Chiral bicyclic lactams. An asymmetric synthesis of cis-(1s, 3r) deltamethrinic acid
作者:A.I. Meyers、Daniel Romo
DOI:10.1016/s0040-4039(00)99569-8
日期:——
Cyclopropanation of a chiral α,β-unsaturated bicyclic lactam derived from tert-leucinol and levulinic acid gave after 4 steps, the title compound in > 99% ee.
Single and Double Diastereoselection in Azomethine Ylide Cycloaddition Reactions with Unsaturated Chiral Bicyclic Lactams
作者:Andrew H. Fray、A. I. Meyers
DOI:10.1021/jo9600870
日期:1996.1.1
Double diastereoselectivity data were analyzed to provide insight into the structural features that influence pi-facial selectivity in 1,3-dipolar cycloadditions of chiral and achiral azomethine ylides to chiral, unsaturated bicyclic lactams. Three major steric contributions to the differences in stability (Delta Delta G(double dagger)) between competing cycloaddition transition states were identified. The first major set of steric interactions involve that between the dipoles and the substituents on the left hemisphere (R(2)) and concave faces of the bicyclic lactams. This effectively hindered both alpha- and beta-approaches in the nonextended transition states shown in Figure 1. The second major steric interaction was provided by the nonbonded interactions (i) between the R(1) angular substituent on the bicyclic lactam and the pi-system of the dipole as shown in Figures 3 and 4. This interaction was shown to be very significant, causing reversal in pi-facial attack of chiral and achiral dipoles when the angular substituent is changed from phenyl or methyl to hydrogen. The high diastereoselectivity observed now opens a route to highly substituted chiral, nonracemic pyrrolidines.
An asymmetric route to enantiomerically pure 1,2,3-trisubstituted cyclopropanes
作者:Daniel Romo、A. I. Meyers
DOI:10.1021/jo00049a038
日期:1992.11
Cycloaddition of various sulfur ylides to the chiral unsaturated lactams 1a, 1b led to cyclopropanated products containing a monosubstituted appendage. The stereochemical outcome is such that all the products are mainly (or exclusively) the kinetically controlled endo-syn-8, -9, or endo-anti-10. The latter occurs by virtue of an epimerization to the thermodynamically favored product. Removal of the chiral auxiliary following Wittig reaction on the intermediate carbinol amines (11, 15) gave chiral, nonracemic 1,2,3-trisubstituted cyclopropanes containing various functionalities (13, 16).
MEYERS, A. I.;ROMO, DANIEL, TETRAHEDRON LETT., 30,(1989) N4, C. 1745-1748