Enantioselective synthesis of α-phenyl- and α-(dimethylphenylsilyl)alkylboronic esters by ligand mediated stereoinductive reagent-controlled homologation using configurationally labile carbenoids
作者:Adam L. Barsamian、Zhenhua Wu、Paul R. Blakemore
DOI:10.1039/c5ob00159e
日期:——
with a combination of O-(α-lithiobenzyl)-N,N-diisopropylcarbamate and ligand 3,3-bis[(4S)-4,5-dihydro-4-isopropyloxazol-2-yl] pentane in toluene solvent (−78 °C to rt) with MgBr2·OEt2 additive. Enantioenriched α-(dimethylsilylphenylsilyl)alkylboronates were obtained in 35–69% yield and 9–57% ee by reaction of B-alkyl pinacol boronates with a combination of lithio(dimethylphenylsilyl)methyl 2,4,6-triisopropylbenzoate
在存在规模的双恶唑啉配体的存在下,通过构型不稳定的外消旋锂类胡萝卜素的作用,研究了硼酸酯的扩链,以对映异构地合成两种标题产物。最初的α-苯基烷基硼酸酯的氧化后处理(NaOOH)产生的对映体富集的2°甲醇,通过B-烷基和B-芳基新戊二醇硼酸酯与以下物质的组合反应,收率35-83%,ee达到70-96%。ø - (α-lithiobenzyl) - ñ,ñ -diisopropylcarbamate和配体3,3-双[(4-小号)-4,5-二氢-4- isopropyloxazol -2-基]戊烷在甲苯溶剂中(-78℃至rt)与MgBr 2 ·OEt 2添加剂。通过使B-烷基频哪醇硼酸酯与硫代(二甲基苯基甲硅烷基)甲基2,4,6-三异丙基苯甲酸酯和配体2,2结合反应,可得到对映体富集的α-(二甲基甲硅烷基苯基甲硅烷基)烷基硼酸酯,产率为35-69%,ee为9-57%-双[(4 S)-4,5-二氢