Pd0/SnII promoted Barbier-type allylation and crotylation of sulfonimines

Article abstract of DOI:10.1016/j.tetlet.2007.07.201

A one-pot Barbier protocol is described for the facile formation of homoallyl sulfonamides from sulfonimines and allyl or crotyl bromide in the presence of SnCl₂, and catalytic Pd₂(dba)₃·CHCl₃ at room temperature.

Full text of DOI:10.1016/j.tetlet.2007.07.201

Tetrahedron Letters 48 (2007) 7177–7180
Pd0/SnII promoted Barbier-type allylation and crotylation
of sulfonimines
Ujjal Kanti Roy and Sujit Roy*
Organometallics and Catalysis Laboratory, Chemistry Department, Indian Institute of Technology, Kharagpur 721302, India
Received 28 May 2007; revised 19 July 2007; accepted 30 July 2007
Available online 2 August 2007
Abstract—A one-pot Barbier protocol is described for the facile formation of homoallyl sulfonamides from sulfonimines and allyl or
crotyl bromide in the presence of SnCl2, and catalytic Pd2(dba)3ÆCHCl3 at room temperature.
Ó 2007 Elsevier Ltd. All rights reserved.
Addition of allyl, propargyl or allenylstannanes to
organic electrophiles such as aldehydes, imines and
epoxides is a well-known tool for carbon–carbon bond
formation in organic chemistry. The far-reaching utility
of these reagents have led to the development of Bar-
bier-like protocols wherein reactive organostannanes
are generated in situ from Sn(0/II/IV).1 It is now well
demonstrated that the generation of allyltin(IV) from
Sn(II) in a Barbier fashion is considerably easier in the
presence of a catalytic d8/d10 transition metal.2 A major
event in the catalytic cycle involves facile allyl transfer
from the transition metal to tin. We and others have suc-
cessfully delineated the strategy for regioselective allyl-
ation, propargylation and allenylation of carbonyls and
epoxides.2–4 In this communication we demonstrate the
further utility of the concept in Barbier-like allylations
of conjugatively stabilized imines in general, and sulfon-
imines in particular, under ambient conditions leading to
the corresponding homoallylamine derivatives.
However, there are no such reports in the realm of tin
chemistry.
Initially we attempted to allylate a set of N-substituted
imines derived from benzaldehyde (Scheme 1). The
reactions were conducted in a one-pot Barbier fashion
utilizing the reagent combination of catalytic Pd2(dba)3Æ
CHCl3, allyl bromide and SnCl2 in dry DCM at room
temperature. The reaction of N-benzylbenzaldimine 1a
led to the isolation of the desired N-benzyl homoallyl-
amine 2a in only 11% yield, along with 68% of the cor-
responding homoallyl alcohol and traces of N,N-diallyl
benzylamine. On the other hand N-phenylbenzaldimine
1b yielded 33% of homoallylamine 2b besides homoallyl
alcohol (40%), and N,N-diallyl aniline (trace). Similar
reaction of N-(4-nitrophenyl)benzaldimine 1c yielded
39% of homoallylamine 2c along with homoallyl alcohol
(30%). Gratifyingly, the reactions of N-benzoylbenzald-
imine 1d, and N-tosylbenzaldimine 1e, were facile and
free from side reactions, and were complete within
14 h. Work-up gave the desired homoallyl benzamide
2d, and homoallyl sulfonamide 2e in 81% and 89%
Homoallylamines are important building blocks for the
preparation of synthetically and biologically important
compounds such as b-amino acids, 1,3-amino alcohols,
1-amino-3,4-epoxides, pyrrolidines and piperidines.5
The most frequently employed methodology for the syn-
thesis of homoallylamines is the allylation of imines with
an allyl-metal reagent.6,7 To our knowledge, there are
only very few reports of facile one-pot, Barbier-like imine
allylations using an allyl halide, the metal reagent being
Mg(0), Zn(0), In(0), Ga(0), Sm(0) or Zn(0)/In(III).8
R'
N
R'
HN
Br
Pd2(dba)3.CHCl3, SnCl2, DCM
Ph
1
Ph
º
Mol sieve 4 A, room temp.
2
1a, R' = PhCH2-
2a, 11%
2b, 33%
2c, 39%
2d, 81%
2e, 89%
1b, R' = Ph-
1c, R' = p-NO2Ph-
1d, R' = PhC(O)-
1e, R' = p-TolSO2-
*
Corresponding author. Tel.: +91 3222 283338; fax: +91 3222
282252; e-mail: sroy@chem.iitkgp.ernet.in
Scheme 1. Allylation of N-substituted benzaldimines.
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.07.201

7178
U. K. Roy, S. Roy / Tetrahedron Letters 48 (2007) 7177–7180
Table 1. One-pot Barbier allylation of sulfonimine 1e: effect of
yields, respectively. The above results indicate that con-
jugatively stabilized imines are better tuned for the pres-
ent Barbier allylation reaction. Due to their ease of
preparation and hydrolytic stability, henceforth we
chose sulfonimines for further study.
catalysta
Entry
Catalyst
Yield of 2e (%)
1
2
3
4
5
6
7
8
9
Pd2(dba)3ÆCHCl3
Pd(dba)2
PdCl2
89
71
Trace
35
17
21
0
25
36
From the screening of various late transition metal cat-
alysts for the allylation of sulfonimine 1e (Table 1),
Pd2(dba)3ÆCHCl3 was adjudged to be the best. Also in
our case, dichloromethane was found to be a better
solvent than THF, benzene, diethyl ether, and DCE.
Attempted reaction with SnCl2 dihydrate gave 56%
of 2e, while reaction in DCM–water (1:1 v/v) led to the
formation of homoallyl alcohol as the major product.
Pd(PPh3)4
PdCl2(MeCN)2
PdCl2(PPh3)2
NiCl2(PPh3)2
PtCl2(PPh3)2
CuCl(SMe2)
a Reagents and conditions: allyl bromide (2 mmol), SnCl2 (1.5 mmol),
˚
catalyst (1 mol %), mol sieve 4 A, sulfonimine (1 mmol).
Table 2. One-pot Barbier allylation and crotylation of sulfoniminesa
Entry
Sulfonimine
Product
% Yield (syn/anti)
Ts
NH
NTs
1
89
1e
2e
Ts
NH
NTs
1f
2
3
4
83
88
80
2f
Cl
Cl
Ts
NH
NH
NTs
1g
O2N
2g
O2N
MeO
Ts
NTs
1h
2h
MeO
Me
Ts
NH
NTs
1i
5
6
7
8
9
84
2i
Me
Ts
NH
NTs
NTs
1j
82
2j
Cl
Cl
Ts
NH
76 (61/39)
72 (71/29)
70 (46/54)
1e
2k
Me
Ts
NH
NTs
1f
2l
Cl
Me
NH
Cl
Ts
NTs
1g
2m
O2N
Me
O2N
Ts
NH
NTs
1j
10
65 (70/30)
2n
Cl
Me
Cl
a Reagents and conditions: bromide (2 mmol), SnCl2 (1.5 mmol), Pd2(dba)3ÆCHCl3 (1 mol %), mol sieve 4 A, sulfonimine (1 mmol).
˚

U. K. Roy, S. Roy / Tetrahedron Letters 48 (2007) 7177–7180
7179
2793; (c) Marshall, J. A. Chem. Rev. 2000, 100, 3163–
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0
Pd / SnCl
2
SnCl Br
2
(I)
Br
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N
R
N
4-tolSO
2
Cl BrSn
2
4-tolSO
2
H O
2
N
O
S
H
R
R
2
(II)
O
4-tol
Scheme 2. Proposed pathway for the allylation of sulfonimines.
Using the optimized parameters, the reaction of allyl
bromide was tested with various sulfonimines (Table
2). The reactions were complete in 13–17 h. Sulfon-
imines 1e–j derived from substituted aromatic aldehydes
gave the corresponding homoallylamines 2e–n as the
exclusive products, and in good to excellent yields (en-
tries 1–10). It should be noted that both electron donat-
ing and withdrawing substituents on the aromatic ring
are amenable to the reaction. The reaction of crotyl bro-
mide with sulfonimines 1e–g and 1j resulted in forma-
tion of the corresponding homoallylamines 2k–n with
100% c-regioselectivity, but in varying syn/anti ratios
(entries 7–10).
5. (a) Felpin, F.-X.; Girard, S.; Vo-Thanh, G.; Robins, R. J.;
Villieras, J.; Lebreton, J. J. Org. Chem. 2001, 66, 6305–
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While mechanistic explorations are warranted, a sug-
gestion is postulated in Scheme 2. Prior formation of
allyltrihalostannane I from allyl bromide and Pd(0)/
Sn(II) occurs via the well-known pathway involving
oxidative addition of allyl bromide across palladium
and insertion of SnCl2, followed by reductive elimina-
tion.2 Subsequently, the allyltin(IV) species could be
activated by the sulfonimine via N-, and O-coordina-
tion as in six-membered transition state II.9 Concomi-
tant SE20 attack followed by hydrolysis would furnish
the homoallylamine.
7. Selected recent references on imine allylation under non-
Barbier conditions: allyl-Mg/Zn: (a) Jain, R. P.; Williams,
R. M. J. Org. Chem. 2002, 67, 6361–6365; (b) Sluis, M. V.
D.; Dalmolen, J.; Lange, B. D.; Kaptein, B.; Kellogg, R.
M.; Broxterman, Q. B. Org. Lett. 2001, 3, 3943–3946; (c)
Jones, P.; Knochel, P. J. Org. Chem. 1999, 64, 186–195; (d)
El-Shehawy, A. A.; Omara, M. A.; Ito, K.; Itsuno, S.
Synlett 1998, 367–368; allyl-B: (e) Wada, R.; Shibuguchi,
T.; Makino, S.; Oisaki, K.; Kanai, M.; Shibasaki, M. J.
Am. Chem. Soc. 2006, 128, 7687–7691; (f) Solin, N.;
Wallner, O. A.; Szabo, K. J. Org. Lett. 2005, 7, 689–691; (g)
Itsuno, S.; Yokoi, A.; Kuroda, S. Synlett 1999, 1987–1989;
allyl-Si: (h) Rabbat, P. M. A.; Valdez, S. C.; Leighton, J. L.
Org. Lett. 2006, 8, 6119–6121; (i) Friestad, G. K.;
Korapala, C. S.; Ding, H. J. Org. Chem. 2006, 71, 281–
289; (j) Shimizu, M.; Itou, H.; Miura, M. J. Am. Chem.
Soc. 2005, 127, 3296–3297; (k) Yamasaki, S.; Fujii, K.;
Wada, R.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc.
2002, 124, 6536–6537; (l) Billet, M.; Klotz, P.; Mann, A.
Tetrahedron Lett. 2001, 42, 631–634; (m) Wang, D.-K.;
Zhou, Y.-G.; Tang, Y.; Hou, X.-L.; Dai, L.-X. J. Org.
Chem. 1999, 64, 4233–4237; (n) Nakamura, K.; Nakamura,
H.; Yamamoto, Y. J. Org. Chem. 1999, 64, 2614–2615;
allyl-Sn: (o) Colombo, F.; Annunziata, R.; Benaglia, M.
Tetrahedron Lett. 2007, 48, 2687–2690; (p) Li, G.-I.; Zhao,
G. Synthesis 2006, 3189–3194; (q) Wallner, O. A.; Olsson,
V. J.; Eriksson, L.; Szabo, K. J. Inorg. Chim. Acta 2006,
359, 1767–1772; (r) Szabo, K. J. Synlett 2006, 811–824; (s)
Das, B.; Laxminarayana, K.; Ravikanth, B.; Ramarao, B.
Tetrahedron Lett. 2006, 47, 9103–9106; (t) Yin, Y.; Zhao,
G.; Li, G.-L. Tetrahedron 2005, 61, 12042–12052; (u)
Fernandes, R. A.; Stimac, A.; Yamamoto, Y. J. Am. Chem.
Soc. 2003, 125, 14133–14139; (v) Aspinall, H. C.; Bissett, J.
S.; Greeves, N.; Levin, D. Tetrahedron Lett. 2002, 43, 323–
325; (w) Fang, X.; Johannsen, M.; Yao, S.; Gathergood,
N.; Hazell, R. G.; Jorgensen, K. A. J. Org. Chem. 1999, 64,
4844–4849; (x) Nakamura, H.; Nakamura, K.; Yamamoto,
Y. J. Am. Chem. Soc. 1998, 120, 4242–4243.
In summary, we have presented a Pd(0)/SnCl2 mediated
Barbier-type allylation of imines.10 Due to the opera-
tional simplicity and mild conditions, this one-pot
allylation is expected to be attractive, and useful.
Investigations are underway to broaden the scope using
other conjugated imine systems possessing donor atoms.
Acknowledgements
S.R. thanks the DST for financial support. U.K.R.
thanks the UGC for a fellowship.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2007.07.201.
References and notes
1. Reviews: (a) Li, C.-J. Chem. Rev. 2005, 105, 3095–3165;
(b) Denmark, S. E.; Fu, J. Chem. Rev. 2003, 103, 2763–

7180
U. K. Roy, S. Roy / Tetrahedron Letters 48 (2007) 7177–7180
8. For imine allylation under Barbier conditions, see: (a)
5 min at room temperature. Anhydrous SnCl2 (285 mg,
1.5 mmol) and N-tosyl anisaldimine 1h (289 mg, 1 mmol)
were added to the resulting solution sequentially and the
reaction was allowed to stir for 15 h at room temperature
(TLC monitoring: silica gel, eluent: n-hexane–EtOAc 8:2).
Upon completion, the molecular sieves were filtered off,
DCM was removed, and aq NH4F (10%, 5 mL) was
added, followed by saturated aq sodium bicarbonate
until the mixture was slightly alkaline. The organic
product was extracted with ethyl acetate, washed with
water, brine, and dried over anhydrous sodium sulfate.
Solvent removal under reduced pressure followed by
column chromatography over silica gel 60–120 (gradient
elution with EtOAc–hexane 8% to 12%) afforded the
desired N-[1-(4-methoxyphenyl)-but-3-enyl]-4-methyl-benz-
enesulfonamide 2h (265 mg, 80% with respect to N-tosyl
Law, M. C.; Cheung, T. W.; Wong, K.-Y.; Chan, T. H. J.
Org. Chem. 2007, 72, 923–929; (b) Sun, X.-W.; Xu, M.-H.;
Lin, G.-Q. Org. Lett. 2006, 8, 4979–4982; (c) Vilaivan, T.;
Winotapan, C.; Banphavichit, V.; Shinada, T.; Ohfune, Y.
J. Org. Chem. 2005, 70, 3464–3471; (d) Andrews, P. C.;
Peatt, A. C.; Raston, C. L. Tetrahedron Lett. 2004, 45,
243–248; (e) Yanada, R.; Negoro, N.; Okaniwa, M.;
Ibuka, T. Tetrahedron 1999, 55, 13947–13956; (f) Negoro,
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2003, 44, 667–670.
9. For chelation assisted allylation of N-tert-butylsulfinyl
aldimines, see: (a) Foubelo, F.; Yus, M. Tetrahedron:
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1
anisaldimine 1h). H NMR (400 MHz, CDCl3): d 2.37 (s,
3H), 2.40–2.48 (m, 2H), 3.75 (s, 3H), 4.31 (dd, 1H,
J = 13.2 Hz, J = 6.8 Hz), 5.04 (br d, 3H, J = 12.4 Hz),
5.45–5.55 (m, 1H), 6.69 (d, 2H, J = 8.4 Hz), 6.98 (d, 2H,
J = 8.4 Hz), 7.15 (d, 2H, J = 8.4 Hz), 7.55 (d, 2H,
J = 8 Hz); 13C NMR (100 MHz, CDCl3): d 21.44, 41.81,
55.2, 56.66, 113.65, 119.06, 127.13, 127.72, 129.26,
132.36, 133.25, 137.46, 142.97, 158.79; HRMS (ESI):
calcd for C18H21NO3SNa [M+Na]+ = 354.1140; found,
354.1144.
10. General procedure: The procedure given below was
followed in all cases. All products show satisfactory 1H,
13C NMR, and HRMS data, which are given in the
Supplementary data. Synthesis of N-[1-(4-Methoxyphen-
yl)-but-3-enyl]-4-methyl-benzenesulfonamide (2h): Allyl
bromide (242 mg, 2 mmol, 0.17 mL), Pd2(dba)3ÆCHCl3
˚
(10 mg, 0.01 mmol) and activated molecular sieves 4 A
(100 mg) were mixed in 3 mL of dry DCM and stirred for