) 19 and 17 for 2-hexene and 2-octene, respectively) and
DuPont/DSM (n:i ) 36 for 2-hexene).7
Scheme 2. Synthesis of 3,3′,5,5′-Tetrasubstituted Biphenyl
Recently, we have reported the synthesis and application
of the new tetraphosphorus ligand BTPP (biphenyl-2,2′6,6′-
tetrakis(dipyrrolyl phosphoramidite)),8 which shows a high
regioselectivity for the homogeneous isomerization-
hydroformylation of internal olefins (n:i values up to 80.6
for 2-hexene and up to 51.7 for 2-octene). The high
selectivity is ascribed mainly to the enhanced chelating ability
(multichelating modes) and the unique electronic properties
of N-pyrrolylphosphorus moiety (Scheme 1). Meanwhile, it
Scheme 1. Enhanced Chelating Ability of Tetraphosphine
Ligand through Multiple Chelating Modes and Increased Local
Phosphorus Concentration
has been well documented that substitution at the 3,3′-
positions of the binaphthyl9 or biphenyl10 scaffold has a
dramatic effect on the enantio- and regioselectivity of various
reactions. On the basis of those results, we reasoned that on
introducing different functional groups into the 3,3′,5,5′-
positions of the biphenyl, the electronic and steric charac-
teristics of the ligand could be systematic tuned, thereby
changing the character and the environment around the metal
center. Herein, we wish to report our prelimilary result on
the synthesis of ligands and their application to the isomeriza-
tion-hydroformylation of internal olefins.
Biphenyl with 3,3′,5,5′-tetraalkyl or aryl moiety could be
easily prepared in moderate to good yields from iodosub-
stituted derivative 211 with arylboronic acid or trimethylsilyl
acetylene by Suzuki or Sonogashira coupling (Scheme 2).
The chlorination of 112 with sulfuryl chloride in chloroform
at room temperature affords 3b in 82% yield.13 Then, the
new ligands were achieved in a subsequent two straightfor-
ward steps.8 Treatment of the substituted 2,2′6,6′-tetramethox-
ybiphenyls with boron tribromide gave the parent tetraol,
followed by reaction with freshly made chlorodipyrrolylpho-
phine14 in the presence of triethylamine at room temperature
to furnish ligands 5b-5g. The unoptimized yields for the
ligands synthesis ranged from 21% to 34% (Scheme 3).
Tetraol 4b was directly synthesized from m-xylorcinol by a
two-phase oxidation in the presence of ferric chloride.15
With the ligands in hand, isomerization-hydroformylation
of internal olefins was then conducted under optimized
reaction conditions (100 °C, CO/H2 ) 5/5 atm, ligand/metal
ratio ) 3)8 with ligands 5b-5g (for comparison, the data
for ligand 5a are also listed) using 2-octene and 2-hexene
as standard substrates. No 3-formylalkane products were
observed under these reaction conditions. All of the ligands
and particularly alkyl-substituted 5d show among the best
reported linear selectivity both for 2-octene (n:i ) 207.6)
and 2-hexene (n:i ) 362.0) (see Table 1, entry 10 and Table
(5) Selent, D.; Hess, D.; Wiese, K.-D.; Ro¨ttger, D.; Kunze, C.; Bo¨rner,
A. Angew. Chem. 2001, 113, 1739-1741; Angew. Chem., Int. Ed. 2001,
40, 1696-1698.
(6) Billig, E.; Abatjoglou, A. G.; Bryant, D. R. (UCC). European Patent
EP 213639, 1987; U.S. Patent 4748261, 1988.
(7) Burke, P. M.; Garner, J. M.; Kreutzer, K. A.; Teunissen, A. J. J. M.;
Snijder, C. S.; Hansen, C. B. (DSM/Du Pont). PCT Int. Patent WO 97/
33854, 1997.
(8) Yan, Y.; Zhang, X.; Zhang, X. J. Am. Chem. Soc. 2006, 128, 16058–
16061.
(9) For review, see: Chen, Y.; Yekta, S.; Yudin, A. K Chem. ReV. 2003,
103, 3155–3211. For recent examples, see: (a) Rueping, M.; Antonchick,
A. P. Org. Lett. 2008, 10, 1731–1734. (b) Lacasse, M.-C.; Poulard, C.;
Charette, A. B. J. Am. Chem. Soc. 2005, 127, 12440–12441. (c) Long, J.;
Hu, J.; Shen, X.; Ji, B.; Ding, K. J. Am. Chem. Soc. 2002, 124, 10–11. (d)
Chong, J. M.; Shen, L.; Taylor, N. J. J. Am. Chem. Soc. 2000, 122, 1822–
1823.
(10) For recent examples, see: (a) Wang, Y.-G.; Maruoka, K. Org.
Process Res. DeV. 2007, 11, 628–632. (b) Alexakis, A.; Polet, D.; Rosset,
S.; March, S. J. Org. Chem. 2004, 69, 5660–5667. (c) Capozzi, G.; Delogu,
G.; Fabbri, D.; Marini, M.; Menichetti, S.; Nativi, C. J. Org. Chem. 2002,
67, 2019–2026.
(13) DeJongh, D. C.; Van Fossen, R. Y. J. Org. Chem. 1972, 37, 1129–
1135.
(14) (a) Jackstell, R.; Klein, H.; Beller, M.; Wiese, K.-D.; Rottger, D.
Eur. J. Org. Chem. 2001, 20, 3871–3877. (b) van der Slot, S. C.; Duran,
J.; Luten, J.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Organometallics
2002, 21, 3873–3883.
(11) See Supporting Information for details.
(12) Lindsten, G.; Wennerstroem, O.; Isaksson, R. J. Org. Chem. 1987,
52, 547–554.
(15) Davis, T. L.; Walker, J. F. J. Am. Chem. Soc. 1930, 52, 358–361.
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