α-Silyl Controlled Asymmetric Michael Additions of Acyclic and Cyclic Ketones to Nitroalkenes
作者:Dieter Enders、Thomas Otten
DOI:10.1055/s-1999-2715
日期:1999.6
Virtually enantiopure α-t-butyldimethylsilyl ketones (R)-1 and (S)-5 are converted regioselectively to the corresponding trimethylsilyl enol ethers (R)-2 and (S,Z)-6. Subsequent asymmetric Michael addition to nitroalkenes in the presence of SnCl4 affords the 1,4-adducts 3 and 7 in good yields and high diastereo- and enantiomeric excesses. Removal of the t-butyldimethylsilyl group with n-Bu4NF, THF, NH4F/HF lead to the α,β-disubstituted γ-nitro ketones (S,R)-4 (de = 91-92%, ee >98%) and (R,S)-8 (de >96%, ee >98%) in very good overall yields.
几乎对映纯的β-叔丁基二甲基硅基酮(R)-1和(S)-5被选择性地转化为相应的三甲基硅基烯醇醚(R)-2和(S,Z)-6。在SnCl4的存在下,对硝基烯烃进行后续的不对称迈克尔加成反应,可获得1,4-加合物3和7,且产率较高,立体异构体和对应异构体过剩。用n-Bu4NF、THF、NH4F/HF去除叔丁基二甲基硅基团,可获得α,β-二取代的γ-硝基酮(S,R)-4(de = 91-92%,ee >98%)和(R,S)-8(de >96%,ee >98%),总产率非常高。