C O M M U N I C A T I O N S
Table 2. Asymmetric Hydrovinylation of 1-Alkylvinylarenesa
14 is formed in nearly racemic form, contaminated with product
of ethylene addition at the benzylic position.
In summary, we have demonstrated the feasibility of a new
catalytic method for the generation of quaternary centers. Expansion
of the scope of this reaction to heteroaromatic compounds, cyclic
and acyclic dienes, and bicyclic molecules will be reported in due
course.
Acknowledgment. Financial assistance for this research by U.S.
National Science Foundation (CHE-0308378) and the Petroleum
Research Fund of the American Chemical Society (36617-AC1) is
gratefully acknowledged.
Supporting Information Available: Full experimental details of
typical hydrovinylation reaction, spectroscopic and chromatographic
data for characterization of compounds listed. This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(
1) For reviews and history of the problem, see: (a) Douglas, C. J.; Overman,
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(
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a
See eq 2 for details. b Selectivity for HV product. c Determined by GC,
8
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R isomer of 3; all others assigned by analogy to 3. Product from 9 (entry
2
5
11b
7
) assigned by comparison of [R] D with that of a related compound.
d
1
See Supporting Information for details. Rest isomerized product from
(
starting material. 10 mol % catalyst used. Rest starting material. g Enan-
e
f
2
845. (b) Jolly, P. W.; Wilke, G. Hydrovinylation. In Applied Homoge-
tiomeric excess determined via Mosher esters of hydroboration product.10
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(
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moderate, very high enantiomeric excess (∼97%) was observed
for the isolated product. The 2-naphthyl derivative 8 gave excellent
yield (>98%) and selectivity (>99%) for the expected product.
The tetralin derivative 9 represents a different class of substrates
that underwent the hydrovinylation reaction giving >95% ee.
Significant isomerization (∼30%) of the starting material to an
endocyclic olefin is a major distraction of this otherwise useful
reaction. Compounds (e.g., 10b) structurally related to the HV
product 10a from 9 have been synthesized previously via intramo-
(
6) Phosphinites: (a) Park, H.; RajanBabu, T. V. J. Am. Chem. Soc. 2002,
124, 734. Phosphoramidites: (b) Franci o´ , G.; Faraone, F.; Leitner, W. J.
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(g) Zhang, A.; RajanBabu, T. V. Org. Lett. 2004, 6, 1515. Phosphor-
amidites and phospholanes have also been used for highly enantioselective
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7) Arnold, L, A.; Imbos, R.; Mandoli, A.; de Vries, A. H. M.; Naasz, R.;
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8) While this manuscript was being readied for publication, a closely related
paper appeared on the Internet, which has since appeared in press: Shi,
W.-J.; Zhang, Q.; Xie, J.-H.; Zhu, S.-F.; Hou, G.-H.; Zhou, Q.-L. J. Am.
Chem. Soc. 2006, 128, 2780. Advantages of our method include the use
of a readily available ligand (Strem Chemicals), low catalyst loading (1%
vs 10%), higher yields, and higher overall selectivities for a number of
substrates.
11a
lecular asymmetric Heck reactions (∼93% ee), stoichiometric
(
11b
oxazoline directed alkylation (∼99% ee), and enzyme-catalyzed
desymmetrization of a chiral malonate (97% ee).1 By comparison,
the asymmetric hydrovinylation route is significantly shorter (2 steps
from 1-tetralone vs >10 steps), and operationally simpler.
Among the other olefins 11-13, only the acyclic diene 13
undergoes hydrovinylation at low temperatures, and the product
(
1c
(
9) Zhang, A.; RajanBabu, T. V. Org. Lett. 2004, 6, 3159.
10) See Supporting Information for details.
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Soc. 1993, 115, 8477 (corrections: ibid J. Am. Chem. Soc. 1994, 116,
(
(
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