Letter: Facile biomimetic synthesis of dibenzazonine and aporphine alkaloids

CO2 capture by Mn(i) and Re(i) complexes with a deprotonated triethanolamine ligand

CO₂ capture at low concentration by catalysts is potentially useful for developing photocatalytic and electrocatalytic CO₂ reduction systems.

CO₂ capture at low concentration by catalysts is potentially useful for developing photocatalytic and electrocatalytic CO₂ reduction systems. We investigated the CO₂-capturing abilities of two complexes, fac-Mn(X₂bpy)(CO)₃(OCH₂CH₂NR₂) and fac-Re(X₂bpy)(CO)₃(OCH₂CH₂NR₂) (X₂bpy = 4,4′-X₂-2,2-bipyridine and R = –CH₂CH₂OH), which work as efficient catalysts for CO₂ reduction. Both complexes could efficiently capture CO₂ even from Ar gas containing only low concentration of CO₂ such as 1% to be converted into fac-M(X₂bpy)(CO)₃(OC(O)OCH₂CH₂NR₂) (M = Mn and Re). These CO₂-capturing reactions proceeded reversibly and their equilibrium constants were >1000. The substituents of X₂bpy strongly affected the CO₂-capturing abilities of both Mn and Re complexes. The density functional theory (DFT) calculation could be used to estimate the CO₂-capturing abilities of the metal complexes in the presence of triethanolamine.

Rearrangement of 5-trimethylsilylthebaine on treatment with L-selectride: an efficient synthesis of (+)-bractazonine

Treatment of 5-trimethylsilylthebaine with L-Selectride gave rise to a rearrangement to 10-trimethylsilylbractazonine through migration of the phenyl group, whereas treatment of thebaine with strong Lewis acids is known to lead to a similar rearrangement through migration of the alkyl bridge to give, after reduction, (+)-neodihydrothebaine. It is suggested that the rearrangement of the alkyl group of thebaine is favored due to the formation of a tertiary benzylic cation. However, for 5-trimethylsilylthebaine, the lithium ion of L-Selectride acts as the Lewis acid and the beta-silyl effect dominates in the stabilization of any positive charge. This rearrangement provides a clear example of the greater relative migratory aptitude of phenyl groups over alkyl groups, and provides an efficient synthesis of (+)-bractazonine from thebaine.