Paper
Green Chemistry
Acknowledgements
This work was made possible by grants from Aarhus Univer-
sity, Carlsberg Foundation and FNU. F.J.L.D. acknowledges
Regional Government of Andalusia (Junta de Andalucía)
project P09-FQM-4498 for a Ph.D. fellowship.
Notes and references
1 H. Jasch and M. R. Heinrich, Tin Hydrides and Functional
Group Transformations, in Encyclopedia of Radicals in
Chemistry, Biology and Materials, ed. C. Chatgilialoglu and
A. Studer, Wiley, 2012.
2 For selected reviews, see: (a) D. H. R. Barton and
N. Ozbalik, Phosphorus, Sulfur Silicon Relat. Elem., 1989, 43,
349; (b) M. F. Saraiva, M. R. C. Couri, M. Le Hyaric and
M. V. de Almeida, Tetrahedron, 2009, 65, 3563; (c) F. Alonso,
I. P. Beletskaya and M. Yus, Chem. Rev., 2002, 102, 4009;
(d) B. Giese, B. Kopping, T. Göbel, J. Dickhaut, G. Thoma,
K. J. Kulicke and F. Trach, Organic Reactions, Wiley, 2004,
p. 301. For seminal work, see: (e) D. H. R. Barton and
S. W. McCombie, J. Chem. Soc., Perkin Trans. 1, 1975, 16,
1574.
Scheme 2 Dehalogenation of vinylic and aliphatic halides and radical
cyclizations.
3 For selected reviews, see: (a) C. Chatgilialoglu, Organo-
silanes
in
Radical
Chemistry,
Wiley,
2003;
(b) C. Chatgilialoglu and J. Lalevée, Molecules, 2012, 17,
527; (c) C. Chatgilialoglu, Chem.–Eur. J., 2008, 14, 2310;
(d) C. Chatgilialoglu, Acc. Chem. Res., 1992, 25, 188. For
conversion, furnishing the desired product
8 in 52%
(Method A) and 95% (Method B) yield. When aryl iodides are
tethered with an olefin or alkyne in its proximity, entrapment
of the intermediate aryl radical is observed. For example, aryl
iodides 9a, b were annulated to provide the corresponding
dihydrobenzofuran and benzofuran derivatives 10a, b in good
yields. However, these cyclizations occurred only by following
the irradiation-mediated protocol.
seminal work, see:
(e) J. M. Kanabus-Kaminska,
J. A. Hawari, D. Griller and C. Chatgilialoglu, J. Am. Chem.
Soc., 1987, 109, 5267.
4 For selected reviews, see: (a) C. K. Prier, D. A. Rankic and
D. W. C. MacMillan, Chem. Rev., 2013, 113, 5322;
(b) J. W. Tucker and C. R. J. Stephenson, J. Org. Chem.,
2012, 77, 1617; (c) T. P. Yoon, M. A. Ischay and J. Du,
Nat. Chem., 2010, 2, 527. For selected examples of
photoredox-mediated dehalogenation and cyclization reac-
Conclusions
tions, see:
(d) J. D. Nguyen, E. M. D’Amato,
In summary, we have reported two straightforward, metal- and
additive-free protocols for radical dehalogenation, deoxygena-
tion and cyclization reactions. First, we demonstrate that
irradiation from household compact fluorescent light bulbs
can initiate radical reactions using the well-studied reagent
TTMSS as the hydride source under degassed conditions. Next,
we disclose an oxygen-initiation strategy, which only requires
the presence of an air atmosphere (occasionally with gentle
heating). In comparison with traditional strategies, metal or
additives (e.g. tin hydride, AIBN, thiol-based propagators),
special equipments (e.g. for UV-initiation), harsh conditions
(e.g. 100 °C in thermal initiation) or a careful “dosing” of
oxygen can all be avoided. In addition, both protocols provide
moderate to high yields and show excellent tolerance towards
sensitive functional groups. It is believed that the high practi-
cality and mildness of the developed methodologies will be
useful for chemists in many areas.
J. M. R. Narayanam and C. R. J. Stephenson, Nat. Chem.,
2012, 4, 854; (e) J. W. Tucker, J. M. R. Narayanam,
S. W. Krabbe and C. R. J. Stephenson, Org. Lett., 2010, 12,
368; (f) J. M. R. Narayanam, J. W. Tucker and
C. R. J. Stephenson, J. Am. Chem. Soc., 2009, 131, 8756.
5 Such a photoinitiation strategy has been employed in
polymerization chemistry, see: (a) J. Lalevée, N. Blanchard,
M.-A. Tehfe, F. Morlet-Savary and J. P. Fouassier, Macro-
molecules, 2010, 43, 10191. For other examples, see:
(b) M.-A. Tehfe, J. Lalevée, F. Morlet-Savary, B. Graff and
J. P. Fouassier, Macromolecules, 2011, 44, 8374;
(c) J. Lalevée, N. Blanchard, M.-A. Tehfe, M. Peter,
F. Morlet-Savary and J. P. Fouassier, Macromol. Rapid
Commun., 2011, 32, 917.
6 For examples of thermal and UV initiation of TTMSS-based
radical reactions, see: (a) A. Postigo, S. Kopsov, C. Ferreri
and C. Chatgilialoglu, Org. Lett., 2007, 9, 5159;
3358 | Green Chem., 2013, 15, 3355–3359
This journal is © The Royal Society of Chemistry 2013