Unexpected SN2'-type addition-elimination reactions of 1-aryl-2,3-allenols with LiX. Synthesis and synthetic application of 1-aryl-3-halo-1,3-dienes

Article abstract of DOI:10.1016/S0040-4039(02)01207-8

1-Aryl-3-halo-1,3-dienes were prepared from the sequential addition-elimination reaction of 1-aryl-2,3-allenols with LiX (X=Br, Cl) in HOAc in moderate to good yields. Here the aromatic substituent is crucial to this interesting transformation since no re

Full text of DOI:10.1016/S0040-4039(02)01207-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 5723–5726
Unexpected SN2%-type addition–elimination reactions of
1-aryl-2,3-allenols with LiX. Synthesis and synthetic application
of 1-aryl-3-halo-1,3-dienes
Shengming Ma* and Guangwei Wang
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, Shanghai 200032, PR China
Received 23 April 2002; revised 13 June 2002; accepted 24 June 2002
Abstract—1-Aryl-3-halo-1,3-dienes were prepared from the sequential addition–elimination reaction of 1-aryl-2,3-allenols with
LiX (X=Br, Cl) in HOAc in moderate to good yields. Here the aromatic substituent is crucial to this interesting transformation
since no reaction was observed with 1-alkyl or perfluoroalkyl-2,3-allenols. The 1-aryl-3-halo-1,3-dienes prepared can be used as
useful partners in Diels–Alder reactions with dienophiles leading to polycyclic quinone derivatives. © 2002 Elsevier Science Ltd.
All rights reserved.
1,3-Dienes are important intermediates in organic syn-
thesis,1 especially as a partner in Diels–Alder reactions.2
Recently, during our study of allene chemistry,3 we
observed that the Pd(0)-catalyzed coupling-cyclization
of organic halides and 2,3-allenols afforded vinylic
oxiranes4 or 2,5-dihydrofurans,5 whilst the Pd(0)-cata-
lyzed reaction of 2,3-allenols with aryl halides in the
presence of amines afforded a- or g-aminoalcohols
regioselectively and stereoselectively,6 showing the syn-
thetic potential of 2,3-allenols.7–9 A recent study of
Pd-catalyzed synthesis of (Z,E)-2-bromo-1,3-dienes
from a-allenic acetates by Ba¨ckvall et al.10 prompted us
to report an unexpected reaction of 1-aryl-2,3-allenols
with lithium halides affording 1-aryl-3-halo-1,3-dienes.
Using 5 mol% of PdCl2(CH3CN)2 or PdCl2(PPh3)2, the
same product 2a was formed, respectively. Surprisingly,
it is interesting to note that this reaction can occur to
afford 2a even in the absence of any Pd catalyst. Here,
it is obvious that the reaction proceeded via the inter-
mediacy of 1-phenyl-3-bromo-1(E),3-butadiene 3a.
With these results in hand, we studied the reaction in
the absence of a dienophile in order to isolate the
synthetically useful 2-halo-1,3-butadiene derivatives.
When we ran this reaction with LiBr in a mixture of
HOAc and CH3CN (1:19), the reaction was compli-
cated. Heating the mixture of LiBr·H2O with 1a in
HOAc at 50°C afforded 1-phenyl-3-bromo-1,3-butadi-
ene 3a in 70% yield. The yield can be further improved
to 76% when the reaction was carried out in the pres-
ence of 20 mol% of hydroquinone (Scheme 1).
Recently, Ba¨ckvall et al. reported a palladium-catalyzed
reaction of 4,5-allenols with LiBr in the presence of
benzoquinone to afford vinylic tetrahydrofuran deriva-
tives.11 Based on this result we reasoned that the corre-
sponding reaction of 2,3-allenols with lithium halides
would produce 3-bromo-2,5-dihydrofurans. However,
when a mixture of 1-phenyl-2,3-butadienol 1a, LiBr (5
equiv.) and benzoquinone (2.5 equiv.) was treated with
5 mol% of Pd(OAc)2 in HOAc, the reaction afforded an
unexpected product whose structure upon X-ray dif-
fraction analysis was determined to be that of 2a (Fig.
1).
Thus, by applying these standard reaction conditions,
the reactions of differently substituted 1-aryl-2,3-
allenols with LiX in the presence of 20 mol%
hydroquinone in HOAc afforded 1,3-butadienes. Some
typical results are summarized in Table 1.
From the results in Table 1, it is obvious that the yields
for the formation of 3-halo-1-aryl-1,3-butadienes are
from moderate to good. The reaction was complete
within a few hours. Both bromides and chlorides can be
prepared. LiX monohydrate and anhydrous LiX did
not show obvious differences in terms of yields of the
products.
Keywords: allenes; alcohols; substitution; dienes.
* Corresponding author.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01207-8

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S. Ma, G. Wang / Tetrahedron Letters 43 (2002) 5723–5726
Figure 1. Structures 1a, 2a and 3a and the ORTEP representation of 2a.
However, it is interesting to observe that the corre-
sponding reaction of 1-alkyl or perfluoroalkyl-substi-
tuted allenols 1g and 1h did not yield the expected
products (Scheme 4).
The reaction is believed to proceed through an SN2%-
type addition–elimination process.12 In HOAc, the
phenyl group may stabilize the corresponding carboca-
tionic intermediate formed by the interaction of HOAc
with the hydroxy group of 1-phenyl-2,3-allenols.
Scheme 1.
The dienes prepared can be used for the synthesis of
polycyclic quinones via Diels–Alder oxidation reac-
tions. 1,4-Naphthoquinones are a class of compounds
with biological activities such as antiinflammatory, anti-
tumor, antiparasitic and antimicrobial action.13 Thus,
we used benzoquinone as the dienophile to optimize the
reaction conditions for the one-pot addition–elimina-
tion-Diels–Alder process. The reaction afforded the
Diels–Alder adduct 2a in 51% yield at rt in the dark
(Eq. (1)). Using these standard reaction conditions, the
With 2-(n-butyl)-1-phenyl-2,3-butadienol 1e, the reac-
tion afforded E/Z mixtures of 3-halo-1-phenyl-2-(n-
butyl)-1,3-butadienes (Scheme 2). The stereochemistry
was determined by the H–1H NOESY spectra of 3j.
1
This reaction can also be extended to the tertiary
alcohol 1f to afford the corresponding products in good
yields (Scheme 3).
(1)

S. Ma, G. Wang / Tetrahedron Letters 43 (2002) 5723–5726
5725
Table 1. Synthesis of 1-phenyl-3-halo-1,3-butadiene via the
reaction of 1-phenyl-2,3-allenols with LiX in HOAc
Entry
1 (Ar)
LiX
Time (h)
Yield of 3
(%)
1
2
3
Ph (1a)
Ph (1a)
p-CH3OC6H4 LiBr
LiBr·H2O
LiCl
40 min
2
2
76 (3a)
60 (3b)
33 (3c)
Scheme 3.
(1b)
reaction of 1a, LiBr and naphthoquinone afforded 2b in
4
5
6
7
8
p-CH3OC6H4 LiCl
(1b)
o-ClC6H4
(1c)
o-ClC6H4
(1c)
Naphthyl
(1d)
2
53 (3d)
82 (3e)
60 (3f)
81 (3g)
88 (3h)
72% yield (Scheme 5).
LiBr·H2O
1.5
1.5
0.5
0.5
Upon treatment with DDQ, 2a was oxidized to afford
the naphthoquinone derivative 2a% in 87% yield (Eq.
(2)).
LiCl
LiBr·H2O
LiCl·H2O
Naphthyl
(1d)
(2)
In conclusion, we have observed an interesting SN2%-
type addition–elimination reaction of 1-phenyl-2,3-
allenols with LiX (X=Br, Cl). The 2-halo-1,3-dienes
prepared show good reactivities towards quinones. Fur-
ther studies on the scope and synthetic potentials of this
reaction are being carried out in our laboratory.
Scheme 2.
Scheme 4.
Scheme 5.

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S. Ma, G. Wang / Tetrahedron Letters 43 (2002) 5723–5726
441; (b) For the Ru-catalyzed cyclization of allenols with
Acknowledgements
a,b-unsaturated enones, see: Trost, B. M.; Prinkerton, A.
B. J. Am. Chem. Soc. 1999, 121, 10842.
Financial support from the Major State Basic Research
Development Program (Grant No. G2000077500),
National Natural Science Foundation of China, and
Shanghai Municipal Committee of Science and Tech-
nology are greatly appreciated. Shengming Ma is the
recipient of the 1999 Qiu Shi Award for Young Scien-
tific Workers issued by the Hong Kong Qiu Shi Foun-
dation of Science and Technology (1999–2003).
8. For catalytic cycloisomerization of allenols, see: (a) Mar-
shall, J. A.; Wang, X. J. Org. Chem. 1990, 55, 2995; (b)
Marshall, J. A.; Wang, X. J. Org. Chem. 1991, 56, 960;
(c) Olsson, L.-I.; Claesson, A. Synthesis 1979, 743; (d)
Nikam, S. S.; Chu, K.-H.; Wang, K. K. J. Org. Chem.
1986, 51, 745; (e) Gelin, R.; Gelin, S.; Albrand, M. Bull.
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