Defined hypervalent iodine(III) reagents incorporating transferable nitrogen groups: Nucleophilic amination through electrophilic activation

Article abstract of DOI:10.1002/anie.201206420

Only I and N: Hypervalent iodine(III) reagents with two reactive I-N single bonds have been isolated for the first time. Their solid-state and solution structures provide evidence for enhanced electrophilicity at iodine and nucleophilic character of the imine. As a result, improved reactivity in amination reactions and unprecedented nitrogen-transfer reactions under metal-free conditions are realized. Copyright

Full text of DOI:10.1002/anie.201206420

.
Angewandte
Communications
DOI: 10.1002/anie.201206420
Hypervalent Iodine Reagents
Defined Hypervalent Iodine(III) Reagents Incorporating Transferable
Nitrogen Groups: Nucleophilic Amination through Electrophilic
Activation**
Josꢀ A. Souto, Claudio Martꢁnez, Irene Velilla, and Kilian MuÇiz*
À
Direct oxidative amination reactions of hydrocarbons are of
high synthetic importance as they have no or little precedence
in nature.[1] Processes of this type that proceed under metal-
free conditions are particularly desirable owing to their
environmental benigness and practicability. In principle,
hypervalent iodine(III) reagents with their high oxidation
potential are a promising concept for oxidative amination.[2]
In examples in the area, mainly by Domꢀnguez and co-
workers, a reagent combination consisting of amides and
orbital and even undergoes direct C H amination of alkanes
at room temperature.[7,8]
À
In general, hypervalent iodine(III) species containing I N
single bonds are rare.[9,10] More importantly from a synthetic
standpoint, isolated hypervalent iodine(III) reagents bearing
À
a defined I N single bond with a transferable nitrogen group
for metal-free amination reactions of hydrocarbons are
extremely scarce and no general reactivity has been described
so far. In recent work,[11] we reported unusual metal-free
diamination, and allylic and acetylenic amination reactions
based on a new hypervalent iodine(III) reagent of the type
PhI(OAc)N(SO2R)2. We now describe the synthesis and
isolation of unprecedented hypervalent iodine species of the
formula PhI[N(SO2R)2]2, discuss their formation and their
solid-state and solution structures, and report unparalleled
chemical transformations based on electrophilic activation/
nucleophilic amination with these reagents.
À
PhI(O2CCF3)2 was used; an intermediate A with an I N bond
was postulated, which generates an electrophilic nitrogen
source upon heterolytic dissociation.[3] Despite their obvious
synthetic utility, little information has been uncovered on the
structural basis of the intermediary iodine reagents.
We recently found that iodosobenzene diacetate under-
goes protonolysis in the presence of bistosylimide leading to
loss of acetic acid and to immediate formation of the
monomeric species 2a.[11a] However, we noticed that for the
diamination of styrene as a standard transformation, the
isolated compound 2a promoted only a slow reaction. More-
over, addition of a second equivalent of bistosylimide is
required for a quantitative transformation. As a consequence,
we anticipated that 2a is not the active reagent, but rather
a precursor to it. Indeed, in the presence of water, 2a is
Recently, a series of metal-free amination reactions of
compounds with unfunctionalized carbon–hydrogen bonds
have become available. These include direct aromatic ami-
nation,[4] and the oxidative transfer of phthalimide to benzylic
positions and aromatic rings.[5] The involvement of inter-
mediate B with an iodine–nitrogen single bond as a precursor
to nitrogen radicals or electrophiles has been suggested in the
latter cases. However, definite structural proof could not be
obtained for this putative intermediate.[6] In a striking accom-
plishment, Ochiai isolated the hypervalent bromine(III)
converted into the new m-oxo-bridged compound
3
(Scheme 1). This product is also obtained directly from
iodosobenzene diacetate upon treatment with bistosylimide
and water. This formation of 3 is a fast process as monitored
by in situ IR spectroscopy. Characteristic IR bands at
1714 cmÀ1 confirm the presence of 2a as a short-living
intermediate during the formation of 3.[12,13]
À
reagent 1, which is attacked by alkenes at the s* N Br
Compound 3 is an active reagent in the diamination of
styrene; however, as only two bistosylimido units are present,
it gives a maximum yield of 50% together with iodosoben-
zene as the remaining iodine(III) species. Treatment of 3 with
an additional two equivalents of bistosylimide leads to further
chemical transformation and to the clean formation of the
new monomeric iodine(III) compound 4, which incorporates
two bisimido groups (Scheme 1).
[*] Dr. J. A. Souto, Dr. C. Martꢀnez, Dr. I. Velilla, Prof. Dr. K. MuÇiz
Institute of Chemical Research of Catalonia (ICIQ)
Av. Paꢁsos Catalans 16, 43007 Tarragona (Spain)
E-mail: kmuniz@iciq.es
Homepage: http://www.iciq.es
Prof. Dr. K. MuÇiz
The solid-state structure of 4 is depicted in Figure 1.[12] It
Catalan Institution for Research and Advanced Studies (ICREA)
Pg. Lluꢀs Companys 23, 08010 Barcelona (Spain)
À
displays comparably short I N distances of 2.210 ꢁ, owing to
the required stabilization of the electrophilic iodine center.
Compound 4 indeed represents the elusive active reagent in
the diamination of alkenes.[11a–c] When the initial conversion
of styrene was monitored, the relative rate of the reaction
[**] We thank Fundaciꢂn ICIQ and the Spanish Ministerio de Economꢀa
(CTQ2011-25027) for financial support.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201206420.
1324
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1324 –1328

Angewandte
Chemie
Scheme 2. Synthesis of bisimido iodine(III) reagents 5 and 6.
Isolated compound 4 is an excellent reagent for the
diamination of alkenes (Table 1). It promotes rapid and
productive reactions at room temperature within minutes that
significantly surpass earlier examples relying on the in situ
formation of the reagent, which usually requires significantly
longer reaction times and partially harsher conditions.[11b,c]
Representative examples include the diamination of styrene
(7a), 1-octene (7b), allyl benzene (7c) stilbene (7d), and
cyclopentene (7e). The regioselective diamination of buta-
diene 7 f now also proceeds at room temperature. The
robustness of the new process was further demonstrated by
diamination of 7a on a 20 mmol scale (Table 1, entry 2).
Scheme 1. Sequential transformation of iodine(III) compounds 2a and
3 into reagent 4, and formation of 3 as indicated by in situ IR
spectroscopy.
Table 1: Diamination reactions with isolated reagent 4.[a]
Entry Substrate
Product
t [min] Yield Previous best
[%][b] conditions
PhI(OAc)2/
1
25
30
80
2HNTs2,
RT, 12 h, 80%[11b]
2[c]
78[d]
PhI(OAc)2/
2HNTs2,
Figure 1. X-ray crystal structure of 4; ellipsoids at 50% probability.
Selected bond lengths [ꢃ] and angles [8]: I1–C15 2.117(17), I1–N1
2.210(4), I1–N1A 2.210(4); C15-I1-N1 88.37(10), N1-I1-N1A 176.7 (2).
3
4
5
50
90
82
90
66
508C, 12 h,
80%[11b]
PhI(OAc)2/
2HNTs2,
508C, 12 h,
with 4 was found to be three times higher than that with 3.[13]
The superior reactivity of PhI(NTs2)2 (4) over its precursors 2
and 3 can also be considered to be the result of enhanced
electrophilicity at the central iodine(III) atom owing to the
presence of two less stabilizing imido ligands.
The synthesis of 4 from 3 proceeds quantitatively through
protonolysis and thus is again a pKa-driven pathway. In
a related transformation, compound PhI(NMs2)2 (5) is
generated directly from the corresponding precursor 2b
(Scheme 2). Because of its basic m-oxo bridge, compound 3
can serve as a general precursor for protonolysis events to
generate mixed bisimido iodine(III) compounds. For exam-
ple, the compound PhI(NTs2)NMs2 (6) is obtained from the
corresponding protonolysis of 3 with bismesylimide.
90%[11b]
PhI(OAc)2/
2HNTs2,
240
508C, 12 h,
56%[11b]
PhI(OAc)NTs2/
HNTs2,
6
7
300
90
72
91
458C, 96 h,
46%[11b]
PhI(OAc)NTs2/
HNTs2,
RT, 12 h, 75%[11c]
[a] 0.2 mmol scale. [b] Yield of product isolated after purification.
[c] Reaction at a 20 mmol scale. [d] Yield of product isolated after
a single recrystallization from MeOH.
Angew. Chem. Int. Ed. 2013, 52, 1324 –1328
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1325

.
Angewandte
Communications
In investigations of the behavior of reagent 6 in the
diamination of styrene all four possible diamination products
were obtained.[13] This suggests that the individual bissulfo-
nylimide groups in 4 and 5 should be labile and exchangeable
in solution. To further illustrate this finding, isotopically
labeled derivatives of 4 with a 15N-labeled bistosylimide and
a pentadeuterated phenyl substituent were prepared. When
the two species were mixed at room temperature, apparently
completely statistical equilibration of all nitrogen groups took
place at the iodine centers (Scheme 3). An MS experiment
confirmed this observation through the identification of all
four corresponding cationic iodine fragments [PhINTs2]+,
[PhI15NTs2]+, [C6D5INTs2]+, and [C6D5I15NTs2]+.[13]
Scheme 4. Iodine(III)-promoted a-amination of ketones.
cyclic enol ethers 7l–n, which give the corresponding a-
aminated ketones 8l–n. These transformations are of interest
as they serve to differentiate the nucelophilic amination
reactivity of 4 from the putative reagent PhI(N3)2.[14] The
latter is a source of azide radicals and gives exclusive allylic
azidonation in the oxidation of the related TIPS enol ethers.
For the formation of a-azido ketones, the presence of
TEMPO at À788C and significantly higher reaction times of
up to 24 h are required.[16]
The unique potential of reagent 4 is further demonstrated
by the following examples of metal-free amination reactions
(Scheme 5). Importantly, the reagent combinations PhI-
(OAc)2/2HNTs2 and PhI(OAc)NTs2/HNTs2 were ineffective
in these cases, and other hypervalent-iodine oxidants gave
completely different products, if any.[13] First, oxidation of
alkene 9 results in complete intermolecular diamination to
Scheme 3. Dynamic behavior of bissulfonylimido groups in solution.
As a result, compounds 4–6 are characterized by the
enhanced electrophilicity of the iodine(III) center, which
accelerates interaction with the p-system of substrates 7. This
is combined with the corresponding nucleophilic behavior of
the free bistosylimide (Scheme 3, bottom). This is signifi-
cantly different from the previously mentioned pathways for
iodine(III)-mediated aminations through A or B, which are
based exclusively on electrophilic character at nitrogen or
suggest the involvement of radical pathways. In contrast, in
the new complexes of type 4 the bissulfonylimides retain their
nucleophilicity and therefore induce electrophilic character at
iodine, which in addition to the established diamination
reactions from Table 1 allows for new amination chemistry at
comparably low temperatures and under mild conditions.
For example, unprecedented a-amination reactions of
ketones were discovered in the oxidation of the a,b-unsatu-
rated ketone 7g and acetophenone 7h with 4 (Scheme 4),
which presumably proceed through the corresponding enol
form. Indeed, when the preformed silyl enol ethers 7h’–k are
used, the corresponding a-aminated acetophenones 8h–k[12]
are formed within minutes at room temperature. To demon-
strate the utility of these products as synthetic building blocks,
the related a-amination between 7h’ and PhI(NMsTs)2 was
performed and the resulting aminated acetophenone could be
converted into the corresponding monotosylated aminoalco-
hol in two steps.[13]
Importantly, only the use of isolated reagent 4 provides
the neutral conditions essential for successful amination, as
reagent combinations consisting of PhI(OAc)2 and HNTs2
liberate acid and lead to predominant cleavage of the TMS
enol ethers. The a-amination reaction is further successful for
Scheme 5. Unprecedented metal-free amination reactions of 4 over-
riding intramolecular cyclization.
1326
www.angewandte.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1324 –1328

Angewandte
Chemie
Serna, I. Tellitu, E. Domꢀnguez, I. Moreno, R. SanMartin,
give 10 overcoming any preference for intramolecular piper-
azine formation.[16] More strikingly, the 2-vinyl aniline 11
undergoes selective intermolecular diamination to give 12. A
potential indole cyclization was never observed under these
conditions, as had occurred with other iodine(III) reagents.[13]
The tryptamine derivative 13 was found to undergo another
unprecedented amination reaction to provide the 2-aminated
indole 14, in which again preferential intermolecular reac-
tivity over intramolecular reactivity was observed.[17,18]
Finally, the enhanced electrophilicity of 4 provides additional
unexpected reactivity in a new oxidation of 2-acetylenyl
aniline 15 at room temperature. In this case, the expected
common reactions, oxidation of the alkyne or oxidatively
induced cyclization, do not take place. Instead, an intermo-
lecular regioselective aromatic oxidation yields 16 in a reac-
tion that may be considered the aza analogue[19] of a Kita
oxidation.
We have explored the nature of the active iodine(III)
species in metal-free amination reactions. These reagents
were isolated for the first time and identified to be bisimido
iodine(III) compounds PhI[N(SO2R)2]2. Their unprecedented
reactivity enables several new transformations, and defined
hypervalent iodine(III) reagents incorporating transferable
nitrogen groups are now available for the development of
additional direct metal-free amination reactions.
Tetrahedron Lett. 2003, 44, 3483; e) M. Tsukamoto, K. Murata, T.
Sakamoto, S. Saito, Y. Kikugawa, Heterocycles 2008, 75, 1133;
f) Y. Kikugawa, Heterocycles 2009, 78, 571; g) S. Serna, I. Tellitu,
E. Domꢀnguez, I. Moreno, R. SanMartin, Org. Lett. 2005, 7,
3073; h) I. Tellitu, S. Serna, M. T. Herrero, I. Moreno, E.
Domꢀnguez, R. SanMartin, J. Org. Chem. 2007, 72, 1526; i) Y.
Kikugawa, M. Kawase, Chem. Lett. 1990, 581; j) D. J. Wardrop,
M. S. Burge, Chem. Commun. 2004, 1230; k) A. Correa, I.
Tellitu, E. Domꢀnguez, I. Moreno, R. SanMartin, J. Org. Chem.
2005, 70, 2256; l) A. Correa, M. T. Herrero, I. Tellitu, E.
Domꢀnguez, I. Moreno, R. SanMartin, Tetrahedron 2003, 59,
7103; m) A. Correa, I. Tellitu, E. Domꢀnguez, R. SanMartin, J.
Org. Chem. 2006, 71, 8316; n) D. J. Wardrop, E. G. Bowen, R. E.
Forslund, A. D. Sussman, S. L. Weerasekera, J. Am. Chem. Soc.
2010, 132, 1188; o) E. G. Bowen, D. J. Wardrop, Org. Lett. 2010,
12, 5330; p) D. J. Wardrop, E. G. Bowen, Org. Lett. 2011, 13,
2376.
[4] a) A. P. Antonchick, R. Samanta, K. Kulikov, J. Lategahn,
Angew. Chem. 2011, 123, 8764; Angew. Chem. Int. Ed. 2011,
50, 8605; b) S. H. Cho, J. Yoo, S. Chang, J. Am. Chem. Soc. 2011,
133, 5996; c) R. Samanta, J. Lategahn, A. P. Antonchick, Chem.
Commun. 2012, 48, 3194.
[5] a) H. J. Kim, J. Kim, S. H. Cho, S. Chang, J. Am. Chem. Soc. 2011,
133, 16382; b) A. A. Kantak, S. Potavathri, R. A. Barham, K. M.
Romano, B. de-Boef, J. Am. Chem. Soc. 2011, 133, 19960.
[6] For an indirect structural assignment: K. Moriyama, K. Ishida,
H. Togo, Org. Lett. 2012, 14, 946.
[7] a) M. Ochiai, T. Kaneaki, N. Tada, K. Miyamoto, H. Chuman, M.
Shiro, S. Hayashi, W. Nakanishi, J. Am. Chem. Soc. 2007, 129,
12938; b) M. Ochiai, K. Miyamoto, T. Kaneaki, S. Hayashi, W.
Nakanishi, Science 2011, 332, 448.
Received: August 9, 2012
Revised: October 1, 2012
Published online: December 3, 2012
[8] This is in remarkable contrast to the corresponding imidoiodane-
(III) compounds, which require the presence of a metal catalyst
Keywords: amides · amination · iodine(III) reagents ·
nucleophilicity · oxidation
À
for aziridination and C H insertion reactions: a) P. Dauban,
.
R. H. Dodd, Synlett 2003, 1571; b) D. Karina, R. H. Dodd, Curr.
Org. Synth. 2011, 15, 1507.
[9] Compounds with IIII N bonds usually lack stability unless they
À
are supported by chelation. For exceptions such as amidoiodane
derivatives of cyclic imides such as phthalimide, succinimide,
glutarimide, and saccharine: a) L. Hadjiarapoglou, S. Spyroudis,
A. Varvoglis, Synthesis 1983, 207; b) M. Papadopoulou, A.
Varvoglis, Chem. Res. Synop. 1983, 66; c) M. Papadopoulou, A.
Varvoglis, Chem. Res. Synop. 1984, 166; for isolable N-phenyl-
iodonio carboxamide tosylates: d) I. M. Lazbin, G. F. Koser, J.
Org. Chem. 1987, 52, 476; for the synthesis of cyclic benzioda-
[1] a) R. Hili, A. K. Yudin, Nat. Chem. Biol. 2006, 2, 284; b) Amino
Group Chemistry (Ed.: A. Ricci), Wiley-VCH, Weinheim, 2008;
c) G. Dequirez, V. Pons, P. Dauban, Angew. Chem. 2012, 124,
7498; Angew. Chem. Int. Ed. 2012, 51, 7384.
[2] For current reviews on iodine(III) reagents: a) S. Schꢂfer, T.
Wirth, Angew. Chem. 2010, 122, 2846; Angew. Chem. Int. Ed.
2010, 49, 2786, and references therein; b) V. V. Zhdankin, P. J.
Stang, Chem. Rev. 2008, 108, 5299; c) T. Dohi, Y. Kita, Chem.
Commun. 2009, 2073; d) M. Uyanik, K. Ishihara, Chem.
Commun. 2009, 2086; e) M. Ngatimin, D. W. Lupton, Aust. J.
Chem. 2010, 63, 653; f) M. S. Yusubov, D. V. Maskaev, V. V.
Zhdankin, Arkivoc 2009, 1, 370; g) Hypervalent Iodine in
Organic Chemistry: Chemical Transformations (Eds.: R. M.
Moriarty, O. Prakash), Wiley-Interscience, New York, 2008;
h) M. A. Ciufolini, N. A. Braun, S. Canesi, M. Ousmer, J. Chang,
D. Chai, Synthesis 2007, 3759; i) M. Ochiai, Chem. Rec. 2007, 7,
12; j) Topics in Current Chemistry, Vol. 224 (Ed.: T. Wirth),
Springer, Berlin, 2003; k) A. Duschek, S. F. Kirsch, Angew.
Chem. 2011, 123, 1562; Angew. Chem. Int. Ed. 2011, 50, 1524;
l) A. Varvoglis, Hypervalent Iodine in Organic Synthesis, Aca-
demic Press, London, 1997; m) V. V. Zhdankin, J. Org. Chem.
2011, 76, 1185.
zoles containing an IIII N bond: e) V. V. Zhdankin, A. Y.
À
Koposov, L. Su, V. V. Boyarskikh, B. C. Netzel, V. G. Young, Jr.,
Org. Lett. 2003, 5, 1583; f) V. V. Zhdankin, R. M. Arbit, B. J.
Lynch, P. Kiprof, J. Org. Chem. 1998, 63, 6590; g) V. V. Zhdankin,
R. M. Arbit, M. McSherry, B. Mismash, V. G. Young, Jr., J. Am.
Chem. Soc. 1997, 119, 7408; h) V. V. Zhdankin, A. E. Koposov,
J. T. Smart, R. R. Tykwinski, R. McDonald, A. Morales-
Izquierdo, J. Am. Chem. Soc. 2001, 123, 4095; i) D. G. Naae,
J. Z. Gougoutas, J. Org. Chem. 1975, 40, 2129; j) T. M. Balthazor,
D. E. Godar, B. R. Stults, J. Org. Chem. 1979, 44, 1979. However,
these compounds are usually unreactive toward alkenes.
[10] The isolation and structural characterization of iminoiodane(III)
compounds[8] constitutes a remarkable achievement: a) A. K.
Mishra, M. M. Olmstead, J. J. Ellison, P. P. Power, Inorg. Chem.
1995, 34, 3210; b) A. Yoshimura, V. N. Nemykin, V. V. Zhdankin,
Chem. Eur. J. 2011, 17, 10538.
[11] a) C. Rçben, J. A. Souto, Y. Gonzꢃlez, A. Lishchynskyi, K.
MuÇiz, Angew. Chem. 2011, 123, 9650; Angew. Chem. Int. Ed.
2011, 50, 9478; b) J. Souto, Y. Gonzꢃlez, A. Iglesias, D. Zian, A.
Lishchynskyi, K. MuÇiz, Chem. Asian J. 2012, 7, 1103; c) A.
Lishchynskyi, K. MuÇiz, Chem. Eur. J. 2012, 18, 2212; d) J. A.
[3] For selected examples on alkene oxidation involving electro-
philic nitrogen from activation with PIFA: a) I. Tellitu, E.
Domꢀnguez, Trends Heterocycl. Chem. 2011, 15, 23; b) E.
Malamidou-Xenikaki, S. Spyroudis, M. Tsanakopoulou, D.
Hadjipavlou-Litina, J. Org. Chem. 2009, 74, 7315; c) I. Tellitu,
A. Urrejola, S. Serna, I. Moreno, M. T. Herrero, E. Domꢀnguez,
R. SanMartin, A. Correa, Eur. J. Org. Chem. 2007, 437; d) S.
Angew. Chem. Int. Ed. 2013, 52, 1324 –1328
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1327

.
Angewandte
Communications
Souto, D. Zian, K. MuÇiz, J. Am. Chem. Soc. 2012, 134, 7242;
e) J. A. Souto, P. Becker, A. Iglesias, K. MuÇiz, J. Am. Chem.
Soc. 2012, 134, 15505.
Soc. 1992, 114, 3993; d) P. Magnus, M. B. Roe, C. Hulme, Chem.
Commun. 1995, 263.
[16] For examples of PhI(OAc)2-mediated intramolecular formation
of pyrrolidines from alkenes: a) B. M. Cochran, F. E. Michael,
Org. Lett. 2008, 10, 5039; b) H. M. Lovick, F. E. Michael, J. Am.
Chem. Soc. 2010, 132, 1249; c) for an elegant enantioselective
version: U. Farid, T. Wirth, Angew. Chem. 2012, 124, 3518;
Angew. Chem. Int. Ed. 2012, 51, 3462.
[12] CCDC 811767 (3), 893042 (4), 902658 (8i), 862030 (14), and
893041 (16) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
[17] For recent examples of cyclization reactions of tryptamine
derivatives with hypervalent iodine: a) D. Kajiyama, T. Saitoh, S.
Yamaguchi, S. Nishiyama, Synthesis 2012, 1667; with halonium
sources: b) O. Lozano, G. Blessley, T. Martinez del Campo, A. L.
Thompson, G. T. Giuffredi, M. Bettati, M. Walker, R. Borman,
V. Gouverneur, Angew. Chem. 2011, 123, 8255; . Chem. Int. Ed.
2011, 50, 8105; c) J. Kim, M. Movassaghi, J. Am. Chem. Soc.
2010, 132, 14376; d) P. Ruiz-Sanchis, A. S. Svetlana, F. Albericio,
M. Alvarez, Chem. Eur. J. 2011, 17, 1388; with selenium sources:
A. J. Oelke, D. J. France, T. Hofmann, G. Wuitschik, S. V. Ley,
Angew. Chem. 2010, 122, 6275; Angew. Chem. Int. Ed. 2010, 49,
6139.
[18] The observed 2-amination is also an interesting contrast to
a recent investigation on the oxidation of 3-methylindole with
PhI(OAc)2: Y.-X. Li, H.-X. Wang, S. Ali, X.-F. Xia, Y.-M. Liang,
Chem. Commun. 2012, 48, 2343.
[19] For an intramolecular version: L. M. Pardo, I. Tellitu, E.
Domꢀnguez, Tetrahedron 2010, 66, 5811.
[13] Further details are included within the Supporting Information.
[14] While compound 4 is stable under laboratory conditions and can
be handled conveniently, PhI(N3)2 must be generated in situ
from PhIO and TMSN3 and is unstable above À308C: a) M.
Arimoto, H. Yamaguchi, E. Fujita, Y. Nagao, M. Ochiai, Chem.
Pharm. Bull. 1989, 37, 3221; b) M. Arimoto, H. Yamaguchi, E.
Fujita, M. Ochiai, Y. Nagao, Tetrahedron Lett. 1987, 28, 6289;
c) J. Ehrenfreund, E. Zbiral, Tetrahedron 1972, 28, 1697. The
superiority of 4 over PhI(N3)2 is further evidenced by its
isolation, storage, and large-scale application (Table 1, entry 2).
For the corresponding radical-mediated bisazodination reactions
see also: d) P. Magnus, M. B. Roe, Tetrahedron Lett. 1996, 37,
303; e) R. Chung, E. Yu, C. D. Incarvito, D. J. Austin, Org. Lett.
2004, 6, 3881.
[15] a) P. Magnus, J. Lacour, P. A. Evans, M. B. Roe, C. Hulme, J. Am.
Chem. Soc. 1996, 118, 3406; b) P. Magnus, J. Lacour, J. Am.
Chem. Soc. 1992, 114, 767; c) P. Magnus, J. Lacour, J. Am. Chem.
1328
www.angewandte.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2013, 52, 1324 –1328