The first Diels-Alder reaction of a 9,10-bis(1,3-dithiol-2-ylidene)- 9,10-dihydroanthracene derivative: Synthesis and crystal structure of a novel donor-π-anthraquinone diad

Article abstract of DOI:10.1039/a907768e

An exocyclic diene derivative of 9,10-bis(1,3-dithiol-2-yl-idene)-9,10- dihydroanthracene undergoes Diels-Alder reaction with naphthoquinone to provide the D-π-A diad 10.

Full text of DOI:10.1039/a907768e

The first Diels–Alder reaction of a 9,10-bis(1,3-dithiol-2-ylidene)-9,10-
dihydroanthracene derivative: synthesis and crystal structure of a novel
donor–p–anthraquinone diad
Christian A. Christensen,a Martin R. Bryce,*a Andrei S. Batsanov,a Judith A. K. Howard,a Jan O. Jeppesenb
and Jan Becherb
a
Department of Chemistry, University of Durham, Durham, UK DH1 3LE. E-mail: m.r.bryce@durham.ac.uk
Department of Chemistry, Odense University, Campusvej 55, DK 5230 Odense M, Denmark
b
Received (in Cambridge, UK) 27th September 1999, Accepted 20th October 1999
An exocyclic diene derivative of 9,10-bis(1,3-dithiol-2-yl-
idene)-9,10-dihydroanthracene undergoes Diels–Alder reac-
tion with naphthoquinone to provide the D–p–A diad 10.
Derivatives of the p-electron donor 1 are emerging as versatile
components of organic conductors,1 nonlinear optical materi-
als,2 multi-stage redox assemblies3 and cyclophanes.4 System 1
offers a unique combination of redox and structural properties,
viz. a quasi-reversible two-electron oxidation process to yield a
thermodynamically stable dication [Eox +0.30 to +0.40 V (vs.
Ag/AgCl)].5 The neutral molecule adopts a saddle-shape; on
oxidation the anthracene ring becomes aromatic and planar,
with the 1,3-dithiolium cations almost orthogonal to this
plane.1b,5d
We are developing methodology for the synthesis of new
derivatives of 1.6 Herein we describe the first Diels–Alder
reaction involving system 1, viz. the reaction of the transient
exocyclic diene derivative 9 with naphthoquinone to afford the
aromatised adduct 10. This study is timely in the light of interest
in the Diels–Alder trapping of diene derivatives of tetra-
thiafulvalene7 and 1,3-dithiole-2-one systems.8
Scheme 1 Reagents and conditions: i, MeOTf, CH2Cl2, 20 °C, 1 h; ii,
anthrone, pyridine–AcOH, 55 °C, 3 h, then 120 °C, 3 h; iii, 5, LDA, 278 °C,
2 h, then add 4, THF, 278 °C to 20 °C, 12 h; iv, Bu4NF, THF, 20 °C, 1.5
h; v, PPh3 (3.0 equiv.), CCl4, (excess), MeCN, reflux, 1 h; vi, KI (3 equiv.),
18-crown-6 (3 equiv.), 1,4-naphthoquinone (4 equiv.), PhMe, 90 °C, 5 h,
then DDQ (4 equiv.), 90 °C, 4 h.
Bis(chloromethyl) compound 8 is the precursor to our target
diene 9 (Scheme 1). Hexylsulfanyl substituents enhance the
solubility. The bis-DPTBS protected diol 29 was methylated
with MeOTf to afford the unstable salt 3 which was sufficiently
pure for immediate reaction with the anion of anthrone, which
gave ketone derivative 4 (70% yield from 2). Horner–
Wadsworth–Emmons olefination with the anion of reagent 510
gave compound 6 (77% yield), which yielded the diol derivative
7 (88% yield). Reaction of a concentrated solution of diol 7 and
PPh3 in a mixture of CCl4 and MeCN at 90 °C11 gave the stable
bis(chloromethyl) derivative 8 in 45% yield (SOCl2 in CCl4 at
20 °C gave only 10% of 8). A mixture of 8, KI, 18-crown-6 and
1,4-naphthoquinone was heated in toluene for 5 h, whereupon
2,3-dichloro-5,6-dicyanoquinone (DDQ) was added. After
further heating the aromatised adduct 10† was isolated (63%
yield from 8).
4,5-bis(bromomethyl)-1,3-dithiole systems has been noted
previously,12 but no mechanism for their formation has been
published.13 A possible route is shown in Scheme 2. Loss of
bromide from intermediate 11 would give 12 and hence the
intermediate 13, which could undergo an oxy-Cope type
rearrangement to give 14.
The structures of compounds 10 and 14 (Fig. 1 and 2) were
confirmed by X-ray crystal structure analysis.‡ The asymmetric
The good stability of the dichloro compound 8 contrasts with
the attempted preparation of the bis(bromomethyl) derivative of
7 using conditions described7c,9 for other 4,5-bis(bromo-
methyl)-1,3-dithiole systems. Reaction of diol 7 with CBr4 and
PPh3 in THF at 0 °C gave a complex mixture of products (TLC
analysis) from which the bis(bromomethyl) derivative (if
present) could not be isolated; instead, the formyl derivative 14†
was obtained. The yield of 14 was optimised (61%) by using a
dilute solution of 7 and CBr4 and PPh3 (3.0 equiv.). Formyl
derivatives as byproducts during the synthesis of related
Scheme 2 Reagents and conditions: i, PPh3 (3.0 equiv.), CBr4 (3.0 equiv.),
CH2Cl2, 20 °C, 16 h.
Chem. Commun., 1999, 2433–2434
This journal is © The Royal Society of Chemistry 1999
2433

Notes and references
† Selected data for 10: shining black crystals, mp 229–230 °C (from
CH2Cl2–hexane); dH(CDCl3) 8.30–8.25 (m, 2H), 8.07 (s, 2H), 7.80–7.77
(m, 2H), 7.73–7.68 (m, 2H), 7.65–7.60 (m, 2H), 7.40–7.35 (m, 4H),
2.82–2.72 (m, 4H), 1.64–1.52 (m, 4H), 1.38–1.22 (m, 12H), 0.83 (t, 6H, J
6.8); lmax(CH2Cl2)/nm (lg e) 348 (4.58), 428 (4.53). For 14: orange prisms,
mp 178–179 °C (from CH2Cl2–hexane); dH(CDCl3) 9.70 (s, 1H), 7.65–7.56
(m, 4H), 7.33–7.30 (m, 4H), 2.84–2.74 (m, 4H), 2.43 (s, 3H), 1.63–1.53 (m,
4H), 1.40–1.25 (m, 12H), 0.87 (t, 6H, J 6.4).
‡ Crystal data for 10: C44H40O2S6, M = 793.1, T = 120 K, triclinic, space
¯
group P1 (No. 2), a = 9.925(2), b = 12.940(3), c = 15.319(5) Å, a =
94.16(1), b = 94.13(1), g = 99.06(1)°, U = 1930.8(9) Å3, Z = 2, Dc
=
1.36 g cm23, 13240 reflections (6762 unique), R = 0.039 [4525 data, I >
2s(I)], wR(F2) = 0.086. For 14: C34H38OS6, M = 655.0, T = 120 K,
¯
triclinic, space group P1 (No. 2), a = 15.208(3), b = 16.298(3), c =
16.510(3) Å, a = 111.95(1), b = 95.52(1), g = 113.86(1)°, U = 3320(1)
Å3, Z = 4, Dc = 1.31 g cm23, 25912 reflections (12113 unique), R = 0.042
[8781 data, I
> = 0.096 (Mo-Ka radiation). CCDC
2s(I)], wR(F2)
182/1460. See http://www.rsc.org/suppdata/cc/1999/2433/ for crystallo-
graphic data in .cif format.
Fig. 1 Molecular structure of 10.
1 (a) Y. Yamashita, Y. Kobayashi and T. Miyashi, Angew. Chem., Int. Ed.
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Fig. 2 Molecular structure of 14; CH3 and CHO substituents are evenly
distributed between C(19) and C(20).
unit in the crystal of 10 contains only one independent
molecule, while that of 14 comprises two molecules of similar
but non-identical conformations; in one molecule, one of the n-
hexyl chains is disordered. The anthracenediylidene system is
folded along the C(9)···(10) vector by ca. 39° in 10 and 41º in 14
and both dithiole rings are folded inward along the S…S vectors
(by 8–14°). The anthracenediylidenebis(dithiole) system is U-
shaped, with an acute angle between the S(1)C(16)C(17)S(2)
and S(3)C(19)C(20)S(4) planes: 83° in 10, 82° in 14.
The n-hexyl chains adopting all-trans conformations lie
parallel to the nearly planar anthraquinone (10) or formylthiole
(14) system. Such parallelism particularly highlights the
packing motif characteristic for ‘molecular saddles’: namely, a
pseudo-dimer of mutually engulfing molecules, symmetrically
related via an inversion centre.6b
9 J. O. Jeppesen, K. Takimiya, N. Thorup and J. Becher, Synthesis, 1999,
803.
10 Reagent 5 was prepared from zinc bis[2-thioxo-1,3-dithiole-4,5-bis-
(thiolate)] (C. Wang, A. S. Batsanov, M. R. Bryce and J. A. K. Howard,
Synthesis, 1998, 1615) by the same methods used previously for close
analogues [ref. 5(a)].
Cyclic voltammetry shows a quasi-reversible two-electron
oxidation wave at Eox +0.64 V (10) and Eox +0.54 V (14).
Additionally for 10 a quasi-reversible reduction wave of the AQ
moiety is observed at Ered 20.95 V [CV data were recorded vs.
11 R. Appel, Angew. Chem., Int. Ed. Engl., 1975, 14, 801.
12 R. M. Renner and G. R. Burns, Tetrahedron Lett., 1994, 35, 269; Similar
reactions afford 4-formyl-5-methyl-4A,5A-bis(methylsulfanyl)TTF and
4,5-bis(2-cyanoethylsulfanyl)-4A-formyl-5-methyl-TTF
(ca.
40%
2
Ag/AgCl, electrolyte Bu4N+ClO4 (0.1 M), CH2Cl2, 20 °C,
yields) (J. O. Jeppesen and J. Becher, unpublished results). The former
reaction was also observed (25% yield) by P. Blanchard, PhD Thesis,
Université de Nantes, 1994. A very different mechanism from Scheme
2 was postulated.
scan rate 100 mV s21].
The UV–VIS spectrum of compound 10 displays two bands
characteristic of system 15d,6 at 348 and 428 nm: no absorption
was observed at longer wavelengths where intramolecular
charge-transfer (ICT) bands would be expected. Studies aimed
at photoinducing ICT in system 10, and increasing the acceptor
strength of the AQ moiety,14 are in progress.
13 Other workers have observed the formation of bis(oxydimethylene)-
TTF when chlorinating tetrakis(hydroxymethyl)-TTF [ref. 7(c) and S.
Hsu and L. Chiang, Synth. Met., 1988, 27, B651].
14 N. Martín, J. L. Segura and C. Seoane, J. Mater. Chem., 1997, 7,
1161.
We thank the EPSRC and the Danish Research Academy for
funding.
Communication 9/07768E
2434
Chem. Commun., 1999, 2433–2434