Protic solvent-promoted neutral allylation of aldehydes and ketones with 1,8-bis(allylstannyl)naphthalenes

Article abstract of DOI:10.1055/s-1998-1679

The allylation reactions of carbonyl compounds using 1,8-bis(dibutylstannyl)naphthalene 1 (R = Bu) were dramatically promoted by using a mixture of THF and CF₃CH₂OH (5 : 1) as solvent. The rate acceleration was due to the enhancement

Full text of DOI:10.1055/s-1998-1679

April 1998
SYNLETT
377
Protic Solvent-Promoted Neutral Allylation of Aldehydes and Ketones with 1,8-
Bis(allylstannyl)naphthalenes
*
Naoki Asao, Noriko Abe, Zheng Tan, and Keiji Maruoka
Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
Fax: +81-11-746-2557; E-mail: maruoka@sci.hokudai.ac.jp
Received 19 January 1998
Abstract: The allylation reactions of carbonyl compounds using 1,8-
bis(dibutylstannyl)naphthalene 1 (R = Bu) were dramatically promoted
by using a mixture of THF and CF CH OH (5 : 1) as solvent. The rate
3
2
acceleration was due to the enhancement of the Brønsted acidity of
CF CH OH by the formation of the chelate complex 6 (R = CH CF )
3
2
2
3
resulting from the chelation effect of two neighboring tin atoms.
Recently we reported that 1,8-bis(allylstannyl)naphthalenes 1 are
extremely effective allylation agents for aldehydes and ketones under
neutral conditions without any catalyst since they take advantage of the
chelation-induced Lewis acidity of bidentate bis(stannyl) compounds as
1
shown in 2. This neutral allylation can be executed even in aqueous
media for highly reactive aldehydes such as α-keto and α-halo
aldehydes, which usually exist as hydrates, hemiacetals or as an aqueous
2
solution. This observation prompted us to examine the solvent effect
on the rate acceleration of the neutral allylation with 1,8-
With this information at hand, the allylations of 1 (R = Bu) in the
mixture of CF CH OH and THF (volume ratio = 1:5) were carried out
with several carbonyl substrates and the results are recorded in Table 2.
bis(allylstannyl)naphthalenes 1. Here we wish to report a new, protic
3
2
3
solvent-promoted neutral allylation of carbonyl compounds.
5
1
2
Allylation of benzaldehyde
4
(R
=
Ph,
R
= H) with 1,8-
bis(allyldibutylstannyl)naphthalene 1 (R = Bu) was carried out at 60 °C
for 3.5 h in various solvents (eq 1) and selected results are summarized
in Table 1. Since one of two allyl groups of 1 was transferred to
carbonyl compounds, the chemical yields of allylation products were
calculated based on the amount of 1. In THF solvent, allylation is very
Since the present allylation can be accelerated in protic solvents to a
greater extent than in the polar, aprotic DMSO, the polarity of solvents
is apparently not an important factor. Assuming that the chelate
1
2
sluggish and furnishes homoallylic alcohol 5 (R = Ph, R = H) in only
10% yield (entry 1). Addition of DMSO to THF slightly increased the
complex 6 (R = CH CF ) between 1 (R = Bu) and CF CH OH would
2
3
3
2
rate of allylation (entry 2). Use of the protic solvents MeOH and H O
2
be formed by the latent Lewis acidity of bis(stannyl) group of 1 (R =
Bu ), this chelation should induce the activation of carbonyl substrates
greatly via the effective hydrogen bonding between the carbonyl group
and the coordinated solvent, thereby promoting the allylation reaction
gave better results (entries 3 and 4), and in particular, addition of 17%
CF CH OH in THF (vol ratio, 1:5) markedly enhanced the rate of
3
2
allylation (entry 6). It should be noted that attempted allylation of
benzaldehyde with monoallylic stannane
conditions resulted in total recovery of benzaldehyde. However,
3
under these reaction
through the eight-membered transition state as depicted in 7 (R =
4
6
CH CF ).
2
3
increasing the volume ratio of CF CH OH in THF further enhanced the
3
2
1
2
yield of homoallylic alcohol 5 (R = Ph, R = H) (entries 7 and 8),
thereby providing a synthetically useful allylation procedure, though the
1
corresponding monostannane 3 also gave the allylated product 5 (R =
2
Ph, R = H) in 1~37% yield.

378
LETTERS
SYNLETT
In summary, we have developed a new type of protic solvent-promoted
allylation reaction using 1,8-bis(dibutylstannyl)naphthalene. The rate
acceleration was due to the enhancement of the Brønsted acidity of
(4) Attempted allylation of benzaldehyde with 1-(allyldibutyl-
stannyl)naphthalene in place of 3 gave similar results.
(5) The allylation of benzaldehyde is representative (entry 1 in Table
CF CH OH by the formation of the chelate complex 6 (R = CH CF ) as
3
2
2
3
2): To a solution of 1 (R = Bu) (337 mg, 0.50 mmol) in 1.2 mL of
7
a result of the chelation effect of two neighboring tin atoms. Although
further investigation is needed to establish the mechanism, it is clear that
THF/CF CH OH (vol. ratio = 5:1) was added benzaldehyde (0.25
3
2
mL, 2.5 mmol) at room temperature under Ar. The mixture was
allowed to warm to 60 °C, and stirred for 3.5 h at this temperature.
After cooling to room temperature, the mixture was directly
applied to column chromatography on basic silica gel using a
mixture of hexane and EtOAc (5:1) as eluent to give 1-phenyl-3-
the use of 1 in the mixture of CF CH OH and THF provides a mild and
3
2
convenient procedure for the neutral allylation of carbonyl compounds.
References and Notes
1
2
buten-1-ol, 5 (R = Ph, R = H) (61 mg, 82% yield) as a colorless
(1) Asao, N.; Liu, P.; Maruoka, K. Angew. Chem., Int. Ed. Engl.
1997, 36, 2507.
oil.
(2) Reviews on the reactivity of allylstannane: a) Yamamoto, Y.
Aldrichim. Acta 1987, 20, 45; b) Yamamoto, Y. Acc. Chem. Res.
1987, 20, 243; c) Hull, C.; Mortlock, S. V.; Thomas, E. J.
Tetrahedron 1989, 45, 1007; d) Nishigaichi, Y.; Takuwa, A.;
Naruta, Y.; Maruyama, K. ibid. 1993, 49, 7395.
(6) The similar eight-membered transition state was suggested in the
reaction of tetraallyltin with aldehydes in methanol: See ref. 3.
(7) Brønsted acid catalyzed allylations: a) Denmark, S. E.; Weber, E.
J.; Wilson, T. M.; Willson, T. M. Tetrahedron 1989, 45, 1053;
b) Gevorgyan, V.; Kadota, I.; Yamamoto, Y. Tetrahedron Lett.
1993, 34, 1313.
(3) a) Cokley, T. M.; Marshall, R. L.; McCluskey, A.; Young, D. J.
Tetrahedron Lett. 1996, 37, 1905; b) Cokley, T. M.; Harvey, P. J.;
Marshall, R. L.; McCluskey, A.; Young, D. J. J. Org. Chem. 1997,
62, 1961.