Catalytic 1,4-rhodium(III) migration enables 1,3-enynes to function as one-carbon oxidative annulation partners in C-H functionalizations

Article abstract of DOI:10.1002/anie.201406072

1,3-Enynes containing allylic hydrogens cis to the alkyne are shown to act as one-carbon partners, rather than two-carbon partners, in various rhodium-catalyzed oxidative annulations. The mechanism of these unexpected transformations is proposed to occur through double C-H activation, involving a hitherto rare example of the 1,4-migration of a Rh^III species. This phenomenon is general across a variety of substrates, and provides a diverse range of heterocyclic products.

Full text of DOI:10.1002/anie.201406072

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Chemie
DOI: 10.1002/anie.201406072
À
C H Functionalization
Catalytic 1,4-Rhodium(III) Migration Enables 1,3-Enynes to Function
À
as One-Carbon Oxidative Annulation Partners in C H
Functionalizations**
David J. Burns and Hon Wai Lam*
Abstract: 1,3-Enynes containing allylic hydrogens cis to the
alkyne are shown to act as one-carbon partners, rather than
two-carbon partners, in various rhodium-catalyzed oxidative
annulations. The mechanism of these unexpected transforma-
describe a new mode of oxidative annulation, in which 1,3-
enynes are able to function as one-carbon,[7] rather than two-
carbon reaction partners (Scheme 1b). We propose this
reactivity arises from a hitherto rare example of 1,4-RhIII
À
À
tions is proposed to occur through double C H activation,
migration, which opens up new possibilities in C H function-
involving a hitherto rare example of the 1,4-migration of a RhIII
species. This phenomenon is general across a variety of
substrates, and provides a diverse range of heterocyclic
products.
alization reactions.[8] This phenomenon is general for sub-
strates containing directing groups such as enols, phenols,
carboxylic acids, or imides, resulting in a range of heterocyclic
products.
During our investigations into ruthenium-, rhodium-, and
palladium-catalyzed oxidative annulations of 2-aryl cyclic 1,3-
dicarbonyl compounds with alkynes,[5f,g] the reaction of
substrate 1a with 1,3-enyne 2a in the presence of
[{Cp*RhCl2}2] (2.5 mol%) and Cu(OAc)2 (2.1 equiv) in
dioxane at 1208C was conducted [Eq. (1)]. Surprisingly, in
addition to providing the expected spiroindene 3a in 21%
yield, this reaction also gave benzopyran 4a in 25% yield.[9]
T
he metal-catalyzed, directing-group-promoted oxidative
[1]
À
À
C H functionalization of aromatic Csp2 H bonds with
alkynes[2,3] has been widely exploited to prepare a rich variety
of heterocyclic[4] and carbocyclic products.[5] In the reactions
of unsymmetrical alkynes, high regioselectivity is usually
observed when the two substituents on the alkyne are
electronically well-differentiated. For example, with alkynes
À
containing one alkyl and one aryl substituent, the initial C C
bond formation usually occurs with high regioselectivity at
the alkyne carbon bearing the sp3-hybridized group. This
regioselectivity is maintained in the oxidative annulation of
1,3-enynes, as demonstrated by the groups of Fagnou
(Scheme 1a)[6a] and Ackermann,[6b] for example. Herein, we
A possible mechanism for the formation of 4a is shown in
Scheme 2. Generation of the rhodium diacetate complex 5
from [{Cp*RhCl2}2] and Cu(OAc)2 is followed by cyclorho-
dation of substrate 1a to provide the rhodacycle 6. Coordi-
nation and migratory insertion of the 1,3-enyne 2a with the
regioselectivity observed previously[6] can then provide a new
rhodacycle 7. Reductive elimination of 7 would then give the
expected spiroindene 3a as described with alkynes.[5f,g] How-
ever, an alternative pathway is the reversible protonolysis of 7
with AcOH to provide the alkenylrhodium species 8, which
can then undergo a 1,4-rhodium migration to give a new
allylrhodium species 9A.[10] Notably, this process enables the
Scheme 1. Oxidative annulation reactions of 1,3-enynes.
[*] Dr. D. J. Burns, Prof. H. W. Lam
School of Chemistry, University of Nottingham
University Park, Nottingham, NG7 2RD (UK)
E-mail: hon.lam@nottingham.ac.uk
Homepage: http://www.nottingham.ac.uk/~pczhl
[**] We thank the EPSRC for financial support (funding for D.J.B.
through grant number EP/J018090/1, and a Leadership Fellowship
to H.W.L.) and Martin D. Wieczysty at the School of Chemistry,
University of Edinburgh, for preliminary investigations and assis-
tance in the preparation of substrates.
À
activation of a Csp3 H bond. The 1,4-migration of rhodium(I)
is well-known,[11–13] but the corresponding 1,4-migrations of
rhodium(III) are rare, with the only reports to date being
stoichiometric studies of alkenyl to aryl migrations described
by Ishii and co-workers.[8] Presumably, the s-allylrhodium
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201406072.
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Table 2: Oxidative annulation reactions of 1g with various 1,3-enynes.[a]
Entry 1,3-
Enyne
Product
Yield
[%][b]
1
2b
2c
11b R=OTBS 84
2[c]
11c R=OH
62
Scheme 2. Proposed catalytic cycle.
species 9A can interconvert with the p-allylrhodium species
9B through the intermediacy of other isomers (not shown).
Nucleophilic attack of the p-allylrhodium(III) moiety[14,15] of
9B by the enol oxygen would provide the benzopyran 4a and
the rhodium(I) species 10, which can be then be reoxidized to
5 by Cu(OAc)2.
3
4
2d
2e
11d R=Ph
11e R=H
73
64
A survey of reaction conditions[16] revealed that lowering
the temperature to 608C led to higher yields of benzopyran
4a, but did not significantly alter the yield of spiroindene 3a.
Furthermore, the addition of AcOH (0.1 equiv) led to more
consistently reproducible results. Under these conditions,
benzopyran 4a and spiroindene 3a were obtained in 86% and
12% yield, respectively (Table 1, entry 1).
5[d]
6
2 f
2g
11 f n=1
11g n=2
93
89
Table 1: Oxidative annulation reactions of various 2-aryl-3-hydroxy-2-
cyclohexenones with 1,3-enyne 2a.[a]
7
8
2h
11h
11i
61
61
2i
Entry
Substrate
Yield of 3 [%][b]
Yield of 4 [%][b]
[a] Reactions were conducted with 0.50 mmol of 1g. [b] Yield of isolated
products. [c] Reaction conducted at 908C. [d] Reaction conducted using
0.37 mmol of 1g.
1
2
3
4
5
6
7
8
1a R=CO2Me
1b R=H
1c R=OMe
1d R=F
12
60
64
26
86
20
17
44
78
65
82
84
1e R=CF3
<5[c]
<5[c]
n.d.[d]
<5[c]
The scope of this transformation with respect to the 2-
aryl-3-hydroxy-2-cyclohexenone was then explored (Table 1).
With substrates 1b and 1c, which contain phenyl or 4-
methoxyphenyl groups, respectively, the spiroindenes 3 were
the major products (Table 1, entries 2 and 3). With substrates
containing more electron-withdrawing substituents at the 4-
1 f R=COMe
1g R=NO2
1h R=SO2Me
[a] Reactions were conducted with 0.50 mmol of 1a–h. [b] Yield of
isolated products. [c] The spiroindene was detected in trace amounts.
[d] Not detected.
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position of the aromatic ring, the benzopyran became the
major product (Table 1, entries 4–8). The spiroindene was
formed in only trace amounts in the reactions of substrates
containing trifluoromethyl, acetyl, or sulfone substituents
(Table 1, entries 5, 6, and 8), and was not detected when
a nitro group was present (Table 1, entry 7). These observa-
tions can be rationalized by considering that spiroindene
formation requires the reductive elimination of RhIII from
intermediates analogous to rhodacycle 7 (Scheme 2), with
concomitant oxidation of the substrate. Therefore, it appears
reasonable to assume that the activation barrier of this
reductive elimination is increased with more electron-defi-
cient substrates, as the substrate is more difficult to oxidize.
The alternative pathway leading to the benzopyran 4 then
becomes more competitive.
Next, the scope of this process with respect to the 1,3-
enyne was investigated using substrate 1g, and various enynes
containing allylic hydrogens cis to the alkyne were shown to
be effective one-carbon oxidative annulation partners
(Table 2). None of the alternative spiroindenes were detected
in any of these reactions. 1,3-Enynes containing protected or
unprotected 2-hydroxyethyl groups were tolerated (Table 2,
entries 1 and 2). 1,3-Enynes 2d and 2e, which contain
a phenyl group or a hydrogen atom trans to the alkyne, also
reacted smoothly to provide benzopyrans 11d and 11e
(Table 2, entries 3 and 4). The reaction is not limited to 1,3-
enynes containing methyl substitution cis to the alkyne, as
shown by the successful annulations of 1,3-enynes 2 f and 2g
(Table 2, entries 5 and 6). Notably, a silyl-protected hydroxy-
methyl substituent at the trans-position of 1,3-enyne 2h led to
11h in 61% yield with > 95:5 E:Z selectivity at the enol silane
(Table 2, entry 7).[17] Finally, 1,3-enyne 2h, which contains
a methyl group at the alkenyl carbon proximal to the alkyne
was also effective, providing 11i with > 95:5 E:Z selectivity
(Table 2, entry 8).[17]
groups underwent oxidative annulation with 1,3-enyne 2a to
give a diverse range of five- or six-membered oxygen and
nitrogen heterocycles 13a–e (Scheme 3).[18]
To verify the structural requirements of the 1,3-enyne for
one-carbon annulation to occur, the reaction of 1g with enyne
14, in which there are no allylic hydrogens cis to the alkyne,
was performed. This reaction led to no conversion at the
standard temperature of 608C. However, increasing the
temperature to 908C gave the spiroindene 15 in 53% yield
and only 7% of benzopyran 11e [Eq. (2)]. This experiment
contrasts with that shown in Table 2, entry 4, in which the
corresponding (Z)-1,3-enyne 2e gave benzopyran 11e only.
These results suggest that 1,4-RhIII migration (8 to 9 in
Scheme 2) occurs by a direct pathway that is contingent upon
the close proximity of Rh with the cis-allylic hydrogens. We
postulate that the formation of benzopyran 11e in 7% yield in
Equation (2) results from some type of E/Z isomerization
occurring at the higher temperature of 908C.
To gain further insight into this process, the reaction of 1g
with the hexadeuterated 1,3-enyne [D]6-2a was conducted
[Eq. (3)]. Three compounds were isolated from this experi-
This unusual oxidative annulation was found to be
a general phenomenon, and not merely limited to 2-aryl-3-
hydroxy-2-cyclohexenones. Several other aromatic substrates
containing enol, phenol, carboxylic acid, or imide directing
ment: recovered [D]6-2a in 20% yield with no deuterium
depletion detected, spiroindene [D]6-3g in 19% yield with no
deuterium depletion detected, and benzopyran [D]n-4g in
65% yield, with incomplete deuteration (77% D) at the
alkenyl carbon adjacent to the quaternary center. Several
conclusions can be drawn from these results.
Scheme 3. Oxidative annulation reactions of various substrates with
1,3-enyne 2a. Yields are of isolated products. [a] Reaction conducted in
the presence of K2CO3 (3.0 equiv), and a second portion of
[{Cp*RhCl2}2] (2.5 mol%) was added after 1 h. [b] Using 5 mol% of
[{Cp*RhCl2}2].
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À
First, the formation of spiroindene [D]6-3g suggests that C H
functionalization at the methyl group cis to the alkyne in the
1,3-enyne is involved in the product-determining step, since
the reaction of 1g with the non-deuterated 1,3-enyne 2a led to
none of the spiroindene 3g being detected (Table 1, entry 7).
Second, the deuteration pattern in [D]n-4g is consistent with
the 1,4-RhIII migration mechanism shown in Scheme 2.
However, the incomplete deuteration (77% D) at the internal
alkene suggests that 1,4-RhIII migration may occur by an
acetate-assisted, concerted metalation–deprotonation of 16 to
form rhodacycle 17, followed by deuteronolysis with AcOD
(Scheme 4).[19] Incomplete deuteration would arise as a result
[1] For selected reviews covering directing-group-assisted metal-
À
catalyzed C H functionalizations, see: a) K. M. Engle, J.-Q. Yu,
J. Org. Chem. 2013, 78, 8927 – 8955; b) K. M. Engle, T.-S. Mei, M.
Wasa, J.-Q. Yu, Acc. Chem. Res. 2012, 45, 788 – 802; c) C. S.
Yeung, V. M. Dong, Chem. Rev. 2011, 111, 1215 – 1292; d) J.
Wencel-Delord, T. Droege, F. Liu, F. Glorius, Chem. Soc. Rev.
2011, 40, 4740 – 4761; e) L. Ackermann, Chem. Rev. 2011, 111,
1315 – 1345; f) C.-L. Sun, B.-J. Li, Z.-J. Shi, Chem. Commun.
2010, 46, 677 – 685; g) T. W. Lyons, M. S. Sanford, Chem. Rev.
2010, 110, 1147 – 1169; h) D. A. Colby, R. G. Bergman, J. A.
Ellman, Chem. Rev. 2010, 110, 624 – 655.
[2] For a review of rhodium-catalyzed oxidative annulation of
alkynes and alkenes, see: T. Satoh, M. Miura, Chem. Eur. J. 2010,
16, 11212 – 11222.
[3] For a review of ruthenium-catalyzed oxidative annulation of
alkynes, see: L. Ackermann, Acc. Chem. Res. 2014, 47, 281 – 295.
[4] For representative recent examples of metal-catalyzed oxidative
annulations of alkynes that result in heterocycles, see: a) L.
Wang, L. Ackermann, Org. Lett. 2013, 15, 176 – 179; b) J. Li, L.
Neuville, Org. Lett. 2013, 15, 1752 – 1755; c) N. QuiÇones, A.
Seoane, R. Garcia-Fandino, J. L. MascareÇas, M. Gulꢀas, Chem.
Sci. 2013, 4, 2874 – 2879; d) S. Ding, Y. Yan, N. Jiao, Chem.
Commun. 2013, 49, 4250 – 4252; e) R. Kuram, M. Bhanuchandra,
A. K. Sahoo, Angew. Chem. 2013, 125, 4705 – 4710; Angew.
Chem. Int. Ed. 2013, 52, 4607 – 4612; f) M. C. Reddy, R.
Manikandan, M. Jeganmohan, Chem. Commun. 2013, 49,
6060 – 6062; g) K. Muralirajan, C.-H. Cheng, Chem. Eur. J.
2013, 19, 6198 – 6202; h) D. Zhao, Q. Wu, X. Huang, F. Song, T.
Lv, J. You, Chem. Eur. J. 2013, 19, 6239 – 6244; i) G. Zhang, L.
Yang, Y. Wang, Y. Xie, H. Huang, J. Am. Chem. Soc. 2013, 135,
8850 – 8853; j) W. Dong, L. Wang, K. Parthasarathy, F. Pan, C.
Bolm, Angew. Chem. 2013, 125, 11787 – 11790; Angew. Chem.
Int. Ed. 2013, 52, 11573 – 11576; k) M.-N. Zhao, Z.-H. Ren, Y.-Y.
Wang, Z.-H. Guan, Org. Lett. 2014, 16, 608 – 611; l) A. Seoane, N.
Casanova, N. QuiÇones, J. L. MascareÇas, M. Gulꢀas, J. Am.
Chem. Soc. 2014, 136, 834 – 837; m) Y. Hoshino, Y. Shibata, K.
Tanaka, Adv. Synth. Catal. 2014, 356, 1577 – 1585; n) M. Fukui,
Y. Hoshino, T. Satoh, M. Miura, K. Tanaka, Adv. Synth. Catal.
2014, 356, 1638 – 1644; o) J. Li, L. Ackermann, Tetrahedron 2014,
70, 3342 – 3348.
Scheme 4. Possible mechanism of the 1,4-RhIII migration.
of competitive protonolysis of 17 with the AcOH that is also
present in the reaction, or by adventitious water. Further
support for this mechanism was provided by the reaction of
1g with 1,3-enyne 2a in a dioxane/D2O (5:1) mixture, which
provided [D]n-4g with partial deuteration (28% D) at the
alkenyl carbon, with no deuteration observed at any other site
[Eq. (4)].[20]
[5] For examples of metal-catalyzed oxidative annulations of
alkynes that result in carbocycles, see: a) N. Umeda, H. Tsurugi,
T. Satoh, M. Miura, Angew. Chem. 2008, 120, 4083 – 4086;
Angew. Chem. Int. Ed. 2008, 47, 4019 – 4022; b) Y.-T. Wu, K.-H.
Huang, C.-C. Shin, T.-C. Wu, Chem. Eur. J. 2008, 14, 6697 – 6703;
c) Z. Shi, S. Ding, Y. Cui, N. Jiao, Angew. Chem. 2009, 121, 8035 –
8038; Angew. Chem. Int. Ed. 2009, 48, 7895 – 7898; d) Z. Shi, C.
Tang, N. Jiao, Adv. Synth. Catal. 2012, 354, 2695 – 2700; e) X.
Tan, B. Liu, X. Li, B. Li, S. Xu, H. Song, B. Wang, J. Am. Chem.
Soc. 2012, 134, 16163 – 16166; f) S. Reddy Chidipudi, I. Khan,
H. W. Lam, Angew. Chem. 2012, 124, 12281 – 12285; Angew.
Chem. Int. Ed. 2012, 51, 12115 – 12119; g) J. D. Dooley, S.
Reddy Chidipudi, H. W. Lam, J. Am. Chem. Soc. 2013, 135,
10829 – 10836; h) J. Nan, Z. Zuo, L. Luo, L. Bai, H. Zheng, Y.
Yuan, J. Liu, X. Luan, Y. Wang, J. Am. Chem. Soc. 2013, 135,
17306 – 17309; i) S. Peng, T. Gao, S. Sun, Y. Peng, M. Wu, H. Guo,
J. Wang, Adv. Synth. Catal. 2014, 356, 319 – 324; j) M. V. Pham,
N. Cramer, Angew. Chem. Int. Ed. 2014, 53, 3484 – 3487; k) S.
Kujawa, D. Best, D. J. Burns, H. W. Lam, Chem. Eur. J. 2014, 20,
8599 – 8602; l) A. Seoane, N. Casanova, N. QuiÇones, J. L.
MascareÇas, M. Gulꢀas, J. Am. Chem. Soc. 2014, 136, 7607 – 7610.
[6] For examples of oxidative annulations of 1,3-enynes, see:
a) M. P. Huestis, L. Chan, D. R. Stuart, K. Fagnou, Angew.
Chem. 2011, 123, 1374 – 1377; Angew. Chem. Int. Ed. 2011, 50,
1338 – 1341; b) L. Ackermann, A. V. Lygin, N. Hofmann, Angew.
In conclusion, we have reported an unexpected mode of
III
À
oxidative annulation in Rh -catalyzed C H functionaliza-
tions when 1,3-enynes containing allylic hydrogens cis to the
alkyne are present. The mechanism of these reactions is
À
proposed to occur through double C H activation, including
À
that of a Csp3 H bond, involving a hitherto rare example of the
1,4-migration of a RhIII species. Of broader significance, the
À
generation of an allyl–metal species from sequential C H
functionalization–1,4-metal migration opens up new oppor-
tunities in synthesis, and exploitation of this pathway in other
transformations is underway in our laboratories.
Received: June 10, 2014
Published online: July 22, 2014
À
Keywords: catalysis · C H functionalization · enyne · oxidation ·
rhodium
.
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Chem. 2011, 123, 6503 – 6506; Angew. Chem. Int. Ed. 2011, 50,
6379 – 6382.
[7] For examples of one-carbon oxidative annulation partners in
2009, 48, 6320 – 6323; j) M. Shigeno, T. Yamamoto, M. Mur-
akami, Chem. Eur. J. 2009, 15, 12929 – 12931; k) R. Shintani, S.
Isobe, M. Takeda, T. Hayashi, Angew. Chem. 2010, 122, 3883 –
3886; Angew. Chem. Int. Ed. 2010, 49, 3795 – 3798; l) T. Seiser, N.
Cramer, Angew. Chem. 2010, 122, 10361 – 10365; Angew. Chem.
Int. Ed. 2010, 49, 10163 – 10167; m) K. Sasaki, T. Hayashi,
Tetrahedron: Asymmetry 2012, 23, 373 – 380; n) T. Matsuda, Y.
Suda, A. Takahashi, Chem. Commun. 2012, 48, 2988 – 2990;
o) K. Sasaki, T. Nishimura, R. Shintani, E. A. B. Kantchev, T.
Hayashi, Chem. Sci. 2012, 3, 1278 – 1283.
À
catalytic C H functionalizations that are not alkynes, see
Ref. [5g] and: a) M. Miura, T. Tsuda, T. Satoh, M. Nomura,
Chem. Lett. 1997, 1103 – 1104; b) Y. Lu, D.-H. Wang, K. M.
Engle, J.-Q. Yu, J. Am. Chem. Soc. 2010, 132, 5916 – 5921; c) Y.
Du, T. K. Hyster, T. Rovis, Chem. Commun. 2011, 47, 12074 –
12076; d) C. Zhu, W. Xie, J. R. Falck, Chem. Eur. J. 2011, 17,
12591 – 12595; e) S. Reddy Chidipudi, M. D. Wieczysty, I. Khan,
H. W. Lam, Org. Lett. 2013, 15, 570 – 573; f) T. K. Hyster, K. E.
Ruhl, T. Rovis, J. Am. Chem. Soc. 2013, 135, 5364 – 5367; g) C.
Suzuki, K. Morimoto, K. Hirano, T. Satoh, M. Miura, Adv. Synth.
Catal. 2014, 356, 1521 – 1526; h) J. Li, M. John, L. Ackermann,
Chem. Eur. J. 2014, 20, 5403 – 5408; i) B. Ye, N. Cramer, Angew.
Chem. Int. Ed. 2014, Early View, DOI: 10.1002/anie.201404895.
[8] a) Y. Ikeda, K. Takano, S. Kodama, Y. Ishii, Chem. Commun.
2013, 49, 11104 – 11106; b) Y. Ikeda, K. Takano, M. Waragai, S.
Kodama, N. Tsuchida, K. Takano, Y. Ishii, Organometallics 2014,
33, 2142 – 2145.
[14] For reviews covering rhodium-catalyzed allylic substitutions,
see: a) M. Lautens, K. Fagnou, S. Hiebert, Acc. Chem. Res. 2002,
35, 48 – 58; b) P. A. Evans in Modern Rhodium-Catalyzed
Organic Reactions, Wiley-VCH, Weinheim, 2005.
[15] For selected, recent examples of rhodium-catalyzed allylic
substitutions, see: a) G. C. Tsui, M. Lautens, Angew. Chem.
2012, 124, 5496 – 5500; Angew. Chem. Int. Ed. 2012, 51, 5400 –
5404; b) J. Zhu, G. C. Tsui, M. Lautens, Angew. Chem. 2012, 124,
12519 – 12522; Angew. Chem. Int. Ed. 2012, 51, 12353 – 12356;
c) J. S. Arnold, H. M. Nguyen, J. Am. Chem. Soc. 2012, 134,
8380 – 8383; d) P. A. Evans, E. A. Clizbe, M. J. Lawler, S. Oliver,
Chem. Sci. 2012, 3, 1835 – 1838; e) P. A. Evans, S. Oliver, J. Chae,
J. Am. Chem. Soc. 2012, 134, 19314 – 19317; f) P. A. Evans, S.
Oliver, Org. Lett. 2013, 15, 5626 – 5629; g) J. S. Arnold, E. T.
Mwenda, H. M. Nguyen, Angew. Chem. 2014, 126, 3762 – 3766;
Angew. Chem. Int. Ed. 2014, 53, 3688 – 3692.
[16] The best results were obtained using non-anhydrous dioxane.
Other solvents such as toluene, tAmOH, EtOH, and DMF were
inferior to dioxane. Bases such as K2CO3, K3PO4, or Et3N, or
additives such as AgSbF6 or Ag2CO3 had a detrimental effect.
[17] The E:Z stereochemistries of products 11h and 11i were
determined on the basis of nOe experiments. See the Supporting
Information for details.
[18] The structure of 13e was confirmed by X-ray crystallography.
CCDC 1006281 contains 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.
[19] The proposed concerted metalation–deprotonation mechanism
for 1,4-RhIII migration contrasts with 1,4-RhI migration, which is
generally considered to proceed by an oxidative addition–
reductive elimination sequence. For example, see Refs. [11a] and
[13o].
[9] Unreacted 1,3-enyne 2a was recovered unchanged. Exposure of
1,3-enyne 2a to the reaction conditions in the absence of 1a led
to the recovery of unchanged 2a. No reaction occurred in the
absence of either [{Cp*RhCl2}2] or Cu(OAc)2.
[10] For an example of 1,4-palladium migration to give an allylpalla-
dium(II) species, see: J. Zhao, M. Campo, R. C. Larock, Angew.
Chem. 2005, 117, 1907 – 1909; Angew. Chem. Int. Ed. 2005, 44,
1873 – 1875.
[11] For early reports of 1,4-rhodium(I) migration, see: a) K. Oguma,
M. Miura, T. Satoh, M. Nomura, J. Am. Chem. Soc. 2000, 122,
10464 – 10465; b) T. Hayashi, K. Inoue, N. Taniguchi, M.
Ogasawara, J. Am. Chem. Soc. 2001, 123, 9918 – 9919.
[12] For reviews of 1,4-metal migration, see: a) S. Ma, Z. Gu, Angew.
Chem. 2005, 117, 7680 – 7685; Angew. Chem. Int. Ed. 2005, 44,
7512 – 7517; b) F. Shi, R. C. Larock, Top. Curr. Chem. 2010, 292,
123 – 164.
[13] For selected, recent examples of 1,4-rhodium migration, see:
a) R. Shintani, T. Hayashi, Org. Lett. 2005, 7, 2071 – 2073; b) T.
Miura, T. Sasaki, H. Nakazawa, M. Murakami, J. Am. Chem.
Soc. 2005, 127, 1390 – 1391; c) R. Shintani, K. Okamoto, T.
Hayashi, J. Am. Chem. Soc. 2005, 127, 2872 – 2873; d) H.
Yamabe, A. Mizuno, H. Kusama, N. Iwasawa, J. Am. Chem.
Soc. 2005, 127, 3248 – 3249; e) R. Shintani, K. Takatsu, T.
Hayashi, Angew. Chem. 2007, 119, 3809 – 3811; Angew. Chem.
Int. Ed. 2007, 46, 3735 – 3737; f) T. Matsuda, M. Shigeno, M.
Murakami, J. Am. Chem. Soc. 2007, 129, 12086 – 12087; g) R.
Shintani, K. Takatsu, T. Katoh, T. Nishimura, T. Hayashi, Angew.
Chem. 2008, 120, 1469 – 1471; Angew. Chem. Int. Ed. 2008, 47,
1447 – 1449; h) J. Panteleev, F. Menard, M. Lautens, Adv. Synth.
Catal. 2008, 350, 2893 – 2902; i) T. Seiser, O. A. Roth, N. Cramer,
Angew. Chem. 2009, 121, 6438 – 6441; Angew. Chem. Int. Ed.
À
[20] The experiment in Equation (4) also demonstrates that C H
functionalization of the 4-nitrophenyl ring of 1g is irreversible in
the presence of 2a. Exposure of 1g to the conditions shown in
Equation (4) but in the absence of 2a led to partial deuterium
incorporation (28% D) at the ortho-positions of the 4-nitro-
À
phenyl ring, showing that C H functionalization of 1g is
reversible when the 1,3-enyne is not present. See the Supporting
Information for details.
Angew. Chem. Int. Ed. 2014, 53, 9931 –9935
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
9935