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A. J. McCarroll et al. / Tetrahedron 59 (2003) 4275–4280
methylsilicone as the stationary phase or with the VG
Autospec coupled to a similar GC. Typically the tempera-
ture was programmed from 40 to 2508C at 128/min and the
flow rate was ca. 0.5 mL/min. EPR spectra were recorded
with a Bruker EMX 10/12 spectrometer operating at
9.5 GHz with 100 kHz modulation. Solutions were placed
in 4 mm o.d. quartz tubes and illuminated by UV light from
a 500 W super pressure mercury lamp focussed directly into
the EPR resonant cavity. Cyclic voltammetry was carried
out using a PC-controlled EG and PAR 273A potentiostat
with an undivided, teflon-topped beaker-type cell (ca.
25 mL) equipped with a glassy carbon working electrode
(0.071 cm2), a silver wire quasi-reference electrode and a
platinum wire counter electrode. The number of electrons
passed was determined by comparing the current with that
of ferrocene which is known to give a one-electron wave,
and whose diffusion coefficient is known to be
2£1025 cm2 s21. The scan-rate dependence of the data
was simulated using the Digisim 3.0 program (Bioanalytical
Systems Inc, West Lafayette, Indiana).14
Compound 14b. dH 1.22 (3H, s), 1.83 (6H, s), 2.79 (2H, s),
6.59 (2H, s) 7.0–7.3 (5H, m); dC 16.1 (CH3), 25.2 (2£CH3),
41.5 (C), 47.2 (CH2), 126.6 (CH), 127.8 (CH), 130.1 (CH),
134.1 (C), 136.6.(C), 150.4 (CH), 187.2 (CO); found
Mþ¼226.1366; C16H18O requires 226.1358.
Compound 15b. dH (300 MHz, CDCl3) 1.21 (3H, s, CH3 at
C-4), 1.76 (3H, s, CH3), 1.82 (3H, s, CH3), 2.70 (1H, d,
J1¼12.8 Hz), 3.08 (1H, d, J¼12.8 Hz), 5.87 (1H, s, vCH),
6.46 (1H, s, vCH), 6.99–7.01 (2H, m, ArH), 7.13–7.20
(3H, m, ArH); dC 15.3, 21.1, 24.8, 47.1, 126.3, 127.5, 129.7,
138.7, 142.4, 205.5; found Mþ¼226.1360, C16H18O
requires 226.1358. A mixture of the two isomers was also
obtained (13.2 g, 38.9%).
4.1.3. 4-(2-Methylnaphthalene)-2,4,6-trimethylcyclo
hexa-2,5-dienone (14c). Prepared from 2-(bromomethyl)-
naphthalene and 13 as described above yielding, after
column chromatography, 14c (0.10 g; 7%), together with
much unreacted starting material. The product contained
some 2-(bromomethyl)naphthalene as an impurity which
was not removed by recrystallisation. dH 2.15 (3H, s, CH3),
2.19 (3H, s, CH3), 2.24 (3H, s, CH3), 4.18 (2H, s, CH2), 6.90
(2H, s, vCH), 7.2–7.8 (7H, m, ArH). dC 12.2, 15.9, 19.7,
35.5, 127.8, 128.8, 129.7, 131.9, 133.6, 135.3, 137.5, 150.3.
(Found Mþ 276.1512; C20H20O requires M 276.1514).
4.1.1. 4-Allyl-2,4,6-trimethylcyclohexa-2,5-dienone (14a)
and 2-allyl-2,4,6-trimethylcyclohexa-3,5-dienone (15a).7
To a solution of NaOH (1.6 g; 0.04 mol) in water (20 cm3)
was added mesitol (5.45 g; 0.04 mol), and the mixture was
stirred overnight. A further 0.2 g NaOH and 10 cm3 H2O
was added to obtain complete solution. Allyl bromide
(3.85 g; 0.044 mol) was added dropwise, and the mixture
was stirred for 24 h at room temperature. The mixture was
extracted with pentane (3£50 cm3), and washed with 10%
sodium hydroxide solution (2£50 cm3) and water
(3£50 cm3), then dried (MgSO4), and concentrated. Purifi-
cation by column chromatography (pentane/diethyl ether
9/1) yielded 4-allyl-2,4,6-trimethyl-cyclohexa-2,5-dienone
14a (0.41 g; 11%) and 2-allyl-2,4,6-trimethyl-cyclohexa-
3,5-dienone 15a (0.24 g; 7%), both as colourless oils, with
satisfactory NMR and IR spectra.7
4.1.4. 2,6-Di-t-butyl-4-hexadecyl-4-methylcyclohexa-2,5-
dienone. To 2,6-di-t-butyl-4-methylphenol (4.41 g;
0.02 mol) in dry THF (30 cm3) in a nitrogen atmosphere
was added potassium t-butoxide, followed by further THF
(20 cm3). The mixture was stirred for 1 h (in which time the
mixture went a peach colour) the iodohexadecane (7.05 g;
0.02 mol) was added, and the mixture stirred for 24 h,
refluxed for 6 h, then stirred for 5 days. Water (40 cm3) and
ether (40 cm3) were added, and the organic layer separated,
then washed with water, brine, and water again. The organic
layer was dried (MgSO4), then purified by column
chromatography (PE/EtOAc). The fastest running spot
was isolated (impure) and again purified by column
chromatography (pentane/ether 9/1). A very small amount
(0.07 g; 0.8%) of 2,6-di-t-butyl-4-hexadecyl-4-methylcy-
clohexa-2,5-dienone was isolated as a yellow oil. dH 0.88
(3H, t, J¼6.6 Hz, CH3). 1.12–1.28 (39H, m), 6.40 (2H, s,
vCH) dC 14.1, 22.7, 24.7, 27.1, 29.1, 29.2, 29.4–29.7, 29.9,
30.3, 30.4, 31.9, 34.6, 40.0, 41.4, 146.3, 147.0, 186.7.
(Found Mþ 444.4337. C31H56O requires M 444.4331).
4-Allyl-2,4,6-trimethylcyclohexa-2,5-dienone (14a). nmax
/
cm21 1670 (CvO) 994 and 916 (CHvCH2). dH1.19 (3H, s,
CH3 on C-4), 1.89 (6H, s, CH3 on C-2,6), 2.27 (2H, d,
J¼7.4 Hz, allyl Hs), 4.98–5.03 (2H, m, vCH2), 5.51–5.62
(1H, m, -CHvCH2), 6.66 (2H, s, vCH).
2-Allyl-2,4,6-trimethyl-cyclohexa-3,5-dienone (15a). dH
1.12 (3H, s, CH3), 1.84 (3H, s, CH3), 1.90 (3H, s, CH3),
2.11–2.59 (2H, m, allyl Hs), (4.85–5.02 (2H, m,
CHvCH2), 5.41–5.63 (1H, m, CHvCH2), 5.85 (1H, s,
vCH), 6.69 (1H, s, vCH).
4.1.5. Photoinitiated reaction of 2-benzyl-2,4,6-tri-
methylcyclohexa-3,5-dienone with triethylamine. Die-
none 15b (0.09 g), and triethylamine (0.1 g; 5 equiv.) were
dissolved in acetonitrile (1 cm3). The mixture was degassed
with nitrogen, and illuminated using a 400 W mercury lamp
for 4 h. The products were analysed using GC/MS; peak no.
125, toluene (trace); peak no. 294, 2,4,6-trimethylphenol,
and peak no. 410, bibenzyl, together with several uni-
dentified components.
4.1.2. 2-Benzyl-2,4,6-trimethyl-cyclohexa-3,5-dienone
(15b) and 4-benzyl-2,4,6-trimethyl-cyclohexa-2,5-die-
none (14b). To solution of NaOH (6.0 g 0.15 mol) in water
(100 cm3)wasaddedmesitol(20.4 g;0.2 mol)andthemixture
was stirred (and sonicated) until most passed into solution.
Benzyl bromide (25.6 g; 0.15 mol) was added over a period of
20 min and the mixture was heated at 608C for 2 h, then
allowed tocool (with stirring). The mixture was extracted with
pentane (3£100 cm3) and washed with 10% NaOH solution
(2£50 cm3) then water (4£20 cm3) and dried (MgSO4) and
concentrated. The mixture was separated by column chroma-
tography (pentane/diethyl ether, 9/1) to afford O-benzyl-
mesitol (2.4 g, 7%), 14b (0.9 g, 2.7%) and 15b (2.5 g, 7.4%).
4.1.6. Photoinitiated reaction of 4-benzyl-2,4,6-tri-
methylcyclohexa-2,5-dienone with triethylamine. The
dienone 14b (0.021 g, 0.09 mmol) and triethylamine
(0.022 g, 0.22 mmol) were dissolved in C6D6 (0.5 cm3) in
a quartz tube and irradiated with light from a 400 W