Manganese-Mediated Reactions in Aqueous Media: Chemoselective Allylation and Pinacol Coupling of Aryl Aldehydes

Full text of DOI:10.1021/jo971914f

8632
J . Org. Chem. 1997, 62, 8632-8633
bromide decreased the yield of the allylation product
(36%) under the same reaction conditions. Such a
seemingly abnormal behavior is most likely due to a
competing Wurtz-type coupling of the allyl bromide.9
Throughout the reaction process, no apparent change of
pH value (6-7) of the media was observed. The combined
use of manganese and copper appears critical. No
reaction was observed with either manganese or copper
alone as the metal mediator. Only a catalytic amount of
copper is required for the reaction. The use of a catalytic
amount of Cu(0), Cu(I), or Cu(II) gave the same result.
On the other hand, the use of a stoichiometric amount
of Cu combined with a catalytic amount of Mn (allyl
chloride/Mn/Cu ) 3:0.1:3) provided less than 5% of the
desired product. The use of a catalytic amount of Mn-
(II) or Mn(III) in place of Mn metal completely depressed
the product formation. Subsequently, a variety of alde-
hydes were tested with this allylation method (eq 1).
Ma n ga n ese-Med ia ted Rea ction s in Aqu eou s
Med ia : Ch em oselective Allyla tion a n d
P in a col Cou p lin g of Ar yl Ald eh yd es
Chao-J un Li,* Yue Meng, and Xiang-Hui Yi
Department of Chemistry, Tulane University,
New Orleans, Louisiana 70118
J ihai Ma and Tak-Hang Chan*
Department of Chemistry, McGill University,
Montreal, H3A 2K6, PQ Canada
Received October 16, 1997
The pursuit of synthetic targets with increasing com-
plexity has resulted in the development of reactions
which emphasize chemo-, regio-, diastereo-, and enanti-
oselectivity. In defining strategies and reactions to
construct complex molecules, chemoselectivity is re-
quired.1 Metal-mediated carbonyl addition generally has
a low chemoselectivity among different carbonyls. Re-
cently, the exploration of aqueous medium metal-medi-
ated reactions2 has shown the potential for unusual
chemoselectivity.3 Here, we wish to report an unprec-
edented chemoselectivity related to metal-mediated car-
bonyl addition between aromatic and aliphatic alde-
hydes.4 The allylation of aldehydes5 mediated by
manganese in water in the presence of a catalytic amount
of copper shows exclusive selectivity toward aromatic
aldehydes. Manganese was found to be equally selective
in promoting pinacol-coupling reactions of aryl aldehydes.
The recent interest in aqueous medium metal-medi-
ated carbon-carbon bond formations led to the continu-
ing search for more reactive and selective metal media-
tors for such reactions. As a starting point, we have
studied the use of manganese6 as a potential useful
mediator for metal-promoted reactions. When benzal-
dehyde was stirred with 1 equiv of allyl chloride and a
mixture of manganese-copper7 in water for 8 h at room
temperature, 62% of the corresponding allylation product
was isolated.8 When 3 equiv of allyl chloride and
manganese mediator was used, the isolated yield of the
allylation product increased to 83%. Interestingly, chang-
ing allyl chloride to the usually more reactive allyl
Selected examples are listed in Table 1. It was found
that various aromatic aldehydes were allylated efficiently
by allyl chloride and manganese in water. It is notewor-
thy to mention that aromatic aldehydes bearing halogens
were allylated without any problem (entries 9-11). The
allylation of a hydroxylated aldehyde was equally suc-
cessful (entry 12). On the other hand, aliphatic alde-
hydes are inert under the reaction conditions (entry 15).10
Such an unusual reactivity difference between an aro-
matic aldehyde and an aliphatic aldehyde suggests the
possibility of an unprecedented chemoselectivity.
To test this hypothesis, competitive studies were
carried out between aliphatic and aromatic aldehydes
with different methods (eq 2). By using the present
(1) Trost, B. M. Science 1985, 227, 908.
combination, a single allylation of benzaldehyde was
generated when a mixture of heptaldehyde and benzal-
dehyde was reacted with allyl chloride. Such a selectivity
appears unique; aqueous methodologies mediated by
other metals (Zn, Sn, In) all generated a 1:1 mixture of
allylation products of both aldehydes. A 1:1 mixture of
products was also generated when the allylation was
performed with allylmagnesium bromide11 in ether.
(2) For reviews, see: Li, C. J . Tetrahedron 1996, 52, 5643. Chan,
T. H.; Isaac, M. B. Pure Appl. Chem. 1996, 68, 919. Li, C. J . Chem.
Rev. (Washington, D.C.) 1993, 93, 2023. Lubineau, A.; Auge, J .;
Queneau, Y. Synthesis 1994, 741.
(3) Yanagisawa, A.; Inoue, H.; Morodome, M.; Yamamoto, H. J . Am.
Chem. Soc. 1993, 115, 10356. Petrier, C.; Eihorn, J .; Luche, J . L.
Tetrahedron Lett. 1985, 26, 1449.
(4) For studies toward effecting the selectivity of carbonyl addition
between ketones and aldehydes, see: Reetz, M. T.; Wenderoth, B.
Tetrahedron Lett. 1982, 23, 5259. Okude, Y.; Hirano, S.; Hiyama, T.;
Nozaki, H. J . Am. Chem. Soc. 1977, 99, 3179. Naruta, Y.; Ushida, S.;
Maruyama, K. Chem. Lett. 1979, 919; see also ref 3.
(5) For a recent review, see: Yamamoto, Y. Chem. Rev. (Washington,
D.C.) 1993, 93, 2207.
An intramolecular discrimination study has also been
carried out on a compound bearing both aromatic and
aliphatic carbonyl groups; a complete chemoselectivity
(6) For recent studies on manganese-mediated reactions, see: Cahiez,
C.; Laboue, B. Tetrahedron Lett. 1989, 30, 7369. Hiyama, T.; Obayashi,
M.; Nakamura, A. Organometallics 1982, 1, 1249. Cahiez, G.; Alami,
M. Tetrahedron Lett. 1989, 30, 7373; 1990, 31, 7423. Furstner, A.;
Brunner, H. Tetrahedron Lett. 1996, 37, 7009. Takai, K.; Ueda, T.;
Ikeda, N.; Moriwake, T. J . Org. Chem. 1996, 61, 7990-7991. Takai,
K.; Ueda, T.; Hayashi, T.; Moriwake, T. Tetrahedron Lett. 1996, 37,
7049-7052.
(9) Kasatkin, A. N.; Tsypyshev, O. Y.; Romanova, T. Y.; Tolstikov,
G. A. Organomet. Chem. USSR 1989, 2, 830.
(10) Such a reactivity difference may be originated from the differ-
ence in reductive potentials of aliphatic and aromatic aldehydes.
A
related selectivity was recently observed in the allylation of carbonyl
compounds with an allylmanganese reagent in organic solvent; see:
Cahiez, G. An. Quim. 1995, 91, 561. We thank the reviewer for
pointing out this reference to us.
(7) Commercially available manganese and copper powders were
used directly without pretreatment.
(8) Some allyl chloride was lost during the reaction due to its low
boiling point.
(11) Wakefield, B. J . Organomagnesium Methods in Organic Chem-
istry; Academic Press: New York, 1995.
S0022-3263(97)01914-2 CCC: $14.00 © 1997 American Chemical Society

Communications
J . Org. Chem., Vol. 62, No. 25, 1997 8633
Ta ble 1. Allyla tion of Ald eh yd es Med ia ted by Mn -Cu in
Ta ble 2. P in a col-Cou p lin g of Ald eh yd es Med ia ted by Mn
in Aqu eou s Med iu m
Aqu eou s Med iu m
with manganese in the presence of a catalytic amount of
acetic acid in water, the corresponding pinacol-coupling
product was obtained smoothly. Other aryl aldehydes
(eq 4) were coupled similarly (Table 2). On the other
hand, aryl and aliphatic ketones appeared to be inert
was observed in which the reaction occurs exclusively on
the aromatic carbonyl (eq 3).
under the same reaction conditions, and only the reduced
product was obtained with aliphatic aldehydes.
In conclusion, manganese is highly effective for medi-
ating aqueous medium carbonyl allylations and pinacol-
coupling reactions. This metal offers a higher reactivity
(compared with previously reported ones) and a complete
chemoselectivity toward aromatic aldehydes in the ally-
lation of carbonyl compounds and in pinacol coupling.
The pinacol-coupling reaction is another fundamental
reaction in organic chemistry.12 The pinacol-coupling
reaction in water mediated by Ti(III) has been extensively
studied.13 Other metals such as Zn-Cu have been also
found to promote this reaction under ultrasonic radiation
in aqueous acetone.14 When benzaldehyde was reacted
Ack n ow led gm en t. The research was supported by
the NSF-EPA joint program for a Sustainable Environ-
ment and the Center for Photoinduced Processes (NSF/
LEQSF). Acknowledgment is also made to the donors
of the Petroleum Research Fund, administered by the
ACS, and NSERC for partial support of this research.
(12) For a recent review, see: Wirth, T. Angew. Chem., Int. Ed. Engl.
1996, 35, 61-63.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures for the allylation and pinacol-coupling reactions and
complete characterization of all new compounds reported
herein (2 pages).
(13) For recent publications, see: Gansauer, A. J . Chem. Soc., Chem.
Commun. 1997, 457-458. Barden, C.; Schwartz, J . J . Am. Chem. Soc.
1996, 118, 5484-5485.
(14) Delair, P.; Luche, J . L. J . Chem. Soc., Chem. Commun. 1989,
398.
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