Abstract For further studies of the diastereoselective complex formation of ambidentate chiral chelating ligands, we prepared the racemic phosphinothioformamides. Ph2P(X )C(S)NHC*HR 1R2, with X = 2e- (R1 = Ph,R2 = Et: 1a;R1 = Ph,R2 = iPr:2a; R2 = Me,R2 = Et:3a) and X = O (1b ,2b ) according to a previously reported route. The coordination of 1a -3a to CpM (CO)3Cl (M = Mo, W) in m ethanol gives the diastereomeric P.S-chelate complexes, (Mo: 4-6, W: 7-9). In solution, epimerisation proceeds to an equilibrium ratio of B/A = 1,5 in case of 4, 5, 7, and 8, but less than 1,1 with 6 and 9. A reduced diastereoselectivity (d.e. 10 -20%) is also observed during the formation of the analogous molybdenum complexes 10a-d with phosphine ligands derived from α-amino acid esters. Ph2PC(S)NHC*H(R)COOMe [R = Me (L-Ala), CH2Ph (L-Phe). CHMe2 (L-Val). Ph (D-phenylglycine)]. The results indicate a significant asymmetric induction despite of the four bond distance of the chiral centres.
Direct Catalytic
N
‐Alkylation of α‐Amino Acid Esters and Amides Using Alcohols with High Retention of Stereochemistry
