Palladiumcatalyzed decarboxylative allylation of active methylene compounds proceeded under mild neutralconditions using allylic carbonates, which are much more reactive than allylic acetates or phenoxides used commonly in the reaction.
Origins of Stereoselectivity in the α-Alkylation of Chiral Hydrazones
作者:Elizabeth H. Krenske、K. N. Houk、Daniel Lim、Sarah E. Wengryniuk、Don M. Coltart
DOI:10.1021/jo1019877
日期:2010.12.17
Density functional theory calculations and experiment reveal the origin of stereoselectivity in the deprotonation-alkylation of chiral N-amino cyclic carbamate (ACC) hydrazones. When the ACC is a rigid, camphor-derived carbamate, the two conformations of the azaenolate intermediate differ in energy due to conformational effects within the oxazolidinone ring and steric interactions between the ACC and the azaenolate. An electrophile adds selectively to the less-hindered pi-face of the azaenolate. Although it was earlier reported that use of ACC auxiliaries led to a-alkylated ketones with er values of 82:18 to 98:2, B3LYP calculations predict higher stereosclectivity. Direct measurement of the dr of an alkylated hydrazone prior to removal of the auxiliary confirms this prediction; the removal of the auxiliary under the reported conditions can compromise the overall stereoselectivity of the process.
On the regioselectivity and diastereoselectivity of ACC hydrazone alkylation
作者:Uyen Huynh、Md. Nasir Uddin、Sarah E. Wengryniuk、Stacey L. McDonald、Don M. Coltart
DOI:10.1016/j.tet.2016.11.064
日期:2017.2
The asymmetric α-allylation of 3-pentanone using several different N-amino cyclic carbamate (ACC) auxiliaries is described. The level of asymmetric induction was found to range from er = 93:7 to er = 99:1. The factors that lead to compromised selectivity for the various auxiliaries have been determined. Significantly, we have established that using the easily accessible and inexpensive valine-derived