Trimethyl 4,6-Dicyano-5-hydroxybenzene-1,2,3-tricarboxylate

: A novel synthesis of a fully substituted fluorescent phenol by a one-pot reaction of dimethyl acetylendicarboxylate and malononitrile in the presence of catalysts has been developed. The structure of the synthesized compound was assigned on the basis of its elemental analysis, 1 H-NMR, 13 C-NMR, IR, mass spectral and X-ray data. The photophysical data of the new compound are reported. 113.9, 114.2, 114.4, 155.0 (Ar), 163.7, 165.8 (CO) ppm; MS: m/z = 318 (M + ), 317, 214, 156, 141, 59, 45; Anal. Calcd for C 14 H 10 N 2 O 7 : C, 52.84; H, 3.17; N, 8.80; Found: C, 52.79; H, 3.15; N, 8.62.

Optoelectronic devices such as optical fibers, switches, tunable lasers and amplifiers, modulators with various applications need compounds emitting in the blue spectral region [1]. Multi-component reactions (MCRs) are of increasing significance in organic and medicinal chemistry. MCRs allow organic compounds to be synthesized in a few steps or in a one-pot operation [2].
Substituted phenols are of great importance in biosynthesis and also as building blocks in organic synthesis [3,4]. There are a few reports on the synthesis of highly substituted phenols [5]. So the development of a multi-component one-pot procedure for the synthesis of fluorescent poly-functionalized phenol can be seen as urgently interesting for technology upgrading. In continuation of our quest for developing one-pot procedures, here we wish to report a novel one-pot condensation reaction of dimethyl acetylenedicarboxylate 1 and malononitrile in the presence of Ph 3 P (triphenylphosphine) and p-toluenesulfonic acid (p-TSA) for the synthesis of fully substituted phenol 2 with bright fluorescence property (Scheme 1).
Easy, rapid and mild reaction conditions and also high atom economy of this one-pot procedure make the present method useful for the synthesis of highly functionalized phenols. Structure 2 was assigned on the basis of its elemental analysis, 1 H-NMR, 13 C-NMR, IR and mass spectral data. The light green crystals of 2 were obtained by slow crystallization from ethyl acetate and its X-ray structure was determined to confirm unambiguously its structure [6] (Figure 1).

Figure 1. X-Ray crystal structure of 2.
A possible mechanism for the synthesis of 2 is shown in Scheme 2. It is suggested that the zwitterion 3 is produced at first by addition of Ph 3 P to the acetylenic ester. Then the zwitterion 3 condenses with another ester molecule to produce zwitterion 4. Attack of the malononitrile anion at 4, fallowed by loss of Ph 3 P and intramolecular cyclization affords 5. Elimination of CN − from C 2 and addition of CN − to C 6 in the presence of OTS − can produce the intermediate 6. Finally, 6 can be aromatized to 2 by keto-enol tautomerization. Intermediate 6 was detected in the early stage of the reaction by 1 H-NMR and IR spectra. The proton adjacent to the CN group appears at δ = 4.53 for 6 in the 1 H-NMR spectrum and the carbonyl group of 6 has been detected at ν max = 1,801 cm −1 in the IR spectrum of the reaction mixture. At the end of this transformation (after 24 h), there was no carbonyl absorption detectable in the IR spectrum. Probably, the stability gained from aromatic ring generation drives this keto-enol tautomerization.  Table 1).

Experimental
Elemental analysis for C, H and N was performed using a Thermo Finnigan Flash EA1112 instrument. 1 H-NMR and 13 C-NMR spectra were determined on a Bruker 500 spectrometer. IR spectra were measured on a Bruker EQUINOX 55 spectrophotometer with the ATR method. Mass spectra were recorded on a Finnigan-MAT 8430 spectrometer. Photophysical data measurements were made with a Cary Eclipse Fluorescence spectrophotometer.