the formation of phenylacetic acid (12%). Without using PhI,
no Hofmann rearrangement of a-phenylacetamide was detected
(entry 5). Changing the solvent to a mixture of dichloromethane–
H2O nicely improved the catalytic efficiency of the Hofmann
rearrangement: thus, 1 mol% of PhI afforded 3a in 97% yield in
95 : 5 dichloromethane–H2O, although the reaction is relatively
slow (72 h, entry 7). Increasing the water contents of the solvent
mixture decreased the yield of 3a (entries 8 and 9). Use of
5 mol% of PhI in 95 : 5 dichloromethane–H2O accelerated the
rate of reaction and seems to be the optimal conditions (entry 10).
Fig. 1 depicts the catalytic efficiency of substituted iodobenzenes
and some aliphatic alkyl iodides in the iodane(III)-Hofmann
rearrangement of a-phenylacetamide. Introduction of both
electron-donating (p-Me, 3,5-Me2 and 2,4,6-Me3) and electron-
withdrawing groups (p-Cl and p-CF3) into iodobenzene decreased
the yield of 3a. Aliphatic iodides such as methyl, trifluoroethyl,
and 1-adamantyl iodides showed no catalytic efficiency.
We are pleased to find that our new catalytic method has
found a general use in the Hofmann rearrangement of primary
carboxamides (Table 2). All of the unfunctionalized simple
linear, branched, and cyclic aliphatic carboxamides examined
afforded alkylammonium chlorides 3b–k with one less carbon
atom at room temperature in high yields (Table 2, entries 1–10).
The catalytic conditions are compatible with the presence of
various kinds of functionalities such as halogens (F, Cl, Br),
sulfonamides, amines and methoxy and nitro groups.
reactive species, with two water molecules being coordinated
to the iodine centre.16 l3-Iodane 2 undergoes the Hofmann
rearrangement of carboxamides, probably via the intervention
of N-(phenyl-l3-iodanyl)carboxamides 6.6 As a third ligand of
the iodane(III) in 6, we prefer the tetrafluoroborate anion as a
possible candidate, because the linear hypervalent bonding
N–Iꢁ ꢁ ꢁF in 6 seems to be in the preferred combination of the
ligands in terms of trans influences, which control the stability
of hypervalent bonding of l3-iodanes.17
Notes and references
1 A. W. Hofmann, Ber. Dtsch. Chem. Ges., 1881, 14, 2725.
2 Reviews: (a) E. S. Wallis and J. F. Lane, Org. React., 1946, 3, 267;
(b) T. Shioiri, in Comprehensive Organic Synthesis, ed. B. M. Trost
and I. Fleming, Pergamon, Oxford, 1991, vol. 6, p. 795.
3 PhI(OCOCF3)2: (a) A. S. Radhakrishna, M. E. Parham,
R. M. Riggs and G. M. Loudon, J. Org. Chem., 1979, 44, 1746;
(b) G. M. Loudon, A. S. Radhakrishna, M. R. Almond,
J. K. Blodgett and R. H. Boutin, J. Org. Chem., 1984, 49, 4272.
4 PhI(OAc)2: (a) A. L. J. Beckwith and L. K. Dyall, Aust. J. Chem.,
1990, 43, 451; (b) R. M. Moriarty, C. J. Chany, R. K. Vaid,
O. Prakash and S. M. Tuladhar, J. Org. Chem., 1993, 58, 2478;
(c) H. Togo, T. Nabana and K. Yamaguchi, J. Org. Chem., 2000,
65, 8391.
5 PhI(OH)OTs: (a) I. M. Lazbin and G. F. Koser, J. Org. Chem.,
1986, 51, 2669; (b) A. Vasudevan and G. F. Koser, J. Org. Chem.,
1988, 53, 5158.
6 PhI(OMe)OTs: I. M. Lazbin and G. F. Koser, J. Org. Chem., 1987,
52, 476.
7 (PhIO)n: A. S. Radhakrishna, C. G. Rao, R. K. Varma, B. B. Singh
and S. P. Bhatnagar, Synthesis, 1983, 538.
8 J. W. Hilborn, Z.-H. Lu, A. R. Jurgens, Q. K. Fang, P. Byers,
S. A. Wald and C. H. Senanayake, Tetrahedron Lett., 2001,
42, 8919.
Bicyclic amide 4 afforded endo-ammonium chloride 5
stereoselectively in a good yield (Scheme 3), which suggests
retention of stereochemistry of the migrating groups in the
catalytic l3-iodane-induced rearrangement of carboxamides,
as observed in the classical Hofmann rearrangement.2
9 K. Yamada, H. Urakawa, H. Oku and R. Katakai, J. Pept. Res.,
2004, 64, 43.
10 N. Satoh, T. Akiba, S. Yokoshima and T. Fukuyama,
Angew. Chem., Int. Ed., 2007, 46, 5734.
11 K. G. Poullennec and D. Romo, J. Am. Chem. Soc., 2003, 125, 6344.
12 A. A. Zagulyaeva, C. T. Banek, M. S. Yusubov and
V. V. Zhdankin, Org. Lett., 2010, 12, 4644.
Scheme 4 depicts a catalytic cycle for the Hofmann rearrange-
ment of carboxamides, which involves in situ generation of
tetracoordinated square planar hydroxy-l3-iodane 2 as a
13 Electrochemical Hofmann rearrangement has been reported.
See: (a) T. Shono, Y. Matsumura, S. Yamane and S. Kashimura,
Chem. Lett., 1982, 565; (b) Y. Matsumura, Y. Satoh, T. Maki and
O. Onomura, Electrochim. Acta, 2000, 45, 3011.
14 For iodobenzene-catalyzed oxidations, see: (a) T. Fuchigami and
T. Fujita, J. Org. Chem., 1994, 59, 7190; (b) M. Ochiai, Y. Takeuchi,
T. Katayama, T. Sueda and K. Miyamoto, J. Am. Chem. Soc., 2005,
127, 12244; (c) T. Dohi, A. Maruyama, M. Yoshimura,
K. Morimoto, H. Tohma and Y. Kita, Angew. Chem., Int. Ed.,
2005, 44, 6193; (d) Y. Yamamoto and H. Togo, Synlett, 2006, 798;
(e) R. D. Richardson, T. K. Page, S. Altermann, S. M. Paradine,
A. N. French and T. Wirth, Synlett, 2007, 538; (f) M. Ochiai and
K. Miyamoto, Eur. J. Org. Chem., 2008, 4229; (g) T. Dohi,
A. Maruyama, N. Takenaga, K. Senami, Y. Minamitsuji,
H. Fujioka, S. B. Caemmerer and Y. Kita, Angew. Chem., Int. Ed.,
2008, 47, 3787; (h) T. Dohi and Y. Kita, Chem. Commun., 2009, 2073;
(i) S. Quideau, G. Lyvinec, M. Marguerit, K. Bathany, A. Ozanne-
Beaudenon, T. Buffeteau, D. Cavagnat and A. Chenede, Angew.
Chem., Int. Ed., 2009, 48, 4605; (j) M. S. Yusubov, V. N. Nemykin
and V. V. Zhdankin, Tetrahedron, 2010, 66, 5745; (k) M. Uyanik,
T. Yasui and K. Ishihara, Angew. Chem., Int. Ed., 2010, 49, 2175.
15 K. Miyamoto, Y. Sei, K. Yamaguchi and M. Ochiai, J. Am. Chem.
Soc., 2009, 131, 1382.
Scheme 3 Retention of stereochemistry of a migrating group.
16 (a) K. Miyamoto, N. Tada and M. Ochiai, J. Am. Chem. Soc.,
2007, 129, 2772; (b) M. Ochiai, K. Miyamoto, Y. Yokota,
T. Suefuji and M. Shiro, Angew. Chem., Int. Ed., 2005, 44, 75.
17 M. Ochiai, T. Sueda, K. Miyamoto, P. Kiprof and V. V. Zhdankin,
Angew. Chem., Int. Ed., 2006, 45, 8203.
Scheme 4 Catalytic cycle of Hofmann rearrangement.
c
984 Chem. Commun., 2012, 48, 982–984
This journal is The Royal Society of Chemistry 2012