Chemoselective and regiospecific synthesis of iminospiro-γ-lactones from maleic anhydride or citraconic anhydride and alkyl isocyanides with dialkyl acetylenedicarboxylates

Article abstract of DOI:10.1002/hlca.200900292

Isocyanides, dialkyl acetylenedicarboxylates (=dialkyl but-2-ynedioates), and anhydrides such as maleic anhydride (=furan-2,3-dione) or citraconic anhydride (=3-methylfuran-2,3-dione) react in one pot to afford novel iminospiro-γ-lactones in fairly good y

Full text of DOI:10.1002/hlca.200900292

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Chemoselective and Regiospecific Synthesis of Iminospiro-g-lactones from
Maleic Anhydride or Citraconic Anhydride and Alkyl Isocyanides with
Dialkyl Acetylenedicarboxylates
by Mohammad Bayat*, Hossien Imanieh, and Hossien Abbasi
Chemistry Department, Imam Khomeini International University, Qazvin, Iran
(phone: þ 98-281-3780040; fax: þ 98-281-3780040; e-mail: bayat_mo@yahoo.com)
Isocyanides, dialkyl acetylenedicarboxylates (¼dialkyl but-2-ynedioates), and anhydrides such as
maleic anhydride (¼ furan-2,3-dione) or citraconic anhydride (¼ 3-methylfuran-2,3-dione) react in one
pot to afford novel iminospiro-g-lactones in fairly good yields at room temperature (Schemes 1 and 3).
Introduction. – Multicomponent reactions (MCRs) have emerged as a highly
valuable synthetic tool in the context of modern drug discovery [1][2]. The atom-
economical and convergent character, the simplicity of a one-pot procedure, the
possible structural variations, the attainable complexity of the molecules, as well as the
huge number of accessible compounds are among the described advantages of MCRs
[3 – 6]. Thus, they are perfectly amenable to automation for combinatorial synthesis
[7]. Amongst the known multicomponent reactions, isocyanide-based MCRs such as
the versatile Ugi and Passerini reactions are especially valuable [8 – 11].
Iminospiro-g-lactones have been shown to be an important class of molecules
owing to their interesting structures and biological activities [12]. The unique structural
nature of these spirocyclic compounds has attracted the interest of many synthetic
organic chemists [13][14]. The lactone moiety is also present in many natural products,
especially insect pheromones, antifungal substances, and flavor components that occur
in the essential oils of plants. Recently, spiro-g-lactones attained great interest because
of their effect as aldosterone inhibitors [15].
Although the trapping of the 1:1 intermediate formed between dialkyl acetylene-
dicarboxylates (¼dialkyl but-2-ynedioates) and isocyanides with aldehydes [16],
aromatic anhydrides [17], 1,3-diones [18], benzoyl chlorides [19], benzoyl cyanides
[20], and carboxylic acids [21] has been studied in detail by a number of research groups
[5], trapping of the initial 1:1 intermediate formed with citraconic anhydride (¼ 3-
methylfuran-2,5-dione) or maleic anhydride (¼ furan-2,5-dione) has not been reported.
We report here on the MCR of alkyl isocyanides 1 and dialkyl acetylenedicarboxylates
2 in the presence of maleic anhydride (3a) or citraconic anhydride (3b) as trapping
agents for the reactive zwitterionic intermediate. This three-component-condensation
reaction produces highly functionalized iminospiro-g-lactones 4 in fairly good yields
(Scheme 1).
Results and Discussion. – The reaction of alkyl isocyanides 1 with electron-deficient
acetylenic esters 2 in the presence of maleic anhydride (3a) or citraconic anhydride
ꢀ 2010 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Scheme 1
(3b) proceeded spontaneously at room temperature in anhydrous CH2Cl2 and was
completed after 1 d to afford corresponding dialkyl 2-(alkylimino)-7-oxo-1,6-dioxa-
spiro[4.4]nona-3,8-diene-3,4-dicarboxylates or dialkyl 8-methyl variants 4a – 4l in
1
moderate to good yields (50 – 98%). H- and 13C-NMR spectra of the crude products
clearly indicated the formation of the iminospiro-g-lactones. The structures of the
1
products were deduced from their IR and H- and 13C-NMR spectra, and elemental
analyses. The mass spectra of compounds 4a – 4l displayed molecular-ion peaks at the
calculated m/z values. Initial fragmentations involved cleavage of the side chains or
their complete loss and scission of the spirolactone system.
1
The H-NMR spectrum of 4a consisted of a m for the cyclohexyl group (d 1.15 –
1.91) and two single sharp lines for the MeO groups (d 3.67 and 3.82). A m was
observed for the CHꢀN group (d 3.57), and two d (d 6.38 and 7.19, 3J ¼ 5.5 Hz) for two
olefinic H-atoms, in agreement with the suggested structure. The 1H-decoupled
13C-NMR spectrum of 4a showed 17 sharp signals in agreement with the proposed
structure. The characteristic 13C-NMR signal of the spiro atom C(5) was discernible (d
111.40), as well as two signals for two olefinic CH groups (d 123.92 and 149.98) and two
signals for the other two olefinic C-atoms (d 126.27 and 147.50) (see also Exper. Part).
The structural assignment of 4a made on the basis of the 1H- and 13C-NMR spectra, was
supported by its IR spectrum which showed strong absorption at 1835, 1737, 1690, and
1632 cmꢀ1 due to the C¼O and C¼N groups.
The 1H- and 13C-NMR spectra of 4b – 4l were similar to those of 4a, except for the
signals of the alkyl, ester, and alkyl isocyanide moieties (see also Exper. Part).
The regiospecificity observed in the reaction with citraconic anhydride is
attributable to the higher electrophilicity of the C(5)¼O vs. the C(2)¼O group of
this anhydride. The structure of the regioisomers 4d – 4j was confirmed by NOE
experiments. For compound 4h, irradiation of MeꢀC(8) (d 1.93) led to a negative NOE
effect for the Me3C (d 1.39), and its intensity was reduced by ca. 76%. Irradiation of
MeꢀC(8) (d 1.93) had no effect on Me3C (d 1.51). Irradiation of HꢀC(9) (d 5.98) led

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to an increase in the signal intensity by ca. 38% for MeꢀC(8) (d 1.93), and by ca. 9%
for Me3C (d 1.39).
A plausible mechanism for the formation of spirolactones 4 is shown in Scheme 2.
On the basis of the well-established chemistry of isocyanides [8][10][22 – 24], it is
reasonable to assume that compounds 4 result from initial addition of alkyl isocyanides
1 to the acetylenic ester to form intermediate 5, which adds to the C¼O moiety of the
anhydride in a [3 þ 2] fashion or by a stepwise process involving nucleophilic addition
of 5 to the reactive C¼O group of the anhydrides to form nitrilium ions 6, and
cyclization to spirolactones 4.
Scheme 2
Similar results were obtained with other anhydrides yielding the iminospiro-g-
lactones 7a and 7b. Succinic anhydride (¼ 3,4-dihydrofuran-2,5-dione), on treatment
with dimethyl or diethyl acetylenedicarboxylate and cyclohexyl isocyanide in CH2Cl2 at
room temperature afforded the iminospiro-g-lactones 7a and 7b in 70% yield
(Scheme 3).
Scheme 3
In conclusion, the three-component reaction of alkyl isocyanides with electron-
deficient acetylenic esters in the presence of maleic anhydride or citraconic anhydride
provides a simple entry into the synthesis of polyfunctionalized iminospiro-g-lactones
of potential synthetic interest. The present procedure has the advantage that the
reaction runs under neutral conditions and, moreover, the substances can be mixed
without any further activation or modification.
Experimental Part
General. Dialkyl acetylenedicarboxylates, alkyl isocyanides, and other reagents and solvents used in
this work were obtained from Fluka (Buchs, Switzerland) and used without further purification. M.p.:
Gallenkamp-electrothermal-9100 apparatus; not corrected. IR Spectra (KBr): Bruker-Tensor-27
spectrometer; ˜n in cmꢀ1. NMR Spectra: Bruker-DRX-300-Avance instrument, CDCl3 solns.; d in ppm

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rel. to Me4Si as internal standard, J in Hz. MS: Shimadzu-QP-GC-100-EX mass spectrometer; at 70 eV;
in m/z (rel. %). Elemental analyses: Heraeus-CHN-O-Rapid analyzer. These results agreed favorably
with the calculated values.
Compounds 4: General Procedure. To a stirred soln. of maleic anhydride (0.098 g, 1 mmol) and
dimethyl but-2-ynedioate (0.142 g, 1 mmol) in CH2Cl2 (10 ml) was added cyclohexyl isocyanide (0.109 g,
1 mmol) in CH2Cl2 (2 ml) at r.t. over 10 min via a syringe. The mixture was stirred at r.t. for 24 h. The
solvent was evaporated and the residue purified by column chromatography (silica gel 60 (70 – 230 mesh;
Merck), hexane/AcOEt 4 :1): product 4.
Dimethyl 2-(Cyclohexylimino)-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate (4a).
Yield 0.342 g (98%). Yellow powder. M.p. 146 – 1488. IR: 1835, 1737, 1690 (C¼O), 1632 (C¼N).
1H-NMR: 1.15 – 1.91 (m, 5 CH2); 3.57 (m, CHN); 3.67, 3.82 (2s, 2 MeO); 6.38 (d, 3J ¼ 5.5, HꢀC(8)); 7.19
3
(d, J ¼ 5.5, HꢀC(9)). 13C-NMR: 24.48, 25.67, 25.52, 32.63, 33.06 (5 CH2); 53.42, 53.49 (2 MeO); 57.48
(CHN); 111.40 (C(5)); 123.92 (C(8)); 126.27 (C(3)); 147.50 (C(4)); 149.98 (C(9)); 150.48 (C(2)); 158.10,
159.21, 168.12 (3 C¼O). EI-MS: 349 (13, Mþ), 317 (19), 308 (77), 277 (20), 267 (100), 252 (85), 193 (19),
151 (13). Anal. calc. for C17H19NO7 (349.33): C 58.45, H 5.48, N 4.01; found: C 58.6, H 5.6, N 4.1.
Diethyl 2-(Cyclohexylimino)-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate (4b). Yield
1
3
0.263 g (70%). Brown oil. IR: 1808, 1737, 1684 (C¼O), 1631 (C¼N). H-NMR: 1.37, 1.43 (2t, J ¼ 6.9,
2 Me); 1.20 – 1.91 (m, 5 CH2); 3.65 (m, CHN); 4.21, 4.40 (2q, 3J ¼ 6.9, 2 CH2O); 6.38 (d, 3J ¼ 5.5,
HꢀC(8)); 7.19 (d, J ¼ 5.5, HꢀC(9)). 13C-NMR: 13.96, 14.30 (2 MeCH2O); 24.45, 25.16, 25.52, 33.66,
3
33.09 (5 CH2); 62.34, 62.76 (2 CH2O); 57.25 (CHN); 111.14 (C(5)); 123.90 (C(8)); 126.19 (C(3)); 147.70
(C(4)); 150.08 (C(9)); 150.43 (C(2)); 158.97, 160.77, 168.44 (3 C¼O). EI-MS: 185 (14), 184 (90), 157
(27), 86 (100), 84 (60), 50 (29), 47 (90). Anal. calc. for C19H23NO7 (377.40): C 60.47, H 6.14, N 3.71; found:
C 60.6, H 5.9, N 3.6.
Diethyl 2-[(tert-Butyl)imino]-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate (4c). Yield
0.263 g (75%). Brown oil. IR: 1818, 1714, 1685 (C¼O), 1620 (C¼N). 1H-NMR (CDCl3): 1.28, 1.33 (2t,
3J ¼ 7.2, 2 Me); 1.29 (s, t-Bu); 4.21, 4.40 (2q, 3J ¼ 7.2, 2 CH2O); 6.38 (d, 3J ¼ 5.6, HꢀC(8)); 7.19 (d, 3J ¼ 5.6,
HꢀC(9)). 13C-NMR: 12.36, 13.57 (2 MeCH2O); 29.96 (Me3C); 56.04 (Me3C); 61.55, 61.61 (2 CH2O);
111.10 (C(5)); 123.93 (C(8)); 126.22 (C(3)); 147.66 (C(4)); 148.68 (C(2)); 150.01 (C(9)); 159.54, 161.42,
168.25 (3 C¼O). EI-MS: 351 (34, Mþ), 296 (97), 250 (43), 240 (37), 194 (100), 158 (19), 98 (25). Anal.
calc. for C17H21NO7 (351.35): C 58.11, H 6.02, N 3.99; found: C 58.3, H 6.1, N 4.1.
Di(tert-butyl) 2-[(tert-Butyl)imino]-8-methyl-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarb-
oxylate (4d). Yield 0.257 g (61%). Pale brown powder. M.p. 132 – 1348. IR: 1812, 1715, 1685 (C¼O),
1618 (C¼N). 1H-NMR: 1.24, 1.40, 1.52 (3s, 3 t-Bu); 1.93 (d, 4J ¼ 1.5, MeꢀC(8)); 6.01 (q, 4J ¼ 1.5,
HꢀC(9)). 13C-NMR: 13.71 (Me); 27.73, 28.10, 29.56 (3 Me3C); 55.94 (Me3CN); 84.17, 84.38 (2 Me3CO);
111.46 (C(5)); 119.32, 162.18 (C(8), C(9)); 134.65 (C(3)); 141.48 (C(4)); 148.62 (C(2)); 158.21, 160.05,
168.71 (3 C¼O). EI-MS: 421 (1, Mþ), 406 (37), 295 (32), 294 (100), 273 (26), 264 (28), 208 (20), 58 (75),
41 (23). Anal. calc. for C22H31NO7 (421.48): C 62.69, H 7.41, N 3.32; found: C 62.6, H 7.5, N 3.2.
Di(tert-butyl) 2-[(tert-Butyl)imino]-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate
1
(4e). Yield 0.264 g (65%). Pale yellow oil. IR: 1806, 1731, 1694 (C¼O), 1643 (C¼N). H-NMR: 1.35,
1.42, 1.47 (3s, 3 t-Bu); 6.38 (d, 3J ¼ 5.5, HꢀC(8)); 7.20 (d, 3J ¼ 5.5, HꢀC(9)). 13C-NMR: 27.95, 28.02, 28.65
(3 Me3C); 56.74 (Me3CN); 84.05, 85.92 (2 Me3CO); 111.41 (C(5)); 123.21 (C(8)); 125.82 (C(3)); 148.17
(C(4)); 149.28 (C(2)); 150.62 (C(9)); 159.12, 160.81, 167.67 (3 C¼O). EI-MS: 407 (2, Mþ), 240 (8), 198
(27), 166 (23), 155 (16), 135 (52), 109 (12), 86 (21), 84 (100), 58 (98), 41 (83). Anal. calc. for C21H29NO7
(407.46): C 61.90, H 7.17, N 3.44; found: C 61.8, H 7.3, N 3.3.
Diethyl 2-[(Cyclohexyl)imino]-8-methyl-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate
(4f). Yield 0.270 g (69%). Yellow powder. M.p. 146 – 1488. IR: 1792, 1752, 1731 (C¼O), 1625 (C¼N).
1H-NMR: 1.25, 1.35 (2t, 3J ¼ 7.2, 2 Me); 1.30 – 1.81 (m, 5 CH2); 1.98 (d, 4J ¼ 1.5, MeꢀC(8)); 3.67 (m,
3
CHN); 4.26, 4.39 (2q, J ¼ 7.2, 2 CH2O); 6.06 (q, 4J ¼ 1.5, HꢀC(9)). 13C-NMR: 12.21 (Me); 17.09, 17.50
(2 MeCH2); 25.61, 26.20, 26.72, 32.33, 34.10 (5 CH2); 57.25 (CHN); 62.19, 62.36 (2 CH2O); 110.49 (C(5));
119.78, 161.50 (C(8), C(9)); 135.77 (C(3)); 140.80 (C(4)); 150.76 (C(2)); 158.99, 160.58, 168.60 (3 C¼O).
EI-MS: 391 (19, Mþ), 345 (30), 295 (37), 290 (15), 266 (26), 219 (100), 192 (15), 162 (12), 148 (15). Anal.
calc. for C20H25NO7 (391.41): C 61.37, H 6.44, N 3.58; found: C 61.2, H 6.5, N 3.7.

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Diethyl 2-[(tert-Butyl)imino]-8-methyl-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate
1
(4g). Yield 0.274 g (75%). Pale brown oil. IR: 1814, 1731, 1689 (C¼O), 1637 (C¼N). H-NMR: 1.27
(s, t-Bu); 1.22, 1.34 (2t, 3J ¼ 6.6, 2 MeCH2); 1.95 (d, 4J ¼ 1.5, MeꢀC(8)); 4.20, 4.37 (2q, 3J ¼ 6.6, 2 CH2O);
6.04 (q, 4J ¼ 1.5, HꢀC(9)). 13C-NMR: 14.01, 14.07 (2 MeCH2); 12.96 (Me); 29.55 (Me3C); 55.84
(Me3CN); 62.07, 62.54 (2 CH2O); 111.13 (C(5)); 119.67, 161.59 (C(8), C(9)); 134.56 (C(3)); 141.60
(C(4)); 148.30 (C(2)); 159.01, 160.84, 168.37 (3 C¼O). EI-MS: 365 (5, Mþ), 352 (35), 350 (100), 304
(38), 27 (18), 258 (19), 208 (57), 163 (33), 149 (37), 113 (40), 96 (47), 68 (70). Anal. calc. for C18H23NO7
(365.38): C 59.17, H 6.34, N 3.83; found: C 59.3, H 6.2, N 3.7.
Di(tert-butyl) 2-(Cyclohexylimino)-8-methyl-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarbox-
ylate (4h). Yield 0.268 g (60%). Yellow powder. M.p. 158 – 1608. IR: 1820, 1736, 1697 (C¼O), 1640
1
4
(C¼N). H-NMR 1.39, 1.51 (2s, 2 t-Bu); 1.46 – 1.81 (m, 5 CH2); 1.93 (d, J ¼ 1.8, MeꢀC(8)); 3.35 (m,
CHN); 5.98 (q, 4J ¼ 1.8, HꢀC(9)). 13C-NMR: 13.32 (Me); 27.30, 27.82 (2 Me3C); 27.72, 27.79, 28.01, 32.75,
32.84 (5 CH2); 56.42 (CHN); 83.76, 84.02 (2 Me3CO); 111.07 (C(5)); 119.41, 162.12 (C(8), C(9)); 135.85
(C(3)); 140.20 (C(4)); 150.61 (C(2)); 158.22, 159.78, 168.61 (3 C¼O). EI-MS: 336 (45), 335 (100), 318
(60), 290 (37), 237 (24), 148 (26), 98 (21), 58 (76). Anal. calc. for C24H33NO7 (447.52): C 64.41, H 7.43, N
3.13; found: C 64.3, H 7.3, N 3.1.
Dimethyl 2-(Cyclohexylimino)-8-methyl-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate
(4i). Yield 0.344 g (95%). Pale yellow oil. IR: 1828, 1741, 1687 (C¼O), 1645 (C¼N). 1H-NMR:
1.36 – 1.81 (m, 5 CH2); 1.97 (d, 4J ¼ 1.5, MeꢀC(8)); 3.66 (m, NCH); 3.74, 3.92 (2s, 2 MeO); 6.06 (q, 4J ¼
1.5, HꢀC(9)). 13C-NMR: 13.10 (Me); 25.01, 25.17, 25.21, 32.41, 32.74 (5 CH2); 57.42 (CHN); 50.61, 50.86
(2 MeO); 110.91 (C(5)); 119.82, 161.35 (C(8), C(9)); 135.93 (C(3)); 140.24 (C(4)); 150.65 (C(2)); 159.44,
160.97, 168.17 (3 C¼O). EI-MS: 349 (8), 268 (12), 250 (15), 224 (34), 208 (14), 193 (18), 120 (57), 113
(100), 96, (83), 86, (98). Anal calc. for C18H21NO7 (363.36): C 59.50, H 5.83, N 3.85; found: C 59.6, H 5.7,
N 3.7.
Dimethyl 2-(tert-Butylimino)-8-methyl-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate
(4j). Yield 0.317 g (94%). Yellow powder. M.p. 135 – 1378. IR: 1805, 1755, 1687 (C¼O), 1648 (C¼N).
1H-NMR: 1.28 (s, t-Bu); 1.97 (d, 4J ¼ 1.6, MeꢀC(8)); 3.77, 3.92 (2s, 2 MeO); 6.06 (d, 4J ¼ 1.6, HꢀC(9)).
13C-NMR: 12.28 (Me); 29.91 (Me3C); 53.36, 53.44 (2 MeO); 56.03 (Me3CN); 111.30 (C(5)); 119.75,
161.39 (C(8), C(9)); 134.76 (C(3)); 142.01 (C(4)); 148.39 (C(2)); 159.47, 161.21, 168.34 (3 C¼O). EI-MS:
365 (5, Mþ), 322 (100), 296 (11), 258 (12), 208 (23), 179 (23). Anal. calc. for C16H19NO7 (337.33): C 59.97,
H 5.68, N 4.15; found: C 60.1, H 5.8, N 4.1.
Dimethyl 2-[(tert-Butyl)imino]-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate (4k).
1
Yield 0.310 g (96%). Dark brown oil. IR: 1828, 1720, 1695 (C¼O), 1620 (C¼N). H-NMR: 1.27 (s, t-
Bu); 3.82, 3.92 (2s, 2 MeO); 6.38 (d, 3J ¼ 5.5, HꢀC(8)); 7.18 (d, 3J ¼ 5.5, HꢀC(9)). 13C-NMR: 30.06
(Me3C); 53.47, 53.77 (2 MeO); 56.03 (Me3CN); 110.45 (C(5)); 123.94 (C(8)); 126.21 (C(3)); 147.67
(C(4)); 148.07 (C(2)); 149.95 (C(9)); 159.51, 161.47, 168.12 (3 C¼O). EI-MS: 365 (5, Mþ), 322 (100), 296
(11), 258 (12), 208 (23), 179 (23). Anal. calc. for C15H17NO7 (323.30): C 55.73, H 5.30, N 4.33; found: C
55.6, H 5.4, N 4.2.
Di(tert-butyl) 2-(Cyclohexylimino)-7-oxo-1,6-dioxaspiro[4.4]nona-3,8-diene-3,4-dicarboxylate (4l).
Yield 0.216 g (50%). Dark brown powder. M.p. 144 – 1468. IR: 1792, 1752, 1731 (C¼O), 1649 (C¼N).
1H-NMR: 1.40, 1.48 (2s, 2 t-Bu); 1.69 – 1.89 (m, 5 CH2); 3.73 (m, CHN); 6.38 (d, 3J ¼ 5.5, HꢀC(8)); 7.18
(d, 3J ¼ 5.5, HꢀC(9)). 13C-NMR: 27.95, 28.65 (2 Me3CO); 25.16, 25.22, 25.72, 32.75, 32.49 (5 CH2); 57.11
(CHN); 82.57, 84.12 (2 Me3CO); 111.14 (C(5)); 123.94 (C(8)); 127.19 (C(3)); 148.70 (C(4)); 150.08
(C(9)); 150.59 (C(2)); 158.59, 160.77, 168.44 (3 C¼O). EI-MS: 296 (27), 251 (15), 240 (12), 194 (28), 166
(19), 125 (24), 111 (40), 97 (41), 71 (45), 58 (100). Anal. calc. for C21H31NO7 (433.50): C 63.73, H 7.21, N
3.23; found: C 63.8, H 6.9, N 3.1.
Dimethyl 2-(Cyclohexylimino)-7-oxo-1,6-dioxaspiro[4.4]non-3-ene-3,4-dicarboxylate (7a). Yield
0.245 g (70%). Yellow solid. M.p. 115 – 1178. IR: 1825, 1735, 1687 (C¼O), 1630 (C¼N).1H-NMR:
1.20 – 1.91 (m, 5 CH2); 2.56 – 2.67 (m, CH2(8)); 2.81 – 2.90 (m, CH2(9)); 3.65 (m, CHN); 3.87, 3.89 (2s,
2 MeO). 13C-NMR: 24.50, 25.51, 25.54, 32.59, 33.24 (5 CH2); 33.63, 38.70 (2 CH2); 50.51, 53.71 (2 MeO);
68.17 (CHN); 109.10 (C(5)); 128.77, 130.90, 132.40 (C(3), C(4), C(2)); 167.77, 170.89, 173.84 (3 C¼O).
Anal. calc. for C17H21NO7 (351.34): C 58.11, H 6.02, N 3.99; found: C 58.2, H 5.9, N 3.9.

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Diethyl 2-(Cyclohexylimino)-7-oxo-1,6-dioxaspiro[4.4]non-3-ene-3,4-dicarboxylate (7b). Yield
0.269 g (71%). Dark yellow oil. IR: 1830, 1737, 1685 (C¼O), 1634 (C¼N). 1H-NMR: 0.98, 1.03 (2t,
3J ¼ 6.9, 2 Me); 1.16 – 1.85 (m, 5 CH2); 2.41 – 2.52 (m, CH2(8)); 2.82 – 2.96 (m, CH2(9)); 3.62 (m, CHN);
4.15 – 4.40 (2q, 3J ¼ 7.0, 2 MeCH2O). 13C-NMR: 11.16, 14.10 (2 Me); 24.16, 24.28, 25.17, 32.28, 33.39
(5 CH2); 61.94, 62.68 (2 CH2O); 59.46 (CHN); 110.06 (C(5)); 124.12, 128.80, 135.94 (C(3), C(4), C(2));
157.98, 165.18, 170.48 (3 C¼O). Anal. calc. for C19H25NO7 (379.40): C 60.15, H 6.64, N 3.69; found: C
60.3, H 6.5, N 3.6.
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Received August 2, 2009