Ohmura Toshimichi, Taniguchi Hiroki, Suginome Michinori
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan.
J Am Chem Soc. 2006 Oct 25;128(42):13682-3. doi: 10.1021/ja063934h.
An enantioselective silaboration of allenes was achieved using an achiral silylborane in the presence of a palladium catalyst bearing a chiral monodentate phosphine ligand. (R)-2-Bis(3,5-dimethylphenyl)phosphino-1,1'-binaphthyl gave the highest enantioselectivities in the addition of (diphenylmethylsilyl)pinacolborane to the internal C=C bond of terminal allenes at 0 degrees C, giving the corresponding beta-borylallylsilanes in high yields with high enantiomeric excesses. The enantioselectivity depended on the bulkiness of substituents of allenes: the enantiomeric excesses were found to be 91-93% ee (R = tert- and sec-alkyl), 88-90% ee (R = aryl), and 80-82% ee (R = prim-alkyl and Me) at 0 degrees C. Perfect chirality transfer was observed in the intramolecular cyclization reactions of the functionalized allylsilanes, affording highly enantioenriched cyclic alkenylboranes, which underwent Suzuki-Miyaura coupling with aryl halides.
在手性单齿膦配体钯催化剂存在下，使用非手性甲硅烷基硼烷实现了丙二烯的对映选择性硅硼化反应。在0℃下，将（二苯基甲基甲硅烷基）频哪醇硼烷加成到末端丙二烯的内C=C键上时，（R）-2-双（3,5-二甲基苯基）膦基-1,1'-联萘给出了最高的对映选择性，以高收率和高对映体过量得到相应的β-硼基烯丙基硅烷。对映选择性取决于丙二烯取代基的体积：在0℃下，对映体过量分别为91-93%ee（R = 叔烷基和仲烷基）、88-90%ee（R = 芳基）和80-82%ee（R = 伯烷基和甲基）。在功能化烯丙基硅烷的分子内环化反应中观察到了完美的手性转移，得到了高度对映体富集的环状链烯基硼烷，其与芳基卤化物发生了铃木-宫浦偶联反应。
