cas 143140-06-1, (3S-CIS)-(+)-2,3-DIHYDRO-7A-METHYL-3-PHENYLPYRROLO[2,1-B ]OXAZOL-5(7A H)-ONE

Articles about 143140-06-1Total 2 be found

Single and double diastereoselection in azomethine ylide cycloaddition reactions with unsaturated chiral bicyclic lactams
Double diastereoselectivity data were analyzed to provide insight into the structural features that influence π-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 (ΔΔG(≠)) 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 (R2) and concave faces of the bicyclic lactams. This effectively hindered both α- and β-approaches in the nonextended transition states. The second major steric interaction was provided by the nonbonded interactions (i) between the R1 angular substituent on the bicyclic lactam and the π-system of the dipole. This interaction was shown to be very significant, causing reversal in π-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.
Fray,Meyers
p. 3362 - 3374
(2007/10/03)

Asymmetric Lewis Acid-Catalyzed Addition of a Ketene Dithioacetal to a Chiral Bicyclic Lactam. Formation of Cyclobutanopyrrolidinones. A New Class of GABA Derivatives
Additions to unsaturated chiral lactams 8 using methylenedithiolane, gave very high endo-selectivity of the cyclobutane adducts (2 + 2 addition) 13, 16.Removal of the phenylglicinol auxiliary by reductive cleavage products the title compound (+)-20 in very high (>99percent) enantiomeric excess.Absolute stereochemistry of the cyclobutanopyrrolidinone, containing three contiguous stereocenters, was confirmed by X-ray crystallography.
Meyers, A. I.,Tschantz, Matt A.,Brengel, Gregory P.
p. 4359 - 4362
(2007/10/02)