2762 J . Org. Chem., Vol. 66, No. 8, 2001
Casarini et al.
Dim esityl su lfoxid e (1): white solid mp 153.5-154 °C;
1H NMR (CDCl3, 200 MHz, 25 °C) δ 2.20 (6H, s, p-Me), 2.40
(12H, s, o-Me), 6.80 (4H, s, CH); 13C NMR (CDCl3, 50.3 MHz,
25 °C), δ 19.4 (4 o-Me), 20.8 (2 p-Me), 131.0 (CH), 136.4 (2
quat), 138.3 (4 quat), 140.4 (2 quat).
2,2′,6,6′-Tetr a m eth yld ip h en yl su lfoxid e (2): white solid,
mp 146.5 °C; 1H NMR (CDCl3, 400 MHz, 25 °C), δ 2.45 (12H,
s, Me), 7.01 (4H, d, J ) 7.6 Hz, m-CH), 7.20 (2H, t, J ) 7.6
Hz, p-CH); 13C NMR (CDCl3, 100.6 MHz, 25 °C), δ 19.5 (4 Me),
130.4 (4 m-CH), 130.5 (2 p-CH), 138.5 (4 quat), 139.4 (2 quat).
Anal. Calcd for C16H18OS: C, 74.38; H, 7.02; S, 12.41. Found:
C, 74.43: H, 6.94; S, 12.37.
Mesityl p h en yl su lfoxid e (3): 1H NMR (CDCl3, 200 MHz,
25 °C), δ 2.29 (3H, s, p-CH3), 2.42 (6H, s, o-CH3), 6.88 (2H, s,
CH, Mes), 7.42 (5H, m, CH, Ph); 13C NMR (CDCl3, 50.3 MHz,
25 °C), δ 19.3 (o-CH3), 21.2 (p-CH3), 124.5 (CH), 128.8 (CH),
129.5 (CH) 130.7 (CH), 132.1 (quat), 139.9 (2 quat), 142.2
(quat), 144.0 (quat).
Dim esityl su lfon e (4): white solid, mp 204-205 °C;24 1H
NMR (CDCl3, 400 MHz, 25 °C), δ 2.28 (6H, s, p-CH3), 2.42
(12H, s, o-CH3), 6.87 (4H, s, CH); 13C NMR (CDCl3, 100.6 MHz,
25 °C), δ 20.9 (p-CH3), 21.6 (o-CH3), 131.9 (CH), 137.9 (2 quat,
C-S), 138.4 (4 quat), 142.2 (2 quat).
NMR Mea su r em en ts. The assignment of the 13C NMR
signals was carried out by DEPT sequence. The samples for
the low-temperature measurements were prepared by con-
necting to a vacuum line the NMR tubes containing the desired
compounds dissolved in some C6D6 for locking purpose and
condensing therein the gaseous solvents by means of liquid
nitrogen. The tubes were subsequently sealed in vacuo and
introduced into the precooled probe of the 300 MHz spectrom-
eter operating at 75.45 MHz for 13C. The assignment of the
13C signals was obtained by means of DEPT sequences. The
temperatures were calibrated by substituting the sample with
a precision Cu/Ni thermocouple before the measurements.
Total line shape simulations were achieved by using a PC
version of the DNMR-6 program.26 Since at the low temper-
atures required to observe the exchange process the intrinsic
line width of 1 was significantly temperature dependent, the
widths measured for the line of the p-methyl group (which does
not display a noticeable exchange broadening) was assumed
to remain equal to that of the two ortho signals also in the
exchange region. In the case of 2, where there is not a line for
the p-methyl groups, the ratio between the line width of the
compound and that the solvent was determined in the range
-90° to -150 °C where the width was only dependent upon
the viscosity of the solution. The values of this ratio were
extrapolated below -150 °C (they were found, however, to
remain almost constant) where the exchange process start to
take place and the line width of the solvent determined in the
appropriate range (-169° to -179 °C). By multiplying the
solvent line width by this ratio, a reasonable value was
obtained for the intrinsic line width of the ortho signal of 2 in
the temperature range of interest.27 We also checked that
errors as large as 50% on the intrinsic line width affected the
activation energy by less than 0.05 kcal mol-1 in the range
investigated. The high resolution 13C NMR solid-state CP-MAS
spectra were obtained at 75.45 MHz. The compounds were
introduced into a tightly sealed 7 mm zirconia rotor, spun at
the magic angle with a speed of about 3.5 kHz. The line
assignment was obtained by the “nonquaternary suppression”
pulse sequence. The chemical shifts were measured, by
replacement, with respect to the lower frequency signal of the
adamantane (29.4 ppm).
F igu r e 5. X-ray diffraction structures (A and B) for the two
independent molecules of 2 (top). Underneath is shown the
elementary cell containing four molecules of 2 (i.e., the two
pairs of enantiomers A, A′ and B, B′).
propeller-like structures are extremely similar, having
one ring nearly parallel and the other nearly orthogonal
to the SdO bond. The experimental dihedral angles for
the nearly parallel ring are -9.1° and -9.6°, respectively,
for the structures A and B of 2, both values being quite
close to that (-9°) computed for 1. The dihedral angles
for the ring quasi orthogonal to the SdO bond are +113.2
and +112.8 for the structures A and B, respectively: also
these values are in reasonable agreement with that
(+107°) computed for 1. In Figure 5 (bottom) is also
reported the crystal cell of 2 displaying the two indepen-
dent molecules A and B, as well as their enantiomeric
forms A′ and B′.
Exp er im en ta l Section
Ma ter ia l. Dimesityl sulfoxide (1),23 2,2′,6,6′ tetramethyl-
diphenyl sulfoxide (2),23 and mesityl phenyl sulfoxide (3)24 were
prepared according to known procedures. Dimesityl sulfone (4)
was prepared by stirring (4 h) at ambient temperature a
mixture of mesityl sulfonyl chloride (10 mmol), mesitylene (10
mL), and AlCl3 (25 mmol, 3.32 g). After addition of aqueous
NH4Cl and extraction with Et2O, the organic layers were dried
(Na2SO4), and the solvent was removed at reduced pressure.
The crude was purified by crystallization (pentane/Et2O, yield
90%).
DSC Mea su r em en ts. This determination was obtained
with a scanning rate of 5°/min, heating a sample of 2 from
-50 ° to +150 °C.
X-r a y Diffr a ction . Crystal data of 2,2′,6,6′-Tetramethyl-
diphenyl sulfoxide: C16H18OS (258.36), triclinic, space group
(25) Maclean, M. E.; Adams, R. J . Am. Chem. Soc. 1933, 55, 4683.
(26) QCPE program no. 633, Indiana University, Bloomington, IN.
(27) Grilli, S.; Lunazzi, L.; Mazzanti, A. J . Org. Chem. 2000, 65,
3563. Casarini, D.; Lunazzi, L.; Mazzanti, A. J . Org. Chem. 1998, 63,
9125. Casarini, D.; Lunazzi, L.; Mazzanti, A. J . Org. Chem. 1997, 62,
7592.
(23) Bast, S.; Andersen, K. J . Org. Chem. 1968, 33, 846
(24) Czarnik, A. W. J . Org. Chem. 1984, 49, 924 and Lupatelli, P.;
Ruzziconi, R.; Scafato, P.; Degl’Innocenti, A.; Paolobelli, A. P. Synth.
Commun. 1997, 27, 441.