TY - CHAP
T1 - Bifunctional Lewis Base Catalysis With Dual Activation of X3Si Nu and C=O(n → σ*)
AU - Fu, Jiping
AU - Fujimori, Shinji
AU - Denmark, Scott E.
N1 - Publisher Copyright:
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA.
PY - 2016/8/17
Y1 - 2016/8/17
N2 - This chapter focuses on the mechanistic studies and preparative aspects of reactions catalyzed by chiral phosphoramides. The modest reactivity and selectivity observed with chiral Lewis bases as well as the dependence of enantioselectivity on the promoter loading has been addressed in a detailed mechanistic investigation. In a kinetic study, the reaction was found to be of first order in benzaldehyde and allylsilane, however the reaction order in phosphoramide was determined. Although mechanistically intriguing, the dual pathways have opposing effects on the rate and selectivity of the process. First, since the reaction is second order in the catalyst, the rate falls off as the square of catalyst concentration. Second, at lower concentration, a competing, less selective pathway can compromise the overall reaction selectivity. The solution to these challenges involved the introduction of dimeric analogs of phosphoramide with the expectation that the covalent tether would increase the effective concentration of the second catalyst molecule through proximity.
AB - This chapter focuses on the mechanistic studies and preparative aspects of reactions catalyzed by chiral phosphoramides. The modest reactivity and selectivity observed with chiral Lewis bases as well as the dependence of enantioselectivity on the promoter loading has been addressed in a detailed mechanistic investigation. In a kinetic study, the reaction was found to be of first order in benzaldehyde and allylsilane, however the reaction order in phosphoramide was determined. Although mechanistically intriguing, the dual pathways have opposing effects on the rate and selectivity of the process. First, since the reaction is second order in the catalyst, the rate falls off as the square of catalyst concentration. Second, at lower concentration, a competing, less selective pathway can compromise the overall reaction selectivity. The solution to these challenges involved the introduction of dimeric analogs of phosphoramide with the expectation that the covalent tether would increase the effective concentration of the second catalyst molecule through proximity.
KW - Aldol reaction
KW - Allylation reaction
KW - Allyltrichlorosilane
KW - Bisphosphoramide
KW - Catalysis
KW - Chiral ethyl ketones
KW - Chiral methyl ketones
KW - Diastereoselectivity
KW - Directed aldol addition
KW - Donor-acceptor interactions
KW - Electrophilic
KW - Enantioselectivity
KW - Hexacoordinate silicon
KW - Hypercoordinate silicon
KW - Internal stereoselection
KW - Lewis base
KW - Nucleophilic
KW - Pentacoordinate silicon
KW - Phosphine oxides
KW - Phosphoramides
KW - Relative stereoselection
KW - Silanes
KW - Silicenium ions
KW - Stereoselective
KW - Synthetic methods
KW - Trichlorosilyl chlorohydrin
KW - Trichlorosilyl enol ethers
KW - Trichlorosilyl ketene acetals
KW - Trigonal bipyramidal silicon
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U2 - 10.1002/9783527675142.ch9
DO - 10.1002/9783527675142.ch9
M3 - Chapter
AN - SCOPUS:85018331907
SN - 9783527336180
VL - 1
SP - 281
EP - 338
BT - Lewis Base Catalysis in Organic Synthesis
PB - Wiley-VCH
ER -