A tin-free, radical photocatalyzed addition to vinyl sulfones

Article abstract of DOI:10.1002/adsc.201100591

Radical conjugate addition onto vinyl sulfones was achieved by means of a convenient, tin-free procedure. This was based on the photocatalyzed C-H bond activation in aldehydes, amides, ethers and even cycloalkanes by using tetrabutylammonium decatungstate

Full text of DOI:10.1002/adsc.201100591

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DOI: 10.1002/adsc.201100591
A Tin-Free, Radical Photocatalyzed Addition to Vinyl
Sulfones
Davide Ravelli,a Sara Montanaro,a Michele Zema,b Maurizio Fagnoni,a,*
and Angelo Albinia
a
Department of Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy
Fax: : (+39)-0382-987-323; phone: (+ 39)-0382-987-316; e-mail: fagnoni@unipv.it
Department of Earth Sciences, University of Pavia, Via Ferrata 1, 27100 Pavia, Italy
b
Received: July 27, 2011; Published online: December 8, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adcs.201100591.
Abstract: Radical conjugate addition onto vinyl sul-
fones was achieved by means of a convenient, tin-
free procedure. This was based on the photocata-
to make the elimination step milder (as in the Julia–
Kocienski modification).[7–9] Many efforts have also
been recently focused on the development of catalytic
asymmetric synthesis by using sulfones and bis-sul-
fones as starting compounds.[10]
À
lyzed C H bond activation in aldehydes, amides,
ethers and even cycloalkanes by using tetrabutylam-
monium decatungstate (TBADT). The reaction was
likewise effective for the functionalization of b-sub-
stituted vinyl sulfones. The products are useful
building blocks and were obtained in satisfactory
yields both under artificial UV light and under sun-
light, so demonstrating the “green” potential of the
process.
Vinyl sulfones, due to the electrophilic character,
are suitable starting materials for the synthesis of sub-
stituted sulfones via carbon-carbon bond formation,
as Michael acceptors in 1,4-addition reactions,[11] as
dienophiles in cycloadditions,[12,13] as well as in conju-
gate nucleophilic radical addition reactions.[3] The last
method is appealing, but requires the use of harmful
tin derivatives as radical chain carriers.[14] Tin-free
procedures have been investigated and include the
use of organodisilanes (e.g., 1,1,2,2-tetraphenyldisi-
lane),[15] cyanoborohydride (a highly toxic com-
pound,),[16] the Zn/CuI couple[17] and 1-ethylpiperidi-
nium hypophosphite[18] as reductive agents. Moreover,
the process could be initiated by indium[19a] or even
Keywords: green chemistry; photocatalysis; radi-
cals; sulfones; tin-free process
The sulfone moiety plays an important role in the took place under metal-free conditions on water.[19b]
synthesis of organic molecules due to the easy func- Photochemistry has likewise been used. Thus, cyclo-
tionalization and the leaving group aptitude. These alkyl radicals were obtained starting from cyclohex-
derivatives, and in particular phenyl sulfones[1–3] in ene by one-pot hydroboration with catecholborane
view of their stability, easy handling and preparation, followed by irradiation mediated by a Barton carbon-
are excellent intermediates in several synthetic routes ate as the chain carrier.[20] Moreover, various substi-
mainly involving the conversion into other useful tuted alkyl radicals were generated both from (diacyl-
functionalities via carbon-sulfur bond cleavage.[3,4]
oxyiodo)arenes by photolysis[21] and from tetramethy-
ACHTUNGTRENNUNG
These include oxidative desulfonylation to give car- lammonium phenyltrialkylborates by an electron
bonyl derivatives, nucleophilic and radical-mediated transfer reaction with benzophenone triplet.[22]
displacements of allylic and vinylic sulfones, b-elimi-
While in the cases above radicals are generated
nation under ionic or radical conditions and SO2 ex- from halides, an appealing and atom-economical way
trusion processes,[4] as well as reductive desulfonyla- to generate substituted alkyl radicals involves C H
À
tions by using dissolving metals or metal amalgams activation, a process that has been demonstrated to
leading to alkanes or, as in the Julia olefination, to al- be viable by having recourse to a photocatalyst.[23]
kenes.[5,6] The latter reaction is actually one of the The use of tetrabutylammonium decatungstate
most important examples where an aromatic sulfone (TBADT)[24,25] in this role has been recently devel-
acts as activating group, and recently the process has oped in our laboratory and chemoselective hydrogen
been improved by using specific heterocyclic sulfones abstraction has been demonstrated in several classes
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Davide Ravelli et al.
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solvent was adopted in this case due to solubility
problems) and an aldehyde bearing an alkene moiety,
(cis-7-decenal, 4), which gave sulfones 18–20 in 89, 60
and 41% yield, respectively, in the reaction with 11
(entries 3–5). Interestingly, in the last case, the stereo-
chemistry at the double bond was conserved. An aro-
matic aldehyde (benzaldehyde, 5) was found to be
likewise reactive under the present conditions and
adduct 21 was isolated in 65% yield (entry 6), al-
though a larger excess of 11 (0.15M) and a longer ir-
radiation time (40 h, 366 nm) were required.
The photocatalyzed reactions between 1 (or 2) with
11 were further investigated by doubling the concen-
tration of the starting reagents (see entries 1 and 3).
When using a 0.2M amount of the aldehyde and
0.24M 11, compounds 16 and 18 were isolated in
Scheme 1. Photocatalyzed synthesis of substituted sulfones.
of organic molecules.[24] The radical thus formed is comparable yields with respect to those obtained in
trapped by an electrophilic olefin and the photocata- more dilute conditions, although the irradiation time
lyst is then regenerated by hydrogen retrodonation to had to be increased to 40 h. Since we recently demon-
the radical adduct (see Scheme 1).
strated that TBADT-photocatalyzed processes can
The process occurs under mild and energy-saving take place under solar light[28] we investigated the
conditions and makes use of light, the ideal “green” functionalization of unsaturated sulfones under such
reagent,[26] as the energy source, and of a polyoxo- conditions. Noteworthy, the photocatalyzed addition
metalate as a robust catalyst. The aim of this work is of 1 onto 11 was completed in about two days irradia-
to develop a new protocol for the functionalization of tion upon exposing the reaction mixture (placed in a
a,b-unsaturated sulfones by applying the above ap- Pyrex vessel) on a window-ledge (77% yield). More-
proach.
over, the reactions reported in entries 1 and 3 were
A variety of compounds known to act as H donors repeated in a solar light simulator (light flux: 500 W/
in TBADT-photocatalyzed reactions (aldehydes, both m2, 15 h see Supporting Information) and, gratifyingly,
aliphatic[27a,b] and aromatic,[27c] amides,[27d] alkanes,[27e,f] both compounds 16 and 18 were again isolated in
ethers and acetals,[27g–i,28] 1–10) were thus submitted to yields only slightly lower than those with UV lamps.
photocatalysis in the presence of some (substituted)
a,b-unsaturated sulfones (11–15) in order to explore amined; in this case an excess of the donor was in
the feasibility and the scope of the reaction. most cases required in order to increase the overall
Next, different classes of hydrogen donors were ex-
The photoaddition reaction of heptaldehyde (1) alkylation yield. A couple of amides, viz. N-methyl-
with phenyl vinyl sulfone (11) was chosen as a model formamide (6, 0.2M) and formamide (7, 0.2M), were
for optimizing the reaction conditions. Actually, 24 h tested and their reactions with phenyl vinyl sulfone
irradiation (lIRR =366 nm, 12 phosphor-coated lamps; (11, 0.1M) allowed the isolation of the corresponding
see the Experimental Section and Supporting Infor- photoadducts 22 and 23 in 84 and 82% yields, respec-
mation) of an acetonitrile mixture containing 1 tively (entries 7 and 8).
(0.1M), TBADT (2ꢁ10À3 M, 2 mol%) in the presence
The reaction was likewise successful when using
of a slight excess of 11 (0.12M) turned out to give the ethers as hydrogen donors. Thus, tetrahydrofuran (8,
best result and the target phenyl sulfone 16 was isolat- 0.5M) and 1,3-benzodioxole (9, 0.11M) were irradiat-
ed in 72% yield (Table 1, entry 1). Blank experiments ed as above (0.1M 11) to afford sulfones 24 and 25
showed that 1 was not consumed when irradiated in (40 h irradiation) in 59 and 56% yields, respectively
the presence of 11 when omitting the catalyst. Notice (entries 9 and 10). Even alkanes could be employed
further that, using lamps centered at 310 rather than as hydrogen donors, as demonstrated by the reaction
366 nm, the consumption of the starting reagents was between cyclohexane (10, 0.5M) and phenyl vinyl sul-
likewise complete but 16 was obtained in a lower fone (11, 0.1M), where adduct 26 was formed in 66%
yield (45%) and a film sticking to the walls of the yield (entry 11) after 40 h irradiation.
vessel was formed during the irradiation.[29]
We next tested whether the substitution in the b
Substituting methyl vinyl sulfone (12) for 11 al- position affected the reaction. The photocatalyzed ad-
lowed us to obtain adduct 17 in almost the same yield dition of heptaldehyde (1, 0.1M) onto phenyl propen-
(68%, entry 2) but the reaction required a longer irra- yl sulfone (13, 0.12M) afforded keto sulfone 27 in a
diation time (40 h, 366 nm). Further aliphatic alde- low yield (38%) after 40 h irradiation, with the con-
hydes were then tested, viz. 3-phenylpropanal (2), un- version of the aldehyde limited to 74% (entry 12).
decanal (3, an acetonitrile/acetone 2/1 mixture as the Similar results were obtained with formamide and a
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A Tin-Free, Radical Photocatalyzed Addition to Vinyl Sulfones
Table 1. Photocatalyzed alkylation of a,b-unsaturated sulfones.
Entry H Donor
No., Conc.
[M]
Sulfone
No., Conc.
[M]
Products
No., (Yields [%][a])
16, (72, 67,[b,c] 67,[d]
1
1, (0.1)
1, (0.1)
11, (0.12)
12, (0.12)
77[e])
2[c]
17, (68)
3
2, (0.1)
3, (0.1)
4, (0.1)
5, (0.1)
11, (0.12)
11, (0.12)
11, (0.12)
11, (0.15)
18, (89, 91,[b,c] 76[d])
4[f]
19, (60)
20, (41)
21, (65)
5
6[c]
7
8
6, (0.2)
7, (0.2)
11, (0.1)
11, (0.1)
22, (84)
23, (82)
9
8, (0.5)
11, (0.1)
11, (0.1)
24, (59)
25, (56)
10[c]
9, (0.11)
11[c]
12[c]
13[c]
10, (0.5)
1, (0.1)
6, (0.4)
11, (0.1)
13, (0.12)
14, (0.1)
26, (66)
27, (38[g])
28, (66)
14
6, (0.2)
1, (0.1)
15, (0.1)
29, (64)
30, (73)
15[c]
15, (0.12)
[a]
Isolated yields.
Aldehyde (0.2M) and 11 (0.24M).
[b]
[c]
[d]
[e]
[f]
40 h irradiation.
15 h irradiation in a Solar box (500 W/m2) in a Pyrex glass vessel.
Two days (16 h) sunlight irradiation in a Pyrex glass vessel.
2:1 Acetonitrile/acetone mixture as the solvent.
[g]
51% yield based on 74% aldehyde consumption.
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generation of carbon-centered radicals starting from
easily accessible and unusual precursors by the che-
À
moselective activation of a C H bond. The reaction
takes place at room temperature, makes use of a
small amount (2 mol%) of a robust, easily pre-
pared,[28] tungstate photocatalyst and require no tin-
based (or other toxic) chain carriers. The reaction can
be efficiently carried out with no need of external
energy by simply exposing the reaction mixture to
sunlight. The mechanism is depicted in Scheme 1.
In the work above, phenyl vinyl sulfones rather
than related alkyl vinyl sulfones were preferentially
investigated because, as mentioned in the introduc-
tion, the PhSO2 moiety is especially prone to further
elaboration. In particular, the addition of aldehydes
(and amides) onto unsaturated sulfones was satisfac-
tory and led to b-keto sulfones (or related com-
pounds, for example, b-amido sulfones), in turn sus-
ceptible to several easy functionalizations including
desulfonylation to give the corresponding a,b-unsatu-
Figure 1. ORTEP view of 28 with thermal ellipsoids drawn
at 30% probability level. The crystal structure is character-
ized by atomic positional disorder not reported for clarity.
larger excess of the donor (up to 0.6M) led only to a rated derivatives.[4,30]
modest increase of the sulfone conversion (data not
reported).
Taken together, the two steps result in a formal vi-
nylation of aldehydes and of (some) amides. As ap-
We then shifted to cyclic unsaturated sulfones, such parent in the case of aldehyde 4, labile allyl hydro-
as (cyclopentenylsulfonyl)benzene (14). In the event, gens did not seriously interfere with abstraction from
the reaction between N-methylformamide (6, 0.4M) the formyl group in the aldehyde structure that could
and 14 led to complete sulfone conversion and to the be likewise easily activated under the present condi-
isolation of product 28 (trans diastereoisomer) as the tions. Moreover, no loss of stereochemistry occurred,
exclusive product in 66% yield (entry 13), as demon- indicating that energy transfer from excited TBADT
strated by X-rays analysis (Figure 1). A more strained to the aldehyde C=C moiety had no role.
bicyclic sulfone having a norbornene skeleton (2-
Another favorable characteristic of the method is
(phenylsulfonyl)bicyclo[2.2.1]hept-2-ene, 15) followed. the limited hindering by substituents in the b-position,
AHCTUNGTRENNUNG
Thus, the reactions between 6 (or 1), and 15 gave as shown in the case of sulfones 13–15. In contrast,
products 29 and 30 in 64 or 73% yield, respectively, in only a few examples of radical attack onto such deriv-
a chemo- and diastereoselective way (Table 1, en- atives have been reported. Thus, the alkylation of sul-
tries 14 and 15), as again demonstrated by X-rays fone 13 failed when 1,3-dioxolan-2-yl radicals were
analysis in the case of compound 29 (Figure 2) and by generated from 1,3-dioxolane by H abstraction in-
comparison of the spectroscopic data in the case of duced by tert-butylperoxy-l3-iodane photolysis.[31]
sulfone 30.
Similarly, sulfone 13 remained virtually unreacted
The results above demonstrate again the versatility when alkyl radicals were generated from a Barton
of the TBADT-photocatalyzed method for the mild ester, even when used in a 10-fold excess with respect
to the ester[32] and b-phenyl vinyl sulfone underwent
no radical addition.[17]
In the present case the effect was limited and al-
lowed the isolation of the alkylated products in some
cases. As an example, comparison between entry 1
and entry 12 shows that the latter alkylation was less
effective (aldehyde 1 was not completely consumed
even after 40 h irradiation), but still the product was
obtained, although in a modest yield. It thus appears
that the present system offers a more efficient radical
source and lessens the kinetic barrier to alkylation in
a substituted position. Positive results have otherwise
been obtained only under particular conditions, for
example, in the functionalization of a g-acetoxy vinyl
sulfone by a ketyl radical photogenerated from 2-
propanol by triplet benzophenone hydrogen abstrac-
Figure 2. ORTEP view of 29 with thermal ellipsoids drawn
at 30% probability level.
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A Tin-Free, Radical Photocatalyzed Addition to Vinyl Sulfones
tion.[33] In such a case, good alkylation yields required
that a purposely added hydrogen donor was used as
the reaction medium and an equimolar (not a catalyt-
ic) amount of the photomediator was required.[33]
When the double bond of the vinyl sulfone was in-
corporated in a rigid structure, as in the case of sul-
fone 14, a higher yield of the adduct was observed
particularly when the less hindered amide 6 was used
as the H donor and the irradiation time prolonged to
40 h (entry 13). In that reaction, the more stable trans
isomer (compound 28) was isolated as the exclusive
product. Interesting was the case of norbornene deriv-
ative 15 where the rigidity of the bicyclic structure al-
lowed an efficient acylation both with amide 6 (the
time required is comparable to that used with unsub-
stituted sulfone 11) and heptaldehyde 1 in a satisfac-
tory yield (entries 14 and 15). The steric constraint
led to strict stereoselectivity, with both the carbamoyl
(or acyl) radical attack and hydrogen back-donation
from the bulky TBADT-HC taking place at the less
hindered side to yield the syn adducts 29 and 30 ex-
clusively. On the other hand, the scope was here more
limited and 14 or 15 were not photoalkylated when
using cyclohexane or tetrahydrofuran.
tra of compounds 16–30, the absorption spectrum of com-
pound 11 and crystallographic details for compounds 28 and
29.
Acknowledgements
This work was financially supported by MIUR.
References
[1] F. Vçgtle, L. Rossa, Angew. Chem. 1979, 91, 534–549;
Angew. Chem. Int. Ed. Engl. 1979, 18, 515–529.
[2] L. Field, Synthesis 1978, 713–735.
[3] A. El-Awa, M. N. Noshi, X. Mollat du Jourdin, P. L.
Fuchs Chem. Rev. 2009, 109, 2315–2349.
[4] C. Nꢂjera, M. Yus, Tetrahedron 1999, 55, 10547–10658.
[5] J. Ru Hwu, J. Org. Chem. 1983, 48, 4432–4433.
[6] M. Julia, J. M. Paris, Tetrahedron Lett. 1973, 4833–4836.
[7] P. J. Kocienski, A. Bell, P. R. Blakemore, Synlett 2000,
365–367.
´
[8] P. R. Blakemore, W. J. Cole, P. J. Kocienski, A. Morley,
Synlett 1998, 26–28.
[9] J. B. Baudin, G. Hareau, S. A. Julia, O. Ruel, Tetrahe-
Summing up, the present tin-free method allowed
the activation of the carbon-hydrogen bond from suit-
dron Lett. 1991, 32, 1175–1178.
able donors, skipping any preliminary functionaliza- [10] a) A.-N. R. Alba, X. Companyꢃ, R. Rios, Chem. Soc.
Rev. 2010, 39, 2018–2033; b) M. Nielsen, C. B. Jacobsen,
N. Holub, M. W. Paix¼o, K. A. Jørgensen, Angew.
Chem. 2010, 122, 2726–2738; Angew. Chem. Int. Ed.
2010, 49, 2668–2679.
tion, and thus resulting in an atom-economical route.
Moreover, the reaction can also be carried out with a
simple experimental apparatus by using the cheapest
and greenest energy source: sunlight.
[11] a) C. Bournaud, E. Marchal, A. Quintard, S. Sulzer-
Mossꢄ, A. Alexakis, Tetrahedron: Asymmetry 2010, 21,
1666–1673; b) S. A. Moteki, S. Xu, S. Arimitsu, K. Mar-
uoka, J. Am. Chem. Soc. 2010, 132, 17074–17076; c) Q.
Zhu, Y, Lu, Angew. Chem. 2010, 122, 7919–7922;
Angew. Chem. Int. Ed. 2010, 49, 7753–7756; d) H. J.
Lee, S. H. Kang, D. Y. Kim, Synlett 2011, 1559–1562;
e) J. Xiao, Y.-P. Lu, Y.-L. Liu, P.-S. Wong, T.-P. Loh,
Org. Lett. 2011, 13, 876–879.
[12] A. K. Musser, P. L. Fuchs, J. Org. Chem. 1982, 47,
3121–3131.
[13] T. G. Back, K. N. Clary, D. Gao, Chem. Rev. 2010, 110,
4498–4553.
Experimental Section
Typical Procedure for the Tin-Free, Radical-Photo-
catalyzed Addition to Vinyl Sulfones
UV light irradiation: An MeCN solution (30 mL) of the hy-
drogen donor (1–10, 0.1–0.5M) and the vinyl sulfone (11–15,
0.1–0.12M) in the presence of 200 mg of TBADT[28] (2ꢁ
10À3 M) was poured in two quartz tubes and purged for
5 min with nitrogen, serum capped and irradiated with
twelve 15-W phosphor-coated lamps (emission centered at
366 nm). The solvent was removed under vacuum from the
photolyzed solutions and the products isolated by purifica-
tion of the residue by column chromatography (cyclohex-
ane/ethyl acetate as eluants).
Sunlight irradiation: An MeCN solution (30 mL) of hep-
taldehyde (1, 0.1M), and phenyl vinyl sulfone (11, 0.12M) in
the presence of 200 mg of TBADT (2ꢁ10À3 M) was poured
in a cylindrical Pyrex vessel[28] and purged for 5 min with ni-
trogen, capped and exposed to sunlight on a window ledge.
Purification of the end product was carried out as above.
[14] G. S. C. Srikanth, S. L. Castle, Tetrahedron 2005, 61,
10377–10441.
[15] O. Yamazaki, H. Togo, S. Matsubayashi, M. Yokoyama,
Tetrahedron 1999, 55, 3735–3747.
[16] I. Ryu, S. Uehara, H. Hirao, T. Fukuyama, Org. Lett.
2008, 10, 1005–1008.
[17] M. M. Zhao, C. Qu, J. E. Lynch, J. Org. Chem. 2005,
70, 6944–6947.
[18] D. O. Jang, D. H. Cho, Synlett 2002, 1523–1525; D. O.
Jang, D. H. Cho, C.-M. Chung, Synlett 2001, 1923–1924.
[19] a) H. Miyabe, M. Ueda, A. Nishimura, T. Naito, Org.
Lett. 2002, 4, 131–134; b) V. Chudasama, R. J. Fitzmaur-
ice, J. M. Ahern, S. Caddick, Chem. Commun. 2010, 46,
133–135.
Supporting Information
See Supporting Information for experimental details, charac-
[20] A.-P. Schaffner, P. Renaud, Eur. J. Org. Chem. 2004,
2291–2298.
1
terization of products and copies of H and 13C NMR spec-
Adv. Synth. Catal. 2011, 353, 3295 – 3300
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
3299

Davide Ravelli et al.
COMMUNICATIONS
[21] H. Togo, M. Aoki, M. Yokoyama, Tetrahedron 1993,
49, 8241–8256.
[22] A. Y. Polykarpov, D. C. Neckers Tetrahedron Lett.
1995, 36, 5483–5486.
b) M. D. Tzirakis, M. Orfanopoulos, J. Am. Chem. Soc.
2009, 131, 4063–4069; c) D. Ravelli, M. Zema, M.
Mella, M. Fagnoni, A. Albini, Org. Biomol. Chem.
2010, 8, 4158–4164; d) S. Angioni, D. Ravelli, D.
Emma, D. Dondi, M. Fagnoni, A. Albini, Adv. Synth.
Catal. 2008, 350, 2209–2214; e) D. Dondi, A. M. Car-
darelli, M. Fagnoni, A. Albini, Tetrahedron 2006, 62,
5527–5535; f) D. Dondi, D. Ravelli, M. Fagnoni, M.
Mella, A. Molinari, A. Maldotti, A. Albini, Chem. Eur.
J. 2009, 15, 7949–7957; g) D. Dondi, M. Fagnoni, A.
Albini, Chem. Eur. J. 2006, 12, 4153–4163; h) M. D.
Tzirakis, M. Orfanopoulos, Angew. Chem. 2010, 122,
6027–6029; Angew. Chem. Int. Ed. 2010, 49, 5891–5893;
i) D. Ravelli, A. Albini, M. Fagnoni, Chem. Eur. J.
2011, 17, 572–579.
[23] For reviews on the synthetic utility of photocatalysis
see: a) M. Fagnoni, D. Dondi, D. Ravelli, A. Albini,
Chem. Rev. 2007, 107, 2725–2756; b) D. Ravelli, D.
Dondi, M. Fagnoni, A. Albini, Chem. Soc. Rev. 2009,
38, 1999–2011; c) T. P. Yoon, M. A. Ischay, J. Du, Nat.
Chem. 2010, 2, 527–532; d) C. Gambarotti, C. Punta, F.
Recupero, T. Caronna, L. Palmisano, Curr. Org. Chem.
2010, 14, 1153–1169; e) Handbook of Synthetic Photo-
chemistry, (Eds.: A. Albini, M. Fagnoni), Wiley-VCH,
Weinheim 2010.
[24] a) M. D. Tzirakis, I. N. Lykakis, M. Orfanopoulos,
Chem. Soc. Rev. 2009, 38, 2609–2621; b) C. Tanielian,
Coord. Chem. Rev. 1998, 178–180, 1165–1181; c) R. F.
Renneke, M. Kadkhodayan, M. Pasquali, C. L. Hill, J.
Am. Chem. Soc. 1991, 113, 8357–8367.
[28] S. Protti, D. Ravelli, M. Fagnoni, A. Albini, Chem.
Commun. 2009, 7351–7353.
[29] Using the 310 nm-centered lamp results in some com-
petitive absorption by the sulfone and the occurring of
secondary reactions and polymerization (see the ab-
sorption spectra of sulfone 11 in the Supporting Infor-
mation and what is reported in the supporting informa-
tion files of refs.[27i,28]). Therefore irradiation at 366 nm
is generally preferred.
[30] See, for example: S. Marczak, J. Wicha, Synth.
Commun. 1990, 20, 1511–1520; T. Satoh, K. Oguro, J.-I.
Shishikura, N. Kanetaka, R. Okada, K. Yamakawa, Tet-
rahedron Lett. 1992, 33, 1455–1458.
[25] C. L. Hill, Synlett 1995, 127–132.
[26] a) A. Albini, M. Fagnoni, M. Mella, Pure Appl. Chem.
2000, 72, 1321–1326; b) A. Albini, M. Fagnoni, Green
Chem. 2004, 6, 1–6; c) A. Albini, M. Fagnoni, in: Green
Chemical Reactions, (Eds.: P. Tundo, V. Esposito),
Springer Science+Business Media B.V. 2008, pp 173–
189; d) S. Protti, S. Manzini, M. Fagnoni, A. Albini, in:
Eco-Friendly Synthesis of Fine Chemicals, (Ed.: R. Bal-
lini), Royal Society of Chemistry, Cambridge, 2009,
pp 80–111; e) A. Albini, Photochem. Photobiol. Sci.
2010, 9, 1533–1534.
[31] T. Sueda, Y. Takeuchi, T. Suefuji, M. Ochiai, Molecules
2005, 10, 195–200.
[27] For representative examples on the TBADT photocata-
[32] D. H. R. Barton, H. Togo, S. Z. Zard, Tetrahedron Lett.
1985, 26, 6349–6352.
[33] K. Ogura, A. Kayano, M. Akazome, Bull. Chem. Soc.
À
lyzed C H activation, see: a) S. Esposti, D. Dondi, M.
Fagnoni, A. Albini, Angew. Chem. 2007, 119, 2583–
2586; Angew. Chem. Int. Ed. 2007, 46, 2531–2534;
Jpn. 1997, 70, 3091–3101.
3300
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Adv. Synth. Catal. 2011, 353, 3295 – 3300