Stereoselective synthesis and characterization of new enantiomerically pure phosphoric acids

Abstract

Starting from (R)-6,6'-dimethyldiphenyl-2,2'-dicarboxylic acid, a novel class of enantiomerically pure cyclic dialkyl phosphates was synthesized and properly characterized. The absolute configuration was determined by 2D NOESY experiments. The catalytic behavior of the new chiral Bronsted acids was investigated in the stereoselective addition of a silyl keteneacetal to aldimines. The Mannich-type reaction was promoted in up to 94% yields and enantioselectivities up to 55%. On the basis of preliminary molecular mechanic calculations, a model of stereoselection was also proposed to explain the sense of the enantioselectivity observed in the reaction.

Design, synthesis, and evaluation of chiral thiophosphorus acids as organocatalysts

“…With our various CPAs 2-4 in hand, their evaluation in asymmetric organocatalysis was conducted. The reaction could have been chosen from a tremendous number of possibilities [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. We selected the one Guinchard used to evaluate his thioacid hybrid-CPAs (Scheme 5) [31].…”

“…A subclass of organocatalysts introduced independently by Akiyama and Terada in 2004 [1,2], are the C 2 -symmetrical chiral phosphorus acids (CPAs) initially derived from the BINOL scaffold, and later extended to other scaffolds such as VAPOL [3] and SPINOL [4,5] (Figure 1). The great success of these CPAs in asymmetric organocatalysis, is demonstrated by the publication of thousands of articles and reviews [6][7][8][9][10][11][12][13][14][15][16][17]. In all cases the C 2 -symmetry is required because of the prototropic tautomeric equilibrium in the hydroxyphosphoryl (P(=O)OH) moiety which renders the phosphorus atom achiral.…”

19F MRI of Polymer Nanogels Aided by Improved Segmental Mobility of Embedded Fluorine Moieties

“…11 In this vein, recent efforts have focused on developing polymeric 19 F MRI contrast agents as multimodal imaging probes. A variety of polymeric tracers have been developed and tested, including linear polymers, [12][13][14][15][16][17][18][19] star polymers, 20,21 dendritic polymers, [22][23][24] hyperbranched polymers (HBPs), [25][26][27][28][29] and polymeric nanoparticles. [30][31][32] In addition, there also have been efforts to develop activatable "smart" agents that provide on-off 19 F signals in response to certain environmental changes, such as pH, redox potential, small molecule release and proteins.…”