Reactions and interactions between peri-groups in 1-dimethylamino-naphthalene salts: an example of a “through space” amide

Acylation of aldehyde 1

Reaction of the aldehyde 1 with benzoyl chloride in dry ether at 0°C gave immediately a white solid, whose ¹H and ¹³C NMR spectra support its assignment as the chloride salt of cation 18 in which the aldehyde oxygen has been benzoylated and the peri-dimethylamino group has added to the carbonyl group. The methine group created by addition to the aldehyde group has NMR resonances at δ_H: 8.06 and δ_C: 100.9 ppm, and the two N-methyl groups have distinct resonances at δ_H: 3.89 and 4.29 and δ_C: 49.3 and 56.6 ppm. The carbonyl group’s stretch is typical for an ester at 1732 cm⁻¹. Reaction of aldehyde 1 with pivaloyl chloride gave the corresponding chloride salt of cation 19, with methine resonances at δ_H: 7.59 and δ_C: 100.4 ppm, and a carbonyl stretch at 1749 cm⁻¹. Reactions with acetyl chloride or t-butyldimethylsilyl triflate gave the corresponding products which rapidly hydrolysed to give cation 12. This is unusual chemistry, and is similar to the chemistry of a carboxylic amide except that the peri-dimethylamino group provide the extra electron density needed in the carbonyl group “through space” rather than “through bond”. In contrast to aldehyde 1, the closely related phenyl ketone 3 did not react with benzoyl chloride under the same conditions or even in THF at 60°C, indicative of the lower reactivity of an aryl ketone to the adjacent dimethylamino group.

To characterise the bond formed between the two peri-groups, crystals of the chloride salts of cations 18 and 19 were grown by evaporation of acetonitrile solutions and their structures determined by X-ray crystallography at 150 K. The crystal structure of both salts are triclinic in space group P1̅. The structure of cations 18 and 19 are shown in Fig. 1, with selected geometric details in Table 1. The new N–C bond between the peri groups is 1.568(3) Å long in cation 18 and 1.566(2) Å in cation 19. The single C–O bond, which arose from addition to the carbonyl group, is 1.424(3) Å long in 18 and 1.417(2) Å in 19. The N–CH₃ bonds at the positively charged N group are considerably longer (1.507(3)–1.514(2) Å) than in aldehyde 1 (1.468(6)–1.470(6) Å) [8] where the N atom is uncharged. The geometry of the ester groups are typical for such groups [16]. Thus the aldehyde 1 reacts like a “through space amide”, with the dimethylamino nitrogen lone pair donating electron density into the carbonyl’s π^* orbital “through space” to activate the group to O-acylation, just as is seen in the corresponding reaction with acid to give cation 12.

Fig. 1:

Molecular structures of the cations 18 and 19 with atomic displacement parameters drawn at the 50% level. For 18, only one position of the disordered phenyl group is shown.

Table 1:

Selected geometric details of cations 18 and 19.

τ=torsion angles: H3C–N–C–O(C=O)
	a/Å	b/Å	c/Å	d/Å	τ/°
18	1.568(3)	1.424(3)	1.363(3)	1.507(3) 1.509(3)	1.3(2) –120.06(18)
19	1.566(2)	1.417(3)	1.373(2)	1.512(2) 1.514(2)	4.1(2) –124.9(2)
	α/°	β/°	γ/°	δ/°	ε/°
18	105.29(16)	108.50(18)	113.4(2)	108.72(19)	104.07(17)
19	105.31(12)	108.89(15)	112.89(17)	108.93(15)	103.92(14)

The crystal packing arrangements of the chloride salts are shown in Fig. 2. In both cases the chloride ion makes five short contacts to hydrogen atoms in the range 2.65–2.79 Å: to the naphthyl hydrogen ortho to the positively charged nitrogen atom (2.66–2.67 Å), to three N-methyl hydrogens and to the sp³ methine hydrogen.

Fig. 2:

Crystal packing arrangements for 18.Cl (left) and 19.Cl (right).

For cation 12 in the O-protonated salts of aldehyde 1, the N–C bond between the peri groups lies in the range 1.624(4)–1.638(2) Å and the C–O(H) bond lies in the range 1.352(4)–1.362(4) Å, considerably longer (by ca 0.06 Å) and shorter (by ca 0.06 Å), respectively than the corresponding bonds in cations 18 and 19. This difference can be explained in terms of the orientations of the oxygen lone pairs with respect to the C–N bond between the peri groups (Fig. 3). Thus, in the cation of the protonated material one of the hydroxyl oxygen atom’s lone pairs is aligned with the lobe of the antibonding orbital of the N–C bond between peri groups lying out beyond the carbon atom, and thus lengthening the bond. In the acylated salts the two lone pairs of the alkoxy oxygen, irrespective of whether they are considered to be two sp³ lone pairs or one sp² and one p lone pair, do not overlap with the C–N anti-bonding orbital since the (Me₂)N–C–O–C(=O) torsion angles are 145.97(18) and 146.22 (14)° in contrast to 75(2)° for the corresponding (Me₂)N–C–O–H torsion angle for the protonated salt. In solution, away from the constraint of crystal packing on molecular conformations, the situation may of course be different.

Fig. 3:

Comparison of the relative orientation of the O-substituent with respect to the C–N bond between peri-substituents in cation 19 (left) and cation 12 (right).

Thus, the close approach of a dimethylamino group to the aldehyde group in 1 activates the carbonyl group to reaction with electrophiles, either protons or acyl groups. Such n–pi^* interactions between an oxygen and a carbonyl group have been identified as important in stabilising the conformations of small molecules e.g. interactions with ester carbonyl groups in aspirin and N-acyl proline esters [17, 18], and also the conformations of proteins via interactions between amides [19, 20]. These interactions, while not forming a covalent bond, do modify the properties of the two groups [21].

Protonation of a peri-ester 4 and peri-amides 5 and 6

Following the discovery that protonation of naphthalenes bearing peri-related dimethylamino and ketone groups leads to either O-protonation with bond formation between the peri groups for methyl, isopropyl and trifluoromethyl ketones or, for larger ketone substituents such a t-butyl and phenyl, to N-protonation and hydrogen bond formation with the peri group [9], we decided to examine the crystal structures of protonated products where the ketone group is replaced by the less electrophilic ester or amide group. The methyl ester 4 and the N,N-dimethyl- and N,N-diisopropylamides 5 and 6 were prepared by peri-lithiation of 1-dimethylaminonaphthalene and reaction with methyl chloroformate or the corresponding N,N-dialkylcarbamoyl chloride. Compounds 4–6 were reacted with triflic acid in ether to precipitate salts from which crystals were grown by evaporation of appropriate solutions.

The crystal structure of the triflate salt of ester 4 is orthorhombic in space group Pbca. The structure of the cation is shown in Fig. 4 and the crystal packing arrangement in Fig. 5. The structure shows that protonation has taken place on the nitrogen atom, with formation of two rather long hydrogen bonds: one to the ester carbonyl group (2.06(4) Å) and one to a triflate anion (2.23(3) Å). Geometric details of the hydrogen bonding is given Table 2. The peri groups are splayed apart in the naphthalene plane by 4.2 and 3.1° for the dimethylammonium and ester groups respectively, as well as being strongly displaced to opposite sides of the aromatic plane to facilitate the formation of the hydrogen bond to the triflate ion. The hydrogen bond to the ester carbonyl group makes an angle of 95.3(9)° with the carbonyl bond and the (Ar)C–C=O···H torsion is 52(1)°. The naphthalene system is strongly twisted to displace the peri-substituents to opposite sides of the aromatic plane, in contrast to the situation for the N-protonated cations of the bulky phenyl and t-butyl ketones, 16 and 17 (Table 2). The ester carbonyl stretch occurs at 1686 cm⁻¹ in the infra-red spectrum.

Fig. 4:

Molecular structure of the N-protonated cation in 4-H.triflate (top) and in 4-H.picrate [22] (bottom).

Fig. 5:

Crystal packing arrangement of 4-H.triflate salt, with triflate ions shown in space-filling mode.

The room temperature ¹H NMR of a CDCl₃ solution of this salt shows a strongly deshielded ¹H resonance for the N–H group at δ_H: 13.00 ppm, and there is just one signal for the dimethylamino group in both the ¹H and ¹³C NMR spectra. In solution, there is no requirement for the second hydrogen bond to a triflate ion, so there may just be a tight intramolecular hydrogen bond to the ester group lying close to the aromatic plane. Previously, Schuster et al. reported the NMR spectra of the tetrafluoroborate salt of cation 4-H⁺ in nitrobenzene [23] and the crystal structure of the picrate salt of the corresponding ethyl ester [22]. In this latter case the anion is not involved in hydrogen bonding with the protonated dimethylamino group, and consequently, the hydrogen bond between peri groups is much shorter (1.70 Å) and the structure is also much less twisted with the peri N and C substituent atoms lying close to the naphthalene plane, and the angle at hydrogen much closer to linear (174° cf. 128°) and a lower torsion angle about the carbonyl group ((Ar)C–C=O···H: 29° v 52°) (Table 2). Similar hydrogen bonding between peri groups has been observed in the crystal structures of oxime 20 [24] and carboxylic acid 21 [1]. For the latter, there are two crystallographically unique molecules, one of which exists as a zwitterion with an intramolecular hydrogen bond 21 and the other as the uncharged amino acid 22.

The X-ray crystal structure determination of the triflate salt of diisopropylamide 6 at 100 K showed that the crystal system was monoclinic and the space group P2₁/c. The structure of the cation is shown in Fig. 6 and the crystal packing in Fig. 7. Protonation has taken place at the dimethylamino group and there is an intramolecular hydrogen bond to the oxygen atom of the peri-amide group. In contrast to the ester 4, there is no additional hydrogen bond from the protonated dimethylamino group to a triflate anion. The amide group, unlike the ester group in 4, is rotated out of the naphthalene plane by 57.6° due to the steric interaction of the isopropyl groups with the ortho hydrogen atom so that the hydrogen bond lies to one side of the naphthalene plane, in contrast to the ester salt. The hydrogen bond is much shorter than in the ester cation 4-H⁺ (1.60(2) cf. 2.06(4) Å) and is close to linear at hydrogen, unlike in the ester salt. However, the angle the hydrogen bond makes with the carbonyl group (97.6(7)°) and the (Ar)C–C=O···H torsion angle (56.5(7)°) are similar to those in the triflate salt of ester 4 (Table 2). The hydrogen bond does not lie in the plane of the carbonyl group, nor perpendicular to it, but at an intermediate position. The peri groups are splayed apart in the aromatic plane, more notably at the amide group. The hydrogen bonding has affected the amide carbonyl group which is longer than in an unprotonated amide (1.2595(17) cf. 1.23 Å). Solution ¹H NMR shows a strongly deshielded NH resonance, and two sets of N–Me and N-isopropyl signals, and in the infra-red spectrum the carbonyl frequency has moved from 1618 to 1574 cm⁻¹ on salt formation.

Fig. 6:

Molecular structure of N-protonated cation 6-H⁺ .

Fig. 7:

Crystal packing arrangement for 6-H.triflate, with triflate ions shown in space-filling mode.

Reaction of the N,N-dimethylamide 5 with triflic acid gave a white oily solid which on standing for a day followed by trituration with ether gave a white solid whose NMR was consistent with a mixture of the triflate salts of 1-dimethylaminonaphthalene-8-carboxylic acid 21 and dimethylamine. Thus, the amide group has been hydrolysed by atmospheric water to form the corresponding carboxylic acid. Crystals were grown from acetonitrile and studied by X-ray diffraction at 100 K. The crystal structure is monoclinic in space group P2₁/c and is composed of a 1:1:1 ratio of the zwitterionic 1-dimethylammonio-naphthalene-8-carboxylate 21, its O-protonated cation 23 and a dimethylammonium cation along with two triflates. The zwitterion is hydrogen bonded to its O-protonated salt via the carboxylate oxygen, and the two species are arranged across a centre of inversion with a 1:1 disorder in the location of the labile hydrogen atom (Fig. 8). There are two such pairs which are crystallographically unique, and the unit cell contains two of each of these pairs accompanied by eight triflate anions and four dimethylammonium cations (Fig. 9).

Fig. 8:

The two crystallographically unique molecules of 8-dimethylammonium-naphthalene-1-carboxylate, each hydrogen bonded to a molecule of its O-protonated salt. The zwitterion and conjugate acid are related by a centre of inversion, and the central hydrogen atom is disordered across this centre, with just one position shown. The angle between the carboxyl group and the aromatic plane is 5.0° (left) and 34.3° (right), and the former has the shorter intramolecular N-H···O hydrogen bond (1.53(3) v 1.65(3) Å).

Fig. 9:

Crystal packing arrangement for 21.23.Me₂NH₂.(triflate)₂ viewed down the a axis showing alternating layers of 21/23 species (ball and stick mode) and Me₂NH₂/triflate anions (space filling mode) perpendicular to the b axis (left) and (b) view showing the orientation of the naphthalene species (space filling mode) (right).

The two crystallographically unique peri-naphthalene species each contain an internal hydrogen bond between peri groups and in one case the carboxylic group has rotated about 34° out of the naphthalene plane while it is close to the naphthalene plane in the other. This leads to a difference in the lengths of the intramolecular hydrogen bond: 1.65(3) and 1.53(3) Å, respectively. These almost linear hydrogen bonds makes angles of 102(1) and 110(1)° with the carboxyl bond, while the (Ar)C–C=O···H torsion angles are 42(1) and 2(1)°. So the hydrogen bonding arrangements are quite different, though the splaying apart of the substituents are similar with the carboxyl group splayed out further, so that for the case where the carboxyl group is nearly coplanar with the naphthalene there is a close O···H contact with the ortho-H of 2.20 Å. The second carboxyl oxygen is involved in the intermolecular hydrogen bonding to the carboxyl group of another peri-naphthalene. In the two unique carboxy groups the carbon-oxygen bond which is intramolecularly hydrogen bonded is shorter (1.253(3) and 1.244(3) Å) than the bond involved in the intermolecular hydrogen bonding (1.277(3) and 1.275(3) Å). The dimethylammonium cation is hydrogen bonded to two independent triflate ions. The crystal structure contains alternate planes composed of the peri-naphthalene species and then the triflate and dimethylammonium ions.

Interestingly, slow evaporation of a CDCl₃ solution of the triflate salt of ester 4, led to growth of a large crystal of the triflate of the corresponding protonated carboxylic acid 23. The crystal structure of the acid salt is triclinic in space group P1̅ and shown in Fig. 10. The compound is protonated on the dimethylamino group which forms an intramolecular hydrogen bond to the carbonyl of the carboxylic acid group. The –OH of the carboxylic acid is hydrogen bonded to a triflate anion (Table 2). Together with the ready hydrolysis on protonation of the amide 5, it suggests a catalytic role for the hydrogen to which the ester and amide carbonyl groups make a hydrogen bond.

Fig. 10:

Crystal structure of 23.triflate showing hydrogen bonding interactions.

General

Solution NMR spectra were measured on a JEOL ECLIPSE 400 spectrometer at 400 MHz for ¹H and at 100.5 MHz for ¹³C using CDCl₃ as solvent and tetramethylsilane (TMS) as standard at 24°C unless otherwise stated, and measured in p.p.m. downfield from TMS with coupling constants reported in Hz. IR spectra were recorded on a Perkin Elmer Spectrum 100 FT-IR Spectrometer using Attenuated Total Reflection sampling unless otherwise stated, and are reported in cm⁻¹. Mass spectra were recorded at the EPSRC Mass Spectrometry Centre at the University of Swansea. Chemical analysis data were obtained from Mr Stephen Boyer, London Metropolitan University. Ester 4 and amides 5 and 6 were prepared by peri-lithiation of 1-dimethylaminonaphthalene and treatment with methyl chloroformate, N,N-dimethylcarbamoyl chloride or N,N-diisopropylcarbamoyl chloride [26, 27].

Preparation of 2-benzoyloxy-1,1-dimethyl-1,2-dihydrobenzo[cd]indol-1-ium chloride, 18.Cl

A stirred solution of aldehyde 1 (0.10 g, 0.50 mmol) in dry ether (5 mL) under nitrogen was treated with a 1M solution of benzoyl chloride in dry ether (0.625 mL, 0.625 mmol) at room temperature to give a white precipitate. After stirring for 10 min. the solid was filtered and washed with dry ether to give a 18.Cl as a white solid (0.14 g, 82%), m.p. 125–127°C (dec.), δ_H (400 MHz, CDCl₃): 9.12 (1H, d, J=7.3 Hz, Ar-H₁), 8.13 (2H, dd, J=8.4, 1.1 Hz, ortho-Ph-H₂), 8.12 (1H, d, J=8.2 Hz, Ar-H₁), 8.06 (1H, s, 2-H), 8.04 (1H, d, J=8.2 Hz, Ar-H₁), 7.78–7.88 (3H, m, Ar-H₃), 7.74 (1H, dt, J=7.6, 1.1 Hz, para-Ph-H₁), 7.55 (2H, t, J=7.8 Hz, meta-Ph-H₂), 4.29 (3H, s, N-CH₃), 3.89 (3H, s, N-CH₃); δ_C (100.5 MHz, CDCl₃): 164.8 (C=O), 145.1, 135.6, 130.9, 130.6, 130.1, 129.9, 129.2, 128.1, 127.6, 127.3, 127.0, 125.9, 122.9, 117.7 (Ar-C₁₆), 100.9 (2-C), 56.6 (N-CH₃), 49.3 (N-CH₃); ν_max: 3023, 2995, 2953, 1732, 1643, 1603, 1584, 1503, 1471, 1451, 1409, 1371, 1348, 1315, 1264, 1242, 1175, 1099, 1086, 1066, 1034, 1023, 1008, 968, 920, 897, 830, 812, 793, 768, 709, 692, 677 cm⁻¹; found: C: 70.62, H: 5.29 N: 4.23%; C₂₀H₁₈NO₂Cl requires C: 70.69, H: 5.34, N: 4.12%.

Preparation of 1,1-dimethyl-1,2-dihydro-2-(2′,2′-dimethyl)propanoyloxy-benzo[cd]indol-1-ium chloride 19.Cl

A stirred solution of aldehyde 1 (0.10 g, 0.50 mmol) in dry ether (5 mL) under nitrogen was treated with a 1M solution of trimethylacetyl chloride in dry ether (0.625 mL, 0.625 mmol) at room temperature to give a white precipitate. After stirring for 30 min. the solid was filtered and washed with dry ether to give 19.Cl as a white powder (0.15 g, 94%), m.p. 168–172 dec°C. δ_H (400 MHz, CDCl₃) 9.13 (1H, d, J=7.2 Hz, Ar-H₁), 8.05 (1H, d, J=8.2 Hz, Ar-H₁), 7.98 (1H, d, J=8.2 Hz, Ar-H₁), 7.77–7.86 (2H, m, Ar-H₂), 7.60 (1H, d, J=7.5 Hz, Ar-H₁), 7.59 (1H, s, 2-H), 4.24 (3H, s, N-CH₃), 3.88 (3H, s, N-CH₃), 1.34 (9H, s, C(CH₃)₃; δ_C (100.5 MHz, CDCl₃) 176.8 (C=O), 145.2, 131.0, 130.2, 129.9, 128.0, 127.7, 127.4, 127.0, 122.3, 118.2 (Ar-C₁₀), 100.4 (2-CH), 56.6 (N-CH₃), 49.6 (N-CH₃), 39.5 (C(Me)₃), 26.8 (3×CH₃). ν_max: 3022, 2970, 1749, 1505, 1470, 1396, 1275, 1118, 1093, 1049, 1009, 972, 941, 905, 847, 829, 810, 767, 749 cm⁻¹; found: C: 67.53, H: 7.01, N: 4.32%; C₁₈H₂₂N O₂Cl requires C: 67.60, H: 6.93, N: 4.38%.

1-Dimethylammonio-8-methoxycarbonylnaphthalene triflate, 4-H⁺.CF₃SO₃⁻

A stirred solution of methyl 8-dimethylaminonaphthalene-1-carboxylate (0.50 g, 1.84 mmol) in dry ether (20 mL) under nitrogen was treated with a few drops of triflic acid, and stirred for 1 h. The solvent was evaporated under vacuum, and the residue left at 5°C. After 72 h the product had solidified and was collected and washed with ether to give the product, 4-H.triflate, as a pink powder, m.p. 103–104°C dec.; δ_H (400 MHz, CDCl₃): 13.00 (1H, br, N-H), 8.73 (1H, d, J=7.4 Hz, Ar-H₁), 8.33 (1H, d, J=7.6 Hz, Ar-H₁), 8.25 (1H, d, J=8.0 Hz, Ar-H₁), 8.10 (1H, d, J=8.0 Hz, Ar-H₁), 7.80 (1H, t, J=7.9 Hz, Ar-H₁), 7.68 (1H, t, J=7.9 Hz, Ar-H₁), 4.16 (3H, s, O-CH₃), 3.46 (6H, s, N-(CH₃)₂); δ_C (100.5 MHz, CDCl₃): 172.0 (C=O), 138.1, 137.4, 137.2, 136.0, 133.3, 127.2, 126.0, 123.8, 123.0, 122.9 (Ar-C₁₀), 120.7 (q, J=321 Hz, CF₃SO₃⁻), 54.9 (O-CH₃), 47.8 (N-(CH₃)₂); ν_max: 3159, 3074, 2963, 1686, 1516, 1463, 1431, 1224, 1215, 1205, 1172, 1145, 1092, 1025, 993, 870, 840, 797, 784, 762, 751, 635, 574, 516, 501 cm⁻¹; found C: 47.46, H: 4.13, N: 3.53%; C₁₄H₁₆NO₂.CF₃SO₃ requires: C: 47.49, H: 4.25, N: 3.69%.

Slow evaporation of the NMR sample led to the growth of a large crystal of 8-dimethylammonio-naphthalene-1-carboxylic acid triflate, 23.triflate, m.p. 155–157°C, ν_max: 2988 br, 1681, 1624, 1602, 1519, 1466, 1418, 1290, 1219, 1198, 1155, 1027, 876, 839, 780, 768, 722, 634, 626, 586, 572 cm⁻¹.

Reaction of N,N-dimethylamide 5 with triflic acid

A solution of N,N-dimethylamide 5 (0.20 g, 0.82 mmol) in dry ether (4 mL) was treated with a solution of triflic acid (0.124 g, 0.83 mmol) in dry ether (2 mL) under nitrogen to give an oily precipitate. After stirring for 2 h. and then standing for 24 h. the precipitate remained oily. The ether was allowed to evaporate in the air, and the residue left to stand for a further 24 h. Addition of dry ether, stirring and scratching with a glass rod gave a solid which was collected, washed with dry ether and dried (0.187 g) identified as a 1:1.2 mixture of 1-dimethylammonio-naphthalene-8-carboxylate triflate and dimethylammonium triflate. δ_H (400 MHz, CD₃CN): 8.76 (1H, dd, J=7.2, 1.4 Hz, Ar-H₁), 8.25 (1H, dd, J=7.6, 1.4 Hz, Ar-H₁), 8.12 (1H, J=7.3 Hz, Ar-H₁), 7.98 (1H, d, J=7.3 Ar-H₁), 7.65–7.71 (2H, m, Ar-H₂), 6.99 (1.2×2H, br t, J(¹⁴N, ¹H)=44.6 Hz, NH₂), 3.14 (6H, s, N(CH₃)₂), 2.64 (1.2×6H, t, J=5.5 Hz, NH₂(CH₃)₂); δ_C (100.5 MHz, (CD₃CN): 174.4 (C=O), 141.2, 137.5, 137.0, 136.7, 133.0, 128.0, 127.3, 126.9, 125.5, 123.5 (Ar-H₁₀), 118.7 (q, J=310 Hz, CF₃SO₃⁻), 47.0 (1-[NH(CH₃)₂]⁺), 35.9 ([NH₂(CH₃)₂]⁺); ν_max: 3121, 1595, 1467, 1261, 1243, 1223, 1155, 1030, 883, 838, 765, 743, 693, 637, 574, 550, 516, 503 cm⁻¹; HRMS: Found 216.1017, C₁₃H₁₄NO₂ requires 216.1019. Crystals for X-ray crystallography grown from acetonitrile had composition of 21.23.Me₂NH₂.(triflate)₂.

N,N-Diisopropyl-1-dimethylammonio-naphthalene-8-carboxamide triflate, 6-H⁺ CF₃SO₃⁻

A solution of N,N-diisopropylamide (100 mg, 0.34 mmol) in dry ether (4 mL) at 0°C under nitrogen was treated with triflic acid (54 mg, 0.36 mmol) in dry ether (2 mL) and stirred for 30 min. A white precipitate of 6-H⁺.triflate (86 mg, 57% ) was filtered off and washed with dry ether, m.p.: 141–142°C dec.; δ_H (400 MHz, CDCl₃): 12.88 (1H, br, N-H), 8.31 (1H, d, J=7.8 Hz, Ar-H₁), 8.14 (1H, dd, J=7.6, 2.1 Hz, Ar-H₁), 8.08 (1H, d, J=7.8 Hz, Ar-H₁), 7.75 (1H, t, J=8.0 Hz, Ar-H₁), 7.63–7.68 (2H, m, Ar-H₂), 3.83 (1H, hep, J=6.4 Hz, CHMe₂), 3.75 (1H, hep, J=6.6 Hz, CHMe₂), 3.49 (3H, s, NCH₃), 3.36 (3H, s, NCH₃), 1.67 (3H, d, J=6.9 Hz, CH₃ ) 1.57 (3H, d, J=6.9 Hz, CH₃) 1.34 (3H, d, J=6.4 Hz, CH₃ ) 1.08 (3H, d, J=6.4 Hz, CH₃ ); δ_C (100.5 MHz, CDCl₃): 175.1 (C=O), 138.0, 135.9, 133.6, 132.8, 129.5, 127.9, 127.2, 125.8, 122.8, 121.7 (Ar-C₁₀), 120.9 (q, J=320 Hz, CF₃SO₃), 53.6 (CHMe₂), 48.4 (N-CH₃), 48.1 (CHMe₂), 45.9 (N-CH₃), 21.2, 20.7, 19.7 & 19.5 (4×CHCH₃); ν_max: 3070, 3010, 2969, 2293 br, 1574, 1528, 1504, 1471, 1451, 1386, 1377, 1340, 1330, 1269, 1256, 1223, 1148, 1133, 1088, 1028, 995, 839, 814, 778, 756, 741, 669, 648, 635, 606, 572 cm⁻¹; found C: 53.50, H: 5.95, N: 6.15%; C₁₉H₂₇N₂O.CF₃SO₃ requires: C: 53.56, H: 6.07, N: 6.25%.

X-ray crystallography

X-ray diffraction datasets were measured either on an Oxford Diffraction Xcalibur diffractometer equipped with a Sapphire detector using the Crysalis software [28] and an Oxford Cryosystems 700 series Cryostream low temperature system at NTU (18, 19, 4-H.CF₃SO₃, 23.CF₃SO₃), or at the UK National Crystallography Centre, Southampton University [29] (6-H.CF₃SO₃, 21.23.Me₂NH₂.(CF₃SO₃)₂) on a Rigaku AFC12 diffractometer equipped with enhanced sensitivity (HG) Saturn724+ CCD detector mounted at the window of an FR-E+ SuperBright rotating anode generator (Mo Kα, λ=0.71075 Å) with VHF Varimax optics (70 μm focus) using Crystal Clear software [30] for data collection and reduction. Structures were solved and refined using the SHELXS and SHELXL suite of programs [31] using the XSEED interface [32]. Molecular illustrations were made with Mercury [33]. Data is deposited at the Cambridge Crystallographic Data Centre with code numbers CCDC-1429425-1429430.