Abstract:The multi-step synthesis of two benzimidazole trimethine cyanines as possible green sensitizing dyes (Gs3-1, Gs3-2) is reported. Compounds were characterized from UV-Vis, mass spectroscopic and NMR data. The charge density distributions of the two compounds, calculated using the semi-empirical MOPAC 93 package, are in agreement with assignments in NMR spectroscopy. Sensitizing properties of the cyanine dyes were evaluated in actual photographic T-grain emulsions.
“…For the dye formation/ release step we found that 30 min at room temperature in 1:9 DIEA/pyridine was sufficient to completely react 0.3 equiv of lepidinium salt 4 . This contrasts with the 45 min at reflux in 1:5 DIEA/pyridine used by Peng et al After being washed twice with water, the product 5 was obtained in 89% purity and 79% crude yield. 1 Synthetic Route to Unsymmetrical Cyanine Dyes a a (i) (EtO) 3 CH, EtOH, 80 °C, 2 h; (ii) DIEA, DCM, rt, 4 h; (iii) DIEA, pyridine, rt, 30 min. …”
mentioning
confidence: 76%
“…Simple washing is adequate to remove residual aniline and amidine. We envisaged activating the hemicyanine carbon toward a second nucleophilic attack by N - sulfonylation as demonstrated in solution by Peng et al, rather than the more traditional acylation step. This is consistent with the findings of Brooker et al that the less available the nitrogen lone pair is for delocalization, the more reactive the hemicyanine derivative is to nucleophiles .…”
[reaction: see text] Trimethine cyanine dye was synthesized by capture and activation of a hemicyanine intermediate on sulfonyl chloride resin followed by reaction and concomitant cleavage by a heterocyclic carbon nucleophile. A small array of dyes were synthesized and characterized to demonstrate the versatility of this chemistry for a number of hemicyanines and heterocyclic nucleophiles.
“…For the dye formation/ release step we found that 30 min at room temperature in 1:9 DIEA/pyridine was sufficient to completely react 0.3 equiv of lepidinium salt 4 . This contrasts with the 45 min at reflux in 1:5 DIEA/pyridine used by Peng et al After being washed twice with water, the product 5 was obtained in 89% purity and 79% crude yield. 1 Synthetic Route to Unsymmetrical Cyanine Dyes a a (i) (EtO) 3 CH, EtOH, 80 °C, 2 h; (ii) DIEA, DCM, rt, 4 h; (iii) DIEA, pyridine, rt, 30 min. …”
mentioning
confidence: 76%
“…Simple washing is adequate to remove residual aniline and amidine. We envisaged activating the hemicyanine carbon toward a second nucleophilic attack by N - sulfonylation as demonstrated in solution by Peng et al, rather than the more traditional acylation step. This is consistent with the findings of Brooker et al that the less available the nitrogen lone pair is for delocalization, the more reactive the hemicyanine derivative is to nucleophiles .…”
[reaction: see text] Trimethine cyanine dye was synthesized by capture and activation of a hemicyanine intermediate on sulfonyl chloride resin followed by reaction and concomitant cleavage by a heterocyclic carbon nucleophile. A small array of dyes were synthesized and characterized to demonstrate the versatility of this chemistry for a number of hemicyanines and heterocyclic nucleophiles.
“…The immobilization of the hemicyanine onto the resin has the dual function of activating the hemicyanine and of facilitating the removal of the major byproducts. The hemicyanine intermediates are relatively unreactive at room temperature but can be activated by functionalizing the nitrogen with an electron-withdrawing group like by acetylation or sulfonylation [43,44]. In a similar manner, the reaction of the hemicyanine with a sulfonyl chloride polymer-bound resin not only activates the substrate but also allows the removal of the undesired byproducts, mainly the symmetrical CD, by simple washing the resin with compatible solvents.…”
Section: Solid-phase Synthesis Of Asymmetrical Cyaninesmentioning
:
Cyanine dyes (CD) are a functional class of organic molecules used in several applications ranging from photography to bioimaging. CDs most well-known features reside on high molar extinction coefficients up to 105 L mol-1cm-1 and on the absorption spectra, ranging from 500 to 1000 nm, which can be fine-tuned both by extending the length of the central methylene bridge or by modulating the terminal heterocycles. In the last decades, new synthetic methodologies, namely microwave-assisted and the solid-phase procedure, have been developed to overcome the limitation of the classical synthetic protocols. While the microwave approach usually reduces the exposure time of the reagents and products to thermal degradation, the solid-phase methodology allows easier synthetic protocols, which are translated into higher yields and simpler product purification. In the present review, a comprehensive analysis of the solid-phase methods for the synthesis of asymmetrical CDs is discussed, with a critical evaluation of the difference among the currently available solid-state approaches.
“…In our previously published strategy, hemicyanine 7 was synthesized from the reaction of heterocycle 2 with amidine 6 . Hemicyanine intermediates such as 7 are relatively unreactive at room temperature but can be activated by functionalization of the aniline nitrogen with an electron-withdrawing group, for example, by acetylation or sulfonylation. , By reaction of hemicyanine 7 with sulfonyl chloride polystyrene, we demonstrated its activation via concurrent immobilization onto the solid phase (Scheme ). 2 Catch-and-Release Synthesis of Trimethine Cyanine Dye a a Reagents and conditions: (a) 2 , EtOH, triethylorthoformate, reflux; (b) dichloromethane (DCM), diisopropylethylamine (DIEA), polystyrene (PS)-SO 2 Cl; (c) 4 , pyridine, DIEA. …”
We report here a series of studies that explore solid-phase methodologies for the synthesis of various cyanine dyes. The scope of the previously reported catch-and-release method using sulfonyl chloride resin(1) has now been extended to include pentamethine and water-soluble cyanine dyes. We also report a new and chemically distinct synthetic strategy, employing the stepwise attack of heterocyclic carbon nucleophiles on immobilized polyene-chain precursors, allowing the clean synthesis of hydrophobic and hydrophilic trimethine and pentamethine dyes from more easily obtained starting materials. Overall, both approaches appear to be robust and versatile strategies to delivering a wide range of cyanine-based dyes in high purity.
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