Organometallics
ARTICLE
acid (0.50 M) was added to the mixture until the aqueous layer was at
pH = 3. The mixture was washed with brine and extracted with DCM.
The organic layer was dried over anhydrous magnesium sulfate and
decanted. After evaporation of DCM, 1.83 g of N-p-toluenesulfonyl-L-
proline was obtained as white solid in 78% yield and, without further
purification, was dissolved in 10.0 mL of dry DCM. Thionyl chloride
(1.00 mL, 2.00 equiv) was added, and the resulting mixture was stirred
under nitrogen at room temperature for 16 h. The solvent was then
evaporated under reduced pressure to give a yellow, viscous liquid that
was dissolved in 30.0 mL of dry DCM. 4-Aminophenylboronic acid
pinacol ester (0.60 g) was added to the DCM solution, followed by
triethylamine (3.00 mL). The resulting mixture was stirred at 0 °C for
1 h. After evaporation of the solvent under reduced pressure, the crude
product was purified by flash column chromatography on silica gel using
2:1 (v/v) hexanes/ethyl acetate as eluent to give 1.13 g (2.40 mmol) of
7a as a pale yellow solid in 69% overall yield from L-proline. The
D-proline and racemic DL-proline derivatives were prepared using the
same procedure and in the same overall yields. 7: 1H NMR (400 MHz,
CDCl3) δ 8.83 (s, 1H), 7.71ꢀ7.76 (dd, 4H, J = 12.0, 8.0 Hz), 7.56ꢀ7.58
(d, 2H, J = 8.0 Hz), 7.32ꢀ7.34 (d, 2H, J = 8.0 Hz), 4.13ꢀ4.16 (m, 1H),
3.55ꢀ3.60 (m, 1H), 3.18ꢀ3.24 (m, 1H), 2.40 (s, 3H), 2.27ꢀ2.32
(m, 1H), 1.48ꢀ1.82 (comp, 3H), 1.30 (s, 12H); 13C NMR (100 MHz,
CDCl3) δ 169.1, 144.7, 140.1, 135.7, 132.5, 130.1, 127.9, 118.7, 83.7,
63.0, 50.1, 29.5, 24.8, 24.4, 21.6; HRMS (ESI) for C24H32BN2O5S
[M þ H]þ calcd 471.2125, found 471.2039; IR (neat) 3265, 2989, 2972,
(ESI) for C64H86N8NaO10Rh2S2 [M þ Na]þ calcd 1419.3916, found
1419.3378; IR (neat) 3342, 2927, 1677, 1597, 1581, 1510, 1342, 1158 cmꢀ1
.
General Procedure for NMR Analyses with Chiral Shift
Reagents. The bisaryldirhodium(III,III) (1-aza-2-cycloctanoate) was
dissolved in CDCl3, and proton NMR data were obtained. Next, addition of
lanthanide shift reagent or silver(I) salt followed portionwise. Proton NMR
spectra were collected after addition of each shift reagent portion.
’ ASSOCIATED CONTENT
S
Supporting Information. NMR spectra of all new com-
b
pounds. Crystallographic data for compounds 1, 4, and 12. This
acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: mdoyle3@umd.edu.
’ ACKNOWLEDGMENT
We are grateful to the National Science Foundation (CHE-
0456911) for their generous support. We also wish to thank J.-H.
Xie for his early efforts to develop a detailed understanding of
bisaryl dirhodium(III,III) carboxamidates.
1681, 1598, 1538, 1396, 1342 cmꢀ1
.
Procedure for the Synthesis of p-(N-p-Toluenesulfonyl-
pyrolinamido)phenyl Boronic Acid (8a). Compound 7 (470 mg,
1.00 mmol) and sodium periodate (642 mg, 3.00 equiv) were stirred in
8.00 mL of a 4:1 mixture of THF and water for 1 h. Then aqueous
hydrochloric acid (1.00 M, 0.70 mL) was added to the suspension. The
resulting yellow mixture was stirred at ambient temperature for 6 h, then
diluted with water and extracted with ethyl acetate. The combined
organic layer was washed with water and brine, dried over anhydrous
sodium sulfate, and decanted. After evaporation of the solvent, 360 mg of
a light yellow solid of 8 was obtained in 93% yield (0.93 mmol). D-Proline
and racemic DL-proline derivatives were prepared using the same procedure
and in the same overall yields. 8: 1H NMR (400 MHz, CDCl3) δ 8.94 (s,
1H), 8.17 (d, 2H, J = 8.0 Hz), 7.70ꢀ7.76 (dd, 4H, J = 16.0, 8.0 Hz), 7.36 (d,
2H, J = 8.0 Hz), 4.19ꢀ4.22 (m, 1H), 3.57ꢀ3.65 (m, 1H), 3.22ꢀ3.28 (m,
1H), 2.42 (s, 3H), 2.25ꢀ2.35 (m, 1H), 1.81ꢀ1.84 (m, 1H), 1.67ꢀ1.80
(comp, 2H); 13C NMR (100 MHz, CDCl3) δ 171.2, 144.7, 141.3, 136.7,
134.9, 132.5, 130.1, 127.9, 119.0, 63.0, 60.4, 24.5, 21.6, 21.0; HRMS (ESI) for
C18H22BN2O5S [M þ 1]þ calcd 389.1342, found 389.1316; IR (neat)
’ REFERENCES
(1) Nichols, J. M.; Wolf, J.; Zavalij, P.; Varughese, B.; Doyle, M. P.
J. Am. Chem. Soc. 2007, 129, 3504–3505.
(2) Xie, J.-H.; Zhou, L.; Zavalij, P.; Doyle, M. P.; Sun, Y.-X.; Liu, Y.;
Sun, H. Chem. Commun. 2009, 3005–3007.
(3) Xie, J.-H.; Doyle, M. P. J. Mex. Chem. Soc. 2009, 53, 142–145.
(4) For reviews of molecular propellers see: (a) Mislow, K. Acc.
Chem. Res. 1976, 9, 26–33. (b) Meurer, K. P.; V€ogtle, F. Top. Curr. Chem.
1985, 127, 3–75.(c) Willem, R.; Gielen, M.; Hooggzand, C.; Pepermans,
H. Advances in Dynamic Stereochemistry; Gielen, M., Ed.; Academic
Press: New York, 1985; Vol. 1, p 207. (d) Eliel, E. L.; Wilen, S. H.;
Mander, L. N. Stereochemistry of Organic Compounds; Wiley: New York,
1994; p 1156. (e) Kottas, G. S.; Clarke, L. I.; Horinek, D.; Michl, J. Chem.
Rev. 2005, 105, 1281–1376.
(5) (a) Katoono, R.; Kawai, H.; Fujiwara, K.; Suzuki, T. J. Am. Chem.
Soc. 2009, 131, 16896–16904. (b) Wang, B.; Krꢀal, P. Phys. Rev. Lett.
2007, 98, 266102. (c) Alajarin, M.; Lꢀopez-Leonardo, C.; Bernꢀa, J. Org.
Lett. 2007, 9, 4631–4634. (d) Axe, P.; Bull, S. D.; Davidson, M. G.;
Gilfillin, C. J.; Jones, M. D.; Robinson, D. E. J. E.; Tutner, L. E.; Mithcell,
W. L. Org. Lett. 2007, 9, 223–226.
3378, 3338, 2974, 2954, 1686, 1595, 1532, 1327 cmꢀ1
.
Procedure for the Synthesis of Bis[p-(N-p-toluenesulfo-
nylpyrolinamidophenyl)]dirhodium(III) Tetrakis(1-aza-2-cy-
clooctanoate) (9). Rh2(ACO)4(CH3CN)2 (48.0 mg, 0.060 mmol),
compound 8a (116 mg, 5.00 equiv), and NaHCO3 (50.4 mg, 10.0 equiv)
were dissolved in 6.00 mL of CH2Cl2, and copper(II) sulfate (10.0 mol %)
in 1.50 mL of MeOH was added. The resulting purple mixture was
stirred under air at room temperature for 12 h, during which the solution
turned yellowish-brown. After filtration and evaporation of the solvent
under reduced pressure, the crude product was purified by column
chromatography on silica gel using 1:2 hexanes/ethyl acetate as eluent to
give compound 9 as yellowish-brown solid in 40% yield (34.0 mg,
0.024 mmol). D-Proline and racemic DL-proline derivatives were pre-
pared using the same procedure. 9: 1H NMR (400 MHz, CDCl3) δ 8.72
(s, 2H), 7.73ꢀ7.78 (comp, 4H), 7.34ꢀ7.48 (comp, 8H), 6.85ꢀ6.87
(comp, 4H), 4.14ꢀ4.22 (comp, 2H), 3.78 (s, 4H), 3.58ꢀ3.63
(comp, 2H), 3.19ꢀ3.25 (comp, 4H), 2.44 (s, 6H), 2.26ꢀ2.34 (comp,
4H), 1.34ꢀ1.81(comp, 14H); 13C NMR (150 MHz, CDCl3) δ182.0, 168.5,
156.5, 144.4, 136.3, 132.6, 130.5, 129.9, 128.8, 127.8, 121.6, 119.9, 117.7,
114.0, 62.8, 55.4, 50.0, 33.4, 32.6, 29.6, 28.0, 26.0, 25.0, 24.3, 21.5; HRMS
(6) Xie, J.-H.; Zhou, L.; Lubek, C.; Doyle, M. P. Dalton Trans.
2009, 2871–2877.
(7) Parker, D. Chem. Rev. 1991, 91, 1441–1457.
(8) Behnam, B. A.; Hall, D. M.; Modarai, B. Tetrahedron Lett. 1979,
20, 2619–2620.
(9) (a) Wenzel, T. J.; Bettes, T. C.; Sadlowski, J. E.; Sievers, R. E.
J. Am. Chem. Soc. 1980, 102, 5903–5904. (b) Wenzel, T. J.; Sievers, R. E.
J. Am. Chem. Soc. 1982, 104, 382–388. (c) Offermann, W.; Mannschreck,
A. Tetrahedron Lett. 1981, 22, 3227–3230. (d) Audit, M.; Demerseman,
P.; Goasdoue, N.; Platzer, N. Org. Magn. Reson. 1983, 21, 698–705.
(10) Hartley, F. R. Chem. Rev. 1973, 73, 163–190.
(11) Wenzel, T. J.; Sievers, R. E. Anal. Chem. 1981, 53, 393–399.
(12) (a) Ara, I.; Forniꢀes, J.; Gomez, J.; Lalinde, E.; Moreno, M. T.
Organometallics 2000, 19, 3137–3144. (b) Espinet, P.; Forniꢀes, J.;
ꢀ
Martinez, F.; Sotes, M.; Lalinde, E.; Moreno, M. T.; Ruiz, A.; Welch,
A. J. J. Organomet. Chem. 1991, 403, 253–267. (c) Vicente, J.; Chicote,
M.-T.; Alvarez-Falcꢀon, M. M.; Jones, P. G. Organometallics 2005, 24, -
4666–4675.
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