Manganese(III) acetate based tandem oxidation of various α and β-alkoxy α,β-unsaturated ketones

Article abstract of DOI:10.1016/S0040-4020(02)01350-9

We described the unusual results of manganese(III) acetate based tandem oxidation of various α and β-alkoxy α,β-unsaturated ketones to afford the corresponding α′-acetoxy-α′-phenyl substituted oxidation products in good yields. The tandem oxidation to mon

Full text of DOI:10.1016/S0040-4020(02)01350-9

Tetrahedron 58 (2002) 9983–9988
Manganese(III) acetate based tandem oxidation of various a and
b-alkoxy a,b-unsaturated ketones
¨
Cihangir Tanyeli, Devrim Ozdemirhan and Bengu¨ Sezen
*
Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
Received 25 June 2002; revised 30 September 2002; accepted 17 October 2002
Abstract—We described the unusual results of manganese(III) acetate based tandem oxidation of various a and b-alkoxy a,b-unsaturated
ketones to afford the corresponding a0-acetoxy-a0-phenyl substituted oxidation products in good yields. The tandem oxidation to
monoacetoxylation ratio can be tuned by the amount of manganese(III) acetate. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
In the last decade, Manganese(III)-based oxidative free-
radical reactions have been developed into a versatile
protocol for the formation of highly functionalised products
from simple precursors.1–10 In 1976, Williams and Hunter
reported that Mn(OAc)3·2H2O oxidation of enones in AcOH
at reflux affords a0-acetoxy enones in low yields.11 In
Scheme 1.
connection with our synthetic studies with manganese(III)
acetate,12 we found that trapping the a0-keto radicals
obtained from b-alkoxy a,b-unsaturated ketones by
benzene used as a solvent is much faster than acetoxylation,
affording good yields of tandem oxidation products.12d
These interesting results prompted us towards the develop-
ment of a new method in the field of the regioselective
tandem oxidation of a-alkoxy and b-alkoxy a,b-unsatu-
rated ketones. Here, we report our results obtained from the
Mn(OAc)3 oxidation of various a-alkoxy and b-alkoxy a,b-
unsaturated ketones and an optimization of the reaction
conditions.
Characterization of the product revealed the introduction
of a phenyl group together with an acetoxy moiety on the a0
position (Scheme 1). The full results are summarized in
Table 1.
The reaction presumably proceeds via the formation of the
Mn(III) enolate 3, which loses Mn(II) upon one-electron
oxidation to give a0-keto radical 46,10d,16,17 (Scheme 2).
Addition of this radical to benzene yields another radical, 5.
One-electron oxidation of the resultant radical 5 gives a0-
phenyl b-alkoxy a,b-unsaturated ketones 6. The introduc-
tion of aryl groups to ketones was reported to be confined to
acetone, by Vinogradov et al.,18 since a0-keto radicals
generated by higher ketones would result in secondary
radicals which would dimerize, or tertiary radicals that are
prone to further oxidation. In contrast to this conclusion, in
this study, no dimerization was observed. Oxidation of
intermediate 6 by another equivalent of Mn(OAc)3 provides
a0-acetoxy a0-phenyl b-alkoxy a,b-unsaturated ketones 2.
Similarly, cyclopentenones 1b and 1c (entries 2 and 3) give
73 and 68% of tandem oxidation products 2b and 2c,
respectively, together with a small amount of recovered
starting material and some unidentified polymeric products.
2. Results and discussion
As a starting point, various b-alkoxy a,b-unsaturated
ketones 1 were prepared from the corresponding 1,3-
diketones using slightly modified literature procedures13,14
and were then allowed to react with Mn(OAc)3. We have
found that Mn(III)-based oxidation of b-alkoxy a,b-
unsaturated ketones is infact a versatile synthetic procedure
with broad applicability.15 For instance, reaction of 1a with
3 equiv. of Mn(OAc)3 in benzene as the solvent for 8 h at
reflux afforded 61% of tandem oxidation product 2a.
With cyclohexenone derivatives 1d–h, acetoxylation at the
a0-position competes effectively with the tandem oxidation.
For instance, reaction of 3-ethoxy-2-cyclohexenone 1d with
3 equiv. of Mn(OAc)3 in benzene for 8 h at reflux gives 2d
in 56% yield, 7d in 35% yield and monophenylated product
Keywords: enones; manganese and compounds; oxidation.
*
Corresponding author. Tel.: þ90-312-210-32-22; fax: þ90-312-210-12-
80; e-mail: tanyeli@metu.edu.tr
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)01350-9

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C. Tanyeli et al. / Tetrahedron 58 (2002) 9983–9988
Table 1. Tandem oxidation of b-alkoxy a,b-unsaturated ketones with Mn(OAc)3 in benzene
Entry
1
Reactant
Product
2
Yield (%)
61
Product
7
Yield (%)
Time (h)
8
a
–
2
3
b
c
73
68
–
–
8
8
4
5
d
e
56
59
d
e
35
28
12
12
6a
f
62
65
f
26
25
11
10
7b
g
g
8
h
i
60
58
h
i
31
35
12
12
9c
a
The reaction was carried out with racemic mixture of 1f. 2f was isolated as 6:4 diastereomeric mixture, while 7f was isolated as 8:2 E/Z mixture and 6f as only
E isomer by using 1H NMR data.
2g was isolated as 7:3 diastereomeric mixture. Only isolable product 7g has E configuration which was determined from 1H NMR.
2i was isolated as 7:3 diastereomeric mixture.
b
c
Scheme 2.

C. Tanyeli et al. / Tetrahedron 58 (2002) 9983–9988
9985
Table 2. Tandem oxidation of a-alkoxy a,b-unsaturated ketones with Mn(OAc)3 in benzene
Entry
Reactant
Product
9
Yield (%)
Product
10
Yield (%)
Time (h)
8
1
a
72
–
2
3
4
b
c
d
75
63
59
–
8
c
28
32
12
10
d
6d in 5% yield. The isolation of monophenylated product
was also achieved in entry 6 as 6f with 6% yield. As a model
study, monoacetoxylation product 7d was subjected to
Mn(OAc)3 oxidation in a similar manner in entry 4
(3 equiv. Mn(OAc)3 in benzene). As expected from the
proposed reaction mechanism, no product formation was
observed. When 4 equiv. of Mn(OAc)3 was used (entry 4),
we observed drastic increase in the chemical yield of
monoacetoxylated product 7d (53%) and a decrease in
the tandem oxidation product 2d (31%). Similar results
were obtained for entries 5–8. Hence, we decided that the
critical amount of oxidant for six-membered enones was
3 equiv.
3. Experimental
1H and 13C NMR spectra were recorded in CDCl3 on Bruker
Spectrospin Avance DPX 400 spectrometers. Chemical
shifts are given in ppm from tetramethylsilane. Coupling
constants (J) were recorded in Hertz. IR spectra were
obtained from a Perkin–Elmer Model 1600 series FT–IR
spectrometer and are reported in cm21. Mass spectra were
recorded on a Varian MAT 212. Thin layer chromatography
(TLC) was performed on Merck plastic-backed silica gel
plates. Compounds were visualised under a UV lamp.
Column chromatography was performed using silica gel
(Flash Silica 60, 32–63 mm). 1,2- and 1,3-Diketones were
purchased from Aldrich. a-Ethoxy and b-ethoxy a,b-
unsaturated compounds were synthesized according to
literature procedure.13,14
Notably Z-3-ethoxy-2-pentenone (entry 9) behaves very
similarly, giving 2i in 58% yield as a 7:3 diastereomeric
mixture. 35% of monoacetoxylated product 7i was also
isolated.
3.1. General procedure for the Mn(OAc)3 oxidation of b-
alkoxy a,b-unsaturated ketones
In the next step of this study, 3-ethoxy-2-cyclopentenone
(entry 1) was chosen as a model compound. The Mn(OAc)3
oxidation was performed in various solvents. With
nitrobenzene and pyridine, no product formation was
observed. With anisole, aniline and furan, only
uncharacterized oxidation products were obtained. Bromo-
benzene and chlorobenzene each yielded 5-acetoxy-3-
ethoxy-5-phenyl-2-cyclopentenone in 38 and 12% yields,
respectively.
A mixture of Mn(OAc)3 (2.41 g, 9.0 mmol) in benzene (or
corresponding solvent) (100 mL) was refluxed for 45 min.
under a Dean–Stark trap, then cooled to room temperature.
b-Alkoxy a,b-unsaturated ketone (3.0 mmol) was gradually
added and the mixture was allowed to reflux until the dark
brown colour disappeared (TLC monitoring). The reaction
mixture was diluted with ethyl acetate (100 mL) and the
organic phase was washed with 1N HCl (100 mL), saturated
NaHCO3 and brine. The organic phase was dried over
MgSO4 and evaporated in vacuo. The crude product was
separated by flash column chromatography using ethyl
acetate/hexane as eluent to afford the product.
Other substrates various a-alkoxy a,b-unsaturated ketones
8 were next prepared from the corresponding 1,2-diketones
using slightly modified literature procedures.15 On reaction
of 8a with 3 equiv. of Mn(OAc)3 in benzene at reflux for
8 h, 9a was produced in 72% yield. Further examples of
the reaction are summarized in Table 2. We suggest
that reactions follow a similar route to that obtained in
Scheme 2.
3.1.1. 5-Acetoxy-3-ethoxy-5-phenyl-2-cyclopentenone
2a. (0.48 g, 61%) as a white solid, mp 94–968C; Rf
(EtOAc/hexane 1:3) 0.35; nmax (neat) 1740, 1715 cm21; dH
(400 MHz, CDCl3) 7.18–7.34 (5H, m, Ph), 5.25 (1H, s,
CHv), 4.02–4.13 (2H, m, MeCH2O), 3.30 (1H, d,
J¼18 Hz, CHaHbCOAcPh), 3.13 (1H, d, J¼18 Hz, CHaHb-
COAcPh), 2.10 (3H, s, MeCO2), 1.36 (3H, t, J¼7 Hz,
MeCH2O); dC (100.6 MHz, CDCl3) 199.4, 185.8, 170.1,
138.6, 129.0, 128.5, 125.1, 102.5, 84.1, 68.2, 43.0, 21.7,
In conclusion, we have discovered an interesting and
potentially useful Mn(OAc)3 based tandem oxidation
reaction. The applicability of a one-pot double oxidation
method is attractive for further use in synthesis.

9986
C. Tanyeli et al. / Tetrahedron 58 (2002) 9983–9988
14.5; m/z (EI) 260 (9), 218 (32), 217 (28), 200 (25), 105
(100), 77 (22%). HRMS (EI): Mþ, found 260.1049.
C15H16O4 requires 260.1048.
103.6, 64.8, 52.3, 29.8, 28.6, 14.5; HRMS (EI): Mþ, found
216.1147. C14H16O2 requires 216.1151.
3.1.7. 6-Acetoxy-3-ethoxy-2-methyl-6-phenyl-2-cyclo-
hexenone 2e. (0.51 g, 59%) as a colourless oil; Rf
(EtOAc/hexane 1:2) 0.66; nmax (neat) 3020, 2975, 1725,
1695 cm21; dH (400 MHz, CDCl3) 7.14–7.33 (5H, m, Ph),
4.01 (2H, q, J¼7 Hz, MeCH2O), 2.16–2.61 (4H, m,
CH2CH2), 2.14 (3H, s, MeOAc), 1.78 (3H, s, MeCv),
1.37 (3H, t, J¼7 Hz, MeCH2O); dC (100.6 MHz, CDCl3)
195.0, 177.2, 170.5, 137.2, 129.3, 128.5, 127.9, 127.1,
126.9, 121.1, 87.4, 65.5, 59.2, 47.3, 22.1, 20.8, 14.5; HRMS
(EI): Mþ, found 288.1359. C17H20O4 requires 288.1362.
3.1.2. 5-Acetoxy-3-ethoxy-2-methyl-5-phenyl-2-cyclo-
pentenone 2b. (0.60 g, 73%) as a colourless oil; Rf
(EtOAc/hexane 1:2) 0.33; nmax (neat) 1743, 1714 cm21
;
dH (400 MHz, CDCl3) 7.13–7.40 (5H, m, Ph), 4.29 (2H, q,
J¼7 Hz, MeCH2O), 3.66 (1H, d, J¼17 Hz, CHaHb-
COAcPh), 3.33 (1H, d, J¼17 Hz, CHaHbCOAcPh), 2.19
(3H, s, MeCO2), 1.71 (3H, s, MeCv), 1.45 (3H, t, J¼7 Hz,
MeCH2O); dC (100.6 MHz, CDCl3) 204.9, 183.3, 170.3,
140.2, 139.1, 129.0, 127.9, 127.3, 124.9, 114.3, 84.0, 50.9,
35.5, 21.8, 15.7, 6.8; m/z (EI) 276 (18), 275 (83), 247 (13),
231 (11), 218 (22), 217 (100), 215 (29%). HRMS (EI): Mþ,
found 274.1198. C16H18O4 requires 274.1206.
3.1.8. 6-Acetoxy-3-ethoxy-2-methyl-2-cyclohexenone 7e.
(0.18 g, 28%) as a colourless oil; Rf (EtOAc/hexane 1:2)
0.51; nmax (neat) 1733, 1658 cm21; dH (400 MHz, CDCl3)
5.90–5.91 (1H, m, CHOAc), 4.04 (2H, q, J¼7 Hz,
MeCH2O), 2.54–2.63 (1H, m, vCCHaHbCH2), 2.34–
2.39 (1H, m, vCHaHbCH2), 2.15–2.17 (2H, m, CH2CH2-
COAc), 2.14 (3H, s, MeCO2), 1.76 (3H, s, MeCv), 1.33
(3H, t, J¼7 Hz, MeCH2O); dC (100.6 MHz, CDCl3) 198.7,
170.6, 164.8, 120.1, 70.1, 64.7, 32.1, 27.0, 21.2, 15.9, 15.7;
m/z (EI) 213 (100), 153 (11%). HRMS (EI): Mþ, found
212.1052. C11H16O4 requires 212.1049.
3.1.3. 5-Acetoxy-3-ethoxy-2-ethyl-5-phenyl-2-cyclo-
pentenone 2c. (0.59 g, 68%) as a colourless oil; Rf
(EtOAc/hexane 1:2) 0.35; nmax (neat) 1746, 1715 cm21
;
dH (400 MHz, CDCl3) 7.15–7.33 (5H, m, Ph), 4.24 (2H, q,
J¼7 Hz, MeCH2O), 3.64 (2H, d, J¼17 Hz, CH2COAcPh),
2.22 (2H, q, J¼7 Hz, MeCH2Cv), 2.18 (3H, s, MeCO2),
1.43 (3H, t, J¼7 Hz, MeCH2O), 1.04 (3H, t, J¼7 Hz,
MeCH2C¼); dC (100.6 MHz, CDCl3) 201.1, 176.9,
170.6, 139.1, 128.3, 125.7, 124.9, 121.8, 120.5, 119.9,
84.0, 68.4, 42.2, 21.7, 15.4, 15.2, 13.1; m/z (EI) 290
(15), 289 (83), 261 (18), 232 (16), 231 (100), 229 (17%).
HRMS (EI): Mþ, found 288.1371. C17H20O4 requires
288.1362.
3.1.9. 6-Acetoxy-3-ethoxy-5-methyl-6-phenyl-2-cyclo-
hexenone 2f. (0.54 g, 62%) as a colourless oil; Rf
(EtOAc/hexane 1:4) 0.24; nmax (neat) 3016, 2976, 1728,
1685 cm21; dH (400 MHz, CDCl3) (6:4 diastereomeric
mixture) 7.01–7.30 (2£5H, m, Ph), 5.43 (1H, s, CHv),
5.36 (1H, s, CHv), 3.82–3.96 (2£2H, m, MeCH2O), 2.43–
2.48 (2£1H, m, CHMe), 2.23–2.36 (2£2H, m, CH2CHMe),
2.11 (3H, s, MeCO2), 2.10 (3H, s, MeCO2), 1.36 (3H, t,
J¼7 Hz, MeCH2O), 1.35 (3H, t, J¼7 Hz, MeCH2O), 0.91
(3H, d, J¼6 Hz, MeCH), 0.84 (3H, d, J¼6 Hz, MeCH); dC
(100.6 MHz, CDCl3) 195.3, 193.5, 178.2, 177.4, 170.2,
166.5, 140.1, 138.9, 129.5, 128.8, 128.5, 128.3, 127.2,
103.2, 101.3, 64.7, 63.5, 61.4, 60.8, 38.1, 37.5, 35.7, 34.8,
31.3, 30.8, 21.1, 20.6, 14.7, 14.6; HRMS (EI): Mþ, found
288.1356. C17H20O4 requires 288.1362.
3.1.4. 6-Acetoxy-3-ethoxy-6-phenyl-2-cyclohexenone 2d.
(0.46 g, 56%) as a colourless oil; Rf (EtOAc/hexane 1:8)
0.81; nmax (neat) 3066, 1758, 1675 cm21; dH (400 MHz,
CDCl3) 7.19–7.38 (5H, m, Ph), 5.56 (1H, s, CHv), 3.83–
3.95 (2H, m, MeCH2O), 2.10–2.30 (4H, m, CH2CH2-
COAcPh), 2.05 (3H, s, MeCO2), 1.29 (3H, t, J¼7 Hz,
MeCH2O); dC (100.6 MHz, CDCl3) 199.3, 176.6, 169.9,
137.6, 128.6, 128.5, 128.3, 126.8, 126.7, 103.2, 96.1, 64.9,
29.4, 28.2, 21.8, 14.1; HRMS (EI): Mþ, found 274.1211.
C16H18O4 requires 274.1206.
3.1.5. 6-Acetoxy-3-ethoxy-2-cyclohexenone 7d. (0.21 g,
35%) as a colourless oil; Rf (EtOAc/hexane 1:8) 0.66; nmax
(neat) 1736, 1665 cm21; dH (400 MHz, CDCl3) 5.37 (1H, s,
CH¼), 5.29 (1H, dd, J¼5, 13 Hz, CHOAc), 3.92 (2H, q,
J¼7 Hz, MeCH2O), 2.63–2.67 (1H, m, CHaCHbCv),
2.52–2.54 (1H, m, CHaCHbCv), 2.20–2.24 (1H, m,
CHaCHbCOAc), 2.19 (3H, s, MeOAc), 2.07–2.16 (1H, m,
CHaCHbCOAc), 1.37 (3H, t, J¼7 Hz, MeCH2O); dC
(100.6 MHz, CDCl3) 193.4, 177.1, 170.5, 101.5, 72.8,
65.2, 28.3 27.1, 21.2, 14.4; m/z (EI) 217 (19), 200 (14), 199
(100%); HRMS (EI): Mþ, found 198.0883. C10H14O4
requires 198.0892.
3.1.10. 6-Acetoxy-3-ethoxy-5-methyl-2-cyclohexenone
7f. (0.17 g, 26%) as a colourless oil; Rf (EtOAc/hexane
1:4) 0.21; nmax (neat) 1739, 1646 cm21; dH (400 MHz,
CDCl3) (8:2 E/Z mixture) 5.46 (1H, d, J¼5 Hz, CHv), 5.40
(1H, s, CHv), 5.38 (1H, s, CHOAc), 5.09 (1H, d, J¼12 Hz,
CHOAc), 3.89–4.02 (2£2H, m, MeCH2O), 2.83–2.89
(2£1H, m, CHMe), 2.45–2.61 (2£1H, m, vCCHaHb),
2.34–2.43 (2£1H, m, vCCHaCHb), 2.24 (3H, s, MeCO2),
2.23 (3H, s, MeCO2), 1.39–1.43 (2£3H, m, MeCH2O), 1.12
(3H, d, J¼7 Hz, MeCH), 1.09 (3H, d, J¼7 Hz, MeCH); dC
(100.6 MHz, CDCl3) 193.2, 192.7, 176.1, 174.9, 170.9,
170.5, 102.7, 101.4, 101.0, 78.3, 75.8, 65.2, 64.6, 45.5, 37.6,
36.9, 35.7, 33.8, 31.9, 21.2, 21.1, 18.1, 14.4, 13.7; HRMS
(EI): Mþ, found 212.1042. C11H16O4 requires 212.1049.
3.1.6. 3-Ethoxy-6-phenyl-2-cyclohexenone 6d. (0.03 g,
5%) as a colourless oil; Rf (EtOAc/hexane 1:8) 0.72; nmax
(neat) 3150, 1691, 1641 cm21; dH (400 MHz, CDCl3) 7.10–
7.28 (5H, m, Ph), 5.44 (1H, s, CHv), 3.88 (2H, q, J¼7 Hz,
MeCH2O), 3.44–3.49 (1H, dd, J¼5, 10 Hz, CHPh), 2.40–
2.51 (2H, m, vCCH2), 2.12–2.17 (2H, m, CH2CH2CHPh),
1.32 (3H, t, J¼7 Hz, MeCH2O); dC (100.6 MHz, CDCl3)
199.6, 177.7, 140.3, 128.9, 128.7, 127.6, 127.2, 126.6,
3.1.11. 3-Ethoxy-5-methyl-6-phenyl-2-cyclohexenone 6f.
(0.04 g, 6%) as a colourless oil; Rf (EtOAc/hexane 1:4)
0.26; nmax (neat) 3210, 1693, 1643 cm21; dH (400 MHz,
CDCl3) 7.03–7.28 (5H, m, Ph), 5.45 (1H, s, CHv), 3.80–
3.92 (2H, m, MeCH2O), 3.06 (1H, d, J¼11 Hz, CHPh),
2.44–2.49 (1H, dd, J¼4, 16 Hz, CHaHbCHMe), 2.32–2.41

C. Tanyeli et al. / Tetrahedron 58 (2002) 9983–9988
9987
(2H, m, CHaHbCHMe), 1.33 (3H, t, J¼7 Hz, MeCH2O),
0.84 (3H, d, J¼6 Hz, MeCH); dC (100.6 MHz, CDCl3)
198.7, 176.7, 139.7, 128.6, 128.3, 127.9, 127.4, 126.3,
101.3, 65.4, 53.2, 30.2, 21.3, 15.2, 14.3; HRMS (EI): Mþ,
found 230.1302. C15H18O2 requires 230.1307.
7.56 (2£5H, m, Ph), 6.39 (2£1H, s, CHOAcPh), 6.33 (1H, s,
CHv), 6.32 (1H, s, CHv), 3.87–3.93 (2£2H, m,
MeCH2O), 2.19 (3H, s, MeCO2), 2.15 (3H, s, MeCO2),
2.05 (3H, s, MeCv), 1.89 (3H, s, MeCv), 1.29–1.37
(2£3H, m, MeCH2O); dC (100.6 MHz, CDCl3) 205.2, 201.0,
169.9, 168.6, 159.8, 159.2, 137.4, 137.1, 135.2, 133.3,
130.8, 130.0, 129.0, 128.9, 128.7, 127.3, 127.1, 114.1,
113.9, 90.1, 81.9, 63.4, 63.2, 61.0, 21.2, 20.8, 20.0, 15.3,
15.2; HRMS (EI): Mþ, found 262.1198, C15H18O4 requires
262.1205.
3.1.12. 6-Acetoxy-3-ethoxy-5,6-diphenyl-2-cyclohexe-
none 2g. (0.68 g, 65%) as a colourless oil; Rf (EtOAc/
hexane 1:3) 0.42; nmax (neat) 3010, 2973, 1738, 1674 cm21
;
dH (400 MHz, CDCl3) (7:3 diastereomeric mixture) 6.93–
7.16 (10H, m, Ph), 5.71 (1H, s, CHv), 5.60 (1H, s, CHv),
3.75–3.83 (2£3H, m, MeCH2O), 2.33–2.40 (2£2H, m,
CH2CHPh), 1.91 (3H, s, MeCO2), 1.89 (3H, s, MeCO2), 1.13
(3H, t, J¼7 Hz, MeCH2O), 1.09 (3H, t, J¼7 Hz, MeCH2O);
dC (100.6 MHz, CDCl3) 196.7, 194.2, 176.1, 175.7, 172.3,
171.6, 140.4, 139.8, 129.1, 127.9, 127.7, 126.5, 109.8,
102.0, 101.3, 65.3, 64.8, 42.4, 41.2, 36.2, 35.4, 20.1, 19.8,
14.3, 14.1; HRMS (EI): Mþ, found 350.1531. C22H22O4
requires 350.1518.
3.1.17. 1-Acetoxy-4-ethoxy-pent-3-en-2-one 7i. (0.20 g,
35%) as a colourless oil; Rf (EtOAc/hexane 1:10) 0.83; nmax
(neat) 1735, 1685 cm21; dH (400 MHz, CDCl3) 6.44 (1H, s,
CHv), 4.78 (2H, s, CH2OAc), 3.92 (2H, q, J¼7 Hz,
MeCH2O), 2.18 (3H, s, MeCO2), 2.09 (3H, s, MeCv), 1.33
(3H, t, J¼7 Hz, MeCH2O); dC (100.6 MHz, CDCl3) 202.4,
170.2, 159.9, 136.3, 130.8, 114.1, 69.6, 63.5, 20.8, 19.8,
15.2; HRMS (EI): Mþ, found 186.2051. C9H14O4 requires
186.0892.
3.1.13. 6-Acetoxy-3-ethoxy-5-phenyl-2-cyclohexenone
7g. (0.21 g, 25%) as a colourless oil; Rf (EtOAc/hexane
1:3) 0.37; nmax (neat) 3015, 2875, 1734 cm21; dH
(400 MHz, CDCl3) 7.24–7.36 (5H, m, Ph), 5.63 (1H, d,
J¼13 Hz, CHOAc), 5.46 (1H, s, CHv), 3.96 (2H, q,
J¼7 Hz, MeCH2O), 3.50 (1H, dt, J¼5, 13 Hz, CHPh), 2.87
(1H, dd, J¼6, 18 Hz, CHaHbCHPh), 2.70 (1H, dd, J¼5,
18 Hz, CHaHbCHPh), 1.95 (3H, s, MeCO2), 1.33 (3H, t,
J¼7 Hz, MeCH2O); dC (100.6 MHz, CDCl3) 192.8, 175.8,
170.6, 139.6, 129.1, 128.8, 128.5, 127.9, 127.7, 101.4, 76.0,
65.5, 45.0, 37.3, 20.9, 14.4; m/z (EI) 274 (100), 215 (22%);
HRMS (EI): Mþ, found 274.1193. C16H18O4 requires
274.1206.
3.2. General procedure for the Mn(OAc)3 oxidation of
a-alkoxy a,b-unsaturated ketones
A mixture of Mn(OAc)3 (2.41 g, 9.0 mmol) in benzene (or
corresponding solvent) (100 mL) was refluxed for 45 min.
under a Dean–Stark trap, then cooled to room temperature.
a-Alkoxy a,b-unsaturated ketone (3.0 mmol) was gradually
added and the mixture was allowed to reflux until the dark
brown colour disappeared (TLC monitoring). The reaction
mixture was diluted with ethyl acetate (100 mL) and the
organic phase was washed with 1N HCl (100 mL), saturated
NaHCO3 and brine. The organic phase was dried over
MgSO4 and evaporated in vacuo. The crude product was
separated by flash column chromatography using ethyl
acetate/hexane as eluent to afford the product.
3.1.14. 6-Acetoxy-3-ethoxy-4,4-dimethyl-6-phenyl-2-
cyclohexenone 2h. (0.54 g, 60%) as a colourless oil; Rf
(EtOAc/hexane 1:5) 0.68; nmax (neat) 3012, 2970, 1742,
1682 cm21; dH (400 MHz, CDCl3) 7.09–7.28 (5H, m, Ph),
5.50 (1H, s, CHv), 3.82–4.05 (2H, m, MeCH2O), 2.17 (1H,
d, J¼13 Hz, CHaHbCOAcPh), 2.10 (3H, s, MeCO2), 1.87
(1H, d, J¼13 Hz, CHaHbCOAcPh), 1.32 (3H, t, J¼7 Hz,
MeCH2O), 1.29 (3H, s, MeMeC), 1.14 (3H, s, MeMeC); dC
(100.6 MHz, CDCl3) 192.8, 175.7, 170.6, 139.6, 129.1,
128.5, 127.9, 127.7, 126.8, 101.4, 96.5, 76.0, 65.5, 45.0,
37.3, 27.7, 20.9, 14.5; HRMS (EI): Mþ, found 302.1511.
C18H22O4 requires 302.1518.
3.2.1. 5-Acetoxy-2-ethoxy-3-methyl-5-phenyl-2-cylo-
pentenone 9a. (0.59 g, 72%) as a colourless oil; Rf
(EtOAc/hexane 1:6) 0.63; nmax (neat) 1748, 1640 cm21
;
dH (400 MHz, CDCl3) 7.06–7.46 (5H, m, Ph), 4.15 (2H, q,
J¼7 Hz, MeCH2O), 2.91 (1H, d, J¼18 Hz, CHaHb-
COAcPh), 2.46 (1H, d, J¼18 Hz, CHaHbCOAcPh), 2.06
(3H, s, MeCO2), 2.00 (3H, s, MeCv), 1.21 (3H, t, J¼7 Hz,
MeCH2O); dC (100.6 MHz, CDCl3) 203.1, 169.2, 154.7,
140.2, 129.2, 129.0, 127.9, 127.3, 127.1, 90.1, 66.5, 50.0,
37.6, 21.3, 16.1, 15.3; m/z (EI) 216 (60), 188 (100), 173
(27), 159 (26), 145 (28), 131 (33), 118 (37), 105 (36), 103
(35), 91 (32), 77 (33%); HRMS (EI): (M2C2H2O2), found
216.1150. C16H18O4 requires 216.1151.
3.1.15. 6-Acetoxy-3-ethoxy-4,4-dimethyl-2-cyclohexe-
none 7h. (0.21 g, 31%) as a colourless oil; Rf (EtOAc/
hexane 1:5) 0.60; nmax (neat) 1745, 1660 cm21; dH
(400 MHz, CDCl3) 5.30 (1H, dd, J¼7, 12 Hz, CHOAc),
5.09 (1H, s, CHv), 3.74 (2H, q, J¼7 Hz, MeCH2O), 2.01
(3H, s, MeCO2), 1.84–1.90 (2H, m, CH2CHOAc), 1.21 (3H,
t, J¼7 Hz, MeCH2O), 1.19 (3H, s, MeMeC), 1.06 (3H, s,
MeMeC); dC (100.6 MHz, CDCl3) 193.7, 182.2, 170.7,
99.8, 70.9, 65.2, 41.7, 37.7, 27.7, 25.8, 21.3, 14.3; m/z (EI)
227 (100), 215 (7%); HRMS (EI): Mþ, found 226.1212,
C12H18O4 requires 226.1205.
3.2.2. 5-Acetoxy-2-ethoxy-3-ethyl-5-phenyl-2-cylopente-
none 9b. (0.65 g, 75%) as a colourless oil; Rf (EtOAc/
hexane 1:5) 0.65; nmax (neat) 3014, 1748, 1606, 1364, 1239,
738 cm21; dH (400 MHz, CDCl3) 7.26–7.46 (5H, m, Ph),
4.24–4.31 (1H, m, MeCHaHbO), 4.08–4.15 (1H, m,
MeCHaHbO), 3.14 (1H, d, J¼18 Hz, CHaHbCOAcPh),
3.08 (1H, d, J¼18 Hz, CHaHbCOAcPh), 2.53 (2H, q,
J¼8 Hz, MeCH2Cv), 2.19 (3H, s, MeCO2), 1.18–1.26
(2£3H, m, MeCH2O, MeCH2Cv); dC (100.6 MHz, CDCl3)
197.1, 170.0, 155.9, 149.0, 138.2, 129.0, 128.5, 127.1,
124.2, 122.5, 82.1, 66.5, 40.5, 22.0, 21.6, 15.9, 11.9; m/z
(EI) 289 (6), 261 (30), 249 (60), 229 (100), 121 (30%);
3.1.16. 1-Acetoxy-4-ethoxy-1-phenyl-pent-3-en-2-one 2i.
(0.46 g, 58%) as a colourless oil; Rf (EtOAc/hexane 1:10)
0.90; nmax (neat) 3015, 2969, 1742, 1692 cm21; dH
(400 MHz, CDCl3) (7:3 diastereoisomeric mixture) 6.84–

9988
C. Tanyeli et al. / Tetrahedron 58 (2002) 9983–9988
HRMS (EI): Mþ, found 288.3383, C17H20O4 requires
288.1362.
44.5, 37.8, 27.7, 20.2, 19.9, 18.0, 15.8; HRMS (EI): Mþ,
found 239.1281, C13H19O4 requires 239.1284.
3.2.3. 6-Acetoxy-2-ethoxy-6-phenyl-2-cylohexenone 9c.
(0.52 g, 63%) as a colourless oil; Rf (EtOAc/hexane 1:8)
0.80; nmax (neat) 3410, 2970, 1735, 1643 cm21; dH
(400 MHz, CDCl3) 6.50–6.98 (5H, m, Ph), 5.39–5.44
(1H, m, CHv), 4.07–4.20 (2H, m, MeCH2O), 2.15–2.27
(2H, m, CH2), 2.05 (3H, s, MeCO2), 1.98–2.02 (1H, m,
CHaHb), 1.81–1.87 (1H, m, CHaHb), 1.35 (3H, t, J¼7 Hz,
MeCH2O); dC (100.6 MHz, CDCl3) 200.6, 170.3, 146.5,
144.2, 128.4, 122.6, 116.4, 115.6, 114.8, 112.5, 74.5, 62.7,
51.2, 28.8, 21.1, 15.6; m/z (EI) 275 (6), 269 (9), 241 (20),
177 (100), 167 (18), 135 (25%); HRMS (EI): Mþ, found
274.1205, C16H18O4 requires 274.3117.
Acknowledgements
We thank the Middle East Technical University for the
grants (no. AFP-2001-01-03-04 and AFP-2001-07-02-00-
22) and the Turkish Scientific and Technical Research
Council for a grant [no. TBAG-1883 (100T026)].
References
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3.2.4. 6-Acetoxy-2-ethoxy-2-cylohexenone 10c. (0.17 g,
28%) as a colourless oil; Rf (EtOAc/hexane 1:8) 0.66; nmax
(neat) 3415, 2973, 1732, 1623, 1378 cm21; dH (400 MHz,
CDCl3) 5.77–5.80 (1H, m, CHv), 5.30 (1H, dd, J¼5,
13 Hz, CHOAc), 3.71 (2H, q, J¼7 Hz, MeCH2O), 2.39–
2.47 (2H, m, vCCH2), 2.13–2.18 (1H, m, CHaHbCHOAc),
2.10 (3H, s, MeCO2), 1.99–2.08 (1H, m, CHaHbCHOAc),
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189.4, 170.1, 150.5, 116.6, 64.0, 29.2, 22.1, 21.2, 15.2, 14.8;
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cylohexenone 9d. (0.56 g, 59%) as a colourless oil; Rf
(EtOAc/hexane 1:14) 0.41; nmax (neat) 3400, 2976, 1738,
1676 cm21; dH (400 MHz, CDCl3) 6.82–7.05 (5H, m, Ph),
3.69–3.74 (2H, m, MeCH2O), 2.34 (1H, d, J¼18 Hz,
CHaHbCMeMe), 2.16 (1H, d, J¼18 Hz, CHaHbCMeMe),
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J¼7 Hz, MeCH2O), 0.99 (3H, s, MeMeC), 0.91 (3H, s,
MeMeC); dC (100.6 MHz, CDCl3) 196.5, 171.3, 155.6,
142.4, 134.1, 128.8, 128.4, 127.2, 126.2, 114.7, 110.1, 61.4,
45.1, 34.3, 21.4, 20.3, 17.9, 15.7, 14.2; HRMS (EI): Mþ,
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hexane 1:14) 0.33; nmax (neat) 3417, 2988, 1730,
1632 cm21; dH (400 MHz, CDCl3) 5.08 (1H, s, CHOAc),
3.77–3.85 (1H, m, MeCHaHbO), 3.63–3.70 (1H, m,
MeCHaHbO), 2.44 (1H, d, J¼18 Hz, CHaHbCMeMe),
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CMeMe), 1.78 (3H, s, MeCv), 1.14 (3H, t, J¼7 Hz,
MeCH2O), 0.96 (3H, s, MeMeC), 0.86 (3H, s, MeMeC); dC
(100.6 MHz, CDCl3) 189.6, 170.7, 146.6, 142.3, 81.2, 67.8,
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