Selective reductions. 53. Asymmetric reduction of α-fluoromethyl ketones with B-chlorodiisopinocampheylborane and B-isopinocampheyl-9-borabicyclo[3.3.1]nonane. Combined electronic and steric contributions to the enantiocontrol process
作者:P.Veeraraghavan Ramachandran、Aleksandar V. Teodorovic'、Baoqing Gong、Herbert C. Brown
DOI:10.1016/0957-4166(94)80057-x
日期:1994.6
A systematic study of the asymmetric reduction of aryl and alkyl α-fluoroalkyl ketones with (−)-diisopinocampheylchloroborane ((−)-DIP-Chloride, 1), and (−)-B-isopinocampheyl-9-borabicyclo[3.3.1]nonane (R-Alpine-Borane, 2) has been made. In the case of reagent 1, the direction of asymmetric induction in the chiral reduction of aryl trifluoromethyl ketones differs from that of the corresponding mono-
( - ) -芳基的不对称还原,并与烷基α氟烷基酮的系统性研究diisopinocampheylchloroborane(( - ) - DIP-氯化物,1),和( - ) -乙-isopinocampheyl-9-硼杂双环[3.3.1]制备了壬烷(R -Alpine-Borane,2)。在试剂1的情况下,在芳基三氟甲基酮的手性还原中的不对称诱导的方向不同于相应的单和二氟甲基酮的方向。例如,在室温下的纯净条件下,在95%ee和85%ee中,2-氟和2,2-二氟苯乙酮分别被1还原为R-醇,而2,2,2-三氟苯乙酮被还原了,到S-酒精含量为90%的ee。尽管DIP-Chloride可以在不良ee中还原未受阻的前手性二烷基酮,但根据酮中存在的α-氟原子的数量,烷基α-氟代烷基酮在改良的ee中会降低。单氟甲基酮在R-异构体中提供中等的ee,而在相反的异构体中,二氟和三氟甲基酮的ee降低到中等。例如