DABCO catalyzed addition of selenosulfonates to α,β-unsaturated ketonest

Article abstract of DOI:10.1039/b501942g

A novel (1,4-diazabicyclic[2,2,2]octane) (DABCO) catalyzed addition of selenosulfonates to αβ-unsaturated ketones was reported to give the corresponding adducts in good yields under mild conditions. This synthetic approach provides a facile route to the s

Full text of DOI:10.1039/b501942g

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C O M M U N I C A T I O N
DABCO catalyzed addition of selenosulfonates to
a,b-unsaturated ketones†
Yong-Ling Shi and Min Shi*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai, 200032, China.
E-mail: mshi@pub.sioc.ac.cn
Received 7th February 2005, Accepted 8th March 2005
First published as an Advance Article on the web 16th March 2005
Table 1 Lewis base-catalyzed addition of selenosulfonate (1.0 eq.) to
MVK (2.0 eq.)
In the presence of DABCO (30 mol%), the addition of vari-
ous selenosulfonates to a,b-unsaturated ketones proceeded
smoothly to give the corresponding adducts in good yields
under mild conditions.
Recently, we have been investigating on the Baylis–Hillman
reaction of aldehydes and N-tosylated imines (ArCH NTs)
Yield/%a
=
with activated olefins in the presence of a variety of nitrogen
and phosphine Lewis bases.1–3 In this paper, we wish to report
a novel DABCO (1,4-diazabicyclic[2,2,2]octane) catalyzed addi-
tion of selenosulfonates to a,b-unsaturated ketones to give the
corresponding adducts in good yields under mild conditions.
The addition of selenosulfonates to olefins and other carbon–
carbon unsaturated bonds has been known to proceed in the
presence of Lewis acid BF3·OEt2 or through a radical reaction
pattern with either photochemical initiation, or upon heating
with a radical initiator such as AIBN.4,5 However, for a,b-
unsaturated ketones such as methyl vinyl ketone (MVK), no
reactions occurred under these reaction conditions. During our
ongoing investigation on the Baylis–Hillman reaction, we found
that many nitrogen Lewis bases could catalyze the addition of
selenosulfonates to MVK to give the corresponding adduct 1a
in good yields at room temperature. The results are summarized
in Table 1. In the presence of DABCO (30 mol%), 1a was
obtained in 81% yield after 1 h in THF in the reaction
of selenosulfonate (PhSeSO2Ph) with 2.0 eq. MVK (Table 1,
entry 1). Using 4-dimethylamino-pyridine (DMAP) and 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) as Lewis base catalysts,
this reaction proceeded quickly, but 1a was formed in 39 and
25% yields, respectively (Table 1, entries 2 and 3). Triethylamine
(Et3N) also can promote this reaction to give the adduct 1a in
42% yield after 24 h under the similar conditions (Table 1, entry
4). Phosphine Lewis bases such as triphenylphosphine, diphenyl-
methylphosphine, dimethylphenylphosphine, tributylphosphine
and trimethylphosphine showed no catalytic abilities for this
reaction (Table 1, entries 5–9). The solvent effects have been ex-
amined by use of DABCO in toluene, ethanol, dichloromethane
and ether (Et2O). We found that THF is the solvent of choice
(Table 1, entries 10–13).
Entry
Lewis base
Solvent
Time/hb
1a
1
2
3
4
5
6
7
8
9
10
11
12
13
DABCO
DMAP
DBU
Et3N
PPh3
PPh2Me
PPhMe2
PBu3
THF
THF
THF
THF
THF
THF
THF
THF
THF
Toluene
EtOH
CH2Cl2
Et2O
1
81
39
25
42
1/2
1/6
24
24
24
24
24
24
2/3
1/2
1/2
1/2
No reaction
No reaction
No reaction
Trace
Trace
39
—
59
44
PMe3
DABCO
DABCO
DABCO
DABCO
c
a Isolated yields. b The reaction time to consume all of the starting ma-
terials. c Complex reaction from which no products could be identified.
Table 2 DABCO-catalyzed addition of selenosulfonates (1.0 eq.) to
a b-unsaturated ketones (2.0 eq.)
Yield /%a
Entry
Ar
R
1
1
2
3
4
5
6
7
8
9
C6H5
C6H5
C6H5
Et
Ph
i-Pr
Me
Et
1b, 81
1c, 75
1d, 83
1e, 87
1f, 85
1g, 85
1h, 80
1i, 90
1j, 93
1k, 70
1l, 94
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeC6H4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
Under the optimized reaction conditions, we next examined
the addition of a variety of selenosulfonates to a,b-unsaturated
ketones. The results are summarized in Table 2. We found that
all these reactions proceeded smoothly under mild conditions to
give the corresponding adducts 1b–l in good to high yields after
1 h (Table 1, entries 1–11). It should be noted that for a branched
Ph
i-Pr
Me
Et
Ph
i-Pr
10
11
i
a,b-unsaturated ketone (R = Pr), the corresponding adducts 1d,
1h and 1l were obtained in high yields as well (Table 1, entries 3,
a Isolated yields.
7, and 11).
1
Their structures are determined by H and 13C NMR spec-
troscopic data, HRMS, and microanalyses (refer to the supple-
mentary information). The obtained adducts 1 can undergo a
selenoxide elimination upon oxidation with hydrogen peroxide
in THF to afford the corresponding (E)-b-phenylsulfonylenones
2 within 1 h in high yields (Scheme 1).6
† Electronic supplementary information (ESI) available: spectroscopic
data, HRMS, analytical data, experimental procedures. See http://www.
rsc.org/suppdata/ob/b5/b501942g/
1 6 2 0
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 6 2 0 – 1 6 2 1
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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Acknowledgements
We thank the State Key Project of Basic Research (Project 973,
No. G2000048007), Shanghai Municipal Committee of Science
and Technology, Chinese Academy of Sciences (KGCX2-210-
01), and the National Natural Science Foundation of China for
financial support (20025206, 203900502, and 20272069).
Scheme 1 Selenoxide elimination with hydrogen peroxide.
The mechanism for this unusual DABCO catalysed addition
reaction of selenosulfonates to a,b-unsaturated ketones has not
been unequivocally established, but on the basis of previous
investigations4 and the generally accepted reaction mechanism
for Baylis–Hillman reaction,1–3 one plausible explanation is
proposed in Scheme 2. The nucleophilic addition of the in situ
formed zwitterionic enolate A, derived from DABCO and the
corresponding a,b-unsaturated ketone, to the selenosulfonate
Notes and references
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Hyma, Tetrahedron, 1996, 52, 8001–8062; (c) D. Basavaiah, A. J. Rao
and T. Satyanarayana, Chem. Rev., 2003, 103, 811–892.
2 (a) M. Shi, J.-K. Jiang and Y.-S. Feng, Org. Lett., 2000, 2, 2397–2400;
(b) M. Shi and Y.-S. Feng, J. Org. Chem., 2001, 66, 406–411; (c) M.
Shi, C.-Q. Li and J.-K. Jiang, Chem. Commun., 2001, 833–834.
3 (a) M. Shi and Y.-M. Xu, Chem. Commun., 2001, 1876–1877; (b) M.
Shi and Y.-M. Xu, Eur. J. Org. Chem., 2002, 696–701; (c) M. Shi, Y.-M.
Xu, G.-L. Zhao and X.-F. Wu, Eur. J. Org. Chem., 2002, 3666–3679;
(d) M. Shi and Y.-M. Xu, J. Org. Chem., 2003, 68, 4784–4790; (e) G. L.
Zhao, J.-W. Huang and M. Shi, Org. Lett., 2003, 5, 4737–4739.
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−
produces the intermediate B. The generated PhSO2 species
attacks at the terminal carbon of a,b-unsaturated ketones of the
intermediate B to give the final product and regenerate DABCO
Lewis base catalyst (Scheme 2).7
6 (a) T. G. Back, K. Brunner, M. V. Krishna, E. K. Y. Lai, and
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Scheme 2 The plausibel reaction mechanism.
The control experiment has confirmed that this addition
reaction under the optimized conditions was unaffected by the
addition of the radical inhibitors such as TEMPO and 3 eq.
2,6-di-tert-butyl-4-methylphenol (BHT), rendering unlikely the
intervention of a radical pathway.
In conclusion, we have found a novel DABCO catalyzed
addition of selenosulfonates to a variety of a,b-unsaturated
ketones to give the adducts 1 in good to high yields within
short reaction time under mild conditions. This synthetic
approach also provides a facile route to the synthesis of (E)-
b-phenylsulfonylenones 2. Efforts are in progress to elucidate
the mechanistic details of this reaction and to disclose its scope
and limitations.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 6 2 0 – 1 6 2 1
1 6 2 1