Stereoselective Synthesis of Conjugated 2,4-Alkadienoates via the Palladium-Catalyzed Cross-Coupling of 1-Alkenylboronates with 3-Bromo-2-alkenoates
作者:Teiji Yanagi、Takayuki Oh-e、Norio Miyaura、Akira Suzuki
DOI:10.1246/bcsj.62.3892
日期:1989.12
(2E,4E)-, (2Z,4E)-, and (2E,4Z)-2,4-Alkadienoates can be synthesized in high yields by the cross-coupling of ethyl (E)-3-bromoacrylate, methyl (E)-3-bromo-2-methylpropenoate, ethyl (Z)-3-bromocrotonate,1-bromo-2-(ethoxycarbonyl)cyclohexene, and 4-bromocoumarin with 2-[(E)-1-alkenyl]-1,3,2-benzodioxaboroles or diisopropyl (Z)-1-hexenylboronate in the presence of 3 mol% of Pd(OAc)2, 6 mol% of PPh3, and 2 equivalents of Na2CO3 or K2CO3 in alcoholic solvents while retaining the original configuration of the double bonds in β-bromo esters and 1-alkenylboronates. Although the coupling reaction with 1-hexenylboronate with (Z)-3-bromoacrylate gave a mixture of ethyl (2Z,4E)- and (2E,4E)-nonadienoates in a ratio of 63 : 37, it was found that the use of bis(diphenylphosphino)ferrocene as a ligand of palladium brought about the stereoselective coupling under mild conditions.
(2E,4E)-、(2Z,4E)- 和 (2E,4Z)-2,4-烷二烯酸酯可以通过乙基(E)-3-溴丙烯酸酯、甲基(E)-3-溴-2-甲基丙烯酸酯、乙基(Z)-3-溴丙烯酸酯、1-溴-2-(乙氧羰基)环己烯和4-溴香豆素与2-[(E)-1-烯基]-1,3,2-苯并二氧硼烷或二异丙基(Z)-1-己烯基硼酸酯在3摩尔%的Pd(OAc)2、6摩尔%的PPh3和2当量的Na2CO3或K2CO3的存在下,在醇溶剂中交叉耦合合成,且保持β-溴酯和1-烯基硼酸酯中双键的原始构型。尽管1-己烯基硼酸酯与(Z)-3-溴丙烯酸酯的耦合反应生成了63:37比率的乙基(2Z,4E)-和(2E,4E)-九烯酸酯的混合物,但发现使用双(苯基磷)铁烯作为钯的配体在温和条件下能够实现立体选择性耦合。