Asymmetric synthesis and configurational stability of C_2-symmetric hexacoordinated phosphate anions (TARPHATs) with predetermined chirality from tartrate esters

摘要

C_2-Symmetric TARPHAT anions 5 made of a central P~V atom, one tartrato (= dialkyl 2,3-di(hydroxy-#kappa#O)butanedioato(2-)), and two tetrachloropyrocatecholato (=3,4,5,6-tetrachlorobenzene-1,2-diolato(2-)-#kappa#O,#kappa#O') ligand can be easily prepared in decent to high yields (5-86%) as their dimethylammonium salt by using a one-pot process and simple commercially available starting materials. The presence of the chiral tartrato ligands (usually (2R, 3R) leads to the formation of diastereoisomeric anions ((#DELTA#,2R, 3R)/#LAMBDA#,2R,3R). Decent to good control by the chiral ligands-under equilibration conditions-over the #LAMBDA# or #DELTA# configuration of the adducts was observed (d.r., 84:16 in CHCl_3 for the di(tert-butyl) tartrate derivative), the selectivity depending on the nature of the ester chains as well as on the solvent.