Nickel(0)-catalyzed formation of oxaaluminacyclopentenes via an oxanickelacyclopentene key intermediate: Me2AlOTf-assisted oxidative cyclization of an aldehyde and an alkyne with nickel(0)

Article abstract of DOI:10.1021/om100857a

The use of Me₂AlOTf as an additive allowed the oxidative cyclization of pivalaldehyde and diphenylacetylene with nickel(0) in the presence of PCy₃ to give an oxanickelacyclopentene, the structure of which was unambiguously determined

Full text of DOI:10.1021/om100857a

6534 Organometallics 2010, 29, 6534–6540
DOI: 10.1021/om100857a
Nickel(0)-Catalyzed Formation of Oxaaluminacyclopentenes via an
Oxanickelacyclopentene Key Intermediate: Me2AlOTf-Assisted
Oxidative Cyclization of an Aldehyde and an Alkyne with Nickel(0)
Masato Ohashi,*,†,‡ Hiroki Saijo,† Tomoya Arai,† and Sensuke Ogoshi*,†
†Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan, and
‡Center for Atomic and Molecular Technologies, Osaka University, Suita, Osaka 565-0871, Japan
Received September 4, 2010
The use of Me2AlOTf as an additive allowed the oxidative cyclization of pivalaldehyde and diphenyl-
acetylene with nickel(0) in the presence of PCy3 to give an oxanickelacyclopentene, the structure of which
was unambiguously determined by means of X-ray diffraction study. In the presence of TMSCHdCH2,
treatment of the oxanickelacyclopentene with an equimolar amount of AlMe3 quantitatively gave an
oxaaluminacyclopentene with simultaneous generation of ethane and the Ni(0) species (PCy3)Ni-
(TMSCHdCH2)2. The oxaaluminacyclopentene was a suitable precursor for the preparation of allylic
alcohol derivatives due to its reactive Al-C bond, and treatment with HCl or I2 afforded (E)-4,4-dimethyl-
1,2-diphenylpent-1-en-3-ol and (E)-PhCHdC(Ph)CH(tBu)OH, and (Z)-1-iodo-4,4-dimethyl-1,2-diphe-
nylpent-1-en-3-ol and (Z)-PhCIdC(Ph)CH(tBu)OH, respectively, in excellent yield. This sequential
reaction was successfully expanded to a Ni(0)-catalyzed three-component cyclocondensation reaction of
an aldehyde, an alkyne, and AlMe3 that gave the corresponding oxaaluminacyclopentenes in moderate to
good yields. The scope of substrates and the mechanism of the reaction are also reported.
Introduction
which the oxidative cyclization of an alkyne and an imine yielded
a five-membered azanickelacycle intermediate.4b,10 The azaalu-
minacyclopentenes were suitable precursors for the preparation
Oxidative cyclization with low-valent transition metals has
received a great deal of attention because the reaction
permits the efficient construction of a C-C bond between
a variety of unsaturated compounds.1 Among the methods
of oxidative cyclization that are currently available, hetero-
nickelacycles are assumed to be important key intermediates
in the nickel-catalyzed multicomponent coupling reactions
between alkynes and either aldehydes or imines (Scheme 1).
For example, allylic alcohols or allylic amines can be prepared by
reacting a heteronickelacycle with either an alkyl or a reducing
reagent.2-5 The formation of pyran6 and 1,2-dihydropyridine7
derivatives can be achieved by reductive elimination from the
corresponding seven-membered heteronickelacycles that are
generated by insertion of a second alkyne molecule into a
five-membered heteronickelacycle.
To date, we have focused on isolating the heteronickelacycle
key intermediates in these catalytic reactions,4,7,8 and we devel-
oped a novel Ni(0)-catalyzed C-C or C-O bond-forming reac-
tion, wherein two or more unsaturated compounds are bound to
give a more complex product.8,9 Recently, we developed a nickel-
catalyzed three-component cyclocondensation of an imine, an
alkyne, and AlMe3 to yield unique azaaluminacyclopentenes, in
(2) Reductive/alkylative couplings of aldehydes with alkynes: (a)
Oblinger, E.; Montgomery, J. J. Am. Chem. Soc. 1997, 119, 9065–9066.
(b) Tang, X.-Q.; Montgomery, J. J. Am. Chem. Soc. 1999, 121, 6098–6099.
(c) Tang, X.-Q.; Montgomery, J. J. Am. Chem. Soc. 2000, 122, 6950–6954.
(d) Huang, W.-S.; Chan, J.; Jamison, T. F. Org. Lett. 2000, 2, 4221–4223. (e)
Lozanov, M.; Montgomery, J. J. Am. Chem. Soc. 2002, 124, 2106–2107. (f)
Ni, Y.;Amarasinghe, K. K. D.;Montgomery, J. Org. Lett. 2002, 4, 1743–1745.
(g) Takai, K.; Sakamoto, S.; Isshiki, T. Org. Lett. 2003, 5, 653–655. (h) Miller,
K. M.;Huang, W.-S.; Jamison, T. F. J. Am. Chem. Soc. 2003, 125, 3442–3443.
(i) Miller, K. M.; Molinaro, C.; Jamison, T. F. Tetrahedron: Asymmetry 2003,
14, 3619–3625. ( j) Mahandru, G. M.; Liu, G.; Montgomery, J. J. Am.
Chem. Soc. 2004, 126, 3698–3699. (k) Miller, K. M.; Luanphaisarnnont,
T.; Molinaro, C.; Jamison, T. F. J. Am. Chem. Soc. 2004, 126, 4130–4131.
(l) Miller, K. M.; Jamison, T. F. J. Am. Chem. Soc. 2004, 126, 15342–
15343. (m) Luanphaisarnnont, T.; Ndubaku, C. O.; Jamison, T. F. Org. Lett.
2005, 7, 2937–2940. (n) Knapp-Reed, B.; Mahandru, G. M.; Montgomery, J.
J. Am. Chem. Soc. 2005, 127, 13156–13157. (o) Miller, K. M.; Jamison, T. F.
Org. Lett. 2005, 7, 3077–3080. (p) Sa-Ei, K.; Montgomery, J. Org. Lett. 2006, 8,
4441–4443. (q) Moslin, R. M.; Jamison, T. F. Org. Lett. 2006, 8, 455–458. (r)
Moslin, R. M.; Miller, K. M.; Jamison, T. F. Tetrahedron 2006, 62, 7598–7610.
(s) Chaulagain, M. R.; Sormunen, G. J.; Montgomery, J. J. Am. Chem. Soc. 2007,
129, 9568–9569. (t) Yang, Y.; Zhu, S.-F.; Zhou, C.-Y.; Zhou, Q.-L. J. Am. Chem.
Soc. 2008, 130, 14052–14053. (u) Saito, N.; Katayama, T.; Sato, Y. Org. Lett.
2008, 10, 3829–3832. (v) Li, W.; Herath, A.; Montgomery, J. J. Am. Chem. Soc.
2009, 131, 17024–17029. (w) Malik, H. A.; Chaulagain, M. R.; Montgomery, J.
Org. Lett. 2009, 11, 5734–5737. (x) Malik, H. A.; Sormunen, G. J.; Montgomery,
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*To whom correspondence should be addressed. E-mail: ohashi@
chem.eng.osaka-u.ac.jp; ogoshi@chem.eng.osaka-u.ac.jp.
(3) Reductive/alkylative couplings of imines with alkynes: (a) Patel,
S. J.; Jamison, T. F. Angew. Chem., Int. Ed. 2003, 42, 1364–1367. (b)
Patel, S. J.; Jamison, T. F. Angew. Chem., Int. Ed. 2004, 43, 3941–3944.
(4) (a) Ogoshi, S.; Arai, T.; Ohashi, M.; Kurosawa, H. Chem. Com-
mun. 2008, 1347–1349. (b) Ohashi, M.; Kishizaki, O.; Ikeda, H.; Ogoshi, S.
J. Am. Chem. Soc. 2009, 131, 9160–9161.
(5) DFT studies for the Ni-catalyzed reductive coupling reactions: (a)
McCarren, P. R.; Liu, P.; Cheong, P. H.-Y.; Jamison, T. F.; Houk, K. N. J.
Am. Chem. Soc. 2009, 131, 6654–6655. (b) Liu, P.; McCarren, P. R.; Cheong, P.
H.-Y.; Jamison, T. F.; Houk, K. N. J. Am. Chem. Soc. 2010, 132, 2050–2057.
(1) For Reviews, see: (a) Montgomery, J. Acc. Chem. Res. 2000, 33, 467–
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r
pubs.acs.org/Organometallics
Published on Web 10/29/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 23, 2010 6535
Scheme 1. Possible Nickel(0)-Catalyzed Reaction between an
Alkyne and Either an Aldehyde or an Imine
Scheme 2. Reaction of 1a with 2a in the Presence of Ni(cod)2 and
PCy3
yield, together with an η2-PhCHO complex, (η2-PhCHO)Ni-
(PCy3)2 (4a; 42%)11 (Scheme 2). The dimeric structure of 3a was
inferred by analogy with the molecular structure of the complex
derived from the reaction of 2-butyne with benzaldehyde on
Ni(0).4a Exposing the reaction mixture to carbon monoxide
(5 atm) led to the quantitative transformation of 3a into a five-
membered lactone (5a),12 supporting the generation of 3a. By
contrast, the reaction employing pivalaldehyde (2b) instead of
2a did not occur.
These results prompted us to examine Lewis acid-type
additives to facilitate the oxidative cyclization between an
aldehyde and an alkyne with nickel(0), because it was pre-
viously found that the addition of a Lewis acid accelerates
the cyclization reaction drastically.8a,b Me2AlOTf promoted
the oxidative cyclization of 1a with 2a on nickelinthe presence
of PCy3, giving an oxanickelacycle (6a) (Scheme 3). The
oxanickelacycle 6a was also prepared by the following step-
wise procedure. The treatment of the η2-PhCHO complex 4a
with Me2AlOTf gave an η2-PhCHO-AlMe2OTf nickel(0)
complex (7a), whereas the addition of Me3SiOTf instead of
Me2AlOTf yielded the η1:η1-siloxybenzyl nickel(II) complex
(η1:η1-κ(C,O)-Me3SiOCHPh)Ni(PCy3)OTf.8a The oxidative
cyclization of the resulting complex 7a with an equimolar
amount of1aproceeded smoothly to form the oxanickelacycle
6a in 87% yield (Scheme 3). The treatment of 6a with carbon
monoxide (5 atm) resulted in the quantitative formation of the
expected 5a, which was consistent with the structure of 6a, as
depicted in Scheme 3.12
of allylic amines because the Al-C bond reacts with various
electrophiles. In addition, we first reported the formation of an
oxanickelacyclopentene via the oxidative cyclization of benzal-
dehyde and 2-butyne with nickel(0).4a The oxanickelacyclopen-
tene was successfully derivatized into an enone, a lactone, and an
allylic alcohol by thermal decomposition, carbonylation, and
treatment with ZnMe2, respectively. These results provide strong
evidence that oxanickelacyclopentene plays a critical role in a
variety of catalytic reactions. However, the general scope of a
Ni(0)-catalyzed oxidative cyclization of aldehydes and alkynes
has remained unexplored. The catalytic formation of various
oxaaluminacyclopentenes would be desired as a promising syn-
thon for allylic alcohols, which are one of the most versatile key
intermediates in not only organic synthesis but also biologically
active compounds widely distributed in natural products.
We report herein the Me2AlOTf-assisted oxidative cyclization
of aldehydes and alkynes with nickel(0) to give oxanickelacy-
clopentenes and the subsequent transformation of the oxanick-
elacyclopentene intermediates into oxaaluminacyclopentenes
following treatment with AlMe3. The molecular structures
of the five-membered oxanickela- and oxaaluminacycles were
unambiguously confirmed by means of X-ray diffraction anal-
ysis. We also report a Ni(0)-catalyzed three-component cyclo-
condensation of an aldehyde, an alkyne, and AlMe3.
Results and Discussion
Ni(0)/Me2AlOTf-Mediated Formation of Oxaalumina-
cycles. Our initial efforts focused on the oxidative cyclization
of diphenylacetylene (1a) and benzaldehyde (2a) with nickel(0).
Treatment of an equimolar mixture of 1a and 2a with Ni(cod)2
in the presence of PCy3 at room temperature resulted in the
gradual formation of an oxanickelacyclopentene (3a) in 20%
A tBuCHO analogue (6b) was prepared in 92% yield, while in
the absence of Me2AlOTf the cyclization of 1a and 2b with Ni(0)
did not proceed at all (Scheme 3). The molecular structure of 6b
was confirmed by X-ray diffraction analysis, and the ORTEP
drawing of 6b is shown in Figure 1. By contrast to the dimeric
structure of 3a, which is depicted in Scheme 2, complex 6b had
a monomeric framework due to the intramolecular coordina-
tion of one of the oxygen atoms in the trifluoromethanesul-
fonate group to the nickel center. The nickel atom in 6b had a
16-electron, square-planar geometry, as confirmed by the sum of
the bond angles around nickel along the P, O1, O2, and C3 atoms
(362.3°). The Ni-O1 bond length of 1.914(2) A was slightly
longer or equal to that observed previously for well-defined five-
membered oxanickelacycles (1.848(2)-1.890(2) A).4a,13 The
C1-C2 (1.515(5) A) and C2-C3 (1.348(5) A) bond distances
of 6b were nearly identical to the lengths typical of carbon-
carbon single and double bonds, respectively.
(6) (a) Tsuda, T.; Kiyoi, T.; Miyane, T.; Saegusa, T. J. Am. Chem.
Soc. 1988, 110, 8570–8572. (b) Tekevac, T. N.; Louie, J. Org. Lett. 2005, 7,
4037–4039. (c) Murakami, M.; Ashida, S.; Matsuda, T. J. Am. Chem. Soc.
2006, 128, 2166–2167. (d) Tekavec, T. N.; Louie, J. J. Org. Chem. 2008, 73,
2641–2648.
(7) Ogoshi, S.; Ikeda, H.; Kurosawa, H. Angew. Chem., Int. Ed. 2007,
46, 4930–4932.
(8) Isolated examples of heteronickelacycles proposed as a reaction
intermediate: (a) Ogoshi, S.; Oka, M.-a.; Kurosawa, H. J. Am. Chem.
Soc. 2004, 126, 11082–11803. (b) Ogoshi, S.; Ueta, M.; Arai, T.; Kurosawa,
H. J. Am. Chem. Soc. 2005, 127, 12810–12811. (c) Ogoshi, S.; Nagata, M.;
Kurosawa, H. J. Am. Chem. Soc. 2006, 128, 5350–5351. (d) Ogoshi, S.;
Tonomori, K.-i.; Oka, M.-a.; Kurosawa, H. J. Am. Chem. Soc. 2006, 128,
7077–7086. (e) Ogoshi, S.; Ikeda, H.; Kurosawa, H. Purr Appl. Chem. 2008,
80, 1115–1125. (f ) Tamaki, T.; Nagata, M.; Ohashi, M.; Ogoshi, S. Chem.;
Eur. J. 2009, 15, 10083–10091. (g) Ohashi, M.; Taniguchi, T.; Ogoshi, S.
Organometallics 2010, 29, 2386–2389. (h) Ogoshi, S.; Nishimura, A.;
Ohashi, M. Org. Lett. 2010, in press (doi: XXXXX).
(12) The treatment of nickel compounds with carbon monoxide can
yield [Ni(CO)4] (extremely toxic) due to the addition of insufficient
amounts of PCy3, careless handling, or an accident. The reaction
mixture must be handled in a well-ventilated fume hood.
(13) A five-membered unsaturated nickelalactone: (a) Langer, J.;
Walther, D.; Gorls, H. J. Organomet. Chem. 2006, 691, 4874–4881. (b)
Walther, D.; Braunlich, G.; Kempe, R.; Sieler, J. J. Organomet. Chem. 1992,
436, 109–119. (c) Langer, J.; Fischer, R.; Gorls, H.; Walther, D. J. Organo-
met. Chem. 2004, 689, 2952–2962. (d) Langer, J.; Gartner, M.; Gorls, H.;
Walther, D. Synthesis 2006, 2697–2706.
(9) (a) Ogoshi, S.; Haba, T.; Ohashi, M. J. Am. Chem. Soc. 2009, 131,
10350–10351. (b) Ogoshi, S.; Nishimura, A.; Haba, T.; Ohashi, M. Chem.
Lett. 2009, 38, 1166–1167. (c) Ogoshi, S.; Hoshimoto, Y.; Ohashi, M. Chem.
Commun. 2010, 46, 3354–3356.
(10) Baxter, R. D.; Montgomery, J. J. Am. Chem. Soc. 2008, 130,
9662–9663.
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Walther, D. J. Organomet. Chem. 1980, 190, 393–401.

6536 Organometallics, Vol. 29, No. 23, 2010
Ohashi et al.
Scheme 3. Reaction of 1a with 2 in the Presence of Ni(0)/PCy3 and Me2AlOTf
Scheme 4. Formation of Oxaaluminacycle
carbon-oxygen single bond and was significantly longer than
that of the C-O bond lengths observed in (η2-PhCHO)Ni(PCy3)2
and benzophenone (1.325(7) and 1.212(3) A, respectively).14
These results indicate that the resonance structure of an
oxanickela(II)cyclopropane, rather than that of an η2-aldehyde
nickel(0) species, may be dominant in 7a. In 7a, the Ni-P bond
distance between Ni1-P1 (2.172(3) A) was significantly differ-
ent from that between Ni-P2 (2.299(3) A). This difference in
bond distance was probably due to the unsymmetrical struc-
ture of the coordinating CdO moiety in PhCHO-AlMe2OTf.
The Al-O1 and Al-O2 bond lengths were 1.780(8) and
1.807(10) A, respectively, which are nearly identical to those
observed in 6b (1.799(3) A for Al-O1, cf. 1.877(3) A for
Al-O3).
Figure 1. Molecular structure of 6b with thermal ellipsoids at
the 30% probability level. H atoms except for that bound to C1
are omitted for clarity.
Treatment of the oxanickelacycle 6b with AlMe3 in C6D6
at room temperature resulted in the quantitative formation of an
oxaaluminacycle (8b) via nickel/aluminum double transmetala-
tion (Scheme 4). The reaction was conducted in the presence of 2
equiv of TMSCHdCH2 to trap the generated Ni(0) species. The
and
4b,8d
known Ni(0) complex (PCy3)Ni(η2-CH2dCHTMS)2
ethane were detected by using NMR spectroscopy. Although
the complex 8b could not be isolated, dissolving 8b in THF
allowed Me2AlOTf to dissociate from the oxygen atom of the
oxaaluminacycle, giving the isolable dimer 9b (Scheme 4).
The molecular structure of 9b is shown in Figure 3. In the
crystal lattice, one of the aluminum atoms in 9b was coordi-
nated to the solvated THF molecule. To the best of our
knowledge, this is the first example of the catalytic formation
Figure 2. Molecular structure of 7a with thermal ellipsoids at
the 30% probability level. H atoms except for that bound to C1
are omitted for clarity.
The X-ray diffraction analysis of 7a clearly demonstrated
that the oxygen atom in the η2-coordinating carbonyl group
was bound to a Me2AlOTf molecule (Figure 2). The parent
framework of (η2-PhCHO)Ni(PCy3)2 remained intact during
the reaction with Me2AlOTf, in contrast to the corresponding
reaction with Me3SiOTf.8a However, the C1-O1 bond length
of 1.441(12) A in 7a was nearly identical to that of a typical
ꢀ
(14) (a) Kaiser, J.; Sieler, J.; Walther, D.; Dinjus, E.; Golic, L. Acta
Crystallogr. 1982, B38, 1584–1586. (b) Borisenko, K. B.; Bock, C. W.;
Hargittai, I. J. Phys. Chem. 1996, 100, 7426–7434.

Article
Organometallics, Vol. 29, No. 23, 2010 6537
a
Table 1. Ni(0)-Catalyzed Cyclocondensation of 1a, 2b, and AlMe3
yield (%)b
entry ligand (mol %)
additive
10ab
12ab
1
2
3
4
5c
6
7
8
PCy3 (10)
PCy3 (20)
PCyp3 (20)
PPh3 (20)
PnBu3 (20)
PCy3 (40)
PCyp3 (40)
PCyp3 (40)
Me2AlOTf THF (1 equiv)
3
30
56
58
<1
13
60
63
51
27
14
2
14
16
7
Me2AlOTf THF (1 equiv)
3
Me2AlOTf THF (1 equiv)
Me2AlOTf THF (1 equiv)
3
Figure 3. Molecular structure of 9b with thermal ellipsoids at
the 30% probability level. H atoms except for those bound to C1
and C11 atoms are omitted for clarity.
3
Me2AlOTf THF (1 equiv)
Me2AlOTf THF (1 equiv)
3
3
Me2AlOTf THF (1 equiv)
noned
3
13
53
a General conditions: 1a, 2b, and AlMe3 (1.08 M, in hexane), 0.30 mmol
Scheme 5. Transformation of Oxaaluminacycle 9b into Allylic
Alcoholsa
1
each; Ni(cod)2, 0.03 mmol; and THF, 5.0 mL. b Determined by H NMR
analysis of the crude product after protonolysis (using 2-methoxynaphthalene
as an internal standard). c Run for 6 days. d Run with 2 equiv of AlMe3.
three-component coupling product (B) in 51% yield (entry 1).
After protonolysis of the crude products, which contained 10ab
and 12ab, 1H NMR analysis was used to estimate the product
yield of both A and B. The yield and selectivity of the desired
product A was improved by increasing the amount of PCy3 to
20 mol % (entry 2). Use of PCyp3 (20 mol %, Cyp = c-C5H9)
as the ligand improved the selectivity of the desired product
relative to that obtained with PCy3 (entry 3), while neither PPh3
nor PnBu3 was effective (entries 4 and 5). Employing 40 mol %
of PCyp3 further increased the formation of A and suppressed
that of B, giving A as the major product (63%, entry 7).
Interestingly, the reaction in the absence of Me2AlOTf de-
creased both the yield and selectivity of A (entry 8). This result
confirms that Me2AlOTf indeed promotes the double transme-
talation. Montgomery reported a related nickel(0)-catalyzed
cyclocondensation of aldehydes, alkynes, and dialkylsilanes to
give oxasilacyclopentene analogues.10
Using the optimized reaction conditions and diphenyla-
cetylene as the alkyne, the range of aldehydes that are suitable
for the reaction was studied (Table 2). The reaction with 1
mmol of 2b, followed by protonolysis, yielded 10ab in 70%
yield, as estimated by NMR analysis of the crude product
(entry 1). In addition, the three-component coupling product
12abwasalso generated concomitantly(<10%yield), and the
isolated yield of 1ab decreased to 43% due to losses during
purification. Secondary aldehydes, such as 2-methylpropanal
(2c), 2-ethylbutanal (2d), cyclohexanecarbaldehyde (2e), and
2-ethylhexanal (2f), gave the corresponding allyl alcohols
(10ac-af) in moderate to high yields (entries 2-5), with only
a small amount of the side-reaction products (12ac-af) pro-
duced during each reaction. In addition, sterically hindered
primary aldehydes were suitable for the reaction. For exam-
ple, 3,3-dimethylbutanal (2g) underwent cyclocondensation
with 1a and AlMe3 to afford 10ag in 66% yield (entry 6).
However, less-hindered aldehydes such as 1-hexanal (2h) did
not undergo the reaction efficiently (entry 7). Benzaldehyde
(2a) was inefficient due to the rapid formation of the direct
addition product of AlMe3 (entry 8).
a Reaction conditions: for 10ab, HClaq.; for 11, I2 (1.5 equiv), 6 h, then
HClaq
.
of oxa-aluminacyclopentenes, although cycloalumination of
either olefins or acetylenes mediated by Cp2Zr derivatives has
been used in the preparation of organoaluminum compounds.15
In the present study, oxaaluminacyclopentenes served as
useful precursors for the preparation of allylic alcohols, be-
cause the reactive Al-Cbondcanbetreatedwithelectrophiles,
similar to the results previously reported for the related
azaaluminacyclopentenes.4b Indeed, protolysis of 9b gave the
corresponding allylic alcohol (10ab) in 87% yield. In addition,
treatment of 9b with I2 followed by protolysis led to the
formation of 11 in 92% yield (Scheme 5).
Ni(0)-Catalyzed Formation of Oxaaluminacycles via Cyclo-
condensation of an Alkyne, an Aldehyde, and AlMe3. We next
examined the catalytic application of the cyclocondensation of
diphenylacetylene, pivalaldehyde, and AlMe3 in the presence of
a catalytic amount of Ni(cod)2 and PCy3 (10 mol % each)
(Table 1). Because the direct addition reaction of AlMe3 to
aldehydes occurs in benzene or toluene,16 we used THF as the
solvent for the catalytic reaction. However, in the presence of a
stoichiometric amount of Me2AlOTf THF, the expected cy-
3
clocondensation product (A) was obtained in only 30% yield
because of the concomitant formation of the corresponding
(15) Selected reviews: (a) Dzhemilev, U. M.; Ibragimov, A. G. Russ.
Chem. Rev. 2000, 69, 121–135. (b) Dzhemilev, U. M.; Ibragimov, A. G. J.
Organomet. Chem. 1994, 466, 1–4.
(16) (a) Biswas, K.; Prieto, O.; Goldsmith, P. J.; Woodward, S.
Angew. Chem., Int. Ed. 2005, 44, 2232–2234. (b) Biswas, K.; Chapron,
A.; Cooper, T.; Fraser, P. K.; Novak, A.; Prieto, O.; Woodward, S. Pure Appl.
ꢁ
ꢂ
Chem. 2006, 78, 511–518. (c) Mata, Y.; Dieguez, M.; Pamies, O.; Woodward,
ꢁ
ꢂ
S. J. Org. Chem. 2006, 71, 8159–8165. (d) Mata, Y.; Dieguez, M.; Pamies,
O.; Woodward, S. Inorg. Chem. Acta 2008, 361, 1381–1384.

6538 Organometallics, Vol. 29, No. 23, 2010
Ohashi et al.
In addition, 1-phenyl-1-propyne (1b) also underwent cou-
pling with 2b and AlMe3 to give the expected product (10bb)
as a mixture of regioisomers in moderate yield (entry 9). The
regioselectivity was consistent with that observed by Jamison
et al.2d However, neither terminal alkynes, such as phenyla-
cetylene (1c), nor dialkyl-substituted alkynes, such as 3-hex-
yne (1d), reacted efficiently with 2b (entries 10 and 11).
On the basis of the results of the stoichiometric reactions, we
propose that the cyclocondensation reaction might proceed via
the mechanism depicted in Scheme 6. The addition of Me2AlOTf
allows the oxidative cyclization of an aldehyde and an alkyne
with Ni(0) in the presence of sterically hindered trialkylphos-
phines, such as PCy3 and PCyp3, to generate an oxanickelacycle
(D). In this reaction step, an aldehyde-Me2AlOTf adduct is
likely to coordinate predominantly to the Ni(0) center, yielding
an η2-RCHO-AlMe2OTf nickel species (C), which reacts
with an alkyne to give D. The transmetalation between D
and AlMe3 might give a transient intermediate (E). Succes-
sive Ni/Al transmetalation of E would result in the formation
of an oxaaluminacyclopentene (A) and Me2NiLn. Reductive
elimination from the Me2NiLn intermediate might release
ethane to regenerate a Ni(0) species. On the other hand,
reductive elimination from E might proceed to give a three-
component coupling product (B).2a,4a
Conclusion
We demonstrated that the oxidative cyclization of piva-
laldehyde and diphenylacetylene with Ni(0)/PCy3 proceeds
smoothly with the assistance of Me2AlOTf to give an oxanick-
elacyclopentene. The oxanickelacyclopentene was quantitatively
converted into an oxaaluminacyclopentene by addition of
AlMe3. The molecular structures of both the oxanickela- and
the oxaaluminacyclopentenes were confirmed by X-ray crys-
tallography. These stoichiometric reactions were successfully
applied to the catalytic formation of a series of oxaalumina-
cyclopentenes. The resulting oxaaluminacyclopentenes were
demonstrated to be versatile precursors for the preparation
of allylic alcohol derivatives.
Table 2. Ni(0)/PCy3-Catalyzed Cyclocondensation of an Alkyne,
a
an Aldehyde, and AlMe3
alkyne (1)
aldehyde (2)
product
entry
R1, R2
R3
yield (%)b
1
1a R1 = R2 = Ph
2b tBu
10ab 70 (43)
10ac 72 (49)
10ad 66 (36)
Experimental Section
2
1a
1a
1a
1a
1a
1a
1a
2c iPr
2d 3-pentyl
3
General Procedures. All manipulations were conducted under
a nitrogen atmosphere using standard Schlenk or drybox tech-
niques. 1H, 31P, and 13C nuclear magnetic resonance spectra were
recorded on JEOL GSX-270S and Bruker Avance III 400 spectrom-
eters. The chemical shifts in 1H NMR spectra were recorded
relative to either Me4Si or residual protiated solvent (C6D5H (δ
7.16)). The chemical shifts in the 13C NMR spectra were recorded
relative to Me4Si. The chemical shifts in the 31P NMR spectra were
recorded using 85% H3PO4 as external standard. Assignment of
the resonances in 1H and 13C NMR spectra was based on 1H-1H
COSY, HMQC, and HMBC experiments. Elemental analyses
were performed at the Instrumental Analysis Center, Faculty of
Engineering, Osaka University. X-ray crystal data were collected
by a Rigaku RAXIS-RAPID imaging plate diffractometer.
4
2e cyclohexyl 10ae 65 (24)
2f 3-heptyl 10af 79 (59)
5
6
2g neopentyl
2h 1-pentyl
2a Ph
10ag 66 (24)
10ah 15
10aa 21
10bb 52 [71:29]c
7
8
9
1b R1 = Ph, R2 = Me 2b
1c R1 = Ph, R2 = H
1d R1 = R2 = Et
10
11
2b
2b
10cb 19
10db 12
a General conditions: 1, 2, and AlMe3 (1.08 M, in hexane), 1.00 mmol
each; Ni(cod)2, 0.10 mmol; and THF, 10.0 mL. b Determined by 1H
NMR analysis of the crude product (using 2-methoxynaphthalene as an
internal standard). Cited yields in parentheses are of isolated product.
c The value in brackets is a regioisomer ratio, estimated by 1H NMR
analysis of the crude product.
Scheme 6. Plausible Mechanism for the Catalytic Formation of an Oxaaluminacycle A

Article
Materials. The degassed and distilled solvents (THF, toluene,
Organometallics, Vol. 29, No. 23, 2010 6539
(s, Cy), 26.9 (s, Cy), 28.0 (d, J = 9.9 Hz, Cy), 28.2 (d, J = 10.7 Hz,
Cy), 30.4 (s, Cy), 32.5 (d, J = 24.4 Hz, Cy), 86.2 (d, J = 1.6 Hz,
NiO(AlMe2)CHPh-), 126.1 (s, Ph), 126.7 (s, Ph), 126.9 (d, J =
31.3 Hz, NiPhCdCPh-), 128.1 (s, Ph), 128.2 (s, Ph), 128.9 (s, Ph),
129.1 (s, Ph), 129.4 (s, Ph), 129.7 (s, Ph), 129.8 (s, Ph), 137.5 (s, Ph),
144.0 (s, Ph), 146.8 (d, J= 3.8 Hz, PhNiPhCdCPh-), 154.6 (s, Ph).
Anal. Calcd for C42H55AlF3NiO4PS: C, 60.81; H, 6.68. Found: C,
61.06; H, 7.19.
and hexane) used in this work were commercially available. C6D6
was distilled from sodium benzophenone ketyl. All commercially
available reagents were distilled and degassed prior to use.
Oxidative Cyclization of 1a and 2a with Ni(0) in the Presence of
PCy3. To a 0.5 mL C6D6 solution of Ni(cod)2 (5.5 mg, 0.02 mmol),
PCy3 (5.6 mg, 0.02 mmol), and PhCHO (2a; 2.0 μL, 0.02 mmol)
was added diphenylacetylene (1a; 3.6 mg, 0.02 mmol) at room
temperature. The solution was observed to change from yellow to
red. After 5 h, NMR analysis showed that 3a and (η2-PhCHO)Ni-
(PCy3)2 (4a) were generated in 20% and 72% yield, respectively.
The reaction mixture was then treated with carbon monoxide
(5 atm), immediately resulting in a color change to pale yellow. The
full conversion of 3a into lactone 5a was confirmed.
Oxidative Cyclization of 1a and 2b with Ni(0)/PCy3 in the
Presence of Me2AlOTf. To a toluene solution of Ni(cod)2 (137.5
mg, 0.5 mmol), PCy3 (140.2 mg, 0.5 mmol), pivalaldehyde (2b;
54.3 μL, 0.5 mmol), and AlMe2OTf THF (124.2 μL, 0.5 mmol)
3
was added diphenylacetylene (89.1 mg, 0.5 mmol). The solu-
tion was observed to turn purple. After the reaction mixture
was stirred for 30 min, all volatiles were removed under
reduced pressure. The residue was washed with cold pentane to
give 6b as a purple solid (384 mg, 95%). Single crystals suitable for
X-ray diffraction analysis were obtained by recrystallization from
toluene/pentane at -20 °C. 1H NMR (400 MHz, C6D6, rt, δ/ppm):
-0.24 (s, 3H, -OAlMe2), 0.74 (s, 3H, -OAlMe2), 1.0-2.2 (m,
42H, Cy including 9H of NiO(AlMe2)CHC(CH3)3 at δ 1.61), 4.88
(d, J = 3.0 Hz, 1H, NiO(AlMe2)CHC(CH3)3), 6.7-7.8 (m, 10H,
Ph). 31P NMR (109 MHz, C6D6, rt, δ/ppm): δ 21.2 (s). 13C{1H}
NMR (100 MHz, C6D6, rt, δ/ppm): -9.2 (s, -OAlMe2), -5.4 (s,
-OAlMe2), 26.9 (s, Cy), 28.1 (s, Cy), 28.2 (d, J = 6.2 Hz, Cy), 28.6
(s, NiO(AlMe2)CHC(CH3)3), 30.4 (s, Cy), 30.7 (s, Cy), 32.4 (d, J=
19.2 Hz, Cy), 37.9 (s, NiO(AlMe2)CHC(CH3)3), 93.3 (d, J = 4.1
Hz, NiO(AlMe2)CHC(CH3)3), 125.9 (s, Ph), 126.6 (s, Ph), 127.3 (d,
J =29.8Hz, Ni(Ph)CdCPh-), 127.9 (s, Ph), 128.5 (s, Ph), 130.2(s,
Ph), 130.3 (s, Ph), 139.6 (d, J = 3.1 Hz, Ph), 147.1 (d, J = 3.1 Hz,
Ph), 155.6 (s, Ni(Ph)CdCPh-). Anal. Calcd for C40H59AlF3-
NiO4PS: C, 59.34; H, 7.35. Found: C, 59.08; H, 7.45. X-ray
data for 6b. M=809.59, brown, monoclinic, P21/n (No. 14),
a =11.2264(6) A, b = 19.1638(11) A, c = 20.1715(11) A, β =
90.1040(15)°, V=4339.7(4) A3, Z=4, Dcalcd =1.239 g/cm3, T=
0(2) °C, R1 (wR2) = 0.057 (0.125).
Selected spectral data for 3a: 1H NMR (270 MHz, C6D6, rt,
δ/ppm) 6.00 (s, NiOCH(Ph)-); 31P NMR (109 MHz, C6D6, rt,
δ/ppm) 31.5 (s).
Spectral data for 5a: 1H NMR (270 MHz, CDCl3, rt, δ/ppm)
6.27 (s, 1H, -C(O)OCHPh-), 7.1-7.6 (m, 15H, Ph); 13C{1H}
NMR (100 MHz, CDCl3, rt, δ/ppm) 83.9 (-COOCHPh-), 127.1
(Ph), 127.9 (-COC(Ph)dC(Ph)-), 128.6 (Ph), 128.8 (Ph), 128.9
(Ph), 129.1 (Ph), 129.2 (Ph), 129.60 (Ph), 129.64 (Ph), 130.06 (Ph),
130.09 (Ph), 131.4 (Ph), 135.0 (Ph), 159.5 (-COC(Ph)dC(Ph)-),
172.7 (-COC(Ph)dC(Ph). These 1H and 13C chemical shift values
were found to be almost identical to reported values.17 HRMS
(EI): calcd for C22H16O2 312.1150, found m/z 312.1154.
Reaction of 4a with Me2AlOTf. To a 5 mL toluene solution of
4a (744.4 mg, 1.03 mmol) was added AlMe2OTf THF (253.5 μL,
3
1.03 mmol). The solution was observed to turn from orange to red.
After the reaction mixture was stirred for 3 h, all volatiles were
removed under reduced pressure. The residue was washed with cold
hexane to give (η2-PhCHO-AlMe2OTf)Ni(PCy3)2 (7a) as a brown
solid (937 mg, 98%). Single crystals suitable for X-ray diffraction
analysis were obtained by recrystallization from C6H6/hexane at
room temperature. 1H NMR (400 MHz, C6D6, rt, δ/ppm): -0.35
(s, 3H, -OAlMe2), -0.25 (s, 3H, -OAlMe2), 0.8-2.2 (m, 66H,
Cy), 5.05 (t, J = 2.7 Hz, 1H, PhCHO), 7.05-7.15 (m, 3H, m- and
p-Ph), 7.82 (d, J = 5.1 Hz, 2H, o-Ph). 31P NMR (109 MHz, C6D6,
rt, δ/ppm): 27.7 (d, J = 29.0 Hz), 35.4 (d, J = 29.0 Hz). 13C{1H}
NMR (100 MHz, C6D6, rt, δ/ppm): -8.2 (s, -OAlMe2), -7.4 (s,
-OAlMe2), 26.7 (d, J=13.0Hz, Cy), 27.0 (s, Cy), 27.9 (d, J=10.7
Hz, Cy), 28.16 (s, Cy), 28.26 (s, Cy), 28.33 (s, Cy), 28.35 (s, Cy), 30.4
(d, J = 14.6 Hz, Cy), 30.8 (d, J = 24.4 Hz, Cy), 31.8 (s, Cy), 35.0 (d,
J = 13.0 Hz, Cy), 35.7 (d, J = 18.3 Hz, Cy), 65.9 (dd, J = 24.5, 7.7
Hz, PhCHO), 126.4 (s, o-Ph), 127.2 (s, p-Ph), 129.4 (s, m-Ph), 145.7
(d, J = 3.7 Hz, ipso-Ph). X-ray data for 7a: M = 931.77, brown,
monoclinic, P21 (No. 4), a = 10.8100(11) A, b = 18.5525(13) A,
c = 13.4115(12) A, β = 114.532(3)°, V = 2446.9(4) A3, Z = 2,
Treatment of 6b with CO. In a pressure-tight NMR tube, a
0.5 mL C6D6 solution of 6b (80.9 mg, 0.1 mmol) was treated with
carbon monoxide (5 atm). The solution was observed to im-
mediately turn from purple to pale yellow. NMR analysis
showed the quantitative formation of the corresponding lactone
(5b) and Ni(CO)3(PCy3). Further purification was accom-
plished by passing through a silica pad, giving 5b (19 mg,
1
66%). H NMR (400 MHz, CDCl3, rt, δ/ppm): 0.87 (s, 9H,
-C(CH3)3), 5.17 (s, 1H, -C(O)OCHtBu), 6.5-7.4 (m, 10H, Ph).
13C{1H} NMR (100 MHz, CDCl3, rt, δ/ppm): 26.4 (-C(CH3)3),
36.7 (-C(CH3)3), 89.3 (-COOCHtBu), 128.3 (Ph), 128.5 (Ph),
128.6 (Ph), 128.9 (-OOCPhCdCPh-), 129.1 (Ph), 129.5 (Ph),
129.7 (Ph), 129.8 (Ph), 133.7 (Ph), 160.8 (-OOCPhCdCPh-),
172.4 (-OOCPhCdCPh-). HRMS (EI): calcd for C20H20O2
292.1463, found m/z 292.1459.
D
calcd = 1.265 g/cm3, T = -150(2) °C, R1 (wR2) = 0.130 (0.343).
Efforts for elemental analysis of 7a and 9b have been unrewarding
due to their higher reactivities.
Oxidative Cyclization of 1a and 2a with Ni(0)/PCy3 in the
Presence of Me2AlOTf. To a 5 mL toluene solution of 7a, which
was in situ generated by treating 4a (362.8 mg, 0.5 mmol) with
Monitoring the Reaction of 6b with AlMe3. To a 0.5 mL C6D6
solution of 5b (12.2 mg, 0.015 mmol) was added AlMe3 (15 μL,
1.03 M in hexane), resulting in immediate change of the color from
purple to orange. NMR observation revealed the formation of
oxaaluminacycle (8b) with concomitant liberation of ethane. The
quantitative formation of a Ni(0) complex, (PCy3)Ni(TMSCHd
CH2)2, was also confirmed by means of 31P NMR spectroscopy.
Addition of THF to the reaction mixture resulted in the clean
AlMe2OTf THF (124.2 μL, 0.5 mmol), was added a toluene solu-
3
tion(5mL) of1a (89.1 mg, 0.5 mmol). The solution was observed to
turn from red to deep purple. After the reaction mixture was stirred
for 5 min, all volatiles were removed under reduced pressure. The
residuewaswashedwithcoldhexanetogive6a as a purple solid (324
mg, 78%). Further purification was accomplished by recrystalliza-
tion from toluene/hexane at -20 °C. 1H NMR (400 MHz, tol-d8,
-20 °C, δ/ppm): -0.55 (s, 3H, -OAlMe2), 0.17(s, 3H, -OAlMe2),
0.8-2.1 (m, 33H, Cy), 5.69 (d, J = 2.8 Hz, 1H, NiO(AlMe2)-
CHPh-), 6.6-6.8 (m, 10H, Ph), 7.22 (t, 1H, J = 7.2 Hz, Ph), 7.36
(t, 2H, J=7.2Hz, Ph), 8.25(d, 1H, J=7.2Hz, Ph). 31PNMR(109
MHz, C6D6, rt, δ/ppm): 21.2 (s). 13C{1H} NMR (100 MHz, tol-d8,
-20 °C, δ/ppm): -9.9 (s, -OAlMe2), -7.3 (s, -OAlMe2), 23.6
1
formation of Me2AlOTf THF. Selected spectral data for 8b: H
3
NMR (270 MHz, C6D6, rt, δ/ppm): -0.42 (s, 6H, -AlMe2OTf ),
-0.25 (s, 3H, -Al(CH3)OCH(tBu)-), 0.76 (s, 9H, -Al(CH3)-
OCH(tBu)-), 5.42 (s, 1H, -Al(CH3)OCH(tBu)-), 6.9-7.1 (m,
10H, Ph).
Isolation of Oxaaluminacyclopentene (9b). To a toluene solu-
tion of 6b (1.56 g, 1.92 mmol) and vinyltrimethylsilane (563 μL,
3.84 mmol) was added AlMe3 (1.92 mL, 1.03 M in hexane),
resulting in an immediate change of the color to red. After the
reaction mixture was stirred for 3 h, all volatiles were removed
under reduced pressure. To the reaction mixture was added
€
(17) Aksın, O.; Dege, N.; Artok, L.; Turkmen, H.; C-etinkaya, B.
€
Chem. Commun. 2006, 3187–3189.

6540 Organometallics, Vol. 29, No. 23, 2010
Ohashi et al.
hexane, leading to precipitation of (PCy3)Ni(TMSCHdCH2)2,
and the supernatant decanted was concentrated in vacuo. The
resulting residue was dissolved in 3 mL of THF, and the solution
was stirred for 1 day. Removal of volatiles followed by washing
with cold hexane yielded 9b as a white solid (146.5 mg, 25%).
Single crystals suitable for X-ray diffraction analysis were
obtained by recrystallization from THF/pentane at -20 °C.
1H NMR (400 MHz, C6D6, rt, δ/ppm): 0.08 (s, 3H, -AlCH3),
0.70 (s, 9H, -AlOCHC(CH3)3), 5.00 (s, 1H, AlOCHC(CH3)3),
6.8-7.2 (m, 10H, Ph). 13C{1H} NMR (100 MHz, C6D6, rt,
δ/ppm): -12.0 (s, -AlMe), 27.2 (s, -AlOCHC(CH3)3), 37.3 (s,
-AlOCHC(CH3)3), 89.8 (s, -AlOCHC(CH3)3), 125.1 (s, Ph),
127.4 (s, Ph), 128.0 (s, Al(Ph)CdCPh-), 128.78 (s, Ph), 128.81
(s, Ph), 128.9 (s, Ph), 129.7 (s, Ph), 141.4 (s, Ph), 144.9 (s, Ph),
154.2 (s, Al(Ph)CdCPh-). X-ray data for 9b. M = 684.83,
colorless, monoclinic, P21/c (No. 14), a = 18.3171(7) A, b =
10.0174(4) A, c=21.7009(7) A, β=90.4830(11)°, V=3981.8(2)
A3, Z=4, Dcalcd=1.142 g/cm3, T=-150(2) °C, R1 (wR2)=0.046
(0.110).
attributable to the vinyl carbon is obscured by one of the
aromatic carbons at δ 129.3. HRMS (EI): calcd for C19H22O
266.1671, found m/z 266.1674.
Iodinolysis of 9b. To a THF solution (3 mL) of 9b (12.2 mg,
0.02 mmol) was added I2 (15 mg, 0.06 mmol), and the solution
was stirred at room temperature for 6 h. The solution was then
poured into 1 mL of aqueous hydrochloric acid (1.0 M). The
reaction mixture was treated with saturated NaHCO3(aq) and
extracted with diethyl ether. The combined organic layers were
dried by MgSO4, and the solvent was removed under reduced
pressure, giving 11 (15 mg, 92%). 1H NMR (270 MHz, CDCl3,
rt, δ/ppm): 0.90 (s, 9H, - C(CH3)3), 4.89 (s, 1H, -CH(OH)-),
6.9-7.1 (m, 10H, Ph). 13C{1H} NMR (100 MHz, CDCl3, rt, δ/
ppm): 26.8 (s, -C(CH3)3), 37.3 (s, -C(CH3)3), 88.0 (s, -CH-
(OH)-), 126.9 (s, Ph), 127.5 (s, Ph), 127.6 (s, Ph), 129.3 (s, Ph),
129.4 (s, Ph), 130.8 (s, Ph), 130.9 (s, Ph), 137.1 (s, Ph), 144.7 (s,
Ph(I)CdC(Ph)-), 147.4 (s, Ph(I)CdC(Ph)-). HRMS (EI):
calcd for C19H21IO 392.0637, found m/z 392.0633.
Hydrolysis of 9b. A THF solution (3 mL) of 9b (8.8 mg, 0.014
mmol) was poured into 1 mL of aqueous hydrochloric acid
(1.0 M). The reaction mixture was treated with saturated
NaHCO3(aq) and extracted with diethyl ether. The combined
organic layers were dried by MgSO4, and the solvent was
removed under reduced pressure, giving 10ab (7 mg, 87%). 1H
NMR (400 MHz, CDCl3, rt, δ/ppm): 0.92 (s, 9H, -C(CH3)3),
2.17 (s, 1H, -OH), 4.37 (s, 1H, -CH(OH)-), 6.74 (s, 1H,
(Ph)HCdC(Ph)-), 6.93-7.27 (m, 10H, Ph). 13C{1H} NMR
(100 MHz, CDCl3, rt, δ/ppm): 26.8 (s, -C(CH3)3), 36.7 (s,
-C(CH3)3), 84.4 (s, -CH(OH)-), 126.6 (s, Ph), 127.2 (s, Ph),
127.9 (s, Ph), 128.5 (s, Ph), 129.3 (s, Ph), 129.8 (s, Ph), 137.1 (s,
Ph), 140.4 (s, (Ph)HCdC(Ph)-), 144.2 (s, Ph). The resonance
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research (No. 21245028) and Encourage-
ment for Young Scientists (B) (No. 21750102) from MEXT.
S.O. and M.O. acknowledge NAGASE Science and
Technology Foundation and the Japan Petroleum Institute,
respectively, for the Grant for Research.
Supporting Information Available: Detailed experimental
procedures for catalytic reactions, analytical and spectral data
for all new compounds, and crystallographic data (CIF) for 6b,
7a, and 9b. This material is available free of charge via the
Internet at http://pubs.acs.org.