6414 J . Org. Chem., Vol. 61, No. 18, 1996
Hu and Neckers
mined with a Thomas Hoover capillary melting point ap-
paratus and were uncorrected. NMR spectra were taken with
either a Varian Gemini 200 NMR spectrometer or a Varian
Unity Plus 400 NMR spectrometer. Chemical shifts are in
ppm with TMS as the internal standard. GC measurements
were carried out on a Hewlett-Packard (HP) 5890 gas chro-
matography. GC/MS were taken on a Hewlett-Packard 5988
mass spectrometer coupled to an HP 5880A GC, interfaced to
an HP 2623A data processor. Infrared spectra were taken
with a Galaxy series 6020 FTIR spectrometer. Thin layer
chromatography was performed with Whatman silica gel
coated TLC plates. Aldrich silica gel 60 Å (70-270 mesh) was
used in column chromatography. Elemental analysis was
carried out by Atlanta Microlab, Inc. High-resolution mass
spectra were taken at the University of Illinois at Urbana-
Champaign.
Gen er a l P r oced u r es for Ir r a d ia tion of Sa m p les. Alkyl
phenylglyoxylates were dissolved in the proper solvent in 16
mm o.d. (L ) 125 mm) Pyrex test tubes or 5 mm Pyrex NMR
tubes. The tubes were then sealed with a rubber septum
bound by sticky parafilm and degassed by bubbling a dry argon
gas through the solution for 10-15 min. The tube was then
put on a “merry-go-around” in a Rayonet RPR-100 photoreactor
equipped with 16 350 nm GE F8T5‚BLB UV lamps.
Gen er a l P r oced u r es for Isola tin g a n d Qu a n tifyin g
P h otor ea ction P r od u cts. Several (10 × 100 mL) samples
of starting concentration of 0.01 M were irradiated simulta-
neously in the photoreactor. The samples were immersed in
a double-walled Pyrex glass container where water is circu-
lated to maintain constant temperature. The disappearance
of starting alkyl phenylglyoxylate was monitored by TLC.
When all the starting material was gone, the samples were
combined and the solvent was evaporated on a rotary evapora-
tor. The resulting solution was chromatographed under
pressure using hexanes:ethyl acetate (40:1 to 20:1) as eluting
solvent. Quantitative measurements by NMR were performed
as reported.17a
P r oced u r e for Tr a p p in g r-Hyd r oxyp h en ylk eten e by
N-ben zylid en eben zyla m in e (12).15 Phenylglyoxylates and
an equimolar concentration of N-benzylidenebenzylamine (12)
were dissolved in 15 mL of dry benzene in a Pyrex test tube
and 1.5 g of molecular sieves (Davison, 5 Å, 8-12 mesh) added
before the tube was sealed by a rubber septum and degassed
by dry argon. The solution was then allowed to sit for at least
8 h before irradiation was carried out.
Qu a n tu m Yield s. Light intensity was calibrated using the
photofragmentation of valerophenone in benzene (Φacetophenone
) 0.33)38 as an actinometer. Concentrations of glyoxylates and
valerophenone were adjusted to ensure that equal amounts
of photons were absorbed. Quantities of products produced
were monitored by GC. Chlorobenzene was the internal
standard in GC calibration and quantitative measurements.
Due to competitive absorption by ketene D, the values reported
in Table 3 are the highest of three-four measurements for
each reaction.
Tim e-Resolved La ser F la sh P h otolysis. Nanosecond
laser flash photolyses were carried out on a setup described
by Ford and Rodgers39 using a Q-switched Nd:YAG laser as a
pump light. Argon was bubbled continuously through the
sample solution during the measurements.
Isop r op yl p h en ylglyoxyla te (1e)6 (81% yield): 1H NMR
(200 MHz, CDCl3) δ 1.41 (d, J ) 7.1 Hz, 6H), 5.32 (septet, J )
7.1 Hz, 1H), 7.50 (t, J ) 6.0 Hz, 2H), 7.68 (t, J ) 6.0 Hz, 1H),
7.98 (d, J ) 6.0 Hz, 2H); 13C NMR (50 MHz, CDCl3) δ 21.67,
70.66, 128.83, 129.90, 132.42, 134.79, 163.59, 186.70; MS 77
(40), 105 (100), 122 (0.3), 150 (0.3), 192 (0.4, M+).
n -Bu tyl p h en ylglyoxyla te (1f)6 (85% yield): 1H NMR (200
MHz, CDCl3) δ 0.97 (t, J ) 7.2 Hz, 3H), 1.45 (qt, J ) 7.2 Hz,
7.0 Hz, 2H), 1.75 (tt, J ) 7.0 Hz, 6.8 Hz, 2H), 4.40 (t, J ) 6.8
Hz, 2H), 7.52 (t, J ) 6.0 Hz, 2H), 7.71 (t, J ) 6.0 Hz, 1H), 7.99
(d, J ) 6.0 Hz, 2H); 13C NMR (50 MHz, CDCl3) δ 13.56, 18.96,
30.38, 66.04, 128.83, 129.92, 132.37, 134.84, 163.95, 186.44;
MS 77 (38), 105 (100), 123 (3), 150 (0.2), 206 (0.5, M+).
sec-Bu tyl p h en ylglyoxyla te (1g)6 (84% yield): 1H NMR
(200 MHz, CDCl3) δ 0.98 (t, J ) 7.4 Hz, 2H), 1.38 (d, J ) 7.0
Hz, 3H), 1.72 (qd, J ) 7.4 Hz, 7.2 Hz, 2H), 5.17 (tq, J ) 7.2
Hz, 7.0 Hz, 1H), 7.52 (t, J ) 6.9 Hz, 2H), 7.64 (t, J ) 6.9 Hz,
1H), 7.99 (d, J ) 6.9 Hz, 2H); 13C NMR (50 MHz, CDCl3) δ
9.58, 19.30, 28.59, 75.10, 128.80, 129.80, 132.38, 134.74,
163.81, 186.74.
Cycloh exyl p h en ylglyoxyla te (1b)6 (90% yield): 1H NMR
(200 MHz, CDCl3) δ 1.20-2.10 (m, 10H), 5.05 (m, 1H), 7.51 (t,
J ) 6.0 Hz, 2H), 7.63 (t, J ) 6.0 Hz, 1H), 7.89 (d, J ) 6.0 Hz,
2H); 13C NMR (200 MHz, CDCl3) δ 23.45, 24.99, 31.26, 75.22,
128.72, 129.73, 134.62, 163.50, 186.61.
Eth yl p-Br om op h en ylglyoxyla te (1j).8 Bromobenzene
(2.1 g, 13 mmol), 2.6 g (19 mmol) of ethyl oxalyl chloride, and
25 mL of anhydrous methylene chloride were placed in a 50
mL flask equipped with a magnetic stirrer and suspended in
an ice-salt bath. After the solution was stirred for 10 min,
3.4 g (25 mmol) of aluminum chloride was added in small
portions over 10 min. When the solution turned red-brown
and became homogenous, the ice-salt bath was removed and
the mixture was poured over 100 g of crushed ice and 50 mL
of concentrated hydrochloric acid. The decomposed mixture
was washed with 30 mL of 0.1 N sodium hydroxide three
times. After the organic layer was separated and the solvent
was evaporated, the crude product was purified by column
chromatography using dichloromethane as elution solvent: 2.4
g (72%) pure product was obtained; 1H NMR (200 MHz, CDCl3)
δ 1.43 (t, J ) 7.2 Hz, 3H), 4.44 (q, J ) 7.2 Hz, 2H), 7.66 (d, J
) 8.6 Hz, 2H), 7.91 (d, J ) 8.6 Hz, 2H); 13C NMR (50 MHz,
CDCl3) δ 13.99, 62.44, 130.38, 131.23, 131.33, 132.18, 163.05,
184.98; MS 75 (33), 77 (33), 155 (45), 256 (2, M+), 258(2);
HRMS m/e measured 255.9735 (∆ ) 0.0 mDa); calculated
255.9735.
Eth yl p-F lu or op h en ylglyoxyla te (1h ). A procedure simi-
lar to that described for 1j produced this compound in 64%
yield: 1H NMR (200 MHz, CDCl3) δ 1.43 (t, J ) 7.2 Hz, 3H),
4.46 (q, J ) 7.2 Hz, 2H), 7.20 (t, J ) 8.8 Hz, 2H), 8.00-8.15
(dd, J ) 8.8 Hz, 5.5 Hz, 2H); 13C NMR (50 MHz, CDCl3) δ
13.92, 62.33, 115.89, 116.32, 128.95, 132.70, 132.91, 163.30,
164.08, 169.22, 184.43; MS 95 (38), 140 (0.9), 168 (2), 196 (1,
M+); HRMS m/e measured 196.0535 (∆ ) 0.1 mDa); calculated
196.0536.
Eth yl p-Ch lor op h en ylglyoxyla te (1i). A procedure simi-
lar to that described for 1j produced this compound in 81%
yield: 1H NMR (200 MHz, CDCl3) δ 1.42 (t, J ) 7.2 Hz, 3H),
4.45 (q, J ) 7.2 Hz, 2H), 7.28 (t, J ) 8.8 Hz, 2H), 7.90-8.16
(dd, J ) 8.8 Hz, 5.5 Hz, 2H); 13C NMR (50 MHz, CDCl3) δ
14.01, 62.45, 129.22, 130.86, 131.34, 141.51, 163.13, 184.79;
MS 50 (22), 75 (37), 111 (39), 139 (100), 212 (2, M+); HRMS
m/e measured 212.0241 (∆ ) -0.1 mDa), calculated 212.0240.
Eth yl p-Meth oxyp h en ylglyoxyla te (1k ). Anhydrous 1,2-
dichloroethane (25 mL) and 2.7 g (20 mmol) of aluminum
chloride were added to a flask equipped with a magnetic stirrer
suspended in an ice-salt bath. Ethyl oxalyl chloride (4.1 g,
30 mmol) was added over 5 min from a syringe while the
solution was stirred. Anhydrous anisole (2.2 g, 20 mmol) was
also added dropwise over a 30 min period. A brown-red
homogenous solution formed as the anisole was added. The
mixture was stirred at room temperature for 4 h. Purification
was affected in a method similar to that described for 1i and
afforded 2.4 g of pure compound (62% yield): 1H NMR (200
MHz, CDCl3) δ 1.42 (t, J ) 7.1 Hz, 3H), 3.90 (s, 3H), 4.44 (q,
J ) 7.1 Hz, 2H), 6.89 (d, J ) 8.8 Hz, 2H), 8.01 (d, J ) 8.8 Hz,
2H); 13C NMR (50 MHz, CDCl3) δ 13.89, 55.43, 61.99, 114.08,-
125.20, 132.34, 164.89, 184.80; MS 50 (4), 77 (17), 92 (20), 107
(8), 135 (100), 208 (4, M+).
ter t-Bu tyl P h en ylglyoxyla te (1l). To a stirring solution
of 2.5 g (17.3 mmol) of benzoyl formic acid in 40 mL of
anhydrous benzene were added 213 mg (1.7 mmol) of 4-(dim-
ethylamino)pyridine (DMAP) and 2.22 g (30 mmol) of tert-butyl
alcohol. N,N′-Dicyclohexylcarbodiimide (DCC) was added to
the reaction mixture kept in an ice bath. The mixture was
stirred in the ice bath for about 10 min and then stirred at
room temperature for another 8 h. Precipitated urea was
(38) Lewis, F. D.; Hilliard, T. A. J . Am. Chem. Soc. 1972, 94, 3852-
3857.
(39) Ford, W. E.; Rodgers, M. A. J . J . Phys. Chem. 1994, 98, 3822.