New results on the functionalization of terminal alkenes by cross- metathesis reactions

Article abstract of DOI:10.1055/s-1999-2676

The ruthenium-catalyzed reaction of allylbenzene with several types of alkene provides good yields of the cross-metathesis products regardless of the structural characteristics of the alkene.

Full text of DOI:10.1055/s-1999-2676

LETTER
557
New Results on the Functionalization of Terminal Alkenes by
Cross-metathesis Reactions
Olga M. Blanco, Luis Castedo*
Departamento de Química Orgánica y Unidad Asociada al CSIC, Universidad de Santiago de Compostela, 15706 Santiago de Compostela,
Spain.
Fax +34 (98) 1595012
Received 9 February 1999
benzene with high cross-selectivity and in good yield. We
Abstract: The ruthenium-catalyzed reaction of allylbenzene with
also obtained good results with allylalcohol, allylaceta-
mide and in particular allylbromide. The unprecedented
several types of alkene provides good yields of the cross-metathesis
products regardless of the structural characteristics of the alkene.
achievement of cross-metathesis with this last reagent
Key words: Cross-metathesis, Ruthenium, allylic bromides.
shows that the presence of a neighboring heteroatom is
not strictly necessary for cross-selectivity9.
Although both allylbenzene and the other olefins under-
In the course of our research on sugars we wished to pre-
went self-metathesis when subjected to the reaction con-
pare the mannose derivative 4. Our first approach, involv-
ing a Wittig-Horner reaction between the aldehyde 1 and
the stabilized anion of phosphonate 2, afforded very low
yields whatever the base and reaction conditions used. We
ditions in the absence of a partner14, no significant
amounts of self-metathesis products were detected when
the two partners were present in the above 1:2 ratio; as ex-
pected, when just one equivalent of the second olefin was
then decided to try an intermolecular cross-metathesis
used, the self-metathesis product of allylbenzene was ob-
reaction1, despite the lack of precedents, because the nec-
tained in 20% yield as well as the cross-metathesis prod-
essary precursors are readly prepared. Compound 32 re-
acted with acrolein dimethyl acetal in the presence of 5%
of Grubbs’ catalyst (Cl2(PCy3)2Ru = CHPh; Ru) to give
uct (39%). In conclusion, the cross-metathesis reaction is
favoured under the reaction conditions described above, is
not totally dependent on the structural characteristics of
the alkenes, and constitutes a simple method for function-
compound 4 in 77% yield with a 20:1 E/Z ratio (Scheme
1)3.
alization of a variety of terminal olefins. It should prove
There is considerable uncertainty as to the factors that in-
particularly useful for obtaining primary allylic bromides,
fluence the selectivity of intermolecular metathesis reac-
a type of compound of great synthetic value.
tions: some authors4–6 suggest that electronic factors
predominate, while others7,8 seem to have found that steric
parameters and the influence of neighbouring heteroat-
Table 1. Cross-metathesis reactions of allyl compounds.
oms may be the most important determinants of high se-
lectivity. In view of this, the finding that the reaction of
Scheme 1 was highly selective for cross-metathesis, no
self-metathesis products having been detected, led us to
study this type of process more thoroughly. Using allyl-
benzene as reference alkene and two equivalents of the
alkene partner, we found that the reaction proceeds cross-
selectively for a variety of olefins (Table 1)9. The results
obtained with allyltrimethylsilane and allyloxytrimethyl-
silane are similar to those previously reported by other
authors10,11. However, reports that electron-poor olefins
do not participate in Ru-catalyzed cross-metathesis
reactions12,13 were not corroborated: on the contrary, we
found that acrylonitrile and acrolein couple to allyl-
O
OMe
EtO
P
OMe
EtO
BnO
BnO
BnO
BnO
BnO
BnO
2
1 X=O
base
O
OMe
OMe
O
OMe
OMe
X
2 equiv.
5% Ru
3 X=CH2
OBn
OBn
4
Scheme 1
Synlett 1999, No. 5, 557–558 ISSN 0936-5214 © Thieme Stuttgart · New York

558
O. M. Blanco, L. Castedo
LETTER
1H), 3.33 (s, 6H), 2.47-2.39 (dd, J = 10.87, 6.60 Hz,
Acknowledgement
2H). 13C NMR(128.89-128.03, 103.51, 77.08, 75.70,
75.32, 74.28, 74.17, 73.80, 72.62, 72.52, 71.95, 69.53,
53.33, 53.12, 33.58.
Financial support was provided by the Xunta de Galicia (XUGA
20904B93 and 20906B96). O.B. was funded by a postdoctoral con-
tract with the Spanish MEC. We are also grateful to Dr. J. L. Mas-
careñas for helpful discussions.
(5) Crowe, W. E.; Zhang, Z. J. J. Am. Chem. Soc. 1993, 115,
10998.
(6) Crowe, W. E.; Goldberg, D. R. J. Am. Chem. Soc. 1995, 117,
5162.
(7) Crowe, W. E.; Goldberg, D. R.; Zhang, Z. J. Tetrahedron Lett
1996, 37, 2127
(8) Feng, J.; Schuster, M.; Blechert, S. Synlett, 1997, 129.
(9) Brümmer, O.; Rückert, A.; Blechert, S. Chem. Eur. J. 1997, 3,
441.
(10) Metathesis reactions were carried out following the procedure
described for compound 4. All compounds were characterized
by 1H and 13C NMR, IR and mass spectrometry. E/Z isomer
ratios in the crude final reaction mixture were calculated from
500 MHz NMR integrals, and the major isomer was identified
from the coupling constants of the olefinic hydrogens.
(11) For instance, refluxing allylalcohol in dichloromethane for 16
h in the presence of Ru gave the dimer in 90% yield.
References and Notes
(1) Schuster, M.; Blechert, S. Angew. Chem. Int. Ed. Engl. 1997,
36, 2036-2056.
(2) (a) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413-
4450; (b) El Sukkari, H.; Gesson, J.-P.; Renoux, B.
Tetrahedron Lett 1998, 39, 4043-4046; (c) O’ Leary, D. J.;
Blackwell, H. E.; Washenfelder, R. A.; Grubbs, R. H.
Tetrahedron Lett. 1998, 39, 7427-7430.
(3) Hosomi, A.; Sakata, Y.; Sakurai, H. Tetrahedron Lett. 1984,
25, 2383.
(4) 1-α-Allyl-2,3,4,6-tetra-O-benzyl mannopyranoside (3;
800 mg, 1.42 mmol) and acrolein dimethyl acetal (290
mg, 2.83 mmol) were dissolved in 30 mL of CH2Cl2
under argon. Cl2(PCy3)2Ru = CHPh was added (0.07
mmol, 57 mg) and the mixture was refluxed for 16h.
The solvent was removed under reduced pressure and
the product purified by flash chromatography on silica
gel. Compound 4 was obtained in 77% yield (697 mg)
and 20:1 E/Z ratio. 1H NMR(250 Hz, CDCl3) (7.27-7.09
(m, 20 H), 5.91-5.81 (dt, J = 15.8, 6.60 Hz, 1H), 5.59-
5.50 (dd, J = 15.8, 5.10 Hz, 1H), 4.81-4.72 (dt, J = 7.3,
5.39 Hz, 2H), 4.68-4.57 (m, 7H), 4.17-4.09 (m, 1H),
3.96-3.77 (m, 5H), 3.71-3.67 (dd, J = 4.80, 3.03 Hz,
Article Identifier:
1437-2096,E;1999,0,05,0557,0558,ftx,en;L17898ST.pdf
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Synlett 1999, No. 5, 557–558 ISSN 0936-5214 © Thieme Stuttgart · New York