¹H and ¹³C NMR assignments for new heterocyclic TAM leuco dyes, (2Z,2′E)‐2,2′‐(2‐phenyl propane‐1,3‐diylidene) bis(1,3,3‐trimethylindoline) derivatives. Part II

Abstract

The (1)H and (13)C NMR spectra of the novel heterocyclic Leuco-TAM dyes, (2Z, 2'E)-2,2'-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives 1-4 as precursors of triarylmethane (TAM)(+) (Malachite Green FB-analog) dyes were completely assigned by 1D and 2D NMR experiments, including DEPT, COSY, HSQC, HMBC, and NOESY. Especially, the diastereotopic gem-dimethyl protons at the C3 and C3' positions of the FB rings were definitively assigned. The (Z,E) isomers adopt the energetically favored three-bladed propeller conformation in solution.

X-ray Crystal Structure of Hetaryl Leuco-TAM Dyes, (2Z,2'E)-2,2'-(2-Phenyl Propane-1,3-diylidene) Bis(1,3,3-trimethyl indoline) Derivatives

“…These values were in excellent agreement with the experimental values (9.30 and 10.2 Hz), 11 which may imply that the stuctures of the newly synthesized bishetarylaryl methane molecules were very similar to those in the solution state.…”

Unsymmetrically Substituted Leuco-Triarylmethane Molecules Formed from the Reaction of a Fischer's Base and α,β-Unsaturated Iminium Salts via a Michael-Type Reaction

“…We previously reported the synthesis and characterization of the Fisher's base (FB) analogs of LTAM molecules such as symmetrically substituted LTAM, (2Z, 2'E)-2,2'-(2-phenylpropane-1,3-diylidene)-bis(1,3,3-trimethylindoline) derivatives and unsymmetric LTAM (Un-LTAM), (2E, 2'E)-2,2'-{(E)-4-phenylpent-2-ene-1,5-diylidene}bis(1,3,3-trimethylindoline) molecules. [15][16][17][18][19] These LTAM molecules have a central carbon that has two symmetrically substituted FB fragments and one phenyl ring.…”

“…15,16 In the first step, an enamine moiety of FB attacks the carbonyl carbon to form a carbinol anion, which then protonates from the reaction media (or solvent) in the second step. The third step is characterized by the dehydration of the carbinol forming an α,β-unsaturated iminium salt as a crucial intermediate.…”

Unusual Stability of Diastereomers of the Isomeric Pyridine-based Leuco-TAM Dyes 2,2'-(2-(Pyridin-4 or 3-yl)propane-1,3-diylidene)bis(5-chloro-1,3,3-trimethylindoline)

“…16,17 These LTAM molecules have a central carbon bearing two FB fragments and one phenyl ring, as shown in Figure 1. From the 1 H NMR and X-ray crystal analysis of the LTAM molecules studied, the ZE-isomers of the LTAM molecules are known to be formed stereoselectively, having the so-called "threebladed propeller" conformation.…”

“…Among these peaks, those assigned to the ZE isomers were a triplet at 5.22 ppm, two doublets at 4.36 and 4.42 ppm, two singlets at 2.95 and 3.26 ppm, and four singlets at 1.3-1.7 ppm, similar to the previously reported signals for the FB-analog of MG molecules. 16 The residual peaks might belong to the EE and/or ZZ isomers.…”