Triisobutylaluminium promoted reductive rearrangement of substituted vinyl ethers to homologous alcohols

Article abstract of DOI:10.1039/b003277h

Substituted vinyl ethers carrying electron-donating groups in the ether moiety undergo smooth oxygen to carbon rearrangement with triisobutylaluminium to afford chain extended alcohols.

Full text of DOI:10.1039/b003277h

Triisobutylaluminium promoted reductive rearrangement of substituted vinyl
ethers to homologous alcohols
Bérengère du Roizel, Matthieu Sollogoub, Alan J. Pearce and Pierre Sinaÿ*
École Normale Supérieure, Département de Chimie, associé au CNRS, 24 rue Lhomond, 75231 Paris Cedex 05,
France. E-mail: Pierre.Sinay@ens.fr
Received (in Liverpool, UK) 25th April 2000, Accepted 26th June 2000
Published on the Web 19th July 2000
Substituted vinyl ethers carrying electron-donating groups
in the ether moiety undergo smooth oxygen to carbon
rearrangement with triisobutylaluminium to afford chain
extended alcohols.
arrangement over the known competitive hydroalumination–
elimination process3 which would afford 3. The TIBAL
promoted reductive rearrangements† of 4 proceeded smoothly
(64–70%) for electron-rich aromatic derivatives 4a and 4b
Lewis acid promoted oxygen to carbon rearrangements of vinyl
acetals have received considerable attention as synthetically
useful procedures.1 For example, we have developed efficient
methodology for the preparation of carbocycles by the reductive
rearrangement of carbohydrate based vinyl acetals using
TIBAL (triisobutylaluminium) as the Lewis acid.2 We recently
reported3 that unsaturated C-aryl glycosides (hex-5-eno-
pyranosides) such as 1, also undergo the analogous TIBAL
promoted rearrangement into carbocycles, provided that the aryl
moiety is sufficiently electron-donating in nature in order to
stabilise the carbocationic centre of the proposed intermediate 2
(Scheme 1). It is noteworthy that 1 is however no longer a vinyl
acetal but a cyclic benzyl vinyl ether. Given that the Lewis acid
promoted rearrangement of acyclic vinyl acetals4 and allyl
benzyl ethers5 has been reported, we reasoned that an acyclic
variant of 1 should also undergo a Lewis acid promoted
rearrangement. Therefore, as part of our evaluation of the wider
scope of the TIBAL promoted reductive rearrangement, we
herein report the first application of this process to the
rearrangement of acyclic non-carbohydrate based systems.
The substituted vinyl ethers 4 were readily prepared by
standard acetylation of the starting alcohols 3 and methylen-
ation using the Tebbe reagent (Scheme 2).
Table 1 Reaction of substituted vinyl ethers with TIBAL
The substituents were chosen in order to stabilise the
proposed carbocation intermediate and therefore favour re-
Scheme 1
DOI: 10.1039/b003277h
Chem. Commun., 2000, 1507–1508
This journal is © The Royal Society of Chemistry 2000
1507

was allowed to warm to room temperature. After ca. 2 h (as indicated by
TLC), the reaction mixture was cooled to 0 °C and distilled water was added
dropwise until no further gas evolution was observed. The reaction mixture
was then filtered (Celite®) and washed with EtOAc. The organic phase was
then diluted with distilled water and extracted twice with EtOAc. The
organic layers were then combined, dried (MgSO4), filtered and the solvent
was removed in vacuo. Purification of the residue by flash chromatography
(cyclohexane–EtOAc) afforded pure 5.
‡ Selected data for 5e: H(400 MHz; CDCl3) 1.26 (d, 3H, J 6.3, CH3), 1.57
(br s, 1H, OH), 1.63–1.78 (m, 2H, FnCH2CH2), 2.42 (ddd, 1H, J 14.5, 9.6
and 6.6, FnCHaHb), 2.51 (ddd, 1H, J 14.5, 9.6 and 6.2, FnCHaHb), 3.86 (m,
1H, CHOH), 4.10–4.12 (m, 4H, 4 HCp), 4.15 (5H, s, 5 HCp); C(100
MHz; CDCl3) 23.6 (CH3), 25.7 (FnCH2), 40.4 (FnCH2CH2), 67.1 (2
Scheme 2 Reagents and conditions: i, Ac2O, pyridine (for 3a,b); AcCl,
Et3N (for 3c,e); AcBr, AcOH, NH3, toluene (for 3d); ii, 2.0 equiv. Tebbe
reagent, 4.0 equiv. pyridine, THF, 45 °C to rt; iii, 5.0 equiv. TIBAL (1 M
in toluene).†
(Table 1). The related non-reductive rearrangement of benzyl
vinyl ethers has been reported as a side-reaction to Claisen
rearrangements under radical6 or forcing thermal conditions.7
The TIBAL promoted rearrangement of diphenylmethyl iso-
propenyl ether (4c) proceeded in excellent yield. In the case of
triphenylmethyl isopropenyl ether (4d), TIBAL rearrangement
was indeed observed, although in only 35% yield, probably due
to steric hindrance. Finally, the ferrocenylmethyl isopropenyl
ether (4e) underwent smooth TIBAL promoted rearrangement
to afford 4-ferrocenylbutan-3-ol (5e)‡ in 60% yield.
In summary, substituted vinyl ethers carrying electron-
donating groups in the ether moiety undergo smooth TIBAL
promoted rearrangement to afford chain extended alcohols. This
approach constitutes a simple three step homologation proce-
dure for benzylic alcohols, carrying electron-donating sub-
stituents in the aromatic nucleus and other alcohols bearing
adjacent electron-donating groups and furthermore illustrates
the more general nature of the TIBAL induced rearrange-
ment.
CCp), 67.8 (CHOH), 67.8 (CCp), 68.0 (CCp), 68.4 (5
CCp), 88.7
(CCpCH2); m/z (CI, NH3) 276 (100%, M + 18); (calc. for C14H18OFe: C,
65.14; H, 7.03; found: C, 65.07; H, 7.19%).
1 Review: H. Frauenrath, Synthesis, 1989, 721; D. J. Dixon, S. V. Ley and
E. W. Tate, J. Chem. Soc., Perkin Trans. 1, 1999, 2665; A. B. Smith, III,
P. R. Verhoest, K. P. Minbiole and J. J. Lim, Org. Lett., 1999, 1, 909;
A. B. Smith, III, K. P. Minbiole, P. R. Verhoest and T. J. Beauchamp,
Org. Lett., 1999, 1, 913.
2 S. K. Das, J.-M. Mallet and P. Sinaÿ, Angew. Chem., Int. Ed. Engl., 1997,
36, 493 and see also M. Frank, R. Miethchen and H. Reinke, Eur. J. Org.
Chem., 1999, 1259; A. J. Pearce, M. Sollogoub, J.-M. Mallet and P.
Sinaÿ, Eur. J. Org. Chem., 1999, 2103; A. J. Pearce, J.-M. Mallet and P.
Sinaÿ, Heterocycles, 2000, 52, 819; M. Sollogoub, A. J. Pearce, A.
Hérault and P. Sinaÿ, Tetrahedron: Asymmetry, 2000, 11, 283; A. J.
Pearce, R. Chevalier, J.-M. Mallet and P. Sinaÿ, Eur. J. Org. Chem.,
2000, 2203.
3 M. Sollogoub, J.-M. Mallet and P. Sinaÿ, Angew. Chem., Int. Ed., 2000,
39, 362.
We thank the European Community for a TMR Marie Curie
Research Training Grant (#ERBFMBICT983225) to A. J. P.
4
X.-P. Gu, I. Ikeda and M. Okahara, J. Org. Chem., 1988, 53, 2737.
5 J. Wennerberg, F. Ek, A. Hansson and T. Frejd, J. Org. Chem., 1999, 64,
54; J. Wennerberg, L. Eklund, M. Polla and T. Frejd, Chem. Commun.,
1997, 445.
Notes and references
6 A. W. Burgstahler, L. K. Gibbons and I. C. Nordin, J. Chem. Soc., 1963,
† Typical procedure: TIBAL (1 M in toluene, 5 equiv.) was added to a
stirred solution of starting material 4 in dry toluene (1 mL/100 mg), at 0 °C
under argon. The cooling bath was then removed and the reaction mixture
4986.
7 W. J. Le Noble, P. J. Crean and B. Gabrielsen, J. Am. Chem. Soc., 1964,
86, 1649.
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Chem. Commun., 2000, 1507–1508