Rhodium-catalyzed hydroarylation of alkynes with arylboronic acids: 1,4-shift of rhodium from 2-aryl-1-alkenylrhodium to 2-alkenylarylrhodium intermediate
Rhodium-catalyzed hydroarylation of alkynes with arylboronic acids: 1,4-shift of rhodium from 2-aryl-1-alkenylrhodium to 2-alkenylarylrhodium intermediate
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DOI：
10.1021/ja0165234
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发表时间：
2001-10-10
影响因子：
15
通讯作者：
Ogasawara, M
中科院分区：
文献类型：
--
作者：
Hayashi, T;Inoue, K;Ogasawara, M
自从Miyaura在1997年报道了在铑-膦络合物催化下芳基硼酸和烯基硼酸与R，β-不饱和酮在水溶液中的加成反应以来，1该铑催化反应已成功地扩展到以binap为手性配体的催化不对称1，4-加成反应。2-5最近，还报道了芳基硼酸与异丙基苯反应，得到多烷基化产物6，并与末端烯烃如苯乙烯和乙烯基吡啶反应。7在这里，我们报告，作为铑催化的有机硼酸反应的另一个例子，炔的氢化芳基化反应，它以高顺式选择性进行，其催化循环涉及铑从烯基碳到芳基碳的有趣的1，4-移位。在几种反应条件下研究了4-辛炔（1a）与苯基硼酸（2 m）的反应（方案1）。结果表明，在双膦-铑催化剂存在下，在水溶液中炔的加氢苯基化反应可以顺利进行。因此，将1a、2 m（1.2当量于1a）和3mol%的铑催化剂的混合物在100 ℃下加热3小时，所述铑催化剂由Rh-（acac）（C2 H4）2和dppb 8在二氧六环/水（10/1）中产生.蒸发溶剂，然后进行硅胶色谱（己烷），得到87%产率的（E）-4-苯基-4-辛烯9（4am），其异构体纯度通过NMR分析测定超过97%（表1中的条目1）。E异构体的形成表明氢和苯基以顺式方式加到三键上。使用过量的硼酸2 m略微增加了4am的产率，2.0和5.0当量的2 m的产率分别为93和95%（条目2和3）。一些其它的螯合双膦配体dppf，8 dppe，8和binap，8给出了与dppb基本相同的高化学产率，而用三苯基膦的产率低得多（条目4-7）。作为苯基硼酸（2 m）的环状酸酐的三苯基环三硼氧烷（3 m，苯基硼氧烷）3e可以与硼酸（条目8）一起使用。在苯基的4位分别具有三氟甲基和甲基的芳基硼酸2n和2 o以超过90%的产率得到相应的氢化芳基化产物（E）-4an和-4ao（条目9和10）。在与4-甲氧基苯基硼酸（2 p）或其环硼氧烷3 p的反应中，4ap的产率在100 ℃时较低，因为在此温度下水解生成苯甲醚较快。将反应温度降低到60 ℃大大提高了4ap的产率（97%）（条目12）.二苯基乙炔（1c）的氢化芳基化也以顺式选择性进行，在与4-三氟甲基苯基硼酸（2n）的反应中得到（E）-1，2-二苯基-1-（4-三氟甲基苯基）乙烯（4cn）（> 99%E）（条目14）。在被酯或膦酸酯基团取代的乙炔的反应中，区域和顺式选择性如此之高，以至于通过NMR分析没有检测到区域或几何异构体（条目16-18）。在吸电子基团的β位上选择性地引入芳基。
Since Miyaura reported the addition of aryl-and alkenylboronic acids to R, β-unsaturated ketones in an aqueous solvent under catalysis by a rhodium-phosphine complex in 1997, 1 this rhodium-catalyzed reaction has been successfully extended to catalytic asymmetric 1, 4-addition by use of binap as a chiral ligand. 2-5 Recently, it has been also reported that the reaction of arylboronic acids takes place with norbornene giving a multiple alkylation product6 and with terminal olefins such as styrenes and vinylpyridines. 7 Here we report, as another example of the rhodium-catalyzed reaction of organoboronic acids, the hydroarylation of alkynes which proceeds with high syn-selectivity and whose catalytic cycle involves an interesting 1, 4-shift of rhodium from an alkenyl carbon to an aryl carbon. The reaction of 4-octyne (1a) with phenylboronic acid (2m) was examined under several reaction conditions (Scheme 1). It was found that hydrophenylation of the alkyne takes place smoothly in an aqueous solvent in the presence of a bisphosphine-rhodium catalyst. Thus, a mixture of 1a, 2m (1.2 equiv to 1a), and 3 mol% of a rhodium catalyst generated from Rh-(acac)(C2H4) 2 and dppb8 in dioxane/water (10/1) was heated at 100 C for 3 h. Evaporation of the solvent followed by silica gel chromatography (hexane) gave 87% yield of (E)-4-phenyl-4-octene9 (4am), whose isomeric purity determined by NMR analyses is over 97%(entry 1 in Table 1). The formation of the E isomer indicates that hydrogen and phenyl add to the triple bond in a syn fashion. The use of an excess of boronic acid 2m slightly increased the yield of 4am, the yield being 93 and 95% with 2.0 and 5.0 equiv of 2m, respectively (entries 2 and 3). Some other chelating bisphosphine ligands, dppf, 8 dppe, 8 and binap, 8 gave essentially the same high chemical yield as dppb, while the yield was much lower with triphenylphosphine (entries 4-7). Triphenylcyclotriboroxane (3m, phenylboroxine) 3e which is a cyclic anhydride of phenylboronic acid (2m) can be used as well as the boronic acid (entry 8). Arylboronic acids, 2n and 2o, which have trifluoromethyl and methyl, respectively, at the 4-position of the phenyl gave the corresponding hydroarylation products (E)-4an and-4ao in over 90% yield (entries 9 and 10). In the reaction with 4-methoxyphenylboronic acid (2p) or its boroxine 3p, the yield of 4ap was low at 100 C, because the hydrolysis giving anisole is fast at this temperature. Lowering the reaction temperature to 60 C greatly improved the yield of 4ap (97%)(entry 12). The hydroarylation of diphenylethyne (1c) also proceeded with syn-selectivity, giving (E)-1, 2-diphenyl-1-(4-trifluoromethylphenyl) ethene (4cn)(> 99% E) in the reaction with 4-trifluoromethylphenylboronic acid (2n)(entry 14). In the reaction of acetylenes substituted with an ester or phosphonate group, the regio-and syn-selectivity was so high that no regio-or geometrical isomers were detected by NMR analysis (entries 16-18). The aryl group was introduced selectively at the β position to the electron-withdrawing group.