Heteroaromatic ethers of phenols in nickel-catalysed ipso-replacement reactions with magnesium, zinc and tin organometallic compounds

Article abstract of DOI:10.1039/b001333l

Phenols are readily converted in high yield into the heterocyclic ethers, 5-aryloxy-1-phenyl-1H-tetrazole, 1 and 3-aryloxy-1λ⁶,6,2-benzothiazole 1,1-dioxide, 2. X-Ray crystallographic analysis and other evidence shows that, in these ethers, the originally strong phenolic C-QH bond is considerably weakened on derivatization. In nickel-catalysed cross-coupling reactions with brganozinc and organotin compounds, the heterocyclic parts of ethers 1,2 provide good nucleofuges. In similar cross-coupling reactions with organomagnesium halides, ethers 1 again provide good nucleofuges but, in marked contrast, ethers 2 do not. In all reactions, palladium based catalysts were mostly not effective. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b001333l

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Heteroaromatic ethers of phenols in nickel-catalysed ipso-
replacement reactions with magnesium, zinc and tin organometallic
compounds
1
Amadeu F. Brigas*a and Robert A. W. Johnstoneb
a UCEH, Campus de Gambelas, Universidade do Algarve, 8000 Faro, Portugal
b Department of Chemistry, University of Liverpool, Liverpool, UK L69 3BX
Received (in Cambridge, UK) 17th February 2000, Accepted 28th March 2000
Published on the Web 9th May 2000
Phenols are readily converted in high yield into the heterocyclic ethers, 5-aryloxy-1-phenyl-1H-tetrazole, 1 and
3-aryloxy-1λ6,2-benzothiazole 1,1-dioxide, 2. X-Ray crystallographic analysis and other evidence shows that, in
these ethers, the originally strong phenolic C–OH bond is considerably weakened on derivatization. In nickel-
catalysed cross-coupling reactions with organozinc and organotin compounds, the heterocyclic parts of ethers
1,2 provide good nucleofuges. In similar cross-coupling reactions with organomagnesium halides, ethers 1 again
provide good nucleofuges but, in marked contrast, ethers 2 do not. In all reactions, palladium based catalysts
were mostly not effective.
selectively, through heterogeneous catalytic transfer hydrogen-
Introduction
olysis, using a suitable hydrogen donor.9,10 Recently, catalytic
transfer reduction of 1-phenyl-1H-tetrazol-5-yl ethers of allylic
alcohols has been effected without concomitant reduction of
the double bond in the allyl group.11 It has been shown also that
ethers 1 undergo easy nickel-catalysed reaction with organo-
magnesium halides to give cross-coupled products.12 For
these large molecules, based on tetrazoles there are no known
hazards although toxicity of some tetrazoles has been
reported.13
ipso-Substitution of phenolic OH groups to give other func-
tionalities is of considerable relevance to synthesis because of
their natural abundance and availability as petrochemicals.1 To
effect such substitution, activation of the OH group is neces-
sary. This requirement for activation has led to the derivatiz-
ation of phenols to give ethers or esters, in which the original
C–OH phenolic bond has been changed from its partial double
bond nature (bond order about 1.5) to become more like the
single bond found in aliphatic ethers or alcohols (bond order,
1). The most efficient derivatives seem to be those in which the
phenolic hydroxy is connected to a very strongly electron-
withdrawing group, as with the triflates.2,3 These derivatives
become similar to aryl halides in that catalysed ipso-substi-
tution reactions can be carried out under the same sort of mild
conditions as those used with aryl bromides or iodides. These
“halogenoid” derivatives have been mostly triflates up to now.
For example, aryl triflates undergo palladium-catalysed cross-
coupling with a wide variety of organotin compounds. This
“Stille coupling” method has proved to be a more efficient and
general method than previous similar nickel-catalysed cross-
couplings of aryl triflates with Grignard reagents, and has been
widely used for transformations of a variety of halo- or boron-
substituted compounds.4 Also, it has been shown that aryl tri-
flates do undergo easy cross-coupling when catalysed by nickel
in combination with lithium bromide.5 One limitation seems to
be the low yields and lack of selectivity observed in the coupling
of allyltin compounds with aryl triflates and there is still a need
for more practical alternative ethers or esters of phenols,
capable of providing selectivity in the presence of other
functional groups that may be present.6
In the present work, this sensitivity of the ethers 1,2 to
cross-coupling reactions has been extended to organozinc and
organotin compounds, using nickel or palladium catalysts.
None of the reported yields is optimised.
Results and discussion
X-Ray crystallographic structural analysis of phenols and their
ethers 1,2 reveals that the C–O bond in phenols and their simple
ethers has a length of about 134 pm but, in the heteroaromatic
ethers, it is much longer at about 143 pm (bond a in 1 or 2). At
this last length, the C–O bond is as long as or even longer than
those in aliphatic alcohols or ethers.14 The result of this large
increase in bond length is that the original phenolic C–OH
bond has been considerably weakened after conversion of the
phenol into its heterocyclic ether 1,2. At the same time that the
original phenolic C–O bond lengthens, the other ether C–O
bond between oxygen and the heterocycle (bond b in 1 or 2)
becomes as short (133 pm) as in the original phenolic C–O
bond.7 In effect, the heterocycles shift electron density from the
original phenolic C–OH bond into the new ether bonds (b) in
the ethers 1,2; the phenol becomes a “halogenoid”. Semi-
empirical calculations at the MOPAC PM3 level show that the
carbon of the phenolic C–OH bond has a partial electronic
charge density of ϩ0.10 but that this changes to ϩ0.33 on
conversion of the phenol into the phenyl ether 1 (Ar = Ph).15
On the basis of these structural changes and the apparent
similarities in the mechanisms of catalytic transfer reduction16
and cross-coupling,17 it was anticipated that the ethers 1,2
should undergo easy catalytic cleavage by oxidative addition to
a metal, an essential first step to cross-coupling. It has been
5-Chloro-1-phenyl-1H-tetrazole or the more cost-effective
3-chloro-1,2-benzothiazole 1,1-dioxide (pseudosaccharyl chlor-
ide) react easily with phenols to give highly crystalline, stable
O-ethers 1,2, which provide good nucleofuges in catalysed reac-
tions.7 For both ethers, the side-product nucleofuges (saccharin
or 5-phenyltetrazolone) are water soluble and easily separated
from the required reaction products by extraction. Under suit-
able reductive conditions, ethers 1,2 undergo efficient hydro-
genolysis (formally, an ipso replacement by hydrogen) either
with hydrogen gas under pressure8 or, more conveniently and
DOI: 10.1039/b001333l
J. Chem. Soc., Perkin Trans. 1, 2000, 1735–1739
This journal is © The Royal Society of Chemistry 2000
1735

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Table 1 Cross-coupling of 5-aryloxy-1-phenyl-1H-tetrazoles 1 or 3-aryloxy-1λ6,2-benzothiazole 1,1-dioxides 2 (Ar–O–R) and diethylzinc with
transition metal catalysts
Ar–O–R
Catalyst
Ar
Ra
preparationb
Solvent
Time/h
Yield (%)c
Phenyl
Phenyl
S
S
S
T
T
T
S
T
S
S
NiCl2(dppp)/DIBAL-H
NiCl2(dppp)
THF
THF
Dioxane
Dioxane
THF
4
10
12
6
1.2
2
3
4
3
4
74
0
4-Acetylphenyl
4-Acetylphenyl
2-Naphthyl
Phenyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
NiCl2(dppp)d
42e
35e
73
Ni(acac)2/PPh3/DIBAL-H
NiCl2(dppp)/DIBAL-H
NiCl2(dppp)/DIBAL-H
Ni(acac)2/PPh3/DIBAL-H
Ni(acac)2/PPh3/DIBAL-H
Ni(acac)2/PPh3/DIBAL-H
Pd-on-C/CuI
THF
70
Dioxane
Dioxane
Dioxane
THF
59f
52g
39g
12
a S = 3-pseudosaccharyl; T = 1-phenyl-1H-tetrazol-5-yl. b The catalyst was used as such or was pre-reduced by addition of DIBAL-H as indicated.
c Yields were determined by GC unless otherwise stated. d Three-fold excess of Et2Zn was used. e Acetophenone was obtained as a side product in
22.1% yield. f Isolated yield. g Naphthalene was obtained as a minor side product.
reported that cross-coupling of phenyltetrazolyl ethers 1 with
alkyl or aryl Grignard reagents takes place under moderate
conditions and with very short reaction times (Scheme 1; R =
reagent but a pseudosaccharyl ether in the same molecule
would not be affected. This selectivity was quite unexpected but
leads to synthetic opportunities. As is described below,
pseudosaccharyl ethers 2 do undergo catalysed coupling with
organozinc or organotin reagents. Thus, an ether 1 may be
cross-coupled with an organomagnesium halide in the presence
of a pseudosaccharyl ether 2 and then the latter can be cross-
coupled with an organozinc or an organotin reagent.
The reasons for this selectivity to organomagnesium halides
are not clear. Since both ethers 1 and 2 undergo nickel-catalysed
reaction with organozinc or organotin compounds, it would
seem that initial addition of the ethers to Ni(0) may not cleave
the C–O bond (a in structures 3,4) but this step may be com-
pleted by the incoming organometallic reagent (Scheme 2).
Scheme 1
1-phenyltetrazol-5-yl; RЈ = alkyl, aryl; X = Br, Cl).12 Initial
reaction of NiCl2(dppp) with some of the Grignard reagent
generates the true Ni(0) catalyst, to which the ether 1 adds oxid-
atively to give complex A. Decomposition of this complex by
more Grignard reagent RЈMgX (possibly via intermediate B)
leads to regeneration of the catalyst and formation of the cross-
coupled product Ar–RЈ. The heteroaromatic ethers are thought
to be specifically involved in coordination to magnesium
through one of the nitrogen atoms (complex B in Scheme 1).
To confirm the earlier observations on ethers 1, 5-phenoxy-1-
phenyl-1H-tetrazole (1; Ar = phenyl) was reacted with ethyl-
magnesium bromide in the presence of NiCl2(dppp) in refluxing
ether. All of the starting material disappeared within 25
minutes, with formation of the cross-coupled product, ethyl-
benzene, in 78% yield. With this confirmation of reactivity,
cross-coupling of pseudosaccharyl ethers 2 with alkyl Grignard
reagents was attempted using several different nickel or
palladium catalysts (see Experimental section). Under reaction
conditions similar to those used for the cross-coupling of
aryloxytetrazoles 1, the pseudosaccharyl ethers 2 either failed to
give any of the desired cross-coupled product or did so in yields
of no more than about 10%, even when the amount of catalyst
was increased to 0.5 molar equivalents in relation to the ether.
Changes in solvent, catalyst and general reaction conditions
afforded no improvement. This lack of reactivity of ethers 2 is
in significant contrast with the reactivity of ethers 1 under the
same conditions.12 The recovery of unchanged pseudosaccharyl
ethers leads to the possibility of using the two kinds of ether
for selective derivatisation in complex structures such that a
phenyltetrazolyl ether 1 could be cross-coupled with a Grignard
Scheme 2
From this viewpoint, the difference in nucleophilicity of the
nitrogens marked with an asterisk in structures 3,4 may be
important. The nitrogen in complexes 4 may stabilise a complex
with nickel more than the corresponding nitrogen in complexes
3, making the latter more amenable to attack by the organo-
magnesium halide. Semi-empirical calculations of electronic
charge densities in ethers 1,2 show that the partial charge on the
nitrogen (N*) is Ϫ0.18 for the tetrazolyl ether 1 (Ar = Ph) but is
Ϫ0.60 in the pseudosaccharyl ether 2 (Ar = Ph). This indicates
that structure 3 should be less stabilised by coordination of
nickel to the nitrogen (N*) than will be the case for structure 4
(Scheme 2).
Organozinc reagents have attracted much attention.18 They
are less reactive than their magnesium counterparts towards,
for example, carbonyl bonds which property, instead of being
a limitation, can be very advantageous in reactions involving
compounds having such functionalities. In complete contrast
to their lack of reactivity with organomagnesium reagents, the
pseudosaccharyl ethers 2 easily underwent nickel-catalysed
cross-coupling with organozinc compounds. Typically,
a
reducing agent, such as diisobutylaluminium hydride (DIBAL-
H), was added to the nickel compound used as catalyst in order
to prepare nickel(0) in situ. Ethers 2 were cross-coupled with
diethylzinc (Table 1). Palladium catalysts were found to be
much less efficient.
1736
J. Chem. Soc., Perkin Trans. 1, 2000, 1735–1739

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Table 2 Cross-coupling of 5-aryloxy-1-phenyl-1H-tetrazoles 1 and organozinc reagents with nickel catalysts
Aryl group
Organometallica
Catalyst systemb
Solvent
Time/h
Yieldc (%)
2-Naphthyl
2-Naphthyl
PhLi/ZnCl2
PhLi/ZnCl2
Ni(acac)2/PPh3/BuLi
Ni(acac)2/PPh3/DIBAL
THF
THF
8.0
4.0
76d
54
Phenyl
Ni(acac)2/PPh3/DIBAL
THF
4.3
48d
ZnCl2
4-Acetylphenyl
PhLi/ZnCl2
Ni(acac)2/PPh3/DIBAL
Dioxane
4.0
61
a PhLi with ZnCl2 gives the reagent, PhZnCl; 2-thienyl lithium with ZnCl2 gives (2-thienyl)ZnCl. b BuLi or DIBAL are used to reduce the Ni() to
Ni(0). c Yields were determined by GC unless otherwise indicated. d Isolated yield.
Table 3 Cross-coupling of 5-aryloxy-1-phenyl-1H-tetrazoles 1 or 3-aryloxy-1λ6,2-benzothiazole 1,1-dioxides 2 (ArOR) and tetramethyltin with
nickel or palladium catalysts
Ar–O–R
Ar
Ra
Catalyst systemb
Solvent
Time/h
Yield (%)c
2-Naphthyl
1-Naphthyl
1-Naphthyl
2,4-Dimethylpentyl
2-Naphthyl
S
S
S
S
T
T
Pd(PPh3)4/LiCl
Pd(PPh3)4/LiCl
Ni(acac)2/PPh3/DIBAL-H
Pd(PPh3)4/LiCl/PPh3
NiCl2(dppp)/DIBAL-H
Ni(acac)2/PPh3/DIBAL-H
Dioxane
Dioxane
THF
Dioxane
THF
23.0
6.5
3.3
24.0
1.2
4.0
48
63
80
12
23
24
2-Naphthyl
THF
a S = 3-pseudosaccharyl; T = 1-phenyl-1H-tetrazol-5-yl. b DIBAL-H was used to reduce Ni() to Ni(0). c Yields were determined by GC.
This successful coupling of pseudosaccharyl ethers with
Conclusion
organozinc reagents led to an examination of phenyltetrazolyl
Phenyltetrazolyl ethers 1 cross-couple with organomagnesium,
ethers 1 for similar cross-coupling. Under nickel-catalysed con-
-tin and -zinc reagents but pseudosaccharyl ethers 2 react only
ditions, 5-aryloxytetrazoles (1; Ar = phenyl or 2-naphthyl)
with the last two. For all reactions, Ni(0) was found to be the
most efficient catalyst. Pd(0) had no or very little effect for
cross-coupling with organomagnesium and -zinc reagents.
These results open up the possibility for selective cross-
coupling. For example, palladium-catalysed cross-coupling of
triflates with magnesium or zinc reagents would have little or
no effect on a phenyl tetrazolyl or pseudosaccharyl ether but
the latter could be subsequently cross-coupled under nickel-
reacted equally as well with diethylzinc as did the pseudo-
saccharyl ethers 2 under similar conditions (Table 1). For
both types of ether 1,2, ketones could be recovered unchanged
after reaction in the catalyst system. Cross-coupling of
phenyltetrazolyl ethers 1 was also examined for other aryl
and heteroaryl zinc compounds made in situ. In these
cases, the other organozinc reagents reacted satisfactorily
(Table 2).
catalysed conditions. Similarly, the phenyltetrazolyl and pseudo-
saccharyl ethers may be differentiated by their reactivities
towards organomagnesium halides.
In these experiments, as for the others described here, it was
found that with no external reducing agent (generally DIBAL-
H) no cross-coupling occurred. Replacement of DIBAL-H by
n-butyllithium was also beneficial in the preparation of the true
catalyst, Ni(0). For example, the yield of 2-phenylnaphthalene
from phenylzinc chloride and 5-(2-naphthyloxy)-1-phenyl-1H-
Experimental
tetrazole increased from 54 to 76% when butyllithium was used
as a prior reducing agent. Cross-coupling with 2-thienylzinc
chloride indicated that heteroaromatic systems may also be
used, presumably if they are less electronegative than the phenyl-
tetrazole or saccharyl nucleofuges.
Preparation of 5-aryloxy-1-phenyl-1H-tetrazoles 1 and of
3-aryloxy-1λ6,2-benzothiazole 1,1-dioxides (pseudosaccharyl)
ethers 2 has been described.9,10 Gas–liquid chromatograms were
obtained from a “DANI 3800” gas chromatograph equipped
with a flame ionisation detector and an OV-351 capillary
column (25 m). Product yields were calculated by reference to
an internal standard after pre-calibration and were checked by
actual isolation of product.
All reactions involving organometallic species were run
under argon or nitrogen and all glassware was flame-dried just
before reaction or was dried in a hot oven for 24 hours and then
cooled in a slow stream of argon. Unless otherwise stated, all
reagents were used as purchased.
In a further series of experiments, the possibility of using the
widely used organotin reagents19 in cross-coupling with hetero-
aromatic ethers 1,2 was investigated (Table 3). Typical reaction
conditions for cross-coupling with the tin reagents include
nickel and palladium catalysts with DMF, dioxane or THF as
solvents and lithium chloride or triphenylphosphine as a ligand
exchanger. With a similar range of catalysts and reaction condi-
tions, it appeared that the pseudosaccharyl ethers 2 were more
amenable to cross-coupling with tetramethyltin than were the
phenyltetrazolyl ethers 1. Contrary to reports on the cross-
coupling of triflates, which use palladium as catalyst for cross-
coupling with tin reagents,18,19 these results indicate that, for
ethers 1,2, nickel provides much the better results (Table 3). An
80% yield of 1-methylnaphthalene was obtained in the cross-
coupling of 3-(2-naphthyloxy)-1λ6,2-benzothiazole 1,1-dioxide
with tetramethyltin in the presence of Ni(0) but this yield
dropped to 63% with the popular tetrakis(triphenylphosphino)-
palladium/LiCl combination as catalyst.
Catalysts
Dichlorobis(triphenylphosphine)nickel(),20
dichlorobis(di-
phenylphosphine)propanenickel,21 nickel() acetylacetonate,22
and tetrakis(triphenylphosphine)palladium23 were prepared by
published methods. Although no cross-coupling reactions
were observed when finely divided Pd or Ni metals were
intentionally added as catalysts, it cannot be ruled out that
some of the process might be heterogeneous rather than
J. Chem. Soc., Perkin Trans. 1, 2000, 1735–1739
1737

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homogeneous. However, solutions before and after reaction
were clear.
Cross-coupling of 3-aryloxy-1ꢀ6,2-benzothiazole 1,1-dioxides 2
with tetramethyltin
(a) In the absence of triphenylphosphine. In a typical reaction,
a solution of 3-(1-naphthyloxy)-1λ6,2-benzothiazole 1,1-diox-
ide (65.8 mg; 0.21 mmol) in dioxane (15 mL), was treated suc-
cessively with tetramethyltin (0.4 mL; 2.9 mmol), LiCl (250 mg;
5.94 mmol), tridecane (25.6 mg), a few crystals of 2,6-di-tert-
butyl-4-methylphenol and Pd(PPh3)4 (70 mg; 0.06 mmol). The
mixture was stirred and heated under reflux. The progress of
reaction was monitored by TLC. After 6.5 h, 1-methylnaph-
thalene was obtained in 63% yield (Table 3).
Organometallic cross-coupling reagents
Ethylmagnesium bromide (~1.8 M),24 methylmagnesium iodide
(~1.8 M)24 and tetramethyltin25 were prepared by standard
methods. Diethylzinc was purchased (Aldrich). Phenylzinc
chloride was prepared in situ.26 2-Thienylzinc chloride was
prepared in a similar manner from 2-thienyllithium and zinc
chloride.
Attempted cross-coupling of 3-aryloxy-1ꢀ6,2-benzothiazole
(b) In the presence of triphenylphosphine. DIBAL-H (1 M in
toluene; 0.3 mL) was added to a stirred mixture of Ni(acac)2
(68.3 mg; 0.22 mmol) and PPh3 (0.7 g; 2.7 mmol) in diethyl
ether (20 mL) at room temperature. After 10 min, a solution of
tetramethyltin (0.3 mL; 2 mmol), 3-(1-naphthyloxy)-1λ6,2-
benzothiazole 1,1-dioxide (40.8 mg; 0.13 mmol) and tridecane
(15.4 mg) in a mixture of dioxane and diethyl ether (5:2 v/v; 50
mL), was added over a period of 10 min and the stirred reaction
mixture was then gently refluxed. After 3 h, no starting material
remained and 1-methylnaphthalene had been formed in 80%
yield (Table 3).
1,1-dioxides 2 with Grignard reagents
In a typical reaction, NiCl2(dppp) (20.3 mg; 0.037 mmol) was
added to a solution of 3-phenoxy-1λ6,2-benzothiazole 1,1-
dioxide (45.1 mg; 0.17 mmol) and tridecane (internal GC
standard; 25.3 mg) in diethyl ether (20 mL). The mixture was
heated to reflux and a solution of ethylmagnesium bromide (3.5
mmol) was then added via a syringe over a period of about 10
min. Small samples of the reaction mixture (0.1 mL) were peri-
odically extracted and quenched with hydrochloric acid. After
24 h, the yield of ethylbenzene had reached only 5.1%.
Similar experiments in other solvents (THF, DMF, dioxane)
or with other catalysts (Ni(PPh3)4, Ni(acac)2, NiCl2(dppb), Pd/
C, PdCl2, and Pd(Ph3)4) or in the presence or absence of LiCl
or with methylmagnesium bromide gave similar poor yields or
even none of the expected cross-coupled product. A corre-
sponding series of reactions with 2-naphthyloxy-1λ6,2-benzothi-
azole 1,1-dioxide gave at best 13% of 2-ethylnaphthalene in
reaction with ethylmagnesium bromide and NiCl2(dppp)/LiCl
as catalyst in diethyl ether.
Cross-coupling of 5-(2-naphthyloxy)-1-phenyl-1H-tetrazoles 1
with tetramethyltin
In a typical reaction, DIBAL-H (1 M in toluene; 0.04 mL) was
added to a stirred mixture of NiCl2(dppp) (21.0 mg; 0.039
mmol) in diethyl ether (5 mL). A solution of 5-(2-naphthyloxy)-
1-phenyl-1H-tetrazole (100 mg; 0.35 mmol) and tridecane (45
mg) in diethyl ether (40 mL) was added to the reaction mixture
over a period of 10 min, followed by the dropwise addition of
tetramethyltin (0.5 mL; 3.6 mmol) over a period of 10 min. The
mixture was heated under reflux for 1.2 h to give 2-methyl-
naphthalene in 23% yield. Extending the reaction times did not
improve the yield.
Cross-coupling of 3-aryloxy-1ꢀ6,2-benzothiazole 1,1-dioxides 2
with diethylzinc in the absence of triphenylphosphine
A series of reactions was carried out, the reaction conditions
and results being summarised in Table 1. In a typical reaction,
diisobutylaluminium hydride (DIBAL-H; 1 M in toluene; 0.07
mL) was added to a stirred mixture of NiCl2(dppp) (40.5 mg;
0.075 mmol) in THF (5 mL) to produce Ni(0) as a very fine
dispersion. After about 5 min, a solution of 3-phenoxy-1λ6,
2-benzothiazole (101.7 mg; 0.39 mmol) and tridecane (GC
internal standard; 34.6 mg) in THF (15 mL) was added in one
portion to the Ni(0) catalyst, followed by dropwise addition of
diethylzinc (1 M in hexane; 1 mL) over a period of about 10
min. The resulting mixture was heated to reflux and small
samples were extracted at intervals for examination by GC for
the presence of ethylbenzene and by TLC for the presence of the
starting material. After 4 h, no starting material remained and
ethylbenzene had been formed in 74% yield. The experiment
was repeated without DIBAL-H but gave no ethylbenzene.
The remaining experiments (Table 1) were used to investigate
the influences of solvent, the type of nickel complex used and
the addition of triphenylphosphine to stabilise the Ni(0) formed
in situ.
Acknowledgements
The authors are indebted to the Royal Society of Chemistry
(UK), the Eschenmoser Trust and FCT (Portugal) for grants
(A. F. B.).
References
1 Comprehensive Organic Synthesis: Selectivity, Strategy and
Efficiency in Modern Organic Chemistry, eds. B. M. Trost and
I. Fleming, Pergamon, Oxford, 1999, vol. 3, pp. 659–703; vol. 8,
pp. 910–913.
2 A. Padwa, S. M. Sheehan and C. S. Straub, J. Org. Chem., 1999, 64,
8648.
3 P. J. Stang, M. Hanack and L. R. Subramanian, Synthesis, 1982, 85.
4 E. Wenkert, E. L. Michelotti and C. S. Swindell, J. Am. Chem. Soc.,
1979, 101, 2246.
5 J. Y. Bae, J. Ind. Eng. Chem., 1998, 4, 319.
6 A. F. Brigas and R. A. W. Johnstone, J. Chem. Soc., Chem. Commun.,
1994, 1923; M. A. Huffman and N. Yasuda, Synlett, 1999, 471;
M. E. Mower and P. DeShong, J. Org. Chem., 1999, 64, 1684;
M. Rottlander and P. Knochel, J. Org. Chem., 1998, 63, 203.
7 J. A. C. Alves, J. V. Barkley, A. F. Brigas and R. A. W. Johnstone,
J. Chem. Soc., Perkin Trans. 2, 1997, 669.
Cross-coupling of 5-aryloxy-1-phenyl-1H-tetrazoles 1 with
diethylzinc in the presence of triphenylphosphine
8 W. J. Musliner and J. W. Gates, J. Am. Chem. Soc., 1966, 88, 4271.
9 B. J. Hussey, R. A. W. Johnstone and I. D. Entwistle, Tetrahedron,
1982, 38, 3775.
10 A. F. Brigas and R. A. W. Johnstone, Tetrahedron Lett., 1990, 31,
5789.
11 M. L. S. Cristiano, R. A. W. Johnstone and P. J. Price, J. Chem. Soc.,
Perkin Trans. 1, 1996, 1453.
In a typical reaction, DIBAL-H (1 M in toluene; 0.3 mL) was
added to a mixture of Ni(acac)2 (41.2 mg; 0.16 mmol) and PPh3
(164.2 mg; 0.63 mmol) in THF (5 mL). After the mixture had
turned to a black suspension (5 min), a solution of 5-(2-
naphthyloxy)-1-phenyl-1H-tetrazole (81.2 mg; 0.28 mmol) and
1,2,4,5-tetramethylbenzene (27.4 mg) in dioxane (20 mL) was
added to the reaction mixture, followed by dropwise addition
over 10 min of diethylzinc (1 M, 0.5 mL). The resulting mixture
was heated to reflux and small aliquots were taken periodically
for GC analysis. After 4 h the yield of 2-ethylnaphthalene was
52%.
12 R. A. W. Johnstone and W. N. McLean, Tetrahedron Lett., 1988, 29,
5553.
13 Comprehensive Heterocyclic Chemistry: The Structure, Reactions,
Synthesis and Uses of Heterocyclic Compounds, vol. 5, eds. A. R.
Katritzky and C. W. Rees, Pergamon Press, Oxford, 1984, ch. 4.13,
pp. 834–837; J. Y. Lee, M. E. Brune, R. B. Warner, S. B. Buckner,
1738
J. Chem. Soc., Perkin Trans. 1, 2000, 1735–1739

View Article Online
M. Winn, B. De, T. M. Zydowsky, T. J. Opgenorth, D. J. Kerkman
and J. F. DeBernardis, Pharmacology, 1993, 47, 176.
14 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen
and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1987, S1–S41.
15 J. J. P. Stewart, MOPAC 6.00, QCPE No. 455; supplied by CAChe
WorksSystem v. 4.1, Oxford Molecular, Oxford Science Park,
Oxford, UK OX4 4GA.
16 R. A. W. Johnstone, A. H. Wilby and I. D. Entwistle, Chem. Rev.,
1985, 85, 129; J. Q. Yu and J. B. Spencer, Chem. Eur. J., 1999, 5,
2237.
19 W. Shen and L. Wang, J. Org. Chem., 1999, 64, 8873; E. Antonelli,
P. Rosi, C. LoSterzo and E. Viola, J. Organomet. Chem., 1999, 578,
210; A. Dondoni, C. Ghiglione, A. Marra and M. Scoponi, J. Org.
Chem., 1998, 63, 9535.
20 L. Zhu, R. M. Wehmeyer and R. D. Rieke, J. Org. Chem., 1991, 56,
1445.
21 G. R. van Hecke and W. de W. Horrocks, Inorg. Chem., 1966, 5,
1968.
22 R. G. Charles and M. A. Pawlikowski, J. Am. Chem. Soc., 1958, 62,
440.
17 J. C. Bayon, C. Claver and A. M. MasdeuBulto, Coord. Chem. Rev.,
1999, 195, 73; T. Hiyama, H. Matsuhashi, A. Fujita, M. Tanaka,
K. Hirabayash, M. Shimizu and A. Mori, Organometallics, 1996, 15,
5762.
18 M. Kimura, I. Kiyama, T. Tomizawa, Y. Horino, S. Tanaka and
Y. Tamaru, Tetrahedron Lett., 1999, 40, 6795; M. Chavarot
and Z. Pikramenou, Tetrahedron Lett., 1999, 40, 6865; T. Shiota and
T. Yamamori, J. Org. Chem., 1999, 64, 453; M. Okano, M. Amano
and K. Takagi, Tetrahedron Lett., 1998, 39, 3001.
23 G. Booth, in Advances in Inorganic Chemistry and Radiochemistry,
vol. 6, eds. H. J. Emeléus and A. G. Sharpe, Academic Press, New
York, 1964, pp. 1–69.
24 A. Vogel, Textbook of Practical Organic Chemistry, 4th edn.,
revisers, B. S. Furniss, A. J. Hannaford, V. Rogers, P. W. G. Smith
and A. R. Tatchell, Longman, London, 1978, pp. 363–366.
25 W. F. Edgell and C. D. Ward, J. Am. Chem. Soc., 1954, 76,
1169.
26 G. P. Roth and C. E. Fuller, J. Org. Chem., 1991, 56, 3493.
J. Chem. Soc., Perkin Trans. 1, 2000, 1735–1739
1739