Rearrangement reactions; 12:1 synthesis and reactions of isothiocyanate substituted allenes

Article abstract of DOI:10.1055/s-2002-33109

The first method for the preparation of isothiocyanate substituted allenes by [3,3] sigmatropic rearrangement of propargyl thiocyanates is described. These allenes undergo a variety of successive reactions such as ionic or sigmatropic isomerization, electrocyclic ring closure, cycloaddition, and electrophilic addition. Furthermore, intramolecular nucleophilic attack as well as treatment with external nucleophiles lead to heterocyclic products.

Full text of DOI:10.1055/s-2002-33109

PAPER
1423
Rearrangement Reactions; 12:1 Synthesis and Reactions of Isothiocyanate
Substituted Allenes
R
earrangement Relactions 1
a
;
12: Synth
u
esis and Re
a
s
ctions of Isothio
B
cyanate Substitu
a
ted Allenesnert,*a Stefan Groth,a Holger Hückstädt,b Jens Lehmann,a Jana Schlott,a Kai Vrobelb
a
Institut für Chemie der Technischen Universität Chemnitz, Strasse der Nationen 62, 09111 Chemnitz, Germany
Fax +49(371)5311839; E-mail: klaus.banert@chemie.tu-chemnitz.de
b
Fachbereich 8, Organische Chemie II, Universität Siegen, Adolf-Reichwein-Str., 57068 Siegen, Germany
Received 14 March 2002; revised 25 April 2002
Dedicated to Professor Hans-Jürgen Hansen on the occasion of his 65th birthday
Table Transformation of Thiocyanates 3 to Isothiocyanates 4 on
Flash Vacuum Pyrolysis at 400 °C
Abstract: The first method for the preparation of isothiocyanate
substituted allenes by [3,3] sigmatropic rearrangement of propargyl
thiocyanates is described. These allenes undergo a variety of suc-
cessive reactions such as ionic or sigmatropic isomerization, elec-
trocyclic ring closure, cycloaddition, and electrophilic addition.
Furthermore, intramolecular nucleophilic attack as well as treat-
ment with external nucleophiles lead to heterocyclic products.
R2
R2
[3,3]
R1
SCN
C
R1
NCS
4a−e
3a−e
Key words: allenes, rearrangements, addition reactions, Diels–Al-
der reactions, heterocycles
3/4
R1
R2
Conversion Yield (%)
of 3 (%)
of 4a
a
b
c
H
H
98
97
The isomerization of allyl thiocyanate (1) to allyl isothio-
cyanate (2) (mustard oil) is a very old reaction,2 which
was discovered independently by Otto Billeter3a as well as
by Gustav Gerlich3b and which has been thoroughly
investigated4 (Scheme 1). This isomerization is currently
interpreted as a [3,3] sigmatropic rearrangement.5 Howev-
er, analogous attempts to transform long-known propar-
gyl thiocyanates of type 36,7 into isothiocyanates by
heating the pure substances yield only decomposition and
polymerization products.6 Nevertheless, we demonstrated
recently in a short communication8 that flash vacuum py-
rolysis is an effective synthesis strategy to obtain cumu-
lenes 4 (Table). We present now the details of the
transformation 3 4 which can be expanded to the prep-
aration of several other allenyl isothiocyanates. More-
over, we report on the chemistry of these highly reactive
new cumulenes.
H
Me
H
99
97
Me
83b
96
ca. 100
60
d
e
CH2Cl
SiMe3
H
H
11b
ca. 100
a Isolated yield of 4 based on converted 3.
b Under the conditions of flash vacuum pyrolysis, equilibria with 3c/
4c = 17:83 and 3e/4e = 89:11 are established.
liquid chromatography. In the case of 4d the yield is di-
minished since the precursor 3d cannot be vaporized with-
out decomposition.
Functionalized allenes produced by sigmatropic rear-
rangement can be short-lived intermediates owing to an-
other functional group in the molecule, which initiates a
rapid intramolecular consecutive reaction. For example,
the propargyl thiocyanates 3f and 3g, which are easily ac-
cessible from corresponding mesylates 5f and 5g are
transformed to the rearrangement products 6f and 6g on
flash vacuum pyrolysis at 400 and 320 °C, respectively
(Scheme 2).9 Obviously, the intermediate allenes 4f and
4g generated by the [3,3] sigmatropic migration of the
thiocyanato group are isomerized by a succeeding Cope
rearrangement. The allylic inversion of the latter process
is shown by the position of the methyl groups in the case
of the product 6g. Whereas flash vacuum pyrolysis of the
thiocyanate 3f at 400 °C leads to (E)-6f exclusively (80%
yield), pyrolysis in the range of 320-–260 °C gives a mix-
ture of (E)-6f/(Z)-6f = 1.5:1 and allene 4f in 40–64%
yield. A renewed thermolysis of this mixture at 400 °C af-
fords the sole product (E)-6f. Apparently, at least the
Cope rearrangement 4 6 is reversible at higher temper-
[3,3]
S
N
C
C
N
S
1
2
Scheme 1 Sigmatropic isomerizations of allyl thiocyanate to allyl
isothiocyanate
Allenyl isothiocyanates, for example 4a and 4b, can be
obtained in 100 g batches per day from precursors of type
3. An equilibrium of 3 and 4 is established on flash vacu-
um pyrolysis of 3c and 3e, as well as on renewed thermal
reaction of the products 4c and 4e which are separated by
Synthesis 2002, No. 10, Print: 30 07 2002.
Art Id.1437-210X,E;2002,0,10,1423,1433,ftx,en;T02902SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

1424
K. Banert et al.
PAPER
atures. The sequence of sigmatropic isomerization reac-
tions 3 6 can also be observed when a diluted
R
R
R
4
[3,3]
SCN
C
solution of 3 in toluene is heated to 80–110 °C. The as-
signment of the geometrical isomers of 6 is performed not
only by homonuclear NOE difference spectra but also by
comparing the rates of the Diels–Alder reactions of 6 with
the dienophile tetracyanoethylene (TCNE). While (E)-6f
and (E)-6g can be transformed at room temperature to 7f
and 7g, respectively, no reaction under these conditions is
found in the case of (Z)-6f and (Z)-6g for steric reasons.
NCS
NCS
NCS
R
3h,i
4h,i
MeOH
H2O
[3,3]
NCS
H
R
N
OMe
R
MsO
NCS
O
NH4SCN
R
R
R
R
NCS
8h,i
S
10i
5f,g
3f,g
∆
[3,3]
TCNE
h R = H
R = Me
R
R
i
f R = H
g R = Me
C
NC
NCS
NCS
NC
NC
NC
4f,g
NCS
[3,3]
cis-9i
trans-9i
NC
NC
NC
NC
TCNE
[4+2]
R
R
Scheme 3
NCS
NCS
R
R
7f,g
6f,g
isomer (Z,Z)-8i predominates (56% yield of 8i, 1:1:8 dis-
tribution). Flash vacuum pyrolysis of 8i, consisting most-
ly of the (E,Z) isomer, gives also a mixture of
diastereomers which contains mainly (Z,Z)-8i. Apparent-
Scheme 2
In the case of the dithiocyanates 3h,i, the sigmatropic re-
arrangement of the propargyl thiocyanate is followed by a
second [3,3] migration of the other thiocyanato group
which results in the formation of the 2,3-diisothiocyana-
tobuta-1,3-dienes 8h,i (Scheme 3). Heating diluted solu-
tions of 3h at 60–100 °C gives only limited yields of 8h
(20–25%) since this product is very unstable and tends to
rapid polymerization. The instability of the isomerization
product 8h may be the reason why only decomposition
occurred10 on attempts to distill 3h. The success of the
flash vacuum pyrolysis of 3h is also limited (18% yield of
8h) because the starting material cannot be vaporized
without decomposition. However, treatment of 4d with
NH4SCN furnishes 8h in high yields ( 95%). When this
reaction is followed by NMR spectroscopy, the postulated
intermediate 4h cannot be observed, which is also true for
all the transformations 3h 8h mentioned before. Obvi-
ously, the first rearrangement step (3h 4h) is much
slower than the second (4h 8h).
ly, at least the second rearrangement step 4i
8i is re-
versible at higher temperatures.
The assignments of the geometrical configurations of 8i
are based on 13C NMR spectroscopic data including -ef-
fects. Thus, the methyl groups in E positions induce ef-
fects, with
= 1.8 ppm for the signal for C-3 and C-4 of
(E,E)-8i, relative to the corresponding value of (Z,Z)-8i. A
similar -effect ( = 2.3 ppm) is observed by comparing
the chemical shifts for C-3 and C-4 of (E,Z)-8i. Further-
more, the different rates of the Diels–Alder reactions of 8i
and TCNE are informative: (Z,Z)-8i reacts considerably
faster to cis-9i than its stereoisomer (E,Z)-8i to the cy-
cloadduct trans-9i whereas no transformation is found in
the case of (E,E)-8i due to steric reasons. Competition ex-
periments using TCNE as well as (Z,Z)-8i and (E,E)-hexa-
2,4-diene or (E,Z)-8i and (E,Z)-hexa-2,4-diene show that
Diels–Alder reactions of 8i are slower than the analogous
reactions of similar dienes without isothiocyanato groups.
The dithiocyanate 3i is easily accessible from NH4SCN
and the ditosylate11 of hex-3-yne-2,5-diol, which is com-
mercially available as a mixture of meso and rac isomers.
The rearrangement of 3i gives rise to the more stable prod-
uct 8i. Already on distillation at 90 °C/0.001 Torr, 3i af-
fords the products (E,E)-8i, (E,Z)-8i, and (Z,Z)-8i, which
can be separated by chromatography, in almost statistical
1:2:1 distribution (67% yield). If the distillation is con-
ducted at 180 °C/20 Torr, the thermodynamically favored
When 3i or 8i (mixture of geometrical isomers) is heated
in aqueous methanol, the product 10i can be isolated as a
colorless solid with 9% or 32% yield, respectively. The
heterocycle 10i may be a trapping product of the postulat-
ed intermediate 4i. Probably, 10i is formed from 4i by nu-
cleophilic attack of water at the isothiocyanato function
followed by cyclization yielding a thiazole ring and by nu-
cleophilic substitution of the thiocyanato group by meth-
anol.
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactions of Isothiocyanate Substituted Allenes
1425
Surprisingly, the intermediates 4h,i cannot be observed
when thiocyanates 3h,i are isomerized to 8h,i or when 4d
is transformed into 8h at room temperature. This fact can
only be explained by very rapid [3,3] sigmatropic rear-
rangement reactions of 4h,i. However, the analogous
isomerization of buta-2,3-dienyl thiocyanates 11 and 12
(X = SCN), easily accessible from precursors 11
(X = Br)12 and 12 (X = Cl),13 respectively, prove to be
slow at room temperature (Scheme 4). Isothiocyanate 14
is produced in high yield by heating a solution of thiocy-
anate 12 whereas this method gives only poor yields in the
case of the more unstable target compound 13. However,
flash vacuum pyrolysis of 11 (X = SCN) furnished 13 in
high yields. The dienes 13 and 14 can be treated with
TCNE or dimethyl acetylenedicarboxylate to afford the [4
+ 2] cycloaddition products 15, 16, and 17. In the case of
15, the best yield is obtained when the precursor of unsta-
ble 13, namely 11 (X = SCN), is heated with TCNE in
THF. Competition experiments using TCNE as well as 13
and buta-1,3-diene or 14 and 2-methylbuta-1,3-diene
show that Diels–Alder reactions of 13 and 14 are signifi-
cantly slower than the analogous reactions of similar
dienes without isothiocyanato groups.
[3,3]
SCN
C
NCS
NCS
3j
4j
19j
Scheme 6
Recently, we reported on the flash vacuum pyrolysis of
propargyl thiocyanate 3j at 400 °C, which exclusively af-
forded the cyclic product 19j (Scheme 6).15 Obviously,
the [3,3] sigmatropic rearrangement of 3j is followed by
an electrocyclic ring-closure. Actually, the intermediate
4j could be observed when the pyrolysis of 3j was per-
formed at lower temperatures (270–320 °C).
SCN
OH
3k
H2O
(D2O)
dioxane
[3,3]
NCS
C
C
[3,3]
X
C
NCS
4k
O
NH
(D)
∆
HO
(D)
R
R
X = Br, R = H
X = SCN, R = H
R = H
R = Me
11
12
13
14
S
20k
X = Cl, R = Me
X = SCN, R = Me
TCNE
R
NC
NC
NC
NC
H(D)
MeO2C
H(D)
NCS
NCS
MeO2C
O
NH
(D)
R = H
R = Me
HO
(D)
17
15
16
NCS
21k
S
Scheme 4
22k
Scheme 7
Rearrangement of allenyl isothiocyanates 4 bearing a fur-
ther functional group is not limited to [3,3] sigmatropic
processes since the isomerization via ionic intermediates
is also possible. Thus, a slow rearrangement to give 18d
occurs when 4d is dissolved in DMSO (Scheme 5).14 This
transformation can be accelerated by addition of lithium
chloride.
Starting with propargyl thiocyanate 3k, another type of
rapid intramolecular consecutive reaction is observed
since heating in a protic solvent gives rise to the heterocy-
clic product 22k in 56% yield (Scheme 7). Most probably,
the allenyl compound 4k, which is intramolecularly at-
tacked by the alcohol, and possibly the intermediates 20k
or 21k are involved in this transformation. When the reac-
tion is conducted with D2O instead of H2O, deuterium is
incorporated not only at the nitrogen atom, but also into
the position of the side chain. Thus, an intramolecular
hydrogen shift is excluded, and the protic solvent is im-
portant at least in the step of migration of the C=C bond
(4k 21k or 20k 22k). For that reason, 22k cannot be
prepared by heating of 3k in an aprotic solvent, for exam-
ple toluene.
Cl
C
NCS
4d
DMSO
LiCl
Cl
NCS
18d
Scheme 5
Diels–Alder reactions are possible not only starting with
successive products of allenyl isothiocyanates 4 like 8i but
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

1426
K. Banert et al.
PAPER
also by treating the parent compound 4a with cyclopenta- flash vacuum pyrolysis in most cases, proves to be a con-
diene (Scheme 8). This reaction is interesting since some venient access to highly reactive allenyl isothiocyanates 4
norbornyl isothiocyanates are known for their anticarci- which are able to lead to several subsequent products. On
nogenic activities16 and as precursors for agricultural her- treatment with nucleophiles, compounds 4 yield heterocy-
bicides.17 The cycloaddition gives rise to both 23a (56% cles.21 This most promising transformation illustrates that
yield, E/Z = 1.4:1) and 24a (38%, endo/exo = 2.6:1). All cumulenes 4 act predominantly as synthetic equivalent of
four isomeric products can be assigned by their 1H NMR the synthons 29 (Scheme 10), which will be demonstrated
spectra using nuclear Overhauser effects in the case of detailed in a further publication.
(E)- and (Z)-23a and analyzing homonuclear couplings in
the case of endo- and exo-24a. In contrast to the cycload-
dition of cyclopentadiene, electrophilic addition of iodine
to 4a produces regioselectively 25a (77%, E/Z = 3:1).
R2
R1
N
R1
C
S
R2
NCS
29
4
+
Scheme 10
C
NCS
NCS
23a
24a
NCS
I
Melting points were measured on a Büchi SMP-20 and are uncor-
rected. Elemental analyses were carried out on a Vario EL (Elemen-
tar Analysensysteme GmbH Hanau) or by the Firma Beller,
Göttingen; elemental analyses of some isothiocyanates, especially
compounds 4, 8h, 18d, and 25a could not be performed successfully
due to their instability. IR spectra were measured on a Beckman Ac-
culab 4 and a Bruker IFS 28, respectively. UV absorption spectra
were recorded using a Beckman Acta M VII. 1H NMR (400 MHz,
300 MHz, 200 MHz, and 80 MHz) spectra were recorded on Bruker
WH 400, Varian Gemini 300, Bruker AC 200, and Bruker WP 80
NMR spectrometers with TMS or solvent signals, recalculated rel-
ative to TMS, as internal reference. 13C NMR (100 MHz, 75 MHz,
and 50 MHz) spectra were measured on Bruker WH 400, Varian
Gemini 300, and Bruker AC 200 spectrometers. The multiplicities
were determined by the aid of gated spectra or DEPT 135 experi-
ments. Referencing was conducted as described for 1H NMR spec-
tra. Mass spectra (EI) were recorded on a Varian MAT 112 or a
Hewlett Packard 5988 A. Analytical GC was performed on a Sie-
4a
I2
I
25a
NCS
Scheme 8
When low volatility of the starting material 3 is accompa-
nied with low stability of the rearrangement product 4,
flash vacuum pyrolysis is difficult as in the cases of 3h
and 3l (Scheme 9). However, the transformation to the un-
stable cumulene 4l is possible at room temperature in so-
lution (62% yield). Furthermore, allenyl isothiocyanates 4
can be generated in situ in the presence of nucleophiles to
prepare thiazole derivatives. Thus, heating a solution of
thiocyanate 3l in the presence of aniline furnishes the het-
erocycle 26l (65% yield) in a one-pot procedure. On heat-
ing in methanol, the thiocyanate 3b is converted similarly mens L 350 fitted with a 25 m phenylmethylsilicon column using N2
via 4b to the products 27b18 (48%) and 28b (16%). The
nonaromatic compound 28b can be separated by gas chro-
as carrier gas. GC MS (EI) was carried out with a Hewlett Packard
hp 5890 II, hp Engine 5989 A and with a Hewlett Packard hp 5988
A, respectively, with helium as carrier gas. In both cases the column
used was an HP 5 capillary column (5% phenylmethylsilicone
matography and transformed to 27b on treatment with sul-
furic acid.19
gum). Preparative GC was carried out on a Wilkens 1520 using he-
lium as carrier gas. Flash column chromatography was performed
with silica gel, 32-63 m. HPLC was carried out using Knauer
HPLC pump and UV detector ( = 254 mm), column Nucleosil Si
100-5, 4 mm Ø 25 cm. Thiocyanates 3a–e,h were synthesized fol-
lowing literature procedures (3a,6,7a,b,d 3b,7d 3c,7c,d 3d,e,7d 3h7d,10).
In conclusion, we have shown that [3,3] sigmatropic rear-
rangement of propargyl thiocyanates 3,20 performed by
Ph
Ph
N
[3,3]
PhNH2
SCN
Ph
C
5-Thiocyanatohept-1-en-6-yne (3f)
PhNH
Compound 5f15 (2.00 g, 10.5 mmol), dissolved in MeOH (5 mL),
was added dropwise to a solution of ammonium thiocyanate (1.62
g, 21.2 mmol) in MeOH (5 mL) and stirred at 60 °C for 8 h. The sol-
vent was evaporated and the residue dissolved in Et2O (80 mL),
washed with H2O, and dried (MgSO4). Removing the solvent in
vacuo yielded the crude product from which after recondensation at
20 °C/0.001 Torr 3f was obtained.
S
NCS
3l
4l
26l
N
MeO
MeO
S
27b
+
Yield: 1.26 g (79%); colorless liquid.
[3,3]
MeOH
SCN
C
IR (CDCl3): 3306 (C CH), 3082, 2960, 2158 (SCN), 1641, 1439,
1417, 1261, 1012, 809 cm–1.
1H NMR (300 MHz, CDCl3): = 2.08 (dtd, JH–H = 8.1 Hz,
N
NCS
S
3b
4b
J
H–H = 7.0 Hz, JH–H = 2.5 Hz, 2 H, CH2), 2.34 (m, 2 H, CH2), 2.65
28b
(d, 4JH–H = 2.4 Hz, 1 H, 7-H), 3.97 (ddd, 3JH–H = 7.9 Hz, 3JH–H = 6.8
Hz, 4JH–H = 2.4 Hz, 1 H, 5-H), 5.09 (dm, 3JH–H,cis = 10.3 Hz, 1 H,
Scheme 9
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactions of Isothiocyanate Substituted Allenes
1427
3
E-1-H), 5.13 (dm, JH–H,trans = 17.0 Hz, 1 H, Z-1-H), 5.76 (ddt,
3JH–H,trans = 17.0 Hz, 3JH–H,cis = 10.3 Hz, 3JH–H = 6.8 Hz, 1 H, 2-H).
2JH–H = 13.9 Hz, 3JH–H = 9.3 Hz, 1 H, 4-H), 2.64 (d, 4JH–H = 2.5 Hz,
1 H, 7-H), 3.91 (ddd, 3JH–H = 9.3 Hz, 3JH–H = 3.7 Hz, 4JH–H = 2.5 Hz,
3
1 H, 5-H), 5.02 (d, JH–H,trans = 17.4 Hz, 1 H, Z-1-H), 5.05 (d,
13C NMR (75 MHz, CDCl3): = 30.53 (t, C-4 or C-3), 34.88 (t, C-
4 or C-3), 38.19 (d, C-5), 76.08 (d, C-7), 79.09 (s, C-6), 110.13 (s,
SCN), 117.02 (t, C-1), 135.54 (d, C-2).
3
3JH–H,cis = 10.6 Hz, 1 H, E-1-H), 5.76 (dd, JH–H,trans = 17.4 Hz,
3JH–H,cis = 10.6 Hz, 1 H, 2-H).
13C NMR (75 MHz, CDCl3): = 25.63 (q, CH3), 27.93 (q, CH3),
35.77 (d, C-5), 37.47 (s, C-3), 48.30 (t, C-4), 76.19 (d, C-7), 77.35
(s, C-6), 110.44 (s, SCN), 112.90 (t, C-1), 145.40 (d, C-2).
Anal. Calcd for C8H9NS (151.23): C, 63.54; H, 6.00; N, 9.26; S,
21.20. Found: C, 63.10; H, 6.05; N, 9.29; S, 21.79.
3,3-Dimethyl-5-thiocyanatohept-1-en-6-yne (3g)
5,5-Dimethylhept-6-en-1-yn-3-ol was prepared in 87% yield from
3,3-dimethlypent-4-enal22 and ethynylmagnesium bromide23 by a
known method.23
Anal. Calcd for C10H13NS (179.28): C, 67.01; H, 7.32; N, 7.82; S,
17.85. Found: C, 66.14; H, 7.27; N, 7.50; S, 17.19.
2,5-Dithiocyanatohex-3-yne (3i)
The ditosylate11 of hex-3-yne-2,5-diol (15.00 g, 35.5 mmol) and
ammonium thiocyanate (10.00 g, 132 mmol) were dissolved in
DMSO (70 mL) and stirred at r.t. for 3 d. After addition of H2O (100
mL) and extraction with Et2O, the combined extracts were washed
with H2O and dried (MgSO4). Evaporation of the solvent yielded 3i.
Compound 3i is probably composed of meso and rac isomers, since
its precursor was prepared from the commercial mixture of the cor-
responding diastereomeric hex-3-yne-2,5-diols.
IR (CDCl3): 3601 (OH), 3306 (C CH), 2965, 1724, 1641, 1414,
1365, 1260, 1044, 1004 cm–1.
1H NMR (300 MHz, CDCl3): = 1.05 (s, 3 H, CH3), 1.06 (s, 3 H,
CH3), 1.79 (dd, 2JH–H = 14.3 Hz, 3JH–H = 5.4 Hz, 1 H, 4-H), 1.85 (dd,
2JH–H = 14.3 Hz, 3JH–H = 7.0 Hz, 1 H, 4-H), 2.44 (d, 4JH–H = 2.1 Hz,
1 H, HC C), 2.45 (br s, 1 H, OH, concentration dependent), 4.37
3
3
(br t, JH–H ca. 6.0 Hz, 1 H, 3-H), 4.96 (d, JH–H,cis = 11.0 Hz,
3
1 H, E-7-H), 4.97 (d, JH–H,trans = 17.4 Hz, 1 H, Z-7-H), 5.84
Yield: 5.94 g (85%); yellowish oil.
IR (CDCl3): 2034 (SCN) cm–1.
(dd, 3JH–H,trans = 17.4 Hz, 3JH–H,cis = 11.0 Hz, 1 H, 6-H).
13C NMR (75 MHz, CDCl3): = 26.56 (q, CH3), 27.67 (q, CH3),
36.10 (s, C-5), 50.14 (t, C-4), 59.80 (d, C-3), 72.59 (d, C-1), 85.91
(s, C-2), 111.20 (t, C-7), 147.50 (d, C-6).
1H NMR (80 MHz, CDCl3): = 1.75 (d, 3JH–H = 6.75 Hz, 6 H, CH3),
4.16 (q, 3JH–H = 6.75 Hz, 2 H, CH).
GC–MS (70 eV): m/z (%) = 123 (9), 105 (29), 95 (22), 79 (16), 69
13C NMR (100 MHz, CDCl3): = 22.60 (q, CH3), 31.10 (d, CH),
83.61 (s, C), 109.89 (s, SCN).
(40), 55 (100), 52 (33), M+ peak not detected.
This alcohol (2.70 g, 19.5 mmol), Et3N (3.96 g, 39.1 mmol), and
CH2Cl2 (10 mL) were stirred at 0 °C. To this solution, mesyl chlo-
ride (MsCl) (3.36 g, 29.3 mmol) was added dropwise. The mixture
was stirred at r.t. for 12 h, then diluted with CH2Cl2 (50 mL), and
washed with dilute aq HCl (20 mL). The organic layer was washed
with H2O and dried (MgSO4). Removal of the solvent in vacuo gave
5g.
Anal. Calcd for C8H8N2S2 (196.29): C, 48.59; H, 4.11; N, 14.27; S,
32.67. Found: C, 49.20; H, 4.27; N, 13.85; S, 32.23.
4-Thiocyanatobut-2-yn-1-ol (3k)7d
By using the following procedure instead of the described7d one, 3k
can be obtained with a better purity:
Ammonium thiocyanate (12.00 g, 158 mmol) and pure 4-chlorobut-
2-yn-1-ol24 (5.50 g, 52.6 mmol) were dissolved in MeOH (50 mL)
and stirred at r.t. for 7 d. After evaporation of the solvent the residue
was extracted with Et2O, washed with H2O and dried (MgSO4). Af-
ter removal of the Et2O in vacuo and of other volatile compounds at
the oil pump 3k was obtained.
Yield: 3.45 g (82%); brown liquid.
IR (CDCl3): 3305 (C CH), 2967, 1363, 1176, 975 cm–1.
1H NMR (300 MHz, CDCl3): = 1.09 (s, 6 H, CH3), 1.89 (dd,
3
2
2JH–H = 14.7 Hz, JH–H = 5.1 Hz, 1 H, 4-H), 2.02 (dd, JH–H = 14.7
3
4
Hz, JH–H = 7.3 Hz, 1 H, 4-H), 2.74 (d, JH–H = 2.1 Hz, 1 H, 1-H),
Yield: 5.82 g (87%); yellow oil.
3
3.09 (s, 3 H, SO2CH3), 5.01 (d, JH–H,trans = 17.5 Hz, 1 H, Z-7-H),
5.01 (d, 3JH–H,cis = 10.8 Hz, 1 H, E-7-H), 5.14 (ddd, 3JH–H = 7.3 Hz,
3JH–H = 5.1 Hz, 4JH–H = 2.1 Hz, 1 H, 3-H), 5.78 (dd, 3JH–H,trans = 17.5
Hz, 3JH–H,cis = 10.8 Hz, 1 H, 6-H).
(1-Thiocyanatoprop-2-ynyl)benzene (3l)
To a solution of ammonium thiocyanate (1.41 g, 18.5 mmol) in
DMSO (10 mL), (1-bromo-prop-2-ynyl)benzene25 (2.00 g, 12.35
mmol) was added dropwise at 15 °C. After stirring at r.t. for 1 h, the
workup was performed with cold H2O and Et2O. The dried Et2O so-
lution was filtered over a short column with silica gel. Then the sol-
vent was evaporated without warming to yield 3l.
13C NMR (75 MHz, CDCl3): = 26.83 (q, CH3), 27.15 (q, CH3),
36.08 (s, C-5), 39.38 (q, SO2CH3), 47.63 (t, C-4), 69.12 (d, CH),
77.01 (d, CH), 80.41 (s, C-2), 112.17 (t, C-7), 145.87 (d, C-6).
GC–MS (70 eV): m/z (%) = 119 (5), 105 (100), 91 (24), 79 (69), 69
(78), 55 (62), M+ peak not detected.
Yield: 1.55 g (72%); unstable reddish oil.
4
1H NMR (200 MHz, CDCl3): = 2.92 (d, JH–H = 2.5 Hz, 1 H,
Anal. Calcd for C10H16O3S (216.30): C, 55.53; H, 7.46; S, 14.82.
Found: C, 55.53; H, 7.57; S, 15.43.
CH), 5.30 (d, 4JH–H = 2.5 Hz, 1 H, CHPh), 7.5 (m, 5 H, Ph).
13C NMR (50 MHz, CDCl3): = 42.96 (d, CHPh), 78.02 (d,
The crude mesylate 5g (3.40 g, 15.7 mmol) and ammonium thiocy-
anate were dissolved in MeOH (20 mL) and stirred at 40 °C for 2 d.
The solvent was evaporated and the residue dissolved in Et2O (80
mL), washed with H2O, and dried (MgSO4). After removing the sol-
vent in vacuo, the residue was purified by flash chromatography
(CH2Cl2–hexane, 3:5) to yield 3g.
2
1JC–H = 254 Hz, CH), 78.18 (d, JC–H = 50 Hz, C ), 110.34 (s,
SCN), 127.80 (d, Ph), 129.12 (d, Ph), 129.65 (d, Php), 134.31 (s,
Phi).
Flash Vacuum Pyrolysis and Workup of Highly Reactive Prod-
ucts; General Procedure
Yield: 1.30 g (46%); colorless liquid which changes to yellow–or-
ange in the air.
The scale of the flash vacuum pyrolyses was normally in the range
of 0.3–2.0 g. In the case of 3a and 3b, however, pyrolyses on larger
scales up to 100 g within 8 h were also performed. Smaller amounts
(40–100 mg) were converted when separated allenyl isothiocyan-
ates like 4c and 4e or products formed under kinetic control, such as
6f and 8i, were pyrolyzed a second time. The starting material was
IR (CDCl3): 3306 (HC C), 3086, 2969, 2872, 2157 (SCN), 1639,
1415, 1366, 1204, 1001, 672 cm-–1
.
1H NMR (300 MHz, CDCl3): = 1.08 (s, 3 H, CH3), 1.13 (s, 3 H,
CH3), 1.90 (dd, 2JH–H = 13.9 Hz, 3JH–H = 3.9 Hz, 1 H, 4-H), 2.17 (dd,
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

1428
K. Banert et al.
PAPER
deposited in an appropriate flask, which was connected to a glass
tube (about 45 1.5 cm), arranged horizontally and filled with Ra-
schig rings (3 3 mm or 4 4 mm, freshly heat-dried in vacuo). The
other tube joint and a rotary slide valve oil pump (final vacuum
0.001 Torr) were connected through two traps cooled by liquid ni-
trogen. In the case of less volatile starting materials, such as 3c-e,
and 3h, an oil diffusion pump (final vacuum at least 10–5 Torr) was
used, whereas pyrolyses of low boiling 3a and 3b were conducted
at 0.75 and 0.01 Torr, respectively. The glass tube was heated nor-
mally to 400 °C by a pipe still (e.g., type 12/38/400, from Carbo-
lite), while the flash vacuum pyrolysis of 3g was performed at
320 °C and the transformation of 3f was investigated in the range of
260–400 °C. If necessary, the flask with the starting material was
heated by a hot air generator or a heating bath (40–70 °C) in order
to drive the vapor of the substrate through the hot pyrolysis tube
without carrier gas.
4f
1H NMR (300 MHz, CDCl3): = 2.22 (m, 4 H, CH2), 5.03 (d,
3JH–H,cis = 10.0 Hz, 1 H, E-7-H), 5.08 (d, 3JH–H,trans = 17.0 Hz, 1 H,
3
3
Z-7-H), 5.80 (ddt, JH–H,trans = 17.0 Hz, JH–H,cis = 10.0 Hz,
3JH–H = 6.7 Hz, 1 H, 6-H; signal partially covered), 6.08 (dm,
JH–H = 5.9 Hz, 1 H, 1-H or 3-H), the other signal of HC=C= is cov-
ered by the signal of 6-H at = 5.80.
13C NMR (75 MHz, CDCl3): = 28.19 (t, CH2), 32.28 (t, CH2),
89.99 (d, =C=CH), 101.28 (d, =C=CH), 115.78 (t, =CH2), 134.10
(s, NCS), 136.85 (d, =CH), 204.65 (s, =C= ).
(E)-6f
IR (CDCl3): 2108 (NCS) cm–1.
1H NMR (300 MHz, CDCl3): = 3.14 (dt, JH–H = 6.3 Hz,
3
4JH–H = 1.6 Hz, 2 H, 4-H), 5.08 (dq, JH–H,cis = 10.1 Hz, JH–H
3
2
4
3
= JH–H = 1.6 Hz, 1 H, E-6-H), 5.13 (dq, JH–H,trans = 17.3 Hz,
In the case of unstable products like 4a–e (Table 1), 4f, and 8h, it
was useful to minimize polymerization by dilution of the collected
substance with a weighed quantity of an inert solvent before thaw-
ing the trap. Otherwise, a dangerously vigorous reaction is possi-
ble since undiluted allenyl isothiocyanates, especially 4a, tend to
spontaneous very exothermic polymerization at r.t. Although
several other vinylic isothiocyanates such as 4l, 18d, and 25a are
also very unstable as neat substances at 20 °C, they could be han-
dled conveniently in solution and even be separated and purified by
chromatography. In these cases, however, solvent removal had to be
performed in vacuo at low temperature (< 0 °C). For example, 3c
and 4c as well as 3e and 4e were separated on silica gel (hexane–
Et2O, 3:1). Renewed flash vacuum pyrolyses of 4c or 4e led to quan-
titative yields of the equilibration mixtures if vaporization of the
starting materials was conducted at a temperature as low as possi-
ble.
2JH–H = JH–H = 1.6 Hz, 1 H, Z-6-H), 5.24 (dt, JH–H,cis = 10.7 Hz,
4
3
J
H–H ca. 0.6 Hz, 1 H, E-1-H), 5.43 (dt, 3JH-H,trans = 17.3 Hz, JH-H ca.
3
3
0.6 Hz, 1 H, Z-1-H), 5.79 (ddt, JH-H,trans = 17.1 Hz, JH-H,cis = 10.1
3
Hz, JH–H = 6.3 Hz, 1 H, 5-H), 6.04 (s, 1 H, 1 -H), 6.26 (ddd,
3JH–H,trans = 17.3 Hz, 3JH–H,cis = 10.7 Hz, 4JH–H ca. 0.6 Hz, 1 H, 2-H).
13C NMR (75 MHz, CDCl3): = 30.77 (t, C-4), 116.44 (d, CNCS),
116.61 (s, C-1 or C-6), 117.23 (s, C-1 or C-6), 133.90 (d, C-5 or C-
2), 134.04 (d, C-5 or C-2), 135.61 (s, NCS), 139.80 (s, C-3).
GC-MS (70 eV): m/z (%) = 151 (M+, 38), 93 (100), 91 (63), 77 (91),
65 (40), 39 (91).
(Z)-6f
1H NMR (300 MHz, CDCl3): = 2.96 (dq, JH–H = 6.6 Hz, JH–H
3
4
= 1.4 Hz, 2 H, 4-H), 5.12 (dq, JH–H,trans = 17.6 Hz, JH–H = 4JH–H
3
2
= 1.4 Hz, 1 H, Z-6-H), 5.12 (dq, JH–H,cis = 10.0 Hz, JH–H = 4JH–H
= 1.4 Hz, 1 H, E-6-H), 5.35 (d, 3JH–H,cis = 11.0 Hz, 1 H, E-1-H), 5.46
(d, 3JH–H,trans = 17.6 Hz, 1 H, Z-1-H), 5.80 (ddt, 3JH–H,trans = 17.6 Hz,
3
2
Selected spectroscopic and physical data of the products 4a–c are
already published in a preliminary short communication8 (conver-
sion of 3 and yield of 4, see Table 1).
3JH–H,cis = 10.0 Hz, JH–H = 6.6 Hz, 1 H, 5-H), 5.89 (s, 1 H, 1 -H),
3
6.81 (dd, 3JH–H,trans = 17.6 Hz, 3JH–H,cis = 11.0 Hz, 1 H, 2-H).
13C NMR (75 MHz, CDCl3): = 33.65 (t, C-4), 113.96 (d, =CH),
117.47 (t, =CH2), 118.01 (t, =CH2), 130.52 (d, =CH), 134.24
(d, =CH), 136.23 (s, NCS), 137.77 (s, C-3).
4-Chloro-3-isothiocyanatobuta-1,2-diene (4d)
5
1H NMR (400 MHz, CDCl3): = 4.19 (t, JH–H = 1.8 Hz, 2 H,
CH2Cl), 5.45 (t, 5JH–H = 1.8 Hz, 2 H, =CH2).
13C NMR (50 MHz, CDCl3): = 45.15 (t, CH2Cl), 85.57 (t, =CH2),
102.14 (s, CNCS), 138.92 (s, NCS), 206.65 (s, C-2).
The assignment of (E)-6f and (Z)-6f was based on homonuclear
NOE difference spectra, which showed a signal enhancement for 2-
H (3.6%), but not for 4-H, on irradiating the signal for CHNCS of
(E)-6f, whereas irradiation at the frequency of 4-H of (Z)-6f resulted
in an enhancement of the signal for CHNCS (2.0%).
(1-Isothiocyanatopropa-1,2-dienyl)trimethylsilane (4e)
1H NMR (400 MHz, CDCl3): = 0.23 (s, 9 H, SiMe3), 5.04 (s, 2 H,
CH2).
13C NMR (50 MHz, CDCl3): = –2.29 (q, SiMe3), 79.53 (t, CH2),
99.58 (s, CNCS), 133.13 (br s, NCS), 210.72 (s, =C= ).
GC–MS (70 eV): m/z (%) = 169 (M+, 6), 154 (100), 126 (97), 86
(42), 73 (48), 43 (43).
(3-Isothiocyanatopropa-1,2-dienyl)-benzene (4l)
3l (50 mg, 0.29 mmol) was dissolved in C6D6 (0.5 mL). After stir-
ring at r.t. for 24 h, 1H NMR data showed that unstable 4l was gen-
erated in a yield of 62%.
IR (CCl4): 2175 (NCS) cm–1.
1H NMR (300 MHz, CDCl3): = 6.50 (d, 4JH–H = 6.0 Hz, 1 H), 6.73
1-Isothiocyanatohepta-1,2,6-triene (4f) and 3-(Isothiocyanato-
methylene)hexa-1,5-diene (6f)
(d, 4JH–H = 6.0 Hz, 1 H), 7.40 (m, 5 H, Ph).
By flash vacuum pyrolysis of 3f (100 mg, 0.66 mmol) at 400 °C,
(E)-6f (80 mg, 80%) was obtained as a colorless liquid which turned
slowly to yellow on contact with air. Similar flash vacuum pyroly-
ses of 3f at lower temperatures gave mixtures of products: 4f (40%
yield), (Z)-6f (20%), and (E)-6f (32%) were formed at 320 °C,
while pyrolysis at 280 °C resulted in 4f (51%), (Z)-6f (17%), and
(E)-6f (25%). At 260 °C, the transformation of 3f was incomplete
leading to 3f (18% recovered), 4f (64%), (Z)-6f (5%), and (E)-6f
(7%). The reactions 3f, 4f, 6f could also be observed when a dilut-
ed solution of 3f (70 mg, 0.46 mmol) in dry toluene (12 mL) was
heated at 80–110 °C.
1
3
13C NMR (75 MHz, CDCl3): = 93.02 (dd, JC–H = 194 Hz, JC–H
1
= 9 Hz, CHNCS), 103.99 (d, JC–H = 165 Hz, CHPh), 127.10 (s,
NCS or Phi), 128.73 (d, Ph), 128.81 (d, Ph), 128.90 (d, Ph), 131.28
(s, NCS or Phi), 206.48 (s, =C= ).
3-(Isothiocyanatomethylene)-6-methylhepta-1,5-diene (6g)
By flash vacuum pyrolysis of 3g (300 mg, 1.67 mmol) at 320 °C, 6g
[270 mg; 90%; mixture of isomers]. (E)-6g/(Z)-6g = 2.4:1] was ob-
tained as an orange liquid. With flash chromatography (t-BuOMe–
hexane, 1:20), 170 mg (56%) pure product [ratio (E)-6g/(Z)-
6g = 2.4:1] could be isolated.
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactions of Isothiocyanate Substituted Allenes
1429
IR (CDCl3): 2972, 2915, 2116 (NCS), 1623, 1449, 1363, 986, 825
cm–1.
signments of 1 -H and 6-H by comparison with 1H NMR values of
7f.
13C NMR (75 MHz, CDCl3): = 18.11 (q, CH3), 25.03 (q, CH3),
32.37 (t, CH2), 32.46 (t, CH2), 36.76 (s, C-1 or C-2), 43.90 (s, C-1
or C-2), 58.19 (d, C-3), 108.00 (s, CN), 109.21 (s, CN), 109.68 (s,
CN), 109.99 (s, CN), 116.78 (d, C-2 or C-5), 117.95 (d, C-2 or C-
5), 133.89 (s), 138.32 (s), 145.05 (s).
(E)-6g
1H NMR (300 MHz, CDCl3): = 1.71 (s, 3 H, CH3), 1.75 (s, 3 H,
CH3), 3.08 (d, 3JH–H = 7.0 Hz, 2 H, 4-H), 5.01 (tsept, 3JH–H = 7.0 Hz,
4JH–H = 1.4 Hz, 1 H, 5-H), 5.23 (d, 3JH–H,cis = 11.0 Hz, 1 H, E-1-H),
5.40 (d, 3JH–H,trans = 17.4 Hz, 1 H, Z-1-H), 5.98 (s, 1 H, 1 -H), 6.23
(dd, 3JH–H,trans = 17.4 Hz, 3JH–H,cis = 11.0 Hz, 1 H, 2-H).
Anal. Calcd for C16H13N5S (307.37): C, 62.52; H, 4.26. Found: C,
63.01; H, 4.54.
13C NMR (75 MHz, CDCl3): = 18.07 (q, CH3), 25.79 (q, CH3),
26.05 (t, C-4), 115.34 (d, C-1 ), 117.00 (t, C-1), 120.07 (d, C-5),
133.34 (s, C-6), 135.17 (br s, NCS), 134.12 (d, C-2), 141.27 (s, C-
3).
2,3-Diisothiocyanatobuta-1,3-diene (8h)
Heating diluted solutions of 3h10 in CCl4, C6D6, or DMSO-d6 to 60–
100 °C gave limited yields of 8h (20–25%). Prolonged reaction
times caused excessive degradation. Very small amounts of 8h
could be generated by injecting solutions of 3h into a preparative
gas chromatograph (0.25 m Carbowax column, 75 °C, retention
times: 3.6 min for 8h and 13.2 min for 3h). Flash vacuum pyrolysis
of 3h (500 mg, 2.97 mmol) at 400 °C/10–5 mbar required vaporiza-
tion of the starting material at 60–70 °C and produced a substance
(90 mg, 18%), which consisted mainly of 8h and which was diluted
with an inert solvent (at least 1.5 mL) before thawing the trap.
(Z)-6g
1H NMR (300 MHz, CDCl3): = 1.63 (s, 3 H, CH3), 1.74 (s, 3 H,
CH3), 2.88 (d, 3JH–H = 7.1 Hz, 2 H, 4-H), 5.11 (tsept, 3JH–H = 7.1 Hz,
4JH–H = 1.4 Hz, 1 H, 5-H), 5.33 (d, 3JH–H,cis = 11.0 Hz, 1 H, E-1-H),
5.44 (d, 3JH–H,trans = 17.4 Hz, 1 H, Z-1-H), 5.86 (s, 1 H, 1 -H), 6.81
(dd, 3JH–H,trans = 17.4 Hz, 3JH–H,cis = 11.0 Hz, 1 H, 2-H).
13C NMR (75 MHz, CDCl3): = 17.77 (q, CH3), 25.73 (q, CH3),
28.10 (t, C-4), 113.37 (d, C-1 ), 117.58 (t, C-1), 119.65 (d, C-5),
130.69 (d, C-2), 134.07 (br s, NCS), 134.67 (s, C-6), 138.75 (s, C-
3).
Treatment of 4d (40 mg, 0.27 mmol) in DMSO-d6 (0.5 mL) with
NH4SCN (40 mg, 0.53 mmol) for 30 min at r.t. yielded 8h (95%,
1
1H NMR). After a few hours at r.t., H NMR spectra showed the
degradation of 8h already beginning.
IR (CDCl3): 2089 (NCS), 2038 (NCS), 1581 cm–1.
4-(Prop-2-enyl)-3-isothiocyanatocyclohex-4-ene-1,1,2,2-tetra-
carbonitrile (7f)
1H NMR (400 MHz, CDCl3): = 5.43 (d, 2JH–H = 1.0 Hz, 2 H), 5.61
Starting with 3f (810 mg, 5.35 mmol), a mixture of 4f, (E)-6f, and
(Z)-6f (740 mg, 92%, ratio 2:1.6:1) was obtained by flash vacuum
pyrolysis at 320 °C. This mixture was dissolved in THF (5 mL) and,
after adding of tetracyanoethylene (500 mg, 3.90 mmol), stirred at
r.t. for 12 h. Then the substances were separated by flash chroma-
tography (t-BuOMe–hexane, 1:1) to yield two fractions. The first
one contained a mixture of 4f and (Z)-6f [400 mg, 83%, related to
4f and (Z)-6f] as unchanged starting material, and the second one
was 7f [270 mg, 57%, based on (E)-6f] as yellow oil.
(d, 2JH–H = 1.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): = 113.1 (t, 1JC–H = 165 Hz, C-1, C-
4), 130.75 (s, C-2, C-3), 136.45 (s, NCS).
3,4-Diisothiocyanatohexa-2,4-dienes (8i)
Distillation of 3i at 90 °C (bath temperature) and 0.001 Torr pro-
duced 8i [67%, (E,E)-8i:(E,Z)-8i:(Z,Z)-8i = 1:2:1] as a colorless oil,
bp ca. 75–87 °C. When the distillation of 3i was performed at
180 °C/20 Torr, 8i (56%) resulted with (E,E)-8i:(E,Z)-8i:(Z,Z)-
8i = 1:1:8. Flash vacuum pyrolysis of 8i formed under kinetic con-
trol was conducted at 400 °C to shift the product distribution to
(Z,Z)-8i (96% yield of 8i). The stereoisomers of 8i could be ana-
lyzed by GC (150 °C), retention times: 25.9 min (E,E)-8i, 29.9 min
(E,Z)-8i, 31.8 min (Z,Z)-8i, and separated by HPLC [heptane–THF,
39:1, flow rate 8 mL/min, retention times: 6.4 min (Z,Z)-8i, 10.6
min (E,Z)-8i, 11.7 min (E,E)-8i].
IR (CDCl3): 3085, 2926, 2007 (NCS), 1435, 1323, 1131, 995, 817
cm–1.
1H NMR (300 MHz, CDCl3): = 3.07 (d, 3JH–H = 6.4 Hz, 2 H, 1 -
H), 3.15 (br d, JH–H = 18.9 Hz, 1 H, 6-H), 3.25 (br d, JH–H = 18.9 Hz,
3
1 H, 6-H), 5.13 (br s, 1 H, 3-H), 5.29 (d, JH–H,trans = 17.5 Hz, 1
3
H, Z-3 -H), 5.33 (d, JH–H,cis = 10.5 Hz, 1 H, E-3 -H), 5.75 (ddt,
3JH–H,trans = 17.4 Hz, 3JH–H,cis = 10.5 Hz, 3JH–H = 6.5 Hz, 1 H, 2 -H),
5.81 (m, 1 H, 5-H), the assignments could be proved by double res-
onance experiments.
(E,E)-8i
13C NMR (75 MHz, CDCl3): = 32.28 (t, C-6), 36.76 (s, C-1 or C-
2), 37.56 (t, C-1 ), 43.87 (s, C-1 or C-2), 57.85 (d, C-3), 107.84 (s,
CN), 109.15 (s, CN), 109.60 (s, CN), 109.88 (s, CN), 119.27 (d, C-
5), 120.40 (t, C-3 ), 131.48 (d, C-2 ), 132.79 (s, C-4 or NCS), 145.21
(s, C-4 or NCS).
IR (CCl4): 2030 (NCS) cm–1.
1H NMR (400 MHz, CDCl3): = 1.70 (d, 3JH–H = 7.3 Hz, 6 H, CH3),
5.88 (q, 3JH–H = 7.3 Hz, 2 H, CH).
13C NMR (100 MHz, CDCl3): = 13.9 (q, CH3), 123.6 (s, C=CH),
127.2 (d, CH), 135.8 (s, NCS).
GC–MS (70 eV): m/z (%) = 196 (M+, 100), 79 (45), 77 (96).
3-Isothiocyanato-4-(3-methylbut-2-enyl)cyclohex-4-ene-1,1,2,2-
tetracarbonitrile (7g)
6g (150 mg, 0.84 mmol, E/Z = 2.4:1) and tetracyanoethylene (140
mg, 1.09 mmol) were dissolved in dry THF (3 mL) and stirred at r.t.
for 12 h. Then the reaction mixture was separated by flash chroma-
tography (t-BuOMe–hexane, 1:1) to yield unconverted starting ma-
terial (Z)-6g (40 mg, 91%) and 7g [90 mg, 50% based on (E)-6g] as
a light yellow liquid.
(2E,4Z)-8i
IR (CCl4): 2050 (NCS) cm–1.
1H NMR (400 MHz, CDCl3): = 1.83 (d, 3JH–H = 7.6 Hz, 3 H, CH3),
3
3
1.92 (d, JH–H = 7.0 Hz, 3 H, CH3), 5.73 (q, JH–H = 7.0 Hz, 1 H,
CH), 5.80 (q, 3JH–H = 7.6 Hz, 1 H, CH).
13C NMR (100 MHz, CDCl3): = 13.7 (q, CH3), 14.0 (q, CH3),
123.4 (s, C-4), 125.7 (s, C-3), 125.85 (d, CH), 128.25 (d, CH), 134.9
(s, NCS), 137.35 (s, NCS).
IR (CDCl3): 2009 (NCS) cm–1.
1H NMR (300 MHz, CDCl3): = 1.69 (s, 3 H, CH3), 1.80 (s, 3 H,
CH3), 3.00 (br d, 3JH–H = 7.3 Hz, 2 H, 1 -H), 3.12 (dm, 2JH–H = 18.7
Hz, 1 H, 6-H), 3.23 (dm, 2JH–H = 18.7 Hz, 1 H, 6-H), 5.06 (br s, 1 H,
3-H), 5.09 (t, 3JH–H = 7.3 Hz, 1 H, 2 -H), 5.76 (m, 1 H, 5-H), the as-
GC–MS (70 eV): m/z (%) = 196 (M+, 98), 79 (89), 77 (100).
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1430
K. Banert et al.
PAPER
(Z,Z)-8i
13C NMR (50 MHz, DMSO-d6): = 14.11 (q, CH3), 16.35 (t, CH2),
20.24 (q, CH3), 55.01 (q, OCH3), 68.23 (d, CH), 123.22 (s), 128.08
(s), 160.10 (s, C=O).
IR (CCl4): 2060 (NCS) cm–1.
1H NMR (400 MHz, CDCl3): = 1.93 (d, 3JH–H = 6.5 Hz, 6 H, CH3),
5.99 (q, 3JH–H = 6.5 Hz, 2 H, CH).
MS (70 eV): m/z (%) = 186 (M+ – 1, 43), 155 (M – MeOH, 100), 41
(51), 39 (49), 29 (47), 28 (93).
13C NMR (100 MHz, CDCl3): = 13.8 (q, CH3), 123.6 (d, CH),
124.4 (s, C=CH), 136.7 (s, NCS).
GC–MS (70 eV): m/z (%) = 196 (M+, 100), 79 (82), 77 (93).
Anal. Calcd for C8H13NO2S (187.26): C, 51.31; H, 7.00; N, 7.48; S,
17.12. Found: C, 51.27; H, 7.19; N, 7.55; S, 17.15.
UV (cyclohexane): max (log ) = 269 nm (4.83).
4-Thiocyanatobuta-1,2-diene (11, X = SCN)
11 (X = Br, 5.0 g, 38 mmol)12 and ammonium thiocyanate (2.9 g, 76
mmol) were dissolved in DMSO (12 mL) and stirred at r.t. for 12 h.
After dilution with H2O, the reaction mixture was extracted with
pentane several times. The combined extracts were washed repeat-
edly with H2O and then dried (MgSO4). After removal of the solvent
in vacuo, 11 (X = SCN) could be isolated.
Reaction of 8i with TCNE
An excess of 10% TCNE was added to a concentrated solution of a
single stereoisomer of 8i in THF or THF-d8. The reaction mixture
was stirred at r.t. for 12 h. In the case of (Z,Z)-8i, the solvent was
evaporated, and the residue was crystallized from Et2O–pentane to
yield quantitatively cis-9i as a brownish solid, mp 112 °C. Starting
with (E,Z)-8i, no reaction with TCNE could be observed at r.t., thus,
the mixture was heated at 60 °C for 3 d. This procedure afforded
trans-9i (88%), however, the reaction was accompanied by degra-
dation. In the case of (E,E)-8i, no cycloadduct could be found even
after heating with TCNE at 60 °C for 7 d. In order to perform com-
petition experiments, mixtures of equimolar amounts of (Z,Z)-8i
and (E,E)-hexa-2,4-diene or (E,Z)-8i and (E,Z)-hexa-2,4-diene
were treated with substoichiometric amounts of TCNE in acetone-
d6. 1H NMR spectra indicated that Diels–Alder reactions of 8i were
slower than the cycloadditions of the unsubstituted hexa-2,4-dienes
in both cases.
Yield: 3.36 g (80%).
IR (CCl4): 2160, 1950, 1220, 860 cm–1.
1H NMR (400 MHz, CDCl3): = 3.59 (dt, JH–H = 7.7 Hz,
3
5JH–H = 2.3 Hz, 2 H, CH2), 5.03 (dt, 4JH–H = 6.6 Hz, 5JH–H = 2.3 Hz,
2 H, =CH2), 5.34 (m, 1 H, =CH).
13C NMR (100 MHz, CDCl3): = 33.35 (t, CH2), 78.12 (t, =CH2),
85.64 (d, =CH), 111.34 (s, SCN), 210.37 (s, =C= ).
3-Methyl-4-thiocyanatobuta-1,2-diene (12, X = SCN)
12 (X = Cl, 2.5 g, 24.4 mmol)13 and ammonium thiocyanate (3.7 g,
48.8 mmol) were dissolved in DMSO (100 mL) and stirred at r.t. for
12 h. After workup as described for 11 (X = SCN), 12 (X = SCN)
was obtained.
cis-4,5-Diisothiocyanato-3,6-dimethylcyclohex-4-ene-1,1,2,2-
tetracarbonitrile (cis-9i)
IR (CCl4): 2930, 2000 cm–1.
Yield: 3.1 g (100%); nearly colorless oil.
IR (CCl4): 2160, 1955 cm–1.
1H NMR (400 MHz, CDCl3): = 1.82 (t, JH–H = 3.0 Hz, 3 H, CH3),
3.55 (t, JH–H = 2.1 Hz, 2 H, CH2), 4.85 (m, 2 H, =CH2).
13C NMR (100 MHz, CDCl3): = 16.52 (q, CH3), 38.99 (t, C-4),
76.48 (t, C-1), 93.47 (s, C-3), 111.64 (s, SCN), 208.04 (C-2).
3
1H NMR (400 MHz, THF-d8): = 1.81 (d, JH–H = 6.75 Hz, 6 H,
CH3), 3.42 (q, 3JH–H = 6.75 Hz, 2 H, CH).
13C NMR (100 MHz, THF-d8): = 16.08 (q, CH3), 39.77 (d, C-3/C-
6), 43.86 (s, C-1/C-2), 110.40 (s, CN), 111.55 (s, CN), 124.47 (s,
NCS), 142.67 (s, C-4, C-5).
MS (70 eV): m/z (%) = 324 (M+, 55), 196 (M+ – TCNE, 73), 181
(M+ – TCNE – CH3, 91), 163 (100), 138 (M+ – TCNE – SCN, 55),
137 (73).
2-Isothiocyanatobuta-1,3-diene (13)
Compound 13 was prepared from a solution of 11 (X = SCN) in
CDCl3 by heating at 50 °C for 4 d, however, the amount of 13 did
not exceed 40% due to the instability of this product. For isolation
of 13, a solution of 11 (X = SCN) was injected into a preparative gas
chromatograph (3 m Carbowax column, 70 °C) to give 13 (31%, re-
tention time: 2 min) and unchanged 11 (X = SCN, retention time: 15
min). Flash vacuum pyrolysis of 11 (X = SCN, 496 mg, 4.5 mmol,
300 °C/0.0015 Torr) gave pure 13.
UV (cyclohexane): max (log ) = 317 nm (4.03).
Anal. Calcd for C14H8N6S2 (324.4): C, 51.84; H, 2.49; N, 25.91.
Found: C, 51.80; H, 2.58; N, 26.00.
trans-4,5-Diisothiocyanato-3,6-dimethylcyclohex-4-ene-1,1,2,2-
tetracarbonitrile (trans-9i)
3
1H NMR (400 MHz, THF-d8): = 1.65 (d, JH–H = 6.6 Hz, 6 H,
Yield: 437 mg (88%); unstable yellowish liquid.
IR (CCl4): 2122, 2090, 2060 cm–1.
1H NMR (400 MHz, CDCl3): = 5.08 (s, 1 H, 1-H), 5.20 (s, 1 H, 1-
H), 5.33 (d, JH–H = 10.4 Hz, 1 H, E-4-H), 5.60 (d, JH–H = 16.9 Hz, 1
H, Z-4-H), 6.29 (dd, JH–H = 16.9 Hz, JH–H = 10.4 Hz, 1 H, 3-H).
13C NMR (75 MHz, CDCl3): = 113.37 (t, C-1 or C-4), 117.27 (s,
C-2), 117.28 (t, C-1 or C-4), 132.01 (d, C-3), 134.93 (br s, NCS).
GC–MS (70 eV): m/z (%) = 111 (M+, 77), 53 (M+ – NCS, 100).
CH3), 3.84 (m, 2 H, CH).
13C NMR (100 MHz, THF-d8): = 15.42 (q, CH3), 39.35 (d, C-3/C-
6), 46.19 (s, C-1/C-2), 109.01 (s, CN), 111.25 (s, CN), 124.69 (s,
NCS), 142.26 (s, C-4/C-5).
5-Ethyl-4-(1-methoxyethyl)-3H-thiazol-2-one (10i)
3i (5.00 g, 26.7 mmol) was dissolved in MeOH-H2O (9:1, 500 mL)
and heated at reflux (110 °C) for 36 h. After removing the solvent
in vacuo, the residue was recrystallized from acetone to yield 10i
(0.66 g, 13%) as a colorless solid (mp 232 °C). It is possible to ob-
tain 10i from 8i analogously (yield 32%).
UV (cyclohexane): max (log ) = 271 nm (4.00).
IR (KBr): 3370, 3060, 2920, 1520 cm–1.
2-Isothiocyanato-3-methylbuta-1,3-diene (14)
12 (X = Cl, 2.5 g, 24.4 mmol)13 and ammonium thiocyanate (3.7 g,
48.8 mmol) were dissolved in DMSO (100 mL) and stirred at 40 °C
for 3 d under argon to yield 14 (2.1 g, 69%) as a nearly colorless oil
after workup as described for 11 (X = SCN). When 12 (X = SCN)
was heated for 3.5 h in DMSO at 60 °C, 14 was formed quantitative-
ly.
3
1H NMR (200 MHz, DMSO-d6): = 1.07 (t, JH–H = 7.5 Hz, 3 H,
CH3), 1.33 (d, 3JH–H = 6.6 Hz, 3 H, CH3), 2.39 (q, 3JH–H = 7.5 Hz, 2
H, CH2), 3.03 (s, 3 H, OCH3), 4.42 (q, JH–H = 6.6 Hz, 1 H, CH),
11.78 (d, 1 H, NH). The structure of 10i was supported by homonu-
3
clear NOE difference spectra.
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactions of Isothiocyanate Substituted Allenes
1431
IR (CCl4): 2090 (NCS) cm–1.
1H NMR (80 MHz, CDCl3): = 1.93 (s, 3 H, CH3), 5.19 (s, 1 H),
5.21 (s, 1 H), 5.24 (s, 1 H), 5.42 (s, 1 H).
13C NMR (100 MHz, CDCl3): = 19.25 (q, CH3), 110.97 (t, C-1 or
C-4), 116.01 (t, C-1 or C-4), 133.45 (br s, NCS), 136.60 (s, C-2 or
C-3), 137.18 (s, C-2 or C-3).
1H NMR (400 MHz, CDCl3): = 1.84 (s, 3 H, CH3), 3.05 (m, 2 H,
CH2), 3.20 (m, 2 H, CH2), 3.76 (s, 6 H, OCH3).
13C NMR (100 MHz, CDCl3): = 17.76 (q, CH3), 31.55 (t, C-3 or
C-6), 33.73 (t, C-3 or C-6), 52.22 (q, 2 OCH3), 118.52 (s), 126.14
(s), 129.99 (s), 132.47 (s), 136.47 (s, NCS), 166.37 (s, C=O), 167.34
(s, C=O).
MS (70 eV): m/z (%) = 267 (M+, 39), 235 (M+ – MeOH, 44), 176
GC–MS (70 eV): m/z (%) = 125 (M+, 66), 67 (M+ – NCS, 50), 41
(100).
(M+ – MeOH – HSCN, 61).
Anal. Calcd for C12H13NO4S (267.3): C, 53.92; H, 4.90; N, 5.24.
Found: C, 53.76; H, 4.78; N, 5.27.
UV (cyclohexane): max (log ) = 275 nm (3.89).
4-Isothiocyanatocyclohex-4-ene-1,1,2,2-tetracarbonitrile (15)
11 (X = SCN, 0.22 g, 1.98 mmol) was dissolved in THF (1 mL), and
tetracyanoethylene (0.25 g, 3.96 mmol) was added. After heating at
50 °C for 4 d, the solvent was evaporated and the excess of tetracy-
anoethylene was removed by sublimation at 140 °C/0.001 Torr to
obtain the residue of 15.
2-Chloro-3-isothiocyanatobuta-1,3-diene (18d)
To a solution of 4d (148 mg, 1.06 mmol) in DMSO-d6 (633 mg),
lithium chloride (50 mg, 1.18 mmol) was added. The mixture was
stirred at r.t. for 1 h. After recondensation at 0.001 Torr, the solution
of the product was solved in Et2O. This solution was washed three
times with ice–water and dried (MgSO4) at 0 °C. After removing
the solvent without warming, 18d was obtained as a yellowish oil
which tends to polymerization.
Yield: 330 mg, 70%; mp 215–216 °C (decomp.).
IR (KBr): 2140, 1650, 1420, 780 cm–1.
1H NMR (400 MHz, CDCl3): = 3.59 (m, 2 H, CH2), 3.80 (m, 2 H,
CH2), 6.08 (m, 1 H, =CH).
Yield: 73.0 mg (49%).
IR (CCl4): 2045, 2080, 2155 cm–1.
13C NMR (50 MHz, DMSO-d6): = 31.41 (t, C-3 or C-6), 34.08 (t,
C-3 or C-6), 38.54 (s, C-1 or C-2), 39.45 (s, C-1 or C-2), 111.16 (s,
CN), 111.49 (d, C-5), 117.43 (s, CN), 123.77 (s, C-4), 138.85 (s,
NCS).
1H NMR (200 MHz, DMSO-d6): = 5.72 (m, 1 H), 5.80 (m, 1 H),
5.81 (m, 1 H), 5.88 (m, 1 H).
1
13C NMR (50 MHz, DMSO-d6): = 116.42 (t, JC–H = 166 Hz,
CH2), 117.14 (dd, 1JC–H = 168 Hz, 1JC–H = 162 Hz, CH2), 131.53 (s),
MS (70 eV): m/z (%) = 239 (M+, 34), 111 (M+ – TCNE, 100), 53
132.41 (s), 135.35 (br s, NCS).
GC–MS (70 eV): m/z (%) = 147 [M+ (37Cl), 27], 145 [M+ (35Cl),
85], 87 (38), 51 (100).
(M+ – TCNE – SCN, 57).
UV (cyclohexane): max (log ) = 273 nm (3.88).
Anal. Calcd for C11H5N5S (239.3): C, 55.22; H, 2.11; N, 29.27.
Found: C, 55.25; H, 2.28; N, 29.06.
4-Ethenyl-3H-oxazole-2-thione (22k)
3k (0.5 g, 3.93 mmol) was dissolved in dioxane-H2O (1:1, 60 mL)
and heated at reflux for 26 h. After removing the solvent in vacuo,
the residue was dissolved in Et2O, and 4-methoxyphenol (2.5 mg)
was added. The solution was filtered and dried (MgSO4). The sol-
vent was evaporated to yield 0.45 g (90%) of a brownish crystalline
crude product. By flash chromatography (EtOAc–hexane, 2:3), 22k
was obtained. Because of the tendency of 22k to polymerize in so-
lution, recrystallization failed, however, sublimation at 60 °C and
0.01 Torr was possible.
4-Isothiocyanato-5-methylcyclohex-4-ene-1,1,2,2-tetracarboni-
trile (16)
14 (0.8 g, 6.4 mmol) and tetracyanoethylene (1.64 g, 12.8 mmol)
were dissolved in acetone and stirred at r.t. for 12 h. Removal of the
solvent and of the excess of tetracyanoethylene by sublimation at
70 °C/0.001 Torr yielded the residue of 16.
Yield: 1.3 g (80%); mp 132–133 °C (Et2O).
IR (KBr): 2960, 2934, 2070, 1435, 1357, 1250, 1142, 965, 840
cm–1.
1H NMR (400 MHz, acetone-d6): = 1.99 (s, 3 H, CH3), 3.57 (m, 2
Yield: 0.28 g (56%); colorless needles.
IR (KBr): 1489, 1248 (CS), 1145, 1078 cm–1.
1H NMR (200 MHz, acetone-d6): = 5.37 (d, JH–H = 11.6 Hz,
3
H, CH2), 3.77 (m, CH2).
3
1 H, E-2 -H), 5.79 (d, JH–H = 17.5 Hz, 1 H, Z-2 -H), 6.50 (dd,
13C NMR (100 MHz, acetone-d6): = 18.21 (q, CH3), 34.35 (t, C-3
or C-6), 35.74 (t, C-3 or C-6), 39.11 (s, C-1 or C-2), 39.51 (s, C-1
or C-2), 111.24 (s, CN), 111.51 (s, CN), 117.46 (s, C-4 or C-5),
126.71 (s, C-4 or C-5), 139.08 (s, NCS).
3JH–H = 17.5 Hz, 3JH–H = 11.6 Hz, 1 H, 1 -H), 7.60 (s, 1 H, 5-H), 11.9
(br s, 1 H, NH).
13C NMR (50 MHz, acetone-d6): = 117.00 (dd, JC–H = 163 Hz,
1
1
1JC–H = 157 Hz, =CH2), 120.85 (d, JC–H = 162 Hz, CH=CH2),
MS (70 eV): m/z (%) = 253 (M+, 100), 125 (M+ – TCNE, 96), 67
1
130.45 (s, =CNH), 135.07 (d, JC–H = 216 Hz, =CHO), 180.91 (s,
(M+ – TCNE – SCN, 53).
CS), the assignment of CH signals was possible with the help of the
26
different coupling constants 1JC–H
.
UV (cyclohexane): max (log ) = 276 nm (3.93).
Anal. Calcd for C12H7N5S (253.3): C, 56.90; H, 2.79; N, 27.65.
Found: C, 56.59; H, 2.95; N, 27.65.
Anal. Calcd for C5H5NOS (127.17): C, 47.23; H, 3.96. Found: C,
47.38; H, 3.86.
4-Isothiocyanato-5-methylcyclohexa-1,4-diene-1,2-dicarboxyl-
ic Acid Dimethyl Ester (17)
14 (1.7 g, 13.6 mmol) and dimethyl acetylenedicarboxylate (3.86 g,
27.2 mmol) were stirred at 60 °C for 3 d under argon. After remov-
ing the excess of the starting material in vacuo, 17 was obtained.
Reaction of 4a with Cyclopentadiene to (E)-5-Isothiocyanato-
methylenebicyclo[2.2.1]hept-2-ene [(E)-23a], (Z)-5-Isothiocy-
anatomethylenebicyclo[2.2.1]hept-2-ene [(Z)-23a], endo-5-
Isothiocyanato-6-methylenebicyclo[2.2.1]hept-2-ene (endo-
24a), and exo-5-Isothiocyanato-6-methylenebicyclo[2.2.1]hept-
2-ene (exo-24a)
4a (9.7 g, 0.10 mol) was condensed into freshly prepared cyclopen-
tadiene (87.3 g, 1.32 mol), stirred at r.t. for 24 h, and then filtered.
After removing the excess of cyclopentadiene in vacuo, the dimer
Yield: 3.2 g (88%); mp 58 °C (Et2O–pentane).
IR (CDCl3): 2940, 2070, 1710, 1426, 1260, 1214, 1105, 1060, 840
cm–1.
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

1432
K. Banert et al.
PAPER
of cyclopentadiene was distilled at 40 °C over a column (20 cm) in
vacuo. The residue of 23a/24a (15.22 g, 93%) was obtained as a yel-
lowish oil, which contained (E)-23a (35%), (Z)-23a (25%), endo-
24a (28%), and exo-24a (11%). The constitutional isomers 23a and
24a could be separated partly by distillation over a column (20 cm),
bp 45–55 °C/0.007 mbar. Anal. Calcd for C9H9NS (163.24): C,
66.21; H, 5.56; N, 8.58; S, 19.64. Found: C, 65.95; H, 5.49; N, 9.47;
S, 19.80. Complete separation of 23a and 24a was possible by pre-
parative GC (1 m silicon OV 101 column, 120 °C), and both com-
pounds gave rise to the same dominant infrared absorption [IR
(CCl4): 2080 (NCS) cm–1]. The differentiation of all four isomeric
isothiocyantes could only be achieved by analytical GC, however,
the resulting mass spectra were very similiar in all the cases {GC–
MS (70 eV): m/z = 163 [M+]}.
The assignments of the NMR signals were supported by homonu-
clear double resonance and COSY experiments as well as 13C-1H
shift correlation. The attribution of (E)-23a and (Z)-23a was based
on homonuclear NOE difference spectra, which showed – only in
the case of (E)-23a – a signal enhancement for 4-H (5.5%) on irra-
diating the signal for CHNCS and vice versa an enhancement of
3.5%. Moreover, the absolute values of the coupling constants
5
4JH–H (6-H, CHNCS) = 2.4 Hz and JH–H (1-H, CHNCS) = 0.8 Hz
for (E)-23a as well as 4JH–H (6-H, CHNCS) = 1.9 Hz and 5JH-H (1-H,
CHNCS) ca. 0 Hz for (Z)-23a are compatible with the structures.
The assignment of endo-24a and exo-24a was proved by analyzing
3
the homonuclear coupling which resulted in JH–H (4-H, exo-5-
H) = 3.7 Hz and 4JH–H (syn-7-H, exo-5-H) ca. 0 Hz for endo-24a as
well as 3JH–H (4-H, endo-5-H) ca. 0 Hz and 4JH–H (syn-7-H, endo-5-
H) = 1.6 Hz for exo-24a.
(E)-23a
1H NMR (200 MHz, CDCl3): = 1.42 (dm, 2JH–H = 8.6 Hz, 1 H, 7-
Hsyn), 1.68 (dm, 2JH–H = 8.6 Hz, 1 H, 7-Hanti), 1.95 (ddd, 2JH–H = 15.7
Hz, 4JH–H = 3.4 Hz, 4JH–H = 2.4 Hz, 1 H, 6-Hendo), 2.39 (dddd, 2JH–H
= 15.7 Hz, JH–H = 3.3 Hz, JH–H = 2.4 Hz, JH–H = 0.8 Hz, 1 H, 6-
Hexo), 3.05 (m, 1 H, 1-H), 3.26 (m, 1 H, 4-H), 5.91 (dddd, 4JH–H = 2.4
Hz, 4JH–H = 2.4 Hz, 5JH–H = 0.8 Hz, 4JH–H ca. 0.5 Hz, 1 H, CHNCS),
6.00 (ddd, 3JH–H = 5.6 Hz, 3JH–H = 3.2 Hz, 5JH–H = 0.8 Hz, 1 H, 3-H),
6.22 (dd, 3JH–H = 5.6 Hz, 3JH–H = 2.8 Hz, 1 H, 2-H), syn and anti po-
sitions of 7-H are based on the endocyclic double bond.
2,3-Diiodo-1-isothiocyanatopropene (25a)
A solution of iodine (2.54 g, 10 mmol) in CHCl3 (80 mL) was added
dropwise to a solution of 4a (0.97g, 10 mmol) in CHCl3 (14 mL)
and stirred at r.t. for 30 min. The solvent and other volatile compo-
nents were removed at 0 °C in vacuo to yield 2.70 g (77%) of a
brownish mixture of unstable (E)-25a and (Z)-25a (ratio 3:1). The
isomers could be assigned due to the different 4JH–H coupling con-
stant of the allylic system,27 which is larger in the case of (E)-25a
(4JH–H = 1 Hz) than in the case of (Z)-25a (4JH–H not resolved).
3
4
5
13C NMR (50 MHz, CDCl3): = 32.95 (t, C-6), 41.28 (d, C-1),
47.78 (d, C-4), 50.54 (t, C-7), 105.92 (d, CH-N), 132.79 (d, C-3),
137.96 (d, C-2), 148.91 (s, C-5).
(E)-25a
1H NMR (200 MHz, CDCl3): = 4.42 (d, 4J
= 1 Hz, 2 H, CH2),
–
6.80 (t, 4J
= 1 Hz, 1 H, = CH).
–
(Z)-23a
13C NMR (50 MHz, CDCl3): = 12.42 (t, CH2), 103.17 (s, =CI),
124.16 (d, =CH), 137.26 (br s, NCS).
2
1H NMR (200 MHz, CDCl3): = 1.42 (dm, JH–H = 8.6 Hz, 1 H, 7-
Hsyn), 1.68 (dm, 2JH–H = 8.6 Hz, 1 H, 7-Hanti), 1.81 (ddd, 2JH–H = 15.1
Hz, 4JH–H = 3.2 Hz, 4JH–H = 1.8 Hz, 1 H, 6-Hendo), 2.31 (dddd, 2JH–H
(Z)-25a
3
4
5
= 15.1 Hz, JH–H = 3.4 Hz, JH–H = 1.9 Hz, JH–H = 0.7 Hz, 1 H, 6-
exo), 3.05 (m, 1 H, 1-H), 3.70 (m, 1 H, 4-H), 5.69 (ddd, 4JH–H = 1.9
1H NMR (200 MHz, CDCl3): = 4.44 (s, CH2), 6.54 (s, =CH).
H
13C NMR (50 MHz, CDCl3): = 8.31 (t, CH2), 100.88 (s, =CI),
124.16 (d, =CH), 138.59 (br s, NCS).
4
4
Hz, JH–H = 1.8 Hz, JH–H ca. 0.8 Hz, 1 H, CHNCS), 6.07 (ddd,
3JH–H = 5.6 Hz, 3JH–H = 3.2 Hz, 5JH–H ca. 0.7 Hz, 1 H, 3-H), 6.23 (dd,
3JH–H = 5.6 Hz, 3JH–H = 2.8 Hz, 1 H, 2-H).
(5-Benzylthiazol-2-yl)phenylamine (26l)
13C NMR (50 MHz, CDCl3): = 32.44 (t, C-6), 41.54 (d, C-1),
46.72 (d, C-4), 49.66 (t, C-7), 105.34 (d, CH-N), 132.53 (d, C-3),
137.96 (d, C-2), 147.96 (s, C-5).
To 3l (1.50 g, 8.66 mmol), dissolved in THF (10 mL), aniline (1.20
g, 12.89 mmol) was added and the reaction mixture was stirred at
reflux for 2 h under argon. The THF and the excess of aniline were
removed in vacuo within 6 h. After extraction of the residue with
boiling cyclohexane and removal of the solvent, 26l (1.51 g, 65%)
was obtained, which could be recrystallized from benzene.
endo-24a
1H NMR (200 MHz, CDCl3): = 1.47 (dtt, JH–H = 9.3 Hz, JH–H
2
3
4
2
= 1.0 Hz, JH–H = 0.5 Hz, 1 H, 7-Hanti), 1.73 (dt, JH–H = 9.3 Hz,
Yield: 1.51 g (65%); colorless solid; mp 142 °C
3JH–H ca. 2 Hz, 1 H, 7-Hsyn), 3.22 (m, 1 H, 4-H), 3.28 (m, 1 H, 1-H),
1H NMR (200 MHz, CDCl3): = 4.01 (d, 4JH–H = 1.2 Hz, 2 H, CH2),
4.46 (dt, 3JH–H = 3.7 Hz, 4JH–H ca. 1.7 Hz, 1 H, 5-H), 5.05 (d, JH–H
4
7.02 (t, 4JH–H = 1.2 Hz, 1 H, 4-H), 7.29 (m, 10 H, Ph).
= 1.7 Hz, 1 H, C=CH2), 5.17 (m, 1 H, C=CH2), 6.16 (dd, 3JH–H = 5.6
Hz, 3JH–H = 3.0 Hz, 1 H, 3-H), 6.38 (dd, 3JH–H = 5.6 Hz, 3JH–H = 3.2
Hz, 1 H, 2-H).
13C NMR (50 MHz, CDCl3): = 33.25 (t, CH2), 118.12 (d, Ph),
122.82 (d, Ph), 126.23 (s, C-5), 126.70 (d, Ph), 128.33 (d, Ph),
128.61 (d, Ph), 129.40 (d, Ph), 134.61 (d, C-4), 139.55 (s, Phi),
140.66 (s, Phi), 165.54 (s, C-2).
13C NMR (50 MHz, CDCl3): = 46.82 (t, C-7), 47.66 (d, C-4),
50.06 (d, C-1), 59.28 (d, C-5), 107.37 (t, C=CH2), 132.53 (d, C-3),
137.80 (d, C-2), 149.18 (s, C-6).
Anal. Calcd for C16H14N2S (266.37): C, 72.15; H, 5.30; N, 10.52; S,
12.04. Found: C, 71.96; H, 5.23; N, 10.29; S, 12.37.
exo-24a
1H NMR (200 MHz, CDCl3): = 1.84 (dtd, JH–H = 9.3 Hz, JH–H
= 1.7 Hz, 4JH–H = 1.6 Hz, 1 H, 7-Hsyn), 1.89 (dm, 2JH–H = 9.3 Hz, 1
H, 7-Hanti), 3.11 (m, 1 H, 4-H), 3.28 (m, 1 H, 1-H), 3.90 (ddd, 4JH–H
2
3
5-Ethyl-2-methoxythiazole (27b) and (Z)-5-Ethylidene-2-me-
thoxy-4,5-dihydrothiazole (28b)
3b (10.00 g, 90.1 mmol) was dissolved in MeOH (800 mL, 19.8
mol) and heated at reflux for 5 d. MeOH was removed by distilla-
tion at normal pressure. The residue was fractionated in vacuo to
give 8.29 g (64%) of a mixture of 27b and 28b (bp 71–75 °C at 26
mbar) in 3:1 ratio. Heating 4b in MeOH at 65 °C for 3 d gave also
27b and 28b in the same ratio. These compounds could be separated
by preparative GC (1 m silicon OV 101 column, 70 °C, retention
times: 23.8 min for 27b and 36 min for 28b).
= 1.6 Hz, 4JH–H = 1.3 Hz, 4JH–H = 1.3 Hz, 1 H, 5-H), 5.10 (d, JH–H
4
= 1.3 Hz, 1 H, C=CH2), 5.18 (m, 1 H, C=CH2), 6.07 (dd, 3JH–H = 5.6
Hz, 3JH–H = 3.0 Hz, 1 H, 3-H), 6.24 (dd, 3JH–H = 5.6 Hz, 3JH–H = 3.0
Hz, 1 H, 2-H).
13C NMR (50 MHz, CDCl3): = 47.30 (t, C-7), 49.15 (d, C-1),
49.47 (d, C-4), 58.58 (d, C-5), 107.75 (t, C=CH2), 133.88 (d, C-3),
138.90 (d, C-2), 148.54 (s, C-6).
Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactions of Isothiocyanate Substituted Allenes
1433
27b
(6) (a) Henry, L. Ber. Dtsch. Chem. Ges. 1873, 6, 728.
IR (CDCl3): 2969, 1529, 1425, 1255, 1154 cm–1.
(b) Midtgaard, T.; Gundersen, G.; Nielsen, C. J. J. Mol.
Struct. 1988, 176, 159.
1H NMR (200 MHz, CDCl3): = 1.23 (t, 3JH–H = 7.6 Hz, 3 H, CH3),
(7) (a) Yura, Y. Chem. Pharm. Bull. 1962, 10, 1094.
(b) Vizgert, R. V.; Sendega, R. V. Russ. J. Org. Chem. 1969,
5, 475. (c) Meijer, J.; Vermeer, P.; Bos, H. J. T.; Brandsma,
L. Recl. Trav. Chim. Pays-Bas 1974, 93, 26. (d) Austin, P.
W. (Imperial Chemical Industries PLC) Eur. Pat. Appl. EP
244962, 1986; Chem. Abstr. 1988, 108, 89483d.
(8) (a) Banert, K.; Hückstädt, H.; Vrobel, K. Angew. Chem.
1992, 104, 72. (b) Banert, K.; Hückstädt, H.; Vrobel, K.
Angew. Chem., Int. Ed. Engl. 1992, 31, 90.
3
4
2.66 (qd, JH–H = 7.6 Hz, JH–H = 1.3 Hz, 2 H, CH2), 4.01 (s, 3 H,
OCH3), 6.77 (t, 4JH–H = 1.3 Hz, 1 H, =CH).
13C NMR (100 MHz, CDCl3): = 15.46 (q, CCH3), 20.78 (t, CH2),
57.62 (q, OCH3), 131.66 (d, C-4), 133.11 (s, C-5), 173.36 (s, C-2).
GC-MS (70 eV): m/z (%) = 143 (M+, 51), 128 (100), 100 (39), 84
(8), 71 (14), 56 (18).
28b
(9) For preliminary communications on sequences of
IR (CDCl3): 2953, 1641, 1448, 1434, 1324, 1277, 1240, 1190, 1067,
1041 cm–1.
sigmatropic rearrangement reactions like 3
4
6, see:
(a) Banert, K.; Fendel, W.; Schlott, J. Angew. Chem. 1998,
110, 3488. (b) Banert, K.; Fendel, W.; Schlott, J. Angew.
Chem. Int. Ed. 1998, 37, 3289. (c) Banert, K.; Schlott, J.
Tetrahedron 2000, 56, 5413.
3
5
1H NMR (200 MHz, CDCl3): = 1.67 (dt, JH–H = 6.5 Hz, JH–H
= 2.4 Hz, 3 H, CH3), 3.95 (s, 3 H, OCH3), 4.73 (quint, JH–H = 2.4 Hz,
2 H, CH2), 5.48 (qt, 3JH–H = 6.5 Hz, 4JH–H = 2.4 Hz, 1 H, =CH), the
determination of the stereochemistry was performed by NOE differ-
ence spectroscopy.
(10) Johnson, A. W. J. Chem. Soc. 1946, 1009.
(11) Van den Ouweland, G. A. M.; Peer, H. G. (Unilever) DE-
1932800, 1970; Chem. Abstr. 1970, 72, 90265d.
(12) Pornet, J.; Randrianoelina, B.; Miginiac, L. J. Organomet.
Chem. 1979, 174, 1.
13C NMR (100 MHz, CDCl3): = 17.66 (q, CCH3), 56.99 (q,
OCH3), 63.81 (t, C-4), 113.38 (d, =CH), 139.93 (s, C-5), 165.01 (s,
C-2).
(13) Bergmann, E. D.; Herrman, D. J. Am. Chem. Soc. 1951, 73,
4013.
(14) Compare with the rearrangement of 4-chloro-3-methylbuta-
1,2-diene to 2-chloro-3-methylbuta-1,3-diene described in
ref.13
GC-MS (70 eV): m/z (%) = 143 (M+, 50), 128 (100), 86 (19), 71
(67), 58 (16).
Anal. Calcd for C6H9NOS (143.2): C, 50.32; H, 6.33; N, 9.78.
Found: C, 50.19; H, 6.34; N, 9.75.
(15) Banert, K.; Hagedorn, M.; Müller, A. Eur. J. Org. Chem.
2001, 1089.
(16) Zhang, Y.; Kensler, T. W.; Cho, C.-G.; Posner, G. H.;
Talalay, P. Proc. Natl. Acad. Sci. U.S.A. 1994, 91, 3147.
(17) Diveley, W. R.; Buntin, G. A.; Lohr, A. D. J. Org. Chem.
1969, 34, 616.
(18) Alternative synthesis of 27b, see: Cornwell, S. P.; Kaye, P.
T.; Kent, A. G.; Meakins, G. D. J. Chem. Soc., Perkin Trans.
1 1981, 2340.
(19) Other isomerizations of nonaromatic thiazole derivatives to
give aromatic thiazoles, see: Wipf, P.; Rahman, L. T.;
Rector, S. R. J. Org. Chem. 1998, 63, 7132.
(20) Review on [3,3] sigmatropic rearrangement reactions to
produce functionalized allenes, see: Banert, K. Liebigs Ann.
Recueil 1997, 2005.
Rearrangement of 28b to 27b
28b (69.34 mg, 0.485 mmol) was added to concd H2SO4 (2 mL) at
0 °C and stirred at r.t. for 45 min. The reaction mixture was then
poured onto ice (10 g) and neutralized with NaOH. After extraction
with CH2Cl2 and drying (MgSO4), the solvent was evaporated to
yield 27b (27.13 mg, 39%).
Acknowledgement
We are grateful to the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for continued financial support.
References
(21) Review on the synthesis of five-membered heterocycles
from functionalized allenes, see: Banert, K. In Targets in
Heterocyclic Systems - Chemistry and Properties, Vol. 3;
Attanasi, O. A.; Spinelli, D., Eds.; Società Chimica Italiana:
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(22) (a) Boeckman, R. K. Jr.; Ko, S. S. J. Am. Chem. Soc. 1982,
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(1) Part 11: Banert, K.; Melzer, A. Tetrahedron Lett. 2001, 42,
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(2) For reviews on history, see: (a) Hansen, H.-J. Chimia 1999,
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Synthesis 2002, No. 10, 1423–1433 ISSN 0039-7881 © Thieme Stuttgart · New York