Diastereoselective [2 + 2] cycloaddition of dichloroketene with α-oxyaldehydes and α-amino aldehydes
作者:Claudio Palomo、José Ignacio Miranda、Carmen Cuevas、José Manuel Odriozola
DOI:10.1039/c39950001735
日期:——
A new route to natural products containing 1,2-diol and 1,2-amino alcohol subunits based on the [2 + 2] cycloaddition of dichloroketene to α-oxyaldehydes and α-amino aldehydes is demonstrated.
The reduction of (5S)-5-alkyl-2,4-dioxopyrrolidines, so-called tetramic acids, by NaBH4 gives only partial diastereofacial selectivity in the case of the N-substituted analogues 9f-i, unlike the carbamate derivatives 9a-3 which give the reduced cis-pyrrolidinones 10betaa-e. Increasing the steric hindrance of either the N- or C-5-substituents enhances the re-face selectivity. On the other hand, reduction of the heterobicyclic compound 9n leads to a dramatic reversal of the stereoselectivity. Preliminary calculations show that the N-atom of the ring is slightly pyramidalized; the direction of hydride addition could be a consequence of this finding.
Enantioselective and Diastereoselective Formation of<i>syn</i>-3-Hydroxy-4-amino Acids (<i>syn</i>-Statines) via Tetramic Acids
Enantiomerically pure pyrrolidine-2,4-diones (tetramic acids) which can be diastereoselectively hydrogenated to syn-statines (4-amino-3-hydroxy-6-methylheptanoic acids) have been prepared by catalytic hydrogenation of 4-(benzyloxycarbonylamino)-3-oxocarboxylic acid esters.