A joint experimental and computational investigation on homoconjugated push-pull chromophores derived from 7,7-diphenylnorbornane

Article abstract of DOI:10.1002/ejoc.201200159

We report hereon the synthesis, spectroscopic properties and computational studies of novel aromatic homoconjugated compounds derived from 7,7-diphenylnorbornane (DPN). The UV/Vis spectra of these compounds show bands corresponding to the respective chrom

Full text of DOI:10.1002/ejoc.201200159

FULL PAPER
DOI: 10.1002/ejoc.201200159
A Joint Experimental and Computational Investigation on Homoconjugated
Push-Pull Chromophores Derived from 7,7-Diphenylnorbornane
Noelia Herrero-García,[a] María del Rosario Colorado Heras,[a] María del Rosario Torres,[b]
Israel Fernández,*[a] and José Osío Barcina*[a]
Keywords: Donor-acceptor systems / Homoconjugation / Charge transfer / DFT calculations / Transannular interactions
We report hereon the synthesis, spectroscopic properties and
computational studies of novel aromatic homoconjugated
compounds derived from 7,7-diphenylnorbornane (DPN).
The UV/Vis spectra of these compounds show bands corre-
sponding to the respective chromophores as well as new
homoconjugation bands and charge transfer absorptions in
D–DPN–A push-pull derivatives. Homoconjugation between
the aromatic rings strongly depends on the nature of the sub-
stitution at the aryl moieties. Therefore, electronic communi-
cation by homoconjugation can be easily tuned by con-
trolling the electronic nature and positions of the substitu-
ents. The strong homoconjugative interaction is also re-
flected in the reactivity, NMR spectra and NLO properties of
the compounds studied. DFT calculations nicely agree with
the experimental data and shed light on the electronic delo-
calization via homoconjugation.
ported.[17,18] However, electron delocalization by homocon-
jugation in iptycenes such as triptycene is not clear and re-
mains controversial.[19] Very recently, homoconjugated
push-pull systems obtained by [2+2] cycloaddition reaction
Introduction
Over the past years a considerable effort has been de-
voted on the design, synthesis and study of the properties
of conjugated push-pull molecular chromophores (D–π–A)
and their oligomeric and polymeric derivatives.[1–5] Interest
in such systems is justified by their important technological
applications in molecular electronics and optoelectronics[6]
as e.g. nonlinear optical (NLO) materials,[6,7] molecular
wires,[8] solvatochromic probes,[9] or organic photorefrac-
tives.[10]
between
2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) and N,N-dialkylanilino (DAA) (4, Figure 1) or fer-
rocene-substituted alkynes have been described.[20] The re-
sulting D–A chromophores show strong intramolecular CT
interactions and promising third-order nonlinear optical
properties.
Recently, several strategies have been developed in order
to modulate the properties (HOMO–LUMO gap, solubility,
processability) of push-pull systems. Thus, nonplanar D–π–
A chromophores have been reported and the influence of
nonplanarity on their conjugative properties has been inves-
tigated (1, Figure 1).[11–13] A different approach involves the
use of bridges between the donor and acceptor groups with
non-conventional electron delocalization, as in compounds
2 with cross-conjugated bridges,[14] spiro systems 3,[15] and
also compounds with saturated bicyclic connectors.[16] At
this respect, aromatic homoconjugated systems have re-
ceived little attention. Examples of lateral homoconjugated
push-pull systems derived from triptycene have been re-
Figure 1. Examples of nonplanar, cross-conjugated, spiro, and
homoconjugated push-pull chromophores 1–4, respectively.
[a] Departamento de Química Orgánica, Facultad de Ciencias
Químicas, Universidad Complutense de Madrid,
Ciudad Universitaria s/n, 28040 Madrid, Spain
Fax: +34-91-3944103
Aromatic apical homoconjugated compounds derived
from 7,7-diphenylnorbornane (DPN) (5c, Figure 2) are a
family of interesting derivatives featuring non-conventional
electron delocalization within the cofacially arranged aryl
groups.[21–26] Homoconjugated push-pull systems were syn-
thesized and used for the first time to study the nature of
E-mail: israel@quim.ucm.es
josio@quim.ucm.es
[b] Laboratorio de Difracción de Rayos X, Facultad de Ciencias
Químicas, Universidad Complutense de Madrid,
Ciudad Universitaria s/n, 28040 Madrid, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200159.
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face to face aromatic interactions.[21] Further studies dem- plus polarization 6-31+G(d) basis sets.[29] Stationary points
onstrated that these compounds show remarkable second- were characterized as minima by calculating the Hessian
order NLO properties, with βz (1064 nm) values comparable matrix analytically at this level. Calculations of absorption
to those measured for linearly conjugated analogous.[22] spectra were accomplished by using the time-dependent
More recently, the first example of efficient photoinduced density functional theory (TD-DFT)[30] method. The as-
energy transfer mediated by an homoconjugated bridge in signment of the excitation energies to the experimental
the heterodinuclear D–B–A complex [Ru–DPN–Ir]3+ has bands was performed on the basis of the energy values and
been reported.[23]
oscillator strengths. The B3LYP[31] Hamiltonian was chosen
because it was proven to provide reasonable UV/Vis spectra
for a variety of chromophores[26,32] including organometal-
lic species.[33] Total first hyperpolarizabilities (βtot) were
computed according to the following equation using the dif-
ferent βijk tensor components:
Results and Discussion
Synthesis and Structure of DPNs
For this study we have chosen the series of mono- and
disubstituted derivatives of DPN (5 and 6) and 7-(o-fluo-
rophenyl)-7-phenylnorbornane (FDPN, 7) depicted in Fig-
ure 2. The synthesis of these compounds was carried out
according to the methodology described previously by us
(Scheme 1).[21–26] One of the advantages of DPNs is that a
large variety of different molecules can be prepared follow-
ing standard and straightforward procedures. Electrophilic
aromatic substitution reactions on both DPN and FDPN
take place exclusively at the para position, since the ortho
position is sterically hindered by the bridgehead hydrogen
atom of norbornane. The only exception to this behaviour
was found while attempting the synthesis of 7o, the FDPN
derivative with two para nitro groups as substituents
(Scheme 2). While nitration reaction of DPN yields the cor-
responding dinitro derivative 6h in high yield, reaction of
7c under the same conditions yields a 25:75 mixture of 7o
and 8 (Scheme 2). Since these compounds are difficult to
separate, the synthesis of 7o was carried out by nitration of
the mononitro derivative 7l.[21]
The formation of the meta-substituted compound 8 can
be explained considering that, in the first step of the ni-
tration reaction, 7g is obtained as the main reaction prod-
uct due to the deactivating effect of the fluorine atom
(Scheme 2). In the second step, electrophilic aromatic sub-
stitution takes place at the meta position of the fluorinated
ring induced by both the deactivating effects of fluorine and
the nitro group of the adjacent homoconjugated aromatic
ring. Moreover, nitration of 7g affords compound 8 in 86%
yield. This fact, together with the experimental observation
that reaction rate of the second nitration reaction is lower
than the first nitration, is a clear evidence of strong transan-
Figure 2. Mono- and disubstituted derivatives of DPN and FDPN
5–7.
In previous works we have studied electron delocalization
in DPN as well as in derived polymers[24] and oligomers[25]
by absorption spectroscopy and TD-DFT calculations.[26]
The results of these investigations confirm that aromatic
homoconjugation in acyclic systems is an effective mecha-
nism for electron delocalization with an effective homocon-
jugation length for homoconjugated oligomers of 6–7 aryl
rings. Our previous calculations also pointed out the impor-
tance of transannular interactions in push-pull systems de-
rived from DPN. Now, in order to check this hypothesis
and provide further information on electron delocalization
in these aromatic homoconjugated systems, we have per-
formed an extensive joint computational-experimental
study in substituted DPNs, with special emphasis on push-
pull DPN derivatives. The electronic communication be-
tween the donor and acceptor moieties has been studied by
UV/Vis and NMR spectroscopy. The experimental results
were correlated with DFT and TD-DFT calculations.
Computational Details
Geometry optimizations without symmetry constraints nular homoconjugative interaction in DPNs, similar to that
were carried out using the Gaussian09 suite of programs[27] observed in cyclophanes.[34–36] In a previous work we have
at the dispersion corrected meta-hybrid functional M06–2X shown that DPNs can be considered as examples of “open-
functional[28] in combination with the standard double-ζ chain cyclophanes” (protophanes).[24b]
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Homoconjugated Push-Pull Chromophores
used for the analogous DPNs starting from the 2,2-di-
phenylpropane and bicyclic compound 10a (see Supporting
Information).
Figure 3. Structures of reference compounds 9 and 10.
The main structural features of the compounds described
in this work are highlighted by the push-pull system 6i. The
crystal structure of 6i (Figure 4) confirms the characteristic
cofacial arrangement of the aryl groups in DPNs. Thus, the
values of the C15–C14–C7–C8 and C9–C8–C7–C14 torsion
angles are 92.3 and 89.1° respectively. On the other hand,
the value of the C14–C7–C8 bond angle is 107.8° and the
distance between the ipso carbon atoms of the aryl rings
(C14–C8), 2.468 Å, well below the sum of the van der
Waals radii for two phenyl rings (3.4 Å).[37a]
Scheme 1. General synthetic routes for DPN and FDPN deriva-
tives.
Figure 4. X-ray crystal structure of compound 6i.
Scheme 2. Synthesis of nitro derivatives of FDPN.
The crystal packing of 6i (Figure 5) shows some remark-
Compounds 9a–e derived from 2,2-diphenylpropane and able features. It has been described that nitroanilines crys-
10b–c have been prepared as references for the study of the tallize into predictable arrays forming intramolecular hy-
spectroscopic properties of DPNs (Figure 3). It should be drogen bonds between the amino and nitro groups. These
noted that in 10a–c, the most stable conformation is the interactions occur so frequently that can be used to estab-
orthogonal disposition, since the aryl rings cannot adopt lish hydrogen bond rules which are useful tools to predict
the cofacial conformation because of the restricted mobility and design crystalline materials.[38] However, no
of the fused phenyl ring. Therefore, homoconjugative inter- nitro···amino hydrogen bonds are detected in the case of
actions are not expected in these derivatives. On the other 6i. Instead, short amino···amino contacts are observed. The
hand, the most stable conformation of 2,2-diphenylpro- H2C atom of the amino group interacts with the N2’ of
panes is the helicoidal conformation. The synthesis of these the neighbouring molecule: H2C···N2Ј distance of 2.614 Å,
compounds was carried out following the same procedures with N2–H2C–N2Ј angle of 144.6° and distance between
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N2 and N2Ј amino N atoms, 3.352 Å. The shorter distance Table 1. Absorption spectra (λmax, MeOH) of monosubstituted
DPNs and FDPNs.
between amino and nitro groups is observed in the case of
H2D and O1 (2.994 Å). On the other hand, short contacts
are detected between the nitro oxygen atoms and H10 and
H18 hydrogen atoms of the neighbouring aryl rings of two
λ [nm]
λ [nm]
λ [nm]
ε (m–1 cm–1)
ε (m–1 cm–1)
ε (m–1 cm–1)
5a 249 (13800)[a]
5i
233 (11600)
7f 259 (16000)
7g 284 (11800)
7h 246 (10400)[a]
7i 234 (14700)[a]
7j 229 (13700)[a]
7k 234 (16100)[a]
7l 285 (11800)
different molecules (O2···H10 2.597 Å; O1···H18 2.618 Å). 5b 238 (13800)[a]
5j
289 (10000)
5c 229 (13300)[a]
7a
7b
7c
7d
7e
249 (10300)[a]
234 (15100)[a]
226 (12300)[a]
232 (16000)[a]
232 (20200)[a]
On the basis of distance criteria, the interaction between
5d 234 (13600)[a]
the amino groups can be considered as hydrogen bond since
5e 236 (12800)[a]
the distance (2.614 Å) is shorter than the sum of the van
der Waals radii of hydrogen and nitrogen atoms (1.10 Å and
1.55 Å, respectively).[37b]
5f 250 (15000)
5g 250 (11800)
5h 262 (15200)
[a] Homoconjugation band.
Table 2. Absorption spectra (MeOH) of disubstituted DPNs and
FDPNs with X = Y groups.
λ [nm] ε (m–1 cm–1)
λ [nm] ε (m–1 cm–1)
6a
6b
6c
6d
6e
6f
259[b], 272 (20000)[a]
6g
248 (20700), 269 (28400)
284 (16900)
234 (12700), 255 (18600)[a] 6h
242 (18300)[a]
7m 237,[b] 253 (12100)[a]
7n
7o
230 (7000), 247 (11300)[a]
234 (10400), 256 (15000)
235 (17400), 258 (26700)
239 (16900)[a]
273 (11900)
[a] Homoconjugation band. [b] Shoulder.
The influence of electron delocalization by homoconju-
gation is revealed by the bathocromic shift of the chromo-
phores’ bands in comparison to the corresponding spectra
of benzene derivatives:[39] compounds 5f (250 nm) and 6e
(256 nm) and benzoic acid (226 nm); 5g (250 nm) and 6f
(258 nm) and etoxycarbonylbenzene (228 nm); 5h (262 nm),
7f (259 nm) and 6g (269 nm) and acetophenone (242 nm);
5i (233 nm) and trifluoromethylbenzene (210 nm); 5j
Figure 5. Crystal packing of 6i showing the amino···amino short
contacts.
Absorption Spectroscopy Study
Absorption spectroscopy constitutes an appropriate (289 nm), 7g (284 nm), 7l (285 nm) and 6h (284 nm) and
method to study electron delocalization and transannular nitrobenzene (251 nm). Furthermore, the position of the
interactions in aromatic systems. In previous works we have band depends on the effect of the substituent placed on
used UV/Vis spectra to study electron delocalization in the adjacent ring. This effect is similar to the transannular
homoconjugated DPNs[26] as well as oligomers[25] and poly- interaction described for cyclophanes.[34–36] Thus, in the
mers[24] derived from DPN. These studies clearly show that series of nitro derivatives 5j, 6h, 6i, 6j (DPN), 7g, 7l, 7o, 7p
aromatic homoconjugation is an effective mechanism for and 7q (FDPN) there is a correlation between the wave-
electron delocalization that resembles the situation de- length of the absorption band of the nitro groups and the
[40]
scribed for polyphenylenes. We have also performed TD- corresponding Hammett substituent constant σp
of the
DFT calculations on these systems,[26] finding a good agree- substituent placed at the opposite aryl ring. Figure 6 shows
ment between the TD-DFT-computed lowest energy verti- the absorption spectra of compounds 7g, 7o, 7p and 7q as
cal transitions and the experimentally observed absorptions. well as the linear relationship between the wavelengths of
Therefore, TD-DFT calculations can be used to accurately the absorption maxima of the nitro group and the nature
assign the vertical transitions responsible for the observed of the substituents placed at the adjacent aryl ring accord-
spectra in homoconjugated DPNs.
ing to their σp value. A similar situation is observed with
The UV/Vis spectra of DPNs and FDPNs show three the analogous DPN derivatives.
important absorption bands: a) the bands of the corre-
Gas-phase TD-DFT calculations on compounds 7g,
sponding chromophores attached to the aryl rings, b) the 7o,p,q also show the presence of two main absorptions. The
new homoconjugation bands, and c) charge-transfer bands band around 300 nm (which is slightly redshifted in the cal-
in push-pull systems with strong electron-withdrawing and culations due to solvatochromism) is ascribed in all cases
electron-donating groups in their structures. Tables 1, 2, to the promotion of one-electron from the HOMO to the
and 3 show the wavelengths of the absorption maxima of LUMO. As expected, both frontier orbitals are π molecular
the bands for all compounds studied in this work. For those orbitals, thus indicating the π-π* nature of this absorption.
cases where the band appeared as a shoulder, the position Inspection of the involved orbitals reveals that the HOMO
of these absorptions has been established by the derivative is mainly centered in the flouroaryl moiety whereas the
method.
LUMO is centered in the adjacent p-NO2-aryl group (Fig-
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Homoconjugated Push-Pull Chromophores
Table 3. Absorption spectra (MeOH) of disubstituted DPNs and FDPNs with X ϶ Y groups.
λ [nm] ε (m–1 cm–1)
λ [nm] ε (m–1 cm–1)
6i
247 (13200), 293 (9800), 320[b,c]
227 (12250),[a] 277 (8100), 303[b,c]
247 (9800),[a] 260–290[c,d]
7r
7s
7t
7u
7v
225 (12300),[a] 268 (7600), 288[b,c]
242 (16500),[a] 270 (6900)
237 (14300)[a]
6j
6k
7p
7q
286 (7800), 275–340[c,d]
224,[b] 247 (12000)[a]
223 (14500),[a] 281 (7800),[c,d] 288 (7600)
250 (9300), 250–425[c,d]
[a] Homoconjugation band. [b] Shoulder. [c] Charge transfer band. [d] Overlapping bands.
Finally, the effect of homoconjugation in DPNs can be
also observed by comparison of the absorption wavelength
of the nitro derivatives 5j (289 nm) and 6h (284 nm) with
the analogous 2,2-diphenylpropanes 9b and 9d (276 nm).
Similarly, TD-DFT calculations assign this band (for 5j) to
a combination of the HOMO–3 and HOMO–2 to LUMO
vertical transitions (calculated excitation energy of 270 nm).
The shape of these π-molecular orbitals resembles that of
HOMO–3 (7p), confirming the delocalization of electrons
in both aryl moieties due to homoconjugation (see Support-
ing Information).
One of the most relevant features of the compounds
studied in this work is related to the homoconjugation
band. We have previously described that DPN shows a
characteristic homoconjugation band at 229 nm. The posi-
tion of this absorption depends on the torsion angle of the
aryl rings and the extension of the homoconjugation. Thus,
deviations from the cofacial conformation cause hypsoch-
romic shifts of the band. On the other hand, a bathoch-
romic shift is observed in DPN oligomers because of the
extension of the homoconjugation.[25,26]
In the substituted DPNs studied herein, the nature of the
substituents on the aryl rings exerts a very important effect
on the electron delocalization between the aromatic rings.
Thus, electron-withdrawing groups diminish the electron
density and, consequently, the homoconjugative effect is al-
most imperceptible, as revealed by the hypsochromic shift
of the homoconjugation band with e.g. nitro-substituted
DPNs and FDPNs 5j, 6h, 7g, 7l and 7o. In contrast, elec-
tron-donating groups show the opposite effect, as they in-
crease the electron density and consequently the homocon-
jugation between the aryl rings. This is observed with
methyl-, methoxy- and amino-substituted DPNs and
FDPNs 5a, 5b, 6a, 6b, 6c, 7a, 7b, 7h, 7i, 7j, 7m and 7n in
which bathochromic shifts of the corresponding homocon-
jugation bands are observed (see Tables 1, 2, and 3). The
only exception to this behaviour was found in halogen-sub-
stituted DPNs and FDPNs 5d, 5e, 6d, 7d, 7e and 7k. The
homoconjugation band in these derivatives is redshifted,
pointing to a predominance of the conjugative effect of
Figure 6. Absorption spectra of NO2-substituted FDPN and corre-
lation between the absorption wavelength and the σp value of the
substituent placed on the adjacent homoconjugated ring.
ure 7). For this reason, it is not surprising that a more effec-
tive charge transfer (i.e. a redshift) occurs with better π-
donors attached to the para-position of the fluoro-aryl frag-
ment in agreement with the above-mentioned Hammett
plot. Moreover, the band around 230 nm is ascribed to the
HOMO–3 to LUMO transition by our TD-DFT calcula-
tions. As seen in Figure 7, the HOMO–3 is a delocalized
orbital between both aryl substituents thus confirming the
homoconjugated nature[26] of this absorption.
Figure 7. Computed molecular orbitals of compound 7p (isosur-
face value of 0.03 au).
In the case of amino-substituted DPNs and FDPNs, the these atoms on the wavelength of the homoconjugation
absorption band of the chromophore appears overlapped band, as observed in the absorption bands of halogen sub-
with the homoconjugation bands in most of the derivatives stituted benzenes.[39] Strikingly, the homoconjugation band
and can be observed only in compounds where the homo- of FDPN (7c) is blueshifted in comparison with the band
conjugation band is redshifted (vide infra). In these com- of DPN (5c). The reasons for this differential behaviour can
pounds, a similar behaviour is observed: i.e. the absorption be found in the inductive effect of the fluorine atom at
band is redshifted in going from compound to 7u (224 nm) the ortho position (which is in part responsible for the ob-
to 7m (237 nm).
served hypsochromic shift of FDPN)[39] and the influence
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of this atom on the cofaciallity of the aryl rings (which that this virtual orbital is delocalized between both aryl
would diminish the homoconjugation between the aryl moieties thus confirming the electronic communication in
rings).[26]
this species. As expected, no similar delocalized orbital can
The substituents effect on the communication between be found in the non-cofacial analogue 10b. This provokes
the aryl groups in homoconjugated derivatives is clearly re- that both aryl groups are electronically isolated and there-
vealed by comparison with the UV/Vis spectra of the or- fore, this species behaves quite similarly to aniline.
thogonal chromophores 10b and 10c. As mentioned above,
electron-releasing groups such as NO2 diminish the electron
density between the aromatic rings and, consequently,
homoconjugation is less effective. The absorption spectra of
10c shows an absorption maximum at 276 nm, the same
wavelength observed for the diphenylpropane derivatives 9b
and 9d. These bands are characteristic of aromatic nitro
derivatives. The spectra of 5j (289 nm), 6h (284 nm) and 7o
(273 nm) are quite similar, showing the effect of delocaliza-
tion by homoconjugation and the deviation from the cofa-
cial conformation in the case of 7o. The homoconjugation
band in these compounds is blueshifted by the NO2 groups
and is difficult to observe. Interestingly, the situation ob-
served for the amino derivatives is remarkably different.
The absorption spectra of the diamino orthogonal deriva-
tive 10b resembles that of aniline, showing an intense strong
band at 239 nm (230 nm in aniline) and a weak absorption
(1Lb band) at 285 nm (281 nm in aniline) (Figure 8). The
spectra of diphenylpropane derivatives 9a (238 and 289 nm)
and 9c (241 and 289 nm) are similar. While the homoconju-
gation bands are not observed in these compounds, the
spectra of 6b and 7m are dominated by the homoconjuga-
tion bands at 255 and 253 nm, respectively. Moreover, the
homoconjugation band is redshifted up to 272 nm in the
case of compound 6a, in agreement with the higher elec-
tron-donating nature of the NMe2 group. These results
demonstrate that communication by homoconjugation be-
tween aromatic moieties can be easily tuned by controlling
the electronic nature of the substituents attached at the aryl
rings. Interestingly, our TD-DFT calculations assign the
homoconjugation band in 6b to the HOMOǞLUMO+1
vertical transition (λcalc = 262 nm). Figure 9 nicely shows
Figure 9. Computed molecular orbitals of compound 6b (isosur-
face value of 0.035 au).
The position of the homoconjugation bands strongly de-
pends on the nature of the substituents. Figure 10 shows
the absorption spectra of MeO-FDPNs with different sub-
stituents on the homoconjugated aromatic ring. As can be
seen, there is an excellent correlation (r2 = –0.996) between
the position of the homoconjugation band and the σp value
of the respective group. Only the bromo derivative 7s devi-
ates from this behaviour, as observed before for the halo-
gen-substituted DPNs and FDPNs (vide supra). The same
behaviour is observed for the MeO-DPNs 5b, 6c, 6j and 6k
as well as in the series 5a–c, 6a–c, 7a–c, 7h–j and 7m–n.
Figure 10. Absorption spectra of MeO-substituted FDPN and cor-
relation between the absorption wavelength and the σp value of the
substituent placed on the adjacent ring. The absorption spectra of
7n and 7t are omitted for clarity.
The situation observed in push-pull DPNs with strong
electron-donating and releasing groups is particularly inter-
esting. When both electron-withdrawing and -donating sub-
stituents are placed at the para positions, besides the chro-
mophore and homoconjugation absorptions, charge-trans-
fer bands are observed in the corresponding UV/Vis spectra
of compounds 6i, 6j, 6k, 7p, 7q, 7r and 7v (Table 3).
Figure 8. Absorption spectra of amino-substituted compounds.
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Homoconjugated Push-Pull Chromophores
The absorption spectra of compounds 6j, 6k, 7p, 7q and band, with a maximum at 250 nm and cut-off ca. 425 nm.
7r are shown in Figure 11. Compounds 6j and 7q show Previous studies carried out on diphenylmethane and 2,2-
broad absorptions corresponding to two overlapping bands diphenylpropane with nitro and amino groups as substitu-
between 250–375 nm. These bands are the sum of the ents describe the presence of a weak charge-transfer band
charge-transfer band and the nitro group absorption. A as the tail of the long wavelength band of the nitro group.[41]
similar situation is observed in 7p, although in this case a These results nicely illustrate the remarkable effect of
narrower band is observed, in accordance with the less do- homoconjugation in our compounds. In fact, this effect is
nating character of the methyl group. In the case of com- just the consequence of the imposed geometry by the DPN
pound 7r, the charge-transfer band is observed between fragment which places both aromatic rings in a cofacial ori-
250–300 nm and in 6k the residual absorption at longer entation allowing for the observed charge transfer. Obvi-
wavelength can be assigned to the charge-transfer band (see ously, this geometrical constrain is not present in the analo-
supplementary material). The cut-off of the CT bands in gous derivative 9e or orthogonal chromophores 10 (see Fig-
compounds 6j, 7p and 7q lies between 380–390 nm.
ure 13) and therefore, there is no chance for the electrons
to delocalize by homoconjugation.
Figure 11. Absorption spectra of compounds 6j, 6k, 7p, 7q and 7r
showing the charge-transfer bands.
Figure 13. Fully optimized geometries (M06-2X/def2-SVP level) of
compounds 6i and 9e and 10b.
Figure 12 shows the absorption spectra of compound 6i,
7v and the analogous 2,2-diphenylpropane derivative 9e.
Comparison of these spectra reveals the presence of a
charge-transfer band between 300–450 nm in 6i. This band
is not observed or is much less pronounced in 9e (cut-off:
385 nm). The spectrum of 7v shows a broad absorption
band, sum of the NH2, NO2 chromophores and the CT
Comparison of the absorption spectra of 6i with the meta
substituted analogous FDPN leads to some significant con-
clusions. Partial hydrogenation of 8 (Scheme 3) produces a
mixture of meta-substituted nitro/amino derivatives 11 and
12. In the UV/Vis spectra of these compounds (11: λmax
=
283 nm; 12: λmax = 263 nm) no CT band are observed (see
Supporting Information), showing that charge transfer
from the donor to the acceptor groups is favoured by sub-
Scheme 3. Synthesis of meta FDPNs 11 and 12 and resonance
structures of push-pull derivative 6i.
Figure 12. Absorption spectra of compounds 6i and 9e.
Eur. J. Org. Chem. 2012, 2643–2655
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2649

I. Fernández, J. Osío Barcina et al.
FULL PAPER
stituents placed at the para positions of the aromatic rings.
In this regioisomer, the homoconjugative interaction
reaches its maximum, according to the homoconjugated
resonance structure of 6i depicted in Scheme 3.
NLO Properties
In a previous work we described the first study reported
to date on the NLO properties of homoconjugated com-
pounds.[22] Our results show that push-pull systems derived
from DPN and FDPN present significant SHG hyperpolar-
izabilities. The values of βz value measured for our DPNs
and FDPNs are higher than the obtained for non-homo-
conjugated analogous and comparable to conjugated push-
pull systems. Thus, the βz (1064 nm) value measured for Figure 14. Plots of βtot vs. σp substituent constants.
compound 6i was 21ϫ10–30 esu, three times higher than the
observed for 9e and equal to the measured for p-nitroaniline
under the same experimental conditions.
NMR Spectroscopy
To complete this study, we have also checked the influ-
ence of homoconjugation in DPNs and FDPNs by NMR
spectroscopy. The chemical shifts of the most significant
protons and carbon atoms of the compounds studied are
listed in Table 5. These data show that the effect of a certain
group in one of the aryl rings is transferred to the adjacent
ring by means of homoconjugation. In Figure 15, the varia-
Herein we have computed the total first hyperpolarizabil-
ity (βtot) values of different nitro-substituted DPNs and
FDPNs (Table 4). As expected, the computed βtot values are
generally higher in DPNs than in their FDPNs counter-
parts. This is mainly due to the effect of the fluorine atom
at the ortho position, which slightly modifies the cofacial
orientation, leading to a less effective homoconjugation.
Interestingly, push-pull systems exhibit higher βtot values
than compounds possessing an electron-withdrawing group
at the aryl group adjacent to the p-NO2-aryl fragment.
Moreover, the βtot computed for the NH2 systems is com-
parable to the βtot value obtained for truly π-conjugated
push-pull systems,[42] thus indicating that homoconjugation
can be indeed as effective in communicating the donor and
acceptor moieties in our DPNs (or FDPNs) as π conjuga-
tion. Not surprisingly, nice linear relationships were ob-
tained when plotting the computed βtot values vs. the corre-
sponding Hammett substituent constant σps (Figure 14,
correlation coefficient r2, of –0.995 and –0.986 for DPNs
and FDPNs, respectively) as a consequence of the higher
homoconjugation occurring with better π-donor groups.
Table 5. Selected 1H NMR and 13CNMR spectroscopic data (δ,
ppm, CDCl3) of DPNs and FDPNs.
δH15
δC7
δC8
δC11
δC12
δC15
5a
5b
5c
5d
5e
5f
7.04
7.06
7.07
7.09
7.07
7.09
7.09
7.09
7.11
7.12
–
–
–
–
–
–
–
7.09
7.10
7.12
7.12
7.15
63.95
64.04
64.79
64.38
64.44
65.16
64.85
65.08
64.91
65.04
61.37
62.34
62.22
61.68
61.76
62.31
62.31
61.40
61.51
61.84
61.93
62.64
–
–
–
–
–
–
–
–
146.63
146.37
145.97
145.45
145.34
144.87
144.94
144.86
144.96
144.09
–
125.01
125.18
125.29
125.57
125.58
125.77
125.75
125.75
125.79
126.07
–
–
–
–
–
–
–
–
–
5g
5h
5i
Table 4. Computed βtot (B3LYP/def2-SVP//M06-2x/def2-SVP level)
for different DPNs and FDPNs.
–
–
5j
–
7a
7b
7c
7d
7e
7f
133.04
132.69
132.23
131.92
131.90
131.36
130.68
–
–
–
–
–
127.15
127.14
127.47
127.78
127.80
127.97
128.40
–
–
–
–
–
–
–
144.26
–
–
–
–
145.08
144.74
144.58
143.64
142.60
125.58
–
–
–
–
125.23
125.45
125.49
125.87
126.41
R
βtot /10–30 esu
βtot /10–30 esu
7g
7h
7i
7j
7k
7l
NH2
OCH3
Br
29.85
23.77
15.20
9.67
23.70
19.50
12.67
9.24
CN
NO2
9.37
9.84
2650
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 2643–2655

Homoconjugated Push-Pull Chromophores
Figure 15. Correlation between NMR chemical shifts (graph A, C-12; graph B, C-15; graph C, C-7; graph D, H-15) and σp values in
monosubstituted DPNs 5a–j.
tion of the chemical shifts of C-7, C-12, C-15 and H-15 their corresponding σp value). TD-DFT calculations assign
with the σp value of the respective group X in monosubsti- this homoconjugative bands to transitions involving molec-
tuted DPNs 5a–j are shown. Similar graphs are obtained ular orbitals which are delocalized on both aryl moieties.
for FDPNs (see Supporting Information). Although the On the other hand, the position of the bands of the chro-
variations caused by the substituents are, in some cases, not mophores placed in one of the aryl rings is influenced by
quite significant (e.g. the variations in the chemical shifts in the substituents attached at the para position of the cofa-
H-15), from the large number of compounds studied some cially arranged (homoconjugated) aromatic ring. These re-
clear trends can be envisaged. First of all, the most sensitive sults are a clear indication of the importance of transannu-
atom to the influence of groups X is the ipso carbon atom lar homoconjugative interactions in the compounds studied
placed on the adjacent homoconjugated ring (C-12, corre- in this work. Moreover, push-pull systems show intense in-
lation coefficient of –0.951). The chemical shifts increments tramolecular CT bands which are favoured when the sub-
in C-12 are higher and show a better linear correlation than stituents are placed at the para positions of the aromatic
that observed for the C-7 carbon atom of the norbornane rings. Substitution at the meta position diminishes the
structure (r2 = 0.874). This fact confirms that the effects are homoconjugative interaction. Finally, NMR spectra show
transmitted through homoconjugative interactions between that the transannular interactions are transmitted by homo-
the aryl rings and not through bonds via C-7. This phenom- conjugation between the aromatic rings and not through
enon is similar to the transannular π-electronic effect de- the C-7 carbon atom of the norbornane framework.
scribed in cyclophanes.[34–36] The effect of substitution is
In summary, our joint experimental–computational
less pronounced in C-15 and H-15, although there is a good study shows that homoconjugative interactions constitute
correlation with σp in both cases (r2 = 0.983 and 0.941, indeed an effective way to provoke electronic communica-
respectively).
tion which can be easily tuned by controlling the nature and
position of the substituents. Thus, the proper selection of
the substituents may lead to new organic materials with re-
markable optical properties.
Conclusions
We have synthesized a large family of aromatic homo-
conjugated compounds with substituents at the para and
meta positions of the aryl rings, in order to carry out the
first systematic study of the interactions between the aro-
matic moieties in this type of chromophores. The homocon-
jugative interactions in these compounds are clearly demon-
strated by the absorption and NMR spectra, as well as by
their reactivity. The UV/Vis spectra show new homoconju-
gative bands whose wavelength maxima strongly depends
Experimental Section
See the Supporting Information for experimental details.
1
Compound 5a: Yield: 95%. H NMR (300 MHz, CDCl3): δ = 7.38
(d, J = 9.0 Hz, 2 H), 7.26–7.15 (m, 4 H), 7.04 (t, J = 9.0 Hz, 1 H),
6.57 (d, J = 9.0 Hz, 2 H), 3.23 (br. s, 2 H), 3.05–2.95 (m, 2 H),
1.80–1.65 (m, 4 H), 1.40–1.20 (m, 4 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 146.6, 143.5, 136.4, 128.2, 128.0, 127.0, 125.0, 115.2,
on the electronic nature of the substituents (measured by 64.0, 41.7, 28.5, 28.4 ppm. MS (EI, 70 eV): m/z (%) = 263 (100)
Eur. J. Org. Chem. 2012, 2643–2655
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2651

I. Fernández, J. Osío Barcina et al.
[M+], 186 (24), 182 (37), 130 (15), 115 (25), 106 (25), 91 (19). 2 H), 7.22 (t, J = 7.0 Hz, 2 H), 7.11 (t, J = 7.5 Hz, 1 H), 3.12–3.00
FULL PAPER
C19H21N (263.38): calcd. C 86.64, H 8.04, N 5.32; found C 86.48,
H 8.22, N 5.28.
(m, 2 H), 1.70–1.50 (m, 4 H), 1.42–1.28 (m, 4 H) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 150.1 (q, J = 1.4 Hz), 145.0, 128.5, 127.6,
127.5 (q, J = 47.0 Hz), 127.3, 125.8, 125.3 (q, J = 3.9 Hz), 124.0
(q, J = 272.0 Hz), 64.9, 41.7, 28.3, 28.2 ppm. MS (EI, 70 eV): m/z
(%) = 316 (100) [M+], 274 (21), 273 (22), 271 (18), 248 (31), 247
(51), 235 (20), 183 (17), 179 (16), 165 (16), 115 (28), 91 (34), 81
(15). C20H19F3 (316.36): calcd. C 75.91, H 6.06; found C 76.08, H
6.15.
1
Compound 5b: Yield: 88%. H NMR (300 MHz, CDCl3): δ = 7.39
(d, J = 7.2 Hz, 2 H), 7.32 (d, J = 8.7 Hz, 2 H), 7.20 (t, J = 7.2 Hz,
2 H), 7.06 (t, J = 7.2 Hz, 1 H), 6.75 (d, J = 9.0 Hz, 2 H), 3.71 (s,
3 H), 3.10–3.95 (m, 2 H), 1.70–1.60 (m, 4 H), 1.35–1.25 (m, 4 H)
ppm. 13C NMR (CDCl3, 75 MHz): δ = 157.1, 146.4, 138.3, 128.2,
127.1, 125.2, 113.7, 64.0, 55.1, 41.8, 28.5, 28.4 ppm. MS (EI,
70 eV): m/z (%) = 278 (100) [M+], 277 (23), 209 (22), 197 (45), 121
(24), 115 (29), 91 (34). C20H22O (278.39): calcd. C 86.28, H 7.97;
found C 86.05, H 7.81.
Compound 5d: Yield: 60%. 1H NMR (300 MHz, CDCl3): δ = 7.50–
7.30 (m, 4 H), 7.28–7.15 (m, 4 H), 7.09 (t, J = 7.6 Hz, 1 H), 3.10–
3.00 (m, 2 H), 1.80–1.50 (m, 4 H), 1.50–1.20 (m, 4 H) ppm. 13C
NMR (CDCl3, 75 MHz): δ = 145.4, 144.6, 130.9, 128.7, 128.4,
128.3, 127.1, 125.6, 64.4, 41.7, 28.4, 28.3 ppm. MS (EI, 70 eV): m/z
(%) = 284 (140) [M+ + 2], 282 (100) [M+], 247 (100), 205 (55), 203
(30), 201 (40), 189 (59), 179 (30), 165 (43), 125 (46), 115 (40), 109
(65), 91 (45), 67 (36), 55 (28). C19H19Cl (282.81): calcd. C 80.68, H
6.78; found C 80.93, H 6.87.
1
Compound 5j: Yield: 87%. H NMR (300 MHz, CDCl3): δ = 8.08
(d, J = 9.0 Hz, 2 H), 7.58 (d, J = 9.0 Hz, 2 H), 7.40 (d, J = 7.8 Hz,
2 H), 7.24 (t, J = 7.8 Hz, 2 H), 7.12 (t, J = 7.8 Hz, 1 H), 3.15–3.05
(m, 2 H), 1.72–1.62 (m, 2 H), 1.60–1.50 (m, 2 H), 1.45–1.30 (m, 4
H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 153.8, 145.8, 144.1,
128.6, 128.0, 127.3, 126.1, 123.8, 65.0, 41.8, 28.2, 28.1 ppm. MS
(EI, 70 eV): m/z (%) = 293 (94) [M+], 277 (22), 276 (41), 264 (29),
263 (100), 262 (37), 251 (33), 225 (41), 208 (25), 204 (35), 203 (30),
202 (34), 192 (65), 191 (63), 190 (29), 189 (38), 186 (29), 182 (40),
179 (27), 178 (54), 166 (30), 165 (71), 152 (28), 141 (27), 129 (39),
128 (43), 115 (89), 107 (27), 106 (30), 91 (98), 81 (38), 77 (39), 51
(30). C19H19NO2 (293.36): calcd. C 77.78, H 6.53, N 4.78; found C
77.81, H 6.66, N 4.69.
1
Compound 5e: Yield: 25%. H NMR (300 MHz, CDCl3): δ = 7.38
1
(d, J = 7.3 Hz, 2 H), 7.35–7.25 (m, 4 H), 7.21 (t, J = 7.8 Hz, 2 H),
7.07 (t, J = 7.3 Hz, 1 H), 3.10–2.95 (m, 2 H), 1.72–1.52 (m, 4 H),
1.45–1.25 (m, 4 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 145.3,
145.1, 131.4, 129.1, 128.4, 127.1, 125.6, 119.1, 64.4, 41.7, 28.4,
28.3 ppm. MS (EI, 70 eV): m/z (%) = 328 (31) [M+ + 2], 326 (31)
[M+], 247 (71), 205 (35), 204 (27), 193 (31), 192 (80), 191 (55), 189
(25), 179 (35), 178 (35), 169 (37), 166 (27), 165 (58), 143 (30), 141
(26), 129 (45), 128 (28), 117 (40), 115 (49), 101 (29), 95 (28), 91
(100), 77 (22), 51 (19), 41 (29). C19H19Br (327.26): calcd. C 69.71,
H 5.85; found C 69.66, H 5.79.
Compound 6a: Yield: 25%. H NMR (300 MHz, CDCl3): δ = 7.24
(d, J = 9.9 Hz, 4 H), 6.60 (d, J = 9.9 Hz, 4 H), 3.00–2.90 (m, 2 H),
2.84 (s, 12 H), 1.70–1.60 (m, 4 H), 1.32–1.22 (m, 4 H) ppm. 13C
NMR (CDCl3, 75 MHz): δ = 148.0, 135.3, 127.6, 112.7, 62.8, 41.7,
40.7, 28.7 ppm. MS (EI, 70 eV): m/z (%) = 334 (100) [M+], 333
(49), 290 (33), 253 (33), 213 (33), 167 (31), 146 (21), 139 (33), 138
(35), 134 (74), 131 (59), 126 (42), 118 (31), 117 (32), 44 (19), 42
(26). C23H30N2 (334.50): calcd. C 82.58, H 9.05, N 8.38; found C
82.71, H 9.20, N 8.27.
1
Compound 6b: Yield: 97%. H NMR (300 MHz, CDCl3): δ = 7.16
1
Compound 5f: Yield: 80%. H NMR (300 MHz, CDCl3): δ = 7.95
(d, J = 8.7 Hz, 4 H), 6.54 (d, J = 8.4 Hz, 4 H), 3.39 (br. s, 4 H),
2.98–2.90 (m, 2 H), 1.72–1.58 (m, 4 H), 1.80–1.40 (m, 4 H) ppm.
13C NMR (CDCl3, 75 MHz): δ = 143.3, 137.1, 127.8, 115.2, 63.1,
41.7, 28.5 ppm. MS (EI, 70 eV): m/z (%) = 278 (100) [M+], 277
(42), 197 (36), 185 (27), 144 (20), 130 (32), 106 (64), 91 (6), 77 (13).
C19H22N2 (278.40): calcd. C 81.96, H 7.97, N 10.07; found C 82.12,
H 7.73, N 10.18.
(d, J = 8.4 Hz, 2 H), 7.53 (d, J = 8.7 Hz, 2 H), 7.42 (d, J = 7.2 Hz,
2 H), 7.23 (t, J = 7.2 Hz, 2 H), 7.09 (t, J = 7.5 Hz, 1 H), 3.16–3.06
(m, 2 H), 1.72–1.52 (m, 4 H), 1.40–1.20 (m, 4 H) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 172.0, 152.4, 144.9, 130.4, 128.5, 127.4,
127.3, 126.2, 125.8, 65.2, 41.7, 28.2 ppm. MS (EI, 70 eV): m/z (%)
= 292 (64) [M+], 248 (22), 247 (100), 211 (28), 205 (39), 193 (21),
191 (26), 179 (42), 178 (35), 165 (48), 143 (20), 129 (42), 128 (28),
117 (27), 115 (89), 91 (96), 81 (23), 77 (30), 44 (41), 41 (38).
C20H20O2 (292.38): calcd. C 82.15, H 6.90; found C 82.28, H 6.85.
1
Compound 6c: Yield: 85%. H NMR (300 MHz, CDCl3): δ = 7.29
(d, J = 6.7 Hz, 4 H), 6.74 (d, J = 6.7 Hz, 4 H), 3.70 (s, 6 H), 3.02–
2.95 (m, 2 H), 1.70–1.55 (m, 4 H), 1.35–1.20 (m,4 H) ppm. 13C
NMR (CDCl3, 75 MHz): δ = 157.0, 138.7, 128.0, 113.6, 63.3, 55.4,
41.9, 28.5 ppm. MS (EI, 70 eV): m/z (%) = 308 (80) [M+], 277 (55),
227 (50), 200 (23), 159 (23), 145 (30), 121 (100), 91 (25). C21H24O2
(308.42): calcd. C 81.77, H 7.85; found C 81.88, H 7.97.
1
Compound 5g: Yield: 72%. H NMR (300 MHz, CDCl3): δ = 7.89
(d, J = 8.7 Hz, 2 H), 7.51 (d, J = 8.7 Hz, 2 H), 7.42 (d, J = 8.7 Hz,
2 H), 7.23 (t, J = 8.7 Hz, 2 H), 7.09 (t, J = 8.7 Hz, 1 H), 4.33 (q,
J = 7.2 Hz, 2 H), 3.15–3.05 (m, 2 H), 1.72–1.52 (m, 4 H), 1.40–
1.20 (m, 7 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 167.2, 152.0,
144.9, 129.7, 128.4, 127.4, 127.3, 127.3, 125.7, 64.9, 60.8, 41.6, 28.3,
14.3 ppm. MS (EI, 70 eV): m/z (%) = 320 (30) [M+], 248 (21), 247
(100), 205 (32), 191 (28), 179 (20), 178 (24), 165 (36), 143 (22), 129
(33), 117 (35), 115 (51), 91 (77), 77 (15), 41 (19). C22H24O2 (320.43):
calcd. C 82.45, H 7.55; found C 82.42, H 7.67.
1
Compound 6e: Yield: 90%. H NMR (300 MHz, [D6]DMSO): δ =
12.80 (br. s, 2 H), 7.79 (d, J = 8.7 Hz, 4 H), 7.64 (d, J = 8.7 Hz, 4
H), 3.30–3.24 (m, 2 H), 1.58–1.40 (m, 4 H), 1.40–1.20 (m, 4 H)
ppm. 13C NMR (75 MHz, [D6]DMSO): δ = 172.1, 151.8, 130.8,
129.5, 128.8, 66.5, 42.7, 29.0 ppm. MS (EI, 70 eV): m/z (%) = 336
(17) [M+], 292 (26), 291 (100), 205 (25), 191 (19), 189 (18), 179 (24),
178 (26), 165 (29), 143 (20), 135 (25), 129 (36), 128 (20), 117 (26),
115 (60), 91 (51), 81 (46), 77 (24), 44 (72), 41 (31). C21H20O4
(336.39): calcd. C 74.97, H 6.00; found C 74.82, H 6.13.
1
Compound 5h: Yield: 80%. H NMR (300 MHz, CDCl3): δ = 7.81
(d, J = 8.0 Hz, 2 H), 7.51 (d, J = 8.0 Hz, 2 H), 7.41 (d, J = 8.0 Hz,
2 H), 7.21 (t, J = 7.3 Hz, 2 H), 7.09 (t, J = 7.8 Hz, 1 H), 3.15–3.05
(m, 2 H), 2.51 (s, 3 H), 1.72–1.52 (m, 4 H), 1.45–1.20 (m, 4 H)
ppm. 13C NMR (CDCl3, 75 MHz): δ = 197.8, 151.8, 144.9, 134.5,
128.6, 128.5, 127.5, 127.3, 125.8, 65.1, 41.6, 28.3, 26.5 ppm. MS
(EI, 70 eV): m/z (%) = 290 (14) [M+], 91 (11), 43 (100). C21H22O
(290.40): calcd. C 86.85, H 7.64; found C 87.04, H 7.57.
1
Compound 6f: Yield: 72%. H NMR (300 MHz, CDCl3): δ = 7.90
(d, J = 8.7 Hz, 4 H), 7.48 (d, J = 8.7 Hz, 4 H), 4.33 (q, J = 7.2 Hz,
4 H), 3.15–3.05 (m, 2 H), 1.70–1.55 (m, 4 H), 1.42–1.26 (m, 10 H)
ppm. 13C NMR (CDCl3, 75 MHz): δ = 166.4, 150.3, 129.8, 128.0,
127.3, 65.3, 60.7, 41.7, 28.2, 14.3 ppm. MS (EI, 70 eV): m/z (%) =
392 (11) [M+], 347 (18), 320 (24), 319 (100), 205 (17), 191 (19), 165
1
Compound 5i: Yield: 82%. H NMR (300 MHz, CDCl3): δ = 7.53
(d, J = 9.0 Hz, 2 H), 7.45 (d, J = 9.0 Hz, 2 H), 7.40 (d, J = 8.4 Hz,
2652
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 2643–2655

Homoconjugated Push-Pull Chromophores
(25), 143 (24), 129 (30), 117 (31), 115 (30), 91 (28), 77 (10), 41 (16). = 13.6 Hz), 130.8 (d, J = 6.8 Hz), 128.3, 127.5, 127.5, 127.3 (d, J
C25H28O4 (392.49): calcd. C 76.49, H 7.19; found C 76.57, H 7.25.
= 3.2 Hz), 125.9, 119.8 (d, J = 27.9 Hz), 119.5 (d, J = 10.0 Hz),
61.9 (d, J = 3.1 Hz), 42.5, 41.1 (d, J = 8.4 Hz), 28.8, 28.4, 28.0,
27.2 ppm. MS (EI, 70 eV): m/z (%) = 346 (29) [M+ + 2], 344 (37)
[M+], 278 (23), 276 (24), 265 (59), 263 (34), 223 (23), 222 (27), 211
(30), 210 (84), 209 (62), 207 (20), 197 (47), 196 (41), 189 (58), 187
(57), 183 (57), 170 (19), 157 (21), 144 (21), 133 (24), 129 (33), 116
(36), 115 (48), 107 (24), 104 (34), 94 (28), 91 (100), 81 (42), 79 (26),
77 (24), 65 (23), 51 (27), 41 (43). C19H18BrF (345.25): calcd. C
66.08, H 5.26; found C 65.89, H 5.15.
1
Compound 6g: Yield: 85%. H NMR (300 MHz, CDCl3): δ = 7.83
(d, J = 8.4 Hz, 4 H), 7.51 (d, J = 8.4 Hz, 4 H), 3.18–3.08 (m, 2 H),
2.51 (s, 6 H), 1.69–1.58 (m, 4 H), 1.45–1.30 (m, 4 H) ppm. 13C
NMR (CDCl3, 75 MHz): δ = 197.6, 150.5, 134.8, 128.7, 127.6, 65.3,
41.7, 28.2, 26.5 ppm. MS (EI, 70 eV): m/z (%) = 332 (10) [M+], 289
(8), 151 (8), 43 (100). C23H24O2 (332.44): calcd. C 83.09, H 7.28;
found C 82.92, H 7.33.
1
Compound 6h: Yield: 94%. H NMR (300 MHz, CDCl3): δ = 8.12
1
Compound 7v: Yield: 74%. H NMR (300 MHz, CDCl3): δ = 8.08
(d, J = 9.0 Hz, 4 H), 7.58 (d, J = 9.0 Hz, 4 H), 3.18–3.10 (m, 2 H),
1.65–1.55 (m, 4 H), 1.50–1.40 (m, 4 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 151.7, 146.0, 128.1, 124.0, 65.4, 41.9, 28.0 ppm. MS
(EI, 70 eV): m/z (%) = 338 (14) [M+], 308 (37), 279 (36), 278 (100),
277 (41), 197 (37), 189 (24), 186 (30), 185 (28), 149 (28), 144 (24),
130 (33), 106 (69). C19H18N2O4 (338.36): calcd. C 67.43, H 5.36, N
8.28; found C 67.48, H 5.44, N 8.32.
(d, J = 9.0 Hz, 2 H), 7.58 (dd, J = 9.0, 1.5 Hz, 2 H), 7.19 (t, J =
8.6 Hz, 1 H), 6.37 (dd, J = 8.6, 2.4 Hz, 1 H), 6.22 (dd, J = 13.5,
2.4 Hz, 1 H), 3.64 (br. s, 2 H), 3.34 (dt, J = 3.6, 3.6 Hz, 1 H), 3.07–
2.95 (m, 1 H), 1.93–1.07 (m, 8 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 161.5 (d, J = 245.4 Hz), 152.9, 146.8 (d, J = 11.5 Hz),
145.7, 130.0 (d, J = 7.45 Hz), 128.3, 128.2, 123.5, 120.4 (d, J =
14.4 Hz), 111.1 (d, J = 2.3 Hz), 102.8 (d, J = 27.3 Hz), 61.6 (d, J
= 2.7 Hz), 42.6, 41.4 (d, J = 8.2 Hz), 28.8, 28.3, 28.1, 27.2 ppm.
MS (EI, 70 eV): m/z (%) = 326 (100) [M+], 309 (28), 271 (17), 258
(18), 225 (22), 224 (19), 124 (25), 111 (17), 57 (17). C19H19FN2O2
(326.37): calcd. C 69.91, H 5.87, N 8.59; found C 69.83, H 5.97, N
8.63.
Compound 7d: Yield: 63%. 1H NMR (300 MHz, CDCl3): δ = 7.50–
7.35 (m, 3 H), 7.20 (d, J = 8.5 Hz, 2 H), 7.13–6.97 (m, 2 H), 6.88
(ddd, J = 12.0, 8.0, 1.4 Hz, 1 H), 3.35 (dt, J = 4.3, 4.3 Hz), 3.10–
2.95 (m, 1 H), 1.84–1.65 (m, 2 H), 1.55–1.20 (m, 6 H) ppm. 13C
NMR (CDCl3, 75 MHz): δ = 161.7 (d, J = 246.7 Hz), 142.8, 131.9
(d, J = 13.6 Hz), 131.3, 129.4 (d, J = 5.6 Hz), 129.1, 129.1, 128.3,
127.8 (d, J = 8.8 Hz), 124.1 (d, J = 3.2 Hz), 116.3 (d, J = 23.9 Hz),
61.7 (d, J = 2.5 Hz), 42.5, 41.3 (d, J = 8.1 Hz), 28.9, 28.3, 28.1,
27.2 ppm. MS (EI, 70 eV): m/z (%) = 302 (14) [M+ + 2], 300 (46)
[M+], 282 (35), 265 (51), 247 (36), 232 (47), 223 (49), 221 (28), 219
(52), 210 (30), 209 (27), 203 (27), 201 (28), 197 (25), 191 (25), 183
(44), 165 (36), 149 (38), 143 (28), 133 (33), 129 (41), 127 (34), 125
(59), 117 (37), 115 (57), 108 (100), 101 (37), 91 (52), 81 (35), 41
(35). C19H18ClF (300.80): calcd. C 75.85, H 6.03; found C 75.69,
H 6.12.
1
Compound 8: Yield: 60%. H NMR (300 MHz, CDCl3): δ = 8.42
(dd, J = 6.6, 2.9 Hz, 1 H), 8.14 (d, J = 9.1 Hz, 2 H), 8.07 (ddd, J
= 9.0, 4.2, 2.9 Hz, 1 H), 7.65 (dd, J = 9.1, 1.5 Hz, 2 H), 7.08 (dd,
J = 9.1, 9.0 Hz, 1 H), 3.51–3.38 (m, 1 H), 3.29–3.17 (m, 1 H), 1.90–
1.62 (m, 2 H), 1.60–1.31 (m, 6 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 164.4 (d, J = 258.5 Hz), 150.1, 146.4, 143.0 (d, J =
2.9 Hz), 132.8 (d, J = 16.0 Hz), 128.7, 128.7, 125.6 (d, J = 7.5 Hz),
124.4 (d, J = 10.8 Hz), 123.9, 117.5 (d, J = 29.5 Hz), 62.4 (d, J =
2.7 Hz), 43.0, 41.3 (d, J = 7.5 Hz), 28.6, 28.1, 27.8, 27.0 ppm. MS
(EI, 70 eV): m/z (%) = 356 (100) [M+], 339 (59), 297 (46), 267 (34),
207 (34), 81 (54), 67 (36). C19H17FN2O4 (356.35): calcd. C 64.02,
H 4.81, N 7.86; found C 64.21, H 4.69, N 7.73.
Compound 10b: Yield: 95%. 1H NMR (300 MHz, CDCl3): δ = 7.24
(d, J = 6.6, Hz, 2 H), 6.75 (d, J = 6.6, Hz, 2 H), 6.60 (d, J = 2.3 Hz,
1 H), 6.47 (d, J = 8.0 Hz, 1 H), 6.40 (dd, J = 8.0, 2.3 Hz, 1 H),
3.82–3.13 (m, 4 H), 3.06–2.89 (m, 1 H), 2.07–1.77 (m, 6 H), 1.77–
1.43 (m, 2 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 145.3, 144.5,
144.4, 137.2, 135.3, 128.6, 124.4, 115.0, 112.1, 111.1, 41.4, 35.2,
32.6, 27.3 ppm. MS (EI, 70 eV): m/z (%) = 264 (99) [M+], 263 (13),
236 (90), 235 (100), 221 (37), 218 (20), 149 (26), 106 (19), 69 (29),
57 (8). C18H20N2 (264.37): calcd. C 81.77, H 7.63, N 10.60; found
C 81.60, H 7.79, N 10.58.
Compound 10c: Yield: 25%. 1H NMR (300 MHz, CDCl3): δ = 8.33
(d, J = 7.0 Hz, 2 H), 8.11 (d, J = 2.4 Hz, 1 H), 7.96 (dd, J = 8.4,
2.4 Hz, 1 H), 7.61 (d, J = 7.0 Hz, 2 H), 6.71 (d, J = 8.4 Hz, 1 H),
3.35–3.29 (m, 1 H), 2.14–2.0 (m, 4 H), 2.0–1.88 (m, 2 H), 1.73–1.59
(m, 2 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 152.1, 151.1,
147.0, 146.7, 145.4, 128.8, 124.0, 123.8, 121.4, 119.1, 44.1, 35.1,
31.8, 26.4 ppm. MS (EI, 70 eV): m/z (%) = 324 (100) [M+], 296
(56), 295 (86), 279 (26), 250 (38), 249 (95), 204 (34), 203 (67), 202
(94), 189 (29), 136 (17), 101 (14), 77 (25). C18H16N2O4 (324.34):
calcd. C 73.94, H 5.52, N 9.59; found C 74.12, H 5.71, N 9.82.
1
Compound 7e: Yield: 62%. H NMR (300 MHz, CDCl3): δ = 7.46
(td, J = 7.4 Hz, 1 H), 7.35 (s, 4 H), 7.15–7.00 (m, 2 H), 6.88 (ddd,
J = 12.1, 8.1, 1.5 Hz, 1 H), 3.41–3.32 (m, 1 H), 3.08–3.00 (m, 1 H),
1.84–1.65 (m, 2 H), 1.55–1.20 (m, 6 H) ppm. 13C NMR (CDCl3,
75 MHz): δ = 161.7 (d, J = 246.7 Hz), 143.3, 131.9 (d, J = 13.6 Hz),
131.2, 129.5, 129.5, 129.4 (d, J = 5.6 Hz), 127.8 (d, J = 8.7 Hz),
124.1 (d, J = 3.2 Hz), 119.4, 116.3 (d, J = 23.9 Hz), 61.8 (d, J =
2.5 Hz), 42.5, 41.3 (d, J = 8.1 Hz), 28.9, 28.3, 28.1, 27.2 ppm. MS
(EI, 70 eV): m/z (%) = 346 (33) [M+ + 2], 344 (35) [M+], 278 (30),
276 (30), 265 (65), 263 (39), 223 (58), 210 (87), 196 (37), 183 (60),
169 (38), 161 (16), 143 (41), 135 (46), 115 (43), 109 (100), 91 (30),
81 (48), 67 (25), 41 (50). C19H18BrF (345.25): calcd. C 66.08, H
5.26; found C 66.14, H 5.16.
1
Compound 7f: Yield: 75%. H NMR (300 MHz, CDCl3): δ = 7.83
(d, J = 8.5 Hz, 2 H), 7.57 (d, J = 8.2 Hz, 2 H), 7.49 (td, J = 7.6,
2.0 Hz, 1 H), 7.15–6.95 (m, 2 H), 6.88 (ddd, J = 12.0, 7.9, 1.4 Hz,
1 H), 3.40 (dt, J = 4.3, 4.3 Hz, 1 H), 3.12–3.05 (m, 1 H), 2.50 (s, 3
H), 1.82–1.20 (m, 8 H) ppm. 13C NMR (CDCl3, 75 MHz): δ =
197.8, 160.8 (d, J = 246.9 Hz), 149.9, 134.7, 131.4 (d, J = 13.5 Hz),
129.5 (d, J = 5.4 Hz), 128.4, 128.0 (d, J = 8.7 Hz), 127.9, 128.0,
124.2 (d, J = 3.2 Hz), 116.3 (d, J = 23.9 Hz), 62.3 (d, J = 2.6 Hz),
42.5, 41.2 (d, J = 8.2 Hz), 28.8, 28.3, 28.1, 27.2, 26.5 ppm. MS (EI,
70 eV): m/z (%) = 308(14) [M+], 225 (9), 43 (100). C21H21FO
(308.39): calcd. C 81.78, H 6.87; found C 81.94, H 6.68.
1
Compound 11: Yield: 31%. H NMR (300 MHz, CDCl3): δ = 8.08
(d, J = 9.0 Hz, 2 H), 8.14 (dd, J = 9.0, 1.5 Hz, 2 H), 6.79–6.63 (m,
2 H), 6.42 (ddd, J = 8.5, 3.9, 2.9 Hz, 1 H), 3.43–3.34 (m, 3 H),
3.04–2.96 (m, 1 H), 1.95–1.77 (m, 1 H), 1.70–1.52 (m, 2 H), 1.47–
1.35 (m, 5 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 154.3 (d, J
= 237.5 Hz), 152.1, 145.9, 142.6 (d, J = 2.0 Hz), 131.1 (d, J =
14.7 Hz), 128.6, 128.6, 123.5, 116.9 (d, J = 25.5 Hz), 115.5 (d, J =
1
Compound 7k: Yield 87%. H NMR (300 MHz, CDCl3): δ = 7.44
(d, J = 8.1 Hz, 2 H), 7.37 (t, J = 8.46 Hz, 1 H), 7.12 (t, J = 8.09 Hz,
2 H), 7.20–7.04 (m, 3 H), 3.39 (dt, J = 4.1, 4.1 Hz, 1 H), 3.08–3.00
(m, 1 H), 1.82–1.65 (m, 2 H), 1.60–1.20 (m, 6 H) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 160.6 (d, J = 251.5 Hz), 143.6, 131.9 (d, J
Eur. J. Org. Chem. 2012, 2643–2655
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2653

I. Fernández, J. Osío Barcina et al.
FULL PAPER
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4.9 Hz), 114.8 (d, J = 8.5 Hz), 62.4 (d, J = 2.8 Hz), 42.6, 41.4 (d,
J = 8.4 Hz), 28.9, 28.3, 28.2, 27.2 ppm. MS (EI, 70 eV): m/z (%)
= 326 (100) [M+], 283 (15), 258 (17), 138 (27), 124 (14), 81 (10).
C19H19FN2O2 (326.37): calcd. C 69.91, H 5.87, N 8.59; found C
69.86, H 5.99, N 8.45.
[3]
[4]
1
Compound 12: Yield: 30%. H NMR (300 MHz, CDCl3): δ = 8.37
(dd, J = 6.6, 2.9 Hz, 1 H), 7.97 (ddd, J = 9.0, 4.1, 2.9 Hz, 1 H),
7.23 (dd, J = 8.6, 1.5 Hz, 2 H), 7.01 (dd, J = 9.0, 8.5 Hz, 1 H), 6.57
(d, J = 8.6 Hz, 2 H), 3.65–3.48 (br. s, 2 H), 3.37–3.27 (m, 1 H),
3.09 (t, J = 3.8 Hz, 1 H), 1.86–1.61 (m, 2 H), 1.61–1.18 (m, 6 H)
ppm. 13C NMR (CDCl3, 75 MHz): δ = 164.4 (d, J = 258.3 Hz),
144.6, 144.2 (d, J = 2.5 Hz), 135.1 (d, J = 16.1 Hz), 132.8, 128.6,
128.5, 125.5 (d, J = 8.2 Hz), 123.2 (d, J = 10.8 Hz), 117.2 (d, J =
27.0 Hz), 115.1, 61.6 (d, J = 3.0 Hz), 42.8, 41.2 (d, J = 8.2 Hz),
28.8, 28.5, 28.0, 27.2 ppm. MS (EI, 70 eV): m/z (%) = 326 (100)
[M+], 271 (20), 245 (35), 225 (15), 106 (12), 93 (11). C19H19FN2O2
(326.37): calcd. C 69.91, H 5.87, N 8.59; found C 70.12, H 5.76, N
8.71.
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1
Compound 15: Yield: 65%. H NMR (300 MHz, CDCl3): δ = 7.75
(br. s, 1 H), 7.56–7.40 (m, 3 H), 7.35–7.05 (m, 5 H), 3.40 (dt, J =
3.9, 3.9 Hz, 1 H), 3.05 (t, J = 3.2 Hz, 1 H), 1.85–1.61 (m, 2 H),
1.61–1.20 (m, 6 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 160.6
(d, J = 248.1 Hz), 154.6 (d, J = 37.6 Hz), 143.8, 134.1 (d, J =
11.2 Hz), 130.9 (d, J = 14.1 Hz), 130.3 (d, J = 7.0 Hz), 128.3, 128.3,
127.6, 127.5, 125.9, 115.8 (d, J = 3.2 Hz), 115.6 (q, J = 288.8 Hz),
108.9 (d, J = 29.7 Hz), 62.0 (d, J = 2.9 Hz), 42.6, 41.2 (d, J =
8.0 Hz), 28.9, 28.5, 28.1, 27.3 ppm. MS (EI, 70 eV): m/z (%) = 378,
(24) [M+ + H] 377 (100) [M+], 335 (26), 309 (36), 308 (19), 296
(40), 220 (27), 115 (17), 91 (29), 84 (28), 51 (22), 49 (55).
C21H19F4NO (377.38): calcd. C 66.82, H 5.08, N 3.71; found C
66.89, H 5.19, N 3.64.
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[10]
[11]
Compound 16: Yield: 77%. H NMR (300 MHz, CDCl3): δ = 8.10
(d, J = 9.0 Hz, 2 H), 7.98 (br. s, 1 H), 7.61 (dd, J = 9.0, 1.5 Hz, 2
H), 7.55–7.43 (m, 1 H), 7.36 (dd, J = 12.9, 2.2 Hz, 1 H), 7.20 (dd,
J = 8.4, 2.2 Hz, 1 H), 3.47–3.34 (m, 1 H), 3.14–3.02 (m, 1 H), 1.90–
1.15 (m, 8 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 160.7 (d, J
= 248.3 Hz), 154.7 (d, J = 37.6 Hz), 151.5, 146.1, 135.1 (d, J =
11.5 Hz), 130.1 (d, J = 6.6 Hz), 129.0 (d, J = 14.1 Hz), 128.5, 128.5,
123.7, 116.2 (d, J = 3.2 Hz), 115.5 (q, J = 288.8 Hz), 109.1 (d, J =
29.6 Hz), 62.2 (d, J = 2.8 Hz), 42.7, 41.3 (d, J = 7.6 Hz), 28.8, 28.2,
28.0, 27.1 ppm. MS (EI, 70 eV): m/z (%) = 423 (24) [M+ + H], 422
(100) [M+], 405 (53), 392 (32), 363 (27), 354 (73), 333 (21), 321 (33),
220 (28), 91 (17), 81 (41), 57 (27), 55 (30). C21H18F4N2O3 (422.38):
calcd. C 59.70, H 4.30, N 6.63; found C 59.58, H 4.49, N 6.51.
[12]
[13]
[14]
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, UV/Vis spectra, NMR correlations,
molecular orbitals, and Cartesian coordinates of all species dis-
cussed in the text.
Acknowledgments
[15]
[16]
Financial support by the Spanish Ministerio de Ciencia e Innova-
ción (MICINN) [grant numbers CTQ2007-67103-C02-01,
CTQ2007-67730-C02-01 and Consolider-Ingenio 2010 (CSD2007-
0006)] and the Comunidad Autónoma de Madrid (CAM) (P2009/
PPQ1634-AVANCAT) is acknowledged. I. F. is a Ramón y Cajal
Fellow.
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 2643–2655

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Received: February 9, 2012
Published Online: March 15, 2012
Eur. J. Org. Chem. 2012, 2643–2655
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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