Reactions of α,β-Enones with Diazo Compounds: Part 4: Reaction Pathways from (Z)- and (E)-α,β-Enones with Dimethyl Diazomalonate

Article abstract of DOI:10.1002/hlca.200490039

In this study, (E)- and (Z)-enones carrying only a phenyl substituent at their C(β) atom were treaced with dimethyl diazomalonate in the presence of (acetylacetonato)copper(II). According to the configuration of the starting enones, the products were dioxole or dihydrofuran derivatives, significant heterocycles in natural products.

Full text of DOI:10.1002/hlca.200490039

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Helvetica Chimica Acta Vol. 87 (2004)
Reactions of a,b-Enones with Diazo Compounds
Part 41)
Reaction Pathways from (Z)- and (E)-a,b-Enones with Dimethyl Diazomalonate
by Olcay AnaÁ*, F¸sun Seyma G¸ngˆr, fiig√dem Kahveci, and M. SÀerif Cansever
Istanbul Technical University, Faculty of Sciences and Letters, Department of Chemistry, Maslak,
TR-34469 Istanbul
In this study, (E)- and (Z)-enones carrying only a phenyl substituent at their C(b) atom were treaced with
dimethyl diazomalonate in the presence of (acetylacetonato)copper(II). According to the configuration of the
starting enones, the products were dioxole or dihydrofuran derivatives, significant heterocycles in natural
products.
Introduction.
Dioxole and dihydrofuran derivatives are among the most-
significant heterocycles in natural products, and consequently a wide range of methods
for their syntheses has been developed [2 8]. We previously reported the reactions of
several a,b-enones and -enals with ethyl acetodiazoacetate and dimethyl diazomalo-
nate (DMDM) in the presence of (acetylacetonato)copper(II) ([Cu(acac)2])
[1][9][10]. In these reports, we noted that under mild conditions, dihydrofuran
derivatives such as 3 5 should be formed predominantly, by a 1,5-electrocyclic ring-
closing reaction of the related carbonyl ylides derived from properly chosen (E)-
enones existing mainly as s-cis conformers. Substituents at both the enone 1 or 2 and the
diazocarbonyl compound that can stabilize the concerted transition state of the initially
formed enone ylide by conjugation had a beneficial influence on the reaction rate. On
the other hand, while steric inhibitions at the C(b) atom (as in 1-(2-methylcyclopent-1-
en-1-yl)ethanone (6)) retarded the reactions, steric crowdings at the remaining part,
i.e., at C (a) and at the carbonyl C-atom of the enone, such as in 2-methyl-1-phenylpent-
1-en-3-one (2), provided a beneficial effect of preventing possible follow-up reactions
(Scheme 1).
Furthermore, the corresponding ylides arising from (E)-enals (with a preference of
s-trans conformation) yielded dioxole derivatives by following a different reaction
route than those reported by Huisgen and March [8] (Scheme 1).
In this study, as a part of our continuous interest in this particular field, we worked
on similar competing reactions of enones to yield dihydrofurans vs. furofurans.
Furthermore, we also tried to find out what product patterns would give (Z)-enones
and (E)-enones with s-trans conformation under similar conditions.
1
)
Part 3: [1].

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409
Scheme 1. Reactions of a,b-Enones with Dimethyl Diazomalonate [1][9][10]
Results and Discussion.
In this study, all enones that were synthesized by
traditional aldol condensation reaction had a phenyl substituent at their C(b) atom to
stabilize the possible concerted transition state of the initially formed enone ylide by
conjugation (see compounds 2, 7, and 8; Table 1).
As the main feature of an aromatic-like transition state must be securing a close
proximity between the two termini especially with respect to dihydrofuran formation,
the synthesized enones were chosen to contain H-substituents at their C(b) atoms.
Thus, 2-methyl-1-phenylpent-1-en-3-one (2) was obtained in 94% yield with a
different method but with similar yields as those reported by Bartoli et al. [12][13]; the
(E)/(Z)-isomer mixture (76 :24) was separated by column chromatography. The 5-
methyl-1-phenylhex-1-en-3-one (8) was synthesized by an aldol condensation accord-
ing to an old procedure reported by Metayer [15]; we now established the (E)/(Z)
isomer ratio (98 :2) and recorded the spectral data.
The 5,7-dimethyl-1-phenyloct-1-en-3-one (7) was also obtained as an (E)/(Z)-
isomer mixture (95 :5), the isomers could be enriched by column chromatography and
were identified by spectral analyses.
Both isomers (E)- and (Z)-7 gave the same mass spectra. The 1H-NMR spectrum of (E)-7 (CDCl3) showed
3
an AB pattern at d 7.50 and 6.72 with J(AB) ˆ 16.2 Hz for the olefinic H-atoms. The four H-atoms at C(4) and

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Helvetica Chimica Acta Vol. 87 (2004)
Table 1. a,b-Conjugated Enones Synthesized by Aldol Condensation Reactions with Benzaldehyde
Starting materiala)
Products
(E)
[%]
(Z)
[%]
Yield
[%]b)
MeCH2COCH2Me
2, (2E)/(2Z)-PhCHˆC(Me)COEt
76 [1][13] 24 [1] 94
Me2CHCH2CH(Me)CH2COMe [14] 7, (7E)/(7Z)-PhCHˆCHCOCH2CH(Me)- 95
5
85
CH2CH(Me)2
(Me)2CHCH2COMe
8, (8E)/(8Z)-PhCHˆCHCOCH2CH(Me)2 98
2
75
[15]
a) All starting materials were commercially available or were prepared by conventional methods. b) Yields of
products isolated by column chromatography.
C(6) are all diastereotopic due to the stereogenic center C(5). One H-atom signal at d 2.60 (HaÀC(4)) is a dd
2
3
2
3
with J ˆ 15.1 and J ˆ 5.7 Hz and another one at d 2.40 (HbÀC(4)) is also a dd with J ˆ 15.1 and J ˆ 8.1 Hz.
Similarly HaÀC(6) is a ddd (2J ˆ 12.5, J ˆ 6.3, 6.0 Hz) at d 1.17 and HbÀC(6) is also a ddd (2J ˆ 12.5, J ˆ 6.1,
3
3
5.9 Hz) at d 1.08. There are 2 m at d 2.17 (1 H) and 1.65 (1 H).
We compared the relative stabilities of s-cis/s-trans conformations of both (E)- and
(Z)-enones 1, 2, 7, and 8 as well as of 6 using geometry-optimization studies which
yielded Etotal values. The latter were calculated by molecular mechanics with the
program Desktop Molecular Modeller on a PC-windows platform (Table 2) and
furnished a tool to rationalize the product distribution of the catalytic reaction of these
enones with DMDM.
Table 2. Calculated Relative Stabilities of Conformers of the Available and Synthesized Enones
Enone
Relative stabilitiesa)
1
2
6
7
8
(E)-1; s-cis > (E)-1; s-trans
(E)-2; s-cis > (E)-2; s-trans > (Z)-2b)
6; s-cis > 6; s-trans
(E)-7; s-cis > (E)-7; s-trans > (Z)-7b)
(E)-8; s-cis > (E)-8; s-trans > (Z)-8b)
a) Based on the calculated DHo values. b) The calculated enone torsion angles (V (C(b)ÀC(a)ÀO) are close to
908 in these cases.
The enones (Z)-2, 6, (E)-7, (Z)-7, and (E)-8) were treated with DMDM in the
presence of [Cu(acac)2] as catalyst (Scheme 2).
The (Z)-enones (Z)-2 and (Z)-7, and enone 6 (with an additional Me substituent at
C(2) ˆ C(b)) did not give any dihydrofuran derivatives, as expected from the
prerequisite of both termini being closest to each other (C(1) and C(5) in the
transition state of Scheme 1) for an electrocyclic 1,5-ring closure reaction [1]; instead

Helvetica Chimica Acta Vol. 87 (2004)
411
dioxole derivatives 9 11, respectively, were formed (Scheme 2,a) under mild
conditions.
To the contrary and in accordance with our rationalization from Table 2, the enones
(E)-7 and (E)-8, being mainly present as s-cis conformers, yielded dihydrofuran
derivatives 12 and 14, respectively, via conjugated-carbonyl ylides, besides some
furofuran derivatives 13 and 15/16, respectively (Scheme 2,b). Thus, these two enones
(E)-7 and (E)-8 having only one alkyl group of long to medium length could also
prevent to some extent the subsequent reaction step as compared to the behavior of
benzalacetone, i.e., furofuran formation is also very sensitive to steric effects. This [3 ‡
2] cycloaddition reaction might also progress via an endo-approach mechanism
(Figure).
Figure. endo Approach
Conclusions. A recent report [16] describes a high-pressure-promoted [4 ‡ 2]
cycloaddition of enol ethers with 3-aryl-2-cyanoprop-2-enoates. Under our conditions
Scheme 2. Reactions of (Z)-2, 6, (E)-7, (Z)-7, and (E)-8 with Dimethyl Diazomalonate

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Scheme 2 (cont.)
and with the proper choice of the starting enones analog, the [3 ‡ 2] cycloaddition
reaction to yield furofurans can easily be achieved without the need of pressure [17].
The obtained furofuran derivatives are promising starting compounds for further
syntheses. This ring structure is an important motif in several compounds acting on the
central nervous system. They may be easily hydrolyzed or alcoholyzed under acidic
conditions to yield corresponding open acetals or carbonyl compounds. Even under our
chromatographic conditions, these furofuran derivatives may easily add water to the
enol CˆCbond ( 12 ! 13 or 14 ! 15) and then may loose MeOH to give corresponding
g-lactone (15 ! 16, see Scheme 2,b).

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413
Experimental Part
General. Dimethyl diazomalonate (DMDM) was prepared according to literature procedures. CC ˆ col-
umn chromatography. IR Spectra: Jasco FT-IR-5300 apparatus. NMR Spectra: Bruker apparatus; at 250 (1H) or
60 MHz (13C); Me4Si as internal standard, d in ppm, J in Hz; at 258. GC/MS: Hewlett-Packard instrument with
HP-1 capillary column (24 m, packed with cross-linked (phenylmethyl)siloxane); column conditions:
isothermal at 1508 for 7 min, then heating to 2808 with 58/min; 0.54 bar He; EI detector; tR in min. MS: VG-
Zapspec double-focusing spectrometer; EI at 70 eV; CI in isobutane.
Enones: General Procedure. Enones 2, 7, and 8 were prepared by aldol condensation reactions [18] between
benzaldehyde and pentano-3-one, 4,6-dimethylheptan-2-one, and 4-methylpentan-2-one, respectively, with
pyrrolidine as an amine catalyst. Results: Table 1.
Reaction of Enones with DMDM: General Procedure. A soln. of 1 equiv. of DMDM in benzene (4 mmol/
1 ml) was added very slowly to a refluxing benzene soln. of 1.5 equiv. of the substrate (2 mmol/1 ml) and
0.007 equiv. of [Cu(acac)2] under N2. Consumption of DMDM was monitored by IR. After the complete
disappearance of the band at 2130 cmÀ1, the mixture was filtered (gravity), and the soln. was passes rapidly
through a short column of neutral aluminium oxide to remove the highly colored impurities and the catalyst.
(E)-2-Methyl-1-phenylpent-1-en-3-one ((E)-2) [1][13]. GC/MS: (E)-2 as the major product (76%). The
oily compound was purified by CC (neutral aluminium oxide, hexane/AcOEt 5 :1); 65% of (E)-2. 1H-NMR
(CDCl3): 7.52 (br. s, PhCH); 7.40 7.14 (m, Ph); 2.83 (q, J ˆ 7.2, CH2(4)); 2.06 (s, MeÀC(2)); 1.14 (t, J ˆ 7.2, Me).
(Z)-2-Methyl-1-phenylpent-1-en-3-one ((Z)-2). GC/MS: (Z)-2 as the minor product (24%). The oily
compound was purified by CC (neutral aluminium oxide, hexane/AcOEt 5 :1): 15% of (Z)-2. 1H-NMR
(CDCl3): 8.08 (br. s, PhCH); 7.40 7.14 (m, Ph); 2.79 (q, J ˆ 7.2, CH2(4)); 2.02 (s, MeÀC(2)); 1.12 (t,J ˆ 7.2,
Me). 13C-NMR (CDCl3): 198.5 (CˆO); 136.2; 135.1; 134.4; 126 128 (Ph); 32.6; 12.1; 18.6. CI-MS: 175 (38,
‡
‡
‡
[M ‡ 1] ), 174 (93, M ), 159 (7), 145 (93), 117 (100), 91 (93), 77 (26), 51 (35). HR-MS: 174.2378 (M ,
‡
C12H15O ; calc.174.2390).
(E)-5,7-Dimethyl-1-phenyloct-1-en-3-one ((E)-7). Yield of (E)-7/(Z)-7 85%. GC/MS: (Z)-7 as the major
product (95%); not isolated in pure form. Data from crude fraction. 1H-NMR (CDCl3): 7.60 7.30 (m, Ph); 7.50
(d, J ˆ 16.2, PhCH); 6.72 (d, J ˆ 16.2, HÀC(2)); 2.60 (dd, J ˆ 15.1, 5.7, CH2(4)); 2.40 (dd, J ˆ 15.1, 8.1, CH2(4));
2.17 (m, HÀC(5)); 1.17 (ddd, J ˆ 12.5, 6.3, 6.0, CH2(6)); 1.08 (ddd, J ˆ 12.5, 6.1, 5.9, CH2(6)); 1.65 (m, HÀC(7));
0.90 (d, J ˆ 6.7, 2 Me); 0.87 (d, J ˆ 6.54, Me(8)). 13C-NMR (CDCl3): 198.2 (CˆO); 142.4 (C(1)); 135.0 126.0
‡
(Ph, C(2)); 48.6; 45.5; 25.8; 22.9; 22.6; 19.2. GC/MS: tR 14.47. EI-MS: 230 (4, M ), 173 (14), 146 (98), 131 (100),
‡
‡
171 (11), 103 (41), 91 (3), 77 (21). HR-MS: 230.3441 (M , C16H22O ; calc. 230.3453).
(Z)-5,7-Dimethyl-1-phenyloct-1-en-3-one ((Z)-7). GC/MS: (Z)-7 as the minor product (5%); not isolated
in pure form. Data from crude fraction. 1H-NMR (CDCl3): 7.60 7.30 (m, Ph); 6.80 (d, J ˆ 12.8, PhCH); 6.16 (d,
J ˆ 12.8, HÀC(2)); 2.40 (dd, J ˆ 15.2, 6.6, CH2(4)); 2.20 (dd, J ˆ 15.2, 8.2, CH2(4)); 2.10 (m, HÀC(5)); 1.60 (m,
‡
HÀC(7)); 0.97 (m, C H(6)); 0.96 0.77 (m, 3 Me). GC/MS: tR 11.25. EI-MS: 230 (9, M ), 173 (13), 146 (74), 131
2
(100), 117 (8), 103 (40), 91 (3), 77 (20).
(E)-5-Methyl-1-phenylhex-1-en-3-one ((E)-8). GC/MS: (E)-8 as the major product (98%); not isolated in
pure form. Data from crude fraction. 1H-NMR (CDCl3): 7.56 (d, J ˆ 16.1, HÀC(1)); 7.40 7.30 (m, Ph); 6.76 (d,
J ˆ 16.3, HÀC(2)); 2.55 (d, J ˆ 7, CH 2); 2.27 (m, C H); 1 (d, J ˆ 6.7, 2 Me). 13C-NMR (CDCl3): 199.1 (CˆO);
‡
143.2; (C(1)); 135.0 126.0 (Ph, C(2)); 50.4; 22.4; 21.8. GC/MS: tR 13.3. EI-MS: 188 (39, M ), 146 (36), 131
‡
‡
(100), 103 (56), 77 (27). HR-MS: 188.2628 (M , C13H16O ; calc. 188.2655).
(Z)-5-Methyl-1-phenylhex-1-en-3-one ((Z)-8). GC/MS: (Z)-8 as the minor product (2%); not isolated in
‡
pure form. Data from crude fraction. GC/MS: tR 11.6 min. EI-MS: 188 (27, M ), 173 (2), 146 (13), 131 (100), 103
(37), 91 (2), 77 (16), 51 (4).
Methyl 2-Ethyl-5-methoxy-2-(1'-methyl-2'-phenylethenyl)-1,3-dioxole-4-carboxylate (9). GC/MS: 9 as the
main product (85%). The compound was purified by CC (neutral aluminium oxide, hexane/AcOEt 5 :1): 68%
of 9. 1H-NMR (CDCl3): 7.25 6.99 (m, Ph); 6.43 (br. s, HÀC(1)); 3.80 (s, COOMe); 3.79 (s, MeO); 2.16 (d, J ˆ
1.8, MeÀC(2')); 1.74 1.65 (m, MeCH2); 0.91 (t, J ˆ 7.3, MeCH2). 13C-NMR (CDCl3): 160 (CO2Me); 142.1
(C(5)); 137.2 (PhÀC(2')); 129.2, 128.5, 126.8, 126.5 (Ph); 129.0 (C(2')); 106.2 (C(2)); 95.1 (C(4)); 53.2 (CO2Me);
‡
52.8 (MeO); 26.1 (MeCH2); 20.7 (MeÀC(1')); 9.9 (MeCH2). GC/MS: tR 18.5. EI-MS: 304 (2, M ), 275 (32), 243
‡
(25), 185 (100), 171 (22), 157 (27), 141 (26), 128 (85), 115 (60), 91 (10), 77 (10), 59 (60). HR-MS: 304.3362 (M ,
‡
C17H20O5 ; calc. 304.3377).
Methyl 5-Methoxy-2-methyl-2-(2'-methylcyclopent-1-en-1-yl)-1,3-dioxole-4-carboxylate (10). GC/MS: 10 as
the main product (86%). The oily compound was purified by CC (neutral aluminium oxide, CCl4/AcOEt 10 :1):
1
72% of 10. H-NMR (CDCl3): 3.69 (s, COOMe); 3.42 (s, MeO); 2.18 (s, MeÀC(2)); 2.45 2.61 (m, other H);

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Helvetica Chimica Acta Vol. 87 (2004)
1.73 (s, MeÀC(2')). 13C-NMR (CDCl3): 161 (COOMe); 158.2 (C(5)); 144.5 (C(1')); 127 (C(2')); 85.6 (C(2));
82.3 (C(4)); 51.1 (COOMe); 43.4 (MeO); 32.4 (C(3')); 25.5 (MeÀC(2)); 21.7 (C(5')); 12.9 (MeÀC(2')); 7.67
‡
(C(4')). GC/MS: tR 13.96. CI-MS: 255 (5, [M ‡ 1] ), 224 (5), 195 (17), 108 (75), 145 (100), 81 (56), 59 (15). HR-
‡
‡
MS: 254.2772 (M , C13H15O5 ; calc. 254.2790).
Methyl-2-(2,4-Dimethylpentyl)-5-methoxy-2-(2'-phenylethenyl)-1,3-dioxole-4-carboxylate (11). GC/MS: 11
present to 4% in the reaction mixture; not isolated in pure form. Data from crude fraction. GC/MS: tR 18.5. EI-
‡
MS: 360 (6, M ), 300 (3), 276 (33), 232 (35), 189 (80), 161 (100), 115 (31), 102 (64), 91 (14), 76 (8), 59 (28).
Dimethyl 5-(2,4-Dimethylpentyl)-2,3-dihydro-3-phenylfuran-2,2-dicarboxylate (12). GC/MS: 12 as the main
product (70%). The compound was purified by CC (silica gel; hexane/AcOEt 10 :1): 52% of 12. 1H-NMR
(CDCl3): 7.27 7.20 (m, Ph); 5.30 (d, J ˆ 3, HÀC(3)); 4.70 (dd, J ˆ 3, HÀC(4)); 3.14 (s, 2 MeO); 2.20 (d, J ˆ 7.2,
CH2ÀC(5)); 1.90 (m, HÀC(4')); 1.70 (m, HÀC(2')); 1.20 (m, CH2); 1.10 (d, J ˆ 6.7, MeÀC(2')); 1.00 (d, J ˆ 6.6,
2 Me). 13C-NMR (CDCl3): 168.5; 168.1; 161.7; 142.5; 127.6; 126.2; 124.5; 96.2; 91.3; 45.8; 45.2; 27.3; 23.3; 22.7;
‡
20.3. GC/MS: tR 21.27. EI-MS: 360 (9, M ), 302 (26), 269 (32), 229 (100), 214 (51), 212 (85), 184 (33), 157 (31),
‡
‡
128 (39), 115 (18). HR-MS: 360.4427 (M , C21H28O5 ; calc. 360.4440).
6ab-(2',4'-Dimethylpentyl-2,3,3ab,4,5,6a-hexahydro-5-hydroxy-5-methoxy-3-phenylfuro[2,3-b]furan-2,2,4-
tricarboxylate (13). GC/MS: 13 as the minor product (20%). This compound was purified by CC (silica gel;
hexane/AcOEt 10 :1): 12% of 13. 1H-NMR (CDCl3): 7.39 7.27 (m, Ph); 4.52 (br. s, HÀC(3)); 4.42 (D2O
exchange); 3.85 (s, COOMe); 3.75 (s, COOMe); 3.83 (s, COOMe); 3.18 3.10 (m, other H); 3.10 (s, MeO); 1.39
(d, J ˆ 7.2, CH2ÀC(6a)); 1.23 (m, C H); 1.08 (m, 2 CH); 1.09 (s, 3 Me). 13C-NMR (CDCl3): 175.3; 172.1; 130.8;
2
128.7; 127.9; 125.2; 107.5; 93.2; 90.1; 51.2; 50.8; 49.9; 47.2; 44.9; 43.9; 42.0; 34.0; 29.3; 26.2; 22.6; 21.0. GC/MS: tR
‡
26.7. EI-MS: 508 (5, M ), 433 (13), 385 (100), 341 (13), 305 (31), 274 (20), 242 (28), 231 (20), 204 (15), 157 (26),
‡
‡
121 (13), 59 (8). HR-MS: 508.548 (M , C26H36O10 ; calc. 508.558).
Dimethyl 2,3-Dihydro-5-(2-methylpropyl)-3-phenylfuran-2,2-dicarboxylate (14). GC/MS: 14 as the major
product (65%). The compound was purified by CC (silica gel, CCl4/acetone 10 :1): 55% of 14. 1H-NMR
(CDCl3): 7.40 7.30 (m, Ph); 5.02 (d, J ˆ 2.6, HÀC(3)); 4.80 (dt, J ˆ 2.6, 1.1, HÀC(4)); 3.84 (s, COOMe); 3.80 (s,
COOMe); 2.08 2.03 (m, CH2CH); 0.94 (d, J ˆ 6.57, 2 Me). 13C-NMR: 173.2; 171.4; 159.3; 145.1; 129.2; 127.5;
‡
123.7; 96.5; 91.8; 52.1; 50.7; 42.5; 23.0; 18.3. GC/MS: tR 13.7. EI-MS: 318 (31, M ), 303 (100), 259 (10), 243 (14),
‡
‡
221 (9), 189 (13), 155 (6), 129 (10), 115 (15), 83 (9), 69 (60), 59 (6). HR-MS: 318.3632 (M , C26H36O10 ; calc.
318.3643).
Trimethyl 2,3,3ab,4,5,6a-Hexahydro-5-hydroxy-5-methoxy-6ab-(2'-methylpropyl)-3-phenylfuro[2,3-b]fur-
an-2,2,4-tricarboxylate (15) and Trimethyl 2,3,3ab,4,5,6a-Hexahydro-6ab-(2'-methylpropyl)-5-oxo-3-phenyl
furo[2,3-b]furan-2,2,4-tricarboxylate (16). GC/MS: 23% of 15 and 4% of 16. These compounds were purified
by CC (silica gel, CCl4/acetone 10 :1). 17% of 15 and a minor amount of 16.
Data of 15: 1H-NMR (CDCl3): 7.50 7.26 (m, Ph); 5.70 (d, J ˆ 9.3, HÀC(4)); 4.88 (d, J ˆ 9.3, HÀC(3)); 4.18
(distorted t, J ˆ 9.4, HÀC(3a)); 3.86 (s, COOMe); 2.20 (D2O exchange, OHÀC(5)); 1.57 (m, CH2CH); 0.60 (d,
J ˆ 6.2, Me); 0.34 (d, J ˆ 6.2, Me). 13C-NMR (CDCl3): 174.0; 173.2; 172.5; 150.3; 128.4; 125.6; 106.3; 93.7; 89.1;
‡
50.5; 50.3; 49.9; 47.2; 44.4; 41.8; 34.0; 29.2; 22.9; 18.5. GC/MS: tR 20.5. EI-MS: 466 (2, M ), 365 (2), 339 (2), 318
(7), 275 (9), 5.3 (26), 221 (73), 204 (98), 189 (100), 162(88), 147 (39), 115 (36), 85 (40), 59 (5).
Data of 16: 1H-NMR (CDCl3): 7.40 7.25 (m, Ph); 5.29 (br. s, HÀC(3)); 4.56 (m, HÀC(3)); 3.95 (m,
HÀC(3a)); 3.82 (s, COOMe); 3.80 (s, COOMe); 3.56 (s, COOMe); 1.24 (m, CH2CH); 0.75 (d, J ˆ 0.68, Me);
‡
0.22 (d, J ˆ 6.7, Me). GC/MS: tR 19.2. EI-MS: 434 (1, M ), 376 (1), 356 (3), 319 (2), 279 (16), 167 (37), 149
(100), 113 (8), 85 (5), 57 (17).
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Received August 11,2003