8784 J . Org. Chem., Vol. 64, No. 24, 1999
Hasegawa et al.
6.45 (d, 2H, J ) 10.2 Hz), 7.00-7.03 (m, 1H), 7.22 (dd, 1H,
J ) 10.2, 3.4 Hz); 13C NMR (50 MHz, CDCl3) δ 16.3 (q), 24.7
(q), 51.2 (s), 55.9 (s), 130.6 (d), 137.6 (s), 143.4 (d), 147.9 (d),
185.2 (s); IR (KBr) 1662, 1638 cm-1; HRMS m/z calcd for C9H9-
OBr3 369.8202, found 369.8230, calcd for C9H9OBr281Br
371.8182, found 371.8171, calcd for C9H9OBr81Br2 373.8162,
found 373.8148, calcd for C9H9O81Br3 375.8142, found 375.8117.
8: mp 98-99 °C (n-C6H14); 1H NMR (200 MHz, CDCl3) δ
1.65 (s, 3H), 1.97 (s, 6H), 6.97 (s, 2H); 13C NMR (50 MHz,
CDCl3) δ 16.5 (q, 2C), 24.5(q), 52.7 (s), 55.2 (s), 137.2 (s, 2C),
143.1 (d, 2C), 185.8 (s); IR (KBr) 1666, 1640 cm-1; m/z calcd
us to propose a reaction mechanism in which fragmenta-
tion of the dienone anion-radical and amine cation-radical
pair is involved.28 Trialkyltin radical-induced reductions
of the same dienones with tri-n-butyltin hydride demon-
strated common features with PET reactions. It was also
found that irradiation of 4-(dibromomethyl)-4-methyl-2,5-
cyclohexadienone with TMSA produced 4-methyltropone.
Exp er im en ta l Section
for C10H11OBr3 383.8359, found 383.8373, calcd for C10H11
-
Gen er a l P r oced u r es. Triethylamine and triallylamine
were distilled with CaH2. Tribenzylamine and diazabicyclo-
octane were purified by sublimation. N,N-Diethyl((trimethyl-
silyl)methyl)amine was prepared according to the literature
procedure.29 Acetonitrile was distilled over P2O5 and subse-
quently with CaH2. Benzene was treated with H2SO4, 5%
NaOH, and CaCl2 and then distilled with CaH2. Methanol
(Wako) was distilled and dried with 3A molecular sieves.
Tetrahydrofuran was distilled from sodium-benzophenone
under N2. Water for the reaction was obtained through an ion-
exchange column. Other reagents and solvents were purchased
and used without further purification.
NMR spectra were recorded in CDCl3 with Me4Si as the
internal standard at 90 and 200 MHz for 1H NMR and 22.49
and 49 MHz for 13C NMR, respectively. Melting points that
are uncorrected are reported. Photoreactions were conducted
in a Pyrex tube (2.5 cm diameter) immersed in a water bath
OBr281Br 385.8339, found 385.8316, calcd for C10H11OBr81Br2
387.8319, found 387.8334, calcd for C10H11O81Br3 389.8299,
found 389.8312.
P r ep a r a tion s of 4-(Dibr om om eth yl)-4-m eth yl-2,5-cy-
cloh exa d ien on es (3, 5). A mixture of p-cresol (20.0 mmol),
bromoform (66.0 mmol), and cetyltrimethylammonium bro-
mide (0.20 mmol) was heated at 54 °C followed by slow
addition of 10 M NaOH and was then heated for an additional
4 h. To this was added ice water followed by extraction with
ether. The ether solution was treated with water and saturated
NaCl and was dried over Na2SO4. The residue obtained by
concentration was subjected to column chromatography (CH2-
Cl2) to give a solid, dienone 3 (3.6 mmol, 18%). This was
recrystallized from CH2Cl2/n-C6H14. Dienone 5 was similarly
synthesized: 5 (30%).
3: mp 60-61 °C (CH2Cl2/n-C6H14); 1H NMR (200 MHz,
CDCl3) δ 1.50 (d, 3H, J ) 2.3 Hz), 5.67 (s, 1H), 6.39 (d, 2H,
J ) 10.6 Hz), 6.95 (d, 2H, J ) 10.6 Hz); 13C NMR (50 MHz,
CDCl3) δ 24.6 (q), 47.5 (s), 50.0 (d), 130.6 (d, 2C), 149.4 (d,
2C), 184.8 (s); IR (KBr) 1680 cm-1; HRMS m/z calcd for C8H8-
OBr2 277.8941, found 277.8938, calcd for C8H8OBr81Br 279.8921,
found 279.8909, calcd for C8H8O81Br2 281.8901, found 281.8896.
5: mp 65-67 °C (CH2Cl2/n-C6H14); 1H NMR (200 MHz,
CDCl3) δ 1.48 (s, 3H), 1.96 (d, 3H, J ) 1.4 Hz), 5.64 (s, 1H),
6.39 (d, 1H, J ) 10.1 Hz), 6.69-6.71 (m, 1H), 6.69 (dd, 1H,
J ) 10.1, 3.2 Hz); 13C NMR (50 MHz, CDCl3) δ 16.1 (q), 24.5
(q), 47.4 (s), 51.0 (d), 130.3 (d), 137.2 (s), 144.7 (d), 149.1 (d),
with
a 500 W Xe-Hg lamp as a light source. Column
chromatography was performed with Wakogel C-200 silica gel.
Preparative TLC was performed on 20 cm × 20 cm plates
coated with Wakogel B-5F silica gel.
P r ep a r a tion s of 4-(Tr ibr om om eth yl)-4-m eth yl-2,5-cy-
cloh exa d ien on es (1, 4, 8). To anhydrous AlBr3 (15.0 mmol)
and carbon disulfide (5 mL) was slowly added a carbon
disulfide solution (4 mL) of p-cresol (10.0 mmol). This mixture
was refluxed for 30 min followed by a carbon disulfide solution
(3 mL) of tetrabromomethane (10.0 mmol) and continuously
refluxed for an additional 3 h. To the residue obtained by
concentration of the reaction solution were added ice water
and concentrated HCl (20 mL). Then, it was allowed to stand
for 30 min followed by extraction with methylene chloride. The
organic layer was treated with 2 M NaOH and water and was
dried over Na2SO4. The residue obtained by concentration was
subjected to column chromatography (CH2Cl2) to give a solid,
dienone 1 (6.0 mmol, 61%). This was recrystallized from CH2-
Cl2/n-C6H14. Dienones 4 and 8 were similarly synthesized
although these yields were quite low: 4 (3%); 8 (8%).
1: mp 146-147 °C (CH2Cl2/n-C6H14) (lit.30 mp 146-147 °C);
1H NMR (200 MHz, CDCl3) δ 1.70 (d, 3H, J ) 1.2 Hz), 6.46 (d,
2H, J ) 8.8 Hz), 7.26 (d, 2H, J ) 8.8 Hz); 13C NMR (50 MHz,
CDCl3) δ 24.8 (q), 49.8 (s), 55.9 (s), 130.7 (d, 2C), 148.2 (d, 2C),
184.5 (s); IR (KBr) 1658 cm-1; HRMS m/z calcd for C8H7OBr3
355.8046, found 355.8010, calcd for C8H7OBr281Br 357.8026,
found 357.8031, calcd for C8H7OBr81Br2 359.8006, found
359.8026, calcd for C8H7O81Br3 361.7986, found 361.8008.
4: mp 117-118 °C (n-C6H14) (lit.30 mp 116-117 °C); 1H NMR
(200 MHz, CDCl3) δ 1.68 (s, 3H), 1.98 (d, 3H, J ) 1.4 Hz),
185.6 (s); IR (KBr) 1666, 1632 cm-1; HRMS m/z calcd for C9H10
-
OBr2 291.9098, found 291.9073, calcd for C9H10OBr81Br
293.9078, found 293.9088, calcd for C9H10O81Br2 295.9058,
found 295.9083.
P h otor ea ction s of Dien on es (1, 3, 4, 8) w ith Am in es.31
Dienone (0.56 mmol) and amine (2.80 mmol) were dissolved
in an appropriate solvent (15 mL). This solution was purged
with dry N2 for 5 min and then irradiated for an appropriate
time. Concentration of the photolyzed solution at ambient
temperature gave a residue which was subsequently separated
by column chromatography. While the eluent was usually a 1
to 1 mixture of EtOAc and n-C6H14, in some cases CH2Cl2 was
used. For example, in the cases of 4 and 8, CH2Cl2 was better
for column chromatography. Usually, unreacted dienone and
monodebrominated dienone were obtained as an inseparable
mixture; therefore, those yields were determined by 1H NMR.
Since the mixture of regioisomers 6 and 7 could not be
separated, the ratio (6/7) was determined by 1H NMR analysis
of their mixture in the reaction of 4.
2: mp 80-81.5 °C (C6H6); 1H NMR (200 MHz, CDCl3) δ 2.63
(d, 3H, J ) 2.1 Hz), 6.68 (d, 1H, J ) 13.0 Hz), 6.85 (d, 1H,
J ) 12.6 Hz), 7.06 (dd, 1H, J ) 12.6, 2.1 Hz), 7.46 (dd, 1H,
J ) 13.0, 2.1 Hz); 13C NMR (50 MHz, CDCl3) δ 29.7 (q), 131.0
(s), 137.5 (d), 138.7 (d), 138.8 (d), 141.8 (d), 144.3 (s), 186.0
(s); IR (KBr) 1636, 1572 cm-1; HRMS m/z calcd for C8H7OBr
197.9680, found 197.9657, calcd for C8H7O81Br 199.9660, found
199.9660.
(28) (a) We were also interested in the reactivity of 1 under other
electron transfer conditions. Notably, the reaction of 1 with samarium
diiodide, which is a well-known single electron reductant,28b gave
neither 2 nor 3. The only isolable product was p-cresol in low yields
(11-23%) irrespective of the fact that MeOH was added or not as a
proton source. Although rationalization of these observations seems
to be difficult because of the relatively low mass balance, samarium-
coordinated dienone ketyl derived from 1 may liberate either tribro-
momethyl radical or anion to yield the phenoxy intermediates. It should
be noted here that p-cresol is another reasonable product in the
reductive electron transfer reactions of 4,4-disubstituted-2,5-cyclo-
hexadienones.7,8 (b) Girard, P.; Namy, J . L.; Kagan, H. B. J . Am. Chem.
Soc. 1980, 102, 2693. Molander, G. A. Chem. Rev. 1992, 92, 29.
Molander, G. A.; Harris, C. R. Chem. Rev. 1996, 96, 307.
(29) Hasegawa, E.; Brumfield, M. A.; Mariano, P. S.; Yoon, U. C. J .
Org. Chem. 1988, 53, 5435.
9: mp 79-80 °C (C6H6); 1H NMR (200 MHz, CDCl3) δ 2.25
(s, 3H), 2.27 (s, 3H), 2.47 (s, 3H), 7.29 (s, 1H), 7.72 (s, 1H); 13
C
NMR (50 MHz, CDCl3) δ 23.1 (q), 23.7 (q), 29.8 (q), 128.1 (s),
137.0 (d), 139.7 (d), 140.6 (s), 144.9 (s), 146.0 (s), 184.8 (s); IR
(KBr) 1608, 1572 cm-1; HRMS m/z calcd for C10H11OBr
225.9993, found 225.9990, calcd for C10H11O81Br 227.9973,
found 227.9998.
10: oil; 1H NMR (200 MHz, CDCl3) δ 2.33 (s, 3H), 6.82-
7.09 (m, 5H); 13C NMR (50 MHz, CDCl3) δ 26.3 (q), 132.8 (d),
(30) Merchant, J . R.; Desai, V. B. J . Chem. Soc. 1964, 2258; 1968,
499.