Highly Efficient and Selective Procedures for the Synthesis of γ-Alkylidenebutenolides via Palladium-Catalyzed Ene-Yne Coupling and Palladium- or Silver Catalyzed Lactonization of (Z)-2-En-4-ynoic Acids. Synthesis of Rubrolides A, C, D, and E
作者:Matin Kotora、Ei-ichi Negishi
DOI:10.1055/s-1997-1513
日期:1997.1
The diacetates of rubrolides A, C, D, and E (1 a-d) were prepared in modest yields by the Pd-catalyzed cross coupling-lactonization tandem reaction of 5a or 5b with 6a or 6b using Cl2Pd(PPh3)2 and CuI as catalysts. The feasibility of converting the diacetates into rubrolides was demonstrated by the synthesis of rubrolide C by treatment of 1b with methanolic K2CO3 in THF. A detailed investigation of various parameters and conditions has indicated that formation of the corresponding six-membered lactones 7 and/or the cross coupling-lactonization-Heck substitution products 11 can be serious side reactions under non-optimized conditions and that the use of Pd(PPh3)4 rather than phosphine-free complexes, e.g., Cl2Pd(PhCN)2, or complexes of low phosphine content, e.g., Cl2Pd(PPh3)2, along with CuI and Net3 in MeCN provides satisfactory conditions for the cross coupling-lactonization tandem reaction. Thus, the diacetate of rubrolide A (1 a) was prepared in 70% isolated yield. The optimized conditions reported herein appear to be generally applicable to the stereoselective and regioselective synthesis of γ-alkylidenebutenolides in a highly efficient manner.
以 Cl2Pd(PPh3)2 和 CuI 为催化剂,通过钯催化 5a 或 5b 与 6a 或 6b 的交叉偶联-内酯化串联反应,制备出了红石榴内酯 A、C、D 和 E 的二乙酸酯(1 a-d),收率不高。通过在 THF 中用甲醇 K2CO3 处理 1b 合成红石榴苷 C,证明了将二乙酸酯转化为红石榴苷的可行性。对各种参数和条件的详细研究表明,在非优化条件下,形成相应的六元内酯 7 和/或交叉偶联-内酯化-赫克取代产物 11 可能会产生严重的副反应,因此应使用 Pd(PPh3)4,而不是无磷络合物,例如 Cl2Pd(PhCN)、Cl2Pd(PhCN)2,或膦含量较低的络合物,如 Cl2Pd(PPh3)2,以及在 MeCN 中的 CuI 和 Net3,为交叉偶联-内酯化串联反应提供了令人满意的条件。因此,红石榴内酯 A 的二乙酸酯(1 a)的制备分离收率为 70%。本文报告的优化条件似乎普遍适用于高效合成δ-亚烷基丁烯内酯的立体选择性和区域选择性。