74262-67-2Relevant academic research and scientific papers
A Rapid Injection NMR Study of the Chelation Controlled Mukaiyama Aldol Addition: TiCl4 Versus LiClO4 as the Lewis Acid
Reetz, Manfred T.,Raguse, Burkhard,Marth, Charles F.,Huegel, Helmut M.,Bach, Thorsten,Fox, David N. A.
, p. 5731 - 5742 (2007/10/02)
The concept of chelation controlled addition to chiral alkoxy aldehydes using Lewis acids and mild C-nucleophiles has been extended to include cyclopropylation.The mechanism of the TiCl4-mediated chelation controlled addition of enolsilanes and allylsilan
Acyclic Stereoselection. 36. Simple Diastereoselection in the Lewis Acid Mediated Reactions of Enol Silanes with Aldehydes
Heathcock, Clayton H.,Davidsen, Steven K.,Hug, Kathleen T.,Flippin, Lee A.
, p. 3027 - 3037 (2007/10/02)
The Lewis acid mediated aldol reactions of enol silanes with aldehydes have been investigated.The effects of enol silane structure, both nature of the ligand at the silyloxy carbon and the geometry of the double bond, the aldehyde structure, and the nature of the Lewis acid have been studied.In general, the reactions of prochiral enol silanes with prochiral aldehydes show little simple diastereoselection (Table I).An exception is Z enol silane 7, derived from ethyl tert-butyl ketone, which shows synthetically useful anti selectivity.Enol silane 36 may therefore be used as an anti-selective propionate equivalent.The chiral α-alkoxy aldehyde 43 shows a high diastereofacial preference in its reactions with enol silanes 42c and 42d provided a Lewis acid capable of expanding its coordination beyond four is used (TiCl4 or SnCl4) (Table II).However, with the related ketene acetal 41b, only modest diastereofacial selectivity is seen (Table II).Aldehyde 43 also shows a high diastereofacial preference, in the chelation-controlled sense, in its reactions with prochiral enol silanes 5-9.However, the simple diastereoselection observed in the latter reactions (Table III) is quite different from that observed in the reactions of prochiral aldehydes with the same enol silanes.For example, enol silane 7, which shows good anti selectivity in its reactions with prochiral aldehydes, gives a 15:1 mixture of the two syn aldols in its reaction with 43; while the reverse is true with the propiophenone-derived enol silanes 8 and 9.Finally, the results obtained in this study, along with those reported by other investigators, have been formulated into a coherent mechanistic rationale involving open transition states of the sort depicted in Figures 1 and 3.
Acyclic Stereoselection. 9. Stereochemistry of the Addition of Lithium Enolates to α-Alkoxy Aldehydes
Heathcock, Clayton H.,Young, Steven D.,Hagen, James P.,Pirrung, Michael C.,White, Charles T.,VanDerveer, Don
, p. 3846 - 3856 (2007/10/02)
The stereochemistry of addition of lithium enolates derived from esters and ketones to the α-alkoxy aldehydes 1-5 has been investigated.In all cases, the predominant product is that predicted by application of Felkin's model for asymmetric induction and by assuming the alkoxy group to be the "large" group.The Cram cyclic model for asymmetric induction is not followed.Stereostructures have been assigned by a combination of conversion to products of known stereostructure, 13C and 1H NMR correlations, and single-crystal X-ray analysis.
