Vibrational spectra and rotational isomerism of simple dialkyl dithioesters and N-acylglycine ethyl dithioesters,thiolesters, and dioxygenesters

Simple dialkyl dithioesters and N-acylglycine ethyl dithioesters have been investigated by Raman, resonance Raman and infrared spectroscopies. Based on the data of isotopic substituted derivatives and a normal coordinate analysis, vibrational assignments have been proposed for methyl dithioacetate. Raman spectra of ethyl dithioacetate(CH₃C(=S)S

CH₂CH₃) and methyl dithiopropionate (CH₃CH₂

C (=S)SCH₃) have provided fundamental knowledge on rotational isomerism about the bonds indicated. Raman, resonance Raman and FTIR spectroscopic studies on N-acylglycine ethyl dithioesters indicated the coexistence of three conformers in solution and a combined x-ray crystallographic-resonance Raman spectroscopic approach has been used to set up precise structure-spectra correlations for these conformers. The corresponding conformational states of N-acylglycine thiolesters and dioxygenesters are also discussed briefly.     

Enantioselective organocatalytic reductive amination

The first enantioselective organocatalytic reductive amination reaction has been accomplished. The development of a new chiral phosphoric acid catalyst has provided a convenient strategy for the enantioselective construction of protected primary amines and provided a highly stereoselective method for the reductive amination of heterocyclic amines. A diverse spectrum of ketone and amine substrates can be accommodated in high yield and excellent enantioselectivity. This new protocol realizes a key benefit of reductive amination versus imine reduction, in that ketimines derived from alkyl-alkyl ketones are unstable to isolation, a fundamental limitation that is comprehensively bypassed using this direct organocatalytic reductive amination.