Notes and references
1 T. W. Lyons and M. S. Sanford, Chem. Rev., 2010, 110,
1147–1169.
2 W. R. Bowman and J. M. D. Storey, Chem. Soc. Rev., 2007, 36,
1803–1822.
3 (a) E. Shirakawa and T. Hayashi, Chem. Lett., 2012, 41, 130–134;
´
(b) F. Vallee, J. J. Mousseau and A. B. Charette, J. Am. Chem.
Soc., 2010, 132, 1514–1516; (c) W. Liu, H. Cao and A. Lei, Angew.
Chem., Int. Ed., 2010, 49, 2004–2008.
4 (a) S. Yanagisawa, K. Ueda, T. Taniguchi and K. Itami, Org. Lett.,
2008, 10, 4673–4676; (b) W. Liu, H. Cao, H. Zhang, H. Zhang,
K. H. Chung, C. He, H. Wang, F. Y. Kwong and A. Lei, J. Am.
Chem. Soc., 2010, 132, 16737–16740; (c) C.-L. Sun, H. Li,
D.-G. Yu, M. Yu, X. Zhou, X.-Y. Lu, K. Huang, S.-F. Zheng,
B.-J. Li and Z.-J. Shi, Nat. Chem., 2010, 2, 1044–1049;
(d) E. Shirakawa, K.-i. Itoh, T. Higashino and T. Hayashi,
J. Am. Chem. Soc., 2010, 132, 15537–15539; (e) D. Sustac Roman,
Y. Takahashi and A. B. Charette, Org. Lett., 2011, 13, 3242–3245;
(f) C.-L. Sun, Y.-F. Gu, W.-P. Huang and Z.-J. Shi, Chem.
Commun., 2011, 47, 9813–9815; (g) S. Yanagisawa and K. Itami,
ChemCatChem, 2011, 3, 827–829; (h) W. Liu, H. Cao, J. Xin, L. Jin
and A. Lei, Chem.–Eur. J., 2011, 17, 3588–3592; (i) H. Li,
C.-L. Sun, M. Yu, D.-G. Yu, B.-J. Li and Z.-J. Shi, Chem.–Eur. J.,
2011, 17, 3593–3597.
5 (a) E. Shirakawa, X. Zhang and T. Hayashi, Angew. Chem.,
Int. Ed., 2011, 50, 4671–4674; (b) C.-L. Sun, Y.-F. Gu, B. Wang
and Z.-J. Shi, Chem.–Eur. J., 2011, 17, 10844–10847;
(c) M. Rueping, M. Leiendecker, A. Das, T. Poisson and L. Bui,
Chem. Commun., 2011, 47, 10629–10631.
Scheme 1 Proposed Reaction Mechanisms.
6 A. Studer and D. P. Curran, Angew. Chem., Int. Ed., 2011, 50,
5018–5022.
In intermediate H the homolytic cleavage of the bond depicted
in blue should be favoured, as it results in the formation of a
more stable neopentyl-type radical, which is stabilized by
inductive effect and hyperconjugation.16 This leads to the ring
expansion product G, which itself forms 5i upon rearomatiza-
tion. While both 6-endo/exo-trig and 5-exo-trig cyclizations are
likely to occur in the all-carbon tethers, substrate 4i should be
more prone to follow the latter pathway since it generates a
tertiary cyclohexadienyl radical intermediate H that is stabi-
lized by the methyl group.
7 See the ESIw.
8 E. V. Anslyn and D. A. Dougherty, Modern Physical
Organic Chemistry, University Science Books, 2006.
9 (a) D. R. Fahey and J. E. Mahan, J. Am. Chem. Soc., 1977, 99,
2501–2508; (b) T. T. Tsou and J. K. Kochi, J. Am. Chem. Soc.,
1979, 101, 6319–6332.
10 Strong bases such as LDA, KOtBu and LiOtBu are known to act
as single-electron donors: N. R. E. C. Ashby, A. B. Goel and
R. N. DePriest, J. Org. Chem., 1981, 46, 2429–2431.
11 The formation of an adduct between Ni(PPh3)4 and NaHMDS was
1
also verified by H DOSY NMR, see the ESIw.
12 V. B. Phapale, E. Bunuel, M. Garcıa-Iglesias and D. J. Cardenas,
´ ´
Angew. Chem., Int. Ed., 2007, 46, 8790–8795.
In conclusion, we have reported an intramolecular cycliza-
tion of alkyl iodides promoted by Ni0 catalysis in presence of
NaHMDS. The mechanistic investigations suggest that a
Ni0/NaHMDS/starting material adduct is formed prior to the
SET event leading to the formation of an alkyl radical. It was
demonstrated that Ni0 acts as a catalyst in the reaction rather than
a radical chain initiator in the course of TEMPO experiments.
13 While there are several possible mechanisms to account for
the rearomatization of intermediate E, the one proposed by
Curran and Studer (ref. 6) in their base-promoted homolytic
aromatic substitution reaction can be ruled out as it involves
the formation of a radical anion species. Since radical anion
intermediates bearing a chlorine substituent are known to frag-
ment into the corresponding aryl radical and chloride ion, the
product 5e would not have been formed were this mechanism
operative.
14 (a) E. Lee, C. Lee, J. S. Tae, H. S. Whang and K. S. Li, Tetrahedron
Lett., 1993, 34, 2343–2346; (b) E. Lee, H. S. Whang and
C. K. Chung, Tetrahedron Lett., 1995, 36, 913–914.
15 An oxygen tether substrate led to aryl translocation as in ref. 14a
and recovery of starting material. See the ESIw.
This work was supported by Universite de Montreal,
´ ´
the Natural Science and Engineering Council of Canada
(NSERC), the Canada Research Chair Program and the Canada
Foundation for Innovation. We thank Dr Ce
´
´
dric Malveau
(Universite de Montreal) for NMR experiments. LPBB and
´
16 J. C. Schultz, F. A. Houle and J. L. Beauchamp, J. Am. Chem.
Soc., 1984, 106, 3917–3927.
DSR thank NSERC for graduate scholarships.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 8249–8251 8251