Synthesis of 2,3-substituted cycloalkanones by ceric ammonium nitrate-promoted oxidative tandem additions of 1-ethoxy-1-[(trimethylsilyl)oxy]cyclopropane to α,β-unsaturated cycloalkenones

Full text of DOI:10.1021/jo960446r

6434
J . Org. Chem. 1996, 61, 6434-6437
Sch em e 1
Syn th esis of 2,3-Su bstitu ted
Cycloa lk a n on es by Cer ic Am m on iu m
Nitr a te-P r om oted Oxid a tive Ta n d em
Ad d ition s of
1-Eth oxy-1-[(Tr im eth ylsilyl)oxy]cyclop r op a n e
to r,â-Un sa tu r a ted Cycloa lk en on es
Anna Belli Paolobelli
Dipartimento di Chimica Universita` di Perugia,
06100 Perugia, Italy
Renzo Ruzziconi*
Dipartimento di Chimica, Universita` della Basilicata,
85100 Potenza, Italy
Received March 5, 1996
Cyclopropanols and alkoxycyclopropanes are easily
oxidized by monoelectronic metal oxidants to generate
â-carbonylalkyl radicals, which have revealed themselves
to be versatile intermediates in carbon-carbon bond
formation reactions owing their ability to attack both
electron-rich and electron-poor alkenes.1-3 In the reac-
tions with alkenes bearing an electron-releasing group,
a new radical is formed, a nucleophilic species, which
undergoes rapid oxidation by the metal to give a highly
functionalized product.2a On the contrary, the attack at
an electron-withdrawing group-substituted alkene gener-
ates a hardly oxidizable electrophilic radical which must
be trapped in some way in order to avoid extensive
polymerization. In this respect, the synthesis reported
by Narasaka and coworkers of 1,6-dicarbonyl compounds
by manganese(III) 2-pyridinecarboxylate [Mn(pic)3]-
promoted addition of [(trialkylsilyl)oxy]cyclopropanes to
R,â-unsaturated ketones, esters, and nitriles is repre-
sentative. In this case, the electrophilic adduct radical
was trapped by hydrogen abstraction from added tribu-
tyltin hydride.2b
We recently reported that cerium(IV) ammonium
nitrate (CAN) is able to promote a fast oxidative addition
of 1-ethoxy-1-(silyloxy)cyclopropane to 1,3-butadienes,
affording a mixture of allylic 1,2- and 1,4-nitroxy adducts
in good yield and in very mild conditions.3 To widen the
synthetic scope of this process, we replaced the diene by
other electron-rich alkenes, such as ethyl vinyl ether and
allyltrimethylsilane. However, in these cases, the ex-
pected addition products were obtained as minor com-
ponents among other products derived from the CAN-
promoted direct oxidation of the intermediate â-(al-
koxycarbonyl)alkyl radical (see next section). Owing to
the slight nucleophilic character exhibited by the â-car-
bonylalkyl radicals, a certain selectivity in favor of an
attack at electron-poor carbon-carbon double bonds with
respect to electron-rich ones should be expected. On this
basis, we felt it worthwhile to check the possibility of
obtaining R,â-disubstituted carbonyl compounds by oxi-
dative tandem additions of â-carbonylalkyl radicals to the
corresponding R,â-unsaturated precursors in the presence
of electron-rich alkenes. In this note, we report on the
CAN-promoted addition of 1-ethoxy-1-[(trimethylsilyl)-
oxy]cyclopropane to 2-cycloalkenones in the presence of
ethyl vinyl ether and allyltrimethylsilane, allowing access
to highly functionalized regio- and stereoselectively 2,3-
disubstituted cycloalkanones.
Resu lts a n d Discu ssion
The reaction of 1-ethoxy-1-[(trimethylsilyl)oxy]cyclo-
propane (1) with CAN (2 equiv) at room temperature is
a fast process both in ethanol and in acetonitrile, as
evidenced by the rapid decoloration of the mixture (3-4
min). In ethanol, the main reaction product is ethyl
propanoate (3, 72%, Scheme 1), which forms from the
â-(ethoxycarbonyl)alkyl radical (2•) by hydrogen abstrac-
tion from the solvent. Accordingly, an equivalent amount
of acetaldehyde diethyl acetal was also detected coming
from the fast oxidation of the resulting R-hydroxyethyl
radical by CAN.4 Diethyl adipate (4) is also detected (7%),
most probably deriving from the dimerization of 2•.
Accordingly, no deuterium incorporation in 4 was ob-
served when the reaction was performed in ethanol-d6,
which excludes the formation of 4 occurring by the attack
of 2• at the ethyl acrylate formed, in turn, from 2• by an
oxidative elimination process.5 An unidentified product,
probably an oligomeric species, has also been detected
as a minor component (<5%).
A different pattern of products is observed when
acetonitrile is used as the reaction solvent. Here, ethyl
3-nitropropanoate (5a , 30%) and ethyl 3-nitroxypro-
panoate (5b, 29%) are formed as the main reaction
products, along with 4 (13%) and the above unidentified
(1) (a) Schaafsma, S. E.; Molenaar, E. J . F.; Steinberg, H.; de Boer,
Th. J . Recl. Trav. Chim. Pays-Bas 1968, 87, 1301. (b) Schaafsma, S.
E.; J orritsma, R.; Steinberg, H.; de Boer, Th. J . Tetrahedron Lett. 1973,
827.
(2) (a) Iwasawa, N.; Hayakawa, S.; Isobe, K.; Narasaka, K. Chem.
Lett. 1991, 1193. (b) Iwasawa, N.; Hayakawa, S.; Funahashi, M.; Isobe,
K.; Narasaka, K. Bull. Soc. Chim. J pn 1993, 66, 819.
(3) Belli Paolobelli, A.; Gioacchini, F.; Ruzziconi, R. Tetrahedron Lett.
1993, 34, 6333.
(4) Rate constants of 106-108 M-1 s-1 for oxidation of the 1-hy-
droxyethyl radical to acetaldehyde by a variety of metals have been
reported: Asmus, K.-D.; Bonifacic, M. In Landolt-Bornstein New
Series, Group 2; Fischer, H., Ed.; Springer Verlag: Berlin, 1984; Vol.
13b, pp 311-313.
(5) This mechanism was suggested by Schaafsma for the oxidation
of cyclopropanols by Cu2+ and Fe3+ salts.1
S0022-3263(96)00446-X CCC: $12.00 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 18, 1996 6435
product (<5%). 5a probably derives from 2• by reaction
with NO2 formed in redox processes involving HNO3
produced in each oxidation step.6
Ta ble 1. P r od u cts fr om CAN-P r om oted Oxid a tive
Ad d ition of 1 to th e Cycloa lk en on es 8 in th e P r esen ce of
Electr on -Rich Alk en es
electron-rich
alkene
yield, trans/cisc
The reaction of 1 with CAN in ethanol in the presence
of ethyl vinyl ether gives 3 (48%), the expected addition
product ethyl 5,5-diethoxypentanoate (6) (26%), and 4
(8%). Using a calculated excess of vinyl ethyl ether (3-4
equiv) and considering the reactivity of 2• as being similar
to that of the ethyl radical in hydrogen abstraction from
ethanol (k ) 26 M-1 s-1),7 a rate constant of 5.3 × 102
M-1 s-1 for the addition of 2• to vinyl ethyl ether can be
estimated roughly by means of the competitive method.
To test different electron-rich alkenes, we replaced ethyl
vinyl ether by allyltrimethylsilane using acetonitrile as
the reaction solvent.9 Once again, the expected ethyl
5-hexenoate addition product 7 was isolated in very low
yield (17%), along with 5b (29%), 4 (19%), and 3 (14%).
b
cycloalkenone
producta
%
ratio
8a
11a
62
17.0
OEtd
e
12a
11b
12b
11c
12c
48
42
31
35
35
6.3
2.8
SiMe3
8b
8c
OEtd
SiMe3
e
e
3.0
1.3
OEtd
SiMe3
12.0
a
b
Mixture of trans and cis isomers. Isolated yields calculated
with respect to CAN. Determined by 1H-NMR and GLC analysis.
Solvent, MeOH. Solvent, MeCN.
c
d
e
The above results betray a substantial nucleophilic
character of the â-carbonylalkyl radical, which foreshad-
ows the attack at electron-poor carbon-carbon double
bonds occurring faster than both addition to electron-rich
carbon-carbon double bonds and hydrogen abstraction
from the solvent.10 In this case, the competitivity of the
latter process could be further reduced in favor of the
addition process if ethanol is replaced by methanol as
the reaction solvent.11 Indeed, when a mixture of cy-
cloalkenones 8 (Scheme 2), ethyl vinyl ether, and 1-ethoxy-
1-[(trimethylsilyl)oxy]cyclopropane was added to a red
solution of CAN (∼0.5 M) in methanol at room temper-
ature (CAN/8/1/vinyl ethyl ether 2:1.2:1:6 molar ratio),12
a fast reaction was observed (5-10 min), and after
workup, a crude product was obtained that had spectro-
scopic characteristics consistent with a mixture of cyclic
and acyclic ethyl acetals 9 and 10, respectively. The acid-
catalyzed hydrolysis of the crude mixture in 1:1 chloroform/
50% aqueous trifluoroacetic acid gave 2-(formylmethyl)-
3-[2-(ethoxycarbonyl)ethyl]cycloalkanones 11.
Sch em e 2
In similar conditions, however, using acetonitrile as
the reaction solvent, the oxidative addition of 1 to 8 in
the presence of allyltrimethylsilane allowed us to obtain
the corresponding 2-allyl-3-[2-(ethoxycarbonyl)ethyl]cy-
cloalkanones 12. Results are reported in Table 1. Sat-
isfactory yields calculated with respect to the oxidant and
in most cases fairly good stereoselectivity were obtained,
the trans/ cis ratio ranging from 1.3 to 17, depending on
both the ring size and the electron-rich alkene employed,
making this procedure competitive, if only for its simplic-
ity, with others based on ionic reactions.13
(6) A similar product pattern has been observed in the oxidation of
The mechanism proposed for the overall process is
illustrated in Scheme 3. Oxidation of 1 by CAN gener-
ates the â-carbonylalkyl radical 2•. The fast addition of
2• to the â-carbon of the cycloalkenone in turn generates
an R-carbonylalkyl radical 13, now an electrophilic spe-
cies able to attack the electron-rich carbon-carbon double
bond of the vinyl ether or allylsilane before undergoing
further oxidation by CAN. The new nucleophilic carbon-
centered radical 14 (R-alkoxy or R-(trimethylsilyl)methyl
radical) undergoes rapid oxidation to the intermediate
carbocation 15, which, in turn, evolves into a thermody-
namic mixture of the acetals 9 and 1014 or into the allyl
derivative 12.
a
cyclopentylmethyl radical by CAN in CH3COOH/(CH3CO)2:
Baciocchi, E.; Belli Paolobelli, A.; Ruzziconi, R. Tetrahedron 1992, 48,
4617.
(7) The rate constants for the hydrogen abstraction from ethanol
by a methyl radical, generating 1-ethoxyethyl radical, are 5.9 × 102
M-1 s-1 in water at 25 °C and 1.4 × 102 M-1 s-1 in the gas phase.8 The
ethyl radical has been reported to be less reactive than the methyl
radical for the hydrogen abstraction from a -CH2- group by a factor
of 6.7 at 182 °C in the gas phase (∆Eact.) 2.1 kcal/mol) [Boddy, P. J .;
Steacie, E. W. R. Can. J . Chem. 1960, 38, 1576]. From these data, an
extrapolated reactivity ratio Me•/Et• of ∼23 at 25 °C for the hydrogen
abstraction from ethanol can be estimated.
(8) Thomas, J . K. J . Phys.Chem. 1967, 71, 1919
(9) Indeed, acetonitrile proved to be a better solvent than methanol.
In the latter solvent, substantial amounts of unidentified byproducts
are also formed.
(10) The rate constants of the addition of 5-hexenyl radical to vinyl
methyl ketone and methyl acrylate respectively in 3:2 CH3CN/CH3-
COOH at 25 °C are 4.1 × 105 and 2.1 × 105 M-1 s-1, respectively
[Citterio, A.; Arnoldi, A.; Minisci, F. J . Org. Chem. 1979, 44, 2674
(11) Hydrogen abstraction from methanol by an alkyl radical is ∼2.7
times slower than that from ethanol in H2O at 25 °C.8
(12) Powdered calcium carbonate was also added in order to avoid
the extensive solvolysis of 1 as well as the acetalization of vinyl ethyl
ether catalyzed by the nitric acid produced by CAN in each oxidative
process.
(13) For example, a procedure could be envisaged, albeit a rather
wearysome one, based on the copper(I)-catalyzed reaction of a zinc
homoenolate (see: Nakamura, E.; Aoki, S.; Sekiya, K.; Oshino, H.;
Kuwajima, I. J . Am. Chem. Soc. 1987, 109, 8056) with the R,â-
unsaturated cycloalkenone, followed by the addition of 2-(bromo-
methyl)-1,3-dioxolane or allyl bromide as electrophiles.
(14) Baciocchi, E.; Casu, A.; Ruzziconi, R. Synlett 1990, 679.

6436 J . Org. Chem., Vol. 61, No. 18, 1996
Notes
9.67. 5b (29%): 1H-NMR δ 4.66 (t, J ) 6.1, 2 H), 4.19 (q, J )
7.1, 2 H), 2.97 (t, J ) 6.1, 2 H), 1.28 (t, J ) 7.1, 3 H); IR (neat)
2985-2935, 1733, 1634 (νas NO2), 1283 (νs NO2); MS m/ z
(relative intensity) 118 (M+ - OEt, 17), 99 (2), 73 (19), 71 (15),
59 (16), 46 (100). Anal. Calcd for C5H9NO5: C, 36.81; H, 5.56;
N, 8.58. Found: C, 36.35; H, 5.81; N, 8.79. A minor component
of the mixture (<5%) of high GLC retention time was not
identified.
Sch em e 3
Oxid a tion of 1 w ith CAN in th e P r esen ce of Eth yl Vin yl
Eth er . The same procedure described for the oxidation of 1 in
ethanol was employed, except that a mixture of ethyl vinyl ether
(1.2 g, 17 mmol) and 1 (0.5 g, 2.8 mmol) was added to the red
suspension of CAN and powdered CaCO3. After the usual
workup, GLC-MS analysis of the organic extracts allowed
identification of 3 (48%) and 4 (8%). A third product was isolated
by HPLC and identified as ethyl 5,5-diethoxypentanoate (6, 26%)
on the basis of the following spectroscopic and analytical
characteristics: 1H-NMR δ 4.50 (t, J ) 5.3, 1 H), 4.12 (q, J )
7.1, 2 H), 3.72-3.41 (m, 16 peaks, 4 H), 2.32 (m, 2 H), 1.67 (m,
4 H), 1.27 (t, J ) 7.1, 3 H), 1.19 (t, J ) 7.0, 6 H), IR (neat) 2978,
2933, 1735 cm-1; MS m/ z ( relative intensity) 173 (M+ - OEt,
47), 127 (46), 103 (100), 99 (34), 85 (63), 75 (65), 47 (64). Anal.
Calcd for C11H22O4: C, 60.52; H, 10.16. Found: C, 60.21; H,
9.89.
Oxid a tive Ta n d em Ad d ition of 1 to Cycloa lk en on es 8
in th e P r esen ce of Eth yl Vin yl Eth er . The procedure
described above for the reactions in ethanol was used, except
that methanol was employed as the reaction solvent and
cycloalkenones 8 (3.4 mmol) were added to reactant mixture.
After the usual workup, the crude product, containing a mixture
of cyclic (9) and acyclic (10) acetals (see text), was dissolved in
CHCl3 (40 mL) and cooled to 0 °C, and 50% aqueous trifluoro-
acetic acid (20 mL) was added. After vigorous stirring for 1 h,
the mixture was poured into water and extracted with CHCl3
(3 × 20 mL). The organic extracts collected were washed first
with water (50 mL) and then with 5% aqueous NaHCO3 and
finally dried with Na2SO4. The solvent was evaporated at
reduced pressure, and the residual brown oil was chromato-
graphed on silica gel (eluent, 1:1 petroleum ether/diethyl ether)
to isolate mixtures of stereoisomeric 2,3-substituted cycloal-
kanones 11 which were identified on the basis of the following
spectral and analytical characteristics.15
E t h yl 3-[3-Oxo-2-(2-oxoet h yl)cyclop en t yl]p r op a n oa t e
(11a , 62%). trans-11a : 1H-NMR δ 9.76 (s, 1 H), 4.12 (q, J ) 7.1,
2 H), 2.91-2.65 (8 peaks, AB portion of an ABX system, 2 H),
2.6-2.1 (m, 6 H), 2.1-1.8 (m, 2 H), 1.7-1.4 (m, 2 H), 1.27 (t, J
) 7.1, 3 H); 13C-NMR δ 217.5 (C-1), 199.5, 172.8, 60.2, 49.7 (C-
2), 41.9, 41.2 (C-3), 36.7, 31.6, 29.2, 26.8, 14.0; IR (neat) 2978,
2931, 2732, 1734, 1588, 1442, 1182, 755 cm-1; MS m/ z (relative
intensity) 226 (M+, 1), 183 (8), 163 (25), 125 (17), 110 (59), 97
(100), 82 (35), 55 (87). cis-11a : 1H-NMR absorption of the
aldehydic proton δ 9.84; 13C-NMR δ (characterizing peaks) δ
197.0, 51.1, 47.6, 39.3, 34.2, 20.0, 26.7, 24.6; MS m/ z (relative
intensity) 183 (9), 163 (16), 125 (11), 110 (39), 97 (100), 82 (21),
Exp er im en ta l Section
1H- and 13C-NMR spectra were recorded at 200 and 50 MHz,
respectively, in CDCl3 in the presence of TMS as internal
standard (J values are in hertz). GLC analysis was performed
a 30 m SPB-20 capillary column. Mass spectra were
registered at 70 eV.
on
Rea gen ts a n d Solven ts. Except for ethyl vinyl ether, which
was distilled before use, all the organic reagents (Aldrich), of
the highest grade of purity, were used as received. Ceric
ammonium nitrate (Baker 99%) was dried by heating at 80 °C
for 1 h before use. Absolute ethanol, methanol, and acetonitrile
(Carlo Erba, ACS grade) were used without further purification.
Oxid a tion of 1 w ith CAN in Eth a n ol. To a red solution of
CAN (3.1 g, 5.7 mmol) in 25 mL of ethanol were added powdered
calcium carbonate (2.0 g, 20 mmol) and 1 (0.5 g, 2.8 mmol) at
room temperature under stirring. The mixture was made to
react until complete decoloration (5-6 min), and then it was
poured into water (100 mL) and extracted with CH2Cl2 (3 × 20
mL). The collected extracts were washed with water (50 mL)
and dried with sodium sulfate. The GLC analysis of the solution
showed the presence of substantially two products, which, after
solvent evaporation, were identified as ethyl propanoate (3, 72%)
and diethyl adipate (4, 7%) by comparison of their GLC retention
times and MS, 1H-NMR, and IR absorptions with those of
commercial authentic specimens. A minor product (<5%, prob-
ably an oligomeric species) having a much higher GLC retention
time was not identified. The same experiment was repeated on
a smaller scale (CAN, 125 mg; CaCO3, 80 mg; 1, 20 mg) using
ethanol-d6 (1 mL) as the solvent. The 1H-NMR and GLC-MS
analyses of the reaction mixture showed no deuterium incorpo-
ration in 4.
Oxid a tion of 1 w ith CAN in Aceton itr ile. The same
procedure was used for the oxidation of 1 in acetonitrile. The
GLC-MS analysis of the organic extracts allowed to identification
of 4 (13%) among two other main products. After solvent
evaporation, the latter were isolated by chromatography of the
crude mixture on silica gel (8:2 petroleum ether/diethyl ether
as the eluent), followed by further purification by HPLC, and
identified as ethyl 3-nitropropanoate (5a ) and ethyl 3-nitrox-
ypropanoate (5b) on the base of the following spectroscopic and
analytic characteristics. 5a (30%): 1H-NMR δ 4.74 (t, J ) 6.3,
2 H), 4.20 (q, J ) 7.1, 2 H), 2.74 (t, J ) 6.3, 2 H), 1.28 (t, J )
7.1, 3 H); IR (neat) 2983-2939, 1733, 1559 (νas NO2), 1374 (νsym
NO2) cm-1; MS m/ z (relative intensity) 102 (M+ - OEt, 32), 88
(12), 74 (11), 73 (35), 55 (100), 45 (37). Anal. Calcd for C5H9-
NO4: C, 40.82; H, 6.16; N, 9.52. Found: C, 40.61; H, 6.54; N,
55 (63). Analysis of the stereoisomeric mixture. Calcd for C12
18O4: C, 63.70; H, 8.02. Found: C, 63.96; H, 8.19.
-
H
Eth yl 3-[3-Oxo-2-(2-oxoeth yl)cycloh exyl]pr opan oate (11b,
42%). trans-11b: 1H-NMR δ 9.85 (s, 1 H), 4.14 (q, J ) 7.1, 2 H),
2.65-1.4 (m, 14 H), 1.25 (t, J ) 7.1, 3 H); 13C-NMR δ 209.8 (C-
1), 200.5, 172.8, 60.2, 50.3 (C-2), 42.4 (C-3), 40.8, 40.3, 31.0, 30.0,
28.9, 25.2, 13.9; IR (neat) 2935, 2868, 2723, 1727, 1555, 1447,
1420, 1303, 756 cm-1; MS m/ z (relative intensity) 195 (M+
-
OEt, 4), 177 (16), 139 (21), 124 (53), 111 (100), 110 (60) 97 (42),
55 (83). cis-11b: 1H-NMR absorption of the aldehydic proton δ
9.78; 13C-NMR (characterizing peaks) δ 200.1, 60.1, 48.5 (C-2),
40.8, 40.3 (C-3), 31.5, 27.2, 21.8; MS m/ z (relative intensity) 222
(M+ - H2O, 10), 197 (15), 195 (3), 177 (12), 151 (17), 139 (19),
124 (25), 111(48), 97 (29), 55 (100). Analysis of the isomeric
mixture. Calcd for C13H20O4: C, 64.98; H, 8.39. Found: C,
64.59; H, 8.14.
Eth yl 3-[3-Oxo-2-(2-oxoeth yl)cycloh eptyl]pr opan oate (11c,
35%). trans-11c: 1H-NMR δ 9.76 (s, 1 H), 4.13 (q, J ) 7.1, 2
H), 2.61-1.48 (m, 16 H), 1.22 (t, J ) 7.1, 3 H); 13C-NMR δ 212.3
(C-1), 200.5, 172.8, 60.1, 48.7 (C-2), 43.7, 43.0, 38.1 (C-3), 32.3,
32.0, 24.1, 23.4, 23.1, 13.9; IR (neat) 2928, 2859, 1728, 1699,
(15) The products turned brown in the long run at room temperature
and upon exposure to the air.

Notes
J . Org. Chem., Vol. 61, No. 18, 1996 6437
1372, 1179, 732 cm-1; MS m/ z (relative intensity) 236 (M+
-
4.13 (q, J ) 7.2, 2 H), 2.6-2.1 (br m, 6 H), 2.1-1.8 (br m, 4 H),
1.8-1.5 (br m, 4 H), 1.26 (t, J ) 7.2, 3 H); 13C-NMR δ 211.5
(C-1), 173.1, 136.2, 116.2, 60.3, 54.9 (C-2), 41.4 (C-3), 40.9, 40.6,
31.6, 28.7, 24.5, 23.6, 14.1; IR (neat) 3073, 3032, 2935, 2869,
2828, 1732, 1707, 1635, 1185, 977, 915 cm-1; MS, 70 eV, m/z
(relative intensity) 238 (M+, 5), 197 (7), 150 (15), 137 (100), 95
(28), 81 (32), 55 (46). cis-12b: 13C-NMR (characterizing peaks)
δ 54.6 (C-2), 40.6 (C-3), 33.6, 32.1, 30.3, 27.3, 25.7, 22.7; MS m/ z
(relative intensity) 238 (M+, 7), 197 (18), 151 (26), 137 (100), 95
(43), 81 (50), 55 (70). Analysis of the isomeric mixture. Calcd
for C14H22O3: C, 70.55; H, 9.30. Found: 70.12; H, 9.58.
H2O, 90), 191 (78), 165 (49), 153 (89), 125 (100), 95 (47), 55 (83).
cis-11c: 1H-NMR of the aldehydic proton δ 9.77; 13C-NMR δ
212.9 (C-1), 201.3, 172.9, 60.1, 49.0 (C-2), 44.7, 42.3, 38.0, 32.9,
31.3, 30.0, 23.6, 23.0, 13.9. Analysis of the isomeric mixture.
Calcd for C14H22O4: C, 66.12; H, 8.72. Found: C, 65.89; H, 9.01.
Olefination of the mixture with 1 equiv of methylenetriphen-
ylphosphorane in THF at 0 °C gave a 1:1.5 mixture of two
products, whose GLC retention times and mass spectra were
identical to those of 12c (see below).
Oxid a tive Ad d ition of 1 to Cycloa lk a n on es 8 in th e
P r esen ce of Allyltr im eth ylsila n e. The above procedure was
used, except that acetonitrile was employed as the reaction
solvent. After the usual workup, chromatography of the crude
product on silica gel (eluent, 1:1 petroleum ether/diethyl ether)
allowed isolation of a mixture of the stereoisomeric 2-allyl-3-[2-
(ethoxycarbonyl)ethyl]cycloalkanones 12, having the following
spectroscopic and analytical characteristics.
Eth yl 3-(2-Allyl-3-oxocyclop en tyl)p r op a n oa te (12a , 48%).
trans-12a : 1H-NMR δ 5.72 (ddt, J ) 17.1, 10.0, 7.1, 1 H), 4.99
(dq, J ) 17.1, 1.5, 1 H), 4.95 (dq, J ) 10.0, 1.5, 1 H), 4.14 (q, J
) 7.1, 2 H), 2.51-2.25 (m, 5 H), 2.24-1.99 (m, 3 H), 1.98-1.78
(m, 2 H), 1.65-1.30 (m, 2 H), 1.35 (t, J ) 7.1, 3 H); 13C-NMR δ
218.7 (C-1), 173.0, 135.2, 116.9, 60.2, 54.4 (C-2), 40.5 (C-3), 37.6,
32.2, 31.9, 29.6, 26.6, 14.1; IR (neat) 3076, 2977, 2930, 2873,
1737, 1640, 1442, 1181, 917 cm-1; MS m/ z (relative intensity)
224, (M+, 6), 136 (28), 133 (10), 123 (100), 95 (30), 79 (40), 55
(70). cis-12a : 13C-NMR (characteristic peaks) δ 116.1, 52.8 (C-
2), 38.5, 35.1, 29.1, 24.7, 23.6; MS m/ z (relative intensity) 224
(M+, 4), 151 (14), 136 (25), 123 (100), 95 (58), 79 (78), 67 (60), 55
(69). Analysis of the isomeric mixture. Calcd for C13H20O3: C,
69.61; H, 8.99. Found: 69.42; H, 9.12.
Eth yl 3-(2-Allyl-3-oxocycloh ep tyl)p r op a n oa te (12c, 35%).
trans-12c: 1H-NMR δ 5.80-5.57 (m, 1 H), 5.05-4.92 (m, 2 H),
4.12 (t, J ) 7.2, 2 H), 2.60-2.10 (m, 6 H), 2.00-1.75 (m, 6 H),
1.8-1.5 (m, 4 H), 1.25 (t, J ) 7.2, 3 H); 13C-NMR δ 214.4 (C-1),
173.3, 135.6, 116.5, 60.3, 58.0 (C-2), 41.6 (C-3), 39.3, 35.3, 31.7,
31.1, 29.0, 27.0, 25.5, 14.2; IR (neat) 3075, 3022, 2931-2863,
1733, 1701, 1640, 1448, 1177, 999, 916 cm-1; MS m/ z (relative
intensity) 252 (M+, 7), 206 (17), 178 (20), 151 (82), 95 (62), 81
(85), 55 (100). cis-12c: 13C-NMR (characterizing peaks) δ 135.6,
116.2, 54.9 (C-2), 43.9 (C-3), 37.7, 35.3, 33.9, 33.0, 30.2, 226.1,
24.4; MS m/ z (relative intensity) 252 (M+, 8), 206 (22), 178 (21),
151 (33), 95 (71), 81 (90), 55 (100). Analysis of the isomeric
mixture. Calcd for C15H24O3: C, 71.39; H, 9.59. Found: 70.98;
H, 9.73.
Ack n ow led gm en t. Thanks are due to the Italian
National Research Council (CNR) and Ministero
dell’Universita` e della Ricerca Scientifica e Tecnologica
(MURST) for financial support.
Eth yl 3-(2-Allyl-3-oxocycloh exyl)p r op a n oa te (12b, 31%).
trans-12b: 1H-NMR δ 5.88-5.61 (m, 1 H), 5.10-4.97 (m, 2 H),
J O960446R