A highly chemo- and stereo-selective cleavage of acetals derived from (−)(2R,4R)-2,4-pentanediol with organoaluminum and organotitanium reagents has been demonstrated. The reactions proceed under mild conditions with excellent yields and high chemoselectivities to give, after removal of the auxiliary, chiral alcohols of high enantiomeric purities.
Mechanistic aspects of the formation of chiral allenes from propargylic ethers and organocopper reagents
作者:A. Alexakis、I. Marek、P. Mangeney、J. F. Normant
DOI:10.1021/ja00178a029
日期:1990.10
Propargylic ethers react with organocopperreagents to afford allenes by a syn addition to the triple bond followed by a β-elimination of the resulting alkenyl copper species. With use of chiral propargylic ethers and stoichiometric organocopperreagent, it was shown that the β-elimination step is purely anti, resulting in the formation of a chiral allene with 96% optical yield. The same reaction,
炔丙醚与有机铜试剂反应,通过对三键进行顺式加成,然后β-消除生成的烯基铜物质来提供丙二烯。使用手性炔丙醚和化学计量有机铜试剂,表明 β-消除步骤是纯反的,导致形成具有 96% 光学产率的手性丙二烯。使用格氏试剂 RMgX 和催化量的 Cu I 盐进行相同的反应,通过反或顺整个过程提供丙二烯。关键的步骤是β-消除中间体烯基有机金属物种,它是反型与 RMgI 和顺型与 RMgCl。丙炔乙酸酯,在该反应中也提供丙二烯,但通过 Cu III 中间体,对这种“卤素效应”不敏感
ALEXAKIS, A.;MAREK, I.;MANGENEY, P.;NORMANT, J. F., J. AMER. CHEM. SOC., 112,(1990) N2, C. 8042-8047
作者:ALEXAKIS, A.、MAREK, I.、MANGENEY, P.、NORMANT, J. F.