A Convenient Synthesis and Spectral Studies of Diamines Derivatives

Sudershan R. Gondi*, Michael B. Jacobsson, Christiana Julia Rissing and David Y. Son Department of Chemistry, Southern Methodist University, Dallas, Texas, USA Abstract A new series of substituted anthranilic esters derivatives linked with a 1,3-dithiolane and benzyloximino moiety was synthesized using the simple esterfication reaction and products were fully characterized. The isolated yields of these compounds range from 59 to 96%. 1,3dithiolane ester and the benzyloxy substituted diamine derivatives are white solids and stable to air and moisture. The synthesized compounds can be exhibits UV-vis absorption properties by their structures with a amine or amide group, It is observed that absorption maximum is excellent for 2,6-disubstituted benzyloxy esters which can be explained by electron transfer or conjugation is steric effect in ortho substitution from the amino group and the amide group.


INTRODUCTION
In recent years, crystal engineering and construction of coordination networks with fascinating structural topologies have attracted great attention owing to their potential as functional materials. 1-2 Concurrently, the development of multidimensional networks based primarily on linking metal centers with rigid bridging components, such as 4,4`bipyridine has been initiated. 33 Since then chemiluminescence's of 3-aminophthalhydrazide was first investigated by Albrecht, 4 the acyl hydrazides are growing interest in the development of luminescent materials due to their potential application in emissive devices. 5 Moreover, the attractive and promising practical applications in many other areas have stimulated further investigations in light-emitting devices, nonlinear optics, and functional films, 6 conjugated polymers, 7 logic functions of molecularscale, 8 uranyl salts, saccharides, and aromatic organic molecular crystals which exhibit tribofluorescence or tribophosphorescence from the molecules comprising the crystal and/or nitrogen emission triboluminescence, 9 azopolymers. 10 Metal directed assembly have been used to generate luminescent materials 11 based on complexation of transition metal and multifunctional bridging ligands and is one of many useful strategies to design extended frameworks of various topology and dimensionality. Ligands with amino group of anthranilic acid derivative backbones may affect the properties of the resulting emissions by promoting the coupling of metal atoms through its emission systems. It has been of interest to use photoactive ligands as building blocks to generate supramolecular polymers. Some of these workers have been concerned with the influence of structural changes upon the chemiluminescent properties. [12][13]

PRESENT WORK
The luminescence is appreciably enhanced when the hydroxyl or amine groups are in the ortho position. The efficiency of chromogenic sensing is more remarkably affected by the chemical environment of the anthranilic acid derivatives, depending on the presence of a protecting free amino group or amide group. Taking into account these considerations, it is possible to optimize the uv-vis sensing of the molecules by structure modification. Keeping the above applications in mind, we have investigated the synthesis and characterization of a series of 2,6-and 2,3-diamino benzoic methyl esters derivatives with various electron-donor groups at the 2,6-or 2,3-positions.
3-nitropthalic acid and its anhydrides was chosen as a starting material due to its ready availability and to the fact that it can be easily converted to diamine derivative 5 and 10, a compound that can be selectively functionalized at the amino positions. The electron donor groups chosen for this study were pyridyl, 1,3-dithiolanyl, benzyloximate, and thiophenyl ether, all known for their Lewis basicity and ligating potential. This investigation reflects our ongoing interest in synthesizing new organic ligands for supramolecular design. [14][15][16][17][18][19][20][21] The initial step is the functionalization described herein was the conversion of 3-nitropthalic anhydride and 3-nitropthalic acid to 2,6-diamino benzoic acid methyl ester (5) and 2,3-diamino benzoic acid methyl ester (10)  3-nitrophthalic anhydride under methanol reflux conditions gives mixture of 1 and 6 in ratio of 9:1 (by NMR) in 98% yield. The mixture on treatment with thionyl chloride under heating condition gives corresponding mixture of acid chlorides 2 and 7 from which the acyl azide 3 and 8 were prepared by treating with sodium azide in acetone in 90%. The mixture of acyl azides 3 and 8 under Curtius rearrangement followed by column chromatography purification gives two isolated product 4 and 9 in 70% and 5% respectively. The compound 4 under palladium charcoal treatment gives product 5 in 90% yields. The compound 9 was independently prepared in four steps by regioselective esterfication of 3nitro phthalic acid, followed by its acid chloride 7 in 95% yield, which on acyl azide conversions 8 in 70% yield, followed by and Curties rearrangement. In these it is 100% regioselective conversion, no trace of its corresponding isomer was detected even in crude NMR. The compound 9 under reduction by using palladium charcoal condition gives the 2,3-diamino benzoic acid methyl ester 10 in 80% yield, and acetonide protected diamine 16 (in 5%), is obtained as byproduct. The mechanism is unclear.
Derivatives 13-14 were each synthesized in straightforward two step procedures from 5 and 10 as summarized in Scheme 1. The diamines 5 and 10 on treatment with -bromo acetyl chloride to give the bromo derivatives 11 and 12 in 69% and 66% yields, respectively. The bromo derivatives 11 under treatment with 2-pyridyl methanol gives the pyridyl derivative 13 as an oil in 59% yield after chromatographic purification. Attempts to prepare 14 by reaction of 12 with 2-pyridyl methanol in the presence of triethylamine or NaH were unsuccessful and resulted in the isolation of pyridyl ester product with elimination of aromatic moiety (by nmr), it is understood that due to the steric hindrance, elimination of aromatic moiety might occur. (Scheme 3). Reaction of 5 and 10 with 2.2 eq of 1,3-dithiolane-2-carbonyl chloride 17 in the presence of triethylamine in THF led to the isolation of the bis(1,3-dithiolanyl) products 15 and 16 as white solids in 55% and 73% yield after purifications using column chromatography. The 16 structure is also confirmed by single crystal data. (Scheme 4).  We also attempted to synthesize the 2,3-bis-benzyloxy methyl ester 22 from direct nucleophilic substitution reactions of diamine 10 with -benzyloximino acid chloride in either of TEA or pyridine and sodium hydride method. In both cases, our attempts were unsuccessful and resulted in either the isolation of starting materials or unidentified mixtures of products. But we were successful in synthesizing the 22 in two steps via acetonide protection (Scheme 7). Thus, reaction of 10 with 2,2-dimethoxy propane in presence catalytic amount of para toluene sulfonic acid gave 21 as residual oil in 47% yield after column chromatography purification, and reaction with -benzyloximino acid chloride 22 and workup with dil HCl gave 22 as white solid in 78% yield after chromatographic purification (Scheme 7).  respectively (scheme-9).
All new compounds were isolated as air-and moisture-stable solids. All compounds were fully characterized using 1 H and 13 C NMR spectroscopy and elemental analysis. The solubilities were excellent in common organic solvents, but 13 and 24 was soluble only in DMSO.
Preliminary experiments in which these compounds were mixed with various silver salts resulted in the formation of insoluble suspensions that could not be recrystallized for X-ray crystallographic analysis. However, elemental analysis of the isolated suspensions confirms the presence of silver, suggesting that complexation reactions are indeed occurring. The optical properties of compounds are of primary concern in chromogenic sensing and patterning. The solution-phase UV-vis absorption spectrum was recorded at room temperature in dilute chloroform solutions of about 10 -5 M concentration. As shown in table, In the absorption spectra for all compounds shows around 192 nm band seems to be an inherent property of these compounds and is not due to impurities as was verified by thin layer chromatography and NMR with the same chromophore showed a red-shifted absorption (no peaks and 443 nm, respectively), presumably due to extension of ineffective p-conjugation in ortho isomers.

Conclusions
We have prepared a series of new compounds containing dithiolane or benzyloxy oximate to aromatic rings bonded to substituted anthranilic acid core. The synthetic procedure is straightforward, and the products are obtained in good to excellent yields after chromatographic purification. Excellent solubility properties and the presence of electron donor groups in the modified anthranilic acid derivative described herein may be advantageous in applications such as anthranilic acid derivatives-metal conjugate synthesis, for example. The efficiency of chromogenic sensing is more remarkably affected by the chemical environment of the anthranilic acid derivatives, depending on the presence of a protecting amino group or amide group. Taking into account these considerations, it is possible to optimize the uv-vis sensing of the molecules by structure modification. All these compounds possess multiple sulfur atoms and are thus capable of binding in a multidentate fashion to soft transition metal ions. A reaction of these ligands with late transition metal ions is a current focus in our laboratory.