1
ObserVation of p-Xylylenes by H NMR
p-Xylylene (1) in Oxygenated CD3CN. The CD3CN was
distilled from P2O5 under dry air, and then oxygen was bubbled
through the CD3CN for 30 s. To a tear-shaped flask was added 7
mg of TBAF (22 µmol). To a second tear-shaped flask was added
10 µL of an approximately 0.1 M solution of 12 in CH2Cl2. The
CH2Cl2 was removed at reduced pressure. The dried CD3CN was
added to the acetate flask and the TBAF flask, 0.8 and 0.2 mL,
respectively. Both solutions were transferred to an NMR tube. The
1H NMR spectrum showed that acetate 12 was consumed and
signals consistent with oxygen adducts formed.
(relative intensity) 354 (6) M+, 238 (15), 237 (100), 236 (51), 232
(2), 189 (2), 131 (2), 129 (2), 128 (2), 122 (4), 118 (60), 117 (89),
115 (35), 106 (2), 105 (2), 103 (3), 89 (9), 87 (4), 86 (3), 77 (3),
75 (2), 74 (3). Trimer C 15 (1.1% yield): GC/MS m/z (relative
intensity) 354 (2) M+, 238 (15), 237 (92), 236 (57), 131 (2), 128
(3), 119 (41), 118 (56), 117 (100), 115 (37), 103 (2), 91 (4), 89
(12), 88 (10), 87 (5), 86 (4). Trimer D 15 (2.4% yield): GC/MS
m/z (relative intensity) 355 (2), 354 (7) M+, 353 (2), 239(2), 238
(15), 237 (97), 236 (36), 233(4), 232 (3), 189 (2), 131 (2), 128 (3),
119 (38), 118 (569), 117 (100), 115 (39), 112 (2), 108 (2), 105 (2),
103 (2), 91 (6), 90 (7), 89 (10), 88 (9), 86 (3), 77 (4), 76 (3), 74
(2). The pentane was removed under vacuum from the extract. The
resulting residue was dissolved in CD3CN, and a 1H NMR spectrum
was obtained.
3,5-Dimethyl-4-[(trimethylsilyl)methyl]benzyl Alcohol. 3,5-
Dimethyl-4-[(trimethylsilyl)methyl]benzyl alcohol was prepared in
a 92% yield by lithium aluminum hydride (1.23 mmol) reduction
of 3,5-dimethyl-4-[(trimethylsilyl)methyl]benzoic acid (0.5 mmol)
following a procedure similar to that outlined by Nystrom and
Brown26 for the reduction of phenylacetic acid to â-phenylethanol
that was used above for 4-[(trimethylsilyl)methyl]benzyl alcohol.
1H NMR (300 MHz, CDCl3) δ 6.967 (s, 2H), 4.538 (s, 2H), 2.224
(s, 6H), 2.138 (s, 2H) 0.014 (s, 9H).
[3,5-Dimethyl-4-((trimethylsilyl)methyl)phenyl]methyl Ac-
etate (17). 17 was prepared in an 85% yield from 3,5-dimethyl-
4-[(trimethylsilyl)methyl]benzyl alcohol (0.4 mmol) following the
procedure used for the above preparation of [p-((trimethylsilyl)-
methyl)phenyl]methyl acetate. 1H NMR (400 MHz, CDCl3) δ 6.954
(s, 2H), 4.925 (s, 2H), 2.209 (s, 6H), 2.170 (s, 2H), 2.008 (s, 3H),
-0.003 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 170.7, 138.5, 131.4,
127.8, 117.4, 66.0, 20.4, 20.2, 19.4, -1.1. GC/MS m/z (relative
intensity) 264 (2) M+, 249 (5), 207 (5), 206 (14), 205 (100), 202
(9), 201 (6), 197 (3), 195 (2), 135 (3), 132 (20), 130 (15), 128
(13), 125 (7), 117 (2), 115 (4), 113 (2), 112 (2); HRMS calcd for
C15H24O2Si 264.1546, found 264.1550.
2,6-Dimethyl-p-xylylene (11) in Partially Degassed CD3CN.
11 was prepared from [3,5-dimethyl-4-((trimethylsilyl)methyl)-
phenyl]methyl acetate (17) (1.6 µmol), TBAF (25 µmol) and
naphthalene (0.47 µmol) following the procedure used for the above
preparation of p-xylylene (1) in partially degassed CD3CN. 1H NMR
(400 MHz, CDCl3) δ 6.331 (s, 2H), 5.262 (s, 2H), 5.007 (s, 2H),
1.997 (s, 6H). As the solution was allowed to stand, the 2,6-
dimethyl-para-xylylene (14) was consumed and head-to-head dimer
18 (7.7% yield), head-to-tail dimer 23 (7.3% yield), trimer 20a
(1.3% yield), and insoluble oligomers were formed. Dimer 18: 1H
NMR (400 MHz, CDCl3) δ 6.166 (s, 4H), 3.292 (s, 4H), 2.850 (s,
4H), 2.020 (s, 12H); GC/MS m/z (relative intensity) 264 (13) M+,
249 (10), 133 (19), 132 (100), 129 (19), 128 (13), 117 (18), 115
(26), 114 (12). Dimer 19: 1H NMR (400 MHz, CDCl3) δ 6.348
(s, 4H), 2.97-2.93 (m, 4H), 2.85-2.80 (m, 4H), 2.210 (s, 12H);
GC/MS m/z (relative intensity) 264 (18) M+, 249 (5), 133 (23),
132 (100), 129 (12), 128 (10), 117 (47), 115 (44). Trimer 20a: 1H
NMR35 (400 MHz, CDCl3) δ 6.630 (s, 2H), 6.489 (s, 2H), 6.278
(s, 2H); GC/MS m/z (relative intensity) 397 (2), 396 (6) M+, 147
(4), 146 (2), 145 (2), 143 (2), 134 (3), 133 (26), 132 (100), 129
(9), 128 (6), 127 (3), 126 (2), 117 (19), 115 (21), 111 (2), 103 (2),
89 (5), 88 (10), 86 (2), 85 (2), 53 (2).
1-[p-((Trimethylsilyl)methyl)phenyl]ethanol. To a solution of
209 mg of 4-[(trimethylsilyl)methyl]benzaldehyde (1.09 mmol) in
3 mL of dry ether was added 0.4 mL of 3 M MeMgBr (1.2 mmol),
dropwise. The reaction mixture was heated to reflux for 30 min.
The reaction mixture was worked up in the normal manner to
1
yield 197 mg (95%). H NMR (400 MHz, CD3CN) δ 7.186 and
6.975 (AA′BB′q, J ) 8 Hz), 4.727 (q, J ) 6.4 Hz), 2.073 (s),
1.353 (d, J ) 6.4 Hz), -0.034 (s); 13C NMR (100 MHz, CD3CN)
δ 143.3, 140.1, 128.7, 126.2, 69.9, 26.7, 25.9, -1.9. Anal. Calcd
for C12H20OSi: C, 69.17; H, 9.67. Found: C, 69.29; H, 9.95.
1-[p-((Trimethylsilyl)methyl)phenyl]ethyl Acetate (13). 13 was
prepared in an 87% yield from 1-[p-((trimethylsilyl)methyl)phenyl]-
ethanol (50 mg, 0.24 mmol) with the procedure used for the above
preparation of [p-((trimethylsilyl)methyl)phenyl]methyl acetate. 1H
NMR (400 MHz, CD3CN) δ 7.196 and 7.002 (AA′BB′q, J ) 8
Hz, 4H), 5.763 (q, J ) 6.8 Hz, 1H), 2.085 (s, 2H), 1.991 (s,
3H),1.456 (d, J ) 6.8 Hz, 3H), -0.038 (s, 9H); 13C NMR (100
MHz, CD3CN) δ 171.0, 141.3, 138.5, 129.0, 126.8, 72.8, 26.9, 22.4,
21.5, -1.9.
r-Methyl-p-xylylene (10) in Partially Degassed CD3CN. 10
was prepared from acetate 13 (1.2 µmol), TBAF (25 µmol), and
naphthalene (0.30 µmol) with the procedure used for the above
1
preparation of p-xylylene (1) in partially degassed CD3CN. A H
NMR spectrum was obtained 15 min after the addition of the TBAF.
1H NMR (400 MHz, CD3CN) δ 6.713 (br d, J ) 9.6 Hz, 1H),
6.466 (br d, J ) 9.6 Hz, 1H), 6.314 (br s, 2H) 5.619 (q, J ) 8 Hz,
1H), 4.963 (br s, 2H), 1.848 (d, J ) 8 Hz, 3H). Upon standing, the
1H NMR spectrum showed signals consistent with oxygen adducts
and trace amounts of dimers and trimers.
r-Methyl-p-xylylene (10) in Deoxygenated CD3CN. 10 was
prepared from acetate 13 (5.7 µmol), TBAF (25 µmol), and
naphthalene (0.41 µmol) in 20 mL of CH3CN with the procedure
used for the above preparation of p-xylylene (1) in deoxygenated
CD3CN. The 1H NMR spectrum after 15 min is very similar to the
spectrum obtained for p-QDM 10 in partially degassed CD3CN.
As the solution was allowed to stand, insoluble oligomers were
1
formed. After 14 h, another H NMR spectrum was obtained. It
showed signals with chemical shifts similar to those of the dimer,
trimer, and oxygen adducts of parent p-QDM 1. The spectrum
showed no signals for p-QDM 10.
r-Methyl-p-xylylene (10) in Deoxygenated CH3CN. 10 was
prepared from acetate 13 (20 µmol) and TBAF (45 µmol) in 20
mL of CH3CN with the procedure used for the above preparation
of p-xylylene (1) in deoxygenated CD3CN. As the solution was
allowed to stand, the p-QDM 10 was consumed, and three dimers
14, four trimers 15, oxygen adducts, and insoluble oligomers were
formed. The product mixture was extracted with pentane, and
the extract was analyzed by GC/MS. Dimer A 14 (7.3% yield):
GC/MS m/z (relative intensity) 237 (6), 236 (31) M+, 119 (29),
118 (100), 117 (66), 115 (24), 113 (3), 105 (2), 103 (3), 102 (3),
89 (7), 88 (6). Dimer B 14 (2.6% yield): GC/MS m/z (relative
intensity) 237 (2), 236 (3) M+, 119 (58), 118 (100), 117 (93), 115
(26), 103 (3), 90 (6), 89 (9), 88 (8). Dimer C 14 (5.0% yield):
GC/MS m/z (relative intensity) 236 (9) M+, 120 (3), 119 (36), 118
(97), 117 (100), 115 (24), 103 (3), 89 (12), 88 (7), 86 (6). Trimer
A 15 (1.3% yield): GC/MS m/z (relative intensity) 354 (2) M+,
238 (16), 237 (100), 236 (60), 189 (2), 131 (2), 129 (2), 128 (3),
119 (42), 118 (56), 117 (99), 115 (34), 107 (2), 103 (3), 90 (6), 89
(10), 88 (10), 86 (4). Trimer B 15 (2.2% yield): GC/MS m/z
p-Xylylene (1) and 2,6-Dimethyl-p-xylylene (11) in Partially
Degassed CD3CN. 1 and 11 were prepared from [p-((trimethylsi-
lyl)methyl)phenyl]methyl acetate (12) (0.67 µmol), [3,5-dimethyl-
4-((trimethylsilyl)methyl)phenyl]methyl acetate (17) (1.5 µmol),
TBAF (50 µmol), and naphthalene (0.47 µmol) following the
procedure used for the above preparation of p-xylylene (1) in
partially degassed CD3CN. As the solution was allowed to stand,
the p-xylylene and 2,6-dimethyl-para-xylylene (11) were consumed
and p-xylylene dimer 3 (2.8 × 10-8 mol), head-to-head dimers 18
(35) Benzylic hydrogens were masked by other signals and were not
observed.
J. Org. Chem, Vol. 71, No. 5, 2006 1793