187407-22-3Relevant academic research and scientific papers
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
Kotora, Matin,Negishi, Ei-Ichi
, p. 121 - 128 (2007/10/03)
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., CI2Pd(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 (1a) 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.
