Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes

Article abstract of DOI:10.1002/chem.201701170

A simple regiospecific route to otherwise problematic substituted tetracenes is described. The diverse cores (E)-1,2-Ar¹CH₂(HOCH₂)C=C(CH₂OH)I (Ar¹=Ph, 4-MePh, 4-MeOPh, 4-FPh) and (E)-1,2-I(HOCH₂)C=C(CH₂OH)I, accessed from ultra-low cost HOCH₂C≡CCH₂OH at multi-gram scales, allow the synthesis of diol libraries (E)-1,2-Ar¹CH₂(HOCH₂)C=C(CH₂OH)CH₂Ar² (Ar²=Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic oxidation cleanly provides dialdehydes (E)-1,2-Ar¹CH₂(CHO)C=C(CHO)CH₂Ar², which in many cases undergo titanium(IV) chloride-induced double Bradsher closure, providing a convenient method for the synthesis of regiochemically and analytically pure tetracenes (12 examples). The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out.

Full text of DOI:10.1002/chem.201701170

A Journal of
Accepted Article
Title: Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes
Authors: Simon Woodward, Miriam Ackermann, Saurabh Ahirwar,
Laurence Burroughs, Mary Robert Garrett, John Ritchie,
Jonathan Shine, Björk Tyril, Kevin Simpson, and Peter
Woodward
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To be cited as: Chem. Eur. J. 10.1002/chem.201701170
Link to VoR: http://dx.doi.org/10.1002/chem.201701170
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10.1002/chem.201701170
Chemistry - A European Journal
Manuscript for Chemistry Eur. J.: Woodward, et al.
Straightforward Synthesis of 2- and 2,8-Substituted
Tetracenes
Simon Woodward,*[a] Miriam Ackermann,[a] Saurabh Ahirwar,[a] Laurence
Burroughs,[a] Mary Robert Garrett,[a] John Ritchie,[a] Jonathan Shine,[a] Björk
Tyril,[a] Kevin Simpson[b] and Peter Woodward[a]
[a] Prof Dr S Woodward, M Ackermann, S Ahirwar, Dr L Burroughs, Dr M R Garrett, J Ritchie, J
Shine, B Tyril, P Woodward, GSK Carbon Neutral Laboratories for Sustainable Chemistry,
Jubilee Campus, University of Nottingham, Nottingham NG7 2TU, United Kingdom.
[b]
K Simpson, European Thermodynamics Ltd, 8 Priory Business Park, Kibworth, Leicestershire,
LE8 0RX, United Kingdom.
Abstract: A simple regiospecific route to otherwise problematic substituted tetracenes is
described. The diverse cores (E)-1,2-Ar1CH2(HOCH2)C=C(CH2OH)I (Ar1 = Ph, 4-MePh, 4-MeOPh,
4-FPh) and (E)-1,2-I(HOCH2)C=C(CH2OH)I, accessed from ultra-low cost HOCH2C≡CCH2OH at
multi-gram
scales,
allow
the
synthesis
of
diol
libraries
(E)-1,2-
Ar1CH2(HOCH2)C=C(CH2OH)CH2Ar2 (Ar2 = Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-
biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic
oxidation cleanly provides dialdehydes (E)-1,2-Ar1CH2(CHO)C=C(CHO)CH2Ar2 which in many
cases undergo titanium(IV) chloride induced double Bradsher closure providing a convenient
method for the synthesis of regiochemically and analytically pure tetracenes (12 examples).
The sequence is typically chromatography-free, scalable, efficient and technically simple to carry
out.
Introduction
Of diverse utility in organic electronics[1] (including light emitting, transistor, sensor and solar
cell applications) tetracene (1aa, Scheme 1), and its derivatives, must be synthesised[2] due to
the lack of terrestrial sources.[3] This situation accounts for the 500-fold cost difference between
anthracene and tetracene 1aa (ca. 7 cents/mmol vs. €35/mmol).[4] We sought a route to 1aa,
and simple derivatives, which fulfilled the following characteristics: (i) minimised total step-count
(ii) use of only low cost sustainable starting materials, (iii) diversity orientated intermediates
facilitating the preparation of substituted tetracene libraries, (iv) simple (chromatography-free)
work-up procedures providing analytically pure intermediates and final tetracenes, (v)
applicability to gram scales without yield or purity degradation issues. While many elegant
approaches to (substituted) tetracenes (1) are known[2] failures against one or more of the
criteria (i)-(v) are unfortunately extremely commonplace. Traditional routes to tetracene
derivatives typically involve unidirectional synthesis from ortho substituted phenylene units
wherein only one ring is formed at a time (e.g. C-ring closure in the right of Scheme 1). The nice
commercial (3M) process to 2-chlorotetracene of Gerlach is a good example of such a
disconnection.[5] We thought to use bidirection synthesis, a powerful tool in natural product
preparation,[6] but which is rarely used in accessing tetracenes[7] or indeed polyaromatics[8] in
general.
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Scheme 1. The approach herein to tetracenes (1) using bidirectional[6] closure (B,C-ring
formation) of highly soluble and crystalline bis-aldehydes (2) vs. an exemplary unidirectional
synthesis. Adding substituents to the A/D phenyl groups allows access to acene derivatives.
The proposal on the left of Scheme 1 requires Bradsher[9] (hydroxyalklation) closure of both
aldehydes in 2 directly forming the B and C rings of tetracenes 1 in a single pot. Such two-
directional strategies have no exact precedent in tetracene synthesis as far as we can tell.
Naphthalene formation from simple cis-1,2-substituted alkene(CHO)(CH2Ph) fragments (the
closest analogue of the required B-ring formation in Scheme 1) is described in a handful of
cases.[10] Less than a dozen papers describe ‘one-directional’ H+/Lewis acid closure of
phenylene(CHO)(CH2Ph) units (the reaction most analogous to the required C-ring closure to
tetracene). Anthracenes[11] and benzo[g](iso)quinolones,[12]
a
bis-naphthothieno[2,3-d]
thiophene,[8a] a trinaphthylene[8b] and one very recent tetracene[8c] have been prepared this way.
Contemporary (2016-17) alternatives have highlighted gold[13] and Fe(III)[14] catalysed two-
directional syntheses to dihydrotetracenes and various polyaromatics, respectively. However,
preparation of some cyclisation precursors can be step/chromatographically intensive in such
approaches. Cyclisation promotors for tetracene formation in particular need careful selection:
H+ is commonly used to instigate Bradsher reactions,[8.9] but such conditions can also readily
oxidise the tetracene products to unstable radical cations (that are known to subsequently
decompose to complex mixtures).[15] The use of Lewis acid cyclisation is preferred, but in some
cases even these are overly oxidising towards tetracenes.[16] However, if such issues are
overcome core 2 is an attractive precursor for tetracene library synthesis as no post-cyclisation
C-oxidation state manipulation is required (c.f. quinoid and dihydrotetracene routes to
tetracenes[2]), water being formally the only by-product produced in the Bradsher aromatisation.
Results and Discussion
We proposed that all of the carbons in our tetracene synthesis should arise from low cost and
sustainable 2-butyne-1,4-diol (4 cents/g)[4] and benzyl chloride (3 cents/g)[4] or its simple
derivatives via the diversity orientated iodides 3-4 (Table 1). Copper-catalysed (CuBr·SMe2, 2
mol-%) direct addition of 4-(R1)C6H4CH2MgCl to HOCH2C≡CCH2OH proceeds, under our modified
literature conditions, to the expected (-OMgCl directed[17]) (E)-carbomagnesiation intermediate
which smoothly intercepts iodine providing the new diversity cores 3a-d (see Supporting
Information). Acceptable to good (58-72%) yields, on 10 g scales, are attained by direct
crystallisation of the crude reaction products. In the case of 3c, removal of a Wurtz by-product
is necessary prior to recrystallization but this too is straight forward, even at multi-gram levels.
Increasing the carbomagnesiation reaction temperature to 50-55 oC is the key to attaining high
conversion in these cabocuprations of lower reactivity benzylic Grignard reagents.[17] Equally
conveniently, 4 directly precipitates as an off-white solid from a simple reaction of 2-butyne-
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1,4-diol with iodine in CHCl3 on >10 g scales (90% yield), using our modified conditions.[18] The
simplicity of the preparations of 3-4 has encouraged us regarding their commercial
availability.[19]
Iodides 3-4 are potent precursors for straightforward Negishi-type couplings providing 5
efficiently and quickly (Table 1). Previously, slow addition techniques and specialist ligands have
been necessary to avoid competitive deprotonation in such unprotected alcohol substrates.[20]
However, this is not the case for 5 and a wide range of asymmetric diols can be realised in
excellent yields (85-99%) using a typical S-Phos biaryl ligand.[20] Simple non-proprietary
tricyclohexylphosphine (PCy3) also provides equivalent yields (in all cases tested, Method I).
These catalytic Negishi couplings show very strong ligand inhibition at L/Pd ratios of >1 but use
of a slight deficiency of phosphine in the coupling prevents this becoming an issue. Isolation of
the diols 5 is facilitated by their low solubility in Et2O, typically trituration in this solvent provides
off-white solids (>98% pure) that can be used directly in subsequent transformations.
Acetonitrile can be used to similar effect. Finally, the diols 5 are often highly crystalline and
frequently attained as glinting colourless analytically pure needles from simple hot MeOH:EtOAc
mixtures. By appropriate combination of 3 and benzyl zinc reagent the symmetric diols may also
be readily achieved (i.e. 5aa is attained from 3a and PhCH2ZnCl in 87% yield). Alternatively,
the symmetrical diols can also be attained from 4 and slight excesses of the appropriate benzylic
zinc reagent (Method II). While the scope of this symmetrical coupling is not quite as wide as
that from use of 3a-d (e.g. preparation of 5bb by Method II provides only 56% vs. 93% via
method I) it does allow routine access to the symmetrical diols quickly. For example, 5aa could
be prepared on a >10 g scale by such approaches within a day.
Table 1. Diversity orientated synthesis of the diol tetracene precursors 5.[a]
Iodide
used
Method
R1
R2
Diol 5 (%)
Recrystallisation fromb
m.p. (oC)
3a
4
I
II
I
H
H
H
H
5aa
5aa 62-72
87
1:1 MeOH/AcOEt
-
157-158
-
3a
3a
3a
3a
3b
4
H
H
Me
OMe 5ac
5ab
84
91
82
99
93
56
87
1:1 MeOH/AcOEt
3:1 EtOAc/MeOH
1:1 MeOH/AcOEt
1:1 MeOH/AcOEt
1:1 MeOH/AcOEt
-
150-151
131-132
139-140
154-155
I
I
H
F
5ad
5ae
5bb
5bb
5bf
I
I
H
Ph
Me
Me
iPr
Me
Me
Me
180-181
-
II
I
3b
1:1 MeOH/AcOEt
155-156
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3b
3b
3c
3c
3c
3d
4
I
I
Me
Me
vinyl 5bg
96
92
93
85
85
82
65
iPrOH, -20 oC
1:1 MeOH/AcOEt
3:1 EtOAc/MeOH
MeCN, -20 oC
161-164
153-154
131-132
145-146
119-120
129-130
139-140
Br
5bh
5cb
I
I
OMe
Me
OMe OMe 5cc
I
I
OMe
F
F
F
5cd
5dd
5hh
3:1 EtOAc/MeOH, -20 oC
MeCN, -20 oC
II
Br
Br
MeCN, -20 oC
[a]
Typically reactions were carried out on ca. 6 mmol scales in THF (25 mL) over 15-20 min.
Recrystallisation from refluxing solvent on cooling to 4 oC unless indicated otherwise.
Oxidation of diols 5 to the aldehydes 2 is necessary prior to tetracene cyclisation (Scheme
1). This is sustainably attained by the aerobic CuI/TEMPO-based catalysts (Table 2), optimised
by Stahl;[21] environmentally poorer oxidants (e.g. MnO2, Swern) performed less well (see
Supporting Information). The slightly modified oxidation procedure used herein shows useful
functional group tolerance: both C-Br and styryl functions are preserved even though oxidation
procedure is radical driven.[21] Conveniently these oxidations are self-indicating: initiation of the
catalyst commensurate with the immediate appearance of a dark orange-brown colour which
becomes emerald green on completion of the oxidation (0.3-1 h). After isolation and drying
under vacuum the dials 2 are attained as bright yellow solids in high yield and >98% purity
allowing their direct use for immediate tetracene synthesis without any further purification.
However, all are also easily recrystallized as glinting yellow flakes from iPrOH or iPrOH:EtOAc
mixtures. Oxidation of the diols 5 at a gram scale is straightforward and further scale-up not an
issue: e.g. 2aa could be attained on a 4 g level without the need for any chromatographic
separations. Minor modification of the reaction temperature (to 40 oC) is necessary for diol 5ae
to ensure full solubility and completion of reaction.
Table 2. Copper(I)-catalysed oxidation of diols 5 to aldehydes 2.[a]
5 used
R1
R2
2 (%)
5 used
R1
R2
2 (%)
5aa
5ab
5ac
5ad
5ae
5bb
5bf
H
H
H
H
Me
OMe
F
Ph[b]
Me
iPr
>99
87
88
92
96
93
89
5bg
5bh
5cb
5cc
5cd
5dd
5hh
Me
Me
OMe
OMe
OMe
F
vinyl
Br
Me
OMe
F
87
98
95
H
H
>99
85
Me
Me
F
Br
89
93
Br
[a]
[b]
Typically reactions were carried out on ca. 3 mmol scales in DMF (18 mL) over 1 h.
Reaction at 40 oC.
Preliminary small scale Bradsher closure trials of dialdehyde 2aa with a library of 14 Lewis acids
(Scheme 2, LA, see also Supporting Information) revealed that only In(OTf)3, BF3·OEt2 and TiCl4
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were active towards tetracene (1aa) formation (Scheme 2). Therefore, these three promotors
were all examined in detail. For In(OTf)3 (at 0.6 equivalents) significant conversion to the desired
o
tetracene 1aa could only be achieved by prolonged heating at 83-115 C (Supporting
Information); the rate was insufficient for lower catalyst loadings to be viable at practical scales
(necessary for viable use of such a poorly sustainable LA promotor). Two additional products:
6aa[22] and 7aa[13,23] (Scheme 2) could also be detected in these indium-promoted closures by
comparison with their published 1H NMR data (independent samples of 6aa can be prepared by
much less efficient alternate chemistry[22]). Monitoring the reaction by 1H NMR spectroscopy also
confirmed that 6aa is a genuine ‘half closure’ intermediate on route to tetracene 1aa.
Scheme 2. An intermediate (6aa) and by-product (7aa) in Bradsher closures of aldehyde 2aa
to tetracene (1aa).
Stoichiometric BF3·OEt2 is much more attractive reagent for tetracene formation due to its low
cost. With two equivalents of BF3·OEt2 at scales below 1 mmol (in 2aa), good yields (>80%) of
o
tetracene 1aa are attained at 1,2-dichloroethane reflux (83 C) conditions within 5 h.
Unfortunately, at larger scales (especially >3 mmol) these reactions become capricious,
progressively less clean (with increasing scale) and result ultimately in negligible or no yields of
1aa. The water by-product of the Bradsher cyclisation is the cause of these issues. Efficiently
minimised in small scale reaction mixtures by 1,2-dichloroethane azeotrope formation (b.p. 70.5
oC), in larger scale reactions water promoted H[HOBF3][24] formation competes leading to acid-
induced oxidation of 1aa[15,24] providing 7aa (among many other radical cation derived by-
products). Control studies support this idea: deliberate addition of water (2 equiv.) to the
reaction mixture at the outset, prior to BF3·OEt2 (2.0 equiv.) addition and subsequent reflux,
leads to catastrophic reduction in the 1aa yield regardless of the scale of the reaction.
Deployment of 4Å molecular sieves in the reaction headspace allows production of 1aa at a gram
scale, but initiation of the cyclisation then becomes slow and equally capricious. Kinetic study of
the BF3·OEt2 promoted cyclisation of 2aa (0.28 M) provides insights into these behaviours (see
Supporting Information). Formation of 1aa (and disappearance of 6aa) follow an autocatalytic
o
rate law over 4 h at 63 C. Dial 2aa is rapidly converted to 6aa under these conditions, and
fitting standard autocatalysis rate law forms[25] to the disappearance of 6aa provides k1 ~0 min-1
and k2 = 0.3 M-1 min-1 where k1 and k2 are respectively estimates of the background and
autocatalytic behaviour (see Supporting Information). This strong autocatalysis is the root cause
of the reliability issues in larger scale preparations of 1aa using BF3·OEt2. Controlling the reactive
H[HOBF3] concentration simply becomes impractical at any significant scale in 2aa. By using
only one equivalent of BF3·OEt2 high yields of 6aa could be obtained at room temperature, again
confirming it as an intermediate en route to 1aa. In 2015 the syntheses of three tetracenes
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using a BF3·OEt2 promoted (unidirectional) Bradsher process were disclosed.[11c] The colours
described for these acenes (colourless to pale green) are not in accord with tetracene formation
(which are all typically all brilliant orange). We believe the potential for decomposition effects
during the reaction/workup of these reactions similar to the effects observed herein cannot be
excluded.
In an attempt to overcome the reproducibility issues associated with BF3-H2O autocatalysis
we also screened the little used, low cost, TiCl4 Bradsher conditions of Tius (Method III, Table
3).[10c] To our great delight quench (of the most unpromising brown-green reaction mixtures)
with 1:1 methanol:acetone resulted in spectacular orange precipitates of 1aa. Despite the small
particle size of the 1aa produced, very easy filtration is facilitated by use of Whatman glass
microfiber filter paper (GF/A which is designed to collect particles sized down to 1.6 μm
efficiently). The TiCl4 approach proved rather general for cyclisation of aldehydes 2, subject to
the usual electronic effects on electrophilic aromatic substitution (Table 3). Partial closure
products 6 could often be seen from the filtrates, especially when the donor/acceptor properties
of R1/R2 were different. The initially precipitated tetracenes 1 are attained in purities (>95%)
sufficient for immediate subsequent synthetic/materials application uses. Simple one-step
o
sublimation (200-230 C, 0.1-0.2 mbar, 1 h) easily provides analytically pure materials as
brilliant orange mircocrystals. For electronically deactivated dialdehydes (e.g. 2ad) the use of
larger excesses of TiCl4 (4 equiv.) under neat reaction conditions and longer reaction times
(typically 2 days) are required and low to modest yields are attained with these general
conditions. Attempts to force closure of the species 6 led to variable outcomes (see Supporting
Information). For example, dosing 2dd with TiCl4 aliquots over 4 days led to up to 40%
conversion to 1dd in some runs but mostly decomposition in others. Bradsher cyclisations are
known to be subject to the normal electronic deactivation restrictions of Friedel-Crafts chemistry
and thus the procedures here are best used on electron-rich systems. Activated 2bg was
extensively cross-linked on reaction with even one equivalent TiCl4 at room temperature
providing an insoluble orange macromolecular material. Repeating this synthesis at -78 to -40
oC provides oligomeric 1+6bgn with n ~ 7-8 through controlled polymerisation of the vinyl side
chain and mixed mono and di-Bradsher closure. For both the oligo and macromolecular 1+6bg
characteristic tetracene spectroscopic bands can be identified in their UV-vis and IR spectra.
Interestingly the monomeric tetracenes 1 all show intense refractive index matching in diamond
anvil ATR-IR instruments. The resulting anomalous dispersion leads to the observation of
apparent negative peaks around the diamond absorbance range (2100-2000 cm-1) which are a
useful quick diagnostic for 1 (even in mixtures), especially if a characteristic peak at ~905 cm-1
is also present. In line with this suggestion, no pseudo emission peaks are seen using Ge-crystal
ATR instruments.
Table 3. Method III: titanium(IV) chloride induced Bradsher cyclisations.[a]
2
R1
H
R2
H
X
(eq.)
2
Y (h), T
(oC)
1
Lit. 1
Ref.
26
6 (%)
R3
-
R4
-
[b]
used
2aa
(%)
72
%
3 (40)
51 (3)
-
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2aa
2ab
2ab
2ac
2ad
2ae
2bb
2bf
H
H
H
Me
Me
OMe
F
2
2
2
2
4
2
2
2
2
2 (40)
3 (40)
1 (22)
3 (40)
60 (22)
3 (40)
3 (40)
3 (40)
Note [d]
40
68
27
56[c]
9
71
86
86
62
-
-
6aa (50)
H
-
H
-
4 (1)
27
-
-
H
H
-
6ab (57)
Me
-
H
-
88 (4)
28
29
30
31
-
-
H
H
56 (3)
6ad (37)
H
-
F
-
Ph
-
-
Me
Me
Me
Me
iPr
low (2)
-
-
2bg
vinyl
-
1+6bgn
(65-89)
6bh (45)
-
Oli[e] Oli[e]
2bh
2cb
2cc
2cd
2dd
Me
OMe
OMe
OMe
F
Br
Me
OMe
F
4
2
2
4
4
60 (22)
3 (40)
4
81
86
-
-
-
-
-
-
-
-
-
-
Me
-
Br
-
3 (40)
60 (22)
60 (22)
-
-
-
F
8
Var.
[f]
6cd (39)
6dd (63)
OMe
F
2hh
Br
Br
4
60 (22)
-
31 (3)
32
6hh (54)
Br
Br
[a]
Typically reactions carried out on 1.5 mmol scales in 1,2-dichloroethane (10 mL); TiCl4 added
o
at 0 C, and the mixture stirred at the required temperature. Electronically deactivated
substrates (ad, cd, dd, hh) were run in neat TiCl4 (see Supporting Information).
[b]
The highest/best analogous literature (substituted)tetracene procedure we could identify and
(in parentheses) the number of steps needed to prepare the required precursor from commercial
(<0.1€ mmol-1) materials.
[c]
Higher solubility limits precipitated yield.
Reactions carried out at 22 oC afford a low solubility high polymer containing both tetracene
[d]
and aldehyde groups. Reaction at -78 to -40 oC leads to a soluble oligomer.
[e] ‘Oli’ indicates product is a (CHCH2)n oligomer with n ~ 7-8 generated by polymerisation of the
vinyl sidechain providing a telechelic oligomer with both tetracene and aldehyde pendant groups
present (see Supporting Information).
[f]
Low (<5%) yields were attained under standard conditions, by adding 1,2-dichloroethane co-
solvent and extending the reaction to >3 days up to 40% yields were sometimes attained
together with intractable decomposition products (see Supporting Information).
Conclusions
The synthetic sequence to 1 from the iodides 3-4 constitutes an effective and practical route for
the formation of 2- and 2,8-substituted tetracenes in high analytical purities atypical to most
other literature approaches. All of the tetracenes 1 prepared showed the expected spectroscopic
properties and have solubilities in CH2Cl2 ranging from ca. 10-6 M (2bh) to ~10-3 M (2ac and
fluorine containing tetracenes). The lower solubilities, in part, account for the success of our
direct precipitation work-up strategy. From Table 3 it is clear that the approach described herein
is complimentary, and in the case of electron-rich substituted tetracenes, advantageous to
existing methodology. In particular, the ability to prepare tetracene libraries of various
substituents at significant scales quickly and without the use of chromatography is attractive for
their subsequent use in materials science at larger preparative scales. The electronic properties
of the tetracenes attained are also in line with predictions. For example, 2-methyltetracene
(2ba) shows an measured Eg(opt) of 2.50 eV which is close to the calculated HOMO-LUMO gap
by time dependant DFT of 2.76 eV [CAMB3LY-6-31G(d,p) level of theory] and the accepted value
for the parent 1aa (2.61 eV) [Eg(calc) is typically greater than Eg(opt), see Supporting
Information]. For the tetracenes prepared herein we could control Eg(opt) in the range 2.54-
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2.43 eV by substituent effects. Such ability to easily and systematically vary the HOMO and
LUMO energies of tetracenes are central to their use in organic electronic applications and the
approach herein simplifies the synthetic effort required to enact the required substituents at
useful scales in many cases.
Experimental
Full details for the preparation of 1-7 and their properties are given in the Supporting
Information.
Acknowledgments
This work was initiated under funding from the European Union’s Seventh Programme for
research, technological development and demonstration under grant agreement No 308768. One
of us (JR) is grateful to European Thermodynamics Ltd and the Engineering Physical Sciences
Research Council (EPSRC) for provision of a studentship. SW, LB and JR thank EPSRC’s National
Service for Computational Chemistry (NSCCS) for computational facilities until its closure in
2017. MA thanks the Swiss-European Mobility Programme (SEMP) and is grateful to Prof Steve
Howdle and Ms Liv Monaghan for advice and help with GPC analyses. MRG is grateful for the
award of an Appalachian College Association Fellowship for sabbatical leave support from Berea
College, Kentucky, USA. We are indebted to Dr Callum Welsh (University of Nottingham) and
Prof Jens Pflaum (Universität Würzburg) for helpful discussions on refractive index matching and
anomalous dispersion effects in diamond anvil ATR-IR spectroscopic studies of tetracenes. We
thank Dr Magdalena Foreiter for sample collaboration with Key Organics Ltd and Nottingham
Research Chemicals.
Footnotes and References
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Manuscript for Chemistry Eur. J.: Woodward, et al.
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Graphical Abstract and Table of Contents text
A simple procedure for the preparation of substituted tetracenes from low cost ArCH2Cl and
HOCH2CΞCCH2OH.
Keywords:
Arenes • Aldehydes • Aromaticity • C-C coupling • Acenes • Bradsher cyclisation • Efficient
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