Variation of the backbone conjugation in NLO model compounds: Torsion-angle-restricted, biphenyl-based push-pull-systems

FULL PAPER

DOI: 10.1002/ejoc.200901358

Variation of the Backbone Conjugation in NLO Model Compounds:

Torsion-Angle-Restricted, Biphenyl-Based Push-Pull-Systems

Jürgen Rotzler,^[a]David Vonlanthen,^[a]Alberto Barsella,^[b]Alex Boeglin,*^[b]Alain Fort,^[b]

and Marcel Mayor*^[a,c]

Keywords: Nonlinear optics / Conjugation / Chromophores / Push-pull systems / Torsion angle / Oxidation / Biphenyl

Terminal piperidinyl- and nitro-functionalized biphenyls,

bridged between the 2 and 2Ј positions by a variable number

of methylene groups, are synthesized and fully charac-

terized. These push-pull systems with defined and restricted

torsion angles between their phenyl rings are ideal model

compounds to investigate the influence of the chromophore’s

conjugation in nonlinear optic (NLO) responses. A general

synthetic route that can be implemented to access these

model compounds is reported, starting from dibromo or di-

triflate biphenyls. Hartwig–Buchwald cross-coupling, a se-

lective azacycloalkylation of diaminobiphenyls and a mild

oxidation of primary amines to nitro groups in the presence

of tertiary amine summarizes the synthetic pathway

a

towards the desired model compounds. NLO properties of

the series of torsionally constrained push-pull biphenyls are

collected by electric-field-induced second-harmonic genera-

tion (EFISH) experiments. The results agree qualitatively

with semi-empirical simulations based on the AM1 Hamilto-

nian. A linear dependence of the quadratic response on the

cos²(Φ) of the inter-aryl dihedral angle is observed, which

points to oscillator strength loss as the dominant effect of in-

creasing backbone twist.

that the main contribution to β may be attributed to the

lowest intramolecular charge-transfer (ICT) band charac-

terized by a transition energy, an oscillator strength and a

change in permanent dipole moment, thus defining their

well known two-level model.^[14]ICT is dependent on the

backbone chromophore as well as on the substituents.^[15]

Therefore, the design of efficient organic materials for qua-

dratic nonlinear optics is based on units containing highly

delocalized π-electron moieties and additional electron-do-

nor and electron-acceptor groups on opposite ends of the

chromophore.

Donor-acceptor-substituted biphenyl derivatives are par-

ticularly interesting model compounds exhibiting intramo-

lecular charge-transfer because the extent of “backbone”-

conjugation and thus the extent of charge-transfer between

both substituents depends on a controllable structural fea-

ture, namely the torsion angle between the two phenyl

rings.^[16–19]Correlations between intramolecular torsion

angles and resulting NLO properties were already reported

for quinopyrans by M. A. Ratner and co-workers.^[20]Using

numerical simulations for NLO properties and UV/Vis ab-

sorption spectra, the tuning of transition frequency and

NLO amplitudes was achieved by effecting charge separa-

tion and by stabilizing the charge.^[20]Also biphenyl-based

chromophores have already been considered in theoretical

studies. Ab initio calculations of fluorenyl-based push-pull

systems suggested that the value of β corresponds to the

energy difference between HOMO and LUMO.^[21]By com-

paring the NLO properties of comparable substituted (-NH₂

Introduction

While the discovery of the Kerr effect,^[1]which is the qua-

dratic electric-field-induced change in the refraction index

of a medium, is the earliest nonlinear response reported in

the study of optics, it is the availability of strong electro-

magnetic fields, after the invention of the laser in 1960,^[2]

which made it possible to systematically investigate such ef-

fects. Given the ability to produce optical fields of sufficient

strength, the observation of the phenomenon of second-

harmonic generation (SHG) in quartz in 1961^[3]marks the

advent of nonlinear optical (NLO) studies. Since then, the

search for NLO-active media has been extended to organic

compounds where it has developed into an amazingly broad

field because of numerous potential applications in pho-

tonic technologies, including all-optical switching, data pro-

cessing,^[4–7]or even scanning near-field microscopy.^[8]

To design molecules for quadratic NLO responses, the

first hyperpolarizability β must be optimized. Several mod-

els were developed for a quantitative analysis of the nonlin-

ear optical response.^[9–13]Oudar and Chemla established

[a] Department of Chemistry, University of Basel,

St. Johannsring 19, 4056 Basel, Switzerland

Fax: +41-61-267-1016

E-mail: marcel.mayor@unibas.ch

[b] Institut de Physique et Chimie des Matériaux de Strasbourg,

UMR 7504 UdS-CNRS, 23 rue du Loess, B. P. 43, 67034 Stras-

bourg Cedex 2, France

[c] Institute of Nanotechnology, Karlsruhe Institute of Technol-

ogy,

P. O. Box 3640, 76021 Karlsruhe, Germany

1096

Eur. J. Org. Chem. 2010, 1096–1110

Variation of the Backbone Conjugation in NLO Model Compounds

and -NO₂) biphenyl and fluorene derivatives a considerably

increased response was observed for the planar fluorene

compound, pointing at the importance of the π-conjugation

in the central chromophore. Furthermore, correlations be-

tween backbone torsion angle and NLO properties have al-

ready been reported for zwitterionic compounds.^[16]

Results and Discussion

Molecular Design and Synthetic Strategy

For sizeable quadratic optical responses in linear push-

pull systems a permanent dipole moment induced by elec-

tron-acceptor and -donor substituents and an intense intra-

molecular charge-transfer absorption band are required.

While effects arising from the donor and acceptor substitu-

ents have been investigated extensively,^[21,29–34]hardly any

systematic study of the influence of the backbone’s π-conju-

gation has been reported so far.^[15,16]We recently developed

a series of biphenyl building blocks terminally function-

alized with leaving groups comprising alkyl chains of vari-

ous lengths interlinking both phenyl rings to restrict the

torsion angle of their biphenyl backbone.^[18,35]These func-

tional building blocks are ideally suited as starting materials

of the here reported series of biphenyl-based push-pull sys-

tems as NLO model compounds with varying backbone

conjugation. Nitrogen substituents in varied oxidation

states have been chosen as push-pull substituents. While a

terminal nitro group acts as electron acceptor, a piperidinyl

substituent acts as electron donator on the opposed side.

These substituents on a parent biphenyl core should pro-

vide a donor-acceptor system exhibiting a moderate hyper-

polarizability, leaving investigation space for both, systems

with stronger and weaker hyperpolarizabilities. To keep the

model compounds as comparable as possible the terminal

substituents were maintained throughout the series.

The complexity of the nonlinear optical responses makes

the design of new NLO materials very challenging. Espe-

cially on the molecular level, numerous publications docu-

ment the very basic comprehension of structure-property

relationships, in spite of the fact that great progress has

been made in the last few years.^[16,21–28]Indeed, large π-

conjugated systems with donor and acceptor groups have

been synthesized with a high potential for large nonlinear

optical effects. Despite the advances in chromophore de-

sign, a deeper comprehension of structural features govern-

ing the NLO properties is required to enable reliable theo-

retical predictions and thus, allowing an improved design

of tailor-made NLO materials. Improved theoretical models

on the other hand can only be developed with suitable ex-

perimental data obtained from model compounds in which

a particular structural feature is varied systematically.

Following this systematic approach, we would like to re-

port here the synthesis of the entire series of neutral bi-

phenyl push-pull systems with restricted torsion angles 1a–

1g as NLO model compounds varying mainly in the extent

of backbone π-conjugation (cf. Figure 1). Furthermore, first

optical studies like UV/Vis and EFISH (electric-field-in-

duced second-harmonic generation) experiments were per-

formed to investigate the consequences of the alteration in

torsion angle on their optical properties. The observed cor-

relations are further accompanied by semi-empirical simu-

lations based on the AM1 Hamiltonian.

To preliminarily investigate the suitability of the push-

pull system, the parent 4-nitro-4Ј-piperidinyl-biphenyl was

straight forwardly synthesized by assembling the biphenyl

backbone applying a Suzuki coupling protocol. However,

the synthetic aim of this project was to develop a universal

synthetic strategy for 4-nitro-4Ј-piperidinyl-substituted bi-

phenyl systems based on available building blocks compris-

ing terminal leaving groups such as bromines and triflates.

The synthetic strategies considered are displayed in

Scheme 1.

Figure 1. A) Illustration of the concept to fix the torsion angle Φ

between the two phenyl rings by an additional interphenyl alkyl

bridge of varying length. B) Target push-pull systems with increas-

ing torsion angle from 1c to 1g; 1a and 1b were used as preliminary

model compounds.

Scheme 1. Synthetic routes considered towards the desired bi-

phenyl-based push-pull systems (R³= H for 2, 3 and 7; R³= CH₃

for 1).

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FULL PAPER

In the target compounds the oxidation state of both ter-

minal nitrogen atoms differs by six units. Starting from

symmetric diamino derivatives, which should be obtained

either by palladium-catalyzed Hartwig–Buchwald-type

chemistry^[36,37]or by copper-catalyzed Ullmann-type reac-

tions,^[38,39]the synthetic challenge will be to oxidize exclu-

sively one of the two nitrogen atoms. Furthermore, a suit-

able assembly sequence of the electron-donating piperidinyl

unit and the electron-withdrawing nitro group had to be

found. Two synthetic approaches were considered and are

displayed as A–D and E–F in Scheme 1.

If the piperidinyl donor group is introduced first (E), oxi-

dation of the remaining amino group (F) will be challeng-

ing, as tertiary amines are prone to the formation of N-

oxides. However, a careful choice of the oxidation condi-

tions might overcome this drawback of the E–F strategy.

Alternatively, the oxidation step providing the electron-

withdrawing nitro group could be considered prior to the

assembly of the piperidinyl group (strategy A–D). Mono-

protection of the diamine with a benzoyl group (A) should

provide selectivity^[40]and should reduce the electron density

of the remaining amine providing an increased control over

its oxidation (B), as electron rich anilines are prone to side

reactions during oxidations due to their large reduction po-

tentials. After deprotection (C), the assembly of the piperid-

inyl group was envisaged by an azacycloalkylation. How-

ever, the nucleophilicity of the remaining amino group is

Scheme 2. Assembly of 1a by Suzuki–Miyaura coupling. Synthesis

of the 4,4Ј-diamino derivatives 3a–g applying a Hartwig–Buchwald

protocol. Reagents and conditions: a) Pd(PPh₃)₄, Cs₂CO₃, toluene/

MeOH, 3:1, reflux, 18 h, 26%; b) benzophenone imine, Pd₂(dba)₃·

CHCl₃, BINAP, NaOtBu, toluene, 80 °C, 4 h, 85%-quant.; c)

benzophenone imine, Pd(OAc)₂, BINAP, Cs₂CO₃, THF, 65 °C,

17 h, 98% for 8e, 60% for 8g; d) 3% aq. HCl, THF, room temp.,

2 h, 80%-quant.

decreased due to the electron-withdrawing nitro group. harsh reaction conditions, this was less the case for 4,4Ј-

Interestingly, the extent of this effect is expected to correlate ditriflatebiphenyl systems (2e and 2g) which are prone to

with the backbone conjugation of the biphenyl core.

hydrolysis. To investigate the suitability of the synthetic

strategy, the commercially available 4,4Ј-dibromobiphenyl

(2a) was treated with benzophenone imine as an ammonia

synthon^[44]and sodium tert-butoxide as base in the presence

of catalytic amounts of Pd₂dba₃as Pd⁰source and BINAP

Synthesis

To investigate the suitability of these new types of bi- as ligand in 80 °C toluene (condition b in Scheme 2). To

phenyl-based push-pull systems for EFISH experiments a protect the intermediate air-sensitive catalyst-ligand com-

straight forward assembly of the parent 4-nitro-4Ј-piperid- plex, the reaction was carried out under inert gas and dry

inyl-biphenyl 1a was considered. Particularly appealing is conditions. After 4 h the starting material was consumed as

the synthesis of the biphenyl core by a Suzuki–Miyaura observed by thin-layer chromatography (TLC). The di-

coupling as suitably functionalized phenyl precursors were imine-biphenyl derivative 8a was isolated by precipitation

already available.^[41]As displayed in Scheme 2, 1-(4-iodo- of the catalyst and recrystallization from methanol. In a

phenyl)piperidine

and

4,4,5,5-tetramethyl-2-(4-nitro- first attempt, the diimine 8a was cleaved using ammonium

phenyl)-1,3,2-dioxaborolane were treated with a palladium formate and catalytic amounts of palladium on charcoal.^[44]

catalyst and a base in a refluxing toluene/methanol mixture As only 35% yield of the desired 4,4Ј-diaminobiphenyl (3a)

to provide the desired NLO model compound 1a in 26% was isolated, acidic hydrolysis was considered. Thus, 8a was

yield after column chromatography (CC). Promising pre- dissolved in tetrahydrofurane (THF) and hydrochloric acid

liminary optical investigations of 1a motivated the develop- was added. The desired diamine 3a was isolated by column

ment of a general synthetic route to make the entire series chromatography (CC) in 80% yield over both steps. Start-

of NLO model compounds available.

ing from the ditriflates 2e and 2g, the strong base sodium

Both considered strategies (A–D and E–F) have the 4,4Ј- tert-butoxide was no longer considered. Instead caesium

diaminobiphenyl synthon as a common precursor. Numer- carbonate was used as base in THF together with a

ous catalyst-ligand systems for Hartwig–Buchwald cross- Pd(OAc)₂/BINAP catalyst system.^[44]With these conditions,

coupling reactions to substituted aryl halides, including 4- comparable yields were obtained for the ditriflates as for

bromobiphenyl and 1,4-dibromobenzene^[42]have been re- the dibromides providing good access to the 4,4Ј-diami-

ported.^[43]However, to the best of our knowledge, typical nobiphenyl systems required for both strategies. It is note-

Hartwig–Buchwald conditions were neither applied to ditri- worthy that all these biphenyl diamine derivatives 3a–3g

flate- nor dibromobiphenyl systems. While 4,4Ј-dibromobi- displayed limited stability due to immediate partial

phenyl systems (2a–2d, 2f) as precursors allowed rather oxidation when exposed to air. Thus, elemental

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Variation of the Backbone Conjugation in NLO Model Compounds

analysis was obtained for the corresponding bis(trifluo- strategy A–D was accomplished in spite of the poor yield

roacetic acid) salts, which displayed considerably improved of this intermediate step. An azacycloalkylation was sug-

stabilities.

gested to transform the remaining amine group of 6a into

With the series of diamines 3a–3g in hand, the strategy a piperidinyl substituent. While piperidine subunits are usu-

A–D (Scheme 3) was investigated first, again using the par- ally introduced as nucleophiles substituting a halide in an

ent 4,4Ј-diaminobiphenyl 3a as model compound to explore Ullmann-type coupling reaction,^[47–49]double alkylation of

the potential of the envisaged synthetic route. To distin- arylamines and hydrazines with alkyl dihalides based on a

guish between both terminal amines protection with a ben- microwave-assisted approach was reported recently.^[50,51]

zoyl protection group was considered, which was reported Thus, the amino biphenyl 6a was treated with 1,5-dibromo-

to provide selectively only the monoprotected derivative of pentane and potassium carbonate as a base in a toluene/

1,4-diaminobenzene.^[40]In analogy to the reported pro- ethanol (1:1) mixture at 150 °C for 40 min in the microwave

cedure, the diamine 3a was dispersed in water by adding set-up. The desired 4-nitro-4Ј-piperidinyl-biphenyl (1a) was

sodium dodecyl sulfate (SDS) and benzoic anhydride dis- isolated in 40% yield as an orange solid by CC.

solved in acetonitrile was added at once. After work-up and

With the formation of the model compound 1a the entire

recrystallization from hot toluene a yield of only 50% of strategy A–D was accomplished, but several steps with

the desired monoprotected diamine 4a was obtained, moderate to poor yields considerably disfavour this ap-

pointing at its almost statistical formation. As the selecti- proach. Initial attempts to apply the same strategy to the

vity in the case of 1,4-diaminobenzene probably arises from fluorene diamine starting compound 3c provided even

the different solubilities of the unprotected and the mono- lower yields of the monoprotected intermediate 4c than ob-

protected form, which precipitates the desired monopro- served in the case of 4a, further disqualifying the synthetic

tected product out of the reaction mixture, the fact that 3a strategy.

in water with SDS was a dispersion rather than a solution

The major drawback of the alternative strategy E–F was

already raised questions whether this strategy towards the statistical introduction of the piperidinyl substituent,

monoprotected diamines will be generally applicable to the even though the resulting mixture was expected to be easily

series of diamines 3a–3g, for which differences in their solu- separable into its components by CC. Furthermore, selec-

bility features had been expected.

tive oxidation of primary amines in the presence of tertiary

ones is synthetically challenging. However, as the yield of

monoprotection of the strategy A–D did not exceed statisti-

cal values, the approach E–F with a reduced number of syn-

thetic steps moved again into the focus of interest. The two

synthetic steps are displayed in Scheme 4. To transform one

Scheme 3. Synthetic steps along the strategy A–D. Reagents and

conditions: a) benzoic anhydride, MeCN, H₂O, SDS, room temp.,

10 min, 50%; b) NaBO₃·4H₂O, AcOH, 55–60 °C, 16 h, quant.; c)

10  aq. KOH, DMSO, 80 °C, 60 h, 25%; d) 1,5-dibromopentane,

K₂CO₃, toluene/EtOH, 1:1, MW, 150 °C, 40 min, 40%.

However, with reasonable quantities of 4a in hand we

further investigated the proposed strategy. Interestingly, the

benzoyl protection group should also support the control

over the oxidation of the remaining amine, as deactivated

anilines containing electron-withdrawing groups are

smoothly oxidized to the corresponding nitroarenes upon

treatment with sodium perborate, whereas activated anilines

containing electron-donating groups notoriously tend to

overoxidation.^[45]And indeed, treating the monoprotected

4a with an excess of sodium perborate tetrahydrate in acetic

acid at 60 °C provided the protected nitro derivative 5a

quantitatively without overoxidation. Strong basic condi-

tions were considered to cleave the benzamide protection

group of 5a. By treatment with 10  aqueous potassium

hydroxide in dimethyl sulfoxide (DMSO)^[46]the amine 6a

was obtained in a poor yield of 25% after CC as a red

Scheme 4. Top: synthesis of the target structures 1a–b and 1d–g

following the strategy E–F. Bottom: synthesis of the target structure

1c based on an individual strategy. Reagents and conditions: a) 1,5-

dibromopentane, K₂CO₃, toluene/EtOH, 1:1, MW, 150 °C, 40 min,

34–44%; b) NaBO₃·4H₂O, H₃PW₁₂O₄₀, CTAB (hexadecyltrimethy-

lammonium bromide) (10 cmc in water), 55–60 °C, 16 h, 45–64%;

c) HNO₃/AcOH, –43 °C, 6 h, 15%; d) I₂, AcOH, room temp.,

10 min, then concd. H₂SO₄, NaNO₂, reflux, 30 min, 76%; e) MeI,

KI, KOH, DMSO, room temp., 2 h, 95%; f) piperidine, CsOAc,

solid. As there was only a final step remaining the synthetic CuI, DMSO, 90 °C, 24 h, 15%.

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Table 1. Screening results for the reaction of 3a to 7a.

Solvent

Equiv. diha-

lide

Temperature [°C]

Reaction time

[min]

Obtained ratio

(mono/di)

Conversion^[a]

(mono+di)

1

2

3

4

5

6

7

8

water

1.10

1.50

1.10

120

150

120

120–150

150

145

20

40

50:50^[b]

45:55

20%

47%

14%

40%

50%

53%

2%

toluene/water 1:1

toluene/EtOH 1:1

toluene/EtOH 10:1

acetone

100:0

mono Ͼ di^[b]

84:16

77:23

100:0

80

75

14%

[a] Conversion is related to the reisolated starting material. [b] Ratios determined qualitatively by TLC.

of the two terminal amino groups of the model compound ing stability towards a second cycloalkylation reaction. This

3a into a piperidinyl substituent, a microwave-assisted hypothesis is further corroborated by the fact that K₂CO₃

double alkylation with 1,5-dibromopentane^[50]was consid- is not dissolved in the most promising solvent mixture (tol-

ered,^[51]mainly due to its reported superior yields compared uene/EtOH, 1:1) suggesting the deprotonation at the phase

with thermally activated heterocyclization reactions of an- boundary as the rate determining and reaction controlling

iline derivatives. Following a reported protocol,^[51]commer- step.

cially available 4,4Ј-diaminobiphenyl (3a) was treated in the

The best compromise between chemoselectivity and con-

microwave reactor with 1,5-dibromopentane in water with version was found empirically for entry 5 and similar reac-

potassium carbonate (K₂CO₃) as a base. The desired mono- tion conditions were thus applied for the transformations

piperidinyl derivative 7a was isolated in a poor yield of only of the diamines 3b–3g to the piperidine derivatives 7b–7g.

10% and the formation of a black tar at the bottom of the The obtained yields and observed chemoselectivities are

reaction vessel, probably arising from the large amount of summarized in Table 2. For all diamines yields between

undissolved starting material was observed. In a second at- 30% and 45% of the corresponding mono-piperidinyl-func-

tempt toluene was added to increase the solubility of 3a. tionalized biphenyl system were obtained, pointing at the

The two-phase mixture was exposed for 20 min to micro- general applicability of the transformation procedure. With

wave irradiation at 120 °C. To our surprise only the forma- the exception of the fluorene derivative 7c, very comparable

tion of the mono-piperidinyl derivative 7a was observed by chemoselectivities were observed. The slightly increased for-

TLC with comparable low yields as obtained in pure water. mation of the doubly piperidinyl-functionalized fluorene

Inspired by this unexpected chemoselectivity different sol- may point at an increased activation of the second amine

vent mixtures were screened, as summarized in Table 1. The by the first piperidinyl substituent due to the pronounced

yields of the reactions were determined by reverse phase electronic coupling of both phenyl rings in the flat fluorene

HPLC (RP18) using acetonitrile as eluent.

core.

In water almost equal quantities of mono- and dipiperid-

inyl (45:55) functionalized biphenyl were observed and large

amounts of starting material was lost to side reactions (En-

tries 1 and 2). By addition of toluene both starting materi-

als, the benzidine 3a and the 1,5-dibromopentane, were dis-

solved in the organic phase while the microwave energy was

absorbed by the aqueous phase. While the promising

chemoselectivity of the system was corroborated (Entries 3

and 4), low yields disfavoured these reaction conditions. To

bring the microwave absorbing species into the organic

phase, ethanol (EtOH) was considered instead of water. In

a 1:1 mixture of toluene and ethanol a conversion of 50%

of the starting benzidine 3a was observed with a chemose-

Table 2. Azacycloalkylation of amines 3a–3g.

Product

% Yield^[a]

Selectivity (mono/di)

7a

7b

7c

7d

7e

7f

41

40

43

44

32

41

34

42:8

n.d.

43:15

44:7

32:3

41:5

34:8

7g

[a] Yields of the desired monoazacycloalkylated products 7 isolated

by CC.

Finally, to accomplish the synthesis of the target struc-

lectivity of 84:16 in favour of the desired mono-piperidinyl- tures 1a–1g, the remaining amino group had to be oxidized

substituted biphenyl system 7a (Entry 5). A further increase to a nitro group. Unfortunately, most oxidants that are rou-

in the dibromopentane concentration decreased the chemo- tinely used for the oxidation of primary amines to nitro

selectivity by a comparable conversion (Entry 6), while a groups are also able to oxidize tertiary amines. And indeed,

decrease in the EtOH fraction (Entry 7) or the use of ace- immediate overoxidation to 1-(4Ј-nitrobiphenyl-4-yl)piper-

1

tone as neat solvent (Entry 8) increased the chemoselectiv- idine 1-oxide (isolated and characterized by H NMR and

ity by drastically reducing the conversion. We hypothesize IR spectroscopy) was observed by applying standard oxi-

that the activated secondary amine of the formed mono- dation conditions such as in situ generated peracetic acid as

piperidinyl-functionalized biphenyl system might be par- an oxidizing agent and sulfuric acid as a catalyst, or sodium

tially protonated during the reaction to explain its surpris- perborate in acetic acid.^[45,52]Smooth oxidation conditions

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Variation of the Backbone Conjugation in NLO Model Compounds

for the conversion of anilines to nitrobenzene derivatives the biphenyl unit. The observed bathochromic shift com-

profiting from a water soluble tungstophosphoric acid pared to biphenyl (247 nm) probably arises from enlarge-

(H₃PW₁₂O₄₀·nH₂O) as catalyst and phase-transfer oxidant ment of the conjugated π-system due to substitution with

and sodium perborate as an oxidant in micellar media have lone pair containing nitrogen units.^[57]The long wavelength

been reported.^[53]According to the hypothesized mecha- absorption λ_maxat 398 nm which levels off around 560 nm

nism, oxidation occurs in micelles of organic molecules is assigned to a charge-transfer band.^[58,59]Because a strong

where the concentration of the sterically demanding active donor and a strong acceptor was used in the target push-

species is low, providing very mild oxidation condi- pull systems 1c–1g, the participation of the HOMO–

tions.^[54,55]By applying the described conditions to com- LUMO transition decreases considerably for the long-wave-

pound 7a (Scheme 4), the target push-pull system 1a was length absorption and the ICT-affected correction term

isolated in 55% yield after CC as a red solid without detect- reaches zero. Thus λ_maxvalues of this charge-transfer band

able formation of the N-oxide.

were used as indicator of the π-conjugation instead of its

Similar reaction conditions applied to the diamines 3a– onset which reflects the HOMO–LUMO transition.^[58]The

3g provided the desired target structures 1b and 1d–1g in subfragment absorption (λ_maxca. 268 nm) remains the same

reasonable yields between 45% and 64%. However, in the throughout the whole series, whereas a hypsochromic as

case of the fluorene derivative 7c the formation of the de- well as a hypochromic shift was observed for the charge-

sired nitro derivative was not observed, probably different transfer absorption with increasing torsion angle Φ (Fig-

solubility properties of 7c arising from the acidity of the ure 2). Values for Φ were obtained by semi-empirical calcu-

hydrogen-atoms in C9 position avoided its oxidation. Nev- lations (MOPAC 2002 program^[60]using the AM1 semi-em-

ertheless, besides the moderate yields it is noteworthy that, pirical Hamiltonian^[61]). The absorption data for the

to the best of our knowledge, it is the first time that suitable bridged compounds 1c–1g are summarized in Table 3.

oxidation conditions for oxidation of primary amines to ni-

tro groups in the presence of alkylated amino groups were

found. As displayed at the bottom of Scheme 4, the ter-

minally nitro- and piperidinyl-substituted fluorene deriva-

tive 1c comprising two methyl groups at the C9 position

was synthesized based on previously reported synthetic

steps.^[47,56]In short, nitration and iodination of fluorene

provided the terminally nitro- and iodo-functionalized

fluorene 10, which was methylated to remove the acidic hy-

drogen-atoms in the C9 position. Finally, the piperidine

group was introduced by substituting the iodine atom in an

Ullmann coupling-reaction to provide 1c as a red solid in

poor yields of about 2% over the four steps. However, the

focus was set on the completion of the series of model com-

pounds and thus this already reported procedure was not

further optimized for the system under investigation.

1

All new compounds were fully characterized by H and

Figure 2. Cumulated absorption spectra of the push-pull systems

1c–1g.

¹³C NMR spectroscopy, mass spectrometry and refraction

index or melting points. The purity of the target structures

is further documented by elemental analysis.

Summarizing the synthetic section, with the strategy E–

F almost the entire series of push-pull model compounds

was obtained in reasonable quantities enabling NLO in-

vestigations. Despite only moderate yields for both steps (E:

30–45%; F: 45–64%), the shortness and the general applica-

bility clearly favours this strategy over the initially privi-

leged approach A–D.

Table 3. λ_maxof the CT-bands and the corresponding extinction

coefficients ε of 1c–1g.

λ_max.(CT) [nm]

ε [Lmol^–1cm^–1]

1c

1d

1e

1f

418

416

388

371

351

21703

20782

12074

7551

1g

3019

Optical Properties

The hypochromic shift can be explained by an increase

The π-conjugation in the bridged target compounds 1c– in the transition energy due to larger torsion angles when

1g was investigated by UV/Vis measurements. The in 2 and going from 1c to 1g. By increasing torsion angle Φ the con-

2Ј position unsubstituted push-pull system 1a showed ab- jugation is less pronounced leading to higher excitation en-

sorption maxima at 268 (ε = 19840 Lmol^–1cm^–1) and ergies and therefore to absorption at lower wavelengths. Ac-

398 nm (ε = 19646 Lmol^–1cm^–1). The shorter wavelength cording to studies of similar compounds the hypsochromic

absorption band can be assigned to a subfragment band of shift can be related to cos²(Φ) (Figure 3).^[58,59]

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1101

A. Boeglin, M. Mayor et al.

FULL PAPER

bridge (1g): the dynamical variations in torsion angles

driven by solvent motion are the most likely explanations

for these exceptions. Indeed, especially for compound 1b,

the equilibrium geometry corresponds to the lowest torsion

angle, i.e. the best conjugation, compatible with the steric

constrains. In this situation, the calculations will overesti-

mate the actual response because less favourable geometries

are not taken into account. It is noteworthy that the 2,2Ј-

dimethyl biphenyl building block has already been inte-

grated in molecular devices to tailor electronic transport

properties.^[35,63]In these compounds the interring torsion

angle of the 2,2Ј-dimethyl biphenyl subunit was found to be

close to 90°, at least in the solid state. Assuming a compar-

able torsion angle Φ for 1b, the measured and calculated

values would be shifted horizontally to cos²(Φ) = 0 and

would fit nicely with the linear progression calculated for

the remaining members of the series.

Figure 3. Correlation of λ_maxto the calculated cos²(Φ).

The quadratic NLO responses have been plotted as a

function of the cos²(Φ) of the equilibrium torsion angle in

Figure 4. The finite-frequency, zero-frequency and finite-

field results give rise to nearly linear progressions, if we

overlook the values for compound 1b as argued above.

This correlation beautifully illustrates the dependence of

the conjugation to the torsion angle Φ in such biphenyl

systems.

Quadratic Response

The molecular µβ values were measured using an EFISH

setup.^[62]Multiple measurements were performed for each

molecule with different concentrations. The experimental

results are shown in Table 4. The experimental uncertainties

vary from 5% to 15% as the signal level intensities decrease

except for 1b for which the spread in repeated measure-

ments was unusually large. The numerical simulations were

performed with the MOPAC 2002 program^[60]using the

AM1 semi-empirical Hamiltonian.^[61]The permanent

ground-state dipole moments and the zero frequency hyper-

polarizability tensor components obtained for the resulting

equilibrium geometry have been combined to yield the

theoretical µβ values listed in Table 4, together with the op-

timized inter-aryl torsion angle.

Figure 4. Quadratic nonlinear response as a function of the calcu-

lated equilibrium torsion angle Φ. Black curve: EFISH results; grey

curve: scaled results; light grey curve: MOPAC 2002 predictions

with the AM1 Hamiltonian. The values of compound 1b were not

considered for the least-squares fits displayed by the solid lines.

Table 4. Experimental EFISH results, two-level-system extrapo-

lated zero-frequency values and MOPAC 2002 predictions with the

AM1 Hamiltonian expressed in 10^–48esu.

µβ(1.907 µm) µβ(0) from

µβ(0) by

Torsion angle^[a]

TLS

AM1

The finite-frequency measurements include the disper-

sion effect resulting from the shifts in transition energies of

the absorption bands, but, because of the excitation wave-

length used, it is hardly discernible in the plot. In any case,

the fact that the dispersion corrected results follow the

cos²(Φ) law almost as well as the calculated values is an

indication that it is the overlap between the π_zorbitals of

the central carbon atoms which is the relevant parameter.

Because the absorption bands at short wavelengths show

1a

1b

1c

1d

1e

1f

245Ϯ15

70Ϯ35

410Ϯ40

400Ϯ20

230Ϯ10

130Ϯ20

75Ϯ10

190

55

300

295

180

105

60

136

83

192

163

132

76

38.4°

58.4°

0.1°

18.1°

46.1°

70.3°

83.5°

1g

62

[a] Equilibrium position torsion angle.

The predicted response is consistently 30% below the ex- much less dependence on torsion angle than the CT bands,

perimental values extrapolated to zero frequency with the we may assume that the two-level model should be able to

dispersion relation of the two-level model^[14]using the CT- account for the observed trend. In this model, the quadratic

band frequencies deduced from the UV/Vis absorption response is proportional to the product of the oscillator

spectra. This trend is not followed by the open dimethyl strength, the change in dipole moment upon excitation and

compound (1b) nor by the one containing the longest the ground-state dipole moment. We are thus led to the

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Variation of the Backbone Conjugation in NLO Model Compounds

extractions were distilled before use. When the Schlenk technique

was used, the solvents were degassed with argon for several min-

utes. Characterizations were performed with the following instru-

ments: ¹H NMR and ¹³C NMR spectra were recorded with a

Bruker DPX NMR (400 MHz) or a Bruker BZH NMR (250 MHz)

instrument, the J values are given in Hz (Ϯ0.1 Hz). Mass spectra

were recorded with a Bruker Esquire 3000 plus (for ESI), a Finni-

gan MAT 95Q (for EI) or a Voyager-De^TMPro (for MALDI-TOF)

instrument. The elementary analyses were performed with an Ana-

lysator 240 instrument from Perkin–Elmer. The absorption spectra

were recorded with an Agilent 8453 Diode Array Spectrophotome-

ter using 1 cm cuvettes (1ϫ10^–5m solutions in chloroform). The

measurements were performed at room temperature. For column

chromatography silica gel 60 (40–63 µm) from Fluka was used.

conclusion that the dominant effect of increasing torsion

angles lies in the resulting loss of oscillator strength while

the permanent dipoles of the ground and the CT states are

affected to a lesser degree.

Conclusions

To provide a series of push-pull systems that vary in the

extent of π-conjugation of their central chromophores, a

universal synthetic route towards terminal piperidinyl- and

nitro-functionalized biphenyls comprising a restricted inter-

ring torsion angle due to an interlinking chain of varying

length between the 2 and 2Ј position was developed. By TLC was carried out on silica gel 60 F₂₅₄glass plates with a thick-

ness of 0.25 mm from Merck. Elementary analysis of the diamines

3f–3g was performed on the TFA salts of these compounds. This

was not possible for amines 7a–7g because of the air sensitivity of

these compounds.

following the most straightforward synthetic pathway E–F,

target molecules 1a–1g were synthesized, starting from the

corresponding dibromo or ditriflate derivatives 2a–2g in

only three steps (Scheme 4). Conditions for a Hartwig–

Buchwald hetero-cross-coupling reaction to exchange the

bromide and triflate substituents to amino groups were de-

veloped with the biphenyl model compound 2a, using

benzophenone imine as an ammonia synthon. Similar reac-

tion conditions were subsequently successfully applied to all

biphenyl dihalides 2b–2d and 2f and ditriflates 2e and 2g,

providing the corresponding diamines 3a–3g in good yields.

Furthermore, a microwave-assisted azacycloalkylation al-

lowed the rather selective and inexpensive assembly of a

piperidine ring at only one terminal amine group of the

diaminobiphenyls 3a–3g. By systematic solvent-screening

encouraging selectivities and moderate conversions were

reached with all diamines to provide the amino-piperidinyl

derivatives 7a–7g. Finally, a mild and selective oxidation of

aminobiphenyls bearing a piperidinyl donor group was de-

veloped and applied successfully to the synthesis of model

compounds 1a, 1b and 1d–1g. The series was complemented

by the dimethylfluorene derivative 1c, which was assembled

by an alternative route. The NLO properties of this series

of torsion-angle-restricted, biphenyl-based push-pull sys-

tems have been successfully investigated by EFISH mea-

surements. The results agree qualitatively with semi-empiri-

cal simulations based on the AM1 Hamiltonian. In particu-

lar, the linear dependence of the quadratic response on the

cos²(Φ) of the inter-aryl dihedral angle points to oscillator

strength loss as the dominant effect of increasing backbone

twist, which would indicate that the change in permanent

dipole moment upon CT transition is much less affected.

To probe this aspect will require conducting experiments

where the chromophores are excited at resonance, such as

two-photon absorption cross-section measurements. It will

then be of interest to see how more sophisticated electronic

structure calculations will fare in describing the effect of the

gradual twist of the conjugation path.

EFISH Measurements: The excitation source was a Nd:YAG laser,

actively Q-switched at 10 Hz, emitting 7 ns pulses at 1.064 µm

wavelength. In order to avoid absorption of the fundamental and

second harmonic beams, the pulses were Raman-shifted to

1.907 µm through a high-pressure hydrogen cell, bringing the sec-

ond-harmonic signal to 953 nm, beyond the absorption band of

the studied molecules. The nonlinear signal was selected by using

an appropriate interferential filter placed before a photomultiplier.

In order to determine the absolute value of the second-harmonic

generation, a quartz wedge was used as a reference,^[14]taking its

quadratic susceptibility d₁₁= 1.2ϫ10^–9esu at 1.064 µm and ex-

trapolating it to 1.1ϫ10^–9esu at 1.907 µm. The molecules in chlo-

roform were oriented by an electrical pulse of 2 kV/mm amplitude

and of 5 µs duration synchronized to the laser excitation.

Representative Procedure A (Syntheses of Diamino Derivatives 3):^[44]

Toluene was degassed in an oven-dried Schlenk tube. In a Schlenk

tube Pd₂(dba)₃·CHCl₃(4 mol-%) and BINAP (12 mol-%) were dis-

solved in degassed toluene (0.16  with respect to the dibromobi-

phenyl). The black solution was stirred for 15 min at room temp.,

while dibromobiphenyl (2) and NaOtBu were added. To this dark-

red solution benzophenone imine was added dropwise. The red re-

action mixture was stirred at 80 °C until the starting material had

been consumed as monitored by TLC. Afterwards, the mixture was

cooled to room temp. and diluted with diethyl ether (4ϫvolume of

toluene). The suspension was filtered through Celite and concen-

trated under reduced pressure. The crude was purified by

recrystallization from methanol to afford N,N-bis(diphenylmeth-

ylene)biphenyldiamine (8) as a yellow solid. Diimine 8 was dis-

solved in THF (0.15 ) and 3  aq. HCl (30% by volume of THF)

was added. The pale yellow reaction mixture was stirred at room

temp. until the starting material was consumed as monitored by

TLC. Afterwards the solution was partitioned between 0.5  aq.

HCl and hexane/EtOAc (2:1). The organic layer was washed three

times with 0.5  aq. HCl and the combined aqueous layers made

alkaline with 1  aq. NaOH. The brown liquid was extracted with

dichloromethane, dried with sodium sulfate, filtered, and concen-

trated in vacuo. The crude was purified by column chromatography

(SiO₂, hexane/EtOAc, 1:1, 5% NEt₃) to afford diamine 3.

Benzidine (3a): From 4,4Ј-Dibromobiphenyl (200 mg, 1.00 equiv.,

0.641 mmol) (2a), N⁴,N^4Ј-bis(diphenylmethylene)biphenyl-4,4Ј-di-

amine (8a) (177.5 mg, 54%) was obtained as a yellow solid after

purification by column chromatography (SiO₂, hexane/EtOAc, 5:1,

5% NEt₃) and recrystallization from methanol. Diimine 8a

Experimental Section

General Remarks: All chemicals were directly used for the syntheses

without purification where nothing else is remarked. Dry solvents

were purchased from Fluka. The solvents for chromatography and

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1103

A. Boeglin, M. Mayor et al.

FULL PAPER

(73.0 mg, 1.00 equiv., 0.142 mmol) was cleaved following general

119.5 (C_t, 2 C), 29.0 (C_s, 2 C) ppm. MS (MALDI-TOF): m/z (%)

procedure A to achieve benzidine (3a) (21.5 mg, 82%).

= 540 (98), 539 (100).

Analytical Data of 8a: M.p. 237–239 °C; R_f= 0.24 (hexane/EtOAc,

Analytical Data of 3d: M.p. 157–159 °C; R_f= 0.43 (hexane/EtOAc,

1:5, 5% NEt₃). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.44 (d,

1

5:1, 5% NEt₃). H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.75 (d,

3

³J_H,H= 7.0 Hz, 4 H), 7.47 (t, J_H,H= 7.3 Hz, 2 H), 7.41 (m, 4 H),

3

4

³J_H,H= 8.2 Hz, 2 H), 6.59 (dd, J_H,H= 8.2, J_H,H= 2.4 Hz, 2 H),

3

4

7.34 (d, J_H,H= 8.5 Hz, 4 H), 7.30–7.24 (m, 6 H), 7.18–7.12 (m, 4

6.53 (d, J_H,H= 2.4 Hz, 2 H), 3.61 (br. s, 4 H), 2.74 (s, 4 H) ppm.

3

H), 6.75 (d, J_H,H= 8.5 Hz, 4 H) ppm. ¹³C NMR (101 MHz,

¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 144.6 (C_q, 2 C), 137.6

(C_q, 2 C), 125.9 (C_q, 2 C), 123.7 (C_t, 2 C), 114.7 (C_t, 2 C), 113.7

(C_t, 2 C), 29.4 (C_s, 2 C) ppm. MS (EI⁺, 70 eV): m/z (%) = 211 (16),

210 (100), 209 (27).

CDCl₃, 25 °C): δ = 168.6 (C_q, 2 C), 150.5 (C_q, 2 C), 140.2 (C_q, 2

C), 136.7 (C_q, 2 C), 135.9 (C_q, 2 C), 131.1 (C_t, 2 C), 130.0 (C_t, 4

C), 129.8 (C_t, 4 C), 129.1 (C_t, 2 C), 128.6 (C_t, 4 C), 128.5 (C_t, 4

C), 127.0 (C_t, 4 C), 121.9 (C_t, 4 C) ppm. MS (MALDI-TOF): m/z

(%) = 514 (25), 513 (53), 512 (100). C₃₈H₂₈N₂(512.65): calcd. C

89.03, H 5.50, N 5.46; found C 88.81, H 5.67, N 5.23.

3,10-Diamino-5,6,7,8-tetrahydrodibenzo[a,c]cyclooctene (3f): From

dibromide 2f (1.20 g, 1.00 equiv., 3.28 mmol), diimine 8f (1.57 g,

85%) was obtained as a yellow powder. Diimine 8f (1.56 g,

1.00 equiv., 2.76 mmol) was cleaved following general procedure A

yielding in 605 mg (71%) of the diamine 3f as a white solid after

purification by column chromatography (SiO₂, hexane/EtOAc, 1:1,

5% NEt₃). For analytical purpose a small amount of 3f was dis-

solved in 2-propanol. While stirring at room temp., concd. TFA

(1 mL) was added in one lot. The solution was stirred at room

temp. for 15 min. Afterwards the TFA salt of 3f was precipitated

with ice cold Et₂O, filtered, washed with plenty of ether and dried.

Analytical Data of 3a: M.p. 118 °C; R_f= 0.26 (hexane/EtOAc, 1:1,

1

3

5% NEt₃). H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.34 (d, J_H,H

= 8.6 Hz, 4 H), 6.72 (d, ³J_H,H= 8.6 Hz, 4 H), 3.65 (br. s, 4 H) ppm.

¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 145.4 (C_q, 2 C), 132.2

(C , 2 C), 127.7 (C , 4 C), 115.9 (C , 4 C) ppm. IR: ν = 3402 (w),

˜

q

t

3319 (w), 3171 (w), 3019 (w), 1602 (m), 1496 (s), 1263 (s), 1175

(m), 848 (s) cm^–1. MS (EI⁺, 70 eV): m/z (%) = 185 (13), 184 (100),

183 (10), 156 (5), 92 (7).

9H-Fluorene-2,7-diamine (3c): General procedure A was followed

using 1.00 g (1.00 equiv., 3.09 mmol) 2,7-dibromofluorene (2c) to

afford 440 mg (81%) 2,7-diamino-9H-fluorene (3c) after purifica-

tion by column chromatography (SiO₂, hexane/EtOAc, 1:3, 5%

NEt₃).

Analytical Data of 8f: M.p. 121–122 °C; R_f= 0.34 (hexane/EtOAc,

3

5:1). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.77 (d, J_H,H

=

3

7.0 Hz, 4 H), 7.47 (t, J_H,H= 7.2 Hz, 2 H), 7.44–7.38 (m, 4 H),

7.30–7.21 (m, 6 H), 7.16–7.10 (m, 4 H), 6.97 (d, J_H,H= 8.0 Hz, 2

3

4

H), 6.61 (dd, J_H,H= 8.0, J_H,H= 2.1 Hz, 2 H), 6.53 (d, J_H,H

=

2

3

Analytical Data of 8c: M.p. 219–220 °C; R_f= 0.27 (hexane/EtOAc,

1:3, 5% NEt₃). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.75 (d,

2.1 Hz, 2 H), 2.41 (dd, J_H,H= 13.1, J_H,H= 8.3 Hz, 2 H), 1.89–

1.76 (m, 4 H), 1.15–1.05 (m, 2 H) ppm. ¹³C NMR (101 MHz,

CDCl₃, 25 °C): δ = 168.3 (C_q, 2 C), 150.6 (C_q, 2 C), 142.8 (C_q, 2

C), 139.7 (C_q, 2 C), 136.4 (C_q, 2 C), 135.5 (C_t, 2 C), 130.6 (C_t, 2

C), 129.6 (C_q, 2 C), 129.3 (C_t, 4 C), 129.0 (C_t, 4 C), 128.4 (C_t, 2

C), 128.2 (C_t, 4 C), 127.8 (C_t, 4 C), 121.7 (C_t, 2 C), 118.5 (C_t, 2

C), 32.5 (C_s, 2 C), 29.5 (C_s, 2 C) ppm. MS (MALDI-TOF): m/z

(%) = 568 (48), 567 (73), 566 (100).

3

³J_H,H= 7.0 Hz, 4 H), 7.46 (t, J_H,H= 7.3 Hz, 2 H), 7.42–7.38 (m,

6 H), 7.28–7.23 (m, 6 H), 7.17–7.13 (m, 4 H), 6.89–6.86 (m, 2 H),

3

4

6.66 (dd, J_H,H= 8.0, J_H,H= 1.9 Hz, 2 H), 3.62 (s, 2 H) ppm. ¹³C

NMR (101 MHz, CDCl₃, 25 °C): δ = 167.8 (C_q, 2 C), 149.7 (C_q, 2

C), 143.7 (C_q, 2 C), 139.9 (C_q, 2 C), 137.1 (C_q, 2 C), 136.4 (C_q, 2

C), 130.6 (C_t, 2 C), 129.6 (C_t, 4 C), 129.3 (C_t, 4 C), 128.5 (C_t, 2

C), 128.2 (C_t, 4 C), 128.0 (C_t, 4 C), 119.9 (C_t, 2 C), 119.2 (C_t, 2

C), 118.0 (C_t, 2 C), 36.8 (C_s, 1 C) ppm. MS (MALDI-TOF): m/z

(%) = 526 (6), 525 (11), 524 (100).

Analytical Data of 3f: R_f= 0.22 (hexane/EtOAc, 1:1, 5% NEt₃).

3

¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.02 (d, J_H,H= 7.9 Hz,

2

2 H), 6.61–6.54 (m, 4 H), 3.62 (br. s, 4 H), 2.57 (dd, J_H,H= 13.2,

³J_H,H= 8.5 Hz, 2 H), 2.16–2.06 (m, 2 H), 2.06–1.97 (m, 2 H), 1.51–

1.42 (m, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 145.5

(C_q, 2 C), 143.8 (C_q, 2 C), 131.5 (C_q, 2 C), 130.1 (C_t, 2 C), 115.7

(C_t, 2 C), 112.7 (C_t, 2 C), 32.9 (C_s, 2 C), 29.7 (C_s, 2 C) ppm. MS

(EI⁺, 70 eV): m/z (%) = 239 (18), 238 (100), 237 (5), 209 (21),

208 (9), 196 (6), 195 (20), 104 (6). Elemental analysis calcd. for

C₁₆H₁₈N₂(TFA salt): C 51.51, H 4.32, N 6.01; found C 51.55, H

4.33, N 5.97.

Analytical Data of 3c: M.p. 168–169 °C; R_f= 0.12 (hexane/EtOAc,

1

1:1, 5% NEt₃). H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.42 (d,

3

³J_H,H= 8.0 Hz, 2 H), 6.85–6.82 (m, 2 H), 6.67 (dd, J_H,H= 8.0,

⁴J_H,H= 2.2 Hz, 2 H), 3.72 (s, 2 H), 3.65 (br. s, 4 H) ppm. ¹³C NMR

(101 MHz, CDCl₃, 25 °C): δ = 144.3 (C_q, 2 C), 144.1 (C_q, 2 C),

133.5 (C_q, 2 C), 119.2 (C_t, 2 C), 113.8 (C_t, 2 C), 112.0 (C_t, 2 C), 36.7

(C_s, 1 C) ppm. MS (MALDI-TOF): m/z (%) = 197 (38), 196 (100).

9,10-Dihydrophenanthrene-2,7-diamine (3d): General procedure A

was followed using 400 mg (1.00 equiv., 1.18 mmol) 2,7-dibromo-

9,10-dihydrophenanthrene (2d) to afford 584 mg (92%) N²,N⁷-

bis(diphenylmethylene)-9,10-dihydrophenanthrene-2,7-diamine (8d)

as a pale yellow powder. The diimine 8d (570 mg, 1.00 equiv.,

1.08 mmol) was used without further purification to achieve di-

amine 3d (185 mg, 83%) after purification by column chromatog-

raphy (SiO₂, hexane/EtOAc, 1:5, 5% NEt₃) as a white solid.

Representative Procedure B (Syntheses of Diamino Derivatives 3

Starting from the Triflate-Substituted Tricyclic Biphenyl Deriva-

tives):^[44]THF (absol.) was degassed by three freeze and thaw cy-

cles. Pd(OAc)₂(10 mol-%), BINAP (15 mol-%), ditriflate

(1.00 equiv.) and caesium carbonate (2.80 equiv.) were given in a

Schlenk tube and dissolved in degassed THF (0.07  with respect

to the ditriflate). To this yellow/orange suspension benzophenone

Analytical Data of 8d: M.p. 230 °C; R_f= 0.47 (hexane/EtOAc, 5:1). imine (2.40 equiv.) was added dropwise and the resulting reaction

3

¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.74 (d, J_H,H= 7.0 Hz, mixture was stirred at 65 °C until the starting material had been

3

4 H), 7.46 (t, J_H,H= 7.2 Hz, 2 H), 7.42–7.37 (m, 6 H), 7.29–7.23 consumed as monitored by TLC (overnight). Afterwards, the mix-

4

(m, 6 H), 7.17–7.13 (m, 4 H), 6.62 (d, J_H,H= 2.1 Hz, 2 H), 6.55

(dd, ³J_H,H= 8.2, ⁴J_H,H= 2.2 Hz, 2 H), 2.64 (s, 4 H) ppm. ¹³C NMR

(101 MHz, CDCl₃, 25 °C): δ = 167.8 (C_q, 2 C), 149.8 (C_q, 2 C),

139.8 (C_q, 2 C), 137.2 (C_q, 2 C), 136.4 (C_q, 2 C), 130.6 (C_t, 2 C),

129.7 (C_q, 2 C), 129.5 (C_t, 4 C), 129.3 (C_t, 4 C), 128.6 (C_t, 2 C),

128.2 (C_t, 4 C), 128.0 (C_t, 4 C), 123.3 (C_t, 2 C), 121.0 (C_t, 2 C),

ture was cooled to room temp. and diluted with diethyl ether

(4ϫvolume of toluene). The suspension was filtered through Celite

and concentrated under reduced pressure. The crude was purified

by recrystallization from methanol to afford N,N-bis(diphenyl-

methylene)biphenyldiamine (8) as a yellow solid. Cleavage of the

diimine 8 was performed according to procedure A.

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Variation of the Backbone Conjugation in NLO Model Compounds

3,9-Diamino-6,7-dihydro-5H-dibenzo[a,c]cycloheptene (3e): Accord-

ing to representative procedure B, ditriflate 2e (1.40 g, 1.00 equiv.,

2.85 mmol) was reacted to diimine 8e (1.54 g, 98%) which was iso-

lated as a yellow powder. The diimine 8e was cleaved without fur-

ther purification. Diimine 8e (1.51 g, 1.00 equiv., 2.73 mmol) was

dissolved in THF (30 mL), adding 3  aq. HCl (10 mL). Purifica-

tion of the crude was performed by column chromatography (SiO₂,

hexane/EtOAc, 1:1, 5% NEt₃). Diamine 3e (496 mg, 81%) was iso-

lated as a colourless oil. The TFA salt of 3e was obtained in the

same manner as the TFA salt of 3f.

calcd. (%) for C₁₇H₂₀N₂(TFA salt): C 52.50, H 4.62, N 5.83; found

C 52.53, H 4.61, N 5.88.

N-(4Ј-Aminobiphenyl-4-yl)benzamide (4a):^[40]To a stirred hetero-

geneous suspension of diamine 3a (461 mg, 1.00 equiv., 2.50 mmol)

in water (15 mL) sodium dodecyl sulfate (SDS) (120 mg) was

added. Then benzoic anhydride (566 mg, 1.00 equiv., 2.50 mmol)

dissolved in acetonitrile (2.5 mL) was added at once to the still

heterogeneous brown suspension. After stirring for 10 min at room

temperature the grey suspension was diluted with acetonitrile

(10 mL). After evaporation of the organic solvent solid sodium hy-

drogen carbonate was added in portions to adjust to pH 7. The

remaining aqueous layer containing grey precipitate was filtered

and the solid washed with water (100 mL). The solid, grey product

8a was azeotroped with toluene and dried on high vacuum. The

product was dissolved in toluene, and the precipitated byproduct

was filtered. The remaining liquid was concentrated to afford prod-

uct 4a (363 mg, 50%); m.p. 228 °C; R_f= 0.12 (hexane/EtOAc, 3:1).

¹H NMR (400 MHz, [D₆]DMSO, 25 °C): δ = 10.25 (s, 1 H), 7.96

Analytical Data of 8e: M.p. 212–213 °C; R_f= 0.41 (hexane/EtOAc,

3

5:1). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.76 (d, J_H,H

=

3

7.2 Hz, 4 H), 7.46 (t, J_H,H= 7.2 Hz, 2 H), 7.44–7.38 (m, 4 H),

3

7.32–7.21 (m, 6 H), 7.18–7.11 (m, 4 H), 7.07 (d, J_H,H= 8.0 Hz, 2

3

4

H), 6.63 (dd, J_H,H= 8.0, J_H,H= 2.1 Hz, 2 H), 6.58 (d, J_H,H

=

3

2.0 Hz, 2 H), 2.23 (t, J_H,H= 6.9 Hz, 4 H), 1.91 (quint, J_H,H

6.9 Hz, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 168.1

(C_q, 2 C), 150.0 (C_q, 2 C), 139.8 (C_q, 2 C), 139.7 (C_q, 2 C), 136.4

(C_q, 2 C), 135.9 (C_t, 2 C), 130.6 (C_t, 2 C), 129.6 (C_q, 2 C), 129.6

(C_t, 4 C), 129.3 (C_t, 4 C), 128.5 (C_t, 2 C), 128.2 (C_t, 4 C), 127.8

(C_t, 4 C), 121.3 (C_t, 2 C), 119.0 (C_t, 2 C), 33.1 (C_s, 1 C), 31.3 (C_s,

2 C) ppm. MS (EI⁺, 70 eV): m/z (%) = 554 (9), 553 (42), 552 (100),

475 (6), 276 (8), 237 (5), 199 (13).

3

(d, J_H,H= 7.2 Hz, 2 H), 7.79 (d, J_H,H= 8.7 Hz, 2 H), 7.64–7.50

3

(m, 3 H), 7.53 (d, J_H,H= 8.6 Hz, 2 H), 7.36 (d, J_H,H= 8.5 Hz, 2

H), 6.63 (d, ³J_H,H= 8.5 Hz, 2 H), 5.20 (br. s, 2 H) ppm. ¹³C NMR

(101 MHz, [D₆]DMSO, 25 °C): δ = 165.3 (C_q, 1 C), 147.9 (C_q, 1

C), 137.0 (C_q, 1 C), 136.0 (C_q, 1 C), 135.0 (C_q, 1 C), 131.4 (C_q, 1

C), 128.3 (C_t, 2 C), 127.5 (2 C, C_t), 127.1 (C_t, 1 C), 126.7 (C_t, 2

Analytical Data of 3e: R_f= 0.34 (hexane/EtOAc, 1:1, 5% NEt₃).

C), 125.2 (C , 2 C), 120.6 (C , 2 C), 114.2 (C , 2 C) ppm. IR: ν =

˜

t

3

¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.13 (d, J_H,H= 8.0 Hz,

3340 (m), 3039 (w), 1650 (s), 1604 (m), 1512 (s), 1404 (w), 1319

(w), 1265 (w), 903 (w), 810 (s), 710 (m), 648 (s) cm^–1. MS (MALDI-

TOF): m/z (%) = 288 (100).

3

4

2 H), 6.64 (dd, J_H,H= 8.0, J_H,H= 2.4 Hz, 2 H), 6.58 (d, J_H,H

=

3

2.4 Hz, 2 H), 3.62 (br. s, 4 H), 2.43 (t, J_H,H= 7.0 Hz, 4 H), 2.12

(quint, J_H,H= 7.0 Hz, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃,

3

N-(4Ј-Nitrobiphenyl-4-yl)benzamide (5a):^[45]Sodium perborate tet-

rahydrate (544 mg, 5.00 equiv., 3.54 mmol) was dissolved in concd.

acetic acid (9 mL) and heated to 60 °C. To this colourless solution

a pale brown suspension of N-(4Ј-aminobiphenyl-4-yl)benzamide

(4a) (204 mg, 1.00 equiv., 0.707 mmol) in concd. acetic acid

(14 mL) was added dropwise over a period of 35 min. Afterwards

the scarlet red suspension was stirred for 15 h at 60 °C. The pale

red suspension containing sodiumborate was cooled down to room

temp. and then the solvent was removed under reduced pressure.

The brown residue was dissolved in H₂O and EtOAc. The red or-

ganic layer was separated, the aqueous layer reextracted with

EtOAc (2ϫ30 mL). Then the combined organic layers were washed

with H₂O (1ϫ20 mL) and brine (1ϫ20 mL), dried with sodium

sulfate, filtered and the solvents evaporated to dryness. Column

chromatography with SiO₂using hexane/EtOAc (1:1) as eluent af-

forded N-(4Ј-nitrobiphenyl-4-yl)benzamide (5a) as a red-brown so-

lid. The crude was recrystallized from methanol and dried in high

vacuum for 5 h to afford product 5a (226 mg, quantitative) as a

25 °C): δ = 145.1 (C_q, 2 C), 140.5 (C_q, 2 C), 131.8 (C_q, 2 C), 128.8

(C_t, 2 C), 115.3 (C_t, 2 C), 113.2 (C_t, 2 C), 32.8 (C_s, 1 C), 31.7 (C_s,

2 C) ppm. MS (MALDI-TOF): m/z (%) = 225 (36), 224 (100).

Elemental analysis calcd. (%) for C₁₅H₁₆N₂(TFA salt): C 50.45, H

4.01, N 6.19; found C 49.68, H 4.09, N 6.28.

3,11-Diamino-6,7,8,9-tetrahydro-5H-dibenzo[a,c]cyclononene (3g):

By applying representative procedure B, ditriflate 2g (1.40 g,

1.00 equiv., 2.70 mmol) was converted to diimine 8g (930 mg,

60%), which was isolated as a yellow powder. The diimine 8g was

cleaved without further purification, to achieve diamine 3g

(391 mg, quant.) as a colourless oil. The TFA salt of 3g was ob-

tained in the same manner as the TFA salt of 3f.

Analytical Data of 8g: M.p. 146–147 °C; R_f= 0.73 (hexane/EtOAc,

1

1:1, 5% NEt₃). H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.77 (d,

3

³J_H,H= 7.1 Hz, 4 H), 7.47 (t, J_H,H= 7.2 Hz, 2 H), 7.45–7.38 (m,

3

4 H), 7.31–7.21 (m, 6 H), 7.18–7.11 (m, 4 H), 6.88 (d, J_H,H

=

3

4

8.0 Hz, 2 H), 6.63 (dd, J_H,H= 7.9, J_H,H= 2.1 Hz, 2 H), 6.47 (d,

⁴J_H,H= 2.0 Hz, 2 H), 2.40–2.29 (m, 2 H), 1.85–1.74 (m, 2 H), 1.55–

1.43 (m, 2 H), 1.17–0.97 (m, 4 H) ppm. ¹³C NMR (101 MHz,

CDCl₃, 25 °C): δ = 168.4 (C_q, 2 C), 150.4 (C_q, 2 C), 142.1 (C_q, 2

C), 139.7 (C_q, 2 C), 136.8 (C_q, 2 C), 136.5 (C_t, 2 C), 130.7 (C_t, 2

C), 129.6 (C_t, 4C), 129.3 (C_t, 4 C), 128.9 (C_t, 2 C), 128.4 (C_t, 2 C),

128.2 (C_t, 4 C), 127.8 (C_t, 4 C), 121.1 (C_t, 2 C), 118.4 (C_t, 2 C),

32.9 (C_s, 2 C), 29.0 (C_s, 2 C), 28.0 (C_s, 1 C) ppm. MS (EI⁺, 70 eV):

m/z (%) = 582 (10), 581 (45), 580 (100), 213 (9).

1

yellow solid; m.p. 257–258 °C; R_f= 0.25 (hexane/EtOAc, 3:1). H

NMR (400 MHz, [D₆]DMSO, 25 °C): δ = 10.46 (s, 1 H), 8.30 (d,

3

³J_H,H= 8.8 Hz, 2 H), 8.00–7.95 (m, 6 H), 7.84 (d, J_H,H= 8.8 Hz,

3

2 H), 7.62 (t, J_H,H= 7.2 Hz, 1 H), 7.56 (t, J_H,H= 7.2 Hz, 2 H)

ppm. ¹³C NMR (101 MHz, [D₆]DMSO, 25 °C): δ = 165.6 (C_q, 1

C), 146.1 (C_q, 1 C), 146.0 (C_q, 1 C), 140.1 (C_q, 1 C), 134.6 (C_q, 1

C), 132.4 (C_q, 1 C), 131.6 (C_t, 1 C), 128.3 (C_t, 2 C), 127.6 (C_t, 2

C), 127.5 (C_t, 2 C), 127.1 (C_t, 2 C), 124.0 (C_t, 2 C), 120.4 (C_t, 2 C)

ppm. IR: ν = 3364 (w), 1659 (s), 1589 (m), 1504 (s), 1420 (w), 1350

˜

Analytical Data of 3g: R_f= 0.42 (hexane/EtOAc, 1:1, 5% NEt₃).

(s), 1249 (w), 833 (s) cm^–1. MS (MALDI-TOF): m/z (%) = 319

3

¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 6.91 (d, J_H,H= 7.7 Hz,

(100).

2 H), 6.59–6.53 (m, 4 H), 3.62 (br. s, 4 H), 2.57–2.48 (m, 2 H),

2.14–2.10 (m, 2 H), 1.79–1.68 (m, 2 H), 1.55–1.35 (m, 4 H) ppm.

¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 145.2 (C_q, 2 C), 143.3

(C_q, 2 C), 132.7 (C_q, 2 C), 130.1 (C_t, 2 C), 115.3 (C_t, 2 C), 112.5

4Ј-Nitrobiphenyl-4-amine (6a):^[46]N-(4Ј-nitrobiphenyl-4-yl)benz-

amide (5a) (260 mg, 1.00 equiv., 0.817 mmol) was dissolved in di-

methyl sulfoxide (5 mL). To this yellow solution 10  aq. KOH

(C_t, 2 C), 33.2 (C_s, 2 C), 29.0 (C_s, 2 C), 28.2 (C_s, 1 C) ppm. MS (10 mL) and EtOH (1 mL) was added. The reaction mixture was

(MALDI-TOF): m/z (%) = 253 (28), 252 (100). Elemental analysis heated to 80 °C for 60 h, then neutralized with 1  aq. HCl (until

Eur. J. Org. Chem. 2010, 1096–1110

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1105

A. Boeglin, M. Mayor et al.

FULL PAPER

solution is pale yellow) and extracted with tert-butyl methyl ether

1

3

5% NEt₃). H NMR (400 MHz, CDCl₃, 25 °C): δ = 7.45 (d, J_H,H

3

(3ϫ70 mL), dried with sodium sulfate, filtered, and concentrated = 8.9 Hz, 2 H), 7.38 (d, J_H,H= 8.6 Hz, 2 H), 6.99 (d, J_H,H

=

3

in vacuo. The resulting oil was purified by column chromatography

(SiO₂, toluene/EtOAc, 1:1) to afford 4Ј-nitrobiphenyl-4-amine (6a)

(43.3 mg, 25%) as a dark red solid; m.p. 202–203 °C; R_f= 0.53

(toluene/EtOAc, 1:1). ¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 8.24

8.8 Hz, 2 H), 6.74 (d, J_H,H= 8.6 Hz, 4 H), 3.67 (s, 2 H), 3.19 (t,

³J_H,H= 5.5 Hz, 4 H), 1.74 (quint, ³J_H,H= 5.6 Hz, 4 H), 1.60 (quint,

³J_H,H= 5.6 Hz, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C): δ

= 150.7 (C_q, 1 C), 145.0 (C_q, 1 C), 132.1 (C_q, 1 C), 131.6 (C_q, 1

C), 127.3 (C_t, 2 C), 126.9 (C_t, 2 C), 116.7 (C_t, 2 C), 115.4 (C_t, 2

3

(d, J_H,H= 8.9 Hz, 2 H), 7.66 (d, J_H,H= 8.9 Hz, 2 H), 7.47 (d,

³J_H,H= 8.7 Hz, 2 H), 6.78 (d, J_H,H= 8.7 Hz, 2 H), 3.90 (br. s, 2 C), 50.7 (C , 2 C), 25.8 (C , 2 C), 24.3 (C , 1 C) ppm. IR: ν = 3391

3

˜

s

H) ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 147.5 (C_q, 2 C), (w), 3316 (w), 3208 (w), 3019 (w), 2930 (w), 2809 (w), 1604 (m),

147.5 (C_q, 1 C), 128.5 (C_q, 1 C), 128.4 (C_t, 2 C), 126.4 (C_t, 2 C),

124.1 (C_t, 2 C), 115.3 (C_t, 2 C) ppm. MS (MALDI-TOF): m/z (%)

= 216 (17), 215 (64), 214 (60), 198 (100).

1499 (s), 1447 (m), 1385 (m), 1333 (m), 1264 (s), 1234 (s), 1124 (s),

1023 (m), 918 (m), 803 (s), 578 (s) cm^–1. MS (MALDI-TOF): m/z

(%) = 253 (26), 252 (100). Side product: ¹H NMR (400 MHz,

3

CDCl₃, 25 °C): δ = 7.48 (d, J_H,H= 8.8 Hz, 4 H), 7.00 (d, J_H,H

=

1-(4Ј-Nitrobiphenyl-4-yl)piperidine (1a):^[50]4Ј-Nitrobiphenyl-4-

amine (6a) (20.0 mg, 1.00 equiv., 93.4 µmol) was dissolved in tolu-

ene (3.5 mL) and ethanol (3.5 mL). The orange solution was trans-

ferred to a pressure tube, and potassium carbonate (15.5 mg,

1.20 equiv., 0.112 mmol) and 1,5-dibromopentane (14.0 µL,

1.10 equiv., 0.103 mmol, 23.9 mg) were added. The reaction mix-

ture was placed in a microwave synthesis system operating at

140 °C for 1 h (3 min ramp time). Afterwards the mixture was

quenched with water (10 mL) and extracted with dichloromethane

(3ϫ15 mL). The extract was dried with sodium sulfate, filtered and

concentrated under reduced pressure. Purification was performed

by column chromatography (SiO₂, CH₂Cl₂). According to this pro-

cedure 1-(4Ј-nitrobiphenyl-4-yl)piperidine (1a) (10.5 mg, 40%) was

3

8.8 Hz, 4 H), 3.20 (t, J_H,H= 5.5 Hz, 8 H), 1.75 (quint, J_H,H

3

5.6 Hz, 8 H), 1.60 (quint, J_H,H= 5.6 Hz, 4 H) ppm. ¹³C NMR

(101 MHz, CDCl₃, 25 °C): δ = 150.8 (C_q, 2 C), 131.8 (C_q, 2 C),

126.9 (C_t, 4 C), 116.7 (C_t, 4 C), 50.6 (C_s, 4 C), 25.8 (C_s, 4 C), 24.3

(C_s, 2 C) ppm. MS (MALDI-TOF): m/z (%) = 321 (17), 320 (100).

2,2Ј-Dimethyl-4Ј-(piperidin-1-yl)biphenyl-4-amine (7b): In accord-

ance to general procedure C, 2,2Ј-dimethylbiphenyl-4,4Ј-diamine

(3b) (150 mg, 1.00 equiv., 0.707 mmol) was converted into product

7b (79.7 mg, 40%), which was isolated as a pale purple powder;

m.p. 135–136 °C; R_f= 0.60 (hexane/EtOAc, 3:1, 5% NEt₃). ¹H

3

NMR (400 MHz, CDCl₃, 25 °C): δ = 6.99 (d, J_H,H= 8.3 Hz, 1

3

4

H), 6.91 (d, J_H,H= 8.0 Hz, 1 H), 6.85 (d, J_H,H= 2.6 Hz, 1 H),

obtained as an orange solid; m.p. 220 °C; R_f= 0.69 (CH₂Cl₂). 6.80 (dd, ³J_H,H= 8.3, ⁴J_H,H= 2.6 Hz, 1 H), 6.61 (d, ⁴J_H,H= 2.5 Hz,

3

4

¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 8.24 (d, J_H,H= 9.0 Hz, 1 H), 6.55 (dd, J_H,H= 8.0, J_H,H= 2.5 Hz, 1 H), 3.61 (br. s, 2 H),

3

2 H), 7.69 (d, J_H,H= 9.0 Hz, 2 H), 7.55 (d, J_H,H= 8.9 Hz, 2 H), 3.19 (t, J_H,H= 5.6 Hz, 4 H), 2.05 (s, 3 H), 2.00 (s, 3 H), 1.75

7.00 (d, J_H,H= 8.8 Hz, 2 H), 3.28 (t, J_H,H= 5.8 Hz, 4 H), 1.76– (quint, J_H,H= 5.6 Hz, 4 H), 1.64–1.55 (m, 2 H) ppm. ¹³C NMR

1.67 (m, 4 H), 1.67–1.59 (m, 2 H) ppm. ¹³C NMR (101 MHz, (101 MHz, CDCl₃, 25 °C): δ = 145.0 (C_q, 1 C), 137.3 (C_q, 1 C),

CDCl₃, 25 °C): δ = 152.3 (C_q, 1 C), 147.4 (C_q, 1 C), 146.0 (C_q, 1 136.9 (C_q, 2 C), 132.2 (C_q, 2 C), 130.7 (C_t, 1 C), 130.5 (C_t, 1 C),

3

C), 128.1 (C_t, 2 C), 127.9 (C_q, 1 C), 126.4 (C_t, 2 C), 124.1 (C_t, 2

117.7 (C_q, 1 C), 116.3 (C_t, 1 C), 113.6 (C_t, 1 C), 112.3 (C_t, 1 C),

C), 115.8 (C_t, 2 C), 49.6 (C_s, 2 C), 25.5 (C_s, 2 C), 24.3 (C_s, 1 C) 50.8 (C_s, 2 C), 26.0 (C_s, 2 C), 24.3 (C_s, 1 C), 20.3 (C_p, 1 C), 20.0

ppm. IR: ν = 2949 (w), 2844 (w), 1589 (m), 1506 (s), 1337 (s), 1242

(C_s, 1 C) ppm. MS (MALDI-TOF): m/z (%) = 282 (4), 281 (36),

˜

(s), 1224 (s), 1111 (m), 852 (s), 756 (s) cm^–1. MS (MALDI-TOF):

m/z (%) = 283 (55), 282 (100). C₁₇H₁₈N₂O₂(282.34): calcd. C 72.32,

H 6.43, N 9.92; found C 72.02, H 6.51, N 9.93. UV/Vis (chloro-

form): λ_max(ε) = 268 nm (19840 Lmol^–1cm^–1), λ_max(ε) = 398 nm

(19646 Lmol^–1cm^–1).

280 (100).

7-(Piperidin-1-yl)-9H-fluorene-2-amine (7c): By following the syn-

thetic procedure C, from 2,7-diaminofluorene (3c) (250 mg,

1.00 equiv., 1.27 mmol) 7-(piperidin-1-yl)-9H-fluorene-2-amine (7c)

(145 mg, 43%) was obtained. Purification was performed by col-

umn chromatography (SiO₂, hexane/EtOAc, 1:1, 5% NEt₃); m.p.

186–187 °C; R_f= 0.36 (hexane/EtOAc, 1:1, 5% NEt₃). ¹H NMR

Representative Procedure C [Syntheses of 4Ј-(Piperidin-1-yl)bi-

phenyl-4-amine Derivatives 7]:^[50]Diamine 3 (1.00 equiv.) and

K₂CO₃(1.20 equiv.) were weighed into a pressure tube. 1,5-Di-

bromopentane (1.10 equiv.) was added and the mixture was dis-

solved in the according solvent system (see Table 1) (0.1  with

respect to the diamine). The reaction tube was placed in a micro-

wave-synthesis system, operated at 150 °C for 40 min. Afterwards

1  aq. HCl was added and the mixture stirred for another 30 min

at room temp. EtOAc was added and the aqueous layer was sepa-

rated. The organic layer was reextracted twice with 1  aq. HCl.

The combined aqueous layers were made alkaline by 1  aq. NaOH

and extracted with dichloromethane. The pale yellow organic layer

was dried with sodium sulfate, filtered and the solvent removed

under reduced pressure. The pale brown solid was purified by col-

umn chromatography (SiO₂; hexane/EtOAc, 3:1, 5% NEt₃) to af-

ford the product 7.

3

(400 MHz, CDCl₃, 25 °C): δ = 7.49 (d, J_H,H= 8.3 Hz, 1 H), 7.44

3

4

(d, J_H,H= 8.0 Hz, 1 H), 7.10 (d, J_H,H= 2.1 Hz, 1 H), 6.93 (dd,

³J_H,H= 8.3, J_H,H= 2.1 Hz, 1 H), 6.84 (d, J_H,H= 2.1 Hz, 1 H),

4

3

4

6.67 (dd, J_H,H= 8.0, J_H,H= 2.1 Hz, 1 H), 3.75 (s, 2 H), 3.65 (br.

3

s, 2 H), 3.16 (t, J_H,H= 5.4 Hz, 4 H), 1.74 (quint, J_H,H= 5.5 Hz,

4 H), 1.62–1.54 (m, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃,

25 °C): δ = 150.8 (C_q, 1 C), 144.5 (C_q, 1 C), 144.5 (C_q, 1 C), 143.5

(C_q, 1 C), 134.3 (C_q, 1 C), 133.4 (C_q, 1 C), 119.6 (C_t, 1 C), 118.9

(C_t, 1 C), 115.8 (C_t, 1 C), 113.8 (C_t, 2 C), 112.0 (C_t, 1 C), 51.7 (C_s,

2 C), 36.9 (C_s, 1 C), 26.0 (C_s, 2 C), 24.3 (C_s, 1 C) ppm. MS

(MALDI-TOF): m/z (%) = 266 (25), 265 (98), 264 (100). C₁₈H₂₀N₂

(264.37): calcd. C 81.78, H 7.62, N 10.60; found C 81.72, H 7.66,

N 10.37.

7-(Piperidin-1-yl)-9,10-dihydrophenanthren-2-amine (7d): The gene-

4Ј-(Piperidin-1-yl)biphenyl-4-amine (7a): From benzidine 3a

(50.0 mg, 1.00 equiv., 0.271 mmol) colourless, solid product 7a

(29.5 mg, 43%) and 4,4Ј-bis(piperidin-1-yl)biphenyl (6.3 mg) were

obtained by purification with column chromatography (SiO₂; hex-

ral procedure C was followed using 174 mg (1.00 equiv.,

0.829 mmol) 9,10-dihydrophenanthren-2,7-diamine (3d). Column

chromatography (SiO₂, hexane/EtOAc, 1:1, 5% NEt₃) was per-

formed to isolate product 7d (101 mg, 44%) as a red oil. R_f= 0.43

ane/EtOAc, 3:1, 5% NEt₃). A second column chromatography (hexane/EtOAc, 1:1, 5% NEt₃). ¹H NMR (400 MHz, CDCl₃,

3

(SiO₂, CH₂Cl₂, 3% MeOH) provided pure, colourless, solid product

7a (29.0 mg, 42%); m.p. 101–102 °C; R_f= 0.86 (hexane/EtOAc, 1:1,

25 °C): δ = 7.52 (d, J_H,H= 8.5 Hz, 1 H), 7.47 (d, J_H,H= 8.2 Hz,

3

4

1 H), 6.85 (dd, J_H,H= 8.5, J_H,H= 2.6 Hz, 1 H), 6.78 (d, J_H,H=

1106

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Eur. J. Org. Chem. 2010, 1096–1110

Variation of the Backbone Conjugation in NLO Model Compounds

3

4

2.5 Hz, 1 H), 6.61 (dd, J_H,H= 8.2, J_H,H= 2.4 Hz, 1 H), 6.54 (d,

Representative Procedure D (Mild Oxidation of Amines 7):^[53]Phos-

photungstic acid hydrate (0.45 mol-%) was dissolved in CTAB

(10 cmc, 0.02  in water) and stirred for 5 min at room temp. After-

wards, sodium perborate tetrahydrate (7.00 equiv.) was added and

⁴J_H,H= 2.3 Hz, 1 H), 3.59 (br. s, 2 H), 3.17 (t, J_H,H= 5.5 Hz, 4

3

H), 2.83–2.73 (m, 4 H), 1.72 (quint, J_H,H= 5.5 Hz, 4 H), 1.58

(quint, J_H,H= 5.5 Hz, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃,

3

25 °C): δ = 144.8 (C_q, 1 C), 137.8 (C_q, 1 C), 137.0 (C_q, 1 C), 123.9 the resulting milky, colourless solution was heated to 60 °C. Then

(C_q, 1 C), 123.3 (C_t, 2 C), 116.1 (C_q, 1 C), 115.0 (C_q, 1 C), 114.7 a warm solution of amine 7 (1.00 equiv.) in CTAB was added drop-

(C_t, 2 C), 113.7 (C_t, 2 C), 50.8 (C_s, 2 C), 29.8 (C_s, 1 C), 29.5 (C_s, 1 wise to the mixture. The cloudy, red-brown reaction mixture was

C), 25.8 (C_s, 2 C), 24.3 (C_s, 1 C) ppm. MS (MALDI-TOF): m/z

(%) = 279 (100), 278 (95).

stirred for 15 h at 60 °C and then cooled to room temp. The orange,

organic layer was extracted with tBME, washed with H₂O, dried

with anhydrous sodium sulfate, filtered and concentrated under re-

duced pressure. Purification was performed by column chromatog-

raphy (SiO₂, CH₂Cl₂/hexane, 2:1).

3-Amino-9-(piperidin-1-yl)-6,7-dihydro-5H-dibenzo[a,c]cycloheptene

(7e): By following the synthetic procedure C, using 439 mg (1.00

equiv., 1.96 mmol) diamine 3e product 7e (224 mg, 39%) was iso-

lated as a colourless oil. Purification was performed by column

chromatography (SiO₂, hexane/EtOAc, 1:1, 5% NEt₃). R_f= 0.46

(hexane/EtOAc, 1:1, 5 % NEt₃). ¹H NMR (400 MHz, CDCl₃,

1-(4Ј-Nitrobiphenyl-4-yl)piperidine (1a): The general procedure D

was followed using 2.62 mg (0.45 mol-%, 0.91 µmol) phosphotung-

stic acid hydrate in CTAB (0.6 mL, 10 cmc, 0.02 ) and 320 mg

(10.0 equiv., 2.08 mmol) sodium perborate tetrahydrate. Amine 7a

(52.0 mg, 1.00 equiv., 0.206 mmol) in CTAB (10 mL) was added

dropwise to the mixture. The cloudy, brown reaction mixture was

stirred for 15 h at 60 °C. Purification was performed by column

chromatography (SiO₂, CH₂Cl₂). According to this procedure the

red, solid target compound 1a (32.0 mg, 55%) was isolated; m.p.

3

25 °C): δ = 7.21 (d, J_H,H= 8.3 Hz, 1 H), 7.14 (d, J_H,H= 8.0 Hz,

3

4

1 H), 6.87 (dd, J_H,H= 8.4, J_H,H= 2.6 Hz, 1 H), 6.82 (d, J_H,H

=

3

4

2.6 Hz, 1 H), 6.64 (dd, J_H,H= 8.1, J_H,H= 2.5 Hz, 1 H), 6.58 (d,

⁴J_H,H= 2.4 Hz, 1 H), 3.64 (br. s, 2 H), 3.19 (t, J_H,H= 5.5 Hz, 4

3

H), 2.47 (t, J_H,H= 7.0 Hz, 2 H), 2.42 (t, J_H,H= 7.0 Hz, 2 H),

2.13 (quint, J_H,H= 7.0 Hz, 2 H), 1.77–1.69 (m, 4 H), 1.62–1.54

3

(m, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 145.1 (C_q,

1 C), 140.6 (C_q, 1 C), 140.1 (C_q, 2 C), 131.7 (C_q, 1 C), 128.8 (C_q,

1 C), 128.4 (C_q, 2 C), 116.7 (C_t, 1 C), 115.2 (C_t, 1 C), 114.3 (C_t, 1

C), 113.1 (C_t, 1 C), 50.9 (C_s, 2 C), 32.9 (C_s, 1 C), 32.1 (C_s, 1 C),

31.7 (C_s, 1 C), 25.9 (C_s, 2 C), 24.2 (C_s, 1 C) ppm. MS (MALDI-

TOF): m/z (%) = 293 (62), 292 (100).

1

220 °C; R_f= 0.71 (CH₂Cl₂). H NMR (400 MHz, CDCl₃, 25 °C):

3

δ = 8.24 (d, J_H,H= 9.0 Hz, 2 H), 7.68 (d, J_H,H= 9.0 Hz, 2 H),

3

7.55 (d, J_H,H= 8.9 Hz, 2 H), 7.00 (d, J_H,H= 8.9 Hz, 2 H), 3.28

3

(t, J_H,H= 5.5 Hz, 4 H), 1.77–1.68 (m, 4 H), 1.67–1.60 (m, 2 H)

ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 152.3 (C_q, 1 C),

147.4 (C_q, 1 C), 146.0 (C_q, 1 C), 128.1 (C_t, 2 C), 127.9 (C_q, 1 C),

126.4 (C_t, 2 C), 124.1 (C_t, 2 C), 115.8 (C_t, 2 C), 49.6 (C_s, 2 C), 25.5

3-Amino-10-(piperidin-1-yl)-5,6,7,8-tetrahydrodibenzo[a,c]cyclooct-

ene (7f): By applying general procedure C, diamine 3f (581 mg,

1.00 equiv., 2.44 mmol) was converted into product 7f (308 mg,

41%), which was isolated as a colourless oil. Purification was per-

formed by column chromatography (SiO₂, hexane/EtOAc, 1:1, 5%

NEt₃). R_f= 0.31 (hexane/EtOAc, 3:1, 5 % NEt₃). ¹H NMR

(C , 2 C), 24.3 (C , 1 C) ppm. IR: ν = 2949 (w), 2844 (w), 1589

˜

s

(m), 1506 (s), 1337 (s), 1242 (s), 1224 (s), 1111 (m), 852 (s), 756 (s)

cm^–1. MS (MALDI-TOF): m/z (%)

=

283 (55), 282 (100).

C₁₇H₁₈N₂O₂(282.34): calcd. C 72.32, H 6.43, N 9.92; found C

72.02, H 6.51, N 9.93.

3

(400 MHz, CDCl₃, 25 °C): δ = 7.10 (d, J_H,H= 8.2 Hz, 1 H), 7.03

1-(2,2Ј-Dimethyl-4Ј-nitrobiphenyl-4-yl)piperidine (1b): By following

the general procedure D 2,2Ј-dimethyl-4Ј-(piperidin-1-yl)biphenyl-

4-amine (7b) (50.0 mg, 1.00 equiv., 0.178 mmol) in CTAB (15 mL)

was added dropwise to a warmed mixture of phosphotungstic acid

hydrate (1.57 mg, 0.45 mol-%, 0.545 µmol) in CTAB (0.4 mL,

10 cmc, 0.02 ) and sodium perborate tetrahydrate (192 mg,

7.00 equiv., 1.25 mmol). The pale yellow reaction mixture was

stirred for 15 h at 60 °C. Column chromatography (SiO₂, CH₂Cl₂)

provided the solid, yellow target compound 1b (35.6 mg, 64%);

m.p. 116–117 °C; R_f= 0.69 (CH₂Cl₂). ¹H NMR (400 MHz, CDCl₃,

3

4

(d, J_H,H= 7.9 Hz, 1 H), 6.86–6.79 (m, 2 H), 6.60 (d, J_H,H

=

3

4

2.3 Hz, 1 H), 6.58 (dd, J_H,H= 7.9, J_H,H= 2.4 Hz, 1 H), 3.62 (br.

s, 2 H), 3.19 (t, J_H,H= 5.5 Hz, 4 H), 2.68–2.52 (m, 2 H), 2.22–

1.96 (m, 4 H), 1.73 (quint, J_H,H= 5.5 Hz, 2 H), 1.63–1.54 (m, 2

3

H), 1.54–1.44 (m, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C):

δ = 151.5 (C_q, 1 C), 145.5 (C_q, 1 C), 143.8 (C_q, 1 C), 143.3 (C_q, 1

C), 132.0 (C_q, 1 C), 131.5 (C_q, 1 C), 130.0 (C_t, 1 C), 129.7 (C_t, 1

C), 117.0 (C_t, 1 C), 115.7 (C_t, 1 C), 113.8 (C_t, 1 C), 112.7 (C_t, 1

C), 50.7 (C_s, 2 C), 33.4 (C_s, 1 C), 32.9 (C_s, 1 C), 29.8 (C_s, 1 C), 29.7

(C_s, 1 C), 26.0 (C_s, 2 C), 24.3 (C_s, 1 C) ppm. MS (MALDI-TOF):

m/z (%) = 308 (13), 307 (26), 306 (100).

4

3

25 °C): δ = 8.13 (d, J_H,H= 2.4 Hz, 1 H), 8.05 (dd, J_H,H= 8.4,

3

⁴J_H,H= 2.4 Hz, 1 H), 7.26 (d, J_H,H= 8.3 Hz, 1 H), 6.93 (d, J_H,H

= 8.3 Hz, 1 H), 6.87–6.85 (m, 1 H), 6.85–6.80 (m, 1 H), 3.21 (t,

³J_H,H= 5.6 Hz, 4 H), 2.17 (s, 3 H), 2.01 (s, 3 H), 1.78–1.69 (m, 4

H), 1.64–1.58 (m, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C):

δ = 151.7 (C_q, 1 C), 149.0 (C_q, 1 C), 146.8 (C_q, 1 C), 138.5 (C_q, 2

C), 135.7 (C_q, 1 C), 130.8 (C_t, 1 C), 129.2 (C_t, 1 C), 124.5 (C_t, 1

C), 120.6 (C_t, 1 C), 117.5 (C_t, 1 C), 113.5 (C_t, 1 C), 50.3 (C_s, 2 C),

25.8 (C_s, 2 C), 24.3 (C_s, 1 C), 20.1 (C_p, 1 C), 20.0 (C_p, 1 C) ppm.

MS (MALDI-TOF): m/z (%) = 310 (100). C₁₉H₂₂N₂O₂(310.40):

calcd. C 73.52, H 7.14, N 9.03; found C 73.41, H 7.20, N 8.77. UV/

Vis (chloroform): λ_max(ε) = 270 nm (17598 Lmol^–1cm^–1), λ_max(ε)

= 354 nm (3003 Lmol^–1cm^–1).

3-Amino-11-(piperidin-1-yl)-6,7,8,9-tetrahydro-5H-dibenzo[a,c]cyclo-

nonene (7g): The general procedure C was followed using 363 mg

(1.00 equiv., 1.44 mmol) diamine 3g. Column chromatography

(SiO₂, hexane/EtOAc, 3:1, 5% NEt₃) was performed to isolate

product 7g (154 mg, 34%) and diazacycloalkylated side product

(43.2 mg, 8%). R_f= 0.30 (hexane/EtOAc, 3:1, 5% NEt₃). ¹H NMR

3

(400 MHz, CDCl₃, 25 °C): δ = 6.99 (d, J_H,H= 8.9 Hz, 1 H), 6.92

3

(d, J_H,H= 7.8 Hz, 1 H), 6.83–6.77 (m, 2 H), 6.59–6.53 (m, 2 H),

3

3.48 (br. s, 2 H), 3.17 (t, J_H,H= 5.5 Hz, 4 H), 2.62–2.54 (m, 1 H),

2.54–2.46 (m, 1 H), 2.16–2.04 (m, 2 H), 1.81–1.64 (m, 6 H), 1.62–

1.54 (m, 2 H), 1.54–1.43 (m, 2 H), 1.43–1.34 (m, 2 H) ppm. ¹³C

NMR (101 MHz, CDCl₃, 25 °C): δ = 151.4 (C_q, 1 C), 145.3 (C_q, 1

C), 143.2 (C_q, 1 C), 142.9 (C_q, 1 C), 133.3 (C_q, 1 C), 132.9 (C_q, 1 1-(7-Nitro-9,10-dihydrophenanthren-2-yl)piperidine (1d): Following

C), 130.0 (C_t, 1 C), 129.8 (C_t, 1 C), 116.8 (C_t, 1 C), 115.3 (C_t, 1

C), 113.6 (C_t, 1 C), 112.5 (C_t, 1 C), 50.8 (C_s, 2 C), 33.8 (C_s, 1 C),

33.1 (C_s, 1 C), 29.1 (C_s, 2 C), 28.3 (C_s, 1 C), 26.0 (C_s, 2 C), 24.3

the general procedure D using 2.94 mg (0.45 mol-%, 1.02 µmol)

phosphotungstic acid hydrate in CTAB (0.7 mL, 10 cmc, 0.02 ).

After adding sodium perborate tetrahydrate (360 mg, 7.00 equiv.,

(C_s, 1 C) ppm. MS (MALDI-TOF): m/z (%) = 322 (2), 321 (25), 2.34 mmol) the temperature was raised to 60 °C. Amine 7d

320 (100).

(93.0 mg, 1.00 equiv., 0.334 mmol) in CTAB (20 mL) was added

Eur. J. Org. Chem. 2010, 1096–1110

www.eurjoc.org

1107

A. Boeglin, M. Mayor et al.

FULL PAPER

dropwise to the mixture. The red reaction mixture was stirred for

17 h at 60 °C. Column chromatography (SiO₂, CH₂Cl₂) was used

for purification. According to this procedure the solid, red target

120.7 (C_t, 1 C), 116.7 (C_t, 1 C), 113.6 (C_t, 1 C), 50.1 (C_s, 2 C), 33.1

(C_s, 1 C), 32.8 (C_s, 1 C), 29.5 (C_s, 1 C), 29.0 (C_s, 1 C), 25.8 (C_s, 2

C), 24.3 (C_s, 1 C) ppm. MS (EI⁺, 70 eV): m/z (%) = 337 (24), 336

(100), 335 (42), 289 (5). C₂₁H₂₄N₂O₂(336.43): calcd. C 74.97, H

compound 1d (57.4 mg, 56%) was isolated; m.p. 114–115 °C; R_f=

1

0.61 (CH₂Cl₂). H NMR (400 MHz, CDCl₃, 25 °C): δ = 8.08 (dd, 7.19, N 8.33; found C 74.55, H 7.13, N 8.23. UV/Vis (chloroform):

4

³J_H,H= 8.6, J_H,H= 2.4 Hz, 1 H), 8.04 (d, J_H,H= 2.3 Hz, 1 H), λ_max(ε) = 271 nm (20019 Lmol^–1cm^–1), λ_max(ε) = 370 nm (7551

3

7.69 (d, J_H,H= 8.6 Hz, 1 H), 7.64 (d, J_H,H= 8.7 Hz, 1 H), 6.86

Lmol^–1cm^–1).

3

4

(dd, J_H,H= 8.7, J_H,H= 2.4 Hz, 1 H), 6.77 (d, J_H,H= 2.4 Hz, 1

H), 3.29 (t, ³J_H,H= 5.7 Hz, 4 H), 2.96–2.82 (m, 4 H), 1.75–1.66 (m,

4 H), 1.66–1.59 (m, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃,

25 °C): δ = 152.4 (C_q, 1 C), 145.2 (C_q, 1 C), 141.6 (C_q, 1 C), 139.3

(C_q, 2 C), 136.9 (C_q, 1 C), 125.9 (C_t, 1 C), 123.1 (C_t, 1 C), 122.7

(C_t, 1 C), 122.4 (C_t, 1 C), 114.5 (C_t, 1 C), 114.1 (C_t, 1 C), 49.4 (C_s,

2 C), 29.2 (C_s, 1 C), 29.0 (C_s, 1 C), 25.5 (C_s, 2 C), 24.3 (C_s, 1 C)

ppm. MS (MALDI-TOF): m/z (%) = 309 (11), 308 (43), 307 (100).

C₁₉H₂₀N₂O₂(308.38): calcd. C 74.00, H 6.54, N 9.08; found C

73.63, H 6.61, N 9.03. UV/Vis (chloroform): λ_max(ε) = 274 nm

(14713 Lmol^–1cm^–1), λ_max(ε) = 416 nm (20782 Lmol^–1cm^–1).

3-Nitro-11-(piperidin-1-yl)-6,7,8,9-tetrahydro-5H-dibenzo[a,c]cyclo-

nonene (1g): In accordance to the general procedure D 3.76 mg

(0.45 mol-%, 4.27 µmol) phosphotungstic acid hydrate in CTAB

(1 mL, 10 cmc, 0.02 ) and 460 mg (7.00 equiv., 2.99 mmol) sodium

perborate tetrahydrate were used. Amine 7g (137 mg, 1.00 equiv.,

0.427 mmol) in CTAB (33 mL) was added dropwise to the mixture

at 60 °C. The orange-yellow reaction mixture was stirred for 15 h

at 60 °C. By column chromatography (SiO₂, CH₂Cl₂/hexane, 2:1)

the crude was purified to achieve the push-pull system 1g (75 mg,

50%) as a yellow solid; m.p. 125–126 °C; R_f= 0.44 (CH₂Cl₂/hex-

1

4

ane, 2:1). H NMR (400 MHz, CDCl₃, 25 °C): δ = 8.10 (d, J_H,H

3

4

3-Nitro-9-(piperidin-1-yl)-6,7-dihydro-5H-dibenzo[a,c]cycloheptene

(1e): In accordance to the general procedure D 6.20 mg (0.45 mol-

%, 7.15 µmol) phosphotungstic acid hydrate in CTAB (0.2 mL,

10 cmc, 0.02 ) and 771 mg (7.00 equiv., 5.01 mmol) sodium perbo-

rate tetrahydrate were used. Amine 7e (209 mg, 1.00 equiv.,

0.715 mmol) in CTAB (14 mL) was added dropwise to the mixture

at 60 °C. The red reaction mixture was stirred for 15 h at 60 °C. By

column chromatography (SiO₂, CH₂Cl₂) the crude was purified to

achieve the push-pull system 1e (135 mg, 59%) as a dark red solid;

m.p. 109–110 °C; R_f= 0.58 (CH₂Cl₂). ¹H NMR (400 MHz, CDCl₃,

= 1.9 Hz, 1 H), 8.05 (dd, J_H,H= 8.3, J_H,H= 1.9 Hz, 1 H), 7.30

3

(d, J_H,H= 8.3 Hz, 1 H), 6.96 (d, J_H,H= 7.9 Hz, 1 H), 6.88–6.80

(m, 2 H), 3.22 (t, J_H,H= 5.3 Hz, 4 H), 2.76–2.59 (m, 2 H), 2.30–

3

2.20 (m, 1 H), 1.97–1.70 (m, 7 H), 1.66–1.28 (m, 6 H) ppm.

¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 152.2 (C_q, 1 C), 149.6

(C_q, 1 C), 147.2 (C_q, 1 C), 144.3 (C_q, 1 C), 141.8 (C_q, 1 C), 130.7

(C_q, 1 C), 130.3 (C_t, 1 C), 128.8 (C_t, 1 C), 123.6 (C_t, 1 C), 120.6

(C_t, 1 C), 116.6 (C_t, 1 C), 113.7 (C_t, 1 C), 50.4 (C_s, 2 C), 33.7 (C_s,

1 C), 33.2 (C_s, 1 C), 28.9 (C_s, 1 C), 28.8 (C_s, 1 C), 28.2 (C_s, 1 C),

25.9 (C_s, 2 C), 24.3 (C_s, 1 C) ppm. MS (MALDI-TOF): m/z (%) =

351 (10), 350 (18), 336 (26), 235 (43), 321 (86), 320 (45), 319 (100).

C₂₂H₂₅N₂O₂(349.45): calcd. C 75.40, H 7.48, N 7.99; found C

75.12, H 7.42, N 7.79. UV/Vis (chloroform): λ_max(ε) = 269 nm

(18523 Lmol^–1cm^–1), λ_max(ε) = 351 nm (3019 Lmol^–1cm^–1).

3

4

25 °C): δ = 8.16 (dd, J_H,H= 8.4, J_H,H= 2.4 Hz, 1 H), 8.09 (d,

⁴J_H,H= 2.4 Hz, 1 H), 7.45 (d, J_H,H= 8.4 Hz, 1 H), 7.27 (d, J_H,H

= 8.6 Hz, 1 H), 6.92 (dd, J_H,H= 8.5, J_H,H= 2.5 Hz, 1 H), 6.84

3

4

3

(d, J_H,H= 2.4 Hz, 1 H), 3.27 (t, J_H,H= 5.5 Hz, 4 H), 2.59 (t,

³J_H,H= 7.0 Hz, 2 H), 2.46 (t, J_H,H= 7.0 Hz, 2 H), 2.23 (quint,

3

2-Nitro-9H-fluorene (9): Compound 9 was synthesized according to

a literature procedure.^[64]Yield 15% (colourless solid); m.p. 162 °C;

R_f= 0.39 [hexane/ethyl acetate (5:1)]. ¹H NMR (400 MHz, CDCl₃,

³J_H,H= 7.0 Hz, 2 H), 1.77–1.69 (m, 4 H), 1.66–1.58 (m, 2 H) ppm.

¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 152.4 (C_q, 1 C), 148.6

(C_q, 1 C), 146.2 (C_q, 1 C), 140.8 (C_q, 1 C), 140.5 (C_q, 1 C), 129.3

(C_t, 1 C), 129.1 (C_q, 1 C), 128.4 (C_t, 1 C), 123.5 (C_t, 1 C), 121.8

(C_t, 1 C), 115.9 (C_t, 1 C), 113.8 (C_t, 1 C), 49.9 (C_s, 2 C), 32.9 (C_s,

1 C), 31.8 (C_s, 1 C), 31.7 (C_s, 1 C), 25.7 (C_s, 2 C), 24.3 (C_s, 1

C) ppm. MS (EI⁺, 70 eV): m/z (%) = 323 (24), 322 (100), 321 (51),

275 (6), 191 (7). C₂₀H₂₂N₂O₂(322.41): calcd. C 74.51, H 6.88, N

8.69; found C 74.41, H 6.90, N 8.43. UV/Vis (chloroform): λ_max

(ε) = 269 nm (17538 Lmol^–1cm^–1), λ_max(ε) = 388 nm (12074

Lmol^–1cm^–1).

4

3

25 °C): δ = 8.40 (d, J_H,H= 2.0 Hz, 1 H), 8.30 (dd, J_H,H= 8.4,

⁴J_H,H= 2.0 Hz, 1 H), 7.89–7.86 (m, 2 H), 7.63–7.61 (m, 1 H), 7.48–

7.41 (m, 2 H), 4.01 (s, 2 H) ppm. ¹³C NMR (101 MHz, CDCl₃,

25 °C): δ = 148.0 (C_q, 2 C), 144.8 (C_q, 1 C), 143.9 (C_q, 1 C), 139.4

(C_q, 1 C), 128.8 (C_t, 1 C), 127.4 (C_t, 1 C), 125.4 (C_t, 1 C), 123.1

(C_t, 1 C), 121.3 (C_t, 1 C), 120.5 (C_t, 1 C), 119.8 (C_t, 1 C), 37.0 (C_s,

1 C) ppm. MS (EI⁺, 70 eV): m/z (%) = 212 (10), 211 (68), 194 (26),

166 (13), 165 (100), 164 (41), 163 (30).

7-Iodo-2-nitro-9H-fluorene (10): Compound 10 was synthesized ac-

cording to a literature procedure.^[65]Yield 76% (yellow powder). R_f

3-Nitro-10-(piperidin-1-yl)-5,6,7,8-tetrahydrodibenzo[a,c]cyclooctene

(1f): In accordance to the general procedure D 8.71 mg (0.45 mol-

%, 9.89 µmol) phosphotungstic acid hydrate in CTAB (2.3 mL,

10 cmc, 0.02 ) and 1.07 g (7.00 equiv., 6.93 mmol) sodium perbo-

rate tetrahydrate were used. Amine 7f (303 mg, 1.00 equiv.,

0.989 mmol) in CTAB (80 mL) was added dropwise to the mixture

at 60 °C. The orange reaction mixture was stirred for 15 h at 60 °C.

By column chromatography (SiO₂, CH₂Cl₂/hexane, 2:1) the crude

was purified to achieve the push-pull system 1f (149 mg, 45%) as

an orange solid; m.p. 124–125 °C; R_f= 0.34 (CH₂Cl₂/hexane, 2:1).

1

= 0.56 (hexane/EtOAc, 3:1). H NMR (400 MHz, CDCl₃, 25 °C):

3

δ = 8.40 (s, 1 H), 8.31 (d, J_H,H= 8.4 Hz, 1 H), 7.99 (s, 1 H), 7.85

3

(d, J_H,H= 8.4 Hz, 1 H), 7.79 (d, J_H,H= 8.3 Hz, 1 H), 7.61 (d,

³J_H,H= 8.1 Hz, 1 H), 3.99 (s, 2 H) ppm. ¹³C NMR (101 MHz,

CDCl₃, 25 °C): δ = 147.1 (C_q, 2 C), 146.7 (C_q, 1 C), 143.4 (C_q, 1

C), 139.0 (C_q, 1 C), 136.5 (C_t, 1 C), 134.7 (C_t, 1 C), 123.3 (C_t, 1

C), 122.7 (C_t, 1 C), 120.5 (C_t, 1 C), 120.1 (C_t, 1 C), 94.8 (C_q, 1 C),

36.6 (C_s, 1 C) ppm. MS (MALDI-TOF): m/z (%) = 338 (11), 337

(100).

4

¹H NMR (400 MHz, CDCl₃, 25 °C): δ = 8.14 (d, J_H,H= 2.4 Hz,

3

4

3

1 H), 8.06 (dd, J_H,H= 8.4, J_H,H= 2.4 Hz, 1 H), 7.37 (d, J_H,H

=

7-Iodo-9,9-dimethyl-2-nitro-9H-fluorene (11):^[56]7-Iodo-2-nitrofluor-

ene (10) (200 mg, 1.00 equiv., 0.593 mmol), iodomethane (80.0 µL,

2.05 equiv., 1.22 mmol, 173 mg) and potassium iodide (10.8 mg,

0.110 equiv., 653 µmol) were dissolved in dimethyl sulfoxide (2 mL)

3

8.4 Hz, 1 H), 7.10 (d, J_H,H= 9.2 Hz, 1 H), 6.86–6.83 (m, 2 H),

3.24 (t, ³J_H,H= 5.5 Hz, 4 H), 2.81 (dd, ³J_H,H= 8.2, ²J_H,H= 13.3 Hz,

3

2

1 H), 2.69 (dd, J_H,H= 8.2, J_H,H= 13.4 Hz, 1 H), 2.30–2.20 (m,

1 H), 2.19–1.94 (m, 3 H), 1.79–1.70 (m, 4 H), 1.66–1.49 (m, 4 H) under argon. Powdered potassium hydroxide (141 mg, 4.25 equiv.,

ppm. ¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 152.5 (C_q, 1 C),

2.52 mmol) was added in 15 portions to the solution. The green

147.8 (C_q, 1 C), 147.1 (C_q, 1 C), 144.3 (C_q, 1 C), 143.0 (C_q, 1 C), reaction mixture was stirred at room temp. for 1 h and quenched

130.0 (C_t, 1 C), 129.4 (C_t, 1 C), 129.2 (C_q, 1 C), 124.2 (C_t, 1 C), with water. After extraction with dichloromethane (3ϫ50 mL), the

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Eur. J. Org. Chem. 2010, 1096–1110

Variation of the Backbone Conjugation in NLO Model Compounds

combined organic layers were dried with sodium sulfate, filtered

and concentrated. The resulting solid was purified by column

chromatography (SiO₂, hexane/EtOAc, 5:1) to afford 7-iodo-9,9-

dimethyl-2-nitrofluorene (11) (205 mg, 95%) as a yellow solid; m.p.

2 C), 24.3 (C_s, 1 C) ppm. MS (MALDI-TOF): m/z (%) = 283 (55),

282 (100).

1

215–216 °C; R_f= 0.62 (hexane/EtOAc, 3:1). H NMR (400 MHz,

Acknowledgments

4

CDCl₃, 25 °C): δ = 8.29–8.24 (m, 2 H), 7.84 (d, J_H,H= 1.2 Hz, 1

3

4

H), 7.79 (d, J_H,H= 8.1 Hz, 1 H), 7.75 (dd, J_H,H= 8.0, J_H,H

=

The authors acknowledge the Swiss National Science Foundation

(SNSF) and the National Center of Competence in Research

“Nanoscale Science” for financial support. We also thank Lukas

Jundt and Nicola Polimene for the synthetic support during their

laboratory course.

3

1.5 Hz, 1 H), 7.54 (d, J_H,H= 8.0 Hz, 1 H), 1.53 (s, 6 H) ppm.

¹³C NMR (101 MHz, CDCl₃, 25 °C): δ = 157.0 (C_q, 1 C), 154.0

(C_q, 1 C), 147.6 (C_q, 1 C), 144.7 (C_q, 1 C), 136.7 (C_t, 1 C), 136.4

(C_q, 1 C), 132.5 (C_t, 1 C), 123.5 (C_t, 1 C), 122.9 (C_t, 1 C), 120.3

(C_t, 1 C), 118.3 (C_t, 1 C), 95.5 (C_q, 1 C), 47.5 (C_q, 1 C), 26.6 (C_p,

2 C) ppm. MS (EI⁺, 70 eV): m/z (%) = 366 (16), 265 (100), 350

(64), 304 (15), 177 (18), 176 (25).

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1-(9,9-Dimethyl-7-nitro-9H-fluorene-2-yl)piperidine (1c):^[47]To

a

pale yellow solution of 7-iodo-9,9-dimethyl-2-nitro-9H-fluorene

(11) (140 mg, 1.00 equiv., 0.383 mmol) in dimethyl sulfoxide

(2 mL), piperidine (0.170 mL, 4.40 equiv., 1.69 mmol, 144 mg), cae-

sium acetate (174 mg, 2.37 equiv., 0.909 mmol) and copper iodide

(3.65 mg, 5 mol-%, 19.2 µmol) were added. The red-brown reaction

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4

= 8.22–8.19 (m, 2 H), 7.66–7.60 (m, 2 H), 6.98 (d, J_H,H= 2.1 Hz,

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3

1 H), 6.94 (dd, J_HH= 8.5, J_H,H= 2.2 Hz, 1 H), 3.31 (t, J_H,H

=

5.6 Hz, 4 H), 1.75 (quint, ³J_H,H= 5.5 Hz, 4 H), 1.67–1.60 (m, 2 H),

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(C_q, 1C), 153.8 (C_q, 1 C), 153.4 (C_q, 1 C), 146.5 (C_q, 1 C), 145.7

(C_q, 1 C), 127.4 (C_q, 1 C), 123.6 (C_t, 1 C), 122.3 (C_t, 1 C), 118.4

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307 (12), 293 (57), 292 (100). C₂₀H₂₂N₂O₂(322.41): calcd. C 74.51,

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³J_H,H= 9.0 Hz, 2 H), 7.68 (d, J_H,H= 9.0 Hz, 2 H), 7.55 (d, J_H,H

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= 8.9 Hz, 2 H), 7.00 (d, J_H,H= 8.9 Hz, 2 H), 3.28 (t, J_H,H

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5.5 Hz, 4 H), 1.77–1.68 (m, 4 H), 1.67–1.60 (m, 2 H) ppm.

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Received: November 24, 2009

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Article Doi

Variation of the backbone conjugation in NLO model compounds: Torsion-angle-restricted, biphenyl-based push-pull-systems

DOI: 10.1002/ejoc.200901358

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