The reactions between 1′,3′,3′‐trimethylspiro[2H‐1‐benzopyran‐2,2′‐indolines] and 1,1‐bis[4‐(dimethylamino)phenyl] ethylene; products and mechanism

Abstract

The N-alkylhistidine ligands and the dicarboxylic amino acids all contain a chiral centre. CU(D-A)(L-A) ("the meso complex") and {CU(L-A), + CU(D-A),) ("the racernic complex") have different configurations and may be called "stereoselective isomers", from Laurie". The configuration of the stereoselective isomers can be derived from those possible for the corresponding octahedral complexes ; for histidine we find : meso-CuDL, related to the octahedral all-cis complex, has the two amino nitrogens cis in the coordination plane ofcopper; the rtrcetnic complex, CULL + CUDD, related to the octahedral trctns-amino C, complex, has the two amino nitrogens trans in the coordination plane of copper. Because one donor atom in CuHA, is protonated and, therefore, "free", a choice between cis or truns amino nitrogens in the meso and the racemic complex cannot be made. In principle small effects (by interligand repulsions*) are to be expected in these compounds, and these are also found in the CuHA, complexes (except for dimethylhistidine), but, no effects are found in the CuA, complexes of histidine and methylhistidine; the cause of the effects in CuHA, (and in CuA, of benzylhistidine) may be other than by interligand repulsions. A more quantitative explanation has to wait for more quantitative information about the structure of the species in solution. The structure of bis(dimethylhistidinat0)copper being similar to that one of dihistidinatocopper, implies that an imidazole group cis to a dimethylamino group (c$ the racemic complex) offers more steric hindrace than two dimethylamino groups cis to each other (cJ the meso complex), because this effect is undoubtly due to steric hindrance (cf Table 111). Acknowledgement* By interligand repulsions we indicate steric and coulombic 26 S. H. Loiwie, Chem. Conini. 1967, 155. repulsions between the two ligands in the complex. ' D . J. Zwarzenburg and Th. A. M . M . Mnas, Rec. Trav. Chim. Pays-Bas 94,8 (1975).The reactions of spiropyrans and chromenes with "Michler's ethylene" are catalysed by acid like the reactions between salicylaldehydes and "Michler's ethylene"'.