On the most powerful chemical traps for bis(methoxycarbonyl)carbene (=2-methoxy-1-(methoxycarbonyl)-2-oxoethylidene)

Article abstract of DOI:10.1002/hlca.200890054

The efficiency and validity of different chemical substrates for trapping bis(methoxycarbonyl)carbene (=2-methoxy-1-(methoxycarbonyl)-2-oxoethylidene; 1) is dependent on the conditions of carbene generation. On conventional photolysis of dimethyldiazomalonate (=2-diazopropanedioic acid dimethyl ester; 2) by long-wave UV light (through a Pyrex filter, λ > 290 nm), the most powerful trap for carbene 1 in the series of substrates Me₂S, MeOH, cyclohexane, and pyridine is Me₂S (with an efficiency ratio of ca. 6 :4 : 2 : 1, resp.). When short-wave decomposition of diazomalonate 2 is employed (through a quartz filter, λ > 210 nm), more reliable and useful chemical traps for bis(methoxycarbonyl)carbene (1) are pyridine and cyclohexane, whose adducts with 1 are rather stable under short-wave-irradiation conditions. Application of alcohols for the trapping of 1 proves to be preferential when simultaneous monitoring of carbene and oxoketene formation during photolysis is necessary.

Full text of DOI:10.1002/hlca.200890054

Helvetica Chimica Acta – Vol. 91(2008)
501
On the Most Powerful Chemical Traps for Bis(methoxycarbonyl)carbene
¼2-Methoxy-1-(methoxycarbonyl)-2-oxoethylidene)
(
by Vladimir V. Shevchenko*, Natalya G. Zhegalova, Andey O. Borzenko, and Valerij A. Nikolaev
Department of Organic Chemistry, Saint-Petersburg State University, Universitetsky pr. 26,
Saint-Petersburg, 198504, Russia
(
phone: þ 78125741554; fax: þ 78124493123; e-mail: shevchenko@ecohim.ru)
The efficiency and validity of different chemical substrates for trapping bis(methoxycarbonyl)car-
bene (¼2-methoxy-1-(methoxycarbonyl)-2-oxoethylidene; 1) is dependent on the conditions of carbene
generation. On conventional photolysis of dimethyldiazomalonate (¼2-diazopropanedioic acid dimethyl
ester; 2) by long-wave UV light (through a Pyrex filter, l > 290 nm), the most powerful trap for carbene 1
in the series of substrates Me S, MeOH, cyclohexane, and pyridine is Me S (with an efficiency ratio of ca.
2
2
6
:4 :2 :1, resp.). When short-wave decomposition of diazomalonate 2 is employed (through a quartz
filter, l > 210 nm), more reliable and useful chemical traps for bis(methoxycarbonyl)carbene (1) are
pyridine and cyclohexane, whose adducts with 1 are rather stable under short-wave-irradiation
conditions. Application of alcohols for the trapping of 1 proves to be preferential when simultaneous
monitoring of carbene and oxoketene formation during photolysis is necessary.
1
. Introduction. – Chemical identification of carbenes and quantitative determi-
nation of carbene products in reaction mixtures are typically realized by using so-called
carbene trapsꢁ [1]. Besides traditional alkenes [1][2], compounds bearing heteroatoms
with unshared electron pairs in their structure are also generally used [1][3 – 6]
Scheme 1). The most frequently employed compounds for this purpose, especially
ꢀ
(
upon laser-flash photolysis of diazo compounds and other precursors of carbenes, are
pyridine [3], sulfides [4], alcohols [5], and some other substrates [6]. But, to the best of
our knowledge [1], the direct experimental comparison of the efficiency of these
chemical traps in reactions of carbenes generated by photochemical decomposition of
diazo compounds was not carried out yet.
Scheme 1
2
. Results and Discussion. – We represent herein the results of a comparative study
of the efficiency of pyridine (Py), dimethyl sulfide (Me S), methanol (MeOH), and
2
cyclohexane (C H ) as traps of bis(methoxycarbonyl)carbene ¼ (2-methoxy-1-(me-
6
12
thoxycarbonyl)-2-oxoethylidene; 1), generated by conventional (steady) photolysis of
ꢂ 2008 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta – Vol. 91(2008)
dimethyl 2-diazomalonate (2). The tentative evaluation of the photochemical stability
of the carbene adducts 3 – 6 with the substrates listed above under conditions of the
photolysis will be considered as well.
For a more reliable identification and quantitative determination of the reaction
products formed during photochemical decomposition of diazomalonate 2, the
assumed adducts of photochemical reactions, namely pyridinium ylide 3, sulfonium
ylide 4, 2-alkoxymalonates 5a,b, and 2-cyclohexylmalonate 6, were prepared by
independent synthesis.
2
.1. Preparation of Adducts. Two methods were used to synthesize pyridinium ylide
3
(Scheme 2), i.e., reaction of 2-bromomalonate 7 with pyridine in the presence of Et N
3
1
[
7][8a], and long-wave ) irradiation (through Pyrex filter, l > 290 nm) of diazomal-
onate 2 in pyridine solution. Both ways gave rise to good yields of ylide 3 (65 – 87%),
but in terms of the availability of starting material and the ease of scaling the synthesis,
the reaction of bromomalonate 7 with pyridine was favored over the photolysis of
diazomalonate 2. The structure of pyridinium ylide 3 was confirmed by the preparation
of the cycloadduct 8, which is formed by reaction of ylide 3 with dimethyl
acetylenedicarboxylate (DMAD) followed by spontaneous elimination of methyl
formate from the intermediate tetrahydro-1H pyrrole derivative 9 [3a][8b]
(
Scheme 2).
The sulfonium ylide 4 was prepared by long-wave irradiation of diazomalonate 2 in
Me S solution during 16 h [4a][9], and substituted malonates 5a,b and 6 were
2
synthesized by catalytic decomposition of 2 in the presence of the corresponding
substrate MeOH, EtOH, or cyclohexane by analogy with the known procedures [10]
(
Scheme 3). Relevant spectroscopic data of 5 and 6 are given in the Exper. Part.
.2. Comparison Study of the Efficiency of Pyridine, Me S, MeOH, and Cyclohexane
2
2
as Traps of Carbene 1. The generation of bis(methoxycarbonyl)carbene (1) was
accomplished by long-wave or short-wave irradiation of solutions of diazomalonate 2
containing the carbene traps pyridine, Me S, MeOH, and cyclohexane. After
2
completion of diazomalonate photolysis (14 – 23 h; TLC monitoring of the reaction),
1
the composition of the product mixture was determined by H-NMR spectroscopy
(
Fig.). Then the mixture was separated by column chromatography (silica gel). The
1
assignment of the H-NMR signals of the product mixture was achieved by comparison
1)
In the following, ꢀlong-waveꢁ means Pyrex-filtered light with l > 290 nm, and ꢀshort-waveꢁ means
quartz-filtered light with l > 210 nm.

Helvetica Chimica Acta – Vol. 91(2008)
503
Scheme 2
Scheme 3
1
with the H-NMR data of the compounds 3 – 6 obtained by independent synthesis. All
1
adducts 3 – 6 exhibited well-defined signals in the H-NMR spectrum, which enabled a
reliable quantitative analysis of the product mixture. The relative yields of 3 – 6 were
1
determined by the ratio of the integrals of the following H-NMR signals (Fig.): d 7.74
(
(
t, 2 arom. H), 8.16 (t, 1arom. H), and 8.60 ( d, 2 arom. H) of pyridinium ylide 3, d 2.89
s, 6 H, 2 Me) of sulfonium ylide 4; d 4.45 (s, 1 H, CHOMe) of 2-methoxymalonate 5a,
and d 3.19 (characteristic d, CHC H ) of 2-cyclohexylmalonate 6. The results are
6
11
shown in Scheme 4.
Initially, generation of bis(methoxycarbonyl)carbene (1) was accomplished by
long-wave irradiation of diazomalonate 2 in cyclohexane containing equimolar
amounts of pyridine, Me S, and MeOH with the molar ratio 1:10 of diazomalonate 2
2
to each trap. In doing so, it was assumed that in the presence of pyridine, Me S, and
2
MeOH, cyclohexane will operate only as an inert solvent, since one would expect that
the above-mentioned nucleophilic reagents are much more reactive with respect to the

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Helvetica Chimica Acta – Vol. 91(2008)

Helvetica Chimica Acta – Vol. 91(2008)
505
Scheme 4
a) R ¼ MeO C. ) Preparative yields in parentheses.
b
2
2
electrophilic singlet (MeO C) C: (1) than the hydrocarbon cyclohexane [1] ).
2
2
However, as shown by the data listed in Scheme 4, photolysis of diazo compound 2
in cyclohexane solution, in the presence of pyridine, Me S, and MeOH with the molar
2
ratio diazomalonate 2/nucleophile/cyclohexane 1:10 :60, gives rise to the formation of
the four reaction products 3, 4, 5a, and 6. That is, besides the anticipated pyridinium
ylide 3 and sulfonium ylide 4, as well as the insertion product 5a of carbene 1 into the
OꢀH bond of MeOH, a substantial amount (27%) of 2-cyclohexylmalonate 6 was
identified in the reaction mixture – the insertion product of carbene 1 into the CꢀH
bond of cyclohexane. The highest yield under these reaction conditions was observed
for sulfonium ylide 4 (46%), and the lowest for pyridinium ylide 3 (3%). Thus the
relative efficiency of carbene traps under the above-mentioned conditions (2/
nucleophile/cyclohexane 1:10 :60) decreases in the series Me S > cyclohexane >
2
MeOH > pyridine with the ratio 15.3 :9 :8 :1, neglecting a statistical factor for
cyclohexane.
Generation of carbene 1 by photolysis of diazomalonate 2 with long-wave light in
the presence of equimolar amounts of all four reagents and a 10-fold excess of each of
them relative to diazomalonate 2 also gives the four products 3 – 6. But under these
conditions (2/nucleophile/cyclohexane 1:10 :10), the relative efficiency of the traps is
slightly different and decreases in the series Me S > MeOH > cyclohexane > pyridine
2
with the ratio 6.3 :3.5 :1.8 :1.
It was also established by a reference experiment, that on long-wave irradiation, the
resulting adducts 3 – 6 of carbene 1 with the traps are photochemically rather stable,
and their ratio during photolysis remains essentially unchanged (ca. 6 :4 :2 :1 ).
Hence, on generation of carbene 1 by long-wave photolysis of diazomalonate 2, the
most powerful traps for (MeO C) C: (1) are Me S and MeOH, and the efficiency of
2
2
2
pyridine, which is normally used in laser-flash photolysis of diazo compounds and other
precursors of carbenes [3], is 6 and 4 times lower under the same reaction conditions.
2)
The mechanism of the formation of ylides 3 and 4 and insertion products 5 and 6, as well as the
feasible involvement in these processes of the excited states of diazo compound 2 and the
corresponding dimethyl 3H-diazirine-3,3-dicarboxylate are not considered in this paper.

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Helvetica Chimica Acta – Vol. 91(2008)
2
.3. Stability of the Adducts. To ascertain the validity of the investigated reagents as
carbene traps in the steady photolysis of diazomalonate 2 by short-wave light, the
stability of the obtained adducts 3 – 6 was estimated under short-wave irradiation in
solution of anhydrous MeOH during 2 – 12 h. Analysis of the resulting reaction mixture
as described above established that pyridinium ylide 3 and CꢀH insertion adduct 6 of
carbene 1 with cyclohexane are quite stable and remain essentially unchanged over a
few hours irradiation under these conditions. However, sulfonium ylide 4 rapidly
decomposes on short-wave irradiation giving rise predominantly to the product of a
Stevens rearrangement [4a][11] (for a few examples of a thermal Stevens rearrange-
ment, see [11a, b]) (Scheme 5).
Scheme 5
Also the insertion product 5 of bis(methoxycarbonyl)carbene (1) in the OꢀH bond
of MeOH or EtOH, i.e., the 2-alkoxymalonates 5a and 5b, undergoes partial
photochemical decomposition to dimethyl malonate (10; 21and 13 % yield, resp.),
after 2 h of short-wave irradiation in absolute EtOH (Scheme 6). Presumably, dimethyl
malonate (10) is formed by photochemical cleavage of the 2-alkoxymalonate 5 through
the Norish-II-type mechanism [12].
Scheme 6
3
. Conclusions. – Thus, it was established that in the series of substrates Me S,
2
MeOH, cyclohexane, and pyridine, the most powerful trap for bis(methoxycarbonyl)-
carbene (1) generated by conventional long-wave photolysis of dimethyl diazomalo-
nate (2) is Me S. On steady short-wave irradiation of 2, in spite of the lower efficiency,
2
pyridine and cyclohexane are by far more reliable and useful traps of 1 since the
resulting adducts are photochemically stable and remain essentially intact during short-
wave photochemical runs. However, it is appropriate to mention that the formed
pyridinium ylide 3 has a very strong absorption band in the same UV region as
diazomalonate 2 (244 and 251nm, resp.), which causes an increase of the decom-
position time of the diazo compound. This seems to be the reason why the use of
pyridine for trapping of carbene 1 during conventional short-wave photolysis of
diazomalonates seems to be inexpedient.

Helvetica Chimica Acta – Vol. 91(2008)
507
In comparison with Me S, alcohols have an almost two times lower efficiency as
2
traps for carbene 1 and, in addition, their adducts 5 experience partial photochemical
decomposition during short-wave irradiation. Nevertheless, in some cases, application
of MeOH or EtOH as carbene trap during short-time photolysis of diazocarbonyl
compounds proves to be the method of choice, since an alcohol could simultaneously
serve as the trap for highly reactive ketenes, which are usually produced by Wolff
rearrangement of actually all diazocarbonyl compounds [13].
Experimental Part
1
. General. Reactions were carried out in dry abs. solvents which were purified according to the
standard procedures. Irradiation of dimethyl diazomalonate (¼2-diazopropanedioic acid dimethyl ester;
), ylide 3, and 2-substituted malonates 5 and 6 was carried out at 18 – 208 by means of a Hg lamp Hanau
2
S-81 (100 – 130 Wt) in 80 ml or 25 ml vessels through a quartz or Pyrex filter (l > 210 or 290 nm, resp.).
The photolysis progress was usually monitored by TLC, apart from reactions of 2 when the amount of
evolved N was measured. Column chromatography (CC) and flash chromatography (FC): silica gel L 40
2
(
100 mm). Anal. TLC: Silufol-UV-254 plates, benzene or petroleum ether/Et O as eluents. UV/VIS
2
Spectra: Specord-M-40 instrument; region 200 – 500 nm; 0.3 – 6 mm MeOH solns.; 0.05 – 1.0 cm cuvette;
lmax in (log e). IR Spectra: Specord-IR-75 instrument; 0.002 – 0.030m CHCl solns. NMR Spectra: Bruker-
3
1
13
AM-300 spectrometer; 300 MHz for H, 75.5 MHz for C; Me Si as internal reference; acid-free CDCl
4
3
solvent, stored over dry K CO ; d in ppm, J in Hz.
2
3
2
. Preparations of Adducts. 2.1. 2-Pyridinium Bis(methoxycarbonyl)methylide (¼1-[2-Methoxy-2-
(
methoxycarbonyl)-2-oxoethyl]pyridinium Inner Salt; 3). Method A. A soln. of 2 (1.01 g, 6.4 mmol) in
freshly distilled pyridine (75 ml) was irradiated by long-wave UV light during 12 h. Then the pyridine was
evaporated at 18 – 208/10 – 15 Torr, then 1 – 2 Torr. The crystalline yellowish residue was washed with hot
Et O (50 ml) on a Hirsch funnel: 0.79 g (65%) of 3. M.p. 185 – 1868. UV: 244 (4.89), 390 (3.59).
2
1
H-NMR: 8.60 (d, J ¼ 5.82, 2 arom. H); 8.17 (t, J ¼ 7.26, 1arom. H); 7.75 ( t, J ¼ 7.26, 2 arom. H); 3.72 (s,
13
2
Me). C-NMR: 51.0 (Me); 77.7 (CꢀCOOMe); 126.2 (2 arom. C); 141.7 (3 arom. C); 150.4 (2 arom.
þ
C); 165.7 (COOMe). EI-MS: 209 (27, M ), 178 (38), 151 (53), 148 (38), 120 (26), 93 (100), 79 (30), 78
(
20), 65 (29), 63 (23), 59 (14), 52 (27), 51 (18). Anal. calc. for C H NO (209.20): C 56.75, H 5.29, N
10 11 4
6
.55; found: C 56.41, H 5.30, N 6.70.
Method B. The 2-bromomalonate 7 (20 g, 95 mmol) was added dropwise during 10 min to stirred
pyridine (118.7 g, 1.5 mol), and the mixture was stirred for 24 h. Then Et N (14.1 g, 0.14 mol) was added,
3
and the mixture was stirred for 5 h. The solvent was evaporated at 18 – 208/10 – 15 Torr, then 1 – 2 Torr.
The residue was extracted with a mixture of hot benzene (350 ml) and CHCl (7 ml), and the obtained
3
soln. was concentrated: 17.2 g (87%) of 3. M.p. 184 – 1858.
2.2. Indolizine-1,2,3-tricarboxylic Acid Trimethyl Ester (8). To a soln. of 3 (1.05 g, 5 mmol) in CHCl3
(
20 ml), but-2-ynedioic acid dimethyl ester (DMAD; 0.71g, 5 mmol, 0.61ml) was added, and the
mixture was refluxed for 5 h (TLC: full conversion of 3). The solvent was evaporated at 10 – 15 Torr, and
the crude dark-red oil was subjected to CC (aluminium oxide (17 g), benzene). After concentration of
the main fraction at 10 – 15 Torr, the residue was purified again by CC (Et O/petroleum ether 1:1). The
2
combined fraction of the product was dried (MgSO ) and concentrated: 0.218 g (15%) of 8. M.p. 146 –
4
1
1
(
478 (MeOH) [8b]. H-NMR: 3.91( s, 2 MeO); 4.01( s, 1MeO); 7.06 ( dd, J ¼ 6.5, 6.5, 1arom. H); 7.39
dd, J ¼ 6.4, 9.4, 1arom. H); 8.35 ( d, J ¼ 9.4, 1arom. H); 9.53 ( d, J ¼ 6.5, 1arom. H). EI-MS: 291(96,
þ
M ), 260 (100), 233 (6), 230 (9), 202 (22), 188 (15), 143 (19), 130 (9), 115 (13).
2
.3. Dimethylsulfonium Bis(methoxycarbonyl)methylide (¼ [2-Methoxy-1-(methoxycarbonyl)-2-oxo-
ethyl]dimethylsulfonium Inner Salt; 4). A soln. of 2 (3.01g, 19 mmol) in freshly distilled Me S (70 ml)
2
was irradiated by long-wave UV light during 17 h. The Me S was removed at 40 – 458/1atm, then 1–
2
2
Torr. The crystalline yellowish residue was washed with hot Et O (50 ml) on a Hirsch funnel: 2.99 g
2
1
(
83%) of 4. M.p. 168 – 1698 (MeOH/Et O 1:4) [4a]. UV: 237 (4.76), 293 (2.18). H-NMR: 2.89 (s, 2 Me);
2
13
3
.71( s, 2 Me). C-NMR: 28.2 (MeS); 51.2 (MeO); 59.0 (CꢀCOOMe); 167.2 (COOMe).

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Helvetica Chimica Acta – Vol. 91(2008)
2
.4. 2-Substituted Methyl Esters 5 and 6. General Procedure A (G.P. A). [Rh (OAc) ] (1 3 mg,
2
4
0
.0316 mmol) was added to the soln. of 10 equiv. of EtOH, MeOH, or cyclohexane in CH Cl (5 ml)
2
2
under Ar. Then, 1equiv. of diazomalonate 2 (0.5 g, 3.16 mmol) was added dropwise under Ar during
0 min. The mixture was stirred for 48 h (TLC monitoring). After filtration of the mixture through silica
gel (2 g) and washing with CH Cl (10 ml), the solvents were evaporated at 15 – 20 Torr, and the residue
3
2
2
was purified by CC (Et O/petroleum ether gradient). The desired product was distilled at 1– 2 Torr.
2
2.4.1. 2-Methoxypropanedioic Acid Dimethyl Ester (5a). According to the G.P. A, with MeOH
(
1.01 g, 1.27 ml, 31.6 mmol) and 2 (0.5 g, 3.16 mmol): 0.36 g (70%) of 5a. B.p. 75 – 808/1– 2 Torr [5a].
1
13
H-NMR: 3.51( s, 1MeO); 3.83 ( s, 2 MeO); 4.45 (s, CH). C-NMR: 53.3 (MeO); 59.1(MeO); 80.6
(
C(2)); 167.1 (C(1)).
2
.4.2. 2-Ethoxypropanedioic Acid Dimethyl Ester (5b). According to the G.P. A, with EtOH (0.89 g,
1
1
1
(
(
.13 ml, 19.4 mmol) and 2 (0.31g, 1. 94 mmol): 0.22 g (64%) of 5b. B.p. 75 – 808/1– 2 Torr [5a]. H-NMR:
13
.30 (t, J ¼ 6.9, MeCH O); 3.66 (q, J ¼ 6.9, MeCH O); 3.82 (s, 2 MeO); 4.54 (s, CH). C-NMR: 15.3
2
2
MeCH O); 53.2 (MeO); 67.4 (MeCH O); 79.2 (C(2)); 167.4 (C(1)).
2 2
2.4.3. 2-Cyclohexylpropanedioic Acid Dimethyl Ester (6). According to the G.P. A, with cyclohexane
1
2.66 g, 3.42 ml, 31.6 mmol) and 2 (0.5 g, 3.16 mmol): 0.15 g (22%) of 6. B.p. 90 – 928/1– 2 Torr. H-NMR:
0
2
.85 – 1.31 (m, 5 H); 1.62 – 1.77 (m, 5 H); 2.01– 2.16 ( m, 1 H); 3.19 (d , J ¼ 9.42, CHCOOMe); 3.73 (s,
13
MeO). C-NMR: 26.3, 26.5, 31.1, 38.4 (4 cyclohexyl C); 52.6 (MeO); 58.5 (CHCOOMe); 169.6
þ
(COOMe). EI-MS: 214 (12, M ), 183 (17), 155 (2), 133 (39), 132 (100), 101 (28), 100 (39), 95 (62), 81
(
11), 74 (8), 67 (12), 59 (9), 55 (15), 41 (19), 39 (12).
3. Photochemical Experiments. 3.1. Photolysis of Dimethyl Diazomalonate (2) in Cyclohexane
Solution in the Presence of Pyridine/Me S/MeOH. A mixture of 2 (0.5 g, 3.1mmol), Me S (1.86 g,
2
2
3
0 mmol), MeOH (0.96 g, 30 mmol), and pyridine (2.37 g, 30 mmol) in cyclohexane (18 ml, 0.1665 mol)
in a 25 ml photolysis reactor with a Pyrex filter was irradiated for 14.5 h (TLC monitoring). The solvent
and nucleophilic reagents were removed at 18 – 208/10 – 15 Torr, then 1 – 2 Torr. The residue was diluted
1
with CHCl (10 ml), and a 0.5 ml sample of the soln. was subjected to H-NMR analysis of the product
3
mixture. The rest of the soln. was treated with Et O (20 ml), and the crystalline ylides 3 and 4 were
2
separated by decantation. The solvents were evaporated at r.t./10 – 15 Torr, and the residue was separated
by CC (petroleum ether/Et O/EtOH gradient). The individual fractions after CC were dried (MgSO )
2
4
3
and concentrated. The isolated compounds were microdistilled or recrystallized: 0.166 g (25%; 27% )) of
3
3
3
6
, 0.095 g (19%; 24% )) of 5a, 0.244 g (44%; 46% )) of 4, and 0.013 g (2%; 3% )) of 3.
3
.2. Photolysis of Dimethyl Diazomalonate (2) in Cyclohexane/Me S/MeOH/Pyridine 1:1:1:1. A
2
mixture of 2 (0.5 g, 3.1mmol), Me S (4.65 g, 75 mmol), MeOH (2.4 g, 75 mmol), pyridine (5.93 g,
2
7
5 mmol), and cyclohexane (6.3 g, 75 mmol) in a 25 ml photolysis reactor with a Pyrex filter was
irradiated for 23 h (TLC monitoring). Workup was performed as described in Exper. 3.1: 0.073 g (11%;
3
3
3
3
1
4% )) of 6, 0.111 g (22%; 28% )) of 5a, 0.280 g (47%; 50% )) of 4, and 0.045 g (7%; 8% )) of 3.
.3. Photochemical Stability of Pyridinium Ylide 3. Pyridinium ylide 3 was irradiated by long- and
short-wave light during 12 h in MeOH or Me S soln. (60 ml), with addition of cyclohexane or MeOH
3
2
(
10 mol-equiv.), resp. Workup was performed as described in Exper. 3.1. Only starting 3 was isolated after
irradiation, in 91and 95% yield, resp.
.4. Photochemical Stability of 2-Alkoxymalonates 5 and 2-Cyclohexylmalonate 6. General
3
Procedure B (G.P. B). Compound 5 or 6 was irradiated by short-wave light in abs. EtOH in a 25 ml
photolysis reactor during 2 h. Then EtOH was removed at 18 – 208/10 – 15 Torr. The residue was analyzed
1
by H-NMR spectroscopy and the product yields were determined by the internal normalization method
based on the comparison of the intensity of the HꢀC(2) signals of 5 or 6 and dimethyl malonate (10).
According to the G.P. B, 0.235 g (1.46 mmol) of 2-methoxymalonate 5a yielded, after photolysis, 5a
(
(
79%) and 10 (21%).
According to the G.P. B, 0.6 g (3.42 mmol) of 2-ethoxymalonate 5b, yielded after photolysis, 5b
87%) and 10 (13%).
3)
Yield by H-NMR analysis of the crude product mixture, determined by means of the method of
internal normalization.
1

Helvetica Chimica Acta – Vol. 91(2008)
509
According to the G.P. B, 0.19 g (0.87 mmol) of 2-cyclohexylmalonate 6 yielded, after photolysis, only
(87%).
6
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Received October 5, 2007