Intermolecular addition reaction to alkenes of acylmolybdenum complexes generated by oxidative addition of aryl or alkenyl halides with molybdenum(0) carbonyl complexes

Article abstract of DOI:10.1055/s-2007-973858

Acylmolybdenum species, generated by oxidative addition of aryl or alkenyl halides with molybdenum(0) carbonyl complex followed by carbon monoxide insertion, added to various kinds of alkenes intermolecularly to give simple addition products in good yields without formation of carbonylative Heck-type products. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-973858

LETTER
929
Intermolecular Addition Reaction to Alkenes of Acylmolybdenum
Complexes Generated by Oxidative Addition of Aryl or Alkenyl Halides
with Molybdenum(0) Carbonyl Complexes
Intermolecular
Ad
e
dition Reac
n
tion to
A
lken
i
es of
A
c
cylmolybd
h
enumComp
ilexes ro Sangu, Toru Watanabe, Jun Takaya, Nobuharu Iwasawa*
Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
Fax +81(3)57342931; E-mail: niwasawa@chem.titech.ac.jp
Received 18 January 2007
O
M(CO)6
Abstract: Acylmolybdenum species, generated by oxidative addi-
tion of aryl or alkenyl halides with molybdenum(0) carbonyl com-
plex followed by carbon monoxide insertion, added to various kinds
of alkenes intermolecularly to give simple addition products in good
yields without formation of carbonylative Heck-type products.
R-[M]-X
RX
oxidative
addition
CO
insertion
R
[M]-X
1
[M] = M(CO)n
acylmetal
intermediate A
O
M = group 6 metals
R = aryl, alkenyl
protonation
Key words: molybdenum hexacarbonyl, acylmolybdenum, oxida-
tive addition of aryl or alkenyl halides
R
R'
R'
3
O
[M]
X
R'
insertion
R
β-hydride
R'
O
elimination
alkylmetal
intermediate B
The generation of acyl transition metal species and their
addition to alkenes is one of the most useful methods in
the preparation of various ketones through Umpolung.1 In
the generation of acyl transition metal species, most of the
reported methods employ addition of a highly nucleo-
philic organometallic species to a carbonyl ligand,2 acyla-
tion of an anionic transition metal species,3 oxidative
addition of acyl derivatives,4,5,6 and metal exchange be-
tween acyl metals and transition metal complexes.7
R
4
Scheme 1
We first examined the reaction of iodobenzene (1a) and
ethyl acrylate (2a) with group 6 metal carbonyl complexes
(Table 1). After screening the reaction conditions,16
Mo(CO)6 was found to be the best promoter for this reac-
tion among the group 6 metals examined (Table 1, entries
1–3). When a mixture of 1a, 2a (10.0 equiv) and Mo(CO)6
(1.0 equiv) was heated in DMF at 160 °C, the desired
addition product 3a was obtained in 73% yield without
formation of the b-hydride elimination product 4a
(Table 1, entry 2). It should be noted that this is a rare
example of a Mo(CO)6-promoted transformation of an
sp2-carbon–halogen bond through oxidative addition.
On the other hand, oxidative addition of aryl or alkenyl
halides to low valent, late transition metal complexes such
as Pd(0) followed by carbon monoxide insertion is a well
known process to generate acyl transition metals.8
However, they usually give olefinic addition products in
the reaction with alkenes through b-hydride elimination
(carbonylative Heck reaction).9,10 Thus, to our knowledge,
there are no reports of the simple intermolecular addition
reaction11 onto alkenes using acyl transition metals gener-
ated by oxidative addition of aryl or alkenyl halides fol-
lowed by carbon monoxide insertion.12
Table 1 Examination of Group 6 Metals
M(CO)6 (1.0 equiv)
Ph-I
+
CO2Et
2a (10.0 equiv)
O
We expected that the use of low-valent, early transition
metals would be suitable for such reactions since the high-
er polarity of early transition metal–carbon bonds would
favor protonation over b-hydride elimination. According-
ly, we have chosen group 6 metal carbonyls as possible
promoters due to their reducing ability (Scheme 1).13,14
DMF, 160 °C, 6 h
1a
O
+
Ph
CO2Et
Ph
CO2Et
3a
4a
In this paper, we report the first example of Mo(CO)6-pro-
moted intermolecular addition reactions of acyl metals
leading to various aryl–alkyl or alkenyl–alkyl ketones in
good yields without formation of b-hydride elimination
products.15
Entry
M(CO)6
Cr(CO)6
Mo(CO)6
W(CO)6
Yield of 3a (%) Yield of 4a (%)
1
2
3
~7
73
5
0
0
0
SYNLETT 2007, No. 6, pp 0929–0933
0
3.
0
4.
2
0
0
7
Advanced online publication: 26.03.2007
DOI: 10.1055/s-2007-973858; Art ID: U00407ST
© Georg Thieme Verlag Stuttgart · New York

930
K. Sangu et al.
LETTER
Table 2 Reaction of Various Aryl and Alkenyl Halides
Table 2 Reaction of Various Aryl and Alkenyl Halides (continued)
Mo(CO)6
(1.0 equiv)
Mo(CO)6
(1.0 equiv)
O
O
O
O
+
+
+
R-X
+
CO2Et
R-X
CO2Et
R
CO2Et Ph
CO2Et
R
CO2Et Ph
CO2Et
DMF,
160 °C
DMF,
160 °C
3a
4a
3a
4a
1
2a
(10.0 equiv)
1
2a
(10.0 equiv)
Entry
R–X
Time (h)
Yield (%)
Entry
17
R–X
Time (h)
1
Yield (%)
Br
Br
R'
I
52 (3q)
1
2
3
4
5
6
7
8
9
R¢ = H (1a)
6
6
1
6
1
1
4
6
6
73 (3a)
65 (3b)
59 (3c)
68 (3d)
74 (3e)
77 (3f)
60 (3g)
67 (3h)
66 (3i)
(1q)
R¢ = OMe (1b)
R¢ = Me (1c)
18
1
50 (3r)c
Ph
(1r)b
R¢ = Cl (1d)
a The reaction was performed at 120 °C.
R¢ = CF3 (1e)
b A mixture of E/Z isomers (84:16) was employed.
c The product was obtained as a mixture of E/Z isomers (93:7).
R¢ = CO2Me (1f)
R¢ = COMe (1g)
R¢ = OPiv (1 h)
R¢ = NHPiv (1i)
Table 2 shows the range of halides that this reaction toler-
ates.17 Aryl iodides 1b–e bearing an electron-donating or
electron-withdrawing substituent at the para position pro-
vided the corresponding ketones 3b–e in good yields
(Table 2, entries 2–5). Various functional groups such as
ketone, ester, amide and pivaloyl-protected amino and hy-
droxy groups were tolerated under these reaction condi-
tions (Table 2, entries 6–10). Sterically demanding o-
iodotoluene (1l) and 1-iodonaphthalene (1m) also partici-
pated in the addition reaction (Table 2, entries 12 and 13).
It is of note that the reaction of a bromo derivative, 1-bro-
monaphthalene (1n) proceeded with a somewhat pro-
longed reaction time without lowering the yield (Table 2,
entry 14). Importantly, heteroaromatic and alkenyl ha-
lides were also employable as substrate and synthetically
useful heteroaromatic ketones and a,b-unsaturated ke-
tones 3o–r were obtained in reasonable yields (Table 2,
entries 15–18).
CON
R' =
10
4
74 (3j)
(1j)
I
11
1
66 (3k)
(1k)
(1l)
I
12
13
1
1
60 (3l)
I
We also examined a range of olefinic counterparts
(Table 3). 1-Iodonaphthalene (1m) and a variety of elec-
tron-deficient alkenes such as ethyl methacrylate (2b)
cyclopentenone (2c) and benzyl acrylate (2d) were sub-
jected to the molybdenum-promoted addition reaction and
the corresponding g-ketoesters 5b–d were obtained in
good yield (Table 3, entries 1–3). Although the use of eth-
yl crotonate provided 5e in low yield (Table 3, entry 4),
acrylonitrile (2f), which often causes deactivation of tran-
sition metals due to its strong coordinating ability, was ap-
plicable to the reaction to give g-ketonitrile 5f in moderate
yield (Table 3, entry 5). Importantly, this reaction could
be applied not only to electron-deficient alkenes but also
to styrenes and vinylsilane 2g–j (Table 3, entries 6–9).
Even the simple alkene 2k could be used in this reaction
although the formation of a small amount of the regio-
isomer was detected (Entry 10).
78 (3m)
(1m)
(1n)
Br
14
6
71 (3n)
S
15
4
7
52 (3o)
51 (3p)
Br
(1o)
(1p)
O
I
16a
In order to obtain information on the reaction mechanism,
we carried out deuterium labeling studies. The reaction of
1m and alkenes 2a or 2g in the presence of three equiva-
Synlett 2007, No. 6, 929–933 © Thieme Stuttgart · New York

LETTER
Intermolecular Addition Reaction to Alkenes of Acylmolybdenum Complexes
931
Table 3 Reaction with Various Alkenes
lents of D2O under a carbon monoxide atmosphere18 re-
vealed that deuterium incorporation was observed at both
of the methylene protons of 3m (X = 33%, Y = 58%) and,
surprisingly, only at the Y position of 5g (X = <5%,
Y = 72%) (Table 4, entries 1 and 2). Moreover, the reac-
tion with styrene–b,b-d2 gave further insight into the
mechanism. Ketone 5g contained deuterium at both the X
and Y positions with >95% deuterium incorporation
(Table 4, entry 3).
Mo(CO)6 (1.0 equiv)
DMF, 160 °C, 1 h
+
product(s)
Ar-I
alkene
2 (10.0 equiv)
1m
Ar = 1-naphthyl
Entry Alkene
Product
Yield (%)
O
1
2
3
65
66
79
CO2Et
Ar
CO2Et
Table 4 Deuterium Labeling Experiment
(2b)
(5b)
CO (1 atm)
I
O
H
X
O
O
Mo(CO)6 (1.0 equiv)
O
+
alkene
R
DMF, 160 °C, 1 h
(5.0 equiv)
Ar
H
Y
(2c)
(5c)
1m
3m or 5g
O
CO2Bn
Deuterium
(2d)a
Ar
CO2Bn
CO2Et
incorp. (%)a
(5d)
Entry Alkene
1
Additive
Yield (%)
X
Y
O
D2O (3.0 equiv)
58 (3m)
33
58
CO2Et
CO2Et
Ar
4
5
(2e)
26
59
(2a)
2
3
D2O (3.0 equiv)
none
56 (5g)b
64 (5g)
<5
72
(5e)
Ph
(2g)
O
O
CN
>95 >95
D
(2f)a,b
Ar
CN
Ph
(5f)
D
(2g-b,b-d2)
a The amount of deuterium incorporation was determined by 1H NMR.
b Determined by 1H NMR.
Ar
R
R
These results strongly indicate that in the reaction with
styrene, isomerization of alkylmolybdenum intermediate
B is occurring through rapid b-hydride elimination and
successive hydrometallation to form molybdenum enolate
C, which is then protonated by the small amount of water
present in DMF as shown in Scheme 2.19,20,21 In the case
of the reaction with ethyl acrylate, protonation could also
occur from alkylmolybdenum intermediate B through its
enolate, and thus both X and Y are partially deuterated.
6
7
8
R = H (2g)
R = H (5g)
61
69
51
R = OMe (2h)
R = Cl (2i)
R = OMe (5h)
R = Cl (5i)
O
SiPh3
(2j)a,c
9
51
Ar
SiPh3
(5j)
10
43
Ph
O
(5k:5k¢ =
Ph
(2k)c
Ar
O
86:14)d,e
Mo(CO)6
R–[Mo]–X
RX
(5k)
CO
insertion
oxidative
addition
R
[Mo]-X
[Mo] = Mo(CO)n
acylmolybdenum
intermediate A
O
Ar
Ph
O
O
R
[Mo]-X
R'
R'
R
R'
(5k¢)
insertion
β-hydride elimination
and
hydrometallation
[Mo]-X
a 3.0 equivalents of alkene were used.
b The reaction was carried out for 5 h.
c The reaction was carried out for 6 h.
alkylmolybdenum
intermediate B
O[Mo]-X
O
d The ratio of regioisomers was determined by 1H NMR.
e A small amount of the b-hydride elimination product was detected
protonation
R
R'
R
R'
(<2%).
molybdenum enolate
intermediate C
Scheme 2
Synlett 2007, No. 6, 929–933 © Thieme Stuttgart · New York

932
K. Sangu et al.
LETTER
Finally, we extended this method to the intramolecular re-
action for the preparation of synthetically useful indanone
and a-tetralone derivatives. As shown in Table 5, o-io-
dostyrene derivatives 6 and o-substituted iodobenzene de-
rivatives bearing a tethered a,b-unsaturated ester moiety 8
gave the desired indanone and a-tetralone derivatives in
good yields (Table 5, entries 1–4). It should be noted that
even simple alkenes tethered to an iodobenzene ring react-
ed smoothly in this intramolecular reaction to give cy-
clized ketones in high yields (Table 5, entries 5 and 6). In
contrast to the palladium-catalyzed reaction,22 this reac-
tion allows the use of 1,2-disubstituted alkenes as sub-
strates and a 6-exo mode of cyclization leading to an a-
tetralone skeleton. This molybdenum-promoted method-
ology could become a useful method in the construction
of substituted indanone and tetralone frameworks.
Acknowledgment
This research was partly supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science,
and Technology of Japan.
References and Notes
(1) (a) Wittig, G.; Davis, P.; Koenig, G. Chem. Ber. 1951, 84,
627. (b) Seebach, D. Angew. Chem., Int. Ed. Engl. 1979, 18,
239.
(2) (a) Corey, E. J.; Hegedus, L. S. J. Am. Chem. Soc. 1969, 91,
4926. (b) Hegedus, L. S.; Perry, R. J. J. Org. Chem. 1985,
50, 4955. (c) Seyferth, D.; Weinstein, R. M.; Wang, W.-L. J.
Org. Chem. 1983, 48, 1144. (d) Seyferth, D.; Hui, R. C. J.
Am. Chem. Soc. 1985, 107, 4551. (e) Söderberg, B. C.;
York, D. C.; Harriston, E. A.; Caprara, H. J.; Flurry, A. H.
Organometallics 1994, 13, 4501. (f) Söderberg, B. C.;
York, D. C. Organometallics 1994, 13, 4501.
(3) (a) Cooke, M. P. Jr.; Parlman, R. M. J. Am. Chem. Soc. 1975,
97, 6863. (b) Cooke, M. P. Jr.; Parlman, E. A. J. Am. Chem.
Soc. 1977, 99, 5222. (c) DeShong, P.; Silder, D. R.;
Rybczynski, P. J.; Slough, G. A.; Rheingold, A. L. J. Am.
Chem. Soc. 1988, 110, 2575.
(4) For the activation of acid chlorides, see: (a) Hori, K.; Ando,
M.; Takaishi, N.; Inamoto, Y. Tetrahedron Lett. 1987, 28,
5883. (b) Andersson, C.-M.; Hallberg, A. J. Org. Chem.
1988, 53, 4257.
(5) For the activation of acid anhydrides, see: (a) Oguma, K.;
Miura, M.; Satoh, T.; Nomura, M. J. Organomet. Chem.
2002, 648, 297. (b) Hong, Y.-T.; Barchuk, A.; Krische, M. J.
Angew. Chem. Int. Ed. 2006, 45, 6885.
(6) For the activation of aldehydes, see: (a) Schwartz, J.;
Cannon, J. B. J. Am. Chem. Soc. 1974, 96, 4721.
(b) Marder, T. B.; Roe, D. C.; Millstein, D. Organometallics
1988, 7, 1451. (c) Willis, M. C.; McNally, S. J.; Beswick, P.
J. Angew. Chem. Int. Ed. 2004, 43, 340. (d) Willis, M. C.;
Randell-Sly, H. E.; Woodward, R. L.; Currie, G. S. Org.
Lett. 2005, 7, 2249. (e) Jo, E.-A.; Jun, C.-H. Eur. J. Org.
Chem. 2006, 2504. (f) Beller, M.; Seayad, J.; Tillack, A.;
Jiao, H. Angew. Chem. Int. Ed. 2004, 43, 3368; and
references cited therein.
(7) (a) Yamane, M.; Kubota, Y.; Narasaka, K. Bull. Chem. Soc.
Jpn. 2005, 78, 331. (b) Hanzawa, Y.; Tabuchi, N.; Saito, K.;
Noguchi, S.; Taguchi, T. Angew. Chem. Int. Ed. 1999, 38,
2395; and references cited therein.
(8) Tsuji, J. Palladium Reagents and Catalysts, Chap. 3.5; John
Wiley: Chester, 2004, 265; and references cited therein.
(9) For the palladium-catalyzed intermolecular carbonylative
Heck reaction, see: Satoh, T.; Itaya, T.; Okuro, K.; Miura,
M.; Nomura, M. J. Org. Chem. 1995, 60, 7267; see also, ref
4.
(10) For the palladium-catalyzed intramolecular carbonylative
Heck reaction, see: (a) Hayashi, T.; Tang, J.; Kato, K. Org.
Lett. 1999, 1, 1487. (b) Negishi, E.; Ma, S.; Amanfu, J.;
Copéret, C.; Miller, J. A.; Tour, J. M. J. Am. Chem. Soc.
1996, 118, 5919.
(11) There are few examples of intermolecular nucleophlic
addition reactions of acyl late-transition-metal intermediates
to olefins to give addition products, for reference, see:
(a) Sauthier, M.; Castanet, Y.; Mortreux, A. Chem.
Commun. 2004, 1520. (b) Shirakawa, E.; Yamamoto, Y.;
Nakao, Y.; Tsuchimoto, T.; Hiyama, T. Chem. Commun.
2001, 1926. (c) Biavati, A.; Chiusoli, G. P.; Costa, M.;
Terenghi, G. Transition Met. Chem. 1979, 4, 398; see also
ref. 7b.
Table 5 Preparation of Indanone and a-Tetralone Derivatives
Mo(CO)6 (1.0 equiv)
substrate
product(s)
DMF, 160 °C, 3–17 h
Entry Substrate
Product
Yield (%)
I
O
R
R
1
2
R = H (6a)
R = H (7a)
52
60
R = Me (6b)a
R = Me (7b)
O
CO2Et
I
CO2Et
n
n
3
4
n = 0 (8a)
n = 1 (8b)
I
n = 0 (9a)
76
73
n = 1 (9b)
O
R
R
5
6
R = H (10a)
R = H (7b)b
50
75
R = Me (10b)c
R = Me (11b)b,d
a 6b was added dropwise over 1 h.
b A small amount of the 6-endo cyclization product was obtained
(<3%).
c The reaction was performed in the presence of 3.0 equiv of H2O.
d The b-hydride elimination product was obtained in 4%.
In summary, we have developed the first example of an
intermolecular addition reaction of an acylmetal species
generated by oxidative addition of aryl or alkenyl halides
to Mo(CO)6. Although the reaction employs a stoichio-
metric amount of Mo(CO)6, a variety of substituted
ketones could be obtained starting from easily available
materials. Further development into a catalytic version of
this reaction is now in progress in our laboratory.
Synlett 2007, No. 6, 929–933 © Thieme Stuttgart · New York

LETTER
Intermolecular Addition Reaction to Alkenes of Acylmolybdenum Complexes
933
(12) Recently, Larock et al. reported a palladium-catalyzed
intramolecular carbonylation of o-iodostyrene derivatives,
see: (a) Gagnier, S. V.; Larock, R. C. J. Am. Chem. Soc.
2003, 125, 4804. See also: (b) Wu, X.; Nilsson, P.; Larhed,
M. J. Org. Chem. 2005, 70, 346.
J = 7.1 Hz, 2 H), 7.45–7.65 (m, 3 H), 7.87 (d, J = 7.7 Hz, 1
H), 7.94 (d, J = 7.3 Hz, 1 H), 7.99 (d, J = 8.4 Hz, 1 H), 8.60
(d, J = 8.6 Hz, 1 H); 13C NMR (75 MHz, CDCl3): d = 14.15,
28.65, 36.64, 60.65, 124.31, 125.73, 126.39, 127.48, 127.85,
128.31, 130.03, 132.61, 133.87, 135.61, 172.80, 202.25; IR
(KBr): 2981, 1732, 1684 cm–1; Anal Calcd for C16H16O3: C,
74.98; H, 6.29. Found: C, 74.69; H, 6.39.
(13) For molybdenum(0)-catalyzed allylic substitution reactions
via oxidative addition of allylic halide equivalents, see:
(a) Trost, B. M.; Lautens, M. J. Am. Chem. Soc. 1982, 104,
5543. (b) Trost, B. M.; Hachiya, I. J. Am. Chem. Soc. 1998,
120, 1104. (c) Belda, O.; Moberg, C. Acc. Chem. Res. 2004,
37, 159. (d) Malkov, A. V.; Gouriou, L.; Lloyd-Jones, G. C.;
Stary, I.; Langer, V.; Spoor, P.; Vinader, V.; Kocovsky, P.
Chem. Eur. J. 2006, 12, 6910; and references cited therein.
(14) Richmond et al. reported that the chelation-assisted
oxidative addition of Ar–X to W(CO)3(EtCN)3 proceeded
smoothly to give air-stable, seven-coordinate tungsten(II)
complexes. However, this reaction was limited to specific
aryl halides bearing a bidentate or tridentate chelating group
and was not applied to synthetic reactions, see:
1-(Naphthalen-1-yl)-3-(4-methoxyphenyl)propan-1-one
(5h)
1H NMR (300 MHz, CDCl3): d = 3.09 (t, J = 7.7 Hz, 2 H),
3.36 (t, J = 7.7 Hz, 2 H), 3.79 (s, 3 H), 6.84 (d, J = 8.7 Hz, 2
H), 7.18 (d, J = 8.7 Hz, 2 H), 7.43–7.66 (m, 3 H), 7.81 (d,
J = 7.3 Hz, 1 H), 7.87 (d, J = 7.8 Hz, 1 H), 7.98 (d, J = 8.3
Hz, 1 H), 8.54 (d, J = 8.5 Hz, 1 H); 13C NMR (75 MHz,
CDCl3): d = 29.74, 44.10, 55.25, 113.93, 124.33, 125.76,
126.41, 127.31, 127.82, 128.36, 129.36, 130.10, 132.48,
133.11, 133.93, 136.08, 158.00, 203.72; IR (KBr): 3048,
1681, 1247 cm–1; Anal Calcd for C20H18O2: C, 82.73; H,
6.25. Found: C, 82.49; H, 6.42.
(a) Richmond, T. G.; King, M. A.; Keison, E. P.; Arif, M. A.
Organometallics 1987, 6, 1995. (b) Buffin, B. P.; Arif, A.
M.; Richmond, T. G. J. Chem. Soc., Chem. Commun. 1993,
1432.
2-Ethyl-1-indanone (11b)
1H NMR (300 MHz, CDCl3): d = 1.01 (t, J = 7.5 Hz, 3 H),
1.49–1.60 (m, 1 H), 1.90–2.05 (m, 1 H), 2.55–2.66 (m, 1 H),
2.82 (dd, J = 3.8, 17.4 Hz, 1 H), 3.32 (dd, J = 7.9, 17.4 Hz, 1
H), 7.36 (t, J = 7.6 Hz, 1 H), 7.46 (d, J = 7.6 Hz, 1 H), 7.58
(t, J = 7.6 Hz, 1 H), 7.75 (d, J = 7.6 Hz, 1 H); 13C NMR (75
MHz, CDCl3): d = 11.60, 24.46, 32.32, 48.75, 123.83,
126.53, 127.28, 134.60, 136.96, 153.82, 208.97; IR (KBr):
2961, 1709 cm–1; Anal Calcd for C11H12O: C, 82.46; H, 7.55.
Found: C, 82.70; H, 7.54.
(15) Larhed et al. reported the palladium-catalyzed carbonylation
of aryl halides using Mo(CO)6 as a carbonyl source, see: Wu,
X.; Ekegren, J. K.; Larhed, M. Organometallics 2006, 25,
1434; and references cited therein, see also ref 12b.
(16) The use of other solvents such as THF, 1,4-dioxane, toluene
and dibutyl ether at reflux temperature resulted in low
conversion.
(17) Typical Procedure: A mixture of aryl iodide 1m (51 mg, 0.20
mmol), Mo(CO)6 (53 mg, 0.20 mmol) and ethyl acrylate (2a,
0.22 mL, 2.0 mmol) was heated in DMF at 160 °C for 1 h
under an Ar atmosphere. After complete consumption of the
aryl iodide 1m was confirmed by TLC, the reaction was
quenched at r.t. with phosphate buffer (pH 7). The product
was extracted with Et2O (4 ×) and the combined organic
extracts were washed with brine and dried over MgSO4. The
solvent was removed under reduced pressure and the residue
was purified by preparative TLC (silica gel, hexane–EtOAc,
5:1) to afford product 3m (40 mg, 78%).
(18) 3m and 5g were obtained in lower yield in the absence of
CO.
(19) For an example of a related mechanism, see: Qian, H.; Pei,
T.; Widenhoefer, R. A. Organometallics 2005, 24, 287; see
also ref 12a.
(20) No H–D exchange was observed when partially deuterated
ketone 5g was heated in DMF at 160 °C.
(21) We tried the reaction using D2O for the quenching but no
deuterium incorporation in the product was observed. Thus,
at present, we believe that the molybdenum enolate
intermediate is protonated during the reaction by the small
amount of water present in DMF.
Spectral Data for Selected Compounds
(22) Palladium-catalyzed intramolecular carbonylative
cyclization was limited to terminal olefins in the case of
indanone synthesis, see ref 12.
Ethyl 4-(naphthalen-1-yl)-4-oxobutanoate (3m)
1H NMR (300 MHz, CDCl3): d = 1.28 (t, J = 7.1 Hz, 3 H),
2.83 (t, J = 6.6 Hz, 2 H), 3.37 (t, J = 6.6 Hz, 2 H), 4.19 (q,
Synlett 2007, No. 6, 929–933 © Thieme Stuttgart · New York

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