α-Arylation of ketones by aryllead triacetates. Effect of methyl and phenyl substitution at the α position

Article abstract of DOI:10.1039/a607543f

An examination of the α-arylation of a number of ketones and their enolate salts by p-methoxyphenyllead triacetate provides further evidence for a very marked selectivity in the arylation reaction. It is found that the reaction proceeds well at tertiary α-carbons and at secondary centres activated by the presence of a phenyl group, but fails where the secondary centre is unactivated and at primary α-carbons.

Full text of DOI:10.1039/a607543f

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á-Arylation of ketones by aryllead triacetates. Effect of methyl and
phenyl substitution at the á position
Jacqueline Morgan, John T. Pinhey* and Bruce A. Rowe
School of Chemistry, University of Sydney, Sydney 2006, Australia
An examination of the á-arylation of a number of ketones and their enolate salts by p-methoxyphenyllead
triacetate provides further evidence for a very marked selectivity in the arylation reaction. It is found that
the reaction proceeds well at tertiary á-carbons and at secondary centres activated by the presence of a
phenyl group, but fails where the secondary centre is unactivated and at primary á-carbons.
In an examination of the reactions of organolead triacetates
extending over a number of years, we have shown that these
electrophilic reagents react with a range of soft carbon acids
such as β-dicarbonyl compounds.1–3 With the latter compounds
the reactions provide ready access to a wide variety of α-aryl, α-
vinyl and α-alk-1-ynyl β-dicarbonyl compounds4–9 (Scheme 1).
arylated compound 4 in >90% yield after 1 h. An important
consequence of this reactivity of aryllead triacetates, which
applies also to the vinyllead and alkynyllead reagents, is that
their reactions provide a ready means of generating highly func-
tionalised quaternary carbon centres around which in some
cases there is considerable steric congestion.
Early in this work we found that simple ketones such as
cyclohexanone and acetophenone were unreactive towards aryl-
lead triacetates under our standard chloroform–pyridine condi-
tions. Attempts were also made to react the potassium enolates
of these two ketones with p-methoxyphenyllead triacetate in
tetrahydrofuran (THF)–pyridine; however, both reactions
resulted only in recovery of the ketones. This was in sharp con-
trast to the behaviour of the arylbismuth(V) compounds of
Barton and co-workers,11,12 which are thought to react with eno-
lates and other carbon acids by a ligand coupling mechanism
similar to that of our aryllead reagents. They reported that
triphenylbismuth carbonate reacts with the potassium enolates
of cyclohexanone and acetophenone to give 2,2,6,6-tetra-
Scheme 1
These reactions, which most likely proceed by a ligand exchange
followed by ligand coupling,10 show a number of significant
features. Firstly, in most cases reactions proceed fastest and
in highest yields with the more acidic β-dicarbonyls, and with
such substrates (e.g. β-diketones and β-keto esters) the general
reaction outlined in Scheme 1 takes place simply on mixing the
organolead triacetate and substrate in chloroform–pyridine at
20–60 ЊC. With the less acidic compounds such as diethyl
malonates the reaction is slow, and for a fast, high-yielding
reaction it has been found best to employ the diethyl malonate
salt.6 This is consistent with a ligand exchange involving the
enolate of the dicarbonyl compound. The other main feature of
these reactions is not readily explained; this concerns the pref-
erence for the electrophilic substitution to proceed at sites with
only one replaceable hydrogen as illustrated with the examples
in Scheme 2. Whereas Meldrum’s acid 1 reacted slowly with p-
phenylcyclohexanone
and
2,2,2-triphenylacetophenone,
respectively, in excellent yields.11
An increase in reactivity of β-dicarbonyls towards arylation
by aryllead triacetates on replacement of one of the α-
hydrogens by a methyl group, as illustrated in Scheme 2, is also
displayed in simple ketones. For example, we found that the
potassium enolate of propiophenone did react with p-methoxy-
phenyllead triacetate in THF–pyridine to give the deoxyben-
zoin derivative 5 in modest yield (15%) (Scheme 3). Also pro-
Scheme 3 Reagents and conditions: p-MeOC6H4Pb(OAc)3, THF, pyri-
dine, room temp., N2
Scheme 2
duced in similar yields were α-acetoxy ketone 6 and a mixture
of the meso and (±) isomers 7, the product of oxidative dimeris-
ation. Propiophenone (36%) was also recovered from this
reaction.
methoxyphenyllead triacetate (1 equiv.) to give only the diaryl-
ated product 2 in very low yield after 24 h, the 5-methyl deriv-
ative 3 reacted rapidly with the same lead reagent to give the
Further confirmation of the effect of substitution at the α-
J. Chem. Soc., Perkin Trans. 1, 1997
1005

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carbon on the ease of arylation was found in the reaction of
the potassium enolate of isobutyrophenone with p-methoxy-
phenyllead triacetate. The α-arylated ketone 8 was formed
in considerably higher yield (51%) and it was not accompanied
by the α-acetoxy ketone. Analysis of the crude reaction product
by GC–MS indicated the presence of a very small amount
(<5%) of the dimer 9, while the remaining starting material
was accounted for as recovered isobutyrophenone (Scheme
4).
phenyl)-2-phenylcyclohexanone 14 in moderate yield (46%) and
a mixture of the meso and (±) isomers of the dimer 15 in 22%
yield (Scheme 6). Recovered 2-phenylcyclohexanone accounted
for the remaining starting material.
Scheme 6 Reagents and conditions: p-MeOC6H4Pb(OAc)3, THF, pyri-
dine, room temp., N2
Unlike 2-methylcyclohexanone and 2,6-dimethylcyclo-
hexanone, 2-phenylcyclohexanone has a sufficiently acidic α-
hydrogen for the arylation to proceed with the ketone itself;
thus, when the ketone and the same aryllead triacetate were
kept in chloroform–pyridine at 40 ЊC for 24 h, a similar yield
(46%) of the diaryl ketone 14 was obtained. This was
unaccompanied by the dimers 15 and is therefore a more useful
synthetic route to compound 14. Moreover, the method could
clearly be used to access a wide range of unsymmetrical 2,2-
diaryl ketones.
The increase in reactivity of simple ketones due to the pres-
ence of an α-aryl group also extends to compounds in which the
α-carbon is secondary. Benzyl methyl ketone was found to react
with p-methoxyphenyllead triacetate in chloroform–pyridine at
40 ЊC to give the arylated ketone 16 in 20% yield after 20 h. As
Scheme 4 Reagents and conditions: p-MeOC6H4Pb(OAc)3, THF, pyri-
dine, room temp., N2
Further compelling evidence for the effect of α-substitution
on the ease of the arylation reaction was found in the reactions
of the enolates of 2-methylcyclohexanone and 2,6-dimethyl-
cyclohexanone. The mixture of the potassium enolates of 2-
methylcyclohexanone, 10 and 11, which are present in the ratio
of 67 : 33 when formed with KH in THF,13 was treated with p-
methoxyphenyllead triacetate in THF–pyridine to give a single
arylated ketone, 2-(p-methoxyphenyl)-2-methylcyclohexanone
12 in a yield of 36% (54% from enolate 10) (Scheme 5). None of
Scheme 5 Reagents and conditions: p-MeOC6H4Pb(OAc)3, THF, pyri-
dine, room temp., N2
the 6-arylated compound was present and no dimers could be
detected. Consistent with this result, the potassium enolate of
2,6-dimethylcyclohexanone reacted with the same aryllead
reagent under the same conditions to produce 2,6-dimethyl-2-
(p-methoxyphenyl)cyclohexanone in good yield (75%) as a mix-
ture of isomers (GC analysis). The only other material present
was 2,6-dimethylcyclohexanone. On the basis of the H NMR
spectrum of the mixture, the major component (>95%) was the
cis-isomer 13. The assignment was based on the chemical shifts
with the arylation of 2-phenylcyclohexanone, this proved to be
a better route to compound 16 than by arylation of the potas-
sium enolate of benzyl methyl ketone. In a reaction conducted
with the potassium enolate and p-methoxyphenyllead triacetate
under the conditions outlined in Scheme 6, a mixture consisting
of the meso and (±) dimers 17 (total of 25%) and the arylated
ketone 16 (5%) was produced.
The examples of ketone α-arylation presented here further
illustrate the unusual selectivity displayed by aryllead triacet-
ates. The preference for arylation at tertiary carbons leading to
quaternary centres, which in many cases are sterically crowded,
is a feature which makes them potentially very useful reagents
for synthesis, especially in the area of natural products
chemistry.
1
of the 6-methyl signals for the two isomers. In the major com-
ponent this was a doublet at δ 0.99, while for the minor com-
ponent the corresponding doublet was at δ 1.01. It has been
found that for such pairs of cyclohexanone isomers, an equa-
torial methyl group resonates at higher field than an axial
methyl, while the aromatic AAЈBBЈ resonances (δ 7.06 and
6.87) were consistent with an equatorial configuration for the p-
methoxyphenyl group.5
We have found that the presence of an α-phenyl group, which
can stabilise the enol tautomer by conjugation, can also result
in enhanced reactivity of ketones to arylation. The potassium
enolate of 2-phenylcyclohexanone reacted in THF–pyridine
with p-methoxyphenyllead triacetate to give 2-(p-methoxy-
Experimental
Melting points were determined on a Kofler hot-stage appar-
atus and are uncorrected. IR Spectra were recorded on a Perkin-
Elmer 221 spectrophotometer and UV spectra on a Perkin-
Elmer 402 instrument. NMR Spectra were determined with
SiMe4 as internal standard on a Varian HA100 instrument; J
values are given in Hz. Microanalyses were performed by the
Australian Microanalytical Service, Melbourne and mass
spectra were recorded on an AEI model MS902 double focus-
ing instrument. Thin layer chromatography was carried out on
glass plates spread with 1 mm layers of Merck Kieselgel 60.
p-Methoxyphenyllead triacetate was prepared as previously
1006
J. Chem. Soc., Perkin Trans. 1, 1997

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reported.14 Light petroleum refers to the fraction of bp 60–
70 ЊC. Analytical gas chromatography (GC) was carried out on
a Hewlett-Packard 402 instrument equipped with a flame ion-
isation detector and one of the following columns: column 1,
3% OV17 (50 : 50 phenyl–methyl silicone gum) on Gas Chrom
Q (100–120 mesh); column 2, 3% OVI (100% methyl silicone
gum) on Gas Chrom Q (100–120 mesh). Ether refers to diethyl
ether.
arylated ketone 8 (51% yield) and material Mw 294 correspond-
ing to the dimer 9 (<5%).
Reaction of 2-methylcyclohexanone potassium enolate with
p-methoxyphenyllead triacetate
The mixture of potassium enolates 10 and 11 (4 mmol) in THF
(20 cm3) was added to a solution of p-methoxyphenyllead tri-
acetate (2.16 g, 4.4 mmol) and pyridine (2.1 g, 27 mmol) in
THF (20 cm3) at room temperature under N2. The mixture was
stirred for 24 h, poured into ether (100 cm3) and then worked up
as in the previous experiment. The oily product was fraction-
ated by thin layer chromatography in light petroleum–ethyl
acetate (49:1) to afford 2-(p-methoxyphenyl)-2-methylcyclo-
hexanone 12 as colourless crystals, mp 96–98 ЊC (Found: C,
76.9; H, 8.3. C14H18O2 requires C, 77.0; H, 8.3%); νmax(CHCl3)/
cmϪ1 1700; λmax(MeOH)/nm 231, 278 and 284 (ε/dm3 molϪ1
cmϪ1 8800, 1600 and 1400); δH (CDCl3) 1.25 (3 H, s, Me), 1.5–
2.8 (8 H, m, 4 × CH2), 3.80 (3 H, s, OMe), 6.87 and 7.10 (4 H,
AAЈBBЈ, 3-H and 5-H, 2-H and 6-H, respectively); m/z 218
(M, 45%), 176 (13), 175 (100), 161 (37), 148 (40), 135 (11), 121
(21), 91 (12) and 77 (10).
Reaction of propiophenone potassium enolate with p-methoxy-
phenyllead triacetate
Propiophenone potassium enolate (2 mmol) in dry THF (6 cm3)
was added dropwise over 2 min to p-methoxyphenyllead tri-
acetate (1.08 g, 2.2 mmol) and dry pyridine (1.04 g, 13 mmol) in
dry THF (6 cm3). The mixture was stirred at room temperature
under N2 for 1 h and then the precipitate was removed by filtra-
tion and washed with light petroleum. The solvent was evapor-
ated from the combined filtrate and light petroleum washings,
and the residue was fractionated by thin layer chromatography
using light petroleum–ether (10:1) as the developing solvent.
Five fractions were obtained, the least polar being pro-
piophenone.
The GC analysis (column 2) of the crude product from the
above reaction showed the yield of the arylated ketone 12 to be
36%. There were no significant peaks which might correspond
to a dimer of 2-methylcyclohexanone or to the acetoxy ketone.
Fraction 2, the next in order of polarity, afforded 2-(p-
methoxyphenyl)-1-phenylpropan-1-one 5 as colourless crystals,
mp 48–50 ЊC (from pentane) (lit.,15 58–59.5 ЊC); δH (CDCl3) 1.50
(3 H, d, 3-H3), 3.71 (3 H, s, OMe), 4.62 (1 H, q, 2-H), 6.80 and
7.19 (4 H, AAЈBBЈ, p-methoxyphenyl 3-H and 5-H, 2-H and 6-
H, respectively), 7.0–7.6 (3 H, m, phenyl 3-H, 4-H and 5-H) and
7.8–8.1 (2 H, m, phenyl 2-H and 6-H).
Fraction 3 yielded meso-2,3-dimethyl-1,4-diphenylbutane-
1,4-dione 7 as colourless crystals, mp 101–102 ЊC [lit.,16 85–
86 ЊC for meso, (±) mixture]; δH (CDCl3) 1.14 (6 H, d, 2 × Me),
3.9–4.2 (2 H, m, 2-H and 3-H), 7.3–7.6 (6 H, m, m- and p-
phenyl-H) and 7.9–8.15 (4 H, m, o-phenyl-H).
Fraction 4 afforded (±)-2,3-dimethyl-1,4-diphenylbutane-1,4-
dione 7 as colourless crystals, mp 86–88 ЊC (from hexane) (lit.,17
86–87 ЊC); δH (CDCl3) 1.29 (6 H, d, 2 × Me), 3.8–4.2 (2 H, m, 2-
H and 3-H), 7.3–7.7 (6 H, m, m- and p-phenyl-H) and 7.9–8.1 (4
H, m, o-phenyl-H).
Fraction 5, the most polar material, yielded 2-acetoxy-1-
phenylpropan-1-one 6 as an oil, νmax(film)/cmϪ1 1740 and 1700
(lit.,18 1740 and 1700 cmϪ1); δH (CDCl3) 1.53 (3 H, d, J 7, Me),
2.14 (3 H, s, COMe), 5.98 (1 H, d, J 7, 2-H), 7.4–7.7 (3 H, m, m-
and p-phenyl-H) and 7.9–8.0 (2 H, m, o-phenyl-H).
Reaction of 2,6-dimethylcyclohexanone potassium enolate with
p-methoxyphenyllead triacetate
The enolate salt (1 mmol) in THF (5 cm3) was added to a stirred
solution of p-methoxyphenyllead triacetate (540 mg, 1.1 mmol)
and pyridine (290 mg, 3.3 mmol) in THF (5 cm3) at room tem-
perature under N2, and the mixture was stirred for 4 h. The
mixture was poured into ether (50 cm3) and worked up as for
the reaction of isobutyrophenone enolate above. The oily resi-
due was fractionated by thin layer chromatography in light
petroleum–ether (17:3) to yield c-2,6-dimethyl-r-2-(p-methoxy-
phenyl)cyclohexanone 13 as a colourless oil (Found: C, 77.8; H,
8.9. C15H20O2 requires C, 77.6; H, 8.7%); νmax(CHCl3)/cmϪ1
1705; λmax(EtOH)/nm 227, 276 and 282 (ε/dm3 molϪ1 cmϪ1 8800,
1600 and 1300); δH (CDCl3) 0.99 (3 H, d, 6-Me), 1.24 (3 H, s,
2-Me), 1.2–2.8 [7 H, m, CH(CH2)3], 3.79 (3 H, s, OMe) 6.87 and
7.06 (4 H, AAЈBBЈ, 3-H and 5-H, 2-H and 6-H, respectively);
m/z 232 (M, 34%), 204 (16), 189 (23), 162 (10), 161 (66), 149
(11), 148 (100), 147 (15), 135 (37), 133 (14), 121 (14), 91 (17) and
77 (13).
Analysis by GC of the crude product using column 1 showed
the yields to be: propiophenone (36%), 2-(p-methoxyphenyl)-1-
phenylpropan-1-one 5 (15%), the meso and (±) dimers 7 (19%
in total) and the α-acetoxy ketone 6 (12%)
Analysis by GC (column 2) of the crude product from the
above reaction showed the yield of arylated ketone 13 to be
75%. No material corresponding to a dimer of 2,6-dimethyl-
cyclohexanone or to the acetoxy ketone could be detected.
Reaction of isobutyrophenone potassium enolate with p-methoxy-
phenyllead triacetate
Reaction of 2-phenylcyclohexanone potassium enolate with
p-methoxyphenyllead triacetate
Isobutyrophenone potassium enolate (2 mmol) in THF (6 cm3)
was added dropwise to a stirred solution of p-methoxyphenyl-
lead triacetate (1.08 g, 2.2 mmol) and pyridine (1.04 g, 13
mmol) in THF (6 cm3) at room temperature under N2. The
mixture was stirred for 1 h and then poured into ether (50 cm3).
The ether solution was filtered, washed with hydrochloric acid
(1 M; 20 cm3), dried (MgSO4) and the solvent was evaporated.
The residual oil was fractionated by thin layer chromatography
in light petroleum–ether (9:1) to yield 2-(p-methoxyphenyl)-2-
methyl-1-phenylpropan-1-one 8 as a colourless oil (Found: C,
80.2; H, 7.1. C17H18O2 requires C, 80.3; H, 7.1%); νmax(film)/
cmϪ1 1670; λmax(MeOH)/nm 230, 243sh, 277 and 285sh (ε/dm3
molϪ1 cmϪ1 15 000, 10 000, 3400 and 2700); δH (CDCl3) 1.57 (6
H, s, 2 × Me), 3.80 (3 H, s, OMe), 6.88 and 7.24 (4 H,
AAЈBBЈ, 3-H and 5-H, 2-H and 6-H, respectively), 7.1–7.4
(3 H, m, m- and p-phenyl-H) and 7.4–7.6 (2 H, m, o-
phenyl-H).
The enolate salt (1 mmol) in THF (3 cm3) was added to a stirred
solution of p-methoxyphenyllead triacetate (540 mg, 1.1 mmol)
and pyridine (520 mg, 6.6 mmol) in THF (3 cm3) at room tem-
perature under N2. After 1 h the mixture was poured into ether
(50 cm3) and worked up as for the reaction of isobutyro-
phenone enolate above to give a solid residue which was frac-
tionated by thin layer chromatography in light petroleum–ether
(4:1). Four fractions were obtained, the least polar of which
was 2-phenylcyclohexanone.
The next more polar product crystallised from light petrol-
eum to afford either meso- or (±)- 2,2Ј-dioxo-1,1Ј-diphenyl-1,1-
bicyclohexyl 15, mp 189–190 ЊC (Found: C, 83.0; H, 7.8.
C24H26O2 requires C, 83.2; H, 7.6%); νmax(CHCl3)/cmϪ1 1700;
λmax(MeOH)/nm 254, 260, 266 and 290 (ε/dm3 molϪ1 cmϪ1 510,
580, 510 and 290); δH (CDCl3) 1.0–3.6 [16 H, m, 2 × (CH2)4],
6.4–6.7 (2 H, m, ArH) and 6.7–7.7 (8 H, m, ArH); m/z 346 (M,
1%), 174 (100), 145 (10) and 91 (30).
Analysis by GC (column 2) of the product prior to chrom-
atography showed the presence of isobutyrophenone (48%),
The next fraction in order of polarity crystallised from light
J. Chem. Soc., Perkin Trans. 1, 1997
1007

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petroleum to give either meso- or (±)- 2,2Ј-dioxo-1,1Ј-diphenyl-
1,1-bicyclohexyl 15, mp 150–151 ЊC (Found: C, 83.1; H, 7.8.
C24H26O2 requires C, 83.2; H, 7.6%); νmax(CHCl3)/cmϪ1 1705;
λmax(MeOH)/nm 256, 262, 267, 272 (ε/dm3 molϪ1 cmϪ1 530, 580,
530 and 540); δH (CDCl3) 1.0–3.3 [16 H, m, 2 × (CH2)4], 5.6–6.0
(1 H, m, ArH), 6.4–8.0 (9 H, m, ArH); m/z 346 (M, 1%), 175
(14), 174 (100), 173 (20), 172 (11), 145 (13), 130 (18), 117 (11)
and 91 (35).
showed the yields to be: benzyl methyl ketone (62%), (±)-dimer
17 (12%), meso-dimer 17 (13%) and arylated ketone 16 (5%).
Reaction of benzyl methyl ketone with p-methoxyphenyllead
triacetate in chloroform–pyridine
Benzyl methyl ketone (161 mg, 1.2 mmol) was added to a stirred
solution of p-methoxyphenyllead triacetate (650 mg, 1.32
mmol) and pyridine (310 mg, 4 mmol) in chloroform (1.5 cm3)
at 40 ЊC. After 24 h the reaction was worked up as for the
reaction of isobutyrophenone potassium enolate above and the
oily product was analysed by GC (column 2). This showed the
presence of the arylated ketone 16 (20% yield), but none of the
dimers 17.
The most polar fraction crystallised from light petroleum to
yield 2-(p-methoxyphenyl)-2-phenylcyclohexanone 14 as colour-
less crystals, mp 113–114 ЊC (Found: C, 81.1; H, 7.1. C19H20O2
requires C, 81.4; H, 7.2%); νmax(CHCl3)/cmϪ1 1705; λmax
-
(MeOH)/nm 271sh, 277 and 283 (ε/dm3 molϪ1 cmϪ1 1500, 1800
and 1600); δH (CDCl3) 1.6–2.1 (4 H, m, 2 × CH2), 2.4–2.7 (4 H,
m, 2 × CH2), 3.79 (3 H, s, OMe), 6.83 and 6.99 (4 H, AAЈBBЈ,
3-H and 5-H, 2-H and 6-H, respectively) and 6.8–7.5 (5 H, m,
5 × phenyl-H); m/z 281 (M ϩ 1, 18%), 280 (59), 252 (65), 224
(27), 223 (100), 197 (35), 179 (19), 165 (29), 152 (23), 121 (18),
115 (48), 91 (31) and 77 (15).
Acknowledgements
This work was supported by a grant from the Australian
Research Council.
Analysis of the crude reaction product by GC (column 2)
showed the yield of the arylated ketone 14 to be 46%, while the
combined yield of meso and (±) dimers 15 was 22%. 2-Phenyl-
cyclohexanone (22%) was recovered from the reaction.
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Reaction of 2-phenylcyclohexanone with p-methoxyphenyllead
triacetate in chloroform–pyridine
2-Phenylcyclohexanone (522 mg, 3.0 mmol) was added to a
stirred solution of p-methoxyphenyllead triacetate (1.62 g, 3.3
mmol) and pyridine (790 mg, 10 mmol) in chloroform (5 cm3) at
40 ЊC and the reaction was monitored by GC using column 2.
These analyses showed that after 1 h the yield of 2-(p-methoxy-
phenyl)-2-phenylcyclohexanone 14 was 5%. This rose to 21%
after 7 h, and after 24 h the yield was 46%. The yield of ketone
14 did not increase after 24 h and all of the analyses indicated
that none of the dimer 15 had been produced.
Reaction of benzyl methyl ketone potassium enolate with
p-methoxyphenyllead triacetate
Benzyl methyl ketone potassium enolate (2 mmol) was reacted
with p-methoxyphenyllead triacetate (1.08 g, 2.2 mmol) under
the same conditions as outlined above for the potassium
enolate of isobutyrophenone, and the reaction was worked up
in the same way. The oily product was fractionated by thin
layer chromatography in light petroleum–ethyl acetate (9:1)
to give benzyl methyl ketone and three more polar
fractions.
The least polar of these crystallised from light petroleum to
yield (±)-3,4-diphenylhexane-2,5-dione (±)-17, mp 110–113 ЊC
(lit.,19 98–100 ЊC); δH (CDCl3) 2.13 (6 H, s, 2 × Me), 3.49 (2 H, s,
3-H and 4-H), 6.8–7.5 (10 H, m, 10 × phenyl-H).
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Organometallic Chemistry II, ed. A. McKillop, Pergamon, Oxford,
1995, vol. 11, p. 503.
The next fraction in order of polarity crystallised from light
petroleum to give meso-3,4-diphenylhexane-2,5-dione meso-17,
mp 200–202 ЊC (lit.,19 201–202 ЊC); δH (CDCl3) 1.88 (6 H, s,
2 × Me), 4.62 (2 H, s, 3-H and 4-H) and 7.2–7.5 (10 H, m,
10 × phenyl-H).
The most polar fraction afforded 1-(p-methoxyphenyl)-1-
phenylpropan-2-one 16 as an oil (Found: Mϩ, 240.1149.
C16H16O2 requires Mϩ, 240.1149); νmax(CHCl3)/cmϪ1 1710;
λmax(MeOH)/nm 231, 270, 278 and 283 (ε/dm3 molϪ1 cmϪ1
12 500, 2000, 2100, 2100 and 1800); δH (CDCl3) 2.22 (3 H, s,
COMe), 3.78 (3 H, s, OMe), 6.86 and 7.15 (4 H, AAЈBBЈ, 3-H
and 5-H, 2-H and 6-H, respectively) and 7.1–7.4 (5 H, m, 5 ×
phenyl-H).
13 H. O. House and V. Kramar, J. Org. Chem., 1963, 28, 3362;
C. A. Brown, J. Org. Chem., 1974, 39, 3913.
14 R. P. Kozyrod and J. T. Pinhey, Org. Synth., 1984, 64, 24.
15 D. Y. Curtin and M. C. Crew, J. Am. Chem. Soc., 1955, 77, 354.
16 H. Alper and E. C. H. Keung, J. Org. Chem., 1972, 37, 2566.
17 C. W. Perry, M. V. Kalnins and K. H. Deitcher, J. Org. Chem., 1972,
37, 4371.
18 T. Shono, Y. Matsumura and Y. Nakagowa, J. Am. Chem. Soc.,
1974, 96, 3532.
19 M. S. Kharasch, H. C. McBay and W. H. Urry, J. Am. Chem. Soc.,
1948, 70, 1269.
Paper 6/07543F
Received 5th November 1996
Accepted 21st November 1996
Analysis by GC (column 2) of the above crude product
1008
J. Chem. Soc., Perkin Trans. 1, 1997