New simple syntheses of (E)-1-azido- (or thiocyanato)-alk-1-enes from alk-1-ynes by hydroboration

Article abstract of DOI:10.1039/a708932e

Stereochemically pure (E)-1-azido- (or thiocyanato)-alk-1-enes have been synthesized in situ and in reasonable yields from alk-1-ynes upon hydroboration with disiamylborane followed by reactions with simple reagents; sodium azide (or potassium thiocyanate

Full text of DOI:10.1039/a708932e

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New simple syntheses of (E)-1-azido- (or thiocyanato)-alk-1-enes
from alk-1-ynes by hydroboration
Yuzuru Masuda,* Miki Murata, Minehito Ikeda and Shinji Watanabe
Department of Materials Science, Kitami Institute of Technology, Kitami 090, Japan
Stereochemically pure (E)-1-azido- (or thiocyanato)-alk-1-
enes have been synthesized in situ and in reasonable yields
from alk-1-ynes upon hydroboration with disiamylborane
followed by reactions with simple reagents; sodium azide
Table 1 Synthesis of thiocyanatoalkenes from alkynes via hydrobor-
ation by disiamylborane
a
%
Yield
(
or potassium thiocyanate) and copper(II) nitrate trihy-
b
c
Alkyne
Product
GC
Isolated
drate, in the presence of copper(II) acetate and a small
amount of water, in polar aprotic solvents.
Hex-1-yne
tert-Butylacetylene
Phenylacetylene
(E)-BuCH᎐CHSCN
(E)-Bu CH᎐CHSCN
᎐
88
81
74
75
72
65
t
(E)-PhCH᎐CHSCN
᎐
Although many useful synthetic reactions using organoboranes
1
have been reported, these do not include a procedure for
a
All yields are for the overall process, and are based on starting alkynes.
Neither Z-isomer nor isothiocyanato-isomer was detected by GC.
After flash column chromatography (silica gel; pentane–dichloro-
b
c
syntheses of alkenyl azides (or thiocyanates).† Previously we
reported a synthesis of (E)-1-chloro- (or bromo)-alk-1-enes by
treatment of (E)-alk-1-enyldialkylboranes [derived from alk-1-
ynes by hydroboration with dialkylborane in tetrahydrofuran
methane). GC purity is 95–99%.
Table 2 Synthesis of azidoalkenes from alkynes via hydroboration by
disiamylborane
(
THF)] with copper() chloride [or copper() bromide–
copper() acetate] in the presence of a small amount of water,
5
in a polar aprotic co-solvent. We here offer an application of
a
%
Yield
the above procedure to the synthesis of alkenyl azides (or thio-
cyanates), potentially useful intermediates in organic synthesis,
from alkynes via alkenyldisiamylboranes.
b
c
Alkyne
Product
(E)-BuCH᎐CHN
3
GC Isolated
Hex-1-yne
Oct-1-yne
tert-Butylacetylene
93
91
84
85
86
75
73
70
78
Thus, although a subsequent reaction of (E)-hex-1-enyldi-
᎐
6
(E)-C H CH᎐CHN
6 13 3
᎐
t
siamylborane [prepared by hydroboration of hex-1-yne with
(E)-Bu CH᎐CHN
᎐
3
bis(1,2-dimethylpropyl)borane in THF] with copper() thio-
1
-Ethynylcyclohexene
(E)-(1-C H )CH᎐CHN
7
6 9 3
᎐
cyanate in the presence of hexamethylphosphorous triamide
Phenylacetylene
Hex-3-yne
(E)-PhCH᎐CHN
᎐
3
(
HMPT) and a small amount of water gave no alkenyl thio-
(E)-EtCH᎐C(Et)N
89
᎐
3
cyanate but a small amount of 1,2-dimethylpropyl thiocyan-
4
5
a
All yields are for the overall process, and are based on starting alkynes.
The Z-isomers were not detected by GC. After flash column chrom-
ate, the additional introduction of copper() acetate to the
reaction mixtures provided (E)-1-thiocyanatohex-1-ene in 80%
yield (GC),‡ accompanied by 1,2-dimethylpropyl thiocyanate
b
c
atography (silica gel; pentane–dichloromethane). GC purity is 96–98%.
(
20%). Following this, several improvements of the reaction
R
H
H
R
H
H
procedure were attempted. Consequently the use of pyridine
in place of HMPT depressed the formation of the above
by-product into trace amounts keeping the product yield high,
and a mixture of potassium thiocyanate and copper() nitrate
trihydrate (2:1) [which should form Cu(NCS) in situ] could be
employed favourably in place of isolated copper() thiocyanate.
i
ii
iii
RC CH
C
C
C
C
Bsia2
SCN
R = alkyl or phenyl
2
Scheme 1 Reagents and conditions: i, Sia BH, THF, Ϫ15 ЊC then 0–
2
5
ЊC; ii, C H N, Cu(OAc) , Cu(NO ) ؒ3H O, KSCN, H O and THF,
5 5 2 3 2 2 2
The thiocyanatoalkenes thus produced were isolated from the
worked-up reaction mixtures by simple column chromato-
Ϫ25 ЊC then Ϫ15 ЊC; iii, 0 ЊC then 20 ЊC
8
graphy. For example, (E)-1-thiocyanatohex-1-ene was afforded
in 75% isolated yield from hex-1-yne. Some representative
results obtained by reactions depicted in Scheme 1 are shown in
Table 1.
nitrate trihydrate and sodium azide in the presence of N,N-
dimethylacetamide (DMA) and a small amount of water read-
ily provided the expected (E)-1-azidohex-1-ene in reasonable
yield [93% (GC) and 85% (isolated)]. HMPT was also usable as
solvent, but the employment of pyridine was not appropriate
Following successful thiocyanation, this led us to attempt a
synthetic approach for azidoalkenes, highly interesting and use-
ful synthetic intermediates (for the construction of azacyclo-
(
product yields, 85 and 25% respectively). Some representative
results by reactions depicted in Scheme 2 are shown in Table 2.
9
propane systems etc.). Thus, a subsequent reaction of (E)-hex-
1
-enyldisiamylborane in THF with copper() acetate, copper()
R1
R2
R1
R2
N3
i
ii
iii
1
R C CR2
C
C
C
C
2
†
The synthesis of azidoalkanes via trialkylboranes has been reported.
H
Bsia2
H
3
4
We also reported the syntheses of azido (or thiocyanato ) alkanes via
trialkylboranes.
1
2
R = alkyl or phenyl, R = H or alkyl
‡
The employment of dicyclohexylborane (a dialkylborane) (see ref. 6,
p. 178) resulted in a lower product yield (55%). Besides, the hydro-
boration of alk-1-ynes by 9-BBN is not a particularly high yielding
reaction (ref. 6, p. 41).
Scheme 2 Reagents and conditions: i, Sia BH, THF, Ϫ15 ЊC then 0–
2
5 ЊC; ii, Me NCOMe, Cu(OAc) , Cu(NO ) ؒ3H O, NaN , H O and
2
2
3
2
2
3
2
THF, Ϫ25 ЊC then Ϫ15 ЊC; iii, 0 ЊC then 20 ЊC
J. Chem. Soc., Perkin Trans. 1, 1998
1013

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It should be noted that the present reaction can be accom-
followed by stirring at Ϫ15 ЊC for 1 h, then at 0–5 ЊC for 2 h
plished without preparing and handling neat copper() azide
and then at 20 ЊC for 10 h. The color of the reaction mixture
(
reported as being explosive when dry), furthermore, it can be
changed from dark green to light green. After the same oper-
Ϫ3
carried out under wet conditions and in the presence of the
relatively non-toxic solvent (DMA).
Although the reaction mechanism can hardly be clarified at
present, the indispensability of copper() acetate (as mediator)
in the reaction seems to suggest the formation of an alkenyl-
copper-like intermediate.
Whilst it is reported that (E)-alkenylpentafluorosilicates react
with copper() thiocyanate in DMF to give (E)-alkenyl thio-
cyanates in reasonable yields. In comparison, the present
reaction has some advantageous features, mainly the use of
the more conveniently obtainable alkenylborane, and higher
product yields in situ. However, for azidoalkenes, apart from the
ations as above, the residue was oxidized with 3 mol dm aq.
3
3
sodium hydroxide (7.5 cm ), 30% hydrogen peroxide (7.5 cm )
3
and THF (10 cm ) with stirring at 0–20 ЊC for 4 h. After the
same work-up as above, chromatography of the organic residue
(consisting of the azidoalkene and an almost quantitative
amount of 3-methylbutan-2-ol) gave (E)-1-azidooct-1-ene (2.63
g, 86%) in a similar manner to that described above; νmax(neat)/
Ϫ1
cm 2105 (N ), 1653 (C᎐C) and 931 (trans-CH᎐CH); δ (90
3
H
10a
MHz; CDCl ) 0.89 (3H, deformed t, Me), 1.1–1.6 [8H, m,
3
(CH ) ], 2.03 (2H, q, J 6.8, CH C᎐C), 5.40 (1H, dt, J 13.4 and
2
4
2
6.8) and 5.86 (1H, d, J 13.4); δ (22.4 MHz; CDCl ) 13.92 (Me),
C
3
22.52, 28.67, 29.32, 29.44, 31.60, 120.65 (᎐CH) and 126.1
9a
ϩ
well-known 2-azidoalk-1-enes, only Z-isomers of 1-azidoalk-
-enes can be synthesized by the reaction between 1,2-epoxy-
(᎐CH); m/z 153.1245 (M ) (C H N requires M, 153.1266).
8
15
3
1
(E)-1-Azido-3,3-dimethylbut-1-ene. The GC retention time
1 13
11a
alkylsilanes and azidotrimethylsilane, whilst the E isomers
are only produced in poor yields by the reaction of 1,2-
epoxyalkylsilanes with sodium azide. In comparison, with
our present reaction, (E)-1-azidoalk-1-enes were easily pro-
vided using the more readily prepared alkenylboranes, and in
reasonable yields too.
and satisfactory spectral data (IR, H NMR, C NMR,
HRMS) were completely consistent with those of the prepared
12a
9a
authentic sample.
Acknowledgements
In conclusion, the present reactions reveal a novel and simple
synthesis of (E)-1-azidoalk-1-enes and of (E)-1-thiocyanato-
alk-1-enes, intriguing synthetic intermediates, in a one pot
process from alkynes via hydroboration.
We thank the Grant-in-Aid for Scientific Research of the
Ministry of Education of Japan (No. 08650999), for support of
this work.
References
Experimental
1
Recent reviews: A. Pelter, K. Smith and H. C. Brown, Borane
Reagents, Academic Press, London, 1988; D. S. Matteson,
Stereodirected Synthesis with Organoboranes, Springer, Berlin, 1995.
A. Suzuki, M. Ishidoya and M. Tabata, Synthesis, 1976, 687.
Y. Masuda, M. Hoshi and A. Arase, Bull. Chem. Soc. Jpn., 1984, 57,
Typical experimental procedure: preparation of (E)-1-thiocyan-
atohex-1-ene
2
3
In an argon-flushed flask, (E)-hex-1-enyldisiamylborane (20
mmol) in THF was prepared by the successive reactions of bor-
1
026.
3
ane (20 mmol) in THF (15 cm ) with 2-methylbut-2-ene (2.81 g,
4 A. Arase, Y. Masuda and A. Suzuki, Bull. Chem. Soc. Jpn., 1974, 47,
2511; A. Arase and Y. Masuda, Chem. Lett., 1976, 1115.
Y. Masuda, M. Hoshi and A. Arase, J. Chem. Soc., Perkin Trans. 1,
3
4
5
(
0 mmol) in THF (10 cm ) at Ϫ15 ЊC for 30 min and then at 0–
ЊC for 2 h and then with hex-1-yne (1.65 g, 20 mmol) in THF
5
6
7
3
6
1992, 2725.
5 cm ) at Ϫ15 ЊC for 30 min, then at 0–5 ЊC for 3 h. To the
H. C. Brown, Organic Synthesis via Boranes, Wiley, New York, 1975,
p. 54.
C. L. Jenkins and J. K. Kochi, J. Am. Chem. Soc., 1972, 94, 856.
8 G. W. Kabalka, T. M. Shoup and N. G. Goudgaon, Tetrahedron
Lett., 1989, 1483.
For general synthesis and application of 2-azidoalk-1-enes [except
for (E)-1-azido-3,3-dimethylbut-1-ene] via iodoalkyl azides see (a)
F. W. Fowler, A. Hassner and L. A. Levy, J. Am. Chem. Soc., 1967,
3
solution, pyridine (30 cm ), copper() acetate (3.65 g, 20 mmol),
copper() nitrate trihydrate (9.70 g, 40 mmol), potassium thio-
3
3
cyanate (7.80 g, 80 mmol), water (0.36 cm ) and THF (30 cm )
were added successively at Ϫ25 ЊC under argon, after which the
mixture was stirred at Ϫ15 ЊC for 1 h, then at 0–5 ЊC for 2 h
and then at 20 ЊC for 20 h. The color of the reaction mixture
changed from dark brown to light green. After filtration of the
contents of the flask, the filtrate was washed with brine and
extracted with diethyl ether. The extract was evaporated and the
residue oxidized with sodium perborate (10 g, 65 mmol) in
9
8
2
9, 2077; A. Hassner and F. W. Fowler, J. Org. Chem., 1968, 33,
686; (b) A. Hassner and F. W. Fowler, Tetrahedron Lett., 1967,
1545; J. Am. Chem. Soc., 1968, 90, 2869; J. Org. Chem., 1986, 51,
3176; A. Hassner, B. A. Belinka, Jr., M. Haber and P. Munger,
Tetrahedron Lett., 1981, 22, 1863; Y. Nomura, Y. Takeuchi,
S. Tomoda and M. M. Ito, Bull. Chem. Soc. Jpn., 1981, 54, 261.
0 (a) K. Tamao, T. Kakui and M. Kumada, Tetrahedron Lett., 1980,
11; (b) It has been shown that the formation of (E)-β-
thiocyanatostyrene from 1-chloro-1-phenyl-2-thiocyanatoethane,
itself derived from styrene, is possible: R. G. Guy and I. Pearson,
Bull. Chem. Soc. Jpn., 1976, 49, 2310.
1 (a) S. Tomoda, Y. Matsumoto, Y. Takeuchi and Y. Nomura, Bull.
Chem. Soc. Jpn., 1986, 59, 3283; (b) Although the stereochemistry is
not obvious, it is demonstrated that azidostyrenes, ArCR᎐CHN ,
have been formed through the azido alcohol or the vinyl chloride:
R. E. Bolton, C. J. Moody, M. Pass, C. W. Rees and G. Tojo,
J. Chem. Soc., Perkin Trans. 1, 1988, 2491; A. L. Beck, W. J. Coates
and C. J. Moody, J. Chem. Soc., Perkin Trans. 1, 1990, 689.
3
3
water (20 cm ) and THF (20 cm ) with stirring at 0–20 ЊC for
8
4
h. The mixture was washed with brine, extracted with di-
1
1
ethyl ether, and the extract dried (Na SO ), filtered and evapor-
2
4
1
ated. Chromatography of the organic residue (consisting of the
thiocyanatoalkene and an almost quantitative amount of
-methylbutan-2-ol derived from the residual disiamylboryl
group by the above oxidative treatment) on a flash column (sil-
ica gel; pentane–dichloromethane) gave pure (E)-1-thiocyanato-
3
Ϫ1
᎐
3
hex-1-ene (2.12 g, 75%); νmax(neat)/cm 3046 (C᎐CH), 2158
(
sh, SC᎐N), 1624 (C᎐C) and 954 (trans-CH᎐CH); δ (90 MHz;
᎐ ᎐ ᎐
H
CDCl ) 0.90 (3H, deformed t, Me), 1.1–1.6 [4H, m, (CH ) ],
.18 (2H, q, J 6.4, CH C᎐C), 5.85 (1H, d, J 14.5) and 6.16 (1H,
dt, J 14.5 and 6.4); δ (22.4 MHz; CDCl ) 13.21 (Me), 21.54,
9.93, 32.04, 109.10 (᎐CH), 110.43 (SCN) and 142.34 (᎐CH);
᎐ ᎐
ϩ
3
2 2
2
2
1
2 (a) T. K. Chakraborty and G. W. Reddy, Tetrahedron Lett., 1990,
C
3
1
1
335; (b) It is reported that formation of (E)-β-azidostyrene from
-bromo-1-phenyl-2-azidoethane, itself derived from styrene, is
possible: A. Hassner, F. P. Boerwinkle and A. B. Levy, J. Am. Chem.
Soc., 1970, 92, 4879.
2
m/z 141 (M ).
Preparation of (E)-1-azidooct-1-ene
To the solution of (E)-oct-1-enyldisiamylborane (20 mmol) in
3
THF prepared as described above, DMA (30 cm ), copper()
acetate (3.65 g, 20 mmol), copper() nitrate trihydrate (9.70 g,
Paper 7/08932E
Received 11th December 1997
Accepted 27th January 1998
3
4
0 mmol), sodium azide (5.20 g, 80 mmol), water (0.36 cm ) and
3
THF (30 cm ) were added successively at Ϫ25 ЊC under argon,
1
014
J. Chem. Soc., Perkin Trans. 1, 1998