Catalyzed Reactions of Enolates and Cations
COMMUNICATIONS
1H), 5.46* (q, J 7.3 Hz, 1H), 5.37 (q, J 6.8 Hz, 1H), 1.93
1.83** (m, 10H), 1.41* (mc, 2H), 1.34 (mc, 3H); 13C NMR
(100 MHz, C6D6): d 151.9, 150.2*, 142.8, 139.9*, 129.0,
128.1*, 127.3, 126.4*, 113.9, 113.3*, 78.4, 76.8*, 44.0, 43.7*,
36.5, 36.4*, 31.3, 31.2*, 13.3 13.0*; HRMS (EI, 70 eV): calcd. for
¥
(M ): 268.1827; found: 268.1822; IR (neat): n 3020, 2910,
2850, 1650, 1490, 1445, 1355, 1325, 1300, 1205, 1100, 1065, 1030,
À
1
965, 905, 810, 780, 760, 725, 700, 640 cm . ** signals of minor
and major isomer not separated, * signals of minor isomer.
2-Adamantan-1-yl-1-phenylpropan-1-one[15] (Table 1; en-
try 5): B(C6F5)3 (1.5 mg, 3 mmol) was dried by gentle heating
(1 min) under vacuum and was dissolved in CH2Cl2 (1 mL).
After addition of the enol ether (804 mg, 3.0 mmol) stirring
was continued for 20 h at room temperature. After quenching
by addition of 3 drops of triethylamine the solvent was
removed and the residue purified by SiO2 chromatography
(cyclohexane/ethyl acetate 99/1) to afford the desired
Figure 2. Deuterium labeling studies as evidence for a non-
concerted mechanism.
product; yield: 680 mg (84%). C19H24O(268.18 g/mol); R
f
(PE:Et2O 98:2): 0.28; 1H NMR (300 MHz, CDCl3): d
7.97 7.80 (m, 2H), 7.51 7.43 (m, 1H), 7.41 7.31 (m, 2H),
3.24 (q, J 7.0 Hz, 1H), 1.87 (bs, 3H), 1.74 1.37 (m, 12H), 1.02
(d, J 7.0 Hz, 3H); 13C NMR (75 MHz, CDCl3): d 205.2,
139.2, 132.6, 128.5, 128.2, 49.3, 40.2, 37.0, 35.9, 28.7, 11.5;
than a concerted Claisen rearrangement.[14] When the
[3,3] rearrangement is catalyzed[14b] by Yamamoto×s
excellent bulky aluminum reagents the best result
(10 mol % catalyst, 45% yield after 13 h) is somewhat
inferior to the result under our conditions (0.25 mol %
catalyst, 84% yield after 5 h).
In summary, we have devised an efficient catalytic
system for the alkylation of enolates based on the Lewis
acid-catalyzed cleavage of enol ethers. We anticipate
that the mild reaction conditions, insensitivity to
ambient exposure, low catalyst loading, high to excel-
lent turnover frequencies, and generality of our system
meet the demands for efficient synthesis and will thus
lead to considerable use in organic synthesis.
¥
HRMS (EI, 70 eV): calcd. for (M ): 268.1827; found: 268.1823;
IR (neat), n 2905, 2850, 1675, 15945, 1560, 1355, 1315, 1245,
À
1
1210, 1180, 1065, 960, 720, 695, 665 cm .
Acknowledgements
A. G. thanks the Fonds der Chemischen Industrie for a
Dozentenstipendium.
References and Notes
Experimental Section
[1] For recent reviews see: a) D. Caine, in Comprehensive
Organic Synthesis, (Eds.: B. M. Trost, I. Fleming),
Pergamon, Oxford, 1991, Vol. 3, p. 1 63; b) D. L.
Hughes, in Comprehensive Asymmetric Catalysis, (Eds.:
E. N. Jacobsen, A. Pfaltz, H. Yamamoto), Springer,
Berlin, 1999, Vol. 1, p. 1273.
[2] For some recent references see: a) M. Palucki, S. L.
Buchwald, J. Am. Chem. Soc. 1997, 119, 11108; b) B. M.
Trost, G. M. Schroeder, J. Am. Chem. Soc. 1999, 121,
6759; c) M. Braun, F. Laicher, T. Meier, Angew. Chem.
2000, 112, 3637; Angew. Chem. Int. Ed. 2000, 39, 3494.
[3] a) B. M. Trost, Science 1991, 254, 1471; b) B. M. Trost,
Angew. Chem. 1995, 107, 285; Angew. Chem. Int. Ed.
Engl. 1995, 34, 259.
[4] M. T. Reetz, Angew. Chem. 1982, 94, 97; Angew. Chem.
Int. Ed. Engl. 1982, 21, 96.
[5] a) J. M. Lansinger, R. C. Ronald, Synth. Commun. 1992,
22, 1793; b) J. F. W. McOmie, M. L. Watts, D. E. West,
Tetrahedron 1968, 24, 2289; c) M. H. Park, R. Takeda, K.
Nakanishi, Tetrahedron Lett. 1987, 28, 3823.
Representative Procedures
1-(1-Phenylpropenyloxy)-adamantane (Table 1; entry 5): Un-
der an argon atmosphere 40 mL of a 1.0 M solution of TiCl4 in
dichloromethane was added at 08C to 150 mL of dry THF.
After the resulting yellow suspension was warmed up to room
temperature TMEDA (12 mL, 80 mmol) was added and the
brown solution was stirred for 10 min. Zinc (6.0 g, 90 mmol)
was added and when the color of the suspension had changed
from brown to dark greenish blue (ca. 30 min) 2.7 mL of 1,1-
dibromoethane (2.7 mL, 22.0 mmol) and 1-adamantyl ben-
zoate (2.56 g, 10.0 mmol) were added simultaneously and the
mixture was stirred overnight. The reaction mixture was
hydrolyzed by 6 mL of a saturated K2CO3 solution. After-
wards the complete reaction mixture was filtered through a
short column of alumina (Merck, aluminum oxide 90 stand-
ardized) using diethyl ether as eluent. The solvent was
removed under reduced pressure and the residue purified by
column chromatography on alumina with light petroleum
ether (bp 40/608C) to give 1-(1-phenylpropenyloxy)-adaman-
tane as a mixture of diastereoisomers (Z:E 80:20); yield: 2.5 g
(9.3 mmol, 93%). Rf (PE): 0.6; 1H NMR (400 MHz, C6D6): d
7.59 7.49** (m, 2.5H), 7.19 7.11** (m, 2H), 7.09 7.03** (m,
[6] a) H. Frauenrath, Synthesis 1989, 721; b) R. J. Ferrier, S.
Middleton, Chem. Rev. 1993, 93, 2779; c) N. A. Petasis,
S.-P. Lu, J. Am. Chem. Soc. 1995, 117, 6394; d) A. B.
Adv. Synth. Catal. 2002, 344, 845 848
847