Photochemical and acid-catalyzed rearrangements of 4-carbomethoxy-4-methyl-3-(trimethylsilyl)-2,5-cyclohexadien-1-one

Article abstract of DOI:10.1021/jo952240g

The synthesis of 4-carbomethoxy-4-methyl-3-(trimethylsilyl)-2,5-cyclohexadien-1-one (1) in 60% overall yield from benzaldehyde is described. Irradiation (366 nm) of 1 in benzene solution gave products of type A photorearrangement; e.g., diastereomers of the 4-(trimethylsilyl)- and 5-(trimethylsilyl)bicyclo[3.1.0]hex-3-en-2-ones 8 and 9. Bicyclohexenones 9a and 9b could not be isolated, but underwent acid-catalyzed protiodesilylative rearrangements on attempted chromatography (silica gel) to give a 1:1 mixture of (E)- and (Z)-4-(carbomethoxymethylmethylene)cyclopent-2-en-1-ones 12 and 13. Irradiation (366 nm) of either 12 or 13 resulted in photoisomerization to a photostationary state that was also a 1:1 mixture. Irradiation of 8a or 8b gave equivalent mixtures of phenols 14 and 15 by way of the type B oxyallyl zwitterion 17. The available experimental evidence suggests that both 9a and 9b undergo regiospecific photorearrangement to phenol 16 with no trace of 3-methyl-4-carbomethoxyphenol (19), the product of ipso substitution of the Me₃Si group at C(4). Phenol 15 was isolated in 65% yield from the photoreaction of 1 in benzene with 20 equiv of CF₃CO₂H. The acid-catalyzed rearrangement of 1 to 3-carbomethoxy-4-methylphenol (21) occurs in 91% yield by way of CO₂Me group rearrangement to C(3) to give the Me₃Si-stabilized carbocation 23.

Full text of DOI:10.1021/jo952240g

J . Org. Chem. 1996, 61, 4555-4559
4555
P h otoch em ica l a n d Acid -Ca ta lyzed Rea r r a n gem en ts of
4-Ca r bom eth oxy-4-m eth yl-3-(tr im eth ylsilyl)-2,5-cycloh exa d ien -1-on e†
Arthur G. Schultz* and Evan G. Antoulinakis‡
Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180-3590
Received December 19, 1995X
The synthesis of 4-carbomethoxy-4-methyl-3-(trimethylsilyl)-2,5-cyclohexadien-1-one (1) in 60%
overall yield from benzaldehyde is described. Irradiation (366 nm) of 1 in benzene solution gave
products of type A photorearrangement; e.g., diastereomers of the 4-(trimethylsilyl)- and
5-(trimethylsilyl)bicyclo[3.1.0]hex-3-en-2-ones 8 and 9. Bicyclohexenones 9a and 9b could not be
isolated, but underwent acid-catalyzed protiodesilylative rearrangements on attempted chroma-
tography (silica gel) to give a 1:1 mixture of (E)- and (Z)-4-(carbomethoxymethylmethylene)cyclopent-
2-en-1-ones 12 and 13. Irradiation (366 nm) of either 12 or 13 resulted in photoisomerization to
a photostationary state that was also a 1:1 mixture. Irradiation of 8a or 8b gave equivalent mixtures
of phenols 14 and 15 by way of the type B oxyallyl zwitterion 17. The available experimental
evidence suggests that both 9a and 9b undergo regiospecific photorearrangement to phenol 16
with no trace of 3-methyl-4-carbomethoxyphenol (19), the product of ipso substitution of the Me3Si
group at C(4). Phenol 15 was isolated in 65% yield from the photoreaction of 1 in benzene with 20
equiv of CF3CO2H. The acid-catalyzed rearrangement of 1 to 3-carbomethoxy-4-methylphenol (21)
occurs in 91% yield by way of CO2Me group rearrangement to C(3) to give the Me3Si-stabilized
carbocation 23.
Substituent effects on the photochemical1 and acid-
Sch em e 1
catalyzed2 rearrangements of 2,5-cyclohexadien-1-ones
are of continuing interest.3 In this paper we report the
preparation, photochemistry, and acid-catalyzed re-
arrangement of 4-carbomethoxy-4-methyl-3-(trimethyl-
silyl)-2,5-cyclohexadien-1-one (1).
Resu lts a n d Discu ssion
The synthesis of 4-carbomethoxy-4-methyl-3-(trimeth-
mobenzoic acid4 or metalation of N,N-diethylbenzamide5
or isopropyl benzoate6a or by other procedures,6b-f rela-
tively poor yields or difficulties associated with hydrolysis
of the carboxylic acid derivative necessitated development
of a new procedure. Trimethylsilylation of benzaldehyde
(2) by the method of Comins and Brown7 provided
2-(trimethylsilyl)benzaldehyde (3) in 87% yield. Oxida-
tion of 3 with KMnO4 in acetone-water gave the desired
carboxylic acid 4,8 and esterification with dimethyl
sulfate/K2CO3 in acetone gave the desired methyl 2-(tri-
methylsilyl)benzoate in 93% overall yield.
ylsilyl)-2,5-cyclohexadien-1-one (1) is shown in Scheme
1. Although it is possible to prepare 2-(trimethylsilyl)-
benzoic acid (4) via metal-halogen exchange from 2-bro-
† Dedicated to Clayton H. Heathcock on the occasion of his 60th
birthday.
‡ Undergraduate research participant.
X Abstract published in Advance ACS Abstracts, J une 1, 1996.
(1) (a) Zimmerman, H. E.; Schuster, D. I. J . Am. Chem. Soc. 1962,
84, 4527-4540. (b) Schultz, A. G. Rearrangement Reactions of Cross-
Conjugated Cyclohexadienones. In CRC Handbook of Organic Photo-
chemistry and Photobiology; Horspool, W. M., Song, P.-S., Eds.; CRC
Press: London, 1995; pp 685-700.
(2) (a) Marx, J . N.; Argyle, J . C.; Norman, L. R. J . Am. Chem. Soc.
1974, 96, 2121-2129. (b) Marx, J . N.; Bombach, E. J . Tetrahedron Lett.
1977, 18, 2391-2394. (c) Vitullo, V. P.; Cashen, M. J .; Marx, J . N.;
Candle, L. J .; Fritz, J . R. J . Am. Chem. Soc. 1978, 100, 1205-1210.
(d) Schultz, A. G.; Harrington, R. E.; Macielag, M.; Mehta, P. G.;
Taveras, A. G. J . Org. Chem. 1987, 52, 5482-5484. (e) Marx, J . N.;
Hahn, Y.-S. P. J . Org. Chem. 1988, 53, 2866-2868. (f) Schultz, A. G.;
Hardinger, S. A. J . Org. Chem. 1991, 56, 1105-1111. (g) Marx, J . N.;
Zuerker, J .; Hahn, Y.-S. P. Tetrahedron Lett. 1991, 32, 1921-1924.
(3) For reviews of the dienone-phenol rearrangement, see: (a) de
Mayo, P. In Elucidation of Structures by Physical and Chemical
Methods; Bentley, K. W., Ed.; Wiley-Interscience: New York, 1963; p
1106. (b) Collins, C. J .; Eastham, J . F. In The Chemistry of the Carbonyl
Group; Patai, S., Ed.; Wiley-Interscience: New York, 1966; p 775. (c)
Waring, A. J . Adv. Alicycl. Chem. 1966, 1, 207. (d) Miller, B. In
Mechanisms of Molecular Migrations; Thyagarajan, B. S., Ed.;
Wiley-Interscience: New York, 1969; Vol. 1, p 275.
(4) (a) Gilman, H.; Arntzen, C. E. J . Am. Chem. Soc. 1947, 69, 1537-
1538. (b) Benkeser, R. A.; Krysiak, H. R. J . Am. Chem. Soc. 1954, 76,
599-603. (c) Parham, W. E.; Sayed, Y. A. J . Org. Chem. 1974, 39,
2051-2053.
(5) Mills, R. J .; Taylor, N. J .; Snieckus, V. J . Org. Chem. 1989, 54,
4372-4385.
(6) (a) Krizan, T. D.; Martin, J . C. J . Am. Chem. Soc. 1983, 105,
6155-6157. (b) Severson, R. G.; Rosscup, R. J . J . Am. Chem. Soc. 1954,
76, 4552-4554. (c) Earborn, E.; Walton, D. R. M.; Young, D. J . J . Chem.
Soc. (B) 1969, 15-20. (d) Nietzschmann, E.; Tzschach, A.; Duchek, I.;
Heinicke, J .; Thust, U.; Kemter, P. Ger. (East) DD 268,697; Chem.
Abstr. 1990, 112, 77534r. (e) The methyl ester: J ung, M. E.; Gaede,
B. Tetrahedron Lett. 1979, 35, 621-625. (f) The tert-butyl ester:
Boybin, D. W. Ph.D. Dissertation, Duke University, 1978.
(7) Comins, D. L.; Brown, J . D. J . Org. Chem. 1984, 49, 1078-1083.
(8) This oxidation was first performed by Aihua Wang, RPI Labo-
ratories.
S0022-3263(95)02240-7 CCC: $12.00 © 1996 American Chemical Society

4556 J . Org. Chem., Vol. 61, No. 14, 1996
Schultz and Antoulinakis
The Birch reduction-methylation of 2-(trimethylsilyl)-
benzoic acid has been mentioned in two review articles
concerned with the Birch reduction of aromatic com-
pounds;9 to our knowledge, this reaction has never been
described in the primary chemical literature. Birch
reduction of methyl 2-(trimethylsilyl)benzoate with lithium
in NH3-THF in the presence of 1 equiv of tert-butyl
alcohol at -78 °C, followed by addition of piperylene to
consume excess metal and alkylation with methyl iodide
gave diene 6 in 89% yield. The outstanding directive
effects of trialkylsilyl substituents10 together with the
potential for absolute stereocontrol by way of the asym-
metric analogue of the conversion 5 f 611 suggest that
this variant of the Birch reduction-alkylation will find
important synthetic application. Allylic oxidation of 6
with t-BuOOH and pyridinium dichromate (catalytic)
provided 1 in 86% yield (∼60% overall from benzalde-
hyde).
silylative rearrangements to give a 1:1 mixture of (E)-
and (Z)-4-(carbomethoxymethylmethylene)cyclopent-2-
en-1-ones 12 and 13. Irradiation (366 nm) of either 12
or 13 in benzene solution resulted in isomerization to a
photostationary state that was the same 1:1 composition
of 12 and 13 obtained from protiodesilylative rearrange-
ment of 9a and 9b.
Irradiation of a solution of 1 in benzene (0.02 M)
through uranyl glass provided a complicated mixture of
products as described in the Experimental Section. The
primary photoproducts were produced by way of the type
A rearrangement1a involving oxyallyl zwitterion 7 to give
diastereomers of the 4-(trimethylsilyl)- and 5-(tri-
methylsilyl)bicyclo[3.1.0]hex-3-en-2-ones 8 and 9.
The rearrangement of 9 to 12 and 13 is related to the
acid-catalyzed rearrangement of 6,6-diphenylbicyclo-
[3.1.0]hex-3-en-2-one to 4-(diphenylmethylene)cyclopent-
2-en-1-one, reported to occur in a mixture of 1 M HCl in
70% dioxane at reflux.14 The considerably more facile
acid-catalyzed rearrangement of 9 is a result of the
stabilizing effect of the â-trimethylsilyl substituent 10
in carbocation 11.
Continued irradiation of the photolysis mixture from
1 resulted in the type B photorearrangement15 of 8 and
9 to give phenols 14, 15, and 16 in a ratio of 2:4:1. The
structures of phenols 14-16 were assigned on the basis
of 1H NMR spectral data. Resonances for aromatic
protons in 14 appeared as a pair of doublets at δ 6.98
and 6.82 (J ) 0.5 Hz). A sharp one-proton singlet for
the phenolic OH group appeared at δ 11.17 (exchangeable
with D2O). The considerable downfield resonance for this
proton is characteristic of phenols with an adjacent
carboalkoxy group.12 Phenol 15 displayed one-proton
doublets at δ 6.86 and 6.64 (J ) 2.4 Hz) and a broad
resonance at δ 5.91 (exchangeable with D2O) for the
phenolic OH group. Phenol 16 displayed sharp one-
proton doublets at δ 7.46 and 6.81 (J ) 8.5 Hz) and a
sharp one-proton singlet at δ 10.89 for the phenolic OH
group, in accord with its location adjacent to the carbo-
methoxy substituent.
The absence of regioselectivity for photorearrangement
of 1 to 8 and 9 is striking when compared to the
regioselectivity for photorearrangement of the 3-methoxy-
2,5-cyclohexadien-1-ones which give only the 4-meth-
oxybicyclo[3.1.0]hex-3-en-2-ones corresponding to 8.12
Indirect trapping studies have shown that selective
product formation is not the result of a regioselective
rearrangement of the type A oxyallyl zwitterion corre-
sponding to 7.13 Rather, both 5-methoxy- and
4-methoxybicyclo[3.1.0]hexenones are produced; however,
in the absence of trapping agents, 5-methoxybicyclo[3.1.0]-
hexenones photorearrange to the 4-methoxy regio-
isomers.
The production of 5-(trimethylsilyl)bicyclohexenones 9a
and 9b presented a unique opportunity to examine the
viability of photorearrangement to the 4-trimethylsilyl
regioisomers 8a and 8b. Unfortunately, attempted chro-
matographic isolation of 9a and 9b resulted in protiode-
Bicyclohexenones 8a and 8b were isolated and irradi-
ated individually to give equivalent mixtures of phenols
14 and 15 (Scheme 2). Although 9a and 9b could not be
isolated and fully characterized, the available experi-
mental evidence (vide supra) suggests that both dia-
stereomers photorearrange to phenol 16 via the type B
oxyallyl zwitterion 18. Whether 9a and 9b also photo-
rearrange to 8a and 8b remains open to question. As
recorded in the previous study of 4-methoxybicyclo[3.1.0]-
(9) (a) Referenced as: R. Urech, personal communication in Hook,
J . M.; Mander, L. N. Nat. Prod. Rep. 1986, 3, 35-85. (b) Rabideau, P.
W.; Marcinow, Z. Org. Reactions 1992, 42, 1-334.
(10) Colvin, E. Silicon in Organic Synthesis; Butterworths: London,
1981.
(11) (a) Schultz, A. G. Acc. Chem. Res. 1990, 23, 207-213. (b)
Schultz, A. G. J . Chinese Chem. Soc. (Taiwan) 1994, 41, 487-495.
(12) Schultz, A. G.; Lavieri, F. P.; Macielag, M.; Plummer, M. J . Am.
Chem. Soc. 1987, 109, 3991-4000.
(13) Schultz, A. G.; Reilly, J . J . Am. Chem. Soc. 1992, 114, 5068-
5073.
(14) Zimmerman, H. E.; Keese, R.; Nasielski, J .; Swenton, J . S. J .
Am. Chem. Soc. 1966, 88, 4895-4904.
(15) Zimmerman, H. E.; Epling, G. A. J . Am. Chem. Soc. 1972, 94,
7806-7811.

Photochemical and Acid-Catalyzed Rearrangements
J . Org. Chem., Vol. 61, No. 14, 1996 4557
Ta ble 1. P r od u ct Distr ibu tion a fr om P h otolysis of 1 in
Ben zen e w ith CF 3CO2H
Sch em e 2
product distribution
CF3CO2H
(equiv)
12
13
14
15
1.0
2.0
5.0
10
4.0
4.0
2.5
2.5
3.0
2.0
2.0
1.5
2.0
3.0
1.0
1.0
1.0
1.0
1.0
6.0
12
12
16
20
32b
Product distribution determined by 1H NMR spectral analysis
a
b
of photoreaction mixtures in C6H6. Phenol 15 was isolated (flash
chromatography on silica gel) in 65% yield.
the π f π* band associated with 1. The λmax for 1 in
benzene solution is 278 nm (ꢀmax ) 200), while the λmax
for 1 in benzene with 10 equiv of CF3CO2H is 288 nm
(ꢀmax ) 658). Griffiths and Hart found that trifluoro-
ethanol or silica gel shifts the position of the π f π* band
of the 2,4-cyclohexadien-1-one chromophore, which cor-
related with a change in photoreactivity.17 Altered
product distribution from photolysis of a 4-vinyl-2,5-
cyclohexadien-1-one in the presence of CF3CO2H also has
been reported.18
The change in regioselectivity of formation of phenols
14 and 15 might be a result of solvation effects on the
type B oxyallyl zwitterion 17 as shown in structure 20.
Steric interactions between the migrating CO2Me group
and bound CF3CO2H might result in preferential migra-
tion to C(4) rather than C(6) of 20. It should be noted
that the Me3Si group in 17 is at an sp2 hybridized carbon
on the cyclohexadienyl ring, not well positioned for
carbocation â-stabilization10 (vide infra).
hex-3-en-2-ones,13 it is clear that the 4-substituted bicy-
clohexenones 8a and 8b do not photorearrange to the
5-substituted isomers 9a and 9b.
The regioselectivity for rearrangement of the type B
oxyallyl zwitterion 17 to 14 and 15 is only 1:2. This is
in marked contrast to the regioselectivity for rearrange-
ment of the intermediate corresponding to 17, wherein
the Me3Si group is replaced by MeO; rearrangement
produces only the phenol resulting from migration of the
CO2Me group to C(2).12 On the other hand, rearrange-
ment of 18 is regiospecific within experimental error to
give 16 with no trace of 3-methyl-4-carbomethoxyphenol
(19), the product of ipso substitution at C(4).
The propensity for rearrangement of 18 is noteworthy,
inasmuch as the type B intermediate with the Me3Si
group replaced by MeO failed to undergo rearrangement
to generate 2-carbomethoxy-4-methoxy-3-methylphenol;
trapping experiments have demonstrated that the type
B oxyallyl zwitterion forms by way of a reversible
photochemical process.13 The Me3Si compared to the
MeO group at C(4) in 18 provides less stabilization of
the oxyallyl zwitterion, which might enhance the migra-
tory aptitude of the CO2Me group.16
An unusual solvent effect was discovered for photo-
reactions of 1 in benzene in the presence of CF3CO2H.
The addition of 1 equiv of CF3CO2H dramatically en-
hanced the rate of photorearrangement of 1 (2 h vs >20
h in benzene). Photoproduct composition was simplified
to include only phenols 14 and 15 and methylenecyclo-
pentenones 12 and 13, suggesting that under these
reaction conditions bicyclohexenones 9a and 9b undergo
the acid-catalyzed protiodesilylative rearrangement faster
than photorearrangement to phenol 16. Furthermore,
it was found that the regioselectivity of type B photo-
rearrangements of 8a and 8b changes with increasing
amounts of CF3CO2H (Table 1) from a 2:1 mixture of 15
and 14 in benzene without added acid to 32:1 in benzene
with 20 equiv of CF3CO2H. Phenol 15 was isolated in
65% yield from the photoreaction of 1 and 20 equiv of
CF3CO2H.
Cyclohexadienone 1 was treated with CF3CO2H in the
dark to examine the regioselectivity of the acid-catalyzed
dienone-phenol rearrangement. After 7 days at room
temperature, 1 was completely converted to phenol 21,19
which was isolated in 91% yield (Scheme 3).
Two pathways for rearrangement of 1 to 21 are shown
in Scheme 3. Protonation of the C(1) carbonyl group
would generate 22, from which migration of the CO2Me
group to C(3) would generate the Me3Si-stabilized carbo-
cation 23. Loss of the Me3Si to solvent would give phenol
21 directly. Alternatively, migration of the CO2Me group
to C(5) of 22 would give carbocation 24 in which the
â-Me3Si group is at an sp2 hybridized carbon atom. Loss
of a proton from 24 would give the 5-trimethylsilyl-
substituted phenol 25. Although 25 was never observed,
it might have been generated and rapidly converted to
21 by protiodesilylation. It has been reported that
2-carbomethoxy-6-(trimethylsilyl)phenol undergoes facile
protiodesilylation at room temperature in CF3CO2H/
CHCl3 solution.20
The enhanced photoreactivity of 1 in the presence of
CF3CO2H may be connected to a shift of the position of
(16) (a) Hammett constants (σp) for MeO and Me3Si groups have
been determined: MeO (-0.27) and Me3Si (-0.07); see: Hansch, C.;
Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165-195. (b) To the extent
that the intermediate in the type B photorearrangement might be
represented as a biradicaloid, it should be noted that the trimethylsilyl
group has been found to exert a small destabilizing effect on adjacent
radicals; see: Zhang, S.; Zhang, X.-M.; Bordwell, F. G. J . Am. Chem.
Soc. 1995, 117, 602-606.
(17) Griffiths, J .; Hart, H. J . Am. Chem. Soc. 1968, 90, 5296-5298.
(18) Schultz, A. G.; Green, N. J . J . Am. Chem. Soc. 1992, 114, 1824-
1829.
(19) For previous preparations of 21, see: Phandis, A. P.; Nanda,
B.; Sarita, A.; Patwardhan, E.; Gupta, A. S. Indian J . Chem. 1984,
23B, 1098 and ref 2d.

4558 J . Org. Chem., Vol. 61, No. 14, 1996
Schultz and Antoulinakis
temperature, and then H2O was added. Solvent was evapo-
rated under reduced pressure, and saturated NaHCO3 solution
was added until the mixture tested basic. The solution was
then extracted three times with CH2Cl2. The combined organic
extracts were dried over Na2SO4, concentrated, and purified
by flash chromatography (silica gel; 2:1 hexane:EtOAc) to give
5 as a clear oil (3.16 g, 98%): 1H NMR (CDCl3, 500 MHz) δ
8.04 (d, 1 H, J ) 7.5 Hz), 7.72 (d, 1 H, J ) 7.3 Hz), 7.51 (t, 1
H, J ) 7.6 Hz), 7.44 (t, 1 H, J ) 7.6 Hz), 3.92 (s, 3 H), 0.37 (s,
9 H); 13C NMR (CDCl3, 125 MHz) δ 168.60, 142.41, 135.52,
Sch em e 3
135.36, 131.36, 129.94, 128.74, 51.83, 0.14; IR (film) 1718 cm-1
;
CIMS m/z (relative intensity) 209 (M+ + 1, 2%), 193 (100%),
177 (8%), 145 (8%). Anal. Calcd for C11H16O2Si: C, 63.42; H,
7.74. Found: C, 63.25; H, 7.81.
6-Ca r bom eth oxy-6-m eth yl-1-(tr im eth ylsilyl)-1,4-cyclo-
h exa d ien e (6). A flame-dried three-neck round bottom flask
(100 mL) equipped with a dry ice condenser, magnetic stirrer,
and N2 inlet was charged with 5 (0.87 g, 4.2 mmol), dry THF
(9 mL), and t-BuOH (0.40 mL, 4.2 mmol). The mixture was
cooled to -78 °C and liquid NH3 (∼60 mL) was added. Lithium
(∼0.064 g, 9.2 mmol) was added in small pieces to the stirred
solution and a deep blue coloration developed. 1,3-Pentadiene
was added dropwise until a color change to yellow occurred.
Methyl iodide (0.78 mL, 13 mmol) was added, and the solution
was stirred at -78 °C for 1 h. The mixture was warmed slowly
to room temperature while the ammonia was removed with a
stream of N2. Saturated NH4Cl solution was added, and the
mixture was diluted with EtOAc, extracted two times with
H2O, once with brine, and dried over Na2SO4. Removal of
solvent in vacuo afforded a yellow oil. Flash chromatography
(silica gel; 2:1 hexane:EtOAc) gave 6 (0.84 g, 89%) as a clear
oil: 1H NMR (CDCl3, 500 MHz) δ 6.14 (m, 1 H), 5.76 (dm, 1
H), 5.52 (dt, 1 H, J ) 11.7, 1.9 Hz), 3.60 (s, 3 H), 2.66 (q, 2 H,
J ) 3.7 Hz), 1.32 (s, 3 H), 0.04 (s, 9 H); 13C NMR (CDCl3, 125
MHz) δ 175.86, 139.44, 134.72, 130.44, 123.86, 51.99, 46.61,
26.85, 26.29, 0.04; IR (film) 2940, 1720 cm-1; CIMS m/z
(relative intensity) 225 (M+ + 1, 100%).
4-Ca r bom eth oxy-4-m eth yl-3-(tr im eth ylsilyl)-2,5-cyclo-
h exa d ien -1-on e (1). To a stirred solution of 6 (3.43 g, 15.3
mmol) in benzene (200 mL) at 0 °C were added Celite 545 (3.0
g), pyridinium dichromate (1.2 g, 3.1 mmol), and 90% t-BuOOH
(5.1 mL, 46 mmol). The resulting solution was stirred at 0 °C
for 1.5 h and then allowed to warm to room temperature and
stirred overnight. The reaction mixture was filtered through
a pad of Celite 545, the solids were washed thoroughly with
EtOAc, and the filtrate was concentrated in vacuo to give a
yellow oil. Flash chromatography (silica gel; 2:1 hexane:
EtOAc) gave 1 (3.10 g, 86%) as a pale orange oil: 1H NMR
(CDCl3, 500 MHz) δ 6.79 (dt, 1 H, J ) 10, 1.4 Hz), 6.51 (q, 1
H, J ) 1.8 Hz), 6.22 (dq, 1 H, J ) 10, 1.7 Hz), 3.60 (s, 3 H),
1.47 (s, 3 H), 0.11 (s, 9 H); 13C NMR (CDCl3, 125 MHz) δ
183.21, 171.50, 164.69, 151.64, 137.12, 128.57, 52.68, 51.18,
23.24, -0.78; IR (film) 1730, 1660, 1625 (shoulder) cm-1; CIMS
m/z (relative intensity) 239 (M+ + 1, 100%), 209 (26%), 167
(8%), 135 (64%); UV (benzene) λmax ) 278 nm (ꢀ ) 200), 300
nm (ꢀ ) 67), 366 nm (ꢀ ) 26); UV (benzene/10 equiv of
CF3CO2H) λmax ) 288 nm (ꢀ ) 658), 300 nm (ꢀ ) 284), 366 nm
(ꢀ ) 21). Anal. Calcd for C12H18O3Si: C, 60.47; H, 7.61.
Found: C, 60.40; H, 7.70.
Treatment of 1 with CF3CO2D gave 21 with no evi-
dence (1H NMR) for incorporation of deuterium at C(5),
thereby ruling out the intermediacy of 25 in the conver-
sion of 1 to 21. Acid-catalyzed dienone rearrangement
to give 23 rather than 24 is, of course, consistent with
the expectation of enhanced stabilization of 23 by the
â-effect of the Me3Si group.10
Exp er im en ta l Section
Gen er a l P r oced u r es. Tetrahydrofuran (THF) was dis-
tilled from benzophenone sodium ketyl under nitrogen. Ben-
zene was distilled from CaH2. Analytical TLC was performed
on 0.25 mm E. Merck silica gel (60F-254) plates using UV light
and iodine as visualizing agents. Purifications by flash column
chromatography used Baker silica gel (40 µm). Radial chro-
matography was performed on a Harrison Research Chroma-
totron, Model 7924T, using a 2 mm plate of silica gel PF. Band
separation was monitored by UV. High resolution mass
spectra were obtained from the mass spectrometry laboratory
at the University of Illinois at Urbana/Champaign. Elemental
analyses were performed by Quantitative Technologies, Inc.,
Whitehouse, NJ , and Atlantic Microlab, Inc., Norcross, GA.
The light source for all photochemistry was a Hanovia 450-W
medium pressure mercury arc lamp. The lamp was placed in
a water-cooled Pyrex immersion well and fitted with a uranyl
glass filter to give light with wavelength mainly at 366 nm.
2-(Tr im eth ylsilyl)ben zoic Acid (4). To a solution of 3
(3.02 g, 17.0 mmol; prepared by the method of Comins and
Brown in 87% yield on a 6 g scale7) in acetone (45 mL) and
water (8 mL) was added KMnO4 (3.22 g, 20.4 mmol). The
solution was stirred at room temperature for 1.5 h. Solvent
was evaporated under reduced pressure, and saturated Na2SO3
solution was added to the residue. The solution was filtered
through a pad of Celite 545, and the dark brown solid was
repeatedly washed with H2O and CH2Cl2. The resulting
colorless filtrate was acidified with 10% HCl and extracted
three times with CH2Cl2. The combined organic extractions
were dried over Na2SO4, and the solvent was removed in vacuo.
4 was obtained as white crystals (3.09 g, 94%): mp 94-95 °C
(lit. 97-98.5 °C);4 1H NMR (CDCl3, 500 MHz) δ 8.20 (d, 1 H,
J ) 7.5 Hz), 7.75 (d, 1 H, J ) 7.3 Hz), 7.57 (t, 1 H, J ) 7.5
Hz), 7.48 (t, 1 H, J ) 7.5 Hz), 0.37 (s, 9 H); CIMS m/z (relative
intensity) 195 (M+ + 1, 3%), 179 (100%), 163 (25%), 123 (80%).
Meth yl 2-(Tr im eth ylsilyl)ben zoa te (5). To a solution of
4 (3.00 g, 15.4 mmol) in acetone (150 mL) was added K2CO3
(5.33 g, 38.6 mmol) and dimethyl sulfate (3.5 mL, 39 mmol).
The solution was refluxed overnight and cooled to room
Ir r a d ia tion of 4-Ca r bom eth oxy-4-m eth yl-3-(tr im eth -
ylsilyl)-2,5-cycloh exa d ien -1-on e (1). A solution of 1 (100
mg, 0.42 mmol) in benzene (22 mL, 19 mM) was degassed with
N2 for 10 min prior to irradiation for 3 h. Concentration of
the reaction mixture, flash column chromatography (silica gel;
7:3 hexane:EtOAc) to remove highly colored polar impurities,
and then radial chromatography (silica gel; 2 mm; 10:1 hexane:
EtOAc) gave 4-carbomethoxy-3-methyl-5-(trimethylsilyl)phenol
1
(15) (14 mg, 14%) as a white solid: mp 98-99 °C; H NMR
(CDCl3, 500 MHz) δ 6.87 (d, 1 H, J ) 2.4 Hz), 6.62 (d, 1 H, J
) 2.4 Hz), 5.91 (s, 1 H, D2O exchangeable), 3.85 (s, 3 H), 2.30
(s, 3 H), 0.22 (s, 9 H); 13C NMR (CDCl3, 125 MHz) δ 171.39,
156.28, 141.81, 138.74, 130.09, 119.20, 117.84, 51.73, 20.57,
-0.27; IR (CH2Cl2) 3475-3200, 1685, 1575 cm-1; CIMS, m/z
(relative intensity) 239 (M+ + 1, 3%), 223 (100%). Anal. Calcd
for C12H18O3Si: C, 60.47; H, 7.61. Found: C, 60.18; H, 7.49.
2-Carbomethoxy-3-methyl-5-(trimethylsilyl)phenol (14) (7 mg,
(20) Danheiser, R. L.; Sard, H. J . Org. Chem. 1980, 45, 4810-4812.

Photochemical and Acid-Catalyzed Rearrangements
J . Org. Chem., Vol. 61, No. 14, 1996 4559
7%) was obtained as a white solid: mp 71-72 °C; 1H NMR
(CDCl3, 500 MHz) δ 11.17 (s, 1 H, D2O exchangeable), 6.98 (d,
1 H, J ) 0.5 Hz), 6.82 (d, 1 H, J ) 0.5 Hz), 3.94 (s, 3 H), 2.52
(s, 3 H), 0.23 (s, 9 H); 13C NMR (CDCl3, 125 MHz) δ 172.24,
161.60, 148.84, 139.84, 127.43, 120.46, 112.31, 52.08, 23.95,
-1.56; IR (CH2Cl2) 3670, 1655, 1605 cm-1; EIMS, m/z (relative
intensity) 238 (M+, 40%), 223 (25%), 206 (100%), 191 (39%);
HRMS (M+) calcd for C12H18O3Si 238.1025, found 238.1026.
2-Carbomethoxy-3-methyl-4-(trimethylsilyl)phenol (16) (3 mg,
3%) was obtained as a white solid: 1H NMR (CDCl3, 500 MHz)
δ 10.89 (s, 1 H), 7.46 (d, 1 H, J ) 8.5 Hz), 6.81 (d, 1 H, J ) 8.5
Hz), 3.95 (s, 3 H), 2.61 (s, 3 H), 0.29 (s, 9 H). Sufficient
material of analytical purity could not be obtained. 6-exo-
Carbomethoxy-6-methyl-4-(trimethylsilyl)bicyclo[3.1.0]hex-3-
en-2-one (8b) (14 mg, 14%) was obtained as a clear oil: 1H
NMR (CDCl3, 500 MHz) δ 6.09 (s, 1 H), 3.70 (s, 3 H), 3.07 (d,
1 H, J ) 4.9 Hz), 2.53 (d, 1 H, J ) 4.9 Hz), 1.23 (s, 3 H), 0.18
(s, 9 H); 13C NMR (CDCl3, 125 MHz) δ 203.28, 176.86, 171.58,
140.79, 52.53, 47.61, 37.78, 35.65, 8.60, -2.67; IR (film) 1700
cm-1; EIMS, m/z (relative intensity) 238 (M+, 22%), 223 (57%),
179 (32%), 165 (83%), 106 (100%). Anal. Calcd for C12H18O3-
Si: C, 60.47; H, 7.61. Found: C, 60.41; H, 7.63. (E)-4-
(Carboxymethylmethylmethylene)cyclopent-2-en-1-one (12) (16
Ir r a d ia t ion of 6-en d o- a n d 6-exo-Ca r b om et h oxy-6-
m eth yl-4-(tr im eth ylsilyl)bicyclo[3.1.0]h ex-3-en -2-on es (8a
a n d 8b). 8a (7 mg, 0.03 mmol) in benzene (3 mL) was
irradiated for 3 h. 1H NMR analysis of the reaction mixture
showed that 15 and 14 were formed in a ratio of 2:1. 8b (6
mg, 0.03 mmol) in benzene (3 mL) was irradiated for 3 h. 1H
NMR analysis of the reaction mixture showed that 15 and 14
were formed in a ratio of 2:1.
3-Ca r bom eth oxy-4-m eth ylp h en ol (21). A solution of 1
(0.10 g, 0.43 mmol) in trifluoroacetic acid (2 mL) was stirred
at room temperature for 7 days. Removal of the solvent in
vacuo followed by flash chromatography (silica gel; 7:3 hexane:
EtOAc) gave 21 (65 mg, 91%) as colorless crystals: mp 72-73
°C (lit. 74-75 °C);19 1H NMR (CDCl3, 500 MHz) δ 7.40 (d, 1
H, J ) 3 Hz), 7.12 (d, 1 H, J ) 9 Hz), 6.92 (dd, 1 H, J ) 9, 3
Hz), 4.81 (s, 1 H, D2O exchangeable), 3.89 (s, 3 H), 2.51 (s, 3
H); 13C NMR (CDCl3, 125 MHz) δ 168.34, 153.55, 132.91,
132.06, 130.05, 119.46, 117.21, 52.04, 20.80; IR (CH2Cl2) 3315,
1685, 1220 cm-1
.
3-Ca r bom eth oxy-4-m eth ylp h en ol (21). 1 (5 mg, 0.02
mmol) was placed in an NMR tube, dissolved in CF3CO2D and
allowed to stand in the dark for 4 days. 1H NMR analysis of
the reaction mixture showed complete conversion of 1 to 21
and that there was no deuterium incorporation in 21. 21: 1H
NMR (CF3CO2D, 500 MHz) δ 9.49 (s, 1 H), 9.22 (d, 1 H, J )
8.6 Hz), 9.06 (d, 1 H, J ) 8.3 Hz), 6.03 (s, 3 H), 4.50 (s, 3 H);
1
mg, 23%) was obtained as a white solid: mp 111-112 °C; H
NMR (CDCl3, 500 MHz) δ 8.09 (d, 1 H, J ) 5.6 Hz), 6.47 (d, 1
H, J ) 5.6 Hz), 3.77 (s, 3 H), 3.33 (s, 2 H), 2.11 (s, 3 H); 13C
NMR (CDCl3, 125 MHz) δ 206.27, 167.69, 155.20, 145.48,
137.60, 123.99, 51.95, 40.94, 14.84; IR (CH2Cl2) 1690, 1630
(shoulder), 1545 cm-1; EIMS, m/z (relative intensity) 166 (M+,
100%), 138 (59%), 135 (27%), 123 (52%), 107 (33%). Anal.
Calcd for C9H10O3: C, 65.05; H, 6.07. Found: C, 64.86; H, 6.14.
A positive NOESY correlation between the proton at 6.47 ppm
and the methyl group protons at 2.11 ppm was observed,
designating (E)-(12). A 1:4 mixture (21 mg) of 6-endo-
carbomethoxy-6-methyl-4-(trimethylsilyl)bicyclo[3.1.0]hex-3-
en-2-one (8a ):(Z)-4-(carboxymethylmethylmethylene)cyclopent-
2-en-1-one (13) was obtained. Recrystallization of the mixture
using EtOAc/hexane gave pure 13 as colorless crystals: mp
1
1: H NMR (CF3CO2D, 500 MHz) δ 9.35 (d, 1 H, J ) 9.8 Hz),
8.99 (s, 1 H), 8.66 (d, 1 H, J ) 9.7 Hz), 5.83 (s, 3 H), 3.71 (s, 3
H), 2.29 (s, 9 H).
Gen er a l P r oced u r e for t h e Ir r a d ia t ion of 4-Ca r b o-
m eth oxy-4-m eth yl-3-(tr im eth ylsilyl)-2,5-cycloh exa d ien -
1-on e (1) in Ben zen e Usin g Tr iflu or oa cet ic Acid a s a
Cosolven t. To a solution of 1 (28 mg, 0.12 mmol) in benzene
(7 mL, 17 mM) was added 1, 2, 5, 10, or 20 equiv of
trifluoroacetic acid. The solutions were degassed with N2 prior
to irradiation for 2 h. Removal of the solvent in vacuo was
followed by 1H NMR analysis. Consult Table 1 for product
distributions.
1
70-71 °C; H NMR (CDCl3, 500 MHz) δ 8.71 (d, 1 H, J ) 5.8
Hz), 6.41 (d, 1 H, J ) 5.8 Hz), 3.80 (s, 3 H), 2.98 (s, 2 H), 2.01
(s, 3 H); 13C NMR (CDCl3, 125 MHz) δ 204.07, 167.04, 156.39,
145.60, 137.56, 124.66, 51.93, 39.26, 17.32; IR (CH2Cl2) 1750,
1675(shoulder) cm-1; EIMS m/z (relative intensity) 166 (M+,
37%), 138 (27%), 123 (25%), 107 (27%); HRMS (M+) calcd for
C9H10O3 166.0630, found 166.0630. A positive NOESY cor-
relation was observed between the protons at 2.98 ppm and
the methyl group protons at 2.01 ppm, designating (Z)-(13).
The resulting mother liquor contained a 1:1 mixture of 8a :13:
1H NMR (CDCl3, 500 MHz) for 8a : δ 5.93 (s, 1 H), 3.57 (s, 3
H), 2.66 (d, 1 H, J ) 4.4 Hz), 2.12 (d, 1 H, J ) 4.4 Hz), 1.41 (s,
3 H), 0.16 (s, 9 H); 13C NMR (CDCl3, 125 MHz) δ 203.72,
174.28, 169.97, 138.88, 52.85, 52.13, 39.65, 36.42, 21.53, -2.21.
Ir r a d ia tion of (E)- a n d (Z)-4-(Ca r boxym eth ylm eth yl-
m eth ylen e)cyclop en t-2-en -1-on es (12 a n d 13). 12 (12 mg,
0.07 mmol) in benzene (5 mL) was irradiated for 3 h. 1H NMR
analysis of the reaction mixture showed a 1:1 mixture of 12
and 13. 13 (7 mg, 0.04 mmol) in benzene (3 mL) was irradiated
for 3 h. 1H NMR analysis of the reaction mixture showed a
1:1 mixture of 12 and 13.
Ack n ow led gm en t. This work was supported by the
National Institute of General Medical Science (Grant
GM 33061). E.G.A. thanks Rensselaer Polytechnic
Institute for The William Pitt Mason Prize from the
chemistry department and The Class of 1902 Research
Prize, awarded to the senior who presents the best
thesis involving research in any branch of engineering
or science.
Su p p or tin g In for m a tion Ava ila ble: Copies of NMR
spectra of compounds 13 and 14 (3 pages). This material is
contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
J O952240G