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migration as shown in Table 1, entry 7, while the second
hydroarylation proceeded with FeCl3.18 The current remote
functionalization was also demonstrated by one-pot migration
and arylative cyclization cascade of 2-(4-penten-1-yl)-1,1’-
biphenyl leading to 9-butyl-9H-fluorene 5b (Scheme 2(b)).
In conclusion, the current study demonstrates the
operationally simple migration of double bonds without the
aid of heteroatom-containing functional groups. Unsaturated
hydrocarbon feedstocks are abundant and inexpensive, and
represent ideal starting materials for the synthesis of
functional materials and pharmaceuticals. The current
protocol provides an atom-efficient and redox-neutral
approach to increase the value of such olefins. Although
aromatic rings were chosen to terminate the migration and
simplify site-selectivity without using heteroatoms, the current
process may offer novel methods for the construction of
olefins that are otherwise difficult to synthesize.
Dierker, L. J. Gooen, J. Am. Chem. Soc.D2O01I:21,0.1130439, /1C397C1C60;0(2e2)3EE.
Larionov, L. Lin, L. Guénée, C. Mazet, J. Am. Chem. Soc. 2014,
136, 16882; (f) L. T. N. Chuc, C.-S. Chen, W.-S. Lo, P.-C. Shen, Y.-
C. Hsuan, H.-H. G. Tsai, F.-K. Shieh, D.-R. Hou, ACS Omega 2017,
2, 698. See also refs. 2a, 2b, 2c, and 2e.
8
9
For reviews on transformation promoted by cooperative
bimetallic catalyst systems, see: (a) S. Kamijo, Y. Yamamoto, In
Multimetallic Catalysis in Organic Synthesis; M. Shibasaki, Y.
Yamamoto, Eds. Wiley-VCH: Weinheim, 2004, pp. 1-52; (b) J. M.
Lee, Y. Na, H. Han, S. Chang, Chem. Soc. Rev. 2004, 33, 302; (c) C.
Wang, Z. Xi, Chem. Soc. Rev. 2007, 36, 1395.
Double-bond migration promoted by a cationic palladium
species via the generation of a cationic intermediate followed
by protodepalladation cannot be ruled out (see eq S2 in ESI).
However, addition of AgOTf as a second catalyst significantly
decreased reaction efficiency (Table 1, entry 8). Thus, the
participation of cationic palladium species by the abstraction of
a chloro group by TaCl5 may be low.
10 The migrations in this study generally did not proceed to
completion, leaving a small amount (<5% yield, except for
migration of 1b and 1h) of other internal alkenes. Prolonged
reaction times with higher loadings of the catalyst did not
increase the conversion.
11 See eqs S3 and 4 in ESI for the reaction of other olefins.
12 Because the efficiency of double-bond transposition of internal
alkene 1h was lower than that of terminal alkenes, a certain
degree of migration might occur through a chain-walking
mechanism without dissociation of intermediate internal
alkenes. If the migration occurred only via stepwise olefin
isomerization, 1h should show comparable reactivity to that of
other terminal alkenes.
13 PdCl2 is known to present as a chloro-bridged polymeric
aggregate. Thus, another effect of TaCl5 is the dissociation of
(PdCl2)n to an oligomeric structure. Isolation and structural
determination of chloro-bridged hetero dinuclear palladium
complexes, see: (a) K. Severin, K. Polborn, W. Beck, Inorg. Chim.
Acta 1995, 240, 339; (b) T. Hosokawa, M. Takano, S.-I.
Murahashi, J. Am. Chem. Soc. 1996, 118, 3990; (c) G. G. Luo, R.-
B. Huang, D. Sun, L.-R. Lin, L.-S. Zheng, Inorg. Chem. Commun.
2008, 11, 1337; (d) M. Weiss, W. Frey, R. Peters,
Organometallics 2012, 31, 6365. Note that the addition of LiCl,
which is often used to dissociate chloro-bridged oligomeric
aggregates, in place of TaCl5 completely shut down the
migration reaction. Thus, an increase in Lewis acidity on the
palladium center by coordination of TaCl5 is another important
factor to promote the current migration reaction.
Notes and references
1
(a) A. George, A. M. Olah, Hydrocarbon Chemistry, 2nd ed.;
John Wiley & Sons, 2003. (b) H. A. Wittcoff, B. G. Reuben, J. S.
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For reviews on double-bond migration, see: (a) R. Uma, C.
Crévisy, R. Grée, Chem. Rev. 2003, 103, 27; (b) N. Kuznik, S.
Krompiec, Coord. Chem. Rev. 2007, 251, 222; (c) S. Krompiec,
M. Krompiec, R. Penczek, H. Ignasiak, Coord. Chem. Rev.
2008, 252, 1819; (d) E. Larionov, H. Li, C. Mazet, Chem.
Commun. 2014, 50, 9816; (e) M. Hassam, A. Taher, G. E.
Arnott, I. R. Green, W. A. L. van Otterlo, Chem. Rev. 2015,
115, 5462.
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14 Although heating a solution of TaCl5 (0.13 mmol) in THF at 60 oC
for 12 h gave an equivalent of 4-chlorobutanol (0.13 mmol), the
migration reaction was not accelerated using 4-chlorobutanol
as an additive in place of TaCl5. Thus, PdCl2 was likely activated
by TaCl5 or TaCl4(O(CH2)4Cl).
15 For recent reviews on the transformation catalyzed by hetero
dinuclear metal complexes, see: (a) P. Buchwalter, J. Rosé, P.
Braunstein, Chem. Rev. 2015, 115, 28; (b) I. G. Powers, C. Uyeda,
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16 (a) R. H. Crabtree, In The Organometallic Chemistry of the
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17 For reviews on remote functionalization based on double bond
migration, see: (a) M. Vilches-Herrera, L. Domke, A. Börner, ACS
Catal. 2014, 4, 1706; (b) A. Vasseur, J. Bruffaerts, I. Marek, Nat.
Chem. 2016, 8, 209; (c) H. Sommer, F. Juliá-Hernández, R.
Martin, I. Marek, ACS Cent. Sci. 2018, 4, 153.
5
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7
T. Gibson, L. J. Tulich, Org. Chem. 1981, 46, 1821.
Most of palladium-catalyzed double bond migration reaction
are limited to one-carbon migration and/or required a
heteroatom-containing directing group to facilitate the
migration. For representative examples, see: (a) H. J. Lim, C. R.
Smith, T. V. RajanBabu, J. Org. Chem. 2009, 74, 4565; (b) J. Fan,
C. Wan, Q. Wang, L. Gao, X. Zheng, Z. Wang, Org. Biomol. Chem.
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Overgaard, T. Skrydstrup, J. Am. Chem. Soc. 2010, 132, 7998; (d)
18 J. Kischel, I. Jovel, K. Mertins, A. Zapf, M. Beller, Org. Lett.
2006, 8, 19. Using PdCl2/TaCl5 as a catalyst, 5a was obtained
in 28% yield.
4 | J. Name., 2012, 00, 1-3
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