Synthesis of 2-alkyl (and aryl)-1-aryl-2-propen-1-ones via m-CPBA mediated oxidation of γ-(benzotriazol-1-yl)allylic selenides

Article abstract of DOI:10.1016/S0040-4039(02)00388-X

Treatment of 2-alkyl (and aryl)-3-aryl-3-(benzotriazol-1-yl)allylic selenides with m-CPBA (1 equiv.) for 10 min in CH₂Cl₂ at rt gave 2-alkyl (and aryl)-1-aryl-2-propen-1-ones in excellent yields.

Full text of DOI:10.1016/S0040-4039(02)00388-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 3021–3024
Synthesis of 2-alkyl (and aryl)-1-aryl-2-propen-1-ones via
m-CPBA mediated oxidation of g-(benzotriazol-1-yl)allylic
selenides
Taehoon Kim and Kyongtae Kim*
School of Chemistry and Molecular Science, Seoul National University, Seoul 151-742, South Korea
Received 7 February 2002; revised 21 February 2002; accepted 25 February 2002
Abstract—Treatment of 2-alkyl (and aryl)-3-aryl-3-(benzotriazol-1-yl)allylic selenides with m-CPBA (1 equiv.) for 10 min in
CH2Cl2 at rt gave 2-alkyl (and aryl)-1-aryl-2-propen-1-ones in excellent yields. © 2002 Published by Elsevier Science Ltd.
Very recently, we reported the synthesis of 2,3-benzo-
1,3a,6a-triazapentalenes through Pummerer-type
reactions of g-(benzotriazol-1-yl)allylic sulfoxides 3,
prepared by the oxidation of the corresponding sulfides
1 (X=S).1
In connection with the formation of such a class of
mesomeric betains by treatment of 3 with trifluoroacetic
anhydride (TFAA) in CH2Cl2 at rt, we became inter-
ested in investigating the oxidation of the correspond-
ing allylic selenides 2 (X=Se). In contrast to stable
4
Keywords: benzotriazoles; enones; oxidation; selenium and compounds.
* Corresponding author.
0040-4039/02/$ - see front matter © 2002 Published by Elsevier Science Ltd.
PII: S0040-4039(02)00388-X

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T. Kim, K. Kim / Tetrahedron Letters 43 (2002) 3021–3024
sulfoxides 3, selenoxides 5 formed by oxidation of 2
would be expected to be unstable due to [2,3] sigmat-
ropic rearrangement of allylic selenoxides to give
unstable selenenate esters 6,2 which liberate benzotria-
zolate ion concomitant with the formation of an oxo-
m-CPBA (1 equiv.) for 10 min in CH2Cl2 at rt gave
enone 8a in 85% yield7 along with diphenyl diselenide
(39%).8 Similar treatment of (Z)-2a under the same
conditions afforded 8a and diphenyl diselenide in 87
and 36% yields, respectively. This result indicates that
elimination of selenenic acid from 5 is independent of
the stereochemistry of 5. Consequently, a mixture of
(E)- and (Z)-2 was subjected to the oxidation reaction
with m-CPBA without separation of the stereoisomers.
Yields of 2 and 8 along with the (E)/(Z) ratios of 10
and 2 are summarized in Table 1.
nium ion 7.3 Hydrolysis of
7 would give title
compounds 8 together with benzotriazole and phenyl-
selenenic acid. Alternatively, compounds 8 might be
formed via hydrolysis of an intermediate 9,4 generated
by possible elimination of benzeneselenate ion from 5,
in which the driving force for the elimination may
originate from delocalization of non-bonding electrons
on the N-1 of the benzotriazole moiety into the olefinic
double bond. This is concomitant with the migration of
the double bond to give an intermediate 9 despite the
absence of b-hydrogen in view of the ready formation
of olefins via a syn-elimination of selenoxides having a
hydrogen atom at b-carbon.5
Enones 8, which are important as a starting material
for the synthesis of various organic compounds, have
been mostly prepared by the Mannich reaction fol-
lowed by b-elimination.14 Similarly, N,N,N%,N%-tetra-
methyldiaminomethane was found to be effective for
the preparation of 8 (Ar=aryl, R=alkyl, aryl) from
aryl arylmethyl ketones and alkyl aryl ketones in acetic
anhydride at 40 and 90°C, respectively.15 There exist
other special methods, giving rise to 8 (Ar=alkyl, aryl,
R=H) which involves the reaction of methyl ketones
with trioxane in the presence of N-methylanilium trifl-
uoroacetate.9,16 Silyl enol ethers were converted to
chloroenone 8 (Ar=Ph, R=Cl) in the presence of
TiCl4, LiAlH4 in CCl4.17 Treatment of 3-iodo-1,2-
diphenyl-1-propanone with DBU gave 8 (Ar=Ph, R=
Me).18 Siloxycyclopropane reacted with SnCl4 in
CH2Cl2 to give a stannane complex, which undergoes
decomposition in DMSO to give 8 (Ar=H, R=
alkyl).19 Recently, Katritzky and co-workers reported
benzotriazole-mediated synthesis of 8.11
In order to prove the premise, we prepared the starting
material 2 by treatment of 2,3-disubstituted (3-benzotri-
azol-1-yl)allylic chloride 101 with benzeneselenol in the
presence of NaOEt in THF.6 The stereochemistry of 2
along with their (E)/(Z) ratios was determined based
on NOE effects arising from the allylic protons and
ortho proton(s) of Ar and R groups as described in the
previous report.1 For example, compound (E)-2j (Ar=
Ph, R=tBu) exhibiting a singlet at 3.95 ppm (500
MHz, CDCl3), assigned to the allylic protons, has NOE
effects with two ortho protons (7.38–7.40 ppm) of the
Ph group and nine protons (1.10 ppm) of the tBu
group, whereas compound (Z)-2j has the NOE effects
arising from the allylic protons (3.68 ppm) and the
protons (1.26 ppm) of the tBu group. Similar NOE
effects were observed for other (E)- and (Z)-2. It
appeared that the stereochemistry was essentially intact
in the course of the conversion of 10 into 2. The
stereoisomers of 2 and 10 were separable by chro-
matography. Treatment of (E)-2a (Ar=R=Ph) with
In summary, apart from the reactions of 2,3-disubsti-
tuted 3-(benzotriazol-1-yl)-2-propenyl phenyl sulfides 1
with m-CPBA, giving rise to the corresponding sulfox-
ides 3, reactions of the analogous selenides 2 under the
same conditions afforded enones 8 in excellent yields.
Table 1. Yields of 2 and 8, and the (E)/(Z) ratios of 10 and 2
Entry
Ar
R
Yielda (%)
10 (E/Z)b
2 (E/Z)b
8c
a
b
c
d
e
f
g
h
i
Ph
Ph
Ph
(4.86:1)
(2.11:1)
(2.99:1)
(1.91:1)
(1.04:1)
(2.68:1)
(3.61:1)
(2.85:1)
(8.01:1)
(2.41:1)
85 (4.83:1)
83 (2.10:1)
83 (2.97:1)
81 (1.87:1)
82 (1.11:1)
82 (2.46:1)
87 (3.65:1)
83 (2.91:1)
81 (7.41:1)
82 (2.45:1)
86 (96)9
85 (100)10
84 (82)11
8513
2-MeC6H4
2-MeC6H4
2-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-FC6H4
4-FC6H4
Ph
4-MeC6H4
4-MeC6H4
4-MeC6H4
b-Naphthyl
Ph
2,5-Me2C6H3
Me
tBu
92 (98)11
9313
9013
8813
85 (85)9
89 (78)12
j
Ph
a Isolated yields.
b The ratios of stereoisomers were determined based on the 1H NMR absorptions of the allylic protons ((E)-2: 3.95–4.44 ppm; (Z)-2: 3.64–4.05
ppm; (E)-10: 4.28–4.87 ppm; (Z)-10: 4.02–4.45 ppm).
c The number in parentheses represents yield in the literature.

T. Kim, K. Kim / Tetrahedron Letters 43 (2002) 3021–3024
3023
Acknowledgements
1486, 1438, 1323, 1208, 1174, 912, 770, 696, 588, 520
cm−1 1H NMR (CDCl3, 300 MHz) l 5.76 (s, 1H of
;
ꢀCH2), 6.09 (s, 1H of ꢀCH2), 7.32–7.39 (m, 3H, ArH),
7.41–7.50 (m, 4H, ArH), 7.54–7.59 (m, 1H, ArH), 7.92–
7.98 (m, 2H, ArH); 13C NMR (CDCl3, 75 MHz) l 121.2,
127.5, 128.8, 129.0, 130.4, 133.5, 137.4, 137.5, 148.7,
197.9 (signal of one aromatic C atom not visible); MS (70
eV) (m/z) 208 (M+, 78.8%), 179 (6.7), 165 (5.0), 105
(100.0), 77 (52.2), 51 (12.7). Anal. calcd for C15H12O: C,
86.51; H, 5.81. Found: C, 86.43; H, 5.75. Refer to refer-
ence for mp of PhSeSePh: Reich, H. J.; Renga, J. M.;
Reich, I. L. J. Am. Chem. Soc. 1975, 97, 5434–5447.
8. The selenenic acids disproportionate rapidly into selenols
and seleninic acids. The reactions of selenols with sele-
nenic acids give diselenides. Refer to Ref. 2, Chapter II,
pp. 25–57.
This work was financially supported by the program of
BK 21.
References
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(159 mg, 0.46 mmol) in THF (30 mL) at rt. The mixture
was additionally stirred for 2 h, followed by addition of
water (50 mL), which was extracted with CH2Cl2 (30
mL×3). The extracts were dried over MgSO4. Removal of
the solvent in vacuo gave a residue, which was chro-
matographed on a silica gel column (3×10 cm, EtOAc:n-
hexane=1:5) to give compound 2a (182 mg, 85%):
Viscous liquid; (E)/(Z)=4.83:1; IR (neat) 3040, 2912,
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9. Gras, J.-L. Tetrahedron Lett. 1978, 19, 2111–2114.
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13. 8d: Liquid; IR (neat) 3008, 2920, 1659, 1590, 1504, 1476,
1452, 1428, 1320, 1273, 1246, 1200, 1112, 1019, 973, 820,
753, 521 cm−1 1H NMR (CDCl3, 300 MHz) l 2.38 (s,
;
3H, CH3), 3.74 (s, 3H, OCH3), 5.74 (s, 1H of ꢀCH2), 5.99
(s, 1H of ꢀCH2), 6.92 (d, J=8.5 Hz, 1H, ArH), 7.01 (dd,
J=7.5, 0.7 Hz, 1H, ArH), 7.18 (d, J=7.9 Hz, 2H, ArH),
7.33 (d, J=8.0 Hz, 2H, ArH), 7.41–7.47 (m, 1H, ArH),
7.52 (dd, J=7.5, 1.7 Hz, 1H, ArH); 13C NMR (CDCl3,
75 MHz) l 21.6, 56.0, 111.9, 120.8, 124.4, 128.2, 129.3,
130.4, 132.8, 134.7, 138.2, 150.6, 158.2, 198.1 (signal of
one aromatic C atom not visible); MS (70 eV) (m/z) 252
(M+, 30.0%), 135 (100.0), 115 (8.8), 92 (8.3), 77 (13.3), 51
(2.3). Anal. calcd for C17H16O2: C, 80.93; H, 6.39. Found:
C, 80.99; H, 6.43. 8f: Mp 107–109°C (CH2Cl2/n-hexane);
IR (KBr) 3040, 2928, 1644, 1587, 1497, 1449, 1304, 1251,
1161, 1022, 976, 841, 776, 515 cm−1 1H NMR (CDCl3,
;
300 MHz) l 3.86 (s, 3H, OCH3), 5.67 (s, 1H of ꢀCH2),
6.14 (s, 1H of ꢀCH2), 6.93 (d, J=7.0 Hz, 2H, ArH),
7.46–7.50 (m, 2H, ArH), 7.63 (dd, J=8.6, 1.8 Hz, 1H,
ArH), 7.77–7.89 (m, 4H, ArH), 8.00 (d, J=8.8 Hz, 2H,
ArH); 13C NMR (CDCl3, 75 MHz) l 55.9, 114.2, 119.3,
124.7, 126.7, 126.8, 128.0, 128.9, 130.3, 132.9, 133.5,
133.7, 134.8, 148.9, 164.2, 196.7 (signals of two aromatic
C atoms not visible); MS (70 eV) (m/z) 288 (M+, 32.3%),
152 (15.2), 135 (100.0), 92 (10.5), 77 (17.1). Anal. calcd
for C20H16O2: C, 83.31; H, 5.59. Found: C, 83.24; H,
5.63. 8g: Liquid; IR (neat) 3048, 2912, 1657, 1587, 1491,
1
737, 692, 520 cm−1; H NMR (CDCl3, 300 MHz) l 3.93
(s, 2H, CH2Se, Z), 4.28 (s, 2H, CH2Se, E), 6.88–7.43 (m,
18H, ArH, E and Z), 7.93 (d, J=7.7 Hz, 1H, ArH, E),
8.12 (dd, J=10.0, 2.0 Hz, 1H, ArH, Z). Anal. calcd for
C27H21N3Se: C, 69.52; H, 4.54; N, 9.01. Found: C, 69.60;
H, 4.52; N, 8.97.
1401, 1320, 1224, 1148, 977, 849, 780, 692, 580, 505 cm−1
;
7. Typical procedure: To a solution of (E)-2a (121 mg, 0.35
mmol) in CH2Cl2 (25 mL) was added m-CPBA (45 mg,
0.35 mmol) at rt. The mixture was stirred for 10 min,
followed by addition of aqueous NaHCO3 (10%), which
was extracted with CH2Cl2 (30 mL×3). The combined
extracts were dried over MgSO4. After removal of the
solvent in vacuo, the residue was chromatographed on a
silica gel column (2×10 cm, EtOAc:n-hexane=1:7) to
give diphenyl diselenide (21 mg, 39%): mp 61–63°C
(CH2Cl2/n-hexane) (lit. mp 60–62°C) and compound 8a
(63 mg, 85%): liquid; IR (neat) 3048, 2920, 1656, 1588,
1H NMR (CDCl3, 300 MHz) l 5.65 (s, 1H of ꢀCH2), 6.07
(s, 1H of ꢀCH2), 7.12 (t, J=7.5 Hz, 2H, ArH), 7.33–7.47
(m, 5H, ArH), 7.93–8.00 (m, 2H, ArH); 13C NMR
(CDCl3, 75 MHz) l 116.0 (2J=21.8 Hz), 120.8, 127.4,
129.0, 129.1, 133.0 (3J=9.3 Hz), 133.8 (4J=2.9 Hz),
137.2, 148.6, 166.2 (1J=253.8 Hz), 196.3; MS (70 eV)
(m/z) 226 (M+, 100.0%), 197 (9.0), 183 (6.7), 123 (100.0),
95 (72.9), 77 (34.0), 51 (12.4). Anal. calcd for C15H11FO:
C, 79.63; H, 4.90. Found: C, 79.70; H, 4.94. 8h: Liquid;
IR (neat) 3016, 2912, 1651, 1587, 1489, 1440, 1198, 1313,
1
1225, 1148, 977, 846, 809, 784, 590, 516 cm−1; H NMR

3024
T. Kim, K. Kim / Tetrahedron Letters 43 (2002) 3021–3024
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(CDCl3, 300 MHz) l 2.17 (s, 3H, CH3), 2.37 (s, 3H,
CH3), 5.99 (dd, J=11.8, 1.1 Hz, 2H, ꢀCH2), 7.05–7.17
(m, 5H, ArH), 7.90–7.99 (m, 2H, ArH); 13C NMR
(CDCl3, 75 MHz) l 20.4, 21.3, 115.9 (2J=21.7 Hz),
127.8, 129.6, 130.6, 130.7, 132.7, 132.8 (3J=9.2 Hz),
133.9 (4J=3.0 Hz), 136.0, 138.4, 149.6, 165.8 (1J=252.9
Hz), 195.4; MS (70 eV) (m/z) 254 (M+, 100%), 131 (35.7),
123 (55.5), 115 (17.0), 95 (19.1), 91 (14.2). Anal. calcd for
C17H15FO: C, 80.29; H, 5.95. Found: C, 80.21; H, 5.99.
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