302911-94-0Relevant 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.
Synthesis and photooxygenation of homochiral 2-methylpyrrole derivatives of chiral amino alcohols: Simple, selective access to chiral bicyclic lactams
Aydogan, Feray,Demir, Ayhan S.
, p. 259 - 265 (2007/10/03)
Homochiral 2-methylpyrrole derivatives are synthesized in high yields starting from chiral amino alcohols and 5-chloro-3-pentene-2-one. The photooxygenation of these compounds in the presence of a photosynthesizer furnishes the pyrrolooxazolone structures in high diastereoselectivities. In all of the examples, trans-isomers are formed as the major products.
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.
Diastereoselective cyclopropanations of chiral bicyclic lactams leading to enantiomerically pure cyclopropanes. Application to the total synthesis of CIS-(1S, 3R)-deltamethrinic acid and R-(-)- dictyopterene C
Romo, Daniel,Romine, Jeffrey L.,Midura, Wanda,Meyers
, p. 4951 - 4994 (2007/10/02)
A novel diastereoselective cyclopropanation based on readily available chiral bicylic lactams (1b-c, 6a-b) has provided a number of enantiomerically pure cyclopropanes. Cyclopropanations of unsaturated lactams (10a-h, 12-14) were performed using sulfur ylides as well as a 3+2 cycloaddition-photolysis sequence and furnished the desired cyclopropane adducts (16, 17, 19, 22) in fair to excellent yields. In all cases involving sulfur ylides, cyclopropanations proceeded with a high degree of exo/endo diastereoselectivity (>;90%). However, the mode of addition, exo vs endo, was found to be highly dependent on the angular substituent of the unsaturated lactam. In the case of diazoalkane cycloadditions, high regioselectivity was observed in all cases although exo/endo selectivity was governed by the diazoalkane employed. Diazoisopropane, being more reactive than diazomethane, normally led to lower diastereomeric ratios. Minor diastereomers could be readily removed by chromatography or in most cases by a single recrystallization to provide diastereomerically pure cyclopropyl bicyclic lactams (16, 17, 19, 22). Applications of this methodology to compounds of biological significance was exemplified by an asymmetric, total synthesis of cis-(1S, 3R)-deltamethrinic acid (34) and R-(-)- dictyopterene C′ (42) in high enantiomeric purity.
