Fritsch-Buttenberg-Wiechell rearrangement to alkynes from gem-dihaloalkenes with lanthanum metal

Article abstract of DOI:10.1016/j.jorganchem.2011.02.014

The first example of the FBW rearrangement using of lanthanum metal and a catalytic amount of iodine was disclosed. When gem-diiodo- and gem-dibromoalkenes were treated with lanthanum metal in the presence of a catalytic amount of iodine, the reductive dehalogenation of these compounds smoothly proceeded to produce the corresponding alkynes in moderate to good yields.

Full text of DOI:10.1016/j.jorganchem.2011.02.014

Journal of Organometallic Chemistry 696 (2011) 1916e1919
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Note
FritscheButtenbergeWiechell rearrangement to alkynes from gem-dihaloalkenes
with lanthanum metal
*
Rui Umeda, Takumi Yuasa, Namika Anahara, Yutaka Nishiyama
Faculty of Chemistry, Materials and Bioengineering, Kansai University, 3-3-35 Yamate-cho Suita, Osaka 564-8680, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The first example of the FBW rearrangement using of lanthanum metal and a catalytic amount of iodine
was disclosed. When gem-diiodo- and gem-dibromoalkenes were treated with lanthanum metal in the
presence of a catalytic amount of iodine, the reductive dehalogenation of these compounds smoothly
proceeded to produce the corresponding alkynes in moderate to good yields.
Received 26 October 2010
Received in revised form
8 February 2011
Accepted 10 February 2011
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Lanthanum metal
FBW rearrangement
Alkynes
gem-Dihaloalkenes
1. Introduction
2. Results and discussion
Recently, the utilizations of lanthanoid metal salts and organo-
lanthanoid compounds as a reagent or catalyst in organic synthesis
have steadily increased [1]. In contrast, there are only a few reports
on the direct use of lanthanoid metals except for cerium, samarium,
and ytterbium metals for organic reactions [2,3]. Among the lan-
thanoid metals, we have been interested in the use of lanthanum
metal which shows i) higher oxidationereduction potential, ii)
higher bond energy with oxygen, and iii) larger atomic radius than
those of other lanthanoid metals [3,4]. During our investigation of
the direct use of lanthanum metal in organic synthesis, it was found
that the reductive dehalogenation of organohalogen compounds
smoothly proceeded by lanthanum metal to generate unstable
species such as the alkyl radical [5], benzyne [6] or o-quinodi-
methane [6b]. To extend the scope of the synthetic protocol
employing lanthanum metal, the application of the
FritscheButtenbergeWiechell (FBW) rearrangement [7], which is
the 1,2-migration from the alkylidene carbene/carbenoid species as
reactive intermediates giving the corresponding alkynes, has been
planned. In this paper, we disclose the first example of the FBW
rearrangement of gem-dihaloalkenes with lanthanum metal giving
the corresponding alkynes [8].
The reductive deiodination of the 1,1-diiodo-1-tridecene (1:
X ¼ I) smoothly proceeded to give 1-tridecyne (2) in 81% yield
together with a small amount of 1-tridecene (3) (7%) and 1-iodo-1-
tridecene (trace) (entry 1 in Table 1). In the absence of iodine, the
reaction did not occur and 1 (X ¼ I) was recovered (entry 2) [9,10].
When 1,1-dibromo-1-tridecene (1: X ¼ Br) instead of diiodo
derivative was treated with lanthanum metal under the same
reaction conditions as that of entry 1, the yield of the terminal
alkyne 2 significantly decreased; however, the yield of 2 was
improved by increasing the amount of iodine (entries 3 and 4). In
the case of dichloro derivative 1 (X ¼ Cl), no reaction took place and
1 (X ¼ Cl) was recovered (95%) [11].
Next, we examined the synthesis of the internal alkynes 5 by the
treatment of 2-aryl-1,1-dihalo-1-propenes 4 with lanthanum metal
(Table 2). When 2-aryl-1,1-diiodo-1-propene (4: X ¼ I, Ar ¼ Ph) was
allowed to react with lanthanum metal under the same reaction
conditions as that of entry 1 in Table 1, 1-phenyl-1-propyne (5:
Ar ¼ Ph) was obtained in 70% yield (entry 1). The 1-(40-methyl-
phenyl)- and 1-(40-methoxyphenyl)-1-propynes were formed by
the reaction of the diiodo derivatives 4 (X ¼ I, Ar ¼ 4-CH3C6H4 and
4-CH3OC6H4) with lanthanum metal in 79 and 91% yields, respec-
tively (entries 2 and 3). For the reaction of the 40-chlorophenyl
diiodo derivative 4 (X ¼ I, Ar ¼ 4-ClC6H4), the yield of the propyne 5
(Ar ¼ 4-ClC6H4) decreased due to the formation of uncharacterized
polymeric materials (entry 4). The reaction of 2-methyl substituted
phenyl derivative (X ¼ I, Ar ¼ 2-CH3C6H4) gave the corresponding
* Corresponding author. Tel.: þ81 6 6368 0902; fax: þ81 6 6339 4026.
E-mail address: nishiya@kansai-u.ac.jp (Y. Nishiyama).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.02.014

R. Umeda et al. / Journal of Organometallic Chemistry 696 (2011) 1916e1919
1917
Table 1
Table 4
Effect of halogen atom on 1 and I2.
FBW rearrangement of 2,2-diaryl-1,1-diiodoethenes 8.
.
.
Entry
X
I2 (mmol)
Recovery (%)a
Yield (%)a
Entry
R
Yield (%)a
1
1
2
3
4
H
75
52
87
40
2
3
CH3
CH3O
Cl
1
2
I
I
0.08
e
e
81
trace
3
68
e
7
93
85
12
95
e
e
3
3
Br
Br
Cl
0.08
0.16
0.16
a
4
Yield was determined by GC by using an internal standard based on 8.
5b
e
a
Yield was determined by GC by using an internal standard based on 1.
For 11 h.
b
Table 2
FBW rearrangement of 2-aryl-1,1-dihalo-1-propenes 4.
Scheme 1. Reaction of gem-diiodoalkene 10.
.
Entry
X
I2 (mmol)
Ar
Yield (%)a
propyne 5 (Ar ¼ 2-CH3C6H4) in low yield. Similarly, FBW rear-
rangement of the dibromo derivatives 4 (X ¼ Br) smoothly pro-
ceeded to afford the propynes 5 in moderate yields (entries 6e9). In
the case of 1-(40-chlorophenyl)-1,1-dibromo-1-propene (4: X ¼ Br,
Ar ¼ 4-ClC6H4), the yield of the alkyne is higher than that of the
diiodo derivative (4: X ¼ I, Ar ¼ 4-ClC6H4) (entry 9).
1
2
3
4
5
6
7
8
9
I
I
I
I
0.08
0.08
0.08
0.08
0.08
0.16
0.16
0.16
0.16
Ph
70
79
91
34
38
60
54
53
52
4-CH3C6H4
4-CH3OC6H4
4-ClC6H4
2-CH3C6H4
Ph
4-CH3C6H4
4-CH3OC6H4
4-ClC6H4
I
Br
Br
Br
Br
The rearrangements of the 1,1-dihalo-2-phenyl-1-alkenes 6
having the longer alkyl chains, such as n-propyl and n-hexyl groups,
were also examined (Table 3). In both cases of the diiodo and
dibromo derivatives 6, the elongation of the alkyl chains did not
influence the yields of 7 (81e93%) (entries 1, 2, 5 and 6). The
reaction of 6 having isopropyl and benzyl groups also occurred to
give the corresponding 7 in 87% and 75% yields, respectively
(entries 3 and 4). The diarylacetylenes 9 were obtained from the
reaction of the corresponding diiodoethenes 8 with lanthanum
metal in moderate to good yields (Table 4).
a
Yield was determined by GC by using an internal standard based on 4.
Table 3
FBW rearrangement of 6 having different alkyl chains.
On the other hand, the reaction of the gem-diiodoalkene 10
substituted with two benzyl groups with lanthanum metal
.
Entry
X
I2 (mmol)
R
Yield (%)a
1
2
3
4
5
6
I
I
I
I
Br
Br
0.08
0.08
0.08
0.08
0.16
0.16
neC3H7
neC6H13
i-C3H7
CH2Ph
neC3H7
neC6H13
85
93
87
75
81
87
a
Yield was determined by GC by using an internal standard based on 6.
Scheme 2. Intramolecular cyclization of 13.

1918
R. Umeda et al. / Journal of Organometallic Chemistry 696 (2011) 1916e1919
Scheme 3. Plausible Reaction Pathway.
predominantly afforded the alkene 11, the reductive deiodinated
product, in 51% yield together with a trace amount of the alkyne 12
(Scheme 1).
4. Experimental
4.1. General procedure for FBW rearrangement by lanthanum metal
On the reaction of 1,1-dibromo-2-methylundec-1-ene (13)
having a long alkyl chain and methyl group at the alkene moiety
with lanthanum metal, intramolecular cyclization took place to
give cyclopentene derivative 14 (59%) as the main product together
with alkyne 15 (15%), and debrominated product 16 (8%) (Scheme
2) [12].
A two-necked flask charged with lanthanum powder (0.40 mmol)
was equipped with a magnetic stirring bar and then a solution of
iodine (for diiodo derivative, 0.08 mmol; for dibromo derivative,
0.16 mmol) and the gem-dihaloalkenes (0.20 mmol) in THF (1.2 mL)
was added to the flask. The mixture was stirred at 67 ꢀC for 3 h under
anargonatmosphere. After the reaction, aq. HCl (5%)wasadded tothe
reaction mixture and extracted with EtOAc (10 mL ꢁ 3). The organic
layerwaswashedwithsaturatedaq. sodiumthiosulfate(30mL), dried
over MgSO4 and filtered. The organic layer was concentrated invacuo.
Purification of theproductbyKugelrohrafforded theanalyticallypure
alkynes. The products were characterized by a comparison of their
spectra data with those of authentic samples.
Although we cannot clearly determine the reaction pathway,
one of the plausible reaction pathways is shown in Scheme 3. Upon
the reaction of 1,1-diiodo- and 1,1-dibromoalkenes, 1-iodo- and 1-
bromoalkenes were detected by GC and GC-mass spectra. These
results indicate that mono halo vinyl radicals may be generated in
situ. Then we suggested that the first step of the reaction is the
reductive dehalogenation of gem-dihaloalkenes by a low-valent
lanthanum species, which was generated in situ by the reaction of
lanthanum metal with a catalytic amount of iodine [13,14], to form
the mono halo vinyl radical. The vinyl radical species are reduc-
tively dehalogenated by lanthanum species to afford the alkylide-
necarbenes (or alkylidenecarbenoids). Alkynes were formed by the
1,2-shift of alkylidenecarbenes (or alkylidenecarbenoids). It is well
known that the alkyl group is less effective than aryl group and
hydrogen atom as migrating groups in the FBW rearrangement [15].
In fact, in the case of 1,1-dibromo-2-methylundec-1-ene (13),
having long alkyl chain and methyl group, 1,5-C-H insertion of
alkylidenecarbene predominantly took place to form cyclopentene
derivative 14 [16]. On the reaction of gem-diiodoalkene 10
substituted with two benzyl groups, vinyl iodide was formed by the
abstraction of hydrogen from THF used as a solvent by mono halo
vinyl radical. The vinyl iodide was reductively deiodinated with
lanthanum species to give alkene 11. Another pathway including
the directly abstraction of alkylidenecarbene from THF cannot be
ruled out.
Acknowledgments
This research was supported by a Grant-in-Aid for Science
Research, and Strategic Project to Support the Formation of
Research Bases at Private Universities from the Ministry of Educa-
tion, Culture Sports, Science and Technology of Japan.
Appendix. Supplementary material
Experimental details, spectroscopic data associated with this
article can be found in the online version, at doi:10.1016/j.
jorganchem.2011.02.014.
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