Diazadithiafulvalenes as electron donor reagents

Article abstract of DOI:10.1039/a906684e

Diazadithiafulvalenes act as excellent electron donors to arenediazonium salts. The diazadithiafulvalenium radical cations trap primary carbon radicals successfully. However, the diazadithiafulvalenium salts which form, undergo rapid ring fragmentation in contrast to their tetrathia counterparts. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a906684e

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Diazadithiafulvalenes as electron donor reagents
Toshio Koizumi,† Nadeem Bashir, Alan R. Kennedy and John A. Murphy*
Department of Pure and Applied Chemistry, The University of Strathclyde,
295 Cathedral Street, Glasgow, UK G1 1XL
Received (in Cambridge, UK) 17th August 1999, Accepted 7th October 1999
Diazadithiafulvalenes act as excellent electron donors to arenediazonium salts. The diazadithiafulvalenium radical
cations trap primary carbon radicals successfully. However, the diazadithiafulvalenium salts which form, undergo
rapid ring fragmentation in contrast to their tetrathia counterparts.
Introduction
The radical-polar crossover reaction affords a means of per-
forming radical and ionic chemistry in one pot.1 Specifically, an
arenediazonium salt 1 acts as electron acceptor from tetra-
thiafulvalene‡ (TTF) liberating dinitrogen and forming an aryl
radical. This can cyclise onto an appropriately placed alkene to
yield a secondary radical. This combines with the radical-cation
of tetrathiafulvalene affording a sulfonium salt 2 which can
then undergo substitution by oxygen or nitrogen nucleophiles
(Scheme 1). This reaction has recently been used in the key step
of a novel synthesis of the complex alkaloid aspidospermidine.2
It has recently been shown electrochemically that diaza-
dithiafulvalenes‡ 3 (DDTFs) are more powerful electron
donors than TTF,3 and so they are good candidates for second
generation catalysts to extend the scope of the radical-polar
Fig. 1 Molecular Structure of C18H18N2O2S2 9 drawn with 50% prob-
crossover reaction. Specifically, the radical-cations of these
compounds may display different kinetics for coupling to
ability ellipsoids and with H atoms as small spheres of arbitrary size.
S1–S2 2.060(1) Å; C1–S1–S2–C18 Ϫ106.1(2), S1–S2–C18–C17
Ϫ84.8(3), S2–S1–C1–C2 Ϫ89.6(3), O1–C9–C10–O2 111.9(4), O1–C9–
N1–C7 1.7(5) and O2–C10–N2–C11 0.0(5)Њ (see ref. 13).
ϩ
ؒ
carbon radicals than TTF , since the N-linked R groups could
retard approach to sulfur. This could permit slower carbon rad-
ical cyclisations to occur prior to the radical termination step.
This paper describes their reactions with arenediazonium salts.4
of the methyl compound 6 in air, establishing the product
structure as 8 by desulfurisation with Raney nickel to afford
N-phenyl-N-methyloxalamide. The same compound has sub-
sequently been formed by other means.7 On the other hand,
Wanzlick et al. had reported that 7 was oxidised to the macro-
cycle 10 in air. Our results support the findings of Baldwin and
Walker. The mechanism may involve the initial reaction with
dioxygen to form the superoxide radical-anion, followed by
reaction to form a dioxetane 11. Cleavage of the weak O–O
bond to form a diradical and fragmentation to the bis-thiyl
radical 12 leads ultimately to macrocycle formation.
The products 16 and 17 were prepared by the route of
Tormos et al.3 Reaction of dimethyl acetylenedicarboxylate
with the dithio-imine 13, (RЈ = Me or Ph) afforded the thio-
carbonyl product 14. Conversion to the selenocarbonyl com-
pound 15 followed by reaction with trimethyl phosphite
afforded 16 or 17 (Scheme 2). Although these compounds are
substituted with electron-withdrawing ester groups, they are
still more powerful electron-donors than TTF.3
Results and discussion
The diazadithiafulvalene 7 was prepared by literature pro-
cedures.5 Thus benzothiazole was reacted with diethyl sulfate to
afford 4 or with iodoethane to form the corresponding iodide
salt. The ethyl product 4 was isolated and treated with triethyl-
amine to obtain the ylide 5, which dimerised to 7. Diazadithia-
fulvalene 7 was isolated when air was rigorously excluded.
However, this compound is highly oxygen-sensitive and a solu-
tion in deuterochloroform rapidly turned red on exposure to air,
indicating its ease of oxidation and afforded a broad 1H NMR
spectrum differing from that reported5 for 7 by Wanzlick
et al. Repeating the preparation in acetonitrile led to a yellow
solution once again, but the solution slowly went red over
24 h and after work-up in air and chromatography without
exclusion of air, one major (colourless) compound was isolated,
1
the oxalamide 9. The H NMR spectrum of this compound
Compounds 16 and 17 were firstly reacted with the diazo-
nium salts 1a and 1b. Surprisingly it was not possible to isolate
clean products from 1b, in marked contrast to its reaction with
TTF, but 1a afforded a single major product on reaction with
both 16 and 17. These were identified as the formamides 18
(70%) and 19 (69%) respectively (Scheme 3). When heterocycle
7 was reacted with 1a, the formamide 20 (39%) was isolated. No
product featuring an intact diazadithiafulvalenium ring system
[the analogue of 2] was detected. Similarly, when 6 was reacted
with 1a, the formamide 21 was isolated.
featured two doublets of quartets consistent with the C2 sym-
metry which was ultimately confirmed by X-ray crystallography
(Fig. 1).
Baldwin and Walker6 reported the oxidative rearrangement
† Current address: National Defense Academy, Hashirimizu, Yokosuka
239, Japan.
‡ IUPAC names for tetrathiafulvalene and diazadithiafulvalene
are 2,2Ј-bi(1,3-dithiol-2-ylidene) and 2,2Ј-bi(1,3-thiazol-2-ylidene),
respectively.
J. Chem. Soc., Perkin Trans. 1, 1999, 3637–3643
This journal is © The Royal Society of Chemistry 1999
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Scheme 1
Scheme 2
The isolation of products 18, 19, 20 and 21 shows that there
carbons8 and the regiochemistry of attack (at the carbon
adjacent to the positive charge) could lead to the products
observed here.
is a marked difference in the reactivity of intermediates formed
from diazadithiafulvalenes compared to tetrathiafulvalene. The
proposed mechanism for formation of the observed products is
shown below. The products may be rationalised by a spon-
taneous opening of the initially formed salt 22 arising from the
better stabilisation of positive charge by the nitrogen than by
the sulfur in TTF salts. Once the ring has cleaved, the salt 23
will readily trap water to afford the enol 24. Protonation and
fragmentation afford the thiazolium salt 25 and the formamide
product. An alternative to the mechanism shown features
direct attack by water on the salt 22. We have shown that
nucleophiles attack tetrathiafulvalenium salts at the internal
It is noteworthy that the dithiadiazafulvalenes afford better
reactions with substrate 1a than 1b. This suggests that the dithia-
diazafulvalene radical-cations combine much more effectively
with primary radicals than with secondary radicals, and hence
their sensitivity to steric factors may be greater than antici-
pated. If this is the case, then it could be probed by a tandem
radical cyclisation. Two substrates were prepared, 28 and 36 as
shown below. Compound 28 should form a secondary radical
29 after the first cyclisation; if trapping by the radical-cations
of diazadithiafulvalenes is slow then the second cyclisation
3638
J. Chem. Soc., Perkin Trans. 1, 1999, 3637–3643

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Scheme 3
Scheme 4
should occur affording the final radical 30, which is primary,
having a greater lifetime to cyclise (Scheme 5). This supports
the proposal that the rate constants for coupling of secondary
and should therefore be efficiently converted into the corre-
sponding formamide 31. This is in effect what occurred, with
31a being isolated in 50% yield and 31b being isolated in 36%
yield (Scheme 4).
The second substrate 36 should allow for a different termin-
ation, by the expulsion of a phenylthiyl radical. In this case, a
comparison with the reactions of tetrathiafulvalene was made.
Reaction with TTF led to isolation of 19% of monocyclised
alcohol 37 and 48% of the bicyclised product 38. Diazadithia-
fulvalene 16 led to a higher yield of bicyclised product 37 (72%)
and no product of monocyclisation was isolated; this is consist-
ent with the radical 39 produced after the initial cyclisation
ϩ
radical to DDTFϩ are lower than to TTF
.
ؒ
ؒ
In conclusion, diazadithiafulvalenes are more powerful elec-
tron donors than TTF. Their radical-cations afford isolable
products from coupling to primary carbon radicals. These
products all feature cleavage of the DDTF ring system. The
diazadithiafulvalene radical-cations apparently couple more
slowly with secondary carbon radicals than tetrathiafulvalen-
ium radical-cations. This suggests that modification of the TTF
nucleus could also usefully alter the rates of coupling and
extend the scope of the radical-polar crossover reaction to
allow slower radical cyclisations to occur.
J. Chem. Soc., Perkin Trans. 1, 1999, 3637–3643
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Scheme 5
purification was required. δH (250 MHz; d6-DMSO) 1.59 (3H, t,
Experimental
J 7.2, Me), 4.88 (2H, q, J 7.2, NCH2), 7.86–7.95 (2H, m, ArH),
8.40–8.44 (1H, m, ArH), 8.50–8.57 (1H, m, ArH) and 10.6 (1H,
s, CH).
Melting points were carried out on a Kofler hot stage apparatus
and are uncorrected. Microanalyses were determined using a
Perkin-Elmer 240B elemental analyser. Infrared spectra were
obtained on a Perkin-Elmer 1720-X FTIR or a Pye-Unicam
SP3-100 spectrometer. Ultraviolet spectra were recorded on a
Philips PU8700 series instrument. 1H NMR spectra were
recorded at 250 MHz on a Bruker WM250, at 270 MHz on a
3-Ethylbenzothiazolium ethyl sulfate 49
To a solution of benzothiazole (4.00 g, 29.6 mmol, 1.00 equiv.)
in freshly distilled toluene (20 ml) was added dropwise a solu-
tion of diethyl sulfate (11.63 ml, 88.8 mmol, 3.00 equiv.). The
resultant solution was heated to 60 ЊC for 6 h. The formation of
a precipitate was noted. The creamy solid was filtered, washed
with ether and dried under vacuum to give the title compound
(6.60 g, 77%); mp 124–126 ЊC (lit.9 126.5 ЊC). δH (250 MHz;
CDCl3) 1.17 (3H, t, J 7.1, Me), 1.68 (3H, t, J 7.2, Me), 4.01 (2H,
q, J 7.1, OCH2), 4.95 (2H, q, J 7.2, NCH2), 7.70–7.85 (2H, m,
ArH), 8.18 (1H, d, J 7.6, ArH), 8.34 (1H, d, J 8.3, ArH) and
10.95 (1H, s, CH).
JEOL EX270 or at 400 MHz on a Bruker AM400 machine. 13
C
NMR spectra were recorded at 67.5 MHz on a JEOL EX270 or
at 100 MHz on a Bruker AM400 machine. NMR experiments
were carried out in deuterochloroform, d4-methanol, d6-
acetone, d3-acetonitrile or d6-dimethyl sulfoxide with tetra-
methylsilane as an internal reference. Chemical shifts are
quoted in parts per million (ppm). The following abbreviations
are used for multiplicities: s, singlet; d, doublet, t, triplet, q,
quartet; m, multiplet. Coupling constants are reported in Hertz
(Hz). In cases where superimposition of the signals of two, or
more, isomers occurred, the signals have been reported as
multiplets (m), unless the coupling constants of each isomer
could be ascertained. Mass spectra were recorded at the EPSRC
Mass Spectrometry Service Centre, Swansea.
Where necessary, solvents were dried and/or distilled before
use. Tetrahydrofuran was distilled from sodium–benzophenone.
Acetonitrile was distilled from phosphorus() oxide. Dichloro-
methane was distilled from calcium hydride. Diethyl ether, tolu-
ene and benzene were dried over sodium wire. Unless otherwise
stated all petrol was of boiling range 40–60 ЊC and was distilled
before use. Chromatography was performed using Sorbsil C60
(May and Baker), Kieselgel 60 (Art 9385) or Kieselgel HF254
silica gels.
3,3Ј-Diethyl-2,2Ј-bi(2,3-dihydrobenzothiazol-2-ylidene) 73a
Triethylamine (1.28 ml, 9.2 mmol, 2.00 equiv.) was added to a
suspension of 3-ethylbenzothiazolium ethyl sulfate (1.33 g, 4.6
mmol, 1.00 equiv.) in dry acetonitrile (4.5 ml) in one flush. Ini-
tially a dark orange coloured solution was observed which
gradually turned a pale yellow colour. On heating the reaction
mixture to 60 ЊC, a yellow coloured solution was observed. The
reaction mixture was allowed to cool to room temperature.
Formation of a precipitate was noted. Further cooling with an
ice–water bath ensured complete product precipitation. Filtra-
tion under nitrogen gave the title compound 7 as a bright yellow
crystalline solid (0.53 g, 70%). This air-sensitive solid was
stored under argon. Found: C, 66.37; H, 5.40; N, 8.74.
C18H18N2S2 requires C, 66.25; H, 5.55; N, 8.60%; m/z (EIϩ) 326
(Mϩ) and 43 (100).
3-Ethylbenzothiazolium iodide5
Iodoethane (27.70 g, 178.0 mmol, 4.00 equiv.) was added to a
solution of benzothiazole (6.00 g, 44.4 mmol, 1.00 equiv.) in dry
dimethylformamide (10 ml). The resultant solution was
refluxed under nitrogen for 2 h. The formation of a precipitate
was noted. The reaction mixture was diluted with ether and
cooled in an ice bath to completely precipitate the product. The
product was thoroughly washed with ether. The title compound
was obtained as a creamy solid (9.08 g, 70.2%). No further
5,8-Diethyldibenzo[c:i][1,2,5,8]dithiadiazecine-6,7(5H,8H)-
dione 95
Dry triethylamine (0.14 g, 1.4 mmol) was added, in one flush, to
a solution of 3-ethylbenzothiazolium iodide 4b (0.20 g, 0.7
mmol, 1.00 equiv.) in dry acetonitrile (3 ml) under nitrogen. A
yellow coloured solution was noted after 30 min of stirring at
room temperature. No product precipitated. The reaction mix-
3640
J. Chem. Soc., Perkin Trans. 1, 1999, 3637–3643

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ture was left stirring under nitrogen overnight. A red coloured
solution was observed. Thin layer chromatography employing
hexane–ethyl acetate (1:1) as the eluent revealed one major
product. The reaction mixture was evaporated to dryness and
purified by chromatography (dichloromethane) affording the
title compound 9 (125 mg, 100%) as colourless plates, mp 168–
169 ЊC (lit.5 166–168 ЊC). νmax(film)/cmϪ1 1669, 1640, 1461,
1377, 1273, 766 and 725; δH (250 MHz; CD3CN) 0.94 (6H, t,
J 7.2, 2 × Me), 3.19 (2H, dq, J 13.6, 7.2, N-CH), 3.62 (2H, dq,
J 13.6, 7.2, N-CH), 7.4–7.6 (6H, m, ArH) and 7.75–7.85 (2H,
m, ArH); δC (62.5 MHz; CD3CN) 12.7, 44.7, 131.0, 132.3,
134.7, 138.1, 139.0, 143.5 and 164.5; m/z (EIϩ) 358 (Mϩ, 12%)
and 136 (100).
ethyl acetate (4:1)] gave N-{2-[(2,3-dihydro-1-benzofuran-3-
yl)methylsulfanyl]phenyl}-N-ethylformamide 20 (53 mg, 39%)
as a red oil [Found: (M ϩ H)ϩ, 314.1212. C18H18NO2S requires
M ϩ H, 314.1215]. νmax(film)/cmϪ1 3063, 2957, 2926, 2871,
2853, 1677, 1650, 1474, 1480 and 753; δH (250 MHz; CDCl3)
1.14 (3H, t, J 7.3, CH3), 3.01 (1H, dd, J 12.4, 9.8, SCH2), 3.30
(1H, dd, J 12.4, 5.0, SCH2), 3.68 (1H, m, ArCH), 3.79 (2H, q,
J 7.3, NCH2), 4.43 (1H, dd, J 9.3, 5.3, OCH2), 4.63 (1H, dd,
J 9.3, 9.3, OCH2), 6.75–6.95 (2H, m, ArH), 7.10–7.40 (6H, m,
ArH) and 8.09 and 8.38 (1H, s, HC᎐O); δ (67.8 MHz; CDCl )
᎐
C
3
13.1, 37.4, 40.4, 41.4, 76.1, 110.2, 120.9, 124.7, 126.6, 128.0,
129.0, 129.3, 130.0, 128.9, 136.7, 138.7, 160.0 and 163.0;
m/z (CI) 331 [(M ϩ NH4)ϩ 75%], 314 [(M ϩ H), 100].
1-(2,3-Dihydrobenzofuran-3-yl)methylthio-2-(N-methyl-N-
formylamino)-1,2-bis(methoxycarbonyl)ethene 18
N-{2-[(2,3-Dihydro-1-benzofuran-3-yl)methylsulfanyl]phenyl}-
N-methylformamide 21
Arenediazonium tetrafluoroborate 1b (57 mg, 0.24 mmol) was
dissolved in degassed acetone (5 ml). To this, the dithiadiaza-
fulvalene3 16 (99 mg, 0.23 mmol) was added. Rapid nitrogen
evolution was observed. The solution was stirred for 24 h and
evaporated to dryness. The residue was subjected to column
chromatography on silica gel (hexane–ethyl acetate, 1:1) to
give 1-(2,3-dihydrobenzofuran-3-yl)methylthio-2-(N-methyl-N-
formylamino)-1,2-bis(methoxycarbonyl)ethene 18 (59 mg,
70%) (Found: Mϩ, 365.0936. C17H19NO6S requires M,
365.0933). νmax(film)/cmϪ1 3017, 2953, 2890, 1737, 1687, 1582,
1235 and 753; δH (400 MHz; CDCl3) 2.91 (1H, dd, J 12.8 and
9.2, CH2S), 2.95 [3H (minor), s, NCH3], 3.02 [3H (major), s,
NCH3], 3.05–3.13 (1H, m, CH2S), 3.60–3.70 (1H, m, CHAr),
3.76 [3H (minor), s, OCH3], 3.77 [3H (major), s, OCH3], 3.92
[3H (minor), s, OCH3], 3.94 [3H (major), s, OCH3], 4.35 (1H,
dd, J 9.4, 5.0, OCH2), 4.58–4.63 (1H, m, OCH2), 6.82 (1H, d,
J 8.0, ArH), 6.88 (1H, t, J 7.4, ArH), 7.16–7.21 (2H, m, ArH),
Diazonium salt 1a (114 mg, 0.46 mmol) was dissolved in
degassed acetone (10 ml) under nitrogen. To this solution,
dithiadiazafulvalene 6 (137 mg, 0.46 mmol) was added. The
solution was stirred for 24 h and evaporated to dryness. The
residue was subjected to column chromatography on silica gel
(hexane–ethyl acetate, 7:3) to give the monocyclised product, 21,
as a brown oil (30 mg, 22%) [Found: (M ϩ H)ϩ, 300.1066.
C17H17NO2S requires M ϩ H, 300.1058]. νmax(film)/cmϪ1 3060,
3010, 2925, 2886, 1680 (C᎐O) and 753; δ (250 MHz; CDCl3)
3.00 (1H, dd, J 9.6 and 5.6, SCH2), 3.24–3.32 (4H, m, NCH3
and SCH2), 3.59–3.70 (1H, m, ArCH), 4.42 (1H, dd, J 9.2 and
5.4, OCH2), 4.62 (1H, dd, J 9.2, 9.0, OCH2), 6.78–6.91 (2H, m,
ArH), 7.14–7.52 (6H, m, ArH) and 8.13 and 8.31 (1H, 2 × s,
᎐
H
HC᎐O); δ (100 MHz; CDCl ) 33.1 (q), 37.7 (t), 41.5 (d), 76.1
᎐
C
3
(t), 110.2 (d), 120.9 (d), 124.7 (d), 127.2 (d), 128.81 (d), 128.85
(s), 128.9 (d), 129.28 (d), 129.32 (d), 135.8 (s), 140.7 (s), 160.1 (s)
and 163.3 (d); m/z (EI) 300 [(M ϩ H)ϩ 9%], 91 (100%).
7.98 [1H (major), s, C(᎐O)H] and 8.10 [1H (minor), s, C(᎐O)H];
᎐
᎐
δC (100 MHz; CDCl3) 30.4, 32.2, 33.6, 41.8, 42.0, 42.2, 52.8,
53.0, 53.5, 53.4, 75.5, 75.7, 110.1, 110.2, 121.0, 124.6, 125.4,
127.9, 129.4, 129.5, 149.1, 160.0, 162.2, 163.2, 163.4 and 163.8.
2-(5-Oxaocta-2,7-dien-1-yloxy)nitrobenzene 26
Diethyl azodicarboxylate (7.2 ml, 8.00 g, 45.9 mmol) was added
dropwise, at 0 ЊC, to a solution of 2-nitrophenol (6.38 g, 45.9
mmol), 4-(allyloxy)but-2-enol10 (4.0 g, 31.2 mmol) and tri-
phenylphosphine (12.0 g, 45.9 mmol) in tetrahydrofuran (70 ml)
over a period of 0.5 h. After stirring for 16 h at rt the mixture
was evaporated to dryness, redissolved in dichloromethane (250
ml) and subsequently washed with sodium hydroxide (2 M, 200
ml), hydrochloric acid (2 M, 200 ml), saturated sodium carbon-
ate (200 ml) and water (2 × 200 ml). The mixture was dried over
anhydrous sodium sulfate, filtered and the solvent removed in
vacuo. Column chromatography [hexane–ethyl acetate (9:1)] of
the residue gave 2-(5-oxaocta-2,7-dien-1-yloxy)nitrobenzene 26
as a yellow oil (4.10 g, 36%) (Found: C, 62.45; H, 6.22; N, 5.64.
C13H15NO4 requires C, 62.45; H, 6.22; N, 5.64%). νmax(film)/
cmϪ1 2857, 1607, 1583, 1526, 1353, 1281 and 745; δH (250 MHz;
CDCl3) 4.01 (2H, ddd, J 5.6, 1.3, 1.3, OCH2), 4.13 (2H, d, J 3.8,
1-(2,3-Dihydrobenzofuran-3-yl)methylthio-2-(N-phenyl-N-
formylamino)-1,2-bis(methoxycarbonyl)ethene 19
The procedure was carried out as for the preparation of 18,
using dithiadiazafulvalene 17,3 (99 mg, 0.18 mmol) and afford-
ing
N-formylamino)-1,2-bis(methoxycarbonyl)ethene 19 (53 mg,
69%) (Found: Mϩ, 427.1133. C22H21NO6S requires
1-(2,3-dihydrobenzofuran-3-yl)methylthio-2-(N-phenyl-
M
427.1090). νmax(film)/cmϪ1 3019, 2953, 2892, 1732, 1690, 1594,
1259 and 753; δH (400 MHz; CDCl3) 2.77 (1H, dd, J 13.3 and
9.5, CH2S), 3.02 (1H, dd, J 13.3 and 5.0, CH2S), 3.45–3.52 (1H,
m, ArCH), 3.76 (3H, s, Me), 3.95 (3H, s, Me), 4.13 (1H, dd,
J 9.4 and 5.0, ArOCH2), 4.33 (1H, dd, J 9.4 and 9.4, ArOCH2),
6.77 (1H, d, J 8.0, ArH), 6.81–6.87 (1H, m, ArH), 7.05 (1H, d,
J 7.4, ArH), 7.12–7.16 (1H, m, ArH), 7.23–7.25 (1H, m, ArH),
7.31–7.46 (4H, m, ArH), 8.27 [1H (minor), s, CHO] and 8.53
[1H (major), s, CHO]; δC (100 MHz; CDCl3) 36.6, 42.6, 53.1,
53.5, 75.6, 110.2, 120.9, 122.9, 124.0, 125.5, 127.2, 128.3, 129.2,
129.4, 129.9, 139.1, 146.4, 160.0, 161.8, 162.2 and 164.1.
OCH ), 4.80 (2H, d, J 3.5, OCH ), 5.25 (2H, m, ᎐CH ), 5.58–
᎐
2
2
2
5.97 (3H, m, ᎐CH), 7.00–7.16 (2H, m, ArH), 7.51 (1H, ddd,
᎐
J 7.2, 7.2, 1.7, ArH) and (1H, dd, J 8.1, 1.5, ArH); δC (100
MHz; CDCl3) 66.0, 66.2, 71.6, 115.1, 117.5, 120.7, 125.8, 126.8,
130.9, 134.1, 134.7, 140.5 and 152.0.
N-{2-[(2-,3-Dihydro-1-benzofuran-3-yl)methylsulfanyl]phenyl}-
N-ethylformamide 20
2-(5-Oxaocta-2,7-dien-1-yloxy)aniline 27
A slurry of sodium borohydride (0.60 g, 15.8 mmol) in ethanol
(30 ml) was added in one flush to a suspension of copper()
acetylacetonate (0.88 g, 3.3 mmol) in ethanol (30 ml). The reac-
tion mixture was left to stir until a clumpy solid had formed and
the evolution of hydrogen gas ceased. 2-(5-Oxaocta-2,7-dien-1-
yloxy)nitrobenzene 26 (3.95 g, 15.8 mmol) was added as a solu-
tion in ethanol (30 ml), followed by addition of sodium boro-
hydride (1.20 g, 31.6 mmol) in ethanol (30 ml). The mixture was
stirred for 3 h, carefully poured onto water (140 ml) and evap-
orated to one quarter of its original volume. The mixture was
A solution of bi(2,3-dihydrobenzothiazol-2-ylidene) 7 (145 mg,
0.44 mmol, 1.02 equiv.) in acetone (1.5 ml) was added to a
solution of 2-allyloxybenzenediazonium tetrafluoroborate (100
mg, 0.43 mmol, 1.00 equiv.) in acetone. The reaction mixture
bubbled vigorously and nitrogen evolution occurred. The reac-
tion mixture was left stirring under nitrogen for 1 h. The form-
ation of a precipitate was noted. The reaction mixture was
evaporated to dryness and the residue adsorbed onto silica gel
(employing dichloromethane). Flash chromatography [hexane–
J. Chem. Soc., Perkin Trans. 1, 1999, 3637–3643
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diluted with more water (35 ml) and extracted with dichloro-
methane (3 × 60 ml). The combined organic phase was dried
over anhydrous sodium sulfate, filtered and evaporated to dry-
ness. Column chromatography [petroleum ether–diethyl ether
(1:1)] of the crude oil gave 2-(5-oxaocta-2,7-dien-1-yloxy)-
aniline 27 as a yellow oil (1.61 g, 47%) (Found: C, 71.17; H,
8.11; N, 6.35. C13H17NO2 requires C, 71.21; H, 7.81; N,
6.39%). νmax(film)/cmϪ1 3467, 3368, 2856, 1615, 1505, 1216 and
741; δH (250 MHz; CDCl3) 3.77 (2H, s, NH2), 3.99 (2H, ddd,
J 5.6, 1.4, 1.4, OCH2), 4.10 (2H, d, J 5.6, OCH2), 4.62 (2H, d,
washed with brine (100 ml), dried over magnesium sulfate, and
evaporated to dryness. The crude product was chromato-
graphed (hexane–ethyl acetate, 7:3 to 1:1) to afford 2-(9-
bromo-5-oxanona-2,7-dien-1-yloxy)nitrobenzene 33 (4.00 g,
24%) (Found: C, 49.17; H, 4.50; N, 4.09. C14H16BrNO4 requires
C, 49.14; H, 4.71; N, 4.09%). νmax(film)/cmϪ1 3078, 3030, 2924,
2854, 1731, 1607, 1583, 1525, 1353, 1106 and 745; δH (250 MHz;
CDCl3) 3.96 (2H, d, J 7.1, OCH2), 4.02 (2H, d, J 6.4, OCH2),
4.13 (2H, d, J 4.5, CH2Br), 4.79 (2H, d, J 4.2, ArOCH2), 5.78–
6.03 (4H, m, 2 × CH᎐CH), 7.01–7.11 (2H, m, ArH), 7.48–7.56
᎐
J 6.2, OCH ), 5.19 (1H, m, ᎐CH ), 5.28 (1H, ddd, J 17.2, 1.6,
(1H, m, ArH) and 7.82 (1H, d, J 8.1, ArH); δC (67.8 MHz;
CDCl3) 32.0, 65.87, 66.3, 69.8, 115.0, 120.4, 125.7, 126.9, 129.1,
130.7, 131.49, 134.1, 140.3 and 151.9.
᎐
2
2
1.6, ᎐CH ), 5.76–5.97 (3H, m, ᎐CH) and 6.65–6.85 (4H, m,
᎐
᎐
2
ArH); δC (100 MHz; CDCl3) 64.6 (t), 66.0 (t), 71.5 (t), 112.1
(d), 115.4, 117.4, 118.5, 121.6, 128.5, 129.8, 134.7, 136.6 and
146.3.
2-(9-Phenylthio-5-oxanona-2,7-dien-1-yloxy)nitrobenzene 34
A suspension of sodium hydride (0.45 g of 60% in oil, 11.3
mmol) in dry tetrahydrofuran (50 ml) was treated with thio-
phenol (0.956 g, 8.7 mmol) and stirred under nitrogen for 30
min in an ice bath. The fresh sodium thiophenoxide suspension
was added slowly to an ice-cold solution of 2-(9-bromo-5-
oxanona-2,7-dien-1-yloxy)nitrobenzene 33 (2.97 g, 8.7 mmol)
in tetrahydrofuran (45 ml). The mixture was allowed to warm to
rt and stirred for 3 h. The reaction mixture was poured into
water (210 ml) and extracted with dichloromethane (3 × 100
ml). The extracts were washed with saturated Na2CO3 solution
(2 × 130 ml), brine (100 ml), dried over magnesium sulfate, and
evaporated to dryness. The residue was subjected to column
(silica gel, hexane–ethyl acetate, 4:1) to give 2-(9-phenylthio-
5-oxanona-2,7-dien-1-yloxy)nitrobenzene 34 (2.82 g, 88%)
(Found: C, 64.60; H, 5.77; N, 4.06. C20H21NO4S requires C,
64.67; H, 5.70; N, 3.77%). νmax(film)/cmϪ1 3075, 3032, 2916,
2854, 1607, 1583, 1525, 1482, 1353, 1280, 1090, 743 and
691; δH (250 MHz; CDCl3) 3.55 (2H, d, J 6.6, CH2S), 3.93
(2H, d, J 5.5, CH2O), 4.00 (2H, d, J 4.5, CH2O), 4.74 (2H,
2-(5-Oxaocta-2,7-dien-1-yloxy)benzenediazonium
tetrafluoroborate 28
A solution of 2-(5-oxaocta-2,7-dien-1-yloxy)aniline 27 (0.60 g,
2.7 mmol) in dichloromethane (9 ml) was added dropwise, at
Ϫ20 ЊC, to a suspension of nitrosonium tetrafluoroborate (0.35
g, 3.0 mmol) in dichloromethane (9 ml) over a period of 0.5 h.
After stirring for a further 40 min the solvent was removed
in vacuo with cooling (dry ice–methanol bath employed). The
residue was washed with diethyl ether (2 × 50 ml), dissolved in
acetone (5 ml) and subsequently poured onto cold diethyl
ether (100 ml). The resultant precipitate was carefully filtered
under nitrogen to give 2-(5-oxaocta-2,7-dien-1-yloxy)benzene-
diazonium tetrafluoroborate 28 (0.58 g, 67%) as a light brown
solid (Found: C, 48.69; H, 4.74; N, 8.60. C13H15BF4N2O2
requires C, 40.09; H, 4.75; N, 8.81%). νmax(film)/cmϪ1 2249,
1591 and 1083; δH (250 MHz; CDCl3) 4.00 (2H, dd, J 4.2, 1.1,
OCH2), 4.13 (2H, d, J 5.0, OCH2), 5.07 (2H, d, J 5.5, OCH2),
5.16–5.31 (2H, m, ᎐CH ), 5.76–5.97 (3H, m, ᎐CH), 7.22–7.28
᎐
᎐
2
d, J 4.6, CH OAr), 5.59–5.87 (4H, m, 2 × CH᎐CH), 7.02–
᎐
(1H, m, ArH), 7.39 (1H, d, J 8.7, ArH) and 8.01 (1H, dd, J 7.5,
8.8, ArH); δC (62.9 MHz; CDCl3) 66.36, 68.25, 71.83, 101.09,
115.21, 117.68, 123.43, 124.54, 132.66, 132.91, 134.49, 144.38
and 162.55.
2
7.07 (2H, m, ArH), 7.16–7.34 (5H, m, ArH), 7.46–7.53
(1H, m, ArH), 7.81 (1H, dd, J 8.0 and 1.5, ArH); δC (67.8
MHz; CDCl3) 36.4, 66.3, 70.8, 115.4, 121.1, 126.2, 126.9,
127.3, 129.4, 129.5, 130.1, 130.3, 131.1, 134.5, 136.3, 140.8 and
152.3.
Reaction of the arenediazonium tetrafluoroborate 28 with the
dithiadiazafulvalene 16 and 17
2-(9-Phenylthio-5-oxanona-2,7-dien-1-yloxy)aniline 35
A typical procedure is as follows: arenediazonium tetrafluor-
oborate 2811 (0.11 g, 0.35 mmol) was dissolved in degassed
acetone (5 ml). To this, the dithiadiazafulvalene 16 (0.15 g, 0.35
mmol) or 17 (0.19 g, 0.35 mmol) was added. Rapid nitrogen
evolution was observed. The solution was stirred for 20 h and
evaporated to dryness. The residue was subjected to column
chromatography on silica gel (hexane–ethyl acetate, 4:5 [for the
reaction with 16] or 1:1 [for the reaction with 17]) to give the
bicyclisation product as a mixture of stereoisomers. 1-[4-(2,3-
dihydrobenzo[b]furan-3-yl)tetrahydrofuran-3-yl]methylthio-2-
(N-methyl-N-formylamino)-1,2-bis(methoxycarbonyl)ethene
31a: (76 mg, 50%) (Found: Mϩ 435.1323. C21H25NO7S requires
M, 435.1352). νmax(film)/cmϪ1 3012, 2952, 2872, 1733, 1687,
1592, 1234 and 753. 1-[4-(2,3-Dihydrobenzo[b]furan-3-yl)tetra-
hydrofuran-3-yl]methylthio-2-(N-phenyl-N-formylamino)-1,2-
bis(methoxycarbonyl)ethene 31b (63 mg, 36%) (Found: Mϩ,
497.1469. C26H27NO7S requires M 497.1508). νmax(film)/cmϪ1
3014, 2952, 2885, 1732, 1691, 1593, 1235 and 754.
Copper() acetylacetonate (1.72 g, 6.6 mmol) was added to
ethanol (20 ml) under nitrogen. To the suspension, sodium
borohydride (0.208 g, 5.5 mmol) was added using ethanol (20
ml). The mixture was stirred until a clumpy solid was formed.
To this mixture, a solution of the 2-(9-phenylthio-5-oxanona-
2,7-dien-1-yloxy)nitrobenzene 32 (2.045 g, 5.5 mmol) in ethanol
(20 ml) was added, followed by further sodium borohydride
(0.416 g, 11.0 mmol) flushed in with ethanol (20 ml). The solu-
tion was stirred for 2.5 h. And then sodium borohydride (0.260
g, 6.9 mmol) was added to the mixture. The solution was stirred
overnight at rt. The reaction mixture was filtered and the filtrate
was poured into water (90 ml). The solution was evaporated to
remove the solvent and extracted with dichloromethane (3 × 70
ml). The combined extracts were washed with brine (50 ml),
dried over magnesium sulfate, and evaporated to dryness. The
crude product was purified by column chromatography on silica
gel (dichloromethane) to give 2-(9-phenylthio-5-oxanona-2,7-
dien-1-yloxy)aniline 35 (1.17 g, 62%) as a yellow oil (Found: C,
70.09; H, 7.04; N, 3.98. C20H23NO2S requires C, 70.35; H, 6.79;
N, 4.10%). νmax(film)/cmϪ1 3466, 3368, 3057, 3029, 2918, 2854,
1614, 1505, 1277, 1216, 1041, 1024 and 739; δH (250 MHz;
CDCl3) 3.53 (2H, d, J 6.5, CH2S), 3.78 (2H, s, NH2), 3.91 (2H,
d, J 5.5, CH2), 3.98 (2H, d, J 6.0, CH2O), 4.58 (2H, d, J 5.9,
2-(9-Bromo-5-oxanona-2,7-dien-1-yloxy)nitrobenzene 33
To a solution of 2-(4-hydroxybut-2-en-1-yloxy)nitrobenzene
3212 (10.0 g, 48 mmol) and 1,4-dibromobut-2-ene (20.5 g, 96
mmol) in dry tetrahydrofuran (300 ml), sodium hydride (2.69 g,
67 mmol) was added slowly in an ice–methanol bath. The mix-
ture was stirred for 2 h in the ice–methanol bath and poured
into hydrochloric acid (2 M, 400 ml). The solution was
extracted with dichloromethane (3 × 150 ml). The extracts were
CH OAr), 5.58–5.91 (4H, m, 2 × CH᎐CH), 6.66–6.83 (4H, m,
᎐
2
ArH) and 7.13–7.34 (5H, m, ArH); δC (67.8 MHz; CDCl3) 35.9,
64.4, 65.6, 70.2, 112.0, 115.3, 118.4, 121.6, 126.3, 128.4, 128.9,
129.7, 129.7, 129.9, 135.8, 136.6 and 146.2.
3642
J. Chem. Soc., Perkin Trans. 1, 1999, 3637–3643

View Article Online
2-(9-Phenylthio-5-oxanona-2,7-dien-1-yloxy)benzenediazonium
tetrafluoroborate 36
azonium tetrafluoroborate (0.154 g, 0.35 mmol) in degassed
acetone (8 ml). After stirring at room temperature for 4 h the
mixture was evaporated to dryness. Column chromatography
[hexane–ethyl acetate (9:1 to 4:1)] gave the monocyclised
product, 1-(2,3-dihydrobenzo[b]furan-3-yl)-7-phenylthio-3-oxa-
hept-5-enol 37 (23 mg, 19%), bicyclised product, 4-(2,3-di-
hydrobenzo[b]furan-3-yl)tetrahydrofuran-3-ylethene 38 (36 mg,
48%) (data as above), and diphenyl disulfide (7 mg, 18%). 37
[Found: (M ϩ NH4)ϩ 360.1633]. C20H26NO3S requires M ϩ
NH4, 360.1633; νmax(film)/cmϪ1 3459, 3011, 2898, 2864, 1610,
1595, 1482, 1460, 1233, 1114, 968 and 754; δH (250 MHz;
CDCl3) 3.28 [1H (minor), dd, J 9.6 and 3.5, ArCH], 3.36 [1H
(major), dd, J 9.6 and 6.7, ArCH], 3.47–3.58 (4H, m, OCH2 and
SCH2), 3.88–3.99 (3H, m, OCH2 and CHOH), 4.43 [1H
(minor), dd, J 9.3 and 5.4, ArOCH2], 4.52 [1H (minor), dd,
J 9.2 and 9.2, ArOCH2], 4.53 [1H (major), dd, J 9.1 and 9.1
ArOCH2], 4.67 [1H (major), dd, J 9.1 and 5.1, ArOCH2], 5.60–
A suspension of nitrosonium tetrafluoroborate (0.244 g, 2.1
mmol) in dichloromethane (7 ml) under nitrogen was cooled to
Ϫ20 ЊC. To this, a solution of 2-(9-phenylthio-5-oxanona-2,7-
dien-1-yloxy)aniline 35 (0.650 g, 1.9 mmol) in dichloromethane
(7 ml) was added dropwise over 0.5 h. The solution was stirred
for 60 min. The solvent was removed under reduced pressure.
The residue was washed with cold ether (50 ml) twice and dis-
solved with acetone (5 ml). The acetone solution was poured
into ether (100 ml) below Ϫ20 ЊC. The ether was removed by
decantation and the residual oil was dissolved with acetone
followed by pouring into ether (100 ml). After decantation,
the oily product was dried under reduced pressure to afford 2-
(9-phenylthio-5-oxanona-2,7-dien-1-yloxy)benzenediazonium
tetrafluoroborate 36 (0.71 g, 85%) as a brown oil (Found: Mϩ,
353.13208. C20H21N2O2S requires M, 353.13237). νmax(film)/
cmϪ1 2261, 1592, 1488, 1296, 1059 and 753. δH (250 MHz;
CDCl3) 3.55 (2H, d, J 6.4, CH2S), 3.94 (2H, d, J 5.6, CH2O),
4.01 (2H, d, J 4.3, CH2O), 5.03 (2H, d, J 4.7, CH2OAr), 5.60–
5.69 (1H, m, CH᎐CH), 5.72–5.83 (1H, m, CH᎐CH), 6.80–6.82
᎐
᎐
(1H, m, ArH), 6.87 (1H, ddd, J 7.4, 7.4 and 0.9, ArH), 7.14–
7.22 (3H, m, ArH) and 7.26–7.36 (4H, m, ArH); δC (67.8 MHz;
CDCl3) 36.1, 45.1, 45.5, 71.4, 71.7, 71.9, 72.5, 73.0, 73.1, 109.9,
110.0, 120.6, 120.7, 125.4, 126.0, 126.6, 126.9, 129.0, 129.1,
129.3, 129.5, 130.3, 135.8 and 160.9.
5.88 (4H, m, 2 × CH᎐CH), 7.12–7.35 (7H, m, ArH), 7.95–8.02
᎐
(1H, m, ArH) and 8.40 (1H, dd, J 8.4 and 1.4, ArH); δC (67.8
MHz; CDCl3) 35.8, 66.1, 68.2, 70.6, 101.1, 115.1, 123.4, 124.5,
126.4, 129.0, 129.2, 129.5, 129.7, 132.4, 133.0, 135.9, 144.2 and
162.5.
Acknowledgements
We thank the National Defense Agency, Japan, for a Fellow-
ship to T. K., EPSRC for funding a studentship to N. B. and the
EPSRC National Mass Spectrometry Service, Swansea, for high
resolution mass spectra.
Reaction of 2-(9-phenylthio-5-oxanona-2,7-dien-1-yloxy)-
benzenediazonium tetrafluoroborate 36 with dithiadiazafulvalene
16
The diazonium salt 36 (0.14 g, 0.32 mmol) was dissolved in
degassed acetone (8 ml) under nitrogen. To this solution, dithia-
diazafulvalene 16 (0.32 mmol) was added. The solution was
stirred for 4 h and evaporated to dryness. The residue was sub-
jected to column chromatography on silica gel (hexane–ethyl
acetate, 9:1) to give the bicyclised product 4-(2,3-dihydro-
benzo[b]furan-3-yl)tetrahydrofuran-3-yl-ethene 38 (50 mg,
72%) and diphenyl disulfide (11 mg, 31%) 38 (Found: Mϩ,
216.1150. C14H16O2 requires M, 216.1150). νmax(film)/cmϪ1
3076, 2975, 2929, 2859, 1639, 1594, 1482, 1459, 1231, 1056, 997,
921 and 752; δH (400 MHz; CDCl3) 2.32–3.14 (2H, m,
References
1 C. Lampard, J. A. Murphy and N. Lewis, J. Chem. Soc., Chem.
Commun., 1993, 295.
2 O. Callaghan, C. Lampard, A. R. Kennedy and J. A. Murphy,
J. Chem. Soc., Perkin Trans. 1, 1999, 995.
3 (a) G. V. Tormos, M. G. Bakker, P. Wang, M. V. Lakshmikantham,
M. P. Cava and R. M. Metzger, J. Am. Chem. Soc., 1995, 117, 8528;
(b) G. V. Tormos, O. J. Neilands and M. P. Cava, J. Org. Chem., 1992,
57, 1008.
4 Preliminary communication: T. Koizumi, N. Bashir and J. A.
Murphy, Tetrahedron Lett., 1997, 38, 7635.
CHCHC᎐C), 3.39–4.65 (7H, m, 3 × CH and ArCH), 4.99–5.32
᎐
2
5 H. W. Wanzlick, H.-J. Kleiner, I. Lasch, H. U. Füldner and
H. Steinmaus, Liebigs Ann. Chem., 1967, 708, 155.
(2H, m, C᎐CH ), 5.62–5.97 (1H, m, CH᎐C), 6.79–6.87 (2H, m,
᎐
᎐
2
ArH) and 7.02–7.29 (2H, m, ArH); δC (100 MHz; CDCl3) 41.2,
42.0, 42.3, 44.3, 46.0, 46.6, 47.9, 48.2, 48.7, 49.1, 49.2, 49.8,
69.7, 70.3, 70.7, 72.0, 73.4, 73.5, 73.6, 73.9, 74.7, 75.1, 75.8,
109.9, 109.9, 110.0, 110.0, 116.5, 116.6, 116.8, 116.9, 117.4,
117.7, 120.6, 126.6, 120.6, 124.6, 124.7, 124.7, 125.1, 128.6,
128.7, 128.7, 128.8, 128.8, 129.0, 129.7, 130.0, 130.7, 136.7,
137.9, 138.4, 160.1, 160.2 and 160.5; m/z (EI) 216 [(M)ϩ 8%],
119 (100%). Diphenyl disulfide: δH (250 MHz; CDCl3) 7.22–
7.34 (6H, m, ArH) and 7.48–7.52 (4H, m, ArH).
6 J. E. Baldwin and J. A. Walker, J. Am. Chem. Soc., 1974, 96, 596.
7 K. Yamaguchi, T. Itoh, K. Nagata, M. Okada and A. Ohsawa, Acta
Crystallogr., Sect. C, 1993, 49, 1514; T. Itoh, K. Nagata, M. Okada
and A. Ohsawa, Tetrahedron, 1993, 49, 4859.
8 B. Patro, A. R. Kennedy, O. Callaghan, X. Franck and J. A.
Murphy, unpublished work.
9 J.-J. Vorsanger, Bull. Soc. Chim. Fr., 1968, 971.
10 S. Ghosh, S. R. Raychaudhuri and R. G. Salomon, J. Org. Chem.,
1987, 52, 83.
11 J. A. Murphy, R. J. Fletcher, C. Lampard and N. Lewis, J. Chem.
Soc., Perkin Trans. 1, 1995, 623.
12 S. Raeppel, F. Raeppel and J. Suffert, Synlett, 1998, 7, 794.
13 Crystal Data. A colourless block of C18H18N2O2S2 of approximate
size 0.20 × 0.20 × 0.20 mm was mounted in oil on a Rigaku AFC7S
diffractometer at 123 K. Monoclinic, space group P21/c,
a = 11.4859(8), b = 9.0253(10), c = 16.4066(11) Å, β = 96.647(5)Њ, U =
1689.3(2) Å3, Z = 4. Measurements were made using λ = 0.71069 Å
radiation and the ω/2θ method to a 2θmax of 55Њ. Of 4327 reflections,
4128 were unique (Rint = 0.033) and 2344 observed with I > 2σ(I).
The structure was solved using direct methods14 and refined to
convergence on F.15 R = 0.047, Rw = 0.057 and S = 1.57 for 236
parameters.CCDCreferencenumber207/376.Seehttp;//www.rsc.org/
suppdata/p1/1999/3637/ for crystallographic files in .cif format.
14 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27,
435.
Reaction of 2-(9-phenylthio-5-oxanona-2,7-dien-1-yloxy)-
benzenediazonium tetrafluoroborate 36 with dithiadiazafulvalene
6
Diazonium salt 36 (154 mg, 0.35 mmol) was dissolved in
degassed acetone (8 ml) under nitrogen. To this solution, dithi-
adiazafulvalene 6 (104 mg, 0.35 mmol) was added. The solution
was stirred for 4 h and evaporated to dryness. The residue was
subjected to column chromatography on silica gel (hexane–
ethyl acetate, 9:1) to give the bicyclised product, 4-(2,3-dihydro-
benzo[b]furan-3-yl)tetrahydrofuran-3-ylethene 38 (55 mg, 72%)
(data as above) and diphenyl disulfide (16 mg, 42%).
15 Texsan, Version 1.6, Crystal Structure Analysis Package, Molecular
Structure Corporation, The Woodlands, Texas 77381, 1992.
Reaction of 2-(9-phenylthio-5-oxanona-2,7-dien-1-yloxy)-
benzenediazonium tetrafluoroborate 36 with TTF
TTF (72 mg, 0.35 mmol) was added in one flush to a solution
of
2-(9-phenylthio-5-oxanona-2,7-dien-1-yloxy)benzenedi-
Paper 9/06684E
J. Chem. Soc., Perkin Trans. 1, 1999, 3637–3643
3643