222629-69-8Relevant articles and documents
Sceptrin – Enantioselective Synthesis of a Tetrasubstituted all-trans Cyclobutane Key Intermediate
Barra, Lena,Dickschat, Jeroen S.
, p. 4566 - 4571 (2017/08/30)
The asymmetric synthesis of both enantiomers of tetrasubstituted all-trans dimethyl 3,4-diacetylcyclobutane-1,2-dicarboxylate with high enantiomeric purity (>98 % ee) using a valine-derived chiral auxiliary in a diastereoselective photodimerization is reported. The absolute configuration was assigned by single-crystal X-ray diffraction analysis. Because this cyclobutane is a key intermediate in the total synthesis of (–)-sceptrin and ageliferin, our findings strengthen the recently revised absolute configurations of these pyrrole-imidazole alkaloids.
Single and double diastereoselection in azomethine ylide cycloaddition reactions with unsaturated chiral bicyclic lactams
Fray,Meyers
, p. 3362 - 3374 (2007/10/03)
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.
A Novel Asymmetric Synthesis of Substituted Cyclopropanes
Meyers, A. I.,Romine, Jeffrey L.,Fleming, Steven A.
, p. 7245 - 7247 (2007/10/02)
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