Direct allylation of benzyl alcohols, diarylmethanols, and triarylmethanols mediated by XtalFluor-E

Article abstract of DOI:10.1016/j.tetlet.2016.12.056

We report the direct allylation of benzyl alcohols, diarylmethanols and triarylmethanols mediated by XtalFluor-E using allyltrimethylsilane. The resulting allylated products are obtained in moderate to high yield.

Full text of DOI:10.1016/j.tetlet.2016.12.056

Accepted Manuscript
Direct allylation of benzyl alcohols, diarylmethanols, and triarylmethanols
mediated by XtalFluor-E
Thomas Lebleu, Jean-François Paquin
PII:
S0040-4039(16)31694-X
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.12.056
TETL 48468
Reference:
Tetrahedron Letters
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Revised Date:
Accepted Date:
2 December 2016
14 December 2016
19 December 2016
Please cite this article as: Lebleu, T., Paquin, J-F., Direct allylation of benzyl alcohols, diarylmethanols, and
triarylmethanols mediated by XtalFluor-E, Tetrahedron Letters (2016), doi: http://dx.doi.org/10.1016/j.tetlet.
2016.12.056
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Direct allylation of benzyl alcohols,
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XtalFluor-E.
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Thomas Lebleu, Jean-François Paquin

1
Tetrahedron Letters
Direct allylation of benzyl alcohols, diarylmethanols, and triarylmethanols
mediated by XtalFluor-E
Thomas Lebleu, Jean-François Paquin
CCVC, PROTEO, Département de chimie, 1045 avenue de la Médecine, Université Laval, Québec, QC, Canada G1V 0A6
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
We report the direct allylation of benzyl alcohols, diarylmethanols and
triarylmethanols mediated by XtalFluor-E using allyltrimethylsilane. The resulting
allylated products are obtained in moderate to high yield.
2009 Elsevier Ltd. All rights reserved.
Available online
Keywords:
Benzyl alcohols
Diarylmethanols
Triarylmethanols
Allylation
Diethylaminodifluorosulfinium tetrafluoroborate
The reagent XtalFluor-E, [(Et2NSF2)BF4], was initially
developed as a safer alternative to diethylaminosulfur trifluoride
(DAST) and related derivatives for deoxofluorination reactions.1
Over the years, we2 as well as others3 have exploited this reagent
as a promoter for a number of transformations. In particular, we
have recently reported its use as a stand-alone promoter for the
SN1 reaction of benzyl alcohols using arenes as nucleophiles (Fig.
1).2f In this Friedel-Crafts benzylation, a benzyl alcohol (1; R1, R2
= H) or diarylmethanol (1; R1 = Ar1, R2 = H) reacts with
XtalFluor-E
to
initially
generate
an
alkoxy-N,N-
diethylaminodifluorosulfane (2).1,4 The latter ionizes to generate
a benzylic carbocation (3)5 that react with the aromatic
nucleophile to generate the 1,1-diarylmethane (4; R1, R2 = H) or
1,1,1-triarylmethane (4; R1 = Ar1, R2 = H).
As a potential extension of this work, we wondered if it would
be possible to intercept the carbocationic intermediate 3 with
other -nucleophiles.6 Herein, we report that allyltrimethylsilane
is a competent nucleophile and its use allows the allylation of
benzyl alcohols (1; R1, R2 = H), diarylmethanols (1; R1 = Ar1,
R2 = H), and triarylmethanols (1; R1 = Ar1, R2 = Ar2) to produce,
as shown in Figure 1, allylated products (5)7,8,9 that are useful,
versatile and valuable synthetic intermediates.
Figure 1. Previous and current work.
We initially tested the conditions used for the Friedel-Crafts
benzylation2f on 4-phenylbenzyl alcohol (6), replacing the
aromatic nucleophile with allyltrimethylsilane to obtain the
desired allylated product 7 in 65% yield (Scheme 1). Further
optimization (amount of allyltrimethylsilane, ratio of
CH2Cl2/HFIP, and temperature) did not improve the yield, so the
conditions shown in Scheme 1 were used for the rest of the study.
———
 Corresponding author. Tel.: +1-418-656-2131 #11430; fax: +1-418-656-7916.
E-mail: jean-francois.paquin@chm.ulaval.ca (J.-F. Paquin)

2
Tetrahedron
The use of diarylmethanols was next examined as we expected
that the addition of a second aryl group would further stabilize
the carbocation and thus favour ionization over the undesired
reaction of the intermediate with residual starting material. As
shown in Table 2, moderate to excellent yield (65-96%) of the
corresponding allylated products (18-33) could be obtained for a
wide range of diarylmethanols. This selection included substrates
bearing an electron-rich or an electron-poor aryl substituent. For
substrates bearing strong electron withdrawing groups (CF3, SF5),
slightly more forcing conditions (CH2Cl2/HFIP (1:1) at rt, or
DCE/HFIP (1:1) at 65 °C) were required.
Scheme 1. Initial result.
The allylation of benzyl alcohols was first investigated
(Table 1). Under the standard conditions, electron-rich benzyl
alcohols provided the desired products (8-10) in moderate to
excellent yields (60-87%). However, when using electron-poor
benzyl alcohols, much lower yields of the allylated products (11-
13) were obtained (26-30%).
Table 1
Table 2
Allylation of benzyl alcohols with allyltrimethylsilane promoted
by XtalFluor-E.
Allylation of diarylmethanols with allyltrimethylsilane promoted
by XtalFluor-E.
In the case of electron-poor benzyl alcohols (15, R = EWG),
the corresponding dibenzylether (17 in Figure 2) was observed as
a major side product by NMR analysis of the crude mixture. We
hypothesize that for electron-rich benzyl alcohols (i.e., R =
EDG), reaction with XtalFluor-E would provide the alkoxy-N,N-
diethylaminodifluorosulfane intermediate 16 that would rapidly
ionize to the carbocation 18 (path leading to the desired allylated
product). In the case of electron-poor benzyl alcohol (i.e., R =
EWG), a slower ionization of intermediate 16 would leave
enough time for its reaction with the remaining benzyl alcohol
(15) to produce 17 via a SN2 reaction10 and thus becoming a
competitive reaction pathway (Figure 2).
a Reaction time was 24 h.
b The reaction was conducted in DCE/HFIP (1:1) at 65 °C.
c The solvent was CH2Cl2/HFIP (1:1).
Finally, the reaction was examined using triarylmethanols as
substrates and the results are shown in Table 3. The desired
allylated products (34-38) were obtained in moderate to excellent
yields (50-91%). Both electron-donating (Me, MeO) and
Figure 2. Dibenzylether derivatives (17) as a major side
products and proposed mechanism for their formation.

3
electron-withdrawing (Cl, CF3) groups were tolerated on the
starting triarylmethanols.
(e) Keita, M.; Vandamme, M.; Mahé, O.; Paquin, J.-F.
Tetrahedron Lett. 2015, 56, 461–464. (f) Desroches, J.;
Champagne, P. A.; Benhassine, Y.; Paquin, J.-F. Org. Biomol.
Chem. 2015, 13, 2243–2246. (g) Keita, M.; Vandamme, M.;
Paquin, J.-F. Synthesis 2015, 47, 3758–3766.
(a) Cochi, A.; Gomez Pardo, D.; Cossy, J. Org. Lett. 2011, 13,
4442–4445. (b) Orliac, A.; Gomez Pardo, D.; Bombrun, A.;
Cossy, J. Org. Lett. 2013, 15, 902–905. (c) Liu, X.; Cheng, S.;
Wang, X.; Xue, W. Synthesis 2013, 45, 3103–3105. (d) Lu, D.-F.;
Liu, G.-S.; Zhu, C.-L.; Yuan. B.; Xu, H. Org. Lett. 2014, 16,
2912–2915. (e) Nonn, M.; Kiss, L.; Haukka, M.; Fustero, S.;
Fülöp, F. Org. Lett. 2015, 17, 1074–1077. (f) Davies, S. G.;
Fletcher, A. M.; Frost, A. B.; Roberts, P. M.; Thomson, J. E. Org.
Lett. 2015, 17, 2254–2257. (g) Brandstätter, M.; Roth, F.;
Luedtke, N. W. J. Org. Chem. 2015, 80, 40–51.
Table 3
Allylation of triarylmethanols with allyltrimethylsilane promoted
by XtalFluor-E.
3.
4.
5.
Sutherland, A.; Vederas, J. C. Chem. Commun. 1999, 1739–1740.
For recent examples where benzylic carbocation intermediates are
involved, see: (a) Onodera, G.; Yamamoto, E.; Tonegawa, S.;
Iezumi, M.; Takeuchi, R. Adv. Synth. Catal. 2011, 353, 2013–
2021; (b) Liébert, C.; Brinks, M. K.; Capacci, A. G.; Fleming, M.
J.; Lautens, M. Org. Lett. 2011, 13, 3000–3003; (c) King, F. D.;
Aliev, A. E.; Caddick, S.; Tocher, D. A. J. Org. Chem. 2013, 78,
10938–10946; (d) Pan, X.;. Li, M.; Gu, Y. Chem. Asian J. 2014, 9,
268–274.
6.
7.
8.
For scales of -nucleophilicity in C–C bond-forming reactions, see
Mayr, H.; Kempf, B.; Ofial, A. R. Acc. Chem. Res. 2003, 36, 66–
77 and references therein.
a The reaction was conducted in DCE/HFIP (1:1) at 65 °C.
b The reaction was conducted in DCE/HFIP (9:1) at 65 °C.
For an example of allylation of benzyl alcohols and derivatives
using a stoichiometric activator, see Kabalka, G. W.; Yao, M.-L.;
Borella, S.; Goins, L. K. Organometallics 2007, 26, 4112–4114.
For selected examples of catalytic allylation of benzyl alcohols
and derivatives, see (a) Kaur, G.; Kaushik, M.; Trehan, S.
Tetrahedron Lett. 1997, 38, 2521–2521. (b) Saito, T.; Yasuda, M.;
Baba, A. Synlett 2005, 1737–1739. (c) Saito, T.; Nishimoto, Y.;
Yasuda, M.; Baba, A. J. Org. Chem. 2006, 71, 8516–8522. (d)
Han, J.; Cui, Z.; Wang, J.; Liu, Z. Synth. Commun. 2010, 40,
2042–2046. (e) Kumar, G. G. K. S. N.; Laali, K. K. Org. Biomol.
Chem. 2012, 10, 7347–7355. (f) Hassner, A.; Bandi, C. R. Synlett
2013, 1275–1279. (g) Fan, X.; Cui, X.-M.; Guan. Y.-H.; Fu, L.-
A.; Lv, H.; Guo. K.; Zhu. H.-B. Eur. J. Org. Chem. 2014, 498–
501. (h) Saito, M.; Tsuji, N.; Kobayashi, Y.; Takemoto, Y. Org.
Lett. 2015, 17, 3000–3003. (i) Orizu, I.; Bolshan, Y. Tetrahedron
Lett. 2016, 57, 5798–5800.
In terms of the mechanism, since allyltrimethylsilane possess
nucleophilic parameters6 similar to the ones of the aromatic
nucleophiles used in the Friedel-Crafts benzylation of benzyl
alcohols and diarylmethanols promoted by XtalFluor-E,2f we
hypothesize that both transformations proceed through a similar
mechanism as shown in Figure 1.
In summary, we have reported the direct allylation of benzyl
alcohols, diarylmethanols and triarylmethanols mediated by
XtalFluor-E using allyltrimethylsilane.
Acknowledgments
9.
For other synthetic access to similar products, see (a) Mahoney, S.
J.; Lou, T.; Bondarenko, G.; Fillion, E. Org. Lett. 2012, 14, 3474–
3477. (b) Wang, G.-Z.; Jiang, J.; Bu, X.-S.; Dai, J.-J.; Xu, J.; Fu,
Y.; Xu, H.-J. Org. Lett. 2015, 17, 3682–3685. (c) Sha, S.-C.;
Jiang, H.; Mao, J.; Bellomo, A.; Jeong, S. A.; Walsh, P. J. Angew.
Chem. Int. Ed. 2016, 55, 1070–1074. (d) Kawashima, H.; Ogawa,
N.; Saeki, R.; Kobayashi, Y. Chem. Commun. 2016, 52, 4918–
4921.
We thank Olivier Laflamme and Pier Alexandre Champagne
(Université Laval) for some initial experiments. This work was
supported by the Natural Sciences and Engineering Research
Council of Canada, OmegaChem and the Université Laval.
10. The formation of di(3-phenylpropyl)ether from the reaction of 3-
phenylpropan-1-ol with XtalFluor-E has been reported previously
(see ref. 1b) and it was proposed that the ether was formed by the
SN2 attack of the alkoxy-N,N-diethylaminodifluorosulfane
intermediate by the unreacted alcohol. We assume a similar
mechanism here, although we cannot exclude a SN1 pathway.
Supplementary Material
Supplementary data associated with this article can be found,
in the online version, at …
References and notes
1.
2.
(a) Beaulieu, F.; Beauregard, L.-P.; Courchesne, G.; Couturier,
M.; Laflamme, F.; L’Heureux, A. Org. Lett. 2009, 11, 5050–5053.
(b) L’Heureux, A.; Beaulieu, F.; Bennet, C.; Bill, D. R.; Clayton,
S.; Laflamme, F.; Mirmehrabi, M.; Tadayon, S.; Tovell, D.;
Couturier, M. J. Org. Chem. 2010, 75, 3401–3411. (c) Mahé, O.;
L’Heureux, A.; Couturier, M.; Bennett, C.; Clayton, S.; Tovell,
D.; Beaulieu, F.; Paquin, J.-F. J. Fluorine Chem. 2013, 153, 57–
60.
(a) Pouliot, M.-F.; Angers, L.; Hamel, J.-D.; Paquin, J.-F. Org.
Biomol. Chem. 2012, 10, 988–993. (b) Pouliot, M.-F.; Angers, L.;
Hamel, J.-D.; Paquin, J.-F. Tetrahedron Lett. 2012, 53, 4121–
4123. (c) Pouliot, M.-F.; Mahé, O.; Hamel, J.-D.; Desroches, J.;
Paquin, J.-F. Org. Lett. 2012, 14, 5428–5431. (d) Mahé, O.;
Desroches, J.; Paquin, J.-F. Eur. J. Org. Chem. 2013, 4325–4331.

HIGHLIGHTS




XtalFluor-E mediates the direct allylation of benzylic alcohols derivatives.
Benzyl alcohols, diarymethanols, and triarylmethanols can be used as substrates.
A wide range of allylated products can be obtained in moderate to excellent yield.
For electron-poor benzyl alcohols, dibenzylethers are observed as major side products.