Functional Group Transformations in Derivatives of 6-Oxoverdazyl

Abstract

Transformations of functional groups, such as OCH2Ph, OCOPh, NO2 and I, in 1,3,5-triphenyl-6-oxoverdazyls 1a-1e were investigated in order to expand the range of synthetic tools for incorporation of the verdazyl system into more complex molecular architectures and to increase spin delocalization. Thus, Pd-catalyzed debenzylation of the OCH2Ph group or basic hydrolysis of the OCOPh group gave the phenol functionality, which was acylated, but could not be alkylated. Orthogonal deprotection of diphenol functionality was also demonstrated in radical 1c. Pt-catalyzed reduction of the NO2 group led to the aniline derivative, which was acylated. Attempted C-C coupling reactions to iodophenyl derivatives 1e and 5e were unsuccessful. Selected verdazyl radicals were characterized by EPR and electronic absorption spectroscopy, and results were analyzed with the aid of DFT computational methods.

Bent-core 6-thioxoverdazyl: a comparison of mesogenic properties with the 6-oxo analogue

“…The reaction time of 15 min was found to be optimal, while longer reaction times gave markedly lower yields. Thus, the dibenzoyloxy intermediate 7 was obtained from 4 in 8% overall yield, which is much less efficient than the similar preparation of the analogous 6-oxo derivative (65% yield), [16] and consistent with results for other 6-thioxoverdazyls. [15] The dibenzoyloxy derivative 7 was hydrolysed under basic conditions and the resulting diphenol 8 was acylated with acid chloride 9 [16] giving the bent-core 6-thioxo derivative 2 [16] as a deep blue crystalline material in 35% yield for two steps.…”

“…The 6-thioxoverdazyl derivative 2 [16] was obtained according to a general synthetic protocol [15] and functional group interconversion methods [16] developed for 6-oxoverdazyls. Thus, benzaldehyde 4-benzoyloxyphenylhydrazone [16] (4) was reacted with thiophosgene to give thiocarbamoyl chloride 5 (Scheme 1).…”

“…Thus, benzaldehyde 4-benzoyloxyphenylhydrazone [16] (4) was reacted with thiophosgene to give thiocarbamoyl chloride 5 (Scheme 1). The chloride was unstable and after partial purification was immediately treated with 4-benzoyloxyphenylhydrazine [16] to give tetrazine 6 in 14% yield after chromatographic purification. Attempted oxidation of 6 under PTC conditions at room temperature gave only unconsumed starting material, which is in contrast to the analogous procedure for 6-oxoverdazyls 1[n].…”

“…Here, we report synthesis of prototypical bentcore derivative of 1,3,6-triphenyl-6-thioxoverdazyl 2 [16] and comparison of its spectroscopic and thermal properties to those of the 6-oxo analogue 3 [16] ( Figure 1). Mesogenic properties of these derivatives are investigated in binary mixtures with nematic host 1 [12] and the results are rationalised with the aid of density functional theory methods.…”

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Two bent-core verdazyl radicals, 2[16] and 3 [16], containing 6-thioxo and 6-oxo groups, respectively, were prepared and their physical properties were compared. Analysis of binary mixtures with bent-core mesogen 1[12] gave virtual N-I ([T NI ]) and N-I re ([T NIre ]) transition temperatures.

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