631902-78-8Relevant academic research and scientific papers
Stereocontrol in radical Mannich equivalents for aminosugar synthesis: haloacetal and 2-(phenylthio)vinyl tethered radical additions to α-hydroxyhydrazones
Friestad, Gregory K.,Jiang, Tao,Fioroni, Gina M.
experimental part, p. 11549 - 11557 (2009/04/06)
Studies of stereocontrol in two types of radical equivalents of Mannich addition reactions offer new insights for application to aminosugar synthesis. In the first method, haloacetal addition (Ueno-Stork reaction) is extended to dihydroxyhydrazones, leading to an adduct with the unexpected 3-epi-l-daunosamine configuration. A neighboring α-benzyloxy substituent causes a dramatic reversal of stereocontrol compared with hydrazones where this substituent is absent; vicinal dipole repulsion is proposed to account for the diastereoselectivity. In the second method, radical addition-cyclization with thiophenol and treatment with fluoride leads to diastereoselective group transfer from a silicon-tethered ethynyl group to the C{double bond, long}N bond of hydrazones, affording anti-hydrazino alcohols with a trans-2-(phenylthio)vinyl substituent. The one-pot process occurs under neutral, tin-free radical conditions, and offers stereocontrol which is complementary to the haloacetal method. Synthetic utility of the radical Mannich concept is demonstrated in a brief asymmetric synthesis of N-trifluoroacetyl-l-daunosamine from achiral precursors.
Tandem thiyl radical addition and cyclization of chiral hydrazones using a silicon-tethered alkyne
Friestad, Gregory K.,Jiang, Tao,Fioroni, Gina M.
, p. 2853 - 2856 (2007/10/03)
A diastereoselective method for addition of a trans-2-(phenylthio)vinyl group to α-hydroxy hydrazones is presented. An ethynyl group, tethered to α-hydroxy hydrazones via a silicon tether, undergoes thiyl radical addition and cyclization under neutral tin-free conditions. In the same pot, desilylation with potassium fluoride or tetrabutylammonium fluoride affords (E)-vinylsulfides. The one-pot process is the synthetic equivalent of an acetaldehyde Mannich reaction with acyclic stereocontrol.
