The resolution of heterohelicenes, a facile method using HPLC: (Preliminary communication)

Abstract

The above-mentioned results are quite different from those obtained when s-triazine is reacted with 0-methylisourea and S-methylisothiourea and guanidine. Three different products i.e. 2-methoxy-, 2-(methy1thio)-and 2-amino-s-triazine are formed respectively. Why in these reactions the intermediate 11 (replace CR, by N) always recyclizes by loss of NH, is unclear at this moment Experimental partMelting points are uncorrected. The PMR spectra were recorded on a Jeol JNM-C 60 spectrometer using tetramethylsilane (T.M.S.) as internal standard. The I5N contents were measured on an A.E.I. MS 902 mass spectrometer.

Facile Two‐Step Synthesis of 1,10‐Phenanthroline‐Derived Polyaza[7]helicenes with High Fluorescence and CPL Efficiency

“…To the best of our knowledge, however, in all cases more than five steps were required for the synthesis of [7]helicene derivatives. We envisioned that polyazahelicenes 1 a (Figure ) with a rare 6‐5‐6‐6‐6‐5‐6 skeleton could be constructed by intramolecular NH/CH oxidative coupling using a hypervalent iodine reagent, as we reported in 2011 . We report here a facile two‐step synthesis of tetra‐ or hexaaza[7]helicenes from commercially available 2,9‐dichloro‐1,10‐phenanthroline ( 2 ), and their characteristic photophysical properties.…”

“…Despite the smaller overlap of the terminal rings in 1 a , the chiral form of 1 a is highly stable even when heated at 80 °C for 24 h and 120 °C for 5 h in mesitylene, and no racemization was observed, which is probably due to the significant twist in the central moiety . The specific rotation of enantiomerically pure (+)‐ 1 a showed [ α ] of +2544 ( c =0.51, CHCl 3 ) which is larger than those of other [7]helicenes containing two five‐membered rings . Figure shows CD and CPL spectra under neutral and acidic conditions.…”

Facile Two‐Step Synthesis of 1,10‐Phenanthroline‐Derived Polyaza[7]helicenes with High Fluorescence and CPL Efficiency

“…[11] Chemists who face this dilemma must synthesize as mall molecule that displays both high CPL activity as well as ahigh quantum yield.Since the pioneering helicene synthesis by Newman in 1955, [12] various approaches have been developed, ] and [2+ +2+ +2] cycloaddition. [21] To the best of our knowledge,h owever, in all cases more than five steps were required for the synthesis of [7]helicene derivatives.W ee nvisioned that polyazahelicenes [22] 1a (Figure 1) with ar are 6-5-6-6-6-5-6 skeleton [23] could be constructed by intramolecular NH/CH oxidative coupling using ah ypervalent iodine reagent, as we reported in 2011. [24] We report here af acile two-step synthesis of tetra-or hexaaza[7]helicenes from commercially available 2,9-dichloro-1,10-phenanthroline (2), [25] and their characteristic photophysical properties.2,9-Di(aminophenyl)-1,10-phenanthroline (3a), obtained from 2 with aniline in 96 %y ield, was used as am odel substrate in the double cyclization with hypervalent iodine reagents.K osersr eagent (PhI(OH)OTs), which was an optimal reagent in our previous study, [24] gave many products containing the desired helicene 1a,inanoverall yield of 24 %.…”

“…Since the pioneering helicene synthesis by Newman in 1955, [12] various approaches have been developed, including radical reaction, [13] CÀHa rylation, [14] CÀHa ctivation, [15] Diels-Alder reaction, [16] metathesis reaction, [17] Pd-catalyzed cross coupling reactions, [18] Friedel-Crafts-type reaction, [19] alkyne cyclization, [20] and [2+ +2+ +2] cycloaddition. [21] To the best of our knowledge,h owever, in all cases more than five steps were required for the synthesis of [7]helicene derivatives.W ee nvisioned that polyazahelicenes [22] 1a ( Figure 1) with ar are 6-5-6-6-6-5-6 skeleton [23] could be constructed by intramolecular NH/CH oxidative coupling using ah ypervalent iodine reagent, as we reported in 2011. [24] We report here af acile two-step synthesis of tetra-or hexaaza [7]helicenes from commercially available 2,9-dichloro-1,10-phenanthroline (2), [25] and their characteristic photophysical properties.…”

“…[29] Thespecific rotation of enantiomerically pure (+ +)-1a showed [a] 25 d of + 2544 (c = 0.51, CHCl 3 )w hich is larger than those of other [7]helicenes containing two five-membered rings. [23] Figure 4s hows CD and CPL spectra under neutral and acidic conditions.Inboth acidic and neutral conditions,the CD spectra of (+ +)-1a show several positive Cotton bands in the longer wavelength region, and no exciton coupling bands between two chromophores.T he spectrum of enantiomer (À)-1a appears as am irror image.T hese observations imply that the electronic structures under neutral and acidic conditions are similar in the ground state.U nder both conditions,h elicene 1a shows strong CPL activities with emission maxima consistent with those observed in the fluorescent spectrum. TheCPL spectra of the enantiomers are mirror images.T he degree of CPL is given by the luminescence dissymmetry ratio,which is defined as g lum = 2(I L ÀI R )(I L + I R ), where I L and I R are the luminescence intensities of left and right circularly polarized light.…”