Transition metal-catalysed acylation of α,β-unsaturated carbonyl compounds with acylstannanes

Article abstract of DOI:10.1039/b105832k

Acylstannanes were found to add to such α,β-unsaturated carbonyl compounds as enones or ynoates in the presence of a nickel or palladium catalyst to give 2-stannyl-4-oxoalk-2-enoates or 1,4-diketones, whereas the three component coupling between acylstannanes, enones and aldehydes provided 2-hydroxymethyl 1,4-diketones.

Full text of DOI:10.1039/b105832k

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Transition metal-catalysed acylation of a,b-unsaturated carbonyl
compounds with acylstannanes
Eiji Shirakawa,*a Youko Yamamoto,a Yoshiaki Nakao,b Teruhisa Tsuchimotoa and Tamejiro
Hiyama*b
a Graduate School of Materials Science, Japan Advanced Institute of Science and Technology, Asahidai,
Tatsunokuchi, Ishikawa 923-1292, Japan. E-mail: shira@jaist.ac.jp
b Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku,
Kyoto 606-8501, Japan
Received (in Cambridge, UK) 3rd July 2001, Accepted 8th August 2001
First published as an Advance Article on the web 13th September 2001
Table 1 Nickel-catalysed acylstannylation of ynoatesa
Acylstannanes were found to add to such a,b-unsaturated
carbonyl compounds as enones or ynoates in the presence of
Entry R1
R2
R3
R4
Time/h Yield (%)b 3+4c
a nickel or palladium catalyst to give 2-stannyl-4-oxoalk-
2-enoates or 1,4-diketones, whereas the three component
coupling between acylstannanes, enones and aldehydes
provided 2-hydroxymethyl 1,4-diketones.
1
2
3
4
5
Ph
Ph
Ph
Ph
Et
Me
Me
Me
Me
Bu
CH3(CH2)4 Me
2.5
3
1.5
24
24
66
85
56
58
47
88+12
98+2
Me3Si
Me
Ph
Et
Me
Et
91+9
66+34
79+21
Well-documented synthetic precursors for five-membered ring
compounds are 1,4-dicarbonyl compounds: furans, pyrroles or
thiophenes are readily prepared by mixing with an acid,1 an
amine2 or a sulfur nucleophile,3 respectively, whereas treatment
of 1,4-diketones with a base gives cyclopentenones.4 On the
other hand, alkenes having a carbonyl group at both of the
carbon atoms behave as good dienophiles in the Diels–Alder
reaction. Although addition of a C–H bond of aldehydes to a,b-
unsaturated carbonyl compounds provides a straightforward
way to 1,4-dicarbonyl compounds,5 the reaction is hard to apply
to synthesis of structurally complex targets. For this purpose,
acylmetalation of a,b-unsaturated carbonyl compounds6 is
apparently beneficial, since metal atoms of resulting organome-
tallic compounds can be replaced by various groups through the
reaction with electrophiles. Here we report the nickel-catalysed
acylstannylation of ynoates,7 the palladium-catalysed addition
of the acyl group of acylstannanes to enones, and the palladium-
catalysed three component coupling between acylstannanes,
enones and aldehydes to give 2-hydroxymethyl 1,4-dike-
tones.8
CH3(CH2)4 Me
a The reaction was carried out in toluene (0.4 mL) at 30 °C using an
acylstannane (0.30 mmol), an ynoate (0.90 mmol) and Ni(cod)2 (15 mmol).
b Isolated yield based on the acylstannane. c Determined by 119Sn NMR.
group. Tributyl(propanoyl)tin (1b) also underwent acylstanny-
lation of 2a (entry 5).
Enones also were found to react with acylstannanes to give
1,4-diketones. However, a palladium complex showed catalytic
activity higher than the nickel complex (Scheme 2). For
example, the reaction of benzoyl(tributyl)tin (1c) with methyl
vinyl ketone (5a) proceeded in the presence of tris(dibenzylide-
neacetone)dipalladium, Pd2(dba)3, in THF at 50 °C for 2 h to
afford 1-phenylpentane-1,4-dione (6a) in 71% yield. Propa-
noylstannane 1b also added to 5a or phenyl vinyl ketone (5b).
An aqueous additive in a stoichiometric amount accelerated the
reaction considerably.
We first examined the reaction of benzoyl(trimethyl)tin (1a)
with methyl oct-2-ynoate (2a) in the presence of 5 mol% of
bis(cycloocta-1,5-diene)nickel, Ni(cod)2. The reaction in tolu-
ene at 30 °C for 2.5 h gave an 88+12 mixture of methyl (Z)-
3-benzoyl-2-trimethylstannyloct-2-enoate (3a) and methyl (E)-
2-benzoyl-3-trimethylstannyloct-2-enoate (4a) in 66% yield
(Scheme 1 and entry 1 of Table 1). Although the reaction in a
more polar solvent such as THF or DMF proceeded with a
perfect preference for 3a over 4a, a considerable amount of the
decarbonylation product, trimethyl(phenyl)tin, also was pro-
duced and the yield of 3a was less than 40%.9 Acylstannylation
of various alkynes with the Ni(cod)2 catalyst was next studied in
toluene (Table 1). In addition to aliphatic ynoates, trimethyl-
silyl- and phenyl-substituted propiolates also can participate in
the reaction with 1a to give regioisomeric mixtures (entries
2–4). The regiochemistry was largely affected by the substituent
on propiolate, where an electron-donating silyl group exhibited
selectivity much higher than an electron-withdrawing phenyl
Scheme 2
Although the SnBu3 group that should be definitely versatile
for further construction of carbon frameworks was lost in the
reaction product with enones, in situ trapping with an
electrophile achieved three component coupling and accord-
ingly indicated the presence of the stannyl group in the product.
Thus acylstannanes, enones and aldehydes reacted in the
presence of a catalytic amount of Pd2(dba)3 to give labile
2-hydroxymethyl 1,4-diketones. As the products easily under-
went a retro-aldol reaction during purification by silica gel
chromatography, the three component coupled products were
isolated after acetylation with acetic anhydride–pyridine
(Scheme 3 and Table 2).
The stannyl group of the ynoate–acylstannylation products
can be easily converted into organic groups through the
palladium-catalysed cross-coupling reaction with organic hal-
ides. Actually, 3a coupled with ethyl 4-iodobenzoate in the
presence of palladium and copper catalysts and gave expected
product 9 with retention of configuration (Scheme 4).
Scheme 1
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Chem. Commun., 2001, 1926–1927
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DOI: 10.1039/b105832k

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Table 2 Palladium-catalysed three component coupling between acyl-
stable alkenylnickel complex 11, which undergoes reductive
elimination to give alkenylstannane 3. In a similar manner,
regioisomer 4 also would be produced. On the other hand,
insertion of an enone may lead to formation of palladium
enolate 12 rather than alkylpalladium complex 12A owing
possibly to relative stability of a Pd–O bond as compared with
a Pd–C bond. Reductive elimination of 12 appears to be
difficult, but the reaction of 12 with such an electrophile as
water or an aldehyde would take place, giving 6 or 8,
respectively.
In conclusion, we have demonstrated that addition of the acyl
group of acylstannanes to ynoates or enones readily takes place
in the presence of a nickel or palladium catalyst. The addition
products are further transformed into 1,4-dicarbonyl com-
pounds having a complicated structure in a separated step or a
tandem reaction. Studies on details of the mechanism as well as
synthetic applications to various unsaturated substrates and
organostannanes are in progress in our laboratories.
stannanes, enones and aldehydesa
Diastereomeric
Time/h Yield (%)b ratio
Entry R1
R5
R6
1
2
3
4
5c
6c
Ph
Ph
Et
Et
Ph
Ph
Me 4-CF3C6H4
1.5
64
37
62
44
44
38
73+27
55+45
51+49
53+47
79+21
69+31
Ph
4-CF3C6H4 24
Me 4-CF3C6H4
1
Ph
4-CF3C6H4
1.5
0.5
1
Me Ph
Me PhCH2CH2
a The reaction was carried out in THF (0.2 mL) at 50 °C using an
acylstannane (0.15 mmol), an enone (0.23 mmol), an aldehyde (0.45 mmol)
and Pd2(dba)3 (3.8 mmol). Then, the reaction mixture was treated with acetic
anhydride (0.68 mmol) and pyridine (0.5 mL) at rt for 2 h. b Isolated yield
based on the acylstannane. c The reaction was carried out in the presence of
Linde molecular sieves Type 4A (60 mg).
We thank the Ministry of Education, Science, Sports and
Culture, Japan, for the Grant-in-Aids for COE Research on
Elements Science, No. 12CE2005 and Scientific Research, No.
12750758. E. S. thanks the Asahi Glass Foundation for financial
support.
Notes and references
1 W. Friedrichsen, Comprehensive Heterocyclic Chemistry II, ed. A. R.
Katritzky, C. W. Rees and E. F. V. Scriven, Pergamon Press, New York,
1996, vol. 2, p. 352.
Scheme 3
2 R. J. Sundberg, Comprehensive Heterocyclic Chemistry II, ed. A. R.
Katritzky, C. W. Rees and E. F. V. Scriven, Pergamon Press, New York,
1996, vol. 2, p. 149.
3 J. Nakayama, Comprehensive Heterocyclic Chemistry II, ed. A. R.
Katritzky, C. W. Rees and E. F. V. Scriven, Pergamon Press, New York,
1996, vol. 2, pp. 641–644.
4 C. H. Heathcock, Comprehensive Organic Synthesis, ed. B. M. Trost and
I. Fleming, Pergamon Press, New York, 1991, vol. 2, pp. 161 and 162.
5 The addition of aldehydes to enones or enoates catalysed by a metal
cyanide or a thiazolium salt: H. Stetter and H. Kuhlmann, Org. React.,
1991, 40, 407.
6 Addition reactions of the acyl group of acylmetals in the presence of a
transition metal catalyst: (a) Y. Hanzawa, N. Tabuchi and T. Taguchi,
Tetrahedron Lett., 1998, 39, 8141; (b) Y. Hanzawa, A. Kakuuchi, M.
Yabe, K. Narita, N. Tabuchi and T. Taguchi, Tetrahedron Lett., 2001, 42,
1737; reactions without transition metal catalysts: (c) E. J. Corey and L.
S. Hegedus, J. Am. Chem. Soc., 1969, 91, 4926; (d) M. P. Cooke Jr. and
R. M. Parlman, J. Am. Chem. Soc., 1977, 99, 5222; (e) L. S. Hegedus and
R. J. Perry, J. Org. Chem., 1985, 50, 4955; (f) M. F. Semmelhack, L.
Keller, T. Sato, E. J. Spiess and W. Wulff, J. Org. Chem., 1985, 50, 5566;
(g) M. Yamashita, H. Tashika and M. Uchida, Bull. Chem. Soc. Jpn.,
1992, 65, 1257.
Scheme 4
The catalytic cycle should be initiated by oxidative addition
of an acylstannane to a nickel(0) or palladium(0) complex as we
discussed previously,7 followed by insertion of a C–C un-
saturated bond to the C–Ni bond of oxidative adduct 10
(Scheme 5). Insertion of an ynoate should afford relatively
7 Transition metal-catalysed acylstannylation of relatively electron-rich
alkynes: (a) E. Shirakawa, K. Yamasaki, H. Yoshida and T. Hiyama,
J. Am. Chem. Soc., 1999, 121, 10221; for 1,3-dienes: (b) E. Shirakawa,
Y. Nakao, H. Yoshida and T. Hiyama, J. Am. Chem. Soc., 2000, 122,
9030; for 1,2-dienes: (c) E. Shirakawa, Y. Nakao and T. Hiyama, Chem.
Commun., 2001, 263. Transition metal-catalysed carbostannylation of
alkynes: (d) E. Shirakawa, H. Yoshida, T. Kurahashi, Y. Nakao and T.
Hiyama, J. Am. Chem. Soc., 1998, 120, 2975; (e) E. Shirakawa, H.
Yoshida, Y. Nakao and T. Hiyama, J. Am. Chem. Soc., 1999, 121, 4290;
(f) E. Shirakawa, H. Yoshida, Y. Nakao and T. Hiyama, Org. Lett., 2000,
2, 2209; (g) H. Yoshida, E. Shirakawa, T. Kurahashi, Y. Nakao and T.
Hiyama, Organometallics, 2000, 19, 5671; (h) H. Yoshida, E. Shirakawa,
Y. Nakao, Y. Honda and T. Hiyama, Bull. Chem. Soc. Jpn., 2001, 74, 637.
See, also ref. 7a.
8 For the three component coupling between acylnickel complexes, enones
and organic halides, see ref. 6f.
9 No carbostannylation product was obtained when 10 mol% of triphenyl-
phosphine, tributylphosphine or pyridine was used as a ligand in a toluene
solvent, and the decarbonylation from 1a predominated.
Scheme 5
Chem. Commun., 2001, 1926–1927
1927