Specific Isotope Enrichment of Methyl Methacrylate
2JP,H ϭ 15.5 Hz, 2 H, 2-H), 7.6Ϫ8.0 (m, 15 H, Ph). Ϫ 13C NMR 3 H, 3-H), 3.58 (s, 3 H, OCH3), 6.36 (chemical shift depending
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2
3
(50.1 MHz, CDCl3): δ ϭ 32.6 (d, JP,C ϭ 60.1 Hz, C-2), 53.1 (s,
strongly on concentration) [dq (“sext”), JP,H ϭ 14.8 Hz, JH,H ϭ
1
3
OCH3), 117.5 (d, JP,C ϭ 89 Hz, C-1Ј), 130.1 (d, JP,C ϭ 13 Hz, C-
3Ј), 133.6 (d, JP,C ϭ 10 Hz, C-2Ј), 134.9 (s, C-4Ј), 164.7 (s, C-1). CDCl3): δ ϭ 12.8 (s, C-3), 36.6 (d, JP,C ϭ 50 Hz, C-2), 53.0 (s,
7.2 Hz, 1 H, 2-H], 7.7Ϫ8.1 (m, 15 H, Ph). Ϫ 13C NMR (50.1 MHz,
2
1
1
3
Ϫ A two-layer system of 50.0 g (0.12 mol) of the phosphonium
bromide in 300 mL of dichloromethane and 2 equiv. (9.6 g; 0.24
mol) of NaOH in 200 mL water were vigorously shaken in a separ-
ation funnel, after which the layers were separated. The water layer
was washed twice with dichloromethane. The combined dichloro-
methane layers were dried with MgSO4 and the solvent was evapo-
rated to yield 40.3 g (0.12 mol; 100%) of the two rotameric forms
OCH3), 116.7 (d, JP,C ϭ 86.7 Hz, C-1Ј), 129.9 (d, JP,C ϭ 13.2 Hz,
C-3Ј), 133.4 (d, JP,C ϭ 8.8 Hz, C-2Ј), 134.7 (s, C-4Ј), 167.6 (d,
2
2JP,C ϭ 1.4 Hz, C-1). Ϫ Using the same procedure as for the depro-
tonation of the C2-phosphonium salt, 58.4 g (0.12 mol) of phos-
phonium iodide was deprotonated to give 42.6 g (0.12 mol; 100%)
of the two rotameric forms of the yellow phosphorane 6. Ϫ M.p.
153Ϫ156°C (from EtOAc). Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ
of 5 as a white solid. Ϫ M.p. 167Ϫ168°C (from EtOAc). Ϫ 1H 1.61 (d, 3JP,H ϭ 13.7 Hz, 3 H, 3-H), 3.13 (60%) ϩ 3.61 (40%) (3 H,
NMR (200 MHz, CDCl3): δ ϭ 2.90 (25%) ϩ 3.52 (75%) (3 H, OCH3), 7.4Ϫ7.9 (m, 15 H, Ph). Ϫ 13C NMR (50.1 MHz, CDCl3):
OCH3), 7.4Ϫ7.8 (m, 15 H, Ph). Ϫ 13C NMR (50.1 MHz, CDCl3): δ ϭ 12.8 (d, JP,C ϭ 10.3 Hz, C-3), 31.7 (d, JP,C ϭ 120.1 Hz, C-
2
1
1
1
δ ϭ 29.5 (d, JP,C ϭ 127.4 Hz, C-2), 49.5 (s, OCH3), 126.8 (d,
2), 48.5 ϩ 49.5 (OCH3), 127.9 (d, JP,C ϭ 90.8 Hz, C-1Ј), 128.2 (d,
1JP,C ϭ 91 Hz, C-1Ј), 128.5 (d, JP,C ϭ 11.7 Hz, C-3Ј), 131.7 (s, C-
3JP,C ϭ 11.7 Hz, C-3Ј), 131.3 (s, C-4Ј), 133.2 (d, JP,C ϭ 7.3 Hz, C-
3
2
2
2
2
4Ј), 132.9 (d, JP,C ϭ 8 Hz, C-2Ј), 171.3 (s, C-1).
2Ј), 170.5 (d, JP,C ϭ 13.2 Hz, C-1) ϩ 171.2 (d, JP,C ϭ 17.6 Hz,
C-1).
(1-13C)5 (5a): According to the above procedure, 4a was converted
into 49.1 g (0.12 mol, 71% from 2a) of phosphonium bromide. Ϫ
(1-13C)6 (6a): According to the same procedure, 40.2 g of the phos-
phorane 5a was converted into 56.9 g (0.12 mol, 100%, of which
79% monomethylated) of phosphonium iodide. Ϫ 1H NMR
(200 MHz, CDCl3): δ ϭ 1.70 (ddd, JP,H ϭ 18.3 Hz, JH,H
7.2 Hz, JC,H ϭ 5.0 Hz, 3 H, 3-H), 3.58 (d, JC,H ϭ 3.8 Hz, 3 H,
OCH3), 6.36 [ddq (“sept”), JP,H ϭ 14.8 Hz, JH,H ϭ 7.2 Hz,
2JC,H ϭ 6.8 Hz, 1 H, 2-H], 7.7Ϫ8.1 (m, 15 H, Ph). Ϫ 13C NMR
(50.1 MHz, CDCl3): δ ϭ 168.3 (s, C-1). Ϫ According to the same
procedure, 56.9 g of phosphonium iodide was converted into 42.6 g
3
1H NMR (200 MHz, CDCl3): δ ϭ 3.60 (d, JC,H ϭ 4.1 Hz, 3 H,
2
2
OCH3), 5.62 (dd, JC,H ϭ 7.6 Hz, JP,H ϭ 13.4 Hz, 2 H, 2-H),
7.6Ϫ8.0 (m, 15 H, Ph). Ϫ 13C NMR (50.1 MHz, CDCl3): δ ϭ 165.1
(d, JP,C ϭ 2.9 Hz, C-1). Ϫ According to the above procedure,
3
3
ϭ
2
3
3
2
3
49.1 g of phosphonium bromide was converted into 40.2 g (0.12
mol, 100%) of 5a. Ϫ 1H NMR (200 MHz, CDCl3): δ ϭ 2.92 (23%)
ϩ 3.51 (77%) (3 H, OCH3), 7.4Ϫ7.7 (m, 15 H, Ph). Ϫ 13C NMR
2
(50.1 MHz, CDCl3): δ ϭ 171.5 (d, JP,C ϭ 11.7 Hz, C-1).
1
(0.12 mol, 100%) of 6a. Ϫ H NMR (200 MHz, CDCl3): δ ϭ 1.61
(2-13C)5 (5b): According to the above procedure, 4b was converted
into 49.2 g (0.12 mol, 70% from 2b) of phosphonium bromide. Ϫ
1H NMR (200 MHz, CDCl3): δ ϭ 3.61 (s, OCH3), 5.62 (dd,
3
(d, JP,H ϭ 13.7 Hz, 3 H, 3-H), 3.13 (55%) ϩ 3.59 (45%) (3 H,
OCH3), 7.3Ϫ7.9 (m, 15 H, Ph). Ϫ 13C NMR (75.5 MHz, CDCl3):
2
2
δ ϭ 170.8 (d, JP,C ϭ 13.3 Hz, C-1) ϩ 171.5 (d, JP,C ϭ 11.7 Hz,
C-1).
2
1JC,H ϭ 134.4 Hz, JP,H ϭ 13.6 Hz, 2 H, 2-H), 7.6Ϫ8.0 (m, 15 H,
Ph). Ϫ 13C NMR (50.1 MHz, CDCl3): δ ϭ 33.1 (d, 1JP,C ϭ 57.1 Hz,
C-2). Ϫ According to the above procedure, 49.2 g of phosphonium
bromide was converted into 39.6 g (0.12 mol, 100%) of 5b. Ϫ 1H
NMR (200 MHz, CDCl3): δ ϭ 2.57 (8%) ϩ 3.52 (82%) (3 H,
OCH3), 7.4Ϫ7.8 (m, 15 H, Ph). Ϫ 13C NMR (50.1 MHz, CDCl3):
(2-13C)6 (6b): According to the same procedure, 39.6 g of the phos-
phorane 5b was converted into 56.9 g (0.12 mol, 100%, of which
83% monomethylated) of phosphonium iodide. Ϫ 1H NMR
(200 MHz, CDCl3): δ ϭ 1.69 (ddd, JP,H ϭ 18.5 Hz, JH,H
7.2 Hz, JC,H ϭ 4.1 Hz, 3 H, 3-H), 3.57 (s, 3 H, OCH3), 6.46 [ddq
3
3
ϭ
1
δ ϭ 29.7 (d, JP,C ϭ 127 Hz, C-2).
2
1
2
3
Note: 1H-NMR spectra of phosphorus ylides are known to exhibit
special properties.[35Ϫ40] Due to internal hindered rotation about
the C1ϪC2 bond, the methoxy protons show two separate signals
at moderate temperature, which coalesce at higher tempera-
tures.[35Ϫ40] According to the literature, the coalescence tempera-
ture of the methoxy signals in the phosphorus ylide 5 in CDCl3 is
30°C[39] or 43°C[37] and in 6 it is 55°C.[40] The methine proton
signal of 5 is only visible from the pure compound; in the presence
of a proton source, the methine doublet is collapsed.[37] Our spectra
are in agreement with these findings. For phosphorane 6 two sig-
nals for the methoxy group are found at room temperature in rela-
tive amounts of approximately 2:3 for the two rotamers. The phos-
phorane 5 shows partial coalescence for the two rotameric forms at
room temperature, therefore the relative amounts of the two broad
signals vary somewhat more.
(d“sext”), JC,H ϭ 133.5 Hz, JP,H ϭ 16 Hz, JH,H ϭ 7.2 Hz, 1 H,
2-H], 7.6Ϫ8.0 (m, 15 H, Ph). Ϫ 13C NMR (50.1 MHz, CDCl3):
1
δ ϭ 37.1 (d, JP,C ϭ 52.7 Hz, C-2). Ϫ According to the same pro-
cedure, 56.9 g of phosphonium iodide was converted into 41.1 g
1
(0.115 mol, 96%) of 6b. Ϫ H NMR (200 MHz, CDCl3): δ ϭ 1.62
(dd, 2JC,H ϭ 4.6 Hz, 3JP,H ϭ 14.2 Hz, 3 H, 3-H), 3.34 (82%) ϩ 3.50
(18%) (3 H, OCH3), 7.3Ϫ7.9 (m, 15 H, Ph). Ϫ 13C NMR
1
(75.5 MHz, CDCl3): δ ϭ 32.6 (d, JP,C ϭ 120 Hz, C-2).
Methyl Methacrylate (1): 42.6 g of phosphorane 6 was ground and
put into a 1-L round-bottom flask. 300 mL of water and 300 mL
of pentane were added, as well as 0.7Ϫ1.5 mg of 4-methoxyphenol
as inhibitor (50Ϫ100 ppm). After addition of 1.2 equiv. (4.4 g) of
paraformaldehyde, the flask was closed tightly and the mixture
stirred overnight. The solids were filtered off and the liquid layers
were separated. The water layer was washed with pentane twice;
the combined pentane layers were dried with MgSO4. The pentane
[1-(Methoxycarbonyl)ethyl]triphenylphosphorane (6): A solution of
40.3 g (0.12 mol) of 5 in 200 mL of dichloromethane in a 250-mL was distilled off and subsequently the product was distilled under
round-bottom flask was cooled to 0°C. 1.5 equiv. (25.7 g, 0.18 mol)
of methyl iodide was added and the solution was stirred overnight
at room temperature. Evaporation of the solvent and the remainder
of the methyl iodide yielded 58.4 g (0.12 mol, 100%, of which 85%
monomethylated, 7.5% not methylated and 7.5% doubly methyl-
ated) of phosphonium iodide {[1-(methoxycarbonyl)ethyl]triphen-
vacuum into a cold trap with liquid nitrogen. This yielded 5.00 g
(50 mmol, 42%) of methyl methacrylate (1). 100 ppm of 4-meth-
oxyphenol was added as inhibitor. Ϫ B.p. 100°C. Ϫ 1H NMR
(600 MHz, CDCl3): δ ϭ 1.94 (dd, 4JH,H ϭ 1.0 Hz, 4JH,H ϭ 1.6 Hz,
3 H, 4-H), 3.76 (s, 3 H, OCH3), 5.56 [dq (“quint”), 4JH,H ϭ 1.6 Hz,
4
2JH,H ϭ 1.7 Hz, 1 H, 3-Htrans], 6.10 [dq (“sext”), JH,H ϭ 1.0 Hz,
ylphosphonium iodide} as
a yellowish foam. Ϫ
1H NMR 2JH,H ϭ 1.7 Hz, 1 H, 3-Hcis]. Ϫ 13C NMR (75.5 MHz, CDCl3): δ ϭ
(200 MHz, CDCl3): δ ϭ 1.70 (dd, 3JP,H ϭ 18.5 Hz, 3JH,H ϭ 7.2 Hz,
18.3 (s, C-4), 51.7 (s, OCH3), 125.4 (s, C-3), 136.1 (s, C-2), 167.8
2913
Eur. J. Org. Chem. 1999, 2909Ϫ2914