Y. Yamamoto et al. / Tetrahedron Letters 45 (2004) 795–797
797
Further reaction of 17 with a carbonyl group of 1 gen-
erates an alkoxy radical 18, which is then converted to a
relatively stable peroxy radical 19 through intramolec-
ular hydrogen atom abstraction and end up with 6
Lett. 2003, 44, 5601–5604; (c) Hirano, K.; Sakaguchi, S.;
Ishii, Y. Tetrahedron Lett. 2002, 43, 3617–3620; (d)
Mosca, R.; Fagnoni, M.; Mella, M.; Albini, A. Tetrahe-
dron 2001, 57, 10319–10328; (e) Torrente, S.; Alonso, R.
Org. Lett. 2001, 3, 1985–1987; (f) Kim, S.; Kim, N.;
Chung, W.-J.; Cho, C. H. Synlett 2001, 937–940.
. These compounds gave satisfactory spectroscopic and
analytical data. The compounds 7a and 8 were known
compound. 7a: Jedlinski, Z.; Kowalczuk, M.; Kurcok, P.;
Grzegorzek, M.; Ermel, J. J. Org. Chem. 1987, 52, 4601–
4602; 8: Enholm, E. J.; Schreier, J. A. J. Heterocyclic
Chem. 1995, 32, 109–111.
2
14
(
R ¼ H, OZnMe, etc.). An excess of methyl radical
allows to couple with a peroxy radical 19 to result in the
actual formation of an alcohol precursor of 10, of which
detection supported above scenario.
5
In conclusion, we have encountered an unexpected
generation of an a-peroxygenated THF b-radical from
THF a-radical in the reaction of aldehydes with
dimethylzinc–air-initiated THF radical, which consti-
tutes one of the critical factors governing initiator
dependent imine/aldehyde chemoselectivity. Further-
more, the present behavior of THF radicals suggests
alternative strategy for the radical addition to carbonyl
derivatives. Although a chemical yield is far from
practical level, the new findings described herein become
the basis of new radical chemistry.
6
. Trace amounts of c-butyrolactone and THF-hydroperox-
ide (Shurvell, H. F.; Southby, M. C. Vib. Spectrosc. 1997,
1
1
product.
5, 137–146) were detected by H NMR of the crude
7
. Diorganozinc–oxygen derived complex has been isolated
as a possible radical precursor. Lewinski, J.; Marciniak,
W.; Lipkowski, J.; Justyniak, I. J. Am. Chem. Soc. 2003,
1
25, 12698–12699.
8. For the reversibility of radical reaction with carbonyl
derivatives, see: (a) Walton, R.; Fraser-Reid, B. J. Am.
Chem. Soc. 1991, 113, 5791–5799; (b) Beckwith, A. L. J.;
Hay, B. P. J. Am. Chem. Soc. 1989, 111, 2674–2681; (c)
Beckwith, A. L. J.; Hay, B. P. J. Am. Chem. Soc. 1989,
1
11, 230–234; (d) Kim, S.; Yoon, J.-Y. In Radicals in
Acknowledgements
Organic Synthesis; Renaud, P., Sibi, M. P., Eds.; Wiley-
VCH: Weinheim, 2001; Vol. 2, Chapter 1.1.3, pp 11–12.
. For the addition to acylsilanes, see: (a) Huang, C.-H.;
Chang, S.-Y.; Wang, N.-S.; Tsai, Y.-M. J. Org. Chem.
2001, 66, 8983–8991, and references cited therein; (b) For
the addition to thioesters, selenoesters, acylgermanes, and
acylphosphonate, see: Kim, S.; Cho, C. H.; Lim, C. J.
J. Am. Chem. Soc. 2003, 125, 9574–9575, and references
cited therein.
This research was partially supported by the 21st Cen-
tury COE (Center of excellence) Program ÔKnowledge
Information Infrastructure for Genome ScienceÕ, a
Grant-in-Aid for Young Scientists (B) and a Grant-
in-Aid for Scientific Research on Priority Areas (A)
ÔExploitation of Multi-Element Cyclic MoleculesÕ from
the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
9
1
1
0. For tributyltin hydride-mediated pinacol coupling, see: (a)
Hays, D. S.; Fu, G. C. J. Org. Chem. 1998, 63, 6375–6381;
(
7
b) Hays, D. S.; Fu, G. C. J. Am. Chem. Soc. 1995, 117,
283–7284.
1. For intramolecular cyclization of a-stannyl radical to a
formyl group, see: Chang, S.-Y.; Shao, Y.-F.; Chu, S.-F.;
Fan, G.-T.; Tsai, Y.-M. Org. Lett. 1999, 1, 945–948.
References and notes
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13. THF a-adduct 5 was obtained rather than b-adduct 6 by
using triethylborane–air as an initiator, probably due to
3
a–c
the fast reaction of 14 with triethylborane. See Refs.
.
14. Bond dissociation energies of HOO–H and HO–H have
been reported to be 87.2 and 119 kcal/mol, respectively.
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4
. For recent impressive a-alkoxy radical reactions, see: (a)
Fern ꢀa ndez, M.; Alonso, R. Org. Lett. 2003, 5, 2461–2464;
(
b) Tsujimoto, S.; Sakaguchi, S.; Ishii, Y. Tetrahedron