Amination of oligofunctionalized dinaphthylmethanes: factors affecting the reaction pathway

The reactions of oligofunctionalized 1,1-dinaphthylmethanes with primary amines and ammonia are described. In the reaction of amines with 2,2′,7,7′-tetrahydroxy-and 2,2′-dihydroxy-1,1-dinaphthylmethanes, the replacement of hydroxy groups by amino groups is accompanied by cleavage of С-С bonds and elimination of a methylene unit. The regiodirection of the process is determined by the number and the nature of substituents in the dinaphthylmethane core. The catalytic amination of 2,2′,7,7′-tetrakis(trifluoromethanesulfonyloxy)-1,1-dinaphthylmethane is not accompanied by destruction of the dinaphthylmethane core. The reaction selectivity and the product structure depend on the nature of the aminating reagent.


Introduction
The broad applicability of aromatic amines has been attracting the attention of chemists for more than one hundred years.The production of dyes, explosives, biologically active compounds, and ligands for metal complex catalysis does not exhaust the list of applications of arylamines.The tendency for constructing complex oligoaminated aromatic systems manifested today 1 drives the search for new substrates for amination and the development of methods for their modification.In this study, 2,2′,7,7′-tetrahydroxy-1,1-dinaphthylmethane containing two pairs of hydroxy groups differing in reactivity is used as the amination substrate. 2We found only one publication on the amination of oligohydroxy-1,1-dinaphthylmethanes.A German patent of 1893 3 describes the reactions of 2,2′,7,7′-tetrahydroxy-1,1-dinaphthylmethane (1) and 2,2′-dihydroxy-1,1′dinaphthylmethane (2) with aniline in the presence of aniline hydrochloride.The authors of the Second, the 1 Н and 13 С NMR spectra of both products did not contain signals for the methylene unit.The 1 Н NMR spectra contained proton signals for phenyl and naphthyl rings and a signal in the region typical of NН protons, while the 13 С NMR spectra contained signals only for aromatic carbon atoms.Third, according to mass spectrometry, the mass of the major product corresponded to 2,2′,7,7′-tetra(phenylamino)binaphthyl (4) and the mass of the minor product corresponded to 2,7-bis(phenylamino)naphthalene (3).
These facts demonstrated that during the reaction of compound 1 with aniline in the presence of aniline hydrochloride, aminolysis is accompanied by cleavage of the bridging С-С bonds and elimination of the methylene unit.In order to study this unusual process, here we investigated in detail the reaction of 2,2′,7,7′-tetrahydroxy-1,1-dinaphthylmethane (1) with primary amines of different nature and with ammonia.
The reaction of 1 with aniline followed the above-indicated route (Scheme 1).The use of microwave radiation intensified the process, and, hence, the temperature could be reduced to 145 °С and the reaction time was shortened to 2 h, the yields of aminated products 3 and 4 being increased to 5% and 58%, respectively.
The reactions of 1 with aliphatic amines (sec-butylamine, cyclohexylamine, hexylamine) gave, as the major products, mono-and diaminated naphthalenes 5а,b and 6a-c in a ratio depending on the structure of the substituent at the nitrogen atom (Scheme 1).Scheme 2. Proposed rationale for the reactions of 1 with primary amines.
The symmetrical structure of diaminonaphthalenes 6 is indicated by the presence of three doublets for the naphthalene ring protons with equal integrated intensities in the 1 Н NMR spectra and by the presence of three singlets for tertiary carbon atoms, two singlets for non-functionalized quaternary carbon atoms, and one low field signal for the carbon atoms С2 and C7 in the amino groups in the 13 С NMR spectra.The presence of six naphthyl proton signals, six 13 С NMR signals for tertiary carbon atoms, and two 13 С NMR signals for functionalized quaternary carbon atoms with chemical shifts corresponding to carbons bonded to amino and hydroxy groups confirmed the formation of unsymmetrical monoaminated naphthalenes 5.
Our results together with the available published data suggested that the reaction of 1 with primary amines follows Scheme 2. The process starts, similarly to the Bucherer reaction, 6 with the concerted protonation of the carbon atoms with enhanced electron density in the naphthalene rings to give stabilized conjugated systems a and b, which then react with the amine.In the subsequent transformations, the molecule loses aromaticity, which can be restored by two pathways (I, II).
According to one pathway (I), the electron density redistribution in intermediate f induces С-С bond cleavage with elimination of water and formaldehyde to give two molecules of aminonaphthol g, their subsequent amination resulting in diaminonaphthalene h.
The second pathway (II) includes a rearrangement of intermediate f, resulting in the formation of a new С-С bond between the 2,2′-aminated α-naphthalene moieties.This course of the process is possible if intermediate f has an additional pair of hydroxy groups in the 7,7′positions, which increase electron density at the 8,8′-carbon atoms located closely in space to the 1,1′-carbon atoms.Owing to the transannular interaction between the 1,8′ or 1′,8 carbon atoms, a new С-С bond is formed and a methylene unit is eliminated, giving rise to 1,8′-binaphthyl l.The reaction ends in the aminolysis of the two remaining hydroxyl groups to give 1,1′-binaphthyl m.With amines having bulky aliphatic N-substituents, which hamper the transannular interaction between the 1,8′ carbon atoms in intermediate f, the reaction mainly follows pathway I.
The bifurcation of the reaction track and the route to binaphthyl m presented in Scheme 2 were confirmed by two additional experiments.First, we carried out amination of 2,7dihydroxynaphthalene 7 by aniline under the same conditions for 1,1-dinaphthylmethane 1 and showed that the reaction gives only one product, namely, 2,7-bis(phenylamino)naphthalene 3 (Scheme 3).Hence, under the conditions of aminolysis of compound 1 that we used, the formation of the new С-С bond cannot occur via cross-linking of two diaminonaphthalene 3 molecules.Scheme 3. Reaction of dihydroxynaphthalene 7 with aniline.

Scheme 4. Reaction of 2 with aniline.
As with the amination of tetrahydroxy-1,1-dinaphthylmethane 1, this reaction was accompanied by cleavage of bridging С-С bonds but no cross-linking of the naphthalene rings took place, the process ending in the formation of 2-phenylaminonaphthalene (8).This fact confirms the effect of 7,7′-substituents in the molecule of 1,1-dinaphthylmethane 1 on the electron density redistribution in intermediate f (Scheme 2), and, hence, on the regiodirection of the whole process.
The reaction of 1,1-dinaphthylmethane 1 with ammonia was performed in a microwave reactor at 145-150 ºС in the presence of ammonium sulfite.This reaction proceeded similarly to amination of 1 with aniline (Scheme 1).However, the high reactivity of the primary amino groups introduced in the naphthalene rings and the presence of formaldehyde formed upon elimination of the methylene unit (Scheme 2) changed the reaction pathway, giving rise to a third product, the diazepine derivative 11, which was formed in 36% yield (Scheme 5).Scheme 5. Reaction of 1 with ammonia.2,7-Diaminonaphthalene 9 and 2,2′,7,7′-tetraamino-1,1′-binaphthyl 10 were isolated in 14% and 11% yields, respectively.The MALDI MS, IR, and 1 Н and 13 С NMR data for compounds 9, 10 were fully consistent with their compositions and structures.
The 1 Н NMR spectrum of compound 11 exhibited four doublets for the Н-(3-6) protons and a singlet for the Н-8 protons of the naphthalene rings with the integrated intensity ratio IН-3:IН-4:IН-5:IН-6:IН-8 . 1:1:1:1:1, which proved the symmetric structure of the rigid cyclic system formed.In addition, a singlet for the proton at the imine carbon and a broadened NH proton signal were present in the low-field region.The 13 С NMR spectrum of 11 exhibited five singlets for tertiary carbon atoms and three signals for non-functionalized quaternary carbon atoms of the naphthalene rings; a signal for the tertiary carbon atom of the imine fragment; and low-field signals for quaternary carbon atoms bonded to amino (148.7 ppm) and imino (158 ppm) groups.The elemental analysis and MALDI MS data for compound 11 were fully consistent with the proposed diazepine structure.
The presence of 1 Н and 13 С NMR signals for the methylene unit of compound 13 attested to the retained 1,1-dinaphthylmethane structure, while the integrated intensity ratio of the naphthalene and benzene ring proton signals and the MALDI MS data indicated that phenylamino groups were substituted for only two triflate fragments.The presence of one singlet at -73.2 ppm in the 19 F NMR spectrum of 1,1-dinaphthylmethane 13 and the presence of one signal for carbon atom bound to the amino group (δ 143.1 ppm) and one for carbon bound to the triflate group (δ 146.3 ppm) in the 13 С NMR spectrum suggested that the substitution involved equivalent carbon atoms, either in 2,2′ or in 7,7′ positions.
This issue was clarified by a special experiment.We trifluoromethaneulfonylated 2,2′dihydroxy-1,1-dinaphthylmethane (2) under conditions used for the synthesis of compound 12 (Scheme 6).The chemical shift (-73.2ppm) of the singlet recorded in the 19 F NMR spectrum of 2,2′-ditrifluoromethanesulfonyloxy-1,1′-dinaphthylmethane (14) was identical to that observed for diamine 13, and the 13 С NMR chemical shift of 2,2′-carbons attached to the triflate groups in compound 14 (145.6 ppm) was similar to the low-field signal (146.3 ppm) present in the spectrum of 13.The foregoing indicates that amination of tetratriflate 12 involved more open 7,7′ positions.An additional piece of evidence for this conclusion is the absence of reaction between ditriflate 14 and aniline under tetratriflate 12 amination conditions.
The reaction of tetratrifluoromethanesulfonyloxy-1,1-dinaphthylmethane 12 with hexylamine was much less selective than the reaction with aniline.Apparently, in this case, triflate fragments were replaced by amino groups non-selectively.The products obtained had functional groups in various ratios and in various positions.In addition, the reaction may give cyclic and oligomeric derivatives.Using column chromatography, two products 15 and 16 were isolated in a pure state in 6.5 and 10% yields, respectively (Scheme 7).
Elemental analysis, mass spectrometry, and NMR data suggest that both products are macroheterocyclic compounds with nitrogen-containing spacers but with different modes of coupling of the ditrifluoromethanesulfonyloxy-1,1-dinaphthylmethane fragments.The 19 F and 13 С NMR spectra of macrocycle 15 each showed one signal for F and C atoms of the trifluoromethyl groups.In the 13 C NMR spectrum of 15, ten carbon signals for the naphthalene rings were recorded, in particular, the singlets for C-2 attached to the triflate groups and C-7 attached to nitrogen spacers, three signals for the other quaternary С atoms, and five signals for tertiary С atoms.
The 1 Н NMR spectrum of 15 exhibited five signals for the aromatic protons with equal integrated intensities.This attested to a symmetric structure of molecule 15, suggesting that the heterocycle has resulted from the reaction of hexylamine with the C-7 atoms of two 1,1dinaphthylmethane molecules 12.
In the 19 F NMR spectrum of macrocycle 16, three singlets for triflate F atoms were recorded.The 13 C NMR spectrum of 16 contained two quartets for triflate C atoms and four signals for the naphthalene-ring carbons (C-2,7) attached to functional groups.In addition, both 13 C and 1 Н NMR signals of the aromatic nuclei of 16 were doubled.This demonstrated the chemical nonequivalence of the ditrifluoromethanesulfonyloxy-1,1-dinaphthylmethane fragments in 16 and implied that the heterocycle may have formed through the reaction of hexylamine with the C-2 atoms of one 1,1-dinaphthylmethane 12 molecule and the C-7 atoms of the other molecule.