Metal-Free, Radical Addition to Alkenes via Desulfitative Chlorine Atom Transfer
crude product was purified by flash chromatography using
silica gel.
The preparation of sulfonyl chlorides and detailed charac-
terization of all compounds can be found in the Supporting
Information.
desired chlorine atom transfer product 10a was ob-
tained but the yield was low. Optimization of the re-
action conditions did not allow us to improve signifi-
cantly the yield. This result demonstrates that the de-
sulfitative chlorine ATRA reaction offers an advant-
age over the iodine ATRA reaction in terms of prod-
uct stability (the chloride product does not undergo
an intramolecular nucleophilic substitution) but, as
anticipated, the limitation due to the lack of reactivity
(electrophilicity) of the intermediate radical is not al-
leviated.
Acknowledgements
We thank the Swiss National Science Foundation (grants 20-
135087) for financial support.
Conclusions
References
The desulfitative chlorine atom transfer radical addi-
tion reaction has shown to be a general strategy for
the formation of carbon-carbon bonds under metal-
free conditions. Sulfonyl chlorides are easily prepared
by simple and cheap procedures. They are stable radi-
cal precursors that can be stored for months without
decomposition. The reaction can be performed in a
variety of solvents such as tert-butanol, 1,2-dichloro-
ethane, and benzene. Commercially and easily avail-
able radical initiators have been used with success to
trigger the reaction.
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Experimental Section
ATRA Reactions of Cl3CSO2Cl (AIBN Initiation)
In a two-necked, flame-dried flask equipped with a reflux
condenser, the alkene (1.0 equiv.), Cl3CSO2Cl (1.1 equiv.),
and AIBN (0.05 equiv.) were weighed. After purging with
N2, the solvent was added, and the reaction mixture was
heated to reflux and monitored by TLC. At the end of the
reaction time (typically 0.5–2 h), the mixture was concen-
trated and the crude product was purified by flash chroma-
tography using silica gel.
ATRA Reactions of Cl3CSO2Cl (DTBD Initiation)
In a quartz round-bottomed flask equipped with a reflux
condenser, the alkene (1.0 equiv.) and DTBD (0.5 equiv.)
were added to a stirred solution of sulfonyl chloride
(2.0 equiv.) in tert-butanol. The reaction mixture was irradi-
ated by a sunlamp (300 W) and heated to reflux. At the end
of the reaction time (typically 2 h), the crude product was
purified by flash chromatography using silica gel.
ATRA Reactions of Ethyl 2-(Chlorosulfonyl)acetate
In a two-necked flask, equipped with a reflux condenser and
charged with ethyl 2-(chlorosulfonyl)acetate 4 (2.0 equiv.),
alkene (1.0 equiv.) and benzene was added DLP (0.2 equiv.)
under an N2 atomosphere. The reaction mixture was heated
to reflux and monitored by TLC. At the end of the reaction
time (typically 2–5 h), the mixture was concentrated and the
[8] For review articles on chlorine-atom transfer radical
additions catalyzed by transition-metal catalysts, see:
a) A. J. Clark, Chem. Soc. Rev. 2002, 31, 1; b) K. Sever-
Adv. Synth. Catal. 2011, 353, 3467 – 3472
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