士酸輔助手性布忍斯特酸複合體組合，將其應用在雙烯基質上，給予我們最高的鏡像異構物超越值。後續有關提升鏡像異構物超越值的相關研究仍在進行中。

The first chapter of this dissertation concerns the first total synthesis of galanal A and B, which has been achieved from naturally occurring geraniol. Key steps in this synthesis are the use of a Lewis acid assisted chiral Brønsted acid (chiral LBA) mediated cationic polyene cyclization and a titanocene-mediated radical cyclization for the asymmetric assembly of the “AB” ring and the construction of the all-carbon quaternary center at the “BC” ring junction, respectively. The second chapter of this dissertation comprises of the literature review of enantioselective polyene cyclizations and studies of a proton-initiated enantioselective polyene cyclization, applied to the diene substrate in the total synthesis of galanal A and B. Screening of ligands and Lewis acids gave us (R)-BINOL-Bn and SnCl4 as, the chiral LBA pair that gives us the highest ee of our substrate. Further improvement of ee is under investigation.