Chiral and achiral charge-transfer chromophores with a dendralene-type backbone by electronically controlled Cycloaddition/Cycloreversion Cascades

FULL PAPER

DOI: 10.1002/ejoc.201000030

Chiral and Achiral Charge-Transfer Chromophores with a Dendralene-Type

Backbone by Electronically Controlled Cycloaddition/Cycloreversion Cascades

Brian B. Frank,^[a]Milan Kivala,^[a]Berta Camafort Blanco,^[a]Benjamin Breiten,^[a]

W. Bernd Schweizer,^[a]Philip R. Laporta,^[b]Ivan Biaggio,^[b]Eike Jahnke,^[c]

Rik R. Tykwinski,^[c]Corinne Boudon,^[d]Jean-Paul Gisselbrecht,^[d]and François Diederich*^[a]

Keywords: Alkynes / Charge transfer / Chirality / Conjugation / Cycloaddition / Cascade reactions

Chiral and achiral push-pull chromophores have been pre-

mers were measured to investigate whether a preferred con-

pared by cascades of sequential [2+2] cycloadditions of tetra- formation of the dendralene-type backbone is induced by the

cyanoethene (TCNE) and tetrathiafulvalene (TTF) to dif-

ferent oligoynes. Thermal [2+2] cycloaddition of TCNE to do-

optically active 1,1Ј-binaphthalene moiety. Electrochemical

studies by cyclic voltammetry (CV) and rotating-disk voltam-

nor-substituted alkynes, followed by electrocyclic ring-open- metry (RDV) showed large cathodic shifts of the first oxi-

ing of the initially formed cyclobutenes, affords donor-substi-

tuted 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs). Similarly,

TTF reacts with electron-deficient CϵC bonds to give the

corresponding buta-1,3-diene derivatives, 1,2-bis(1,3-dithiol-

2-ylidene)ethanes. Thus, achiral [AB]-type oligomers were

synthesized from N,N-dialkylanilino (DAA)-substituted tet-

raynes and hexaynes and chiral [AB]-type oligomers from al-

kyne-substituted 1,1Ј-binaphthalenes. The [AB]-type oligo-

mers exhibit complex conformational equilibria in solution,

as revealed by ¹H and ¹³C NMR spectroscopy. Therefore, the

circular dichroism (CD) spectra of the chiral [AB]-type oligo-

dation potentials for some of the chiral and achiral [AB]-type

oligomers due to sterically enforced π-deconjugation of the

acceptor and donor moieties. The new multivalent systems

feature intense, bathochromically shifted intramolecular

charge-transfer (CT) bands in the UV/Vis spectra. Extended,

donor-substituted TCBDs, which are obtained by mono-ad-

dition of TCNE to the hexaynes, exhibit low optical and elec-

trochemical HOMO–LUMO gaps. In addition, a large third-

order optical nonlinearity was measured for one of these

TCBDs by degenerate four-wave mixing (DFWM).

derivatives,^[14,15]with formation of non-planar donor-ac-

ceptor (D-A) chromophores with intense intramolecular

charge-transfer (CT) interactions.^[16]Some of the N,N-di-

methylanilino (DMA)-substituted TCBDs exhibit high

third-order polarizability,^[3]and one of them {DDMEBT,

2-[4-(dimethylamino)phenyl]-3-[(4-dimethylamino)phenyl]-

ethynylbuta-1,3-diene-1,1,4,4-tetracarbonitrile} was shown

to form high-optical-quality, homogeneous thin films by

vapor-phase deposition.^[17]These films have found first ap-

plications as materials for integrated nonlinear optics

(NLO).^[18,19]In addition, TCBDs substituted with chiral,

N-arylated dinaphthazepine donors have been used as dop-

ants in nematic liquid crystals (LCs) featuring high helical

twisting powers (HTP).^[20]

Hopf et al. showed that a similar cycloaddition reaction

also occurs under the conditions of inverse electron de-

mand. They reported that the strong electron donor tetra-

thiafulvalene (TTF) reacts with electron-deficient CϵC

bonds in cyanoethynylethenes to give the corresponding

butadiene derivatives, 1,2-bis(1,3-dithiol-2-ylidene)ethanes.^[21]

This transformation has also been described by Hirsch and

co-workers for α,ω-dicyanopolyynes.^[22]A related cycload-

dition/cycloreversion involving electron-deficient alkynes

was reported earlier by Dolbier and co-workers.^[23]Re-

Introduction

The thermal [2+2] cycloaddition of tetracyanoethene

(TCNE) to N,N-dialkylanilino (DAA)-substituted alkynes,

followed by electrocyclic ring-opening of the initially

formed cyclobutenes, has the character of a “click”-reac-

tion, affording DAA-substituted 1,1,4,4-tetracyanobuta-

1,3-dienes (TCBDs) in an atom-economic way and with

near quantitative yields without the need for catalysis.^[1–8]

Donor-substituted alkynes also react with other electron-

accepting olefins, such as 7,7,8,8-tetracyanoquinodimeth-

anes (TCNQs),^[9–13]dicyanovinyl (DCV) and tricyanovinyl

[a] Laboratorium für Organische Chemie, ETH Zürich,

Hönggerberg, HCI, 8093 Zürich, Switzerland

Fax: +41-44-632-1109

E-mail: diederich@org.chem.ethz.ch

[b] Lehigh University, Department of Physics, 415 Lewis Lab,

16 Memorial Dr. East, Bethlehem, PA 18015, USA

[c] Institut für Organische Chemie, Friedrich-Alexander-Uni-

versität, Erlangen-Nürnberg,

Henkestrasse 42, 91054 Erlangen, Germany

[d] Laboratoire d’Electrochimie et de Chimie Physique du Corps

Solide, UMR 7177 C.N.R.S, Université de Strasbourg,

4, rue Blaise Pascal, 67000 Strasbourg, France

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejoc.201000030.

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Figure 1. Conjugated [AB]-type oligomers and their oligoyne precursors.

cently, we combined the two electronically controlled cyclo- A-D-A system 3, it was expected that the last, “electroni-

addition reactions in a cascade of successive TCNE and cally confused” triple bond in 10 and 11 will not react with

TTF additions to end-capped tetraynes 1 and 2 (Fig- TTF or TCNE.

ure 1).^[24]After the first [2+2] cycloaddition of 1 and 2 with

TCNE to give the corresponding TCBDs, the CϵC bond

next to the TCBD moiety is sufficiently electron-deficient

to undergo [2+2] cycloaddition with TTF in good yield.

The regioselectivity of the next TCNE addition is deter-

mined by the 1,2-bis(1,3-dithiol-2-ylidene)ethane donor

unit to give the A-D-A systems 3 and 4 in good to excellent

yields (Figure 1). The remaining triple bond in 3 is not suf-

ficiently electron-deficient to undergo [2+2] cycloaddition

to TTF, whereas 4 reacted with TTF to give the [AB]-type

oligomer 5 in 21% yield. The last CC triple bond in 4 is

electron-deficient, while the one in 3 is “electronically con-

fused”, because of the substitution by both a donor (DMA)

and an acceptor moiety (TCBD). Finally, a one-pot proto-

col for the cascade of successive TCNE/TTF cycloadditions

to tetrayne 2 was shown to give 5 in 21% overall yield.

From these results, we anticipated that replacing the phenyl

moiety in 2 by an activating 4-cyanophenyl moiety in tet-

rayne 6 should lead to even higher yields in the one-pot

cycloaddition cascade (Figure 1). We expected the new

[AB]-type oligomer 7 as the sole product from this entirely

electronically controlled transformation.

The N,N-dihexylanilino (DHA)-substituted hexayne 8

was recently obtained as a side product in the synthesis of

new D-A-substituted oligoynes, which will be published

elsewhere.^[25]Together with its N,N-diisopropylanilino-sub-

stituted analogue 9, oligoyne 8 is used here to synthesize

the new extended [AB]-type oligomers 10 and 11 by a cas-

cade of successive TCNE and TTF additions. Similar to the [AB]-type oligomers (R)-13 and (S)-14.

Figure 2. D-A-substituted 1,3-diethynylallene (M)-12,^[26]and chiral

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Charge-Transfer Chromophores with a Dendralene-Type Backbone

Complex conformational equilibria were observed for BINOL] according to a published procedure.^[31,32]Oxidat-

1

solutions (C₂D₂Cl₄) of [AB]-type oligomers 3–5 by H and ive Hay coupling with an excess of prop-2-yn-1-ol provided

¹³C NMR spectroscopy.^[24]Inspired by very recent results alcohol (R)-16 in 51% yield together with buta-1,3-diyne

with donor-substituted 1,3-diethynylallenes (DEAs, Fig- (R,R)-17 (18%, Scheme 1), formed by homo-coupling of

ure 2),^[26,27]we assumed that the presence of a suitable chi- (R)-15. A “one-pot” oxidation/Knoevenagel condensation

ral substituent may induce a preferred conformation of the protocol, starting from (R)-16, yielded the dicyanovinyl de-

dendralene-type backbone^[28–30]in the [AB]-type oligomers. rivative (R)-18 in 32%.^[33]The dicyanovinyl group activates

The circular dichroism (CD) spectrum of enantiopure DEA the adjacent CϵC bond in (R)-18 for the cycloaddition re-

(M)-12 showed Cotton effects associated with the CT ab- action with TTF^[21]to give, after cycloreversion, adduct

sorptions of the TCBD. This clearly indicated chiral induc- (R)-19 in 33% yield. Target compound (R)-13 was sub-

tion from the allene into the TCBD moieties,^[26]which was sequently obtained in 50% yield cycloaddition/cyclorever-

confirmed in theoretical simulations of the CD spectrum.^[27]sion of TCNE. The low yield in this transformation may be

Encouraged by the high HTP values found for N-aryl- explained by the high degree of steric hindrance in (R)-19.

ated dinaphthazepines, which constitute 2,2Ј-bridged 1,1Ј- The constitution of this chiral A-D-A system (A = acceptor,

binaphthalenes,^[20]we decided to also use 1,1Ј-binaphthal- D = donor) was proven by the spectroscopic data (¹H

ene moieties as building blocks for induction of chirality NMR, MS, IR), although complex conformational equilib-

into the new chiral [AB]-type oligomers (R)-13 and (S)-14 ria complicate the interpretation of the ¹H NMR spectrum.

(Figure 2). The alkoxy substituents in the 2,2Ј-positions of VT-NMR spectroscopic experiments (–30 to 100 °C) were

(R)-13 and (S)-14 were expected to enforce strong confor- performed with a C₂D₂Cl₄solution of (R)-13 (see the Sup-

mational preferences and help achieving chiral induction porting Information). Similarly to the previously reported,

into the dendralene-type backbone through intramolecular achiral A-D-A derivatives 3 and 4,^[24]the coalescence of all

1

steric interactions. The conformational equilibria and the signals was not observed in the H NMR spectrum of (R)-

possible presence of preferred chiral conformers are investi- 13 even at 80 to 100 °C. The temperature at which frozen

gated here by a combination of variable temperature (VT)- conformations could be monitored by ¹H NMR spec-

NMR and VT-CD spectroscopy.

troscopy was not reached due to the low solubility of (R)-

13, which also prevented the recording of ¹³C NMR spec-

tra.

Results and Discussion

Synthesis of Chiral [AB]-Type Oligomers Based on 3,3Ј-

Substituted 1,1Ј-Binaphthalenes

Synthesis of Chiral [AB]-Type Oligomer (R)-13

The synthesis of (R)-13 started from alkyne (R)-15,

The bis(diyne) (S)-20 was obtained by Sonogashira

which was prepared from (R)-1,1Ј-bi(2,2Ј-naphthol) [(R)- cross-coupling of 3,3Ј-diiodo-2,2Ј-bis(methoxymethoxy)-

Scheme 1. Synthesis of the chiral [AB]-type oligomer (R)-13. a) Prop-2-yn-1-ol, CuCl, N,N,NЈ,NЈ-tetramethylethylenediamine (TMEDA),

CH₂Cl₂, 18 h, 25 °C, 51% [(R)-16], 18% [(R,R)-17]. b) 1. (R)-16, Dess–Martin periodinane, CH₂Cl₂, 1 h, 25 °C; 2. CH₂(CN)₂, Al₂O₃,

CH₂Cl₂, 1 h, 50 °C, 32% (yield over two steps). c) TTF, MeCN/CH₂Cl₂, 1:1, 13 h, 50 °C, 33%. d) TCNE, CH₂Cl₂, 24 h, 25 °C, 50%.

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Scheme 2. Synthesis of chiral CT-chromophores (S)-23 and (S)-27. a) TCNE, TTF, MeCN/CH₂Cl₂, 3:1, 18 h, 50 °C, 29%. b) TCNE,

CH₂Cl₂, 18 h, 25 °C, 70%.

1,1Ј-binaphthyl [(S)-21]^[34]with 4-(buta-1,3-diyn-1-yl)-N,N- porting Information). Diyne 29 was then subjected to TMS-

dimethylaniline (22)^[4](see the Supporting Information). deprotection, followed by another Hay-type coupling reac-

With the precursor (S)-20 in hands, we attempted the syn- tion with an excess of TMSA to give the unsymmetric

thesis of the chiral [AB]-type oligomer (S)-14 by the one- triyne 28 in 50% yield (Scheme 3). Tetrayne 31 was formed

pot protocol for cascade TCNE/TTF additions (see in 15% yield by homo-coupling of deprotected 29. The use

above).^[24]Interestingly, only the bis-TCNE adduct (S)-23 of an excess of TMSA leads to the preferred formation of

was isolated in 29% overall yield when (S)-20 was treated the hetero-coupled product. Triyne 28 was found to be

with an excess of TCNE and TTF in MeCN/CH₂Cl₂at highly unstable as a solid and in solution; decomposition

50 °C (Scheme 2). The desired addition of TTF to the CϵC to an insoluble black residue was observed already at tem-

bonds directly attached to the naphthalene moieties may peratures exceeding 40 °C. Therefore, evaporation of the

not occur for various reasons. These triple bonds are steri- solvents in vacuo was performed at 30 °C or lower.

cally blocked by the neighboring methoxymethoxy

(OMOM) groups and the TCBD moieties, and in addition,

they may not be sufficiently electron deficient to undergo

[2+2] cycloadditions to TTF due to the electron-donating

OMOM groups. These types of CϵC bonds have been de-

scribed as “electronically confused” (see above).^[24]The C₂-

symmetric diyne (S)-24 was prepared from (S)-3,3Ј-diiodo-

2,2Ј-diethoxy-1,1Ј-binaphthyl [(S)-25]^[35]by twofold Sono-

gashira cross-coupling with 4-ethynyl-N,N-dimethylaniline

(26)^[36](see the Supporting Information). The chiral CT-

chromophore (S)-27 was obtained in 70% yield (that is,

84% for each cycloaddition/cycloreversion step) by reaction

of (S)-24 with TCNE.

During the synthesis of alcohol 32, which is the precur-

sor for a new D-A tetrayne,^[25]hexayne 8 was isolated as a

side product in 38% yield from homo-coupling of depro-

tected 28 (Scheme 3). Although a large excess (15 equiv.)

of prop-2-yn-1-ol was employed in the oxidative coupling

reaction, the homo-coupling product 8 was formed in

slightly higher yield than the cross-coupling product 32.^[38]

Separation of 8 and 32 by flash chromatography (FC) was

straightforward due to the large difference in polarity be-

tween the alcohol and the hexayne. Like their precursor 28,

hexayne 8 and tetrayne 32 exhibit very low thermal stability

and decomposition to black insoluble materials was ob-

served at temperatures above 40 °C for solutions and in the

solid state.

The analogue of 8 bearing N,N-diisopropylanilino resi-

dues instead of DHA donors was synthesized from the tri-

Synthesis of Precursors for Achiral [AB]-Type Oligomer

The precursor for N,N-dihexylanilino (DHA) substituted ethylsilyl (TES)-protected triyne 33 (Scheme 3). The use of

1,3,5-hexatriyne 28 (Scheme 3), diyne 29, was synthesized diisopropylanilino substituents instead of DHA residues

by oxidative Hay coupling of 4-ethynyl-N,N-dihexyl- should facilitate crystal formation for X-ray analysis, while

aniline (30)^[37]with (trimethylsilyl)acetylene (TMSA) (Sup- maintaining good solubility of hexayne 9 and the derived

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Charge-Transfer Chromophores with a Dendralene-Type Backbone

Scheme 3. Oxidative coupling reactions to synthesize donor-substituted oligoynes. a) 1. K₂CO₃, MeOH/THF, 1:1, 2 h, 25 °C; 2. (Trimeth-

ylsilyl)acetylene (TMSA), CuCl, TMEDA, acetone, 3 h, 25 °C, 50 % (28, yield over two steps), 15% (31, yield over two steps). b) 1. 28,

K₂CO₃, MeOH/THF, 1:1, 1 h, 25 °C; 2. Prop-2-yn-1-ol, CuCl, TMEDA, CH₂Cl₂, 2 h, 25 °C, 38 % (8, yield over two steps), 34% (32,

yield over two steps). c) 1. nBu₄NF, THF, 20 min, 0 °C; 2. CuCl, TMEDA, CH₂Cl₂, 2 h, 25 °C, 65% (yield over two steps).

[AB]-type oligomers. The triyne 33 was prepared according furnished the [ABAB] system 7 in a significantly increased

to a known procedure (Supporting Information).^[39]TES- yield of 58% (that is, 87% per cycloaddition/cycloreversion

deprotection with nBu₄NF, followed by oxidative Hay cou- sequence) as compared to 5 (21%, see above). This can be

pling, provided the desired hexayne 9 in 65% yield. Unam- rationalized by comparing the Hammett constants of the

biguous proof of the formation of hexayne 9 was obtained phenyl substituent [σ_p(Ph) = –0.01]^[41]in 2 and the 4-cya-

by X-ray crystallographic analysis (see below). Octatetrayne nophenyl substituent [σ_p(CN) = +0.66]^[41]in 6. The phenyl

6 was obtained by oxidative Hay coupling of the TMS-de- substituent acts as a very weak electron donor, contributing

protected diynes 4-[4-(trimethylsilyl)buta-1,3-diyn-1-yl]benzo- to the “electronic confusion” of the adjacent alkyne moiety.

nitrile (34)^[40]and 4-[4-(trimethylsilyl)buta-1,3-diyn-1-yl]-N,N- In 6, this effect is completely eliminated by the electron-

dimethylaniline (35)^[4](Supporting Information).

withdrawing 4-cyanophenyl moiety. As in the case of 3, 4,

5, and (R)-13 (see above), the NMR spectroscopic charac-

terization of 7 was seriously complicated by the presence of

complex conformational equilibria in solution. Reaction of

the symmetric bis-donor-substituted tetrayne 1 with an ex-

cess of TCNE in CH₂Cl₂afforded bisadduct 36 in 55%

yield (Scheme 4). On the other hand, the same reaction with

one equivalent of TCNE gives exclusively the monoadduct

in 72% yield.^[24]Only traces of the monoadduct were ob-

[2+2] Cycloadditions of Donor-Substituted Oligoynes with

TCNE and TTF

We attempted the cascade of successive TCNE/TTF

[2+2] cycloadditions to the mono-DMA, mono-(4-cyano-

phenyl)-substituted tetrayne 6 (Scheme 4). Reaction of 6

with an excess of TTF and TCNE in the one-pot setup

Scheme 4. [2+2] Cycloaddition/cycloreversion cascades. a) TCNE, TTF, CH₂Cl₂/MeCN, 1:1, 18 h, 50 °C, 58%. b) 2.9 equiv. TCNE,

CH₂Cl₂, 17 h, 25 °C, 55%.

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served in the synthesis of 36. Chromophores 7 and 36 were

Alkynes 37 and 38 can be used to build up two different

obtained as black metallic-like solids, which are stable up [AB]-type oligomers. One by a cascade of successive TTF/

to their melting points. TCNE additions from one side of the pentayne to the other,

Hexayne 8 was used to access the extended version of starting from 37. This reaction sequence leads to the ana-

[AB]-type oligomer 3 (see above).^[24]Surprisingly, reaction logue of 3, [AB]-type oligomer 10 (see above). On the other

of 8 with one equivalent of TCNE gave a 1:1 mixture of hand, successive TTF/TCNE additions may also occur

TCBD 37 (39% yield) and the symmetric bisadduct 38 starting from both sides of the symmetric tetrayne 38. This

(39% yield, Scheme 5). This result is in contrast to the ob- reaction sequence has not been investigated in the case of

served reactivity for tetrayne 1 (see above).^[24]It is assumed the tetrayne 1. Thus, 38 was treated with an excess of TTF

that the additional separation of the TCBD moiety from in CH₂Cl₂/MeCN, 1:1 to give the hybrid TCNE-TTF ad-

the reacting CϵC bond in 37 strongly reduces its electron- duct 39 in 58% yield (Scheme 5). Finally, TCNE addition

withdrawing effect. Thus, this triple bond remains suffi- to 39 gave the [AB]-type oligomer 40 in 96% yield. The

ciently electron-rich in 37 to undergo the second TCNE ad- remaining CϵC bond in 40 is “electronically confused”

dition after a short time without using an excess of TCNE. and, therefore, does not react with TCNE or with TTF.

In the case of 1, a prolonged reaction time and an excess Again, complex conformational equilibria in solution seri-

of TCNE was necessary to obtain bisadduct 36 (see above). ously complicate the interpretation of the ¹H and ¹³C NMR

Monoadduct 37 can be selectively synthesized in 65% yield spectra of 39 and 40.^[24]High-temperature ¹H NMR spectra

by using only 0.8 equiv. of TCNE in the [2+2] cycloaddition were measured up to 80 °C for 39 and up to 100 °C for

1

reaction with 8. In this case, only traces of the bisadduct 38 40 (Supporting Information). Coalescence of the H NMR

were observed and it was possible to isolate unreacted 8 signals was not observed under these conditions. [AB]-type

from the crude reaction mixture by FC. Similar to its pre- oligomers 39 and 40 were obtained as brown solids, which

cursors, pentayne 37 showed low thermal stability with de- are stable up to their melting points at 252–254 °C and 217–

composition reactions occurring at temperatures above 219 °C, respectively.

40 °C. Bisadduct 38 was selectively obtained in 88% yield

The one-pot protocol, which was successfully used in the

by adding two equivalents of TCNE to 8. This yield is synthesis of 5 and 7 (see above),^[24]should give a 1:1 mix-

higher than for bisadduct 36 (55%), which is in agreement ture of the constitutional isomers 10 and 40 in the case of

with the observed difference in reactivity between tetrayne the symmetric hexayne 8. However, separation of the two

1 and hexayne 8. The symmetric tetrayne 38 is stable up to isomers 10 and 40 by FC was not possible and, therefore,

its melting point at 161–163 °C.

the one-pot protocol was not used with hexaynes 8 and 9.

Scheme 5. Synthesis of [AB]-type oligomers 39 and 40. a) 8, 0.8 equiv. TCNE, CH₂Cl₂, 5 h, 25 °C, 65 % (37). b) 8, 1.0 equiv. TCNE,

CH₂Cl₂, 3 h, 25 °C, 39 % (37), 39% (38). c) 8, 2.0 equiv. TCNE, CH₂Cl₂, 18 h, 25 °C, 88 % (38). d) 38, TTF, CH₂Cl₂/MeCN, 1:1, 6 h,

50 °C, 58%. e) 3.6 equiv. TCNE, CH₂Cl₂, 18 h, 25 °C, 96%.

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Charge-Transfer Chromophores with a Dendralene-Type Backbone

Scheme 6. Synthesis of [AB]-type oligomer 43. a) 0.7 equiv. TCNE, CH₂Cl₂, 5 h, 25 °C, 83%. b) 2.0 equiv. TCNE, CH₂Cl₂, 18 h, 25 °C,

65%. c) TTF, MeCN/CH₂Cl₂, 1:1, 4 h, 50 °C, 65%.

1

Hexayne 9 was selectively converted into the expanded viously, the complex H NMR spectrum of 43 is reported

TCBD 41 by [2+2] cycloaddition with 0.7 equiv. of TCNE in the Experimental Section as empiric enumeration of ob-

(Scheme 6). The yield of 41 (83%) was further improved in served signals. The ¹³C NMR spectrum of 43 was not ob-

comparison to 37 (65%, Scheme 5) by the use of 0.7 instead tained due to the low solubility of the compound.

of 0.8 equiv. of TCNE. As described for 37, unreacted 9

could be isolated after the reaction by FC. Twofold cycload-

dition of TCNE to 9 was not observed under these condi-

tions. The thermal stability of 9 and 41 was not investi-

X-ray Structure and Bond Length Alternation in Hexayne 9

gated, as it is assumed that their stability is similar to that

Single crystals of 9 were obtained by slow evaporation of

of 8 and 37; therefore they were handled and stored at tem- a solution of 9 in CH₂Cl₂at 25 °C (Figure 3). The crystals

¯

peratures below 40 °C. TCNE addition to the electron-rich have the triclinic space group P1. The bond angles at the

CϵC bond next to the diisopropylanilino residue in 41 gave CϵC triple bonds, which have values between 176° and

42 in 65% yield. Finally, 42 was treated with TTF to give 179° (see caption to Figure 3), indicate that the 1,3,5,7,9,11-

the diisopropylanilino analogue of 39, hybrid TCNE-TTF dodecahexayne moiety is slightly bent. The molecule adopts

adduct 43, in 65% yield. The [AB]-type oligomer 43 was a gentle S shape. A similar shape was recently found by

obtained as a brown solid which decomposed upon melting Tykwinski et al. in the first crystallographic analysis of a

at 205–208 °C. For the same reasons as described pre- decayne.^[42]The two diisopropylanilino rings in 9 are

Figure 3. ORTEP plot of 9 at 203 K, arbitrary numbering. Atomic displacement parameters are drawn at the 50% probability level.

Selected bond lengths [Å] and bond angles [°]: C16–C17 1.410(3), C17–C18 1.379(3), C13–C18 1.397(4), C13–C14 1.395(3), C14–C15

1.380(3), C15–C16 1.410(3), N19–C16 1.382(3), C12–C13 1.419(3), C2–C12 1.214(3), C2–C3 1.354(3), C3–C4 1.220(3), C4–C5 1.352(3),

C5–C6 1.210(3), C26–C27 1.400(4), C26–C31 1.403(4), C27–C28 1.372(3), C28–C29 1.411(3), C29–C30 1.411(3), C30–C31 1.365(3), C11–

C1–C26 178.3(3), C12–C2–C3 176.7(3), C4–C3–C2 176.7(3), C3–C4–C5 178.2(3), C6–C5–C4 177.8(3), C5–C6–C7 179.1(3). Selected

torsional angles [°]: dihedral angle between best planes through phenyl rings 56, N32–C29–C30–C31 176.9(2), C20–N19–C16–C15 22.1(3),

C23–N19–C16–C15 –174.6(2), N19–C16–C17–C18 –176.6(3), C12–C13–C18–C17 176.5(3), C1–C26–C31–C30 –178.9(3). Quinoid charac-

ter: δr = {[(a + aЈ)/2 – (b + bЈ)/2] + [(c + cЈ)/2 – (b + bЈ)/2]}/2.^[44]δr = 0.024 and 0.038 for diisopropylanilino rings A and B, respectively.

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twisted by ca. 56° with respect to each other (see caption Table 2. Cyclic voltammetry (CV; scan rate v = 0.1 Vs^–1) and rotat-

ing disk voltammetry (RDV) data in CH₂Cl₂(+ 0.1 

to Figure 3). These findings can be explained by crystal

packing forces. Tykwinski et al. reported a similar observa-

nBu₄NPF₆).^[a]

CV

RDV

Slope [mV]^[f]

tion for the X-ray crystal structure of an aryl-substituted

hexayne. They found the terminal aryl groups to be nearly

orthogonal.^[43]The arrangement of neighboring molecules

in the crystal packing of 9 is shown in the Supporting Infor-

mation.

The quinoid character of the diisopropylanilino rings (δr;

for its definition^[44]and bond lengths, see caption to Fig-

ure 3) in 9 was calculated to investigate the efficiency of the

CT conjugation from the diisopropylanilino donors to the

hexayne acceptor moiety. Compound 9 exhibits δr values of

0.024 and 0.038, for the two diisopropylaniline rings A and

B, respectively. This is a large difference in δr values for two

chemically identical donor substituents. The large difference

in δr values for the two diisopropylanilino rings in 9 is most

probably caused by crystal packing forces, which lead to a

substantial twist of one of the rings, thereby reducing the

conjugation to the hexayne moiety.

E° [V]^[b]∆E_p[mV]^[c]E_p[V]^[d]

E_1/2[V]^[e]

8

9

+0.59^[g]

–1.80

+0.57

–1.80

0.59 (2e^–)

–1.77 (1e^–)

+0.53 (2e^–)

–1.78 (1e^–)

+0.93 (1e^–)

+0.57 (1e^–)

–0.57 (1e^–)

–0.95 (1e^–)

+0.91 (1e^–)

+0.56 (1e^–)

–0.60 (1e^–)

–0.96 (1e^–)

75

50

70

60

70

65

60

75

60

70

37

+0.92

+0.56

–0.58

–0.94

+0.91

+0.56

–0.58

–0.93

75

60

41

–2.25

42

43

+0.91

–0.44

–0.59

–0.99

+0.55

+0.44

–0.04

–1.08

–1.27

+0.92

–0.34

–0.66

–1.17

60

70

+0.92 (2e^–)

–0.44 (1e^–)

–0.59 (1e^–)

–1.03 (2e^–)

+0.57 (1e^–)^[h]

+0.47 (2e^–)

–0.04 (1e^–)

–1.10 (2e^–)

–1.28 (2e^–)

+0.94 (2e^–)

–0.37 (1e^–)

–0.69 (1e^–)

–1.22 (2e^–)

60

70

80

70

60

70

40

65

60

75

60

70

75

80

70

36

Electrochemistry

70

130

For further exploration of the electron donor and ac-

ceptor properties of the chiral and achiral [AB]-type oligo-

mers and their precursors, electrochemical investigations

were carried out by cyclic voltammetry (CV) and rotating

[a] All potentials are given vs. the Fc⁺/Fc couple used as internal

standard. [b] E° = (E_pc+ E_pa)/2, where E_pcand E_pacorrespond to

the cathodic and anodic peak potentials, respectively. [c] ∆E_p

=

disk voltammetry (RDV) in CH₂Cl₂with nBu₄NPF₆(0.1 ) E_pa– E_pc. [d] E_p= irreversible peak potential. [e] E_1/2= half-wave

as the supporting electrolyte. The redox potentials vs. Fc⁺/

potential. [f] Logarithmic analysis of the wave obtained by plotting

E vs. log[I/(I_lim– I)]. [g] Reversible electron transfer at scan rates

Fc (ferricinium/ferrocene couple) are listed in Table 1 for

the chiral derivatives and in Table 2 for the achiral deriva-

tives.

Ͼ 2 Vs^–1. [h] Further oxidations lead to electrode inhibition.

Chiral [AB]-Type Oligomers

Compound (S)-24 exhibits an irreversible 2e^–oxidation

Table 1. Cyclic voltammetry (CV; scan rate v = 0.1 Vs^–1) and rotat-

step (+0.36 V from CV) on the two DMA units. For (S)-

ing disk voltammetry (RDV) data in CH₂Cl₂(+ 0.1 

27, the reversible 2e^–oxidation at +0.86 V (CV) involves the

nBu₄NPF₆).^[a]

two independent DMA moieties. Oxidation of the DMA

CV

RDV

units in (S)-27 is rendered more difficult by the conjugation

with the strong TCBD acceptors. In (S)-27, the reduction

of the two TCBDs occurs in two successive reversible 1e^–

processes at –0.81 V and –0.91 V (RDV), respectively. The

third reversible reduction involving 2e^–[–1.27 V (RDV)] is

unresolved. In general, the redox properties of the chiral

TCBD dimer (S)-27 are quite similar to those of its achiral

analogue having a H substituent instead of the binaphthyl

substituent.^[3]The first reduction potential is shifted to a

slightly more negative value for (S)-27 (–0.82 V in CV vs.

–0.69 V), probably due to the presence of the binaphthyl

moiety which acts as an additional electron donating sub-

stituent in (S)-27.

E° [V]^[b]∆E_p[mV]^[c]E_p[V]^[d]

E_1/2[V]^[e]

Slope [mV]^[f]

(R)-19

(R)-13

+0.84

–1.82

–0.81

60

65

–2.05

+0.74

+0.74 (2e^–)^[g]

–0.81 (1e^–)

–1.13 (1e^–)

+0.36 (2e^–)

60

80

60

–1.23

+0.36

(S)-24

(S)-27

+0.86

–0.82

–0.92

–1.31

60

+0.85 (2e^–)

–0.81 (1e^–)

–0.91 (1e^–)

–1.27 (2e^–)

60

125

[a] All potentials are given vs. the Fc⁺/Fc couple used as internal

standard. [b] E° = (E_pc+ E_pa)/2, where E_pcand E_pacorrespond to

the cathodic and anodic peak potentials, respectively. [c] ∆E_p

E_pa– E_pc. [d] E_p= irreversible peak potential. [e] E_1/2= half-wave

potential. [f] Logarithmic analysis of the wave obtained by plotting

E vs. Log[I/(I_lim– I)]. [g] Further oxidations lead to electrode inhi-

bition.

Compound (R)-19 shows one irreversible oxidation

(+0.84 V from CV) centered on the 1,2-bis(1,3-dithiol-2-

ylidene)ethane unit. In RDV, no potential could be deter-

mined. It should be noted that (R)-19 was poorly soluble

during the measurements and its CV was not well-defined.

=

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Charge-Transfer Chromophores with a Dendralene-Type Backbone

For (R)-13, the oxidation also occurs on the extended TTF for 43 (CV).^[24]Thus, it is assumed that “dimeric” 43 is

moiety in a single irreversible 2e^–transfer (+0.74 V). The much more twisted than its “monomeric” analogue. It can

parent TTF undergoes the oxidation steps at –0.08 V and be concluded, that there is no general trend for the redox

+0.4 V under the same conditions.^[45]Thus, oxidation of behavior of this class of nonplanar chromophores and that

this moiety in (R)-19 and (R)-13 becomes more difficult by each compound may behave in a particular way, depending

the conjugation with the dicyanovinyl acceptor.

on the equilibrium between its different conformers in solu-

The CV of (R)-19 shows one reversible reduction on the tion.

dicyanovinyl unit at –1.82 V and another irreversible re-

The two DMA moieties in bisadduct 36 are oxidized in

duction at more negative potential (–2.05 V). For (R)-13, a single two-electron step at +0.92 V (CV). This value is in

the reduction of the TCBD moiety occurs in two 1e^–steps very good agreement with the oxidation potential observed

at –0.81 V and –1.13 V (RDV), respectively, the second one for bisadduct 42 in CV (+0.91 V, see above). The peak

being irreversible. In contrast to previous studies on shapes in cyclic voltammetry and the value of the peak po-

TCBDs, the expected reversible 1e^–reduction of the dicya- tential difference (80 mV) indicate that the two DMA

novinyl unit is not observed, probably due to electrode inhi- moieties in 36 are oxidized stepwise in two reversible one-

bition or poor solubility of the reduced species.

electron transfers. The redox potentials of the two one-elec-

For (R)-13 with its additional TCBD acceptor, the first tron transfers are separated by about 60 mV.

oxidation potential for the extended TTF unit (+0.74 V) is

Compounds 8 [–1.80 V (CV)] and 9 [–1.80 V (CV)] show

shifted cathodically by 100 mV, when compared to (R)-19 irreversible 1e^–reductions on the 1,3,5,7,9,11-dodecahexa-

(+0.84 V). This result clearly indicates the strongly reduced yne moiety, which acts as a weak electron acceptor. For 37

π-conjugation between the TCBD and the extended TTF [–0.58 and –0.94 V (CV)] and 41 [–0.58 and –0.93 V (CV)],

units in (R)-13. ¹H NMR spectra show the presence of com- two reversible 1e^–reductions located on the two dicyanovi-

plex conformational equilibria for (R)-13 (Supporting In- nyl moieties were observed. As already described above for

formation). Additionally, the first reduction of (R)-13 in CV their oxidation, the reduction potentials for compounds

(–0.81 V) is shifted anodically as compared to (R)-19 8/9 and 37/41, respectively, are nearly identical. The re-

(–1.82 V), due to the presence of the additional electroactive duction of the TCBD units in 42 occurs in three steps, the

TCBD acceptor.

first two reductions at –0.44 and –0.59 V, respectively, are

reversible 1e^–transfers, whereas the third reduction step at

–0.99 V (CV) involves a global 2e^–transfer. From the peak

shape and the peak characteristics of this third reduction,

it is clear that it results from the overlap of two reversible

Achiral [AB]-Type Oligomers

Hexaynes 8 (+0.59 V from CV) and 9 (+0.57 V from CV) 1e^–transfers, of which the redox potentials are separated

show an irreversible 2e^–oxidation on the DHA and N,N- by only 50 mV, giving rise to an unresolved CV.^[46,47]The

diisopropylanilino moieties, respectively. For 37 [+0.92 and reduction of 43 involves two reversible 2e^–transfers at –1.08

+0.56 V (CV)] and 41 [+0.91 and +0.56 V (CV)], two well- and –1.27 V (CV) occurring on the two TCBD moieties.

defined, reversible 1e^–oxidations were observed. The poten- From the peak shapes, each peak results from the overlap

tials measured for 8/9 and 37/41, respectively, are similar, as of two reversible 1e^–transfers occurring on the two quite

expected for derivatives with almost identical structures.

independent TCBD redox centers. The lack of either elec-

Tetrayne 42 undergoes a reversible 2e^–oxidation at trostatic or π-conjugation interactions may be due to steric

+0.91 V (CV) involving the two independent diisopropyl- crowding in 43 resulting in a twisted structure (see above),

anilino redox centers. The oxidation of 43 occurs in three in contrast to 42 for which a more planar structure is as-

steps at –0.04 V (1e^–exchange), +0.44 V (2e^–exchange), sumed. For 36, the first two reductions [–0.34 and –0.66 V

and +0.55 V (1e^–exchange), respectively. The two last oxi- (CV)] seem to occur on the two dicyanovinyl moieties,

dations are not well resolved and lead to electrode inhibi- which are conjugated through the butadiyne spacer. This

tion during RDV. The first oxidation of 43 occurs at a very explains the potential difference between the two dicyano-

low potential of –0.04 V; for comparison, the first oxidation vinyl groups. As the two remaining dicyanovinyl groups in

potential of unsubstituted TTF is –0.08 V vs. the Fc⁺/Fc the charged species (dianion) are most probably not planar,

couple.^[45]A similar first oxidation potential was also ob- and therefore not in conjugation with each other, their re-

served for 5 (see Scheme 1); in this case, it was supposed duction occurs at quite similar potentials giving rise to a

that the steric crowding results in a highly twisted structure unique reversible 2e^–step [–1.17 V (CV)]. From its peak

and therefore extended π-conjugation is no longer pos- shape and peak potential difference of 130 mV, it is clear

sible.^{[24] 1}H NMR spectra of 43 also indicate complex con- that this step involves two 1e^–exchanges. The redox poten-

formational equilibria due to steric crowding. Probably, the tials of the two steps are separated by about 80 mV. In gene-

conjugation between the TCBD acceptor and the extended ral, the redox properties of bisadduct 36 are quite similar

TTF donor moiety in 43 is strongly reduced, thus shifting to those of its extended analogue 42.

the first oxidation potential of the latter to lower values.

For the extended TCBDs 37 and 41, a substantially low-

Interestingly, a TCNE-TTF adduct with a very similar ered electrochemical HOMO–LUMO gap of 1.14 V (from

structure to one half of symmetric 43, exhibits the first oxi- CV) is observed, as compared to a known TCBD derivative

dation at a much higher potential of +0.38 V vs. –0.04 V with only one triple bond (1.61 V from CV).^[3,4]As shown

Eur. J. Org. Chem. 2010, 2487–2503

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2495

F. Diederich et al.

FULL PAPER

previously, this is a direct consequence of the reduction in

the D-A conjugation by the longer 1,3,5,7,9-decapentayn-

1-yl spacer in 37 and 41, as compared to the ethynediyl

spacer.^[4,33,48]

UV/Vis and CD Spectroscopy

The UV/Vis absorption spectra of the chiral and achiral

multivalent CT chromophores were recorded to gain fur-

ther insight into their opto-electronic properties. The CD

spectra were measured to investigate whether conforma-

tional preferences and a sense of chirality were induced in

the dendralene-type backbones of the chiral [AB]-type

oligomers.

Figure 4. CD spectrum (top, black line) and UV/Vis spectrum (bot-

tom, gray line) of (R)-13 in MeCN at 298 K.

Chiral [AB]-Type Oligomers

The intense band at 230 nm (5.40 eV, 66800 ^–1cm^–1,

Figure 4) in the UV/Vis spectrum of (R)-13 in MeCN is

assigned to the naphthyl πǞπ* transition by comparison to

the UV/Vis and CD spectra of its precursor (R)-44 (Sup-

porting Information) and to the published spectra of a

closely related derivative.^[49]Corresponding to this band

there is an intense Cotton effect at 236 nm (5.26 eV, ∆ε =

–61 ^–1cm^–1) in the CD spectrum of (R)-13 (MeCN, Fig-

ure 4). In addition, the UV/Vis spectrum of (R)-13 shows a

weak CT absorption at 478 nm (2.60 eV). In the same re-

gion, the CD spectrum shows a bisignate band at 433 nm

(2.87 eV, ∆ε = –6 ^–1cm^–1) and 527 nm (2.36 eV, ∆ε =

+3 ^–1cm^–1). This points at a weak chiral induction from

the binaphthyl moiety into the [AB]-type oligomer. VT-CD

spectroscopy showed no significant change in the spectrum

over the range from –10 to 70 °C (Supporting Information).

The intensity of the weak bisignate band corresponding to

the CT absorption of the dendralene-type backbone did not

change upon lowering the temperature. The weak chiral in-

duction presumably originates from the lack of strong con-

formational preferences in (R)-13. A single stable chiral

conformer should exhibit a higher intensity of the Cotton

effects in the region of the CT absorption, as was recently

observed in conformationally highly preorganized optically

active allenes conjugated to donor-substituted TCBD chro-

mophores [e.g. (M)-12, Figure 2].^[26,27]

trifluoroacetic acid (TFA), followed by neutralization with

NEt₃(Supporting Information). In the CD spectrum, a

weak bisignate band between 350 nm (3.55 eV) and 398 nm

(3.12 eV, ∆ε = +5 and –5 ^–1cm^–1, respectively) is associ-

ated with the CT absorption at 384 nm. Similar to (R)-13

and (S)-23, this points at a weak chiral induction from the

chiral binaphthyl into the two TCBD moieties. The inten-

sities of the induced Cotton effects in (R)-13, (S)-23, and

(S)-27 (∆ε from 3 to 6 ^–1cm^–1) are weaker than those in

the spectra of chiral allenic push-pull conjugates [∆ε from

12 to 30 ^–1cm^–1for (M)-12].^[26,27]This can be explained

by a very low conformational stability in the binaphthyl sys-

tem. It can be concluded that the 1,3-diethynylallene moiety

is superior to the binaphthyl moiety for chiral induction

into donor-substituted TCBDs.

The UV/Vis and CD spectra of (S)-23 and (S)-24 can

be found in the Supporting Information. Compound (S)-23

shows a bisignate band between 413 nm (3.01 eV) and

466 nm (2.67 eV, ∆ε = +3 and –6 ^–1cm^–1, respectively),

which is associated with the broad CT band at 425 nm

(2.92 eV, ε = 40000 ^–1cm^–1) in the UV/Vis spectrum.

The UV/Vis spectrum of (S)-27 shows an intense band

at 226 nm (5.50 eV, ε = 77300 ^–1cm^–1, Figure 5). The cor-

responding Cotton effect in the CD spectrum is located at

232 nm (5.35 eV, ∆ε = +87 ^–1cm^–1). These bands can be

assigned to the binaphthyl moiety. Two CT bands are ob-

Figure 5. CD spectrum (top, black line) and UV/Vis spectrum (bot-

tom, gray line) of (S)-27 in MeCN at 298 K.

Achiral [AB]-Type Oligomers

The absorption spectra for hexaynes 8 and 9 in CH₂Cl₂

served at 384 (3.24 eV, ε = 37900 ^–1cm^–1) and 532 nm at 298 K are shown in Figure 6. As previously observed

(2.34 eV, ε = 18500 ^–1cm^–1) in the UV/Vis spectrum. The with symmetric end-capped hexaynes,^[43,50]the spectra show

CT nature of these bands was proven by acidification with well-resolved vibronic structures in the lower energy region

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Charge-Transfer Chromophores with a Dendralene-Type Backbone

from 350 to 470 nm (3.55 to 2.64 eV). The bands in the = 639 nm, 1.94 eV), when compared to 38 (λ_max= 460 nm,

higher-energy region from 280 to 350 nm (4.44 to 3.55 eV) 2.70 eV), 39 (λ_max= 484 nm, 2.57 eV), and 40 (λ_max

=

are not well resolved in the case of anilino-substituted hexa- 458 nm, 2.71 eV). This is in agreement with the results from

ynes 8 and 9. The presence of the strong DHA and N,N- electrochemistry and clearly reflects the weaker D-A cou-

diisopropylanilino donors significantly changes the absorp- pling in 37 caused by the additional 1,3,5,7,9-decapentayn-

tion spectra of 8 and 9 as compared to phenyl- or p-anisyl- 1,10-diyl spacer (see above). The UV/Vis spectra of 7, 36,

substituted hexaynes reported by Tykwinski et al.^[43]For 8 41, 42, and 43 are very similar to those of their DHA-sub-

and 9, the most intense absorptions are observed at 471 stituted analogues (Supporting Information).

(2.64 eV, ε = 57700 ^–1cm^–1) and 440 nm (2.82 eV, ε =

56000 ^–1cm^–1), respectively, whereas the lowest energy ab-

sorptions for the two hexaynes are found at 517 (2.40 eV, ε

= 26700 ^–1cm^–1) and 515 nm (2.41 eV, ε = 24100 ^–1cm^–1),

respectively. The corresponding values measured in THF

for the p-anisyl-substituted hexayne are 351 (3.54 eV, ε =

164000 ^–1cm^–1) and 476 nm (2.61 eV, ε = 13300 ^–1cm^–1).

This is in agreement with the finding by Tykwinski et al.

that increasing the donor-strength results in bathochromic

shifts for absorptions in both regions.^[43]

Figure 7. UV/Vis spectra of 37, 38, 39, and 40 in CH₂Cl₂at 298 K.

Nonlinear Optical Properties of TCBD 41

The third-order optical nonlinearity of the D-A-substi-

tuted TCBD 41 was determined by measuring the third-

order susceptibility of CH₂Cl₂solutions with varying mo-

lecular concentrations, which gave the rotational average of

[51]

the third-order polarizability γ_rot

.

The γ-values were de-

Figure 6. UV/Vis spectra of hexaynes 8 and 9 in CH₂Cl₂at 298 K.

termined by degenerate four-wave mixing (DFWM) at a

wavelength of 1.5 µm and fused silica with χ⁽³⁾

=

1.9ϫ10^–22m²V^–2as a reference. The extended TCBD 41

exhibits an extraordinarily large γ_rotvalue of

(6Ϯ2)ϫ10^–47m⁵V^–2. For comparison, DDMEBT cur-

rently used in non-linear optics devices, displays under the

same conditions a γ_rotvalue of (1.2Ϯ0.2)ϫ10^–47m⁵V^–2.^[3]

The molar absorptivities of 8 and 9 in the higher energy

region [280 to 350 nm (4.44 to 3.55 eV, in CH₂Cl₂): 40000

to 50000 ^–1cm^–1] are much lower than the ones reported

by Tykwinski (155000 to 200000 ^–1cm^–1in THF) and

Hirsch (164000 to 194000 ^–1cm^–1in CH₂Cl₂).^[43,50]In ad-

dition, the reported hexaynes show a large decrease in in-

tensity when going to the lower energy region of the spec-

trum, whereas 8 and 9 show similar intensities in both re-

gions. This indicates a large effect of the structure of the

end-capping groups on the oscillator strength for extended

Conclusions

We prepared the optically active [AB]-type oligomers

oligoynes. The intensity of the absorptions between 350 and (R)-13, (S)-23, and (S)-27 by TTF and TCNE additions to

470 nm was considerably lowered upon acidification of 8 alkyne-substituted 1,1Ј-binaphthalene derivatives. CD spec-

with TFA. The bands were fully recovered after neutraliza- troscopy revealed chiral induction from the axially chiral

tion with NEt₃, thus revealing their CT character.

binaphthyl moieties into the dendralene-type backbone of

The UV/Vis spectra of extended TCBD 37, and multi- (R)-13 and the TCBD moieties of (S)-23 and (S)-27. How-

valent CT chromophores 38, 39, and 40 were measured in ever, the large conformational heterogeneity of these com-

CH₂Cl₂at 298 K (Figure 7). The D-A substituted chromo- pounds is adverse to high chiral induction, and the induced

phores display intense, broad CT bands with absorption Cotton effects are of low intensity. Introduction of sterically

maxima λ_maxbetween 458 nm (2.71 eV, 40) and 639 nm more demanding substituents in the 2,2Ј-position of the bi-

(1.94 eV, 37). Compound 37 exhibits an additional CT naphthyl moieties actually may lead to stronger chiral in-

band, which is significantly shifted to lower energies (λ_maxduction in future systems.

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2497

F. Diederich et al.

FULL PAPER

performed on an Ultimate 3000 series LC instrument combined

with an MSQ Plus mass spectrometer from Dionex, using a Zorbax

Eclipse Plus C18 column (30ϫ3 mm; 3.5 µm pore size) from Ag-

ilent or a Reprospher C18-Aqua column (30ϫ3 mm; 3 µm pore

size) from Dr. Maisch. Melting points (M.p.) were measured on a

Büchi B-540 melting-point apparatus in open capillaries and are

uncorrected. “Decomp.” refers to decomposition. ¹H NMR and

¹³C NMR spectra were measured on Varian Mercury 300, Bruker

ARX 300, Bruker DRX400, Bruker AV400, or Bruker DRX 500

instruments at 298 K, unless otherwise stated. Chemical shifts are

As a true highlight, we prepared the A–D–A–D chromo-

phore 7 as a single product in 58% yield by a remarkable

one-pot, eight-step, five-component cascade reaction start-

ing from mono-DMA-, mono-4-cyanophenyl-substituted

tetrayne 6. This oligoyne is perfectly tuned for the strictly

electronically controlled domino transformation. In pre-

vious work, electronically less perfectly tuned phenyl-substi-

tuted tetrayne 2 only gave a 21% yield in the same conver-

sion.^[24]

The symmetric 1,3,5,7,9,11-dodecahexaynes 8 and 9 were reported in ppm relative to the signal of tetramethylsilane. Residual

solvent signals in the ¹H and ¹³C NMR spectra were used as an

prepared in good yield by oxidative Hay coupling. Hexa-

internal reference. Coupling constants (J) are given in Hz. The ap-

ynes 8 and 9 were successfully used to construct the new

parent resonance multiplicity is described as s (singlet), bs (broad

extended [AB]-type oligomers 39, 40, and 43 by successive

singlet), d (doublet), dd (doublet of doublet), dt (doublet of trip-

TCNE/TTF additions. The intramolecular CT interactions

lets), t (triplet), q (quartet), sep (septet), and m (multiplet). Infrared

in these new D-A chromophores were analyzed by electro-

spectra (IR) were recorded neat on a Varian 800 FT-IR instrument.

chemistry and by UV/Vis spectroscopy, revealing the im-

pact of strong steric overcrowding on π-electron conjuga-

tion between donor and acceptor moieties. The extended

TCBDs 37 and 41 with low optical and electrochemical

Absorption bands are reported in cm^–1. UV/Vis spectra were re-

corded on a Varian Cary-5 spectrophotometer. The spectra were

measured in CH₂Cl₂or MeCN in a quartz cuvette (1 cm) at 298 K.

The absorption wavelengths are reported in nm with the extinction

HOMO–LUMO gaps are interesting candidates for NLO coefficient ε (^–1cm^–1) in brackets; shoulders are indicated as sh.

Optical rotation values were measured on a Perkin–Elmer 241 Pola-

rimeter. Circular dichroism spectra were measured with a JASCO

J-715 spectropolarimeter. High-resolution- (HR) EI-MS spectra

were measured on a Waters Micromass AutoSpec-Ultima spec-

trometer, HR-ESI-TOF-MS spectra on a Bruker maXis ESI-Q-

TOF spectrometer and HR-FT-ICR-MALDI-MS and ESI-MS

spectra on a Varian IonSpec Fourier Transform (FT) ICR instru-

ment with (3-hydroxypyridine-2-carboxylic acid) (3-HPA) or

({(2E)-3-[4-(tert-butyl)phenyl]-2-methylprop-2-enylidene}malo-

nonitrile) (DCTB) as matrix. The most important signals are re-

ported in m/z units with M⁺as the molecular ion. Elemental analy-

ses were performed by the Mikrolabor at the Laboratorium für

Organische Chemie, ETH Zürich, with a LECO CHN/900 instru-

ment. The nomenclature was generated with ACD Name 9 by Ad-

vanced Chemistry Development Inc.

chromophores. Thus, the third-order optical nonlinearity of

41 was measured by DFWM and an extraordinarily large

γ_rotvalue of (6Ϯ2)ϫ10^–47m⁵V^–2was found.^[33,52]This re-

sult may provide new directions for the design of future

NLO chromophores.

Experimental Section

Materials and General Methods: Reagents and solvents were pur-

chased at reagent grade from GFS Chemicals (TMSA), Acros,

ABCR, Aldrich, and Fluka and used as received. THF was freshly

distilled from Na/benzophenone, toluene from Na and CH₂Cl₂

from CaH₂under N₂atmosphere. For all aqueous solutions, deion-

ized water was used. Hay catalyst refers to a freshly prepared solu-

tion of CuCl (65 mg, 0.66 mmol) and N,N,NЈ,NЈ-tetramethylethyl-

enediamine (TMEDA; 80 mg, 0.69 mmol) in CH₂Cl₂(5 mL) or to

a freshly prepared solution of CuCl (400 mg, 4.0 mmol) and

TMEDA (464 mg, 4.0 mmol) in acetone (100 mL). All reactions,

except Hay couplings, were performed under an inert atmosphere

by applying a positive pressure of argon. Drying was performed in

vacuo at 10^–2Torr. Solvents for flash chromatography (FC), me-

dium pressure liquid chromatography (MPLC), plug filtrations,

and extractions were of technical quality and distilled before use.

The chromatographic separations were carried out on SiO₂60 (par-

ticle size 0.040–0.063 mm, 230–400 mesh; Silicycle). FC was carried

out at an overpressure of 0.1–0.6 bar. MPLC was performed with

a Büchi Sepacore system consisting of a Büchi Pump manager C-

615, a Büchi Pump Module C-601, and a Büchi Fraction collector

C-660. Thin-layer chromatography (TLC) was conducted on SiO₂-

layered glass plates (60 F₂₅₄, Merck); visualization with UV light

(254 or 366 nm). Compounds 4,4Ј-(octa-1,3,5,7-tetrayne-1,8-diyl)-

bis(N,N-dimethylaniline) (1),^[24](R)-3-ethynyl-2,2Ј-dimethoxy-1,1Ј-

binaphthalene [(R)-15],^[31](S)-3,3Ј-diiodo-2,2Ј-bis(methoxymeth-

oxy)-1,1Ј-binaphthyl [(S)-21],^[53]4-(buta-1,3-diyn-1-yl)-N,N-di-

methylaniline (22),^[4](S)-3,3Ј-diiodo-2,2Ј-diethoxy-1,1Ј-binaphthyl

[(S)-25],^[35]4-ethynyl-N,N-dimethylaniline (26),^[36]4-ethynyl-N,N-

dihexylaniline (30),^[37]4-[4-(trimethylsilyl)buta-1,3-diyn-1-yl]benzo-

nitrile (34),^[40]and 4-[4-(trimethylsilyl)buta-1,3-diyn-1-yl]-N,N-di-

methylaniline (35)^[4]were prepared according to literature pro-

cedures. Liquid chromatography/mass spectrometry (LC/MS) was

Electrochemistry: Electrochemical measurements were carried out

at 20 °C in CH₂Cl₂containing 0.1  nBu₄NPF₆in a classical three-

electrode cell. CH₂Cl₂was purchased in spectroscopic grade from

Merck, dried with molecular sieves (4 Å), and stored under Ar

prior to use. nBu₄NPF₆was purchased in electrochemical grade

from Fluka and used as received. The working electrode was a

glassy carbon disk electrode (3 mm in diameter) used either mo-

tionless for cyclic voltammetry (CV; 0.1 to 10 Vs^–1) or as rotating-

disk electrode for rotating disk voltammetry (RDV). The auxiliary

electrode was a Pt wire, and the reference electrode was either an

aqueous Ag/AgCl electrode or a platinum wire used as a pseudo-

reference electrode. All potentials are referenced to the ferricinium/

ferrocene (Fc⁺/Fc) couple, used as an internal standard, and are

uncorrected from ohmic drop. The cell was connected to an Auto-

lab PGSTAT20 potentiostat (Eco Chemie BV, Utrecht, The Ne-

therlands) driven by a GPSE software running on a personal com-

puter.

X-ray Analysis: The structure was solved by direct methods (SIR-

97)^[54]and refined by full-matrix least-squares analysis (SHELXL-

97).^[55]All non H-atoms were refined anisotropically; H-atoms were

refined isotropically.

X-ray Crystal Structure of 9: Crystal data at 203 K for C₃₆H₃₆N₂,

–3

¯

M_r= 496.70, triclinic, space group P1, D_x= 1.129 gcm , Z = 2,

a = 7.5937(3), b = 10.9722(5), c = 18.8897(10) Å, α = 73.854(2)°, β

= 79.346(2)°, γ = 77.172(3)°, V = 1461.28(12) Å³. Bruker-Nonius

2498

www.eurjoc.org

Eur. J. Org. Chem. 2010, 2487–2503

Charge-Transfer Chromophores with a Dendralene-Type Backbone

Kappa-CCD diffractometer, Mo-K_αradiation, λ = 0.7107 Å, µ =

2 H), 7.86–7.90 (m, 2 H), 8.03 (d, J = 9.1 Hz, 1 H), 8.28 (s, 1 H)

ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 56.36, 61.39, 75.46, 92.80,

96.19, 98.58, 110.97, 112.10, 113.17, 114.07, 117.43, 123.66, 124.66,

125.65, 125.72, 125.85, 126.81, 127.86, 127.97, 128.24, 128.62,

0.065 mm^–1.

A

red crystal of

9

(linear dimensions ca.

0.2ϫ0.15ϫ0.02 mm) was obtained by slow evaporation of a solu-

tion of 9 in CH₂Cl₂at 25 °C. Numbers of measured and unique

reflections are 10106 and 6453, respectively (R_int= 0.054). Final 128.87, 129.92, 130.17, 133.63, 135.37, 136.77, 140.04, 154.73,

R(F) = 0.0656, wR(F²) = 0.1622 for 487 parameters and 3704 re-

155.93 ppm. IR (neat): ν = 2960, 2923, 2851, 2179, 2133, 1691,

˜

flections with IϾ2σ(I) and 2.425 Ͻ θ Ͻ 27.485° (corresponding R 1618, 1588, 1556, 1508, 1458, 1408, 1357, 1334, 1260, 1248, 1148,

values based on all 6453 reflections are 0.1269 and 0.2033, respec-

tively).

1076, 1004, 892, 798, 748 cm^–1. HR-EI-MS m/z (%): calcd. for

C₃₀H₁₈N₂O₂⁺: 438.1363; found 438.1361 (100, [M]⁺).

CCDC-758914 contains the supplementary crystallographic data

(excluding structure factors) for this paper. This data can be ob-

tained free of charge from The Cambridge Crystallographic Data

Centre, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:

+44(1223)-336-033; E-mail: deposit@ccdc.cam.ac.uk], or via

www.ccdc.cam.ac.uk/data_request/cif.

[2+2] Cycloaddition of TTF with Alkynes. General Method: A mix-

ture of the alkyne (0.06 mmol, 1 equiv.) and TTF (2–5 equiv. per

reacting CϵC bond) in CH₂Cl₂/MeCN, 1:1 (10 mL) was stirred at

50 °C for the indicated time. The solvent was evaporated in vacuo

and the residue subjected to FC.

(R)-[5-(2,2Ј-Dimethoxy-1,1Ј-binaphthalen-3-yl)-2,3-(di-1,3-dithiol-2-

ylidene)-4-pentyn-1-ylidene]malononitrile [(R)-19]: The title com-

(R)-5-(2,2Ј-Dimethoxy-1,1Ј-binaphthalen-3-yl)penta-2,4-diyn-1-ol

[(R)-16] and (R,R)-3,3Ј-(Buta-1,3-diyne-1,4-diyl)bis(2,2Ј-dimethoxy- pound was prepared from (R)-18 (25 mg, 0.057 mmol), according

1,1Ј-binaphthalene) [(R,R)-17]: To a solution of (R)-15 (133 mg,

0.393 mmol) and prop-2-yn-1-ol (0.23 mL, 223 mg, 3.97 mmol) in

CH₂Cl₂(35 mL), a solution of Hay catalyst in CH₂Cl₂(5 mL) was

added and the resulting solution stirred exposed to air for 18 h at

25 °C. Evaporation of the solvent in vacuo and subsequent purifi-

cation by FC (heptane/AcOEt, 9:1, heptane/AcOEt, 8:2, heptane/

to the general method. The mixture was stirred for 13 h at 50 °C

and purified by FC (CH₂Cl₂) to give (R)-19 as a dark brown solid

(12 mg, 33%). R_f= 0.3 (SiO₂, CH₂Cl₂); m.p. Ͼ 175 °C (decomp.);

[α]²_D⁰= +183 (c = 0.01, CH₂Cl₂). ¹H NMR (500 MHz, CDCl₃): δ

= 3.65 (s, 3 H), 3.78 (s, 3 H), 6.47 (d, J = 6.6 Hz, 1 H), 6.58 (d, J

= 6.6 Hz, 1 H), 6.90–6.94 (m, 2 H), 7.05 (d, J = 8.4 Hz, 1 H), 7.11

AcOEt, 7:3) gave (R,R)-17 as a light brown solid (24 mg, 18%) and (d, J = 8.5 Hz, 1 H), 7.18–7.24 (m, 2 H), 7.29–7.38 (m, 3 H), 7.45

(R)-16 as a light brown solid (78 mg, 51%).

(d, J = 9.1 Hz, 1 H), 7.81 (d, J = 8.2 Hz, 1 H), 7.86 (d, J = 8.1 Hz,

1 H), 7.99 (d, J = 9.1 Hz, 1 H), 8.10 (s, 1 H) ppm. ¹³C NMR

(125 MHz, CDCl₃): δ = 56.48, 61.31, 70.63, 90.41, 94.84, 97.82,

113.48, 113.64, 116.88, 117.20, 117.54, 118.76, 119.66, 121.32,

123.30, 123.59, 124.09, 125.15, 125.19, 125.58, 125.63, 126.60,

126.80, 127.70, 127.88, 129.03, 129.71, 130.43, 133.30, 133.87,

(R)-16: R_f= 0.0 (SiO₂, heptane/AcOEt, 8:2); m.p. 93–96 °C; [α]²_D⁰

1

= +120 (c = 0.1, CHCl₃). H NMR (300 MHz, CD₃OD): δ = 3.50

(s, 3 H), 3.72 (s, 3 H), 4.22 (s, 2 H), 4.33 (s, 1 H), 6.93–6.98 (m, 2

H), 7.12–7.37 (m, 4 H), 7.50 (d, J = 9.1 Hz, 1 H), 7.80–7.86 (m, 2

H), 8.01 (d, J = 9.0 Hz, 1 H), 8.14 (s, 1 H) ppm. ¹³C NMR

(75 MHz, CD₃OD): δ = 50.56, 50.84, 56.25, 61.05, 69.06, 69.57,

75.29, 77.62, 78.44, 83.09, 113.99, 116.35, 118.64, 124.23, 125.34,

126.15, 127.22, 128.27, 128.73, 130.05, 130.80, 131.28, 134.66,

134.02, 147.18, 154.8, 155.13, 157.05, 170.53 ppm. IR (neat): ν =

˜

3062, 2960, 2932, 2836, 2358, 2340, 2207, 1726, 1620, 1592, 1535,

1516, 1494, 1428, 1408, 1331, 1310, 1261, 1247, 1218, 1147, 1072,

1005, 906, 802 cm^–1. HR-FT-MALDI-MS (3-HPA) m/z (%): calcd.

for C₃₆H₂₂N₂O₂S₄Na⁺: 665.0456; found 665.0456 (100, [M +

Na]⁺).

135.28, 136.00, 155.77, 156.79 ppm. IR (neat): ν = 3270, 2933,

˜

2837, 1619, 1592, 1509, 1495, 1456, 1407, 1355, 1335, 1267, 1248,

1220, 1147, 1092, 1016, 913, 807, 748 cm^–1. HR-EI-MS m/z (%):

calcd. for C₂₇H₂₀O₃⁺: 392.1407; found 392.1406 (100, [M]⁺).

[2+2] Cycloaddition of TCNE with Alkynes. General Method: A

mixture of the alkyne (1 equiv.) and the indicated amount of TCNE

(0.7–12.0 equiv. per reacting CϵC bond) in CH₂Cl₂was stirred at

25 °C for the indicated time. The solvents were evaporated in vacuo

and the residue subjected to FC.

(R,R)-17: R_f= 0.1 (SiO₂, heptane/AcOEt, 8:2); m.p. 111–113 °C;

[α]²_D⁰= +162 (c = 0.1, CHCl₃). H NMR (300 MHz, CDCl₃): δ =

1

3.63 (s, 6 H), 3.80 (s, 6 H), 7.08–7.12 (m, 4 H), 7.22–7.42 (m, 8 H),

7.46 (d, J = 9.1 Hz, 2 H), 7.83–7.89 (m, 4 H), 8.01 (d, J = 9.0 Hz,

2 H), 8.22 (s, 2 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 56.52, (R)-3-(Dicyanomethylene)-2-(2,2Ј-dimethoxy-1,1Ј-binaphthalen-3-

61.27, 78.10, 79.38, 113.29, 116.00, 118.15, 123.51, 124.91, 125.23, yl)-4,5-(di-1,3-dithiol-2-ylidene)-1,6-heptadiene-1,1,7,7-tetracarbo-

125.46, 125.58, 126.58, 127.39, 127.75, 127.81, 128.84, 129.78,

nitrile [(R)-13]: The title compound was prepared from (R)-19

(10 mg, 0.016 mmol) and TCNE (24 mg, 0.19 mmol) in CH₂Cl₂

(20 mL), according to the general method. The mixture was stirred

for 24 h and purified by FC (CH₂Cl₂, CH₂Cl₂/AcOEt, 95:5,

CH₂Cl₂/AcOEt, 9:1) to give (R)-13 as a brown solid (6 mg, 50%).

130.08, 133.75, 134.22, 135.28, 154.64, 155.97 ppm. IR (neat): ν =

˜

3055, 2918, 2848, 2359, 2342, 1734, 1620, 1592, 1508, 1456, 1404,

1356, 1333, 1264, 1246, 1147, 1078, 1016, 806, 746 cm^–1. HR-FT-

MALDI-MS (3-HPA) m/z (%): calcd. for C₄₈H₃₄O₄⁺: 674.2452;

found 674.2463 (82, [M]⁺).

R_f= 0.5 (SiO₂, CH₂Cl₂/AcOEt, 99:1); m.p. 225–228 °C; [α]²_D⁰

=

1

+135 (c = 0.01, CH₂Cl₂). H NMR (300 MHz, CD₂Cl₂): δ = 3.11–

3.31 (m, 3 H), 3.81–3.93 (m, 3 H), 6.89–7.50 (m, 10 H), 7.87–8.09

(m, 4 H) (20 out of 22) ppm.^{[56] 13}C NMR (75 MHz, CD₂Cl₂): not

(R)-[5-(2,2Ј-Dimethoxy-1,1Ј-binaphthalen-3-yl)penta-2,4-diyn-1-ylid-

ene]malononitrile [(R)-18]: Dess–Martin periodinane (211 mg,

0.497 mmol, 15% solution in CH₂Cl₂) was added to a solution of

(R)-16 (78 mg, 0.199 mmol) in CH₂Cl₂(30 mL). The resulting solu-

tion was stirred for 1 h at 25 °C, filtered through a plug (SiO₂;

CH₂Cl₂), and concentrated in vacuo to ca. 50% of its original vol-

ume. Malononitrile (27 mg, 0.402 mmol) and Al₂O₃(122 mg,

1.193 mmol) were added, and the solution was stirred for 1 h at

50 °C. Purification by FC (heptane/AcOEt, 8:2, heptane/AcOEt,

7:3, heptane/AcOEt, 1:1) afforded (R)-18 as a light brown oil

(28 mg, 32%). R_f= 0.2 (SiO₂, heptane/AcOEt, 8:2); [α]²_D⁰= +114

available due to low solubility. IR (neat): ν = 3072, 2921, 2851,

˜

2342, 2360, 2209, 1734, 1618, 1587, 1540, 1416, 1353, 1310, 1247,

1149, 1021, 948, 887, 810, 743 cm^–1. UV/Vis (MeCN): λ_max(ε) =

230 (66800), 324 (21800), 478 nm (16600 ^–1cm^–1). CD (MeCN):

λ_max(∆ε) = 224 (+5), 236 (–61), 268 (+10), 337 (–4), 433 (–6),

527 nm (+3 ^–1cm^–1). HR-FT-MALDI-MS (3-HPA) m/z (%):

calcd. for C₄₂H₂₂N₆O₂S₄Na⁺: 793.0579; found 793.0565 (100, [M

+ Na]⁺).

1

(c = 0.1, CHCl₃). H NMR (300 MHz, CDCl₃): δ = 3.55 (s, 3 H),

(S)-2,2Ј-{[2,2Ј-Bis(methoxymethoxy)-1,1Ј-binaphthalene-3,3Ј-diyl]-

3.81 (s, 3 H), 7.05–7.14 (m, 2 H), 7.23–7.37 (m, 4 H), 7.41–7.48 (m,

bis(2,1-ethynediyl)}bis{3-[4-(dimethylamino)phenyl]-1,3-butadiene-

Eur. J. Org. Chem. 2010, 2487–2503

www.eurjoc.org

2499

F. Diederich et al.

FULL PAPER

1,1,4,4-tetracarbonitrile} [(S)-23]: To a solution of (S)-20 (27 mg, 6.50 (d, J = 9.0 Hz, 2 H), 7.35 (d, J = 9.0 Hz, 2 H) ppm. ¹³C NMR

0.038 mmol) in MeCN/CH₂Cl₂, 3:1 (20 mL), TCNE (25 mg, (75 MHz, CDCl₃): δ = –0.39, 14.05, 22.68, 26.77, 27.14, 31.68,

0.191 mmol) and TTF (40 mg, 0.193 mmol) were added. The mix-

ture was stirred for 18 h at 50 °C. Evaporation of the solvent and

subsequent FC (CH₂Cl₂, CH₂Cl₂/AcOEt, 95:5, CH₂Cl₂/AcOEt,

8:2) afforded (S)-23 as a black solid (11 mg, 29%). R_f= 0.7 (SiO₂,

CH₂Cl₂/AcOEt, 95:5); [α]²_D⁰= +15 (c = 0.01, CH₂Cl₂). ¹H NMR

(300 MHz, C₂D₂Cl₄): δ = 2.20 (s, 6 H), 3.07 (s, 12 H), 4.62 (d, J =

6.4 Hz, 2 H), 4.83 (d, J = 6.3 Hz, 2 H), 6.67 (d, J = 9.4 Hz, 4 H),

7.09 (d, J = 8.5 Hz, 2 H), 7.32–7.48 (m, 4 H), 7.73 (d, J = 9.4 Hz,

4 H), 7.86 (d, J = 8.0 Hz, 2 H), 8.34 (s, 2 H) ppm. ¹³C NMR

(75 MHz, C₂D₂Cl₄): δ = 30.18, 40.70, 56.70, 89.84, 94.30, 110.87,

112.07, 112.73, 113.84, 114.07, 114.95, 115.41, 117.27, 126.41,

127.10, 127.21, 130.34, 130.36, 130.46, 132.94, 136.15, 139.64,

139.66, 151.23, 153.08, 155.07, 159.95 ppm. UV/Vis (CH₂Cl₂): λ_max

(ε) = 233 (54100), 291 (25300), 425 nm (40000 ^–1cm^–1). CD

(CH₂Cl₂): λ_max(∆ε) = 237 (+26), 282 (–10), 367 (–7), 413 (+3),

466 nm (–6 ^–1cm^–1). HR-FT-MALDI-MS (3-HPA) m/z (%):

calcd. for C₆₀H₄₀N₁₀O₄Na⁺: 987.3126; found 987.3124 (70, [M +

Na]⁺).

50.98, 62.94, 66.48, 72.79, 79.46, 88.29, 88.68, 105.16, 111.16,

134.76, 148.92 ppm. IR (neat): ν = 2957, 2929, 2858, 2164, 2070,

˜

1602, 1522, 1466, 1406, 1369, 1250, 1197, 1138, 842 cm^–1. HR-EI-

MS m/z (%): calcd. for C₂₇H₃₉NSi⁺: 405.2846; found 405.2846 (90,

[M]⁺).

31: R_f= 0.1 (SiO₂, heptane/CH₂Cl₂, 9:1). ¹H NMR (300 MHz,

CDCl₃): δ = 0.88–0.92 (m, 12 H), 1.31 (br. s, 24 H), 1.55–1.57 (m,

8 H), 3.27 (t, J = 7.7 Hz, 8 H), 6.51 (d, J = 8.9 Hz, 4 H), 7.36 (d,

J = 9.0 Hz, 4 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 14.06,

22.70, 26.79, 27.17, 31.70, 51.01, 64.88, 67.63, 73.37, 80.22, 105.17,

111.23, 134.88, 148.95 ppm. IR (neat): ν = 2924, 2855, 2175, 2062,

˜

1592, 1519, 1464, 1404, 1364, 1292, 1256, 1188, 1110, 977, 810

cm^–1. HR-EI-MS m/z (%): calcd. for C₄₄H₆₀N₂⁺: 616.4751; found

616.4760 (100, [M]⁺).

4,4Ј-(Dodeca-1,3,5,7,9,11-hexayne-1,12-diyl)bis(N,N-dihexylaniline)

(8) and 9-[4-(N,N-Dihexylamino)phenyl]nona-2,4,6,8-tetrayn-1-ol

(32): K₂CO₃(157 mg, 1.13 mmol) and 28 (65 mg, 0.16 mmol) in

MeOH/THF, 1:1 (10 mL) were stirred for 1 h at 25 °C. CH₂Cl₂

(20 mL) was added, the organic layer was washed with H₂O

(10 mL), dried with MgSO₄, and filtered to yield a solution of de-

protected 28, which was directly used in the next step. Prop-2-yn-

1-ol (0.14 mL, 135 mg, 2.41 mmol) and Hay catalyst in CH₂Cl₂

(3 mL) were added. The resulting mixture was stirred exposed to

air for 2 h at 25 °C and purified by FC (heptane, heptane/AcOEt,

8:2, heptane/AcOEt, 1:1) to afford 8 (20 mg, 38%) as an orange

solid and 32 (21 mg, 34%) as a red-brown solid.

(S)-2,2Ј-(2,2Ј-Diethoxy-1,1Ј-binaphthalene-3,3Ј-diyl)bis{3-[4-(dimeth-

ylamino)phenyl]-1,3-butadiene-1,1,4,4-tetracarbonitrile} [(S)-27]:

The title compound was prepared from (S)-24 (73 mg, 0.116 mmol)

and TCNE (41 mg, 0.32 mmol) in CH₂Cl₂(5 mL), according to the

general method. The mixture was stirred for 18 h and purified by

FC (heptane/CH₂Cl₂, 1:1, heptane/CH₂Cl₂, 3:7, heptane/CH₂Cl₂,

1:9, CH₂Cl₂, CH₂Cl₂/AcOEt, 8:2) to give (S)-27 as a red solid

(72 mg, 70%). R_f= 0.1 (SiO₂, CH₂Cl₂); m.p. 202–205 °C; [α]²_D⁰

=

+1467 (c = 0.0033, mg mL^–1, MeCN).^{[57] 1}H NMR (300 MHz,

CDCl₃): δ = 0.60 (t, J = 7.0 Hz, 6 H), 3.14–3.20 (m, 14 H), 3.32–

3.37 (m, 2 H), 6.73 (d, J = 9.3 Hz, 4 H), 7.18 (d, J = 8.3 Hz, 2 H),

7.40–7.52 (m, 4 H), 7.75 (d, J = 9.3 Hz, 4 H), 7.97 (d, J = 8.4 Hz,

2 H), 8.21 (s, 2 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 15.43,

40.20, 69.60, 92.44, 111.15, 111.80, 112.22, 113.64, 114.58, 119.32,

122.32, 125.60, 126.30, 127.18, 128.60, 129.57, 130.27, 132.89,

133.00, 134.19, 136.52, 152.11, 154.02, 164.97, 167.06 ppm. IR

8: R_f= 0.3 (SiO₂, heptane/CH₂Cl₂, 9:1); m.p. Ͼ 40 °C (decomp.).

¹H NMR (300 MHz, CDCl₃): δ = 0.87–0.92 (m, 12 H), 1.25–1.31

(m, 24 H), 1.52–1.57 (m, 8 H), 3.27 (t, J = 7.7 Hz, 8 H), 6.51 (d, J

= 9.1 Hz, 4 H), 7.37 (d, J = 9.0 Hz, 4 H) ppm. ¹³C NMR (75 MHz,

CDCl₃): δ = 14.03, 22.66, 26.74, 27.12, 31.65, 51.02, 63.99, 64.45,

65.30, 67.71, 73.46, 80.31, 104.31, 111.30, 135.26, 149.19 ppm. IR

(neat): ν = 3734, 3628, 2921, 2852, 2360, 2342, 2133, 2033, 1734,

˜

1594, 1519, 1463, 1406, 1365, 1258, 1194, 1125, 1022, 812 cm^–1.

(neat): ν = 3067, 2981, 2919, 2215, 1601, 1539, 1486, 1438, 1377,

˜

UV/Vis (CH₂Cl₂): λ_max(ε) = 280 (48400), 301 (45500), 363 (27900),

1341, 1291, 1206, 1170, 1125, 1064, 1018, 943, 898, 824, 750 cm^–1.

UV/Vis (MeCN): λ_max(ε) = 201 (73900), 226 (77300), 262 (55300),

384 (37900), 532 nm (18500 ^–1cm^–1). CD (MeCN): λ_max(∆ε) =

207 (–42), 232 (+87), 264 (–27), 283 (+13), 307 (–7), 350 (+5),

398 nm (–5 ^–1cm^–1). HR-FT-MALDI-MS (3-HPA) m/z (%):

calcd. for C₅₆H₄₁N₁₀O₂⁺: 885.3409; found 885.3402 (100, [M +

H]⁺).

393 (42000), 442 (57400), 471 (57700), 517 nm (26700 ^–1cm^–1).

+

HR-FT-MALDI-MS (3-HPA) m/z (%): calcd. for C₄₈H₆₀N₂

:

664.4751; found 664.4744 (100, [M]⁺).

32: R_f= 0.3 (SiO₂, heptane/AcOEt, 8:2); m.p. Ͼ 40 °C (decomp.).

¹H NMR (300 MHz, CDCl₃): δ = 0.90 (t, J = 6.6 Hz, 6 H), 1.26–

1.31 (m, 12 H), 1.55–1.66 (m, 5 H), 3.27 (t, J = 7.7 Hz, 4 H), 4.38

(d, J = 4.9 Hz, 2 H), 6.50 (d, J = 9.1 Hz, 2 H), 7.36 (d, J = 9.1 Hz,

2 H) ppm. ¹³C NMR (125 MHz, CDCl₃): δ = 14.23, 22.87, 26.97,

27.36, 31.88, 51.20, 51.89, 63.31, 64.01, 65.03, 67.11, 71.41, 73.24,

4-[6-(Trimethylsilyl)hexa-1,3,5-triyn-1-yl]-N,N-dihexylaniline (28)

and 4,4Ј-(Octa-1,3,5,7-tetrayne-1,8-diyl)bis(N,N-dihexylaniline)

(31): K₂CO₃(1409 mg, 10.19 mmol) was added to a solution of 29

(664 mg, 1.74 mmol) in MeOH/THF, 1:1 (100 mL). The mixture

was stirred for 2 h at 25 °C, and CH₂Cl₂(80 mL) was added. The

organic phase was washed with H₂O (2ϫ50 mL), dried (MgSO₄),

and evaporated to yield deprotected 29 as a brown oil. The oil

was dissolved in acetone (20 mL), and TMSA (2.51 mL, 1.74 g,

17.74 mmol) and Hay catalyst in acetone (100 mL) were added.

The resulting mixture was stirred exposed to air for 3 h at 25 °C.

The mixture was filtered through a plug (SiO₂; acetone), the solvent

evaporated, the residue preadsorbed on SiO₂, and purified by FC

(heptane, heptane/CH₂Cl₂, 98:2, heptane/CH₂Cl₂, 95:5) to afford

28 (355 mg, 50%) as a dark brown solid and 31 (81 mg, 15%) as a

red-brown oil.

77.80, 80.21, 104.74, 111.45, 135.26, 149.37 ppm. IR (neat): ν =

˜

3349, 2923, 2852, 2360, 2341, 2148, 2089, 1700, 1596, 1519, 1464,

1404, 1364, 1294, 1257, 1228, 1186, 1101, 1068, 1016, 884, 810

cm^{– 1}. HR-FT-MALDI-MS (3-HPA) m/z (%): calcd. for

C₂₇H₃₄NO⁺: 388.2635; found 388.2633 (100, [M + H]⁺).

2-[2-(4-Cyanophenyl)-1,2-(di-1,3-dithiol-2-ylideneethyl)]-3,6-bis(dicy-

anomethylene)-7-[4-(dimethylamino)phenyl]-4,5-(di-1,3-dithiol-2-ylid-

ene)-1,7-octadiene-1,1,8,8-tetracarbonitrile (7): Tetrayne 6 (6 mg,

0.018 mmol), TCNE (11 mg, 0.089 mmol), and TTF (18 mg,

0.089 mmol) were dissolved in CH₂Cl₂/MeCN, 1:1 (6 mL). The re-

sulting solution was stirred for 18 h at 50 °C and purified by FC

(CH₂Cl₂, CH₂Cl₂/EtOAc, 95:5, CH₂Cl₂/EtOAc, 9:1) to give 7 as a

black metallic-like solid (10 mg, 58%); R_f= 0.22 (SiO₂, CH₂Cl₂/

EtOAc, 9:1); m.p. Ͼ 221 °C (decomp.). ¹H NMR (500 MHz,

CD₂Cl₂): δ = 3.16, 3.19 (s, 6 H), 6.47–6.50 (m, 1 H), 6.59–6.61 (m,

1 H), 6.77–6.83 (m, 3 H), 7.11 (d, J = 6.5 Hz, 1 H), 7.17 (d, J =

28: R_f= 0.3 (SiO₂, heptane/CH₂Cl₂, 9:1); m.p. Ͼ 40 °C (decomp.).

¹H NMR (300 MHz, CDCl₃): δ = 0.21 (s, 9 H), 0.88–0.92 (m, 6

H), 1.31 (br. s, 12 H), 1.55–1.56 (m, 4 H), 3.26 (t, J = 7.8 Hz, 4 H),

2500

www.eurjoc.org

Eur. J. Org. Chem. 2010, 2487–2503

Charge-Transfer Chromophores with a Dendralene-Type Backbone

6.5 Hz, 1 H), 7.20–7.24 (m, 2 H), 7.31 (d, J = 6.5 Hz, 1 H), 7.38

general method. The mixture was stirred for 18 h and purified by

(d, J = 6.5 Hz, 1 H), 7.57 (d, J = 9.0 Hz, 2 H), 7.89–7.95 (m, 3 H) FC (heptane, heptane/CH₂Cl₂, 1:1, CH₂Cl₂) to give 38 as a dark

ppm. ¹³C NMR (125 MHz, CD₂Cl₂): δ = 40.28, 40.37, 70.69, 70.77, brown solid (39 mg, 88%). R_f= 0.5 (SiO₂, CH₂Cl₂); m.p. 161–

71.57, 71.97, 75.31, 75.94, 109.88, 110.17, 111.57, 112.10, 112.45, 163 °C (decomp.). ¹H NMR (300 MHz, CDCl₃): δ = 0.85–0.94 (m,

112.51, 112.61, 112.84, 113.36, 114.64, 114.86, 115.29, 115.33, 12 H), 1.22–1.38 (m, 24 H), 1.60–1.67 (m, 8 H), 3.41 (t, J = 7.8 Hz,

115.36, 115.49, 115.61, 115.64, 115.73, 115.80, 115.91, 116.02, 8 H), 6.69 (d, J = 9.6 Hz, 4 H), 7.69 (d, J = 9.4 Hz, 4 H) ppm. ¹³C

116.07, 116.23, 116.35, 116.41, 116.45, 117.10, 117.31, 117.43, NMR (75 MHz, CDCl₃): δ = 14.02, 22.63, 26.67, 27.34, 31.55,

117.62, 118.39, 118.67, 118.95, 119.05, 119.11, 119.32, 120.37, 51.61, 67.49, 72.39, 72.58, 78.29, 96.15, 100.17, 109.54, 110.52,

120.61, 122.27, 123.49, 125.55, 125.68, 125.81, 125.87, 126.44, 112.42, 113.42, 114.17, 116.28, 132.65, 148.42, 153.45, 156.76 ppm.

128.97, 129.13, 129.62, 129.68, 130.47, 130.83, 131.82, 131.94, IR (neat): ν = 2925, 2854, 2359, 2215, 1724, 1601, 1487, 1455, 1414,

˜

133.50, 134.07, 140.68, 141.05 ppm. IR (neat): ν = 3066, 2920,

1351, 1259, 1184, 1092, 1015, 865, 796 cm^–1. UV/Vis (CH₂Cl₂):

˜

2851, 2199, 1600, 1486, 1435, 1320, 1208, 1170, 1018, 1000, 941,

λ_max(ε) = 281 (22800), 297 (22800), 318 (23700), 367 (24300), 381

901, 848, 817 cm^–1. UV/Vis (CH₂Cl₂): 402 (sh, 41000), 459 nm (sh, 22000), 419 (23600), 460 nm (38900 ^–1cm^–1). HR-FT-

(117000 ^–1cm^–1). HR-MALDI-MS (3-HPA) m/z (%): calcd. for MALDI-MS (3-HPA) m/z (%): calcd. for C₆₀H₆₁N₁₀⁺: 921.5075;

C₄₇H₂₃N₁₀S₈⁺: 982.9867; found 982.9850 (100, [M + H]⁺).

found 921.5075 (54, [M + H]⁺).

3,8-Bis(dicyanomethylene)-2,9-bis[4-(dimethylamino)phenyl]-1,9-de- 3,12-Bis(dicyanomethylene)-2,13-bis[4-(dihexylamino)phenyl]-

cadiene-4,6-diyne-1,1,10,10-tetracarbonitrile (36): The title com-

pound was prepared from tetrayne 1 (30 mg, 0.09 mmol) and

4,5,10,11-tetra-(1,3-dithiol-2-ylidene)-1,13-tetradecadiene-6,8-diyne-

1,1,14,14-tetracarbonitrile (39): The title compound was prepared

TCNE (23 mg, 0.18 mmol) in CH₂Cl₂(25 mL), according to the from 38 (6 mg, 0.007 mmol), according to the general method. The

general method. The mixture was stirred for 12 h at 25 °C. After

that time, additional TCNE (10 mg, 0.08 mmol) was added and the

mixture was stirred for 5 h at 25 °C. FC (CH₂Cl₂/EtOAc, 99:1) gave

mixture was stirred for 6 h at 50 °C and purified by FC (CH₂Cl₂,

CH₂Cl₂/AcOEt, 98:2, CH₂Cl₂/AcOEt, 9:1, CH₂Cl₂/AcOEt, 1:1) to

give 39 as a brown solid (5 mg, 58%). R_f= 0.8 (SiO₂, CH₂Cl₂/

36 as a black metallic-like solid (29 mg, 55%). R_f= 0.34 (SiO₂, AcOEt, 95:5); m.p. 252–254 °C (decomp.). ¹H NMR (300 MHz,

CH₂Cl₂/EtOAc, 99:1); m.p. Ͼ 260 °C (decomp.). ¹H NMR CDCl₃): δ = 0.72–0.90 (m, 12 H), 1.26–1.43 (m, 24 H), 1.62 (br. s,

(400 MHz, C₂D₂Cl₄): δ = 3.11 (s, 12 H), 6.68 (d, J = 9.3 Hz, 4 H), 8 H), 3.39 (br. s, 8 H), 6.62–6.75 (m, 8 H), 6.99–7.10 (m, 4 H),

7.62 (d, J = 9.3 Hz, 4 H) ppm. ¹³C NMR (125 MHz, C₂D₂Cl₄): δ 7.70–8.10 (m, 4 H) ppm. ¹³C NMR (75 MHz, C₂D₂Cl₄): δ = 14.46,

= 40.21, 72.59, 83.63, 92.76, 100.19, 109.22, 110.15, 112.54, 113.41,

22.96, 26.96, 27.70, 31.84, 51.66, 71.50, 71.60, 74.46, 99.24, 112.58,

112.85, 114.00, 114.36, 115.15, 116.10, 121.70, 122.14, 123.80,

128.71, 132.92, 133.19, 148.63, 148.99, 149.36, 153.63, 153.97,

113.95, 116.16, 132.27, 147.91, 154.82, 156.36 ppm. IR (neat): ν =

˜

2921, 2863, 2214, 2136, 1606, 1537, 1480, 1455, 1386, 1355, 1308,

1217, 1175, 1144, 1059, 1003, 990, 939, 898, 825, 797, 743 cm^–1. 154.07, 156.20, 156.39, 161.12, 165.41 ppm.^[56]IR (neat): ν = 2959,

˜

UV/Vis (CH₂Cl₂): λ_max(ε) = 294 (29400), 311 (sh, 28600), 362 2918, 2850, 2360, 2342, 2209, 1727, 1601, 1489, 1456, 1365, 1259,

(26300), 391 (33200), 471 (62300), 642 nm (4600 ^–1cm^–1). HR- 1182, 1089, 1016, 864, 796 cm^–1. UV/Vis (CH₂Cl₂): λ_max(ε) = 228

MALDI-MS (3-HPA) m/z (%): calcd. for C₃₆H₂₀N₁₀^–: 592.1881;

found 592.1872 ([M]^–). C₃₆H₂₀N₁₀(592.62): calcd. C 72.96, H 3.40,

N 23.64; found C 73.73, H 3.63, N 23.15.

(24600), 244 (19100), 463 (40100), 484 nm (39900 ^–1cm^–1). HR-

FT-MALDI-MS (3-HPA) m/z (%): calcd. for C₇₂H₆₈N₁₀S₈Na⁺:

1351.3286; found 1351.3270 (100, [M + Na]⁺).

2-[4-(Dihexylamino)phenyl]-3-{10-[4-(dihexylamino)phenyl]-

1,3,5,7,9-decapentayn-1-yl}-1,3-butadiene-1,1,4,4-tetracarbonitrile

(37): The title compound was prepared from 8 (17 mg, 0.026 mmol)

and TCNE (2.5 mg, 0.02 mmol) in CH₂Cl₂(6 mL), according to

the general method. The mixture was stirred for 5 h, the residue

was preadsorbed on SiO₂, and purified by FC (pentane, pentane/

3,8,9,12-Tetrakis(dicyanomethylene)-2,13-bis[4-(dihexylamino)-

phenyl]-4,5,10,11-tetra-(1,3-dithiol-2-ylidene)-1,13-tetradecadien-6-

yne-1,1,14,14-tetracarbonitrile (40): The title compound was pre-

pared from 39 (20 mg, 0.015 mmol) and TCNE (7 mg, 0.054 mmol)

in CH₂Cl₂(5 mL), according to the general method. The mixture

was stirred for 18 h and purified by FC (CH₂Cl₂, CH₂Cl₂/AcOEt,

CH₂Cl₂, 1:1, pentane/CH₂Cl₂, 3:7, CH₂Cl₂) to yield 37 as a green 98:2, CH₂Cl₂/AcOEt, 95:5, CH₂Cl₂/AcOEt, 9:1, CH₂Cl₂/AcOEt,

solid (10 mg, 65%). R_f= 0.8 (SiO₂, CH₂Cl₂); m.p. Ͼ 40 °C (de- 8:2) to afford 40 as a dark brown solid (21 mg, 96%). R_f= 0.3

comp.). ¹H NMR (300 MHz, CDCl₃): δ = 0.88–0.94 (m, 12 H), (SiO₂, CH₂Cl₂/AcOEt, 95:5); m.p. 217–219 °C. ¹H NMR

1.25–1.38 (m, 24 H), 1.54–1.64 (m, 8 H), 3.29 (t, J = 7.8 Hz, 4 H),

3.40 (t, J = 7.8 Hz, 4 H), 6.52 (d, J = 9.1 Hz, 2 H), 6.68 (d, J =

9.4 Hz, 2 H), 7.40 (d, J = 9.0 Hz, 2 H), 7.70 (d, J = 9.4 Hz, 2 H)

ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 14.03, 22.64, 22.67, 26.69,

26.74, 27.16, 27.33, 31.56, 31.66, 51.04, 51.55, 60.60, 63.92, 67.43,

69.38, 70.28, 72.78, 73.66, 74.54, 83.13, 84.51, 98.27, 99.72, 103.30,

(300 MHz, CDCl₃): δ = 0.91 (br. s, 12 H), 1.26–1.35 (m, 24 H),

1.64 (br. s, 8 H), 3.25–3.55 (m, 8 H), 6.74–6.77 (m, 4 H), 7.10–7.32

(m, 8 H), 7.70–8.10 (m, 4 H) ppm. ¹³C NMR (75 MHz, C₂D₂Cl₄):

δ = 14.09, 22.68, 26.75, 27.43, 31.60, 51.59, 77.30, 111.61, 112.24,

112.65, 112.86, 114.03, 114.60, 114.85, 115.05, 115.27, 116.32,

133.11, 133.15, 146.96, 147.36, 147.39, 147.81, 153.62,

110.01, 110.91, 111.40, 112.23, 113.39, 114.30, 116.43, 132.64, 153.88 ppm.^[56]IR (neat): ν = 3072, 2923, 2853, 2359, 2341, 2205,

˜

135.67, 149.20, 149.73, 153.26, 157.87 ppm (37 out of 38). IR

2096, 1599, 1487, 1444, 1412, 1344, 1210, 1179, 983, 900, 818 cm^–1.

(neat): ν = 2954, 2924, 2854, 2214, 2170, 2004, 1736, 1590, 1524, UV/Vis (CH₂Cl₂): λ_max(ε) = 252 (42200), 281 (sh, 30700), 458

˜

1485, 1445, 1406, 1349, 1323, 1293, 1258, 1184, 1170, 1084, 989,

813 cm^–1. UV/Vis (CH₂Cl₂): λ_max(ε) = 255 (48300), 332 (48000),

408 (41000), 474 (67000), 639 nm (18500 ^–1cm^–1). HR-FT-

MALDI-MS (3-HPA) m/z (%): calcd. for C₅₄H₆₁N₆⁺: 793.4952;

found 793.4938 (80, [M + H]⁺).

(115200), 581 nm (sh, 21100 ^–1cm^–1). HR-FT-MALDI-MS (3-

HPA) m/z: calcd. for C₇₈H₆₉N₁₄S₈⁺: 1457.3590; found 1457.3600

(100, [M + H]⁺).

4,4Ј-(1,3,5,7,9,11-Dodecahexayne-1,12-diyl)bis(N,N-diisopropylanil-

ine) (9): To a solution of the TES-protected alkyne 33 (82 mg,

0.226 mmol) in THF (8 mL), nBu₄NF (0.45 mL, 118 mg,

0.45 mmol, 1  in THF) was added. The mixture was stirred for

20 min at 0 °C, diluted with CH₂Cl₂, and filtered through a plug

3,12-Bis(dicyanomethylene)-2,13-bis[4-(dihexylamino)phenyl]-1,13-

tetradecadiene-4,6,8,10-tetrayne-1,1,14,14-tetracarbonitrile (38):

The title compound was prepared from 8 (32 mg, 0.048 mmol) and

TCNE (13 mg, 0.098 mmol) in CH₂Cl₂(7 mL), according to the (SiO₂; CH₂Cl₂). The resulting solution of deprotected 33 was con-

Eur. J. Org. Chem. 2010, 2487–2503

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2501

F. Diederich et al.

FULL PAPER

centrated in vacuo to a volume of ca. 20 mL and was directly used

in the next step. Hay catalyst in CH₂Cl₂(5 mL) was added and the

resulting mixture stirred exposed to air for 2 h at 25 °C. The solvent

was evaporated, the residue adsorbed on SiO₂and purified by FC

AcOEt, 1:1, heptane/AcOEt, 2:8) to give 43 as a brown solid (8 mg,

65%). R_f= 0.4 (SiO₂, heptane/AcOEt, 2:8); m.p. 205–208 °C (de-

comp.). ¹H NMR (300 MHz, CDCl₃): δ = 1.24–1.60 (m, 24 H),

3.95–4.25 (m, 4 H), 5.10–5.40 (m, 4 H), 6.56–6.62 (m, 2 H), 6.83–

(heptane, heptane/AcOEt, 9:1, heptane/AcOEt, 8:2, heptane/ 6.90 (m, 4 H), 7.00–7.20 (m, 2 H), 7.79–8.00 (m, 4 H) ppm.^{[56] 13}

C

AcOEt, 1:1, AcOEt) to afford 9 (36 mg, 65%) as a red solid. R_f=

NMR (75 MHz, CDCl₃): not available due to low solubility. IR

0.3 (SiO₂, heptane/AcOEt, 8:2); m.p. Ͼ 40 °C (decomp.). ¹H NMR (neat): ν = 3069, 2922, 2852, 2359, 2205, 2103, 1717, 1598, 1538,

˜

(300 MHz, CDCl₃): δ = 1.29 (d, J = 6.9 Hz, 24 H), 3.86–3.95 (m,

1445, 1366, 1339, 1308, 1260, 1216, 1186, 1116, 1014, 796 cm^–1.

4 H), 6.71 (d, J = 9.2 Hz, 4 H), 7.36 (d, J = 9.1 Hz, 4 H) ppm. ¹³C

UV/Vis (CH₂Cl₂): λ_max(ε) = 230 (18900), 460 (38300), 479 nm (sh,

NMR (75 MHz, CDCl₃): δ = 20.98, 47.52, 63.95, 64.43, 65.27, 36000 ^–1cm^–1). HR-ESI-MS (CH₂Cl₂/MeOH) m/z (%): calcd. for

67.68, 73.50, 80.19, 105.10, 114.96, 134.64, 149.55 ppm. IR (neat):

C₆₀H₄₅N₁₀S₈⁺: 1161.1589; found 1161.1594 (100, [M + H]⁺).

ν = 2962, 2924, 2852, 2132, 2032, 1588, 1515, 1462, 1420, 1371,

˜

Supporting Information (see also the footnote on the first page of

this article): Experimental procedures and spectra (¹H NMR, CD/

UV/Vis; 16 pages).

1328, 1296, 1260, 1185, 1155, 1115, 1018, 816 cm^–1. UV/Vis

(CH₂Cl₂): λ_max(ε) = 282 (51400), 292 (48400), 299 (sh, 45500), 363

(30200), 393 (44300), 440 (56000), 469 (54000), 515 nm

(24100 ^–1cm^–1). HR-ESI-TOF-MS (CH₂Cl₂/MeOH) m/z (%):

calcd. for C₃₆H₃₇N₂⁺: 497.2951; found 497.2940 (22, [M + H]⁺).

Acknowledgments

2-[4-(Diisopropylamino)phenyl]-3-{10-[4-(diisopropylamino)phenyl]-

1,3,5,7,9-decapentayn-1-yl}-1,3-butadiene-1,1,4,4-tetracarbonitrile

(41): The title compound was prepared from 9 (32 mg, 0.064 mmol)

and TCNE (6 mg, 0.046 mmol) in CH₂Cl₂(18 mL), according to

the general method. The mixture was stirred for 5 h and purified

by FC (pentane/AcOEt, 8:2, pentane/AcOEt, 1:1) to give 41 as a

This work was supported by the Swiss ETH Research Council and

the German Fonds der Chemischen Industrie. We thank Dr. J. L.

Alonso-Gómez and P. Rivera-Fuentes (ETHZ) for many fruitful

discussions and Dr. Carlo Thilgen (ETHZ) for his help with the

nomenclature of the compounds described in this paper.

1

green solid (24 mg, 83%). R_f= 0.6 (SiO₂, heptane/AcOEt, 1:1). H

[1] M. I. Bruce, J. R. Rodgers, M. R. Snow, A. G. Swincer, J.

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NMR (300 MHz, CDCl₃): δ = 1.30 (d, J = 6.9 Hz, 12 H), 1.39 (d,

J = 6.9 Hz, 12 H), 3.88–3.98 (m, 2 H), 4.05–4.14 (m, 2 H), 6.72 (d,

J = 9.1 Hz, 2 H), 6.88 (d, J = 9.5 Hz, 2 H), 7.38 (d, J = 9.1 Hz, 2

H), 7.69 (d, J = 9.5 Hz, 2 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ

= 20.77, 20.85, 20.92, 21.03, 47.48, 47.73, 48.46, 48.70, 60.52, 63.82,

67.32, 69.26, 70.12, 72.71, 73.61, 74.40, 83.00, 84.25, 98.15, 99.58,

103.80, 109.89, 110.78, 113.28, 114.15, 114.63, 114.79, 116.29,

131.81, 131.94, 134.76, 134.95, 148.95, 149.80, 153.33, 157.56 ppm.

IR (neat): ν = 2963, 2924, 2852, 2214, 2154, 2027, 1734, 1596, 1484,

˜

1445, 1371, 1333, 1297, 1260, 1188, 1153, 1088, 1014, 794 cm^–1.

UV/Vis (CH₂Cl₂): λ_max(ε) = 255 (40500), 332 (37000), 349 (36000),

409 (33900), 472 (54300), 624 nm (15100 ^–1cm^–1). HR-ESI-TOF-

MS (CH₂Cl₂/MeOH) m/z (%): calcd. for C₄₂H₃₇N₆⁺: 625.3074;

found 625.3071 (51, [M + H]⁺).

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1,13-tetradecadiene-4,6,8,10-tetrayne-1,1,14,14-tetracarbonitrile

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0.022 mmol) and TCNE (6 mg, 0.045 mmol) in CH₂Cl₂(5 mL), ac-

cording to the general method. The mixture was stirred for 18 h

and purified by FC (pentane/AcOEt, 1:1, AcOEt/CH₂Cl₂, 95:5, Ac-

OEt/CH₂Cl₂, 9:1) to give 42 as a brown solid (11 mg, 65%). R_f=

0.5 (SiO₂, heptane/AcOEt, 1:1); m.p. 130–132 °C (decomp.). ¹H

NMR (300 MHz, CDCl₃): δ = 1.40 (d, J = 6.9 Hz, 24 H), 4.06–

4.15 (m, 4 H), 6.89 (d, J = 9.6 Hz, 4 H), 7.67 (d, J = 9.4 Hz, 4 H)

ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 20.87, 20.96, 48.66, 48.86,

67.46, 72.30, 72.63, 78.24, 96.05, 99.96, 109.35, 110.32, 113.21,

113.93, 114.69, 114.79, 116.08, 131.70, 131.82 148.05, 153.34,

156.34 ppm. IR (neat): ν = 2965, 2931, 2359, 2214, 2178, 2073,

˜

1598, 1482, 1445, 1374, 1337, 1309, 1260, 1218, 1188, 1096, 1013,

791 cm^–1. UV/Vis (CH₂Cl₂): λ_max(ε) = 282 (25600), 297 (25600),

318 (26100), 366 (27400), 378 (sh, 24200), 418 (25300), 461 nm

(42900 ^–1cm^–1). HR-FT-MALDI-MS (3-HPA) m/z (%): calcd. for

C₄₈H₃₇N₁₀⁺: 753.3197; found 753.3205 (55, [M + H]⁺).

3,12-Bis(dicyanomethylene)-2,13-bis[4-(diisopropylamino)phenyl]-

4,5,10,11-tetra-1,3-dithiol-2-ylidene-1,13-tetradecadiene-6,8-diyne-

1,1,14,14-tetracarbonitrile (43): The title compound was prepared

from 42 (8 mg, 0.011 mmol), according to the general method. The

mixture was stirred for 4 h at 50 °C and purified by FC (heptane/

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Received: January 11, 2010

Published Online: March 17, 2010

Eur. J. Org. Chem. 2010, 2487–2503

www.eurjoc.org

2503

Article Doi

Chiral and achiral charge-transfer chromophores with a dendralene-type backbone by electronically controlled Cycloaddition/Cycloreversion Cascades

DOI: 10.1002/ejoc.201000030

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Article abstract of DOI:10.1002/ejoc.201000030

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