Claisen rearrangement based methodology for the spiroannulation of a cyclopentane ring. Formal total synthesis of (±)-acorone and isoacorones

Article abstract of DOI:10.1016/S0040-4020(00)00743-2

A Claisen rearrangement based methodology for spiroannulation of a cyclopentane ring to cyclic precursors and its application in the formal total synthesis of acorones 1 is described. Thus, Claisen rearrangement of 2-cycloalkylideneethanols 12 with 2-methoxypropene and a catalytic amount of mercuric acetate generates 4,4-substituted hex-5-en-2-ones 13. Ozonolytic cleavage of the terminal olefin in the enones 13 and intramolecular aldol condensation of the resulting keto-aldehydes 14 furnishes the spiroannulated compounds 15. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00743-2

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 8189±8195
Claisen Rearrangement Based Methodology for the
Spiroannulation of a Cyclopentane Ring. Formal Total Synthesis
of (^)-Acorone and Isoacorones
*
A. Srikrishna and P. Praveen Kumar
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
Received 23 June 2000; revised 2 August 2000; accepted 17 August 2000
AbstractÐA Claisen rearrangement based methodology for spiroannulation of a cyclopentane ring to cyclic precursors and its application in
the formal total synthesis of acorones 1 is described. Thus, Claisen rearrangement of 2-cycloalkylideneethanols 12 with 2-methoxypropene
and a catalytic amount of mercuric acetate generates 4,4-substituted hex-5-en-2-ones 13. Ozonolytic cleavage of the terminal ole®n in the
enones 13 and intramolecular aldol condensation of the resulting keto-aldehydes 14 furnishes the spiroannulated compounds 15. q 2000
Elsevier Science Ltd. All rights reserved.
Sorm and coworkers, in 1948, reported the isolation of two
epimeric sesquiterpene ketones, acorone 1a and isoacorone
1b from the oil of Sweet Flag, Acorus calamus L. Presence
of the novel spiro[4.5]decane carbon framework in acorones
1 was established in 1958 based on the interpretation of
extensive degradation experiments on acorones by Sorm
et al.1 The absolute stereochemistry of acorones 1 was estab-
lished by correlation with cedrene, a tricyclic sesquiterpene
isolated along with acorones from the same source, and was
®nally con®rmed by the single crystal X-ray analysis of a
derivative of acorone. Further phytochemical investigations
led to the characterisation of a number of acorane deriva-
tives.2
the stereocontrolled construction of the spirocyclic carbon
skeleton.3 A successful synthesis of these spiro sesquiter-
penes depends critically, therefore, upon the generation of a
quaternary carbon centre which is suitably substituted for
the annulation to form a functionalised spiro[4.5]decane.
Since the discovery of acoranes, several research groups
have reported the synthesis of a variety of acoranes.4 We
wished to develop general methodology for spiroannulation
of a ®ve-membered ring to an existing ring, and a synthesis
of (^)-acorones 1 was conceived as the test case.5 The retro-
synthetic strategy for acorones 1 via a prochiral precursor is
depicted in Scheme 1. The dienone 2, a precursor employed
by Dolby and McCrae;3b and Martin and Chou3c in their
syntheses of (^)-acorone and isoacorones 1, was identi®ed
as the target molecule for achieving the formal total syn-
thesis. The prochiral monoprotected spiroenedione 3 was
visualised as a precursor of the dienone 2. It was anticipated
that the cyclopentenone 3 could be obtained from the enone
4 via oxidative cleavage of the terminal ole®n followed
by an intramolecular aldol condensation of the resulting
The most important aspect in the synthesis of acorones 1 is
Scheme 1.
Keywords: spiro compounds; annulation; Claisen rearrangement; ozonolysis.
* Corresponding author. Tel.: 191-80-3092215; fax: 191-80-3600683; e-mail: ask@orgchem.iisc.ernet.in
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00743-2

8190
A. Srikrishna, P. P. Kumar / Tetrahedron 56 (2000) 8189±8195
Scheme 2. Reagents: (a) NaH, (EtO)2POCH2COOEt; (b) (CH2OH)2, p-TSA; (c) LiAlH4; (d) CH2vC(Me)OMe, EtCOOH; (e) (i) O3/O2; (ii) PPh3; (f) KOH.
keto-aldehyde. The vinyl ketone 4, being a g,d-unsaturated
ketone, could be obtained by a Claisen rearrangement, and
the allyl alcohol 5 was readily recognised as the requisite
precursor, which could be obtained from cyclohexane-1,4-
dione (6).
annulation of the cyclopentenone ring, attention was turned
to the conversion of spiroenone 3 into the target molecule
spirodienone 2. Thus, two-phase hydrolysis of the ketal
moiety in the spiroenone 3 in methylene chloride and 3N
hydrochloric acid furnished the enedione 10 in 92% yield. A
Wittig reaction based methodology was adopted for the
conversion of the end-dione 10 into the dienone 2. Thus,
regioselective Wittig reaction with methylenetriphenyl-
phosphorane in benzene cleanly transformed the enedione
2 into the dienone 11 in 51% yield along with 33% of
unreacted starting material. Finally, isomerisation of the
exomethylene group in the dienone 11 in the presence of a
catalytic amount of p-toluenesulphonic acid in re¯uxing
benzene furnished the spirodienone 2, whose structure was
con®rmed by comparison of the spectral data with that
reported by Martin and Chou. Since, Dolby and McCrae3b
and Martin and Chou3c have already converted the spiro-
dienone 2 into (^)-acorone 1a and isoacorone 1b, employ-
ing an aldol-cuprate-hydroboration-oxidation protocol, the
present synthesis of the spirodienone 2 constitutes a formal
total synthesis of (^)-acorone and isoacorones. It is worth
noting that in the present sequence, the spirodienone 2 was
obtained via prochiral precursors 3 and 11, and hence has
the potential to serve as precursors for chiral acorones
(Scheme 3).
First attention was focussed on the synthesis of the allyl
alcohol 5 starting from the readily available cyclohexane-
1,4-dione (6), for which a controlled Wittig±Horner±
Emmons reaction, protection of the ketone and regio-
chemical reduction protocol was conceived. Thus, treatment
of cyclohexane-1,4-dione (6) with 1.1 equiv. of the anion
derived from triethyl phosphonoacetate and sodium hydride
in dry THF at 2708C for 10 min, furnished the keto ester 7
in 77% yield.6 Protection of the ketone in the keto ester 7
with ethylene glycol in the presence of a catalytic amount of
p-toluenesulfonic acid (p-TSA) using a Dean±Stark water
separator furnished the ketal 8 in 88% yield. Low tempera-
ture (2708C) reduction of the ester 8 with lithium alu-
minium hydride in ether furnished the allyl alcohol 5 in
90% yield. For the generation of the quaternary centre,
which is required to generate the spiro system, a one-pot
Claisen rearrangement7 was employed. Thus, thermal
activation of the allyl alcohol 5 with 2-methoxypropene in
the presence of a catalytic amount of propionic acid in a
sealed tube ®rst at 1008C and then at 1708C furnished the
Claisen rearrangement product, the g,d-unsaturated ketone
4 in 75% yield (see Scheme 2). Ozonolysis of the enone 4 in
methylene chloride and methanol in the presence of a cata-
lytic amount of sodium bicarbonate followed by reductive
work-up using triphenylphosphine furnished the keto-alde-
hyde 9. Intramolecular aldol condensation of the keto-alde-
hyde 9 with 1N methanolic potassium hydroxide in THF
furnished the spiroenone 3, in 93% yield. The structure of
the spiroenone 3 was established on the basis of the spectral
data, in particular, the presence of two doublets at d 7.56
and 6.08 due to the b and a ole®nic protons, respectively, in
the 1H NMR spectrum, and the nine lines 13C NMR
spectrum with diagnostic resonances, a singlet at d 209.1
due to the carbonyl carbon and two doublets at 172.3 and
131.9 due to the b and a ole®nic carbons, respectively, of a
cyclopentenone. After successful completion of the spiro-
Even though many methodologies have been developed for
cyclopentannulation over the last two decades employing
novel and innovative strategies,8 comparatively, not much
attention was focussed on the development of methods for
the annulation of spirofused cyclopentanes.9 After success-
fully accomplishing the formal total synthesis of acorones,
to establish the generality of the Claisen rearrangement
based spiroannulation of cyclopentanes, 5!3, the sequence
was carried out with a few other cyclic ketones. Thus, the
requisite allyl alcohols 12a±d were prepared from the corre-
sponding cyclic ketones employing Horner±Wadsworth±
Emmons reaction followed by regioselective reduction of
the resulting a,b-unsaturated esters with lithium aluminium
hydride at low temperature. One-pot Claisen rearrangement
of the allyl alcohols 12a±d with 2-methoxypropene and a
catalytic amount of mercuric acetate in a sealed tube
Scheme 3. Reagents: (a) H3O1; (b) Ph3PvCH2; (c) p-TSA.

A. Srikrishna, P. P. Kumar / Tetrahedron 56 (2000) 8189±8195
8191
Scheme 4. Reagents: (a) (i) NaH, (EtO)2POCH2COOEt; (ii) LiAlH4; (b) CH2vC(Me)OMe, Hg(OAc)2; (c) (i) O3/O2; (ii) PPh3; (d) KOH.
furnished the 4,4-disubstituted hex-5-en-2-ones 13a±d,
respectively. Ozonolysis of the enones 13a±d in methanol,
methylene chloride and a catalytic amount of sodium bi-
carbonate followed by reduction of the resulting ozonides
with triphenylphosphine furnished the keto aldehydes 14a±
d, respectively. Finally, intramolecular aldol condensation
of the keto aldehydes 14a±d with methanolic potassium
hydroxide at room temperature, furnished the spiroenones
15a±d in 70±80% yield.10 The structures of all the
compounds 12a±d to 15a±d were established from their
interrelated spectral data (Scheme 4).
6.86 mmol) and a catalytic amount of p-TSA in dry benzene
(60 mL) was re¯uxed using Dean±Stark water separator for
4 h. Benzene was distilled off, saturated aq. NaHCO3
(5 mL) was added to the reaction mixture and extracted
with ether (2£10 mL). The ether layer was washed with
water, brine and dried (Na2SO4). Evaporation of the solvent
under reduced pressure and puri®cation of the product on a
silica gel column using ethyl acetate±hexane (1:20) as
eluent furnished the ketal 8 (1.05 g, 88%) as an oil. IR
.
(neat): nmax 1710, 1650 cm21 1H NMR (200 MHz,
CDCl3): d 5.67 (1H, s, ole®nic H), 4.20 (2H, q, Jˆ7.1 Hz,
OCH2CH3), 3.98 (4H, s, OCH2CH2O), 3.00 (2H, t, Jˆ
6.3 Hz), 2.38 (2H, t, Jˆ6.3 Hz), 1.85±1.70 (4H, m), 1.28
(3H, t, Jˆ7.1 Hz, OCH2CH3). 13C NMR (22.5 MHz,
CDCl3): d 165.7 (s, O±CvO), 159.7 (s, CvCH), 113.8
(d, CvCH), 107.4 (s, O±C±O), 64.0 (2C, t, OCH2CH2O),
59.0 (t, OCH2CH3), 35.4 (t), 34.6 (t), 34.2 (t), 25.5 (t), 13.8
(q, OCH2CH3). Mass: m/z 226 (M1, 88%), 197 (95), 181
(84), 180 (55), 153 (100), 135 (38). HRMS: m/z For
C12H18O4, Calcd.: 226.1217. Found: 226.1205.
In conclusion, we have developed a convenient method for
the spiroannulation of a cyclopentenone ring to cyclic
ketones based on the Claisen rearrangement, and it has
been applied in the formal total synthesis of the spiro-
sesquiterpenes, acorones.
Experimental
8-(2-Hydroxyethylidene)-1,4-dioxaspiro[4.5]decane (5).
To a cold (2708C), magnetically stirred solution of the
ester 8 (1.0 g, 4.46 mmol) in dry ether (10 mL) was added
LiAlH4 (85 mg, 2.2 mmol) in one portion. The reaction
mixture was stirred at 2708C for 2 h and allowed to warm
up to 2208C over a period of 30 min. Ethyl acetate (1 mL)
was carefully introduced to consume the excess reagent and
the reaction was quenched with ice-cold water (5 mL). It
was then ®ltered through a sintered funnel and the residue
washed thoroughly with ether (3£10 mL). The ether layer
was washed with brine and dried (Na2SO4). The solvent was
evaporated and the residue was puri®ed on a silica gel
column using ethyl acetate±hexane (1:10) as eluent to
furnish the allyl alcohol 5 (740 mg, 90%) as an oil. IR
Ethyl 2-(4-oxocyclohexylidene)acetate (7). A suspension
of sodium hydride (60% in oil, 43 mg, 1.1 mmol) in hexanes
under a nitrogen atmosphere was magnetically stirred for
10 min and the solvent was syringed out. The oil free
sodium hydride was then suspended in dry THF (5 mL)
and cooled in an ice bath. Triethyl phosphonoacetate
(0.23 mL, 1.16 mmol) in dry THF (2 mL) was added drop-
wise and the reaction mixture was stirred for 30 min at RT.
It was then cooled to 2708C and a solution of cyclohexane-
1,4-dione (6, 100 mg, 0.89 mmol) in dry THF (2 mL) was
added dropwise. The reaction mixture was stirred for 10 min
at the same temperature. It was then diluted with water
(5 mL) and extracted with ethyl acetate (2£5 mL). The
combined organic layer was washed with water and brine,
and dried (Na2SO4). Evaporation of the solvent and puri®-
cation of the residue on a silica gel column using hexanes as
eluent furnished the unsaturated ester6 7 (125 mg, 77%) as
1
(neat): nmax 3390 cm21. H NMR (200 MHz, CDCl3): d
5.43 (1H, t, Jˆ7.1 Hz, ole®nic H), 4.16 (2H, d, Jˆ7.1 Hz,
CH2OH), 3.97 (4H, s, OCH2CH2O), 2.40±2.25 (4H, m),
1.75±1.50 (4H, m). 13C NMR (22.5 MHz, CDCl3): d
139.4 (s, CvCH), 121.6 (d, CvCH), 108.1 (s, O±C±O),
63.6 (2C, t, OCH2CH2O), 57.5 (t, CH2OH), 35.3 (t), 34.6 (t),
32.8 (t), 24.5 (t). Mass: m/z 184 (M1, 5%), 99 (65), 87 (100),
86 (100). HRMS: m/z For C10H16O3, Calcd.: 184.1099.
Found: 184.1092.
.
an oil. IR (neat): nmax 1710, 1640 cm21 1H NMR
(200 MHz, CDCl3): d 5.82 (1H, t, Jˆ1.4 Hz, CvCH),
4.14 (2H, q, Jˆ7.0 Hz, OCH2CH3), 3.20±3.10 (2H, m),
2.65±2.60 (2H, m), 2.55±2.40 (4H, m), 1.26 (3H, t, Jˆ
7.0 Hz, OCH2CH3). 13C NMR (22.5 MHz, CDCl3): d
208.5 (s, CvO), 165.0 (s, O±CvO), 156.8 (s, CvCH),
115.0 (d, CvCH), 58.8 (t, O±CH2CH3), 38.5 (t), 38.0 (t),
32.9 (t), 25.9 (t), 13.5 (q, CH2CH3). Mass: m/z 182 (M1,
94%), 137 (100), 126 (40), 109 (78), 108 (50). HRMS: m/z
For C10H14O3, Calcd.: 182.0943. Found: 182.0936.
8-(2-Oxopropyl)-8-vinyl-1,4-dioxaspiro[4.5]decane (4).
A solution of the allyl alcohol 5 (270 mg, 1.47 mmol), 2-
methoxypropene (1 mL, 9.8 mmol) and a catalytic amount
of propionic acid was heated ®rst at 1008C for 12 h and then
at 1708C for 36 h in a Carius tube under nitrogen atmos-
phere. The reaction mixture was then cooled, diluted with
ether, washed with aqueous NaHCO3 solution and brine,
Ethyl 2-(1,4-dioxaspiro[4.5]decan-8-ylidene)acetate (8).
A magnetically stirred solution of the keto ester 7
(960 mg, 5.27 mmol), ethylene glycol (0.38 mL,

8192
A. Srikrishna, P. P. Kumar / Tetrahedron 56 (2000) 8189±8195
and dried (Na2SO4). Evaporation of the solvent and puri®-
cation of the residue on a silica gel column using ethyl
acetate±hexane (1:20) as eluent furnished the enone 4
(250 mg, 75% yield) as an oil. IR (neat): nmax 1700,
temperature. The reaction mixture was extracted with
ether (2£10 mL), washed with water, saturated NaHCO3
solution and brine, and dried (Na2SO4). Evaporation of the
solvent and puri®cation of the residue over a silica gel
column using ethyl acetate±hexane (1:5 to 2:5) as eluent
furnished the spirodione 10 (200 mg, 92%) as an oil. IR
1
940 cm21. H NMR (200 MHz, CDCl3): d 5.83 (1H, dd,
Jˆ17.6 and 10.9 Hz, CHvCH2), 5.17 (1H, dd, Jˆ10.9
and 1.0 Hz) and 5.05 (1H, dd, Jˆ17.6 and 1.0 Hz)
[CHvCH2], 3.92 (4H, s, OCH2CH2O), 2.45 (2H, s,
CH2CvO), 2.08 (3H, s, CH3CvO), 1.90±1.50 (8H, m).
13C NMR (22.5 MHz, CDCl3): d 206.5 (s, CvO), 143.0
(d, CHvCH2), 113.3 (t, CHvCH2), 107.9 (s, O±C±O),
63.4 (2C, t, OCH2CH2O), 53.2 (t, CH2CvO), 38.1 (s),
32.2 (2C, t), 31.7 (q, CH3CvO), 30.4 (2C, t). Mass: m/z
224 (M1, 3%), 196 (12), 167 (32), 153 (43), 100 (50), 99
(100). HRMS: m/z For C13H20O3, Calcd.: 224.1412. Found:
224.1418.
1
(neat): nmax 1700, 1670, 1580 cm21. H NMR (300 MHz,
CDCl3): d 7.59 (1H, d, Jˆ5.7 Hz, H-4), 6.19 (1H, d,
Jˆ5.7 Hz, H-3), 2.55±2.40 (6H, m), 2.05±1.85 (4H, m).
13C NMR (22.5 MHz, CDCl3): d 209.1 (C-2), 207.4 (C-8),
170.1 (C-4), 132.2 (C-3), 45.2, 44.6, 38.2 (2 C), 36.1 (2 C).
Mass: m/z 164 (M1, 100%), 136 (25), 108 (22), 107 (20), 94
(42). HRMS: m/z For C10H12O2, Calcd.: 164.0837. Found:
164.0832.
8-Methylspiro[4.5]dec-3,7-diene-2-one (2). To a cold
(08C), magnetically stirred solution of methyltriphenyl-
phosphonium iodide (236 mg, 0.59 mmol) in benzene
(1 mL) was added potassium tert-amyloxide (0.59 mmol)
[prepared from potassium (23 mg, 0.59 mmol) and 0.8 mL
tert-amyl alcohol] in benzene (1 mL) and the resultant
yellow reaction mixture was stirred at RT for 20 min. To
the methylenetriphenylphosphorane thus formed, was added
a solution of the enedione 10 (80 mg, 0.49 mmol) in
benzene (1 mL) and stirred at RT for 1.5 h. The reaction
mixture was then quenched with water (1 mL) and extracted
with ether (2£5 mL). The ether extract was washed with
brine and dried (Na2SO4). Evaporation of the solvent and
puri®cation of the residue over a silica gel column using
ethyl acetate±hexane (1:20 to 1:5) as eluent furnished the
dienone 11 (40 mg, 51%) as an oil. [IR (neat): nmax 1710,
8-(2-Oxopropyl)-1,4-dioxaspiro[4.5]decane-8-aldehyde
(9). Through a cold (2908C) solution of the enone 4
(175 mg, 0.78 mmol) and a catalytic amount of NaHCO3
in methanol (1 mL) and CH2Cl2 (4 mL) was passed a
precooled (2808C) mixture of ozone in oxygen until the
colour of the solution becomes blue. The excess ozone
was ¯ushed off with a stream of oxygen and triphenyl-
phosphine (245 mg, 0.94 mmol) was added to the reaction
mixture. It was then slowly warmed up to RT and mag-
netically stirred for 8 h. Evaporation of the solvent under
reduced pressure and puri®cation on a silica gel column
using ethyl acetate±hexane (1:5 to 1:2.5) as eluent furnished
the keto aldehyde 9 (150 mg, 85%) as an oil. IR (neat): nmax
2700, 1710 cm21. 1H NMR (400 MHz, CDCl3): d 9.76 (1H,
s, H±CvO), 3.93 (4H, s, OCH2CH2O), 2.77 (2H, s,
CH2CvO), 2.12 (3H, s, CH3CvO), 2.10±1.50 (8H, m).
13C NMR (22.5 MHz, CDCl3): d 206.0 (s, CvO), 205.2
(d, H±CvO), 107.3 (s, O±C±O), 63.7 (2C, t, OCH2CH2O),
49.8 (t, CH2CvO), 45.9 (s), 30.4 (2C), 29.9 (q, CH3CvO),
28.2 (2C, t). Mass: m/z 226 (M1, 2%), 198 (13), 155 (70), 99
(90), 86 (100). HRMS: m/z For C12H18O4, Calcd.: 226.1205.
Found: 226.1211.
1
890 cm21. H NMR (200 MHz, CDCl3): d 7.51 (1H, d,
Jˆ5.6 Hz, H-4), 6.07 (1H, d, Jˆ5.6 Hz, H-3), 4.70 (2H, s,
CvCH2), 2.30 (2H, s, CH2CvO), 2.50±2.00 (4H, m),
1.80±1.50 (4H, m). 13C NMR (75 MHz, DEPT, CDCl3): d
209.2 (C, CvO), 172.3 (CH, C-4), 146.9 (C, C-8), 131.8
(CH, C-3), 108.2 (CH2, CvCH2), 46.4 (CH2, C-1), 45.8 (C,
spiro C), 37.7 (2C, CH2), 31.9 (2C, CH2)]. Further elution of
the column furnished the unreacted starting dione 10
(27 mg, 33%).
9,12-Dioxadispiro[4.2;4.2]tetradec-3-en-2-one (3). To a
solution of the keto aldehyde 9 (140 mg, 0.62 mmol) in
THF (8 mL) was added 1N methanolic KOH solution
(0.6 mL, 0.6 mmol). The reaction mixture was stirred at
RT for 8 h and the solvent was removed under reduced
pressure. It was then taken in ether (10 mL) and washed
with brine, and dried (Na2SO4). Evaporation of the solvent
and puri®cation of the residue on a silica gel column using
ethyl acetate±hexane (1:49 to 1:20) as eluent furnished the
spiroenone 3 (120 mg, 93%) as an oil.3c IR (neat): nmax
A catalytic amount of p-TSA was added to a magnetically
stirred solution of the dienone 11 (9 mg, 0.06 mmol) in dry
benzene (1.5 mL) and the reaction mixture was re¯uxed for
2 h. Evaporation of the solvent and puri®cation of the
product on a silica gel column using ethyl acetate±hexane
(1:5 to 2:5) as eluent furnished the dienone 2 (7 mg, 78%) as
1
an oil.3b,c IR (neat): nmax 1710 cm21. H NMR (300 MHz,
CDCl31CCl4): d 7.52 (1H, d, Jˆ5.7 Hz, H-4), 6.06 (1H, d,
Jˆ5.4 Hz, H-3), 5.39 (1H, br s, H-7), 2.21 and 2.14 (2H, AB
quartet, Jˆ18.3 Hz, CH2CvO), 1.71 (3H, s, ole®nic CH3),
2.30±1.60 (6H, m). 13C NMR (75 MHz, DEPT,
CDCl31CCl4): d 208.6 (C, CvO), 171.3 (CH, C-4),
134.0 (C, C-8), 132.3 (CH, C-3), 119.2 (CH, C-7), 47.5
(CH2, C-1), 43.6 (C, C-5), 36.7 (CH2), 33.0 (CH2), 28.2
(CH2), 23.6 (CH3). Mass: m/z 162 (M1, 100%).
1
1710, 1670 cm21. H NMR (300 MHz, CDCl3): d 7.56
(1H, d, Jˆ5.7 Hz, CHvCHCvO), 6.08 (1H, d, Jˆ5.7 Hz,
CHvCHCvO), 3.92 (4H, s, OCH2CH2O), 2.28 (2H, s,
CH2CvO), 1.90±1.50 (8H, m). 13C NMR (75 MHz,
DEPT, CDCl3):
d
209.1 (C, CvO), 172.3 (CH,
CHvCHCvO), 131.9 (CH, CHvCHCvO), 107.7 (C,
O±C±O), 64.3 (2C, CH2, OCH2CH2O), 46.1 (CH2), 45.0
(C), 34.0 (2C, CH2), 32.2 (2C, CH2). Mass: m/z 208 (M1,
10%), 99 (100), 86 (100).
2-Cyclopentylideneethanol (29). A suspension of sodium
hydride (60% in oil, 568 mg, 14.2 mmol) in hexanes under
nitrogen atmosphere was magnetically stirred for 10 min
and the solvent was syringed out. The oil free sodium
hydride was then suspended in dry THF (10 mL) and cooled
in an ice bath. Triethyl phosphonoacetate (3.0 mL,
Spiro[4.5]dec-3-ene-2,8-dione (10). A solution of the
dispiroenone 3 (275 mg, 1.32 mmol) in CH2Cl2 (4 mL)
and 3N aq. HCl (3 mL) was stirred for 30 min at room

A. Srikrishna, P. P. Kumar / Tetrahedron 56 (2000) 8189±8195
8193
15 mmol) in dry THF (20 mL) was added dropwise and the
reaction mixture was stirred for 30 min at room temperature.
It was then cooled in an ice bath and a solution of cyclo-
pentanone (1.0 g, 11.9 mmol) in dry THF (2 mL) was added
dropwise and stirred for 8 h at room temperature. It was then
quenched by careful addition of saturated aq. NH4Cl
solution and extracted with ether (2£15 mL). The combined
ether extract was washed with brine and dried (Na2SO4).
Evaporation of the solvent and puri®cation of the product
on a silica gel column using ethyl acetate±hexane (1:19) as
eluent furnished ethyl cyclopentylideneacetate (1.7 g, 92%)
using sodium hydride (60% in oil, 520 mg, 13 mmol) and
triethyl phosphonoacetate (3.0 mL, 15 mmol) in dry THF
(5 mL) for 8 h and puri®cation of the product over a silica
gel column using ethyl acetate±hexane (1:19) as eluent
furnished ethyl cyclooctylideneacetate (1.85 g, 94%) as an
oil.11 IR (neat): nmax 1730, 1650 cm21. 1H NMR (300 MHz,
CDCl3): d 5.72 (1H, s), 4.13 (2H, q, Jˆ7.0 Hz), 2.76 (2H, t,
Jˆ6.0 Hz), 2.31 (2H, t, Jˆ6.0 Hz), 1.80±1.70 (4H, m),
1.50±1.45 (6H, m), 1.27 (3H, t, Jˆ7.0 Hz). 13C NMR
(75 MHz, CDCl3): d 168.4 (C), 166.3 (C), 115.5 (CH),
59.2 (CH2), 38.7 (CH2), 30.6 (CH2), 27.8 (CH2), 27.6
(CH2), 26.4 (CH2), 25.6 (CH2), 25.2 (CH2), 14.3 (CH3).
Regioselective reduction of ethyl cyclooctylideneacetate
(1.0 g, 5.1 mmol) in dry ether (15 mL) using LAH (97 mg,
2.55 mmol) for 2 h and puri®cation of the product over a
silica gel column using ethyl acetate±hexane (1:9) as eluent
furnished the allyl alcohol 12c (780 g, 99%) as an oil.11 IR
(neat): nmax 3300, 1660 cm21. 1H NMR (300 MHz, CDCl3):
d 5.43 (1H, t, Jˆ7.0 Hz), 4.17 (2H, d, Jˆ7.0 Hz), 2.23 (2H,
t, Jˆ6.0 Hz), 2.19 (2H, t, Jˆ6.0 Hz), 1.70±1.40 (11H, m).
13C NMR (75 MHz, CDCl3): d 145.9 (C), 123.9 (CH), 59.3
(CH2), 37.6 (CH2), 29.0 (CH2), 28.0 (CH2), 27.3 (CH2), 26.1
(CH2), 25.9 (CH2), 25.8 (CH2).
1
as an oil.11 IR (neat): nmax 1710, 1650 cm21. H NMR
(300 MHz, CDCl3): d 5.74 (1H, br s), 4.10 (2H, q,
Jˆ7.0 Hz), 2.74 (2H, t, Jˆ7.5 Hz), 2.40 (2H, t, Jˆ
7.2 Hz), 1.80±1.50 (4H, m), 1.24 (3H, t, Jˆ7.0 Hz). 13C
NMR (75 MHz, CDCl3): d 168.9 (C), 166.8 (C), 111.6
(CH), 59.3 (CH2), 35.9 (CH2), 32.5 (CH2), 26.3 (CH2),
25.4 (CH2), 14.3 (CH3). To a cold (2708C), magnetically
stirred solution of ethyl cyclopentylideneacetate (1.7 g,
11 mmol) in dry ether (10 mL) was added LAH (209 mg,
5.5 mmol) in one portion. The reaction mixture was stirred
at 2708C for 2 h and allowed to warm up to 2208C over a
period of 30 min. Ethyl acetate (2 mL) was carefully intro-
duced to consume the excess reagent and the reaction was
quenched with ice-cold water (5 mL). The solution was
®ltered through a sintered funnel and the residue thoroughly
washed with ether (2£20 mL). The ether layer was
separated, washed with brine and dried (Na2SO4). Evapora-
tion of the solvent and puri®cation of the product on a silica
gel column using ethyl acetate±hexane (1:10) as eluent
furnished the allyl alcohol 12a (1.15 g, 93.5%) as an oil.11
IR (neat): nmax 3300 cm21. 1H NMR (300 MHz, CDCl3): d
5.50±5.40 (1H, m), 4.06 (2H, d, Jˆ7.2 Hz), 2.30±2.18 (4H,
m), 2.00 (1H, br s), 1.70±1.50 (4H, m). 13C NMR (75 MHz,
CDCl3): d 147.5 (C), 119.0 (CH), 60.7 (CH2), 33.6 (CH2),
28.5 (CH2), 26.2 (CH2), 25.9 (CH2).
2-Cyclododecylideneethanol (12d). Wittig±Horner±
Emmons reaction of cyclododecanone (2.0 g, 11 mmol)
using sodium hydride (60% in oil, 560 mg, 14 mmol) and
triethyl phosphonoacetate (3.2 mL, 16 mmol) in dry THF
(30 mL) for 8 h and puri®cation of the product on a silica
gel column using ethyl acetate and hexane (1:19) as eluent
furnished ethyl cyclododecylideneacetate (2.65 g, 96%) as
an oil.11 IR (neat): nmax 1720, 1640 cm21 1H NMR
.
(300 MHz, CDCl3): d 5.75 (1 H, s), 4.14 (2H, q, Jˆ
7.0 Hz), 2.72 (2H, t, Jˆ6.6 Hz), 2.21 (2H, t, Jˆ6.6 Hz),
1.70±1.20 (21H, m), 13C NMR (75 MHz, CDCl3): d 166.9
(C), 163.0 (C), 116.2 (CH), 59.4 (CH2), 32.8 (CH2), 29.8
(CH2), 25.0 (CH2), 24.9 (CH2), 24.1 (CH2), 24.0 (2C, CH2),
23.7 (CH2), 23.4 (CH2), 22.9 (CH2), 22.1 (CH2), 14.3 (CH3).
Regioselective reduction of ethyl cyclododecylideneacetate
(1.0 g, 3.97 mmol) in dry ether (10 mL) with LAH (76 mg,
2.0 mmol) for 30 min and puri®cation of the product on a
silica gel column using ethyl acetate±hexane (1:10) as
eluent furnished the allyl alcohol 12d (820 mg, 99%) as
2-Cyclohexylideneethanol (12b). Horner±Wadsworth±
Emmons reaction of cyclohexanone (1.0 g, 10.2 mmol)
using sodium hydride (60% in oil, 480 mg, 12 mmol) and
triethyl phosphonoacetate (3.0 mL, 15 mmol) in dry THF
(8 mL) for 8 h and puri®cation of the product over a silica
gel column using ethyl acetate±hexane (1:40) as eluent
furnished ethyl cyclohexylideneacetate (1.6 g, 94%) as an
oil.11 IR (neat): nmax 1720, 1660 cm21. 1H NMR (300 MHz,
CDCl3): d 5.47 (1H, br s), 4.06 (2H, q, Jˆ7.2 Hz), 2.78 (2H,
t), 2.15 (2H, t), 1.58 (6H, br s), 1.23 (3H, t, Jˆ6.8 Hz). 13C
NMR (75 MHz, CDCl3): d 166.2 (C), 162.8 (C), 113.2
(CH), 59.2 (CH2), 38.0 (CH2), 29.7 (CH2), 28.7 (CH2),
27.8 (CH2), 26.4 (CH2), 14.4 (CH3). Regioselective
reduction of ethyl cyclohexylideneacetate (1.6 g, 9.52
mmol) in dry ether (20 mL) using LAH (180 mg,
4.73 mmol) for 2 h and puri®cation of the product over a
silica gel column using ethyl acetate±hexane (1:20 to 1:10)
as eluent furnished the allyl alcohol 12b (1.1 g, 92%) as an
oil.11 IR (neat): nmax 3300, 1670 cm21. 1H NMR (300 MHz,
CDCl3): d 5.32 (1H, t, Jˆ7.2 Hz), 4.08 (2H, d, Jˆ7.2 Hz),
2.20±2.00 (4H, m), 1.50 (7H, br s). 13C NMR (75 MHz,
CDCl3): d 144.1 (C), 120.2 (CH), 58.3 (CH2), 36.9 (CH2),
28.7 (CH2), 28.3 (CH2), 27.7 (CH2), 26.6 (CH2).
an oil.11 IR (neat): nmax 3300, 1650 cm21 1H NMR
.
(300 MHz, CDCl3): d 5.50 (1H, t, Jˆ7.2 Hz), 4.18 (2H, d,
Jˆ7.2 Hz), 2.13±2.06 (4H, m), 1.70±1.20 (19H, m). 13C
NMR (75 MHz, CDCl3): d 142.1 (C), 124.0 (CH), 59.3
(CH2), 31.5 (CH2), 28.9 (CH2), 25.0 (CH2), 24.9 (CH2),
24.1 (CH2), 24.0 (CH2), 23.9 (CH2), 23.8 (CH2), 23.2
(CH2), 23.0 (CH2), 22.1 (CH2).
Spiro[4.4]non-3-en-2-one (15a). A solution of the allyl
alcohol 12a (1.0 g, 8.92 mmol), 2-methoxypropene
(3.22 g, 44.6 mmol) and a catalytic amount of mercuric
acetate was heated ®rst at 1008C and then at 1808C for
36 h in Carius tube under nitrogen atmosphere. The reaction
mixture was then cooled, diluted with ether, washed with
aqueous NaHCO3 solution and dried (Na2SO4). Evaporation
of the solvent and puri®cation of the product on a silica gel
column using ethyl acetate±hexane (1:20 to 1:9) as eluent
furnished the ketone 13a (700 mg, 52%) as an oil. IR (neat):
2-(Cyclooctylidene)ethanol (12c). Horner±Wardsworth±
Emmons reaction of cyclooctanone (1.26 g, 10 mmol)
n
max 1710, 1635, 910 cm21. 1H NMR (300 MHz, CDCl3): d
5.86 (1H, dd, Jˆ17.1 and 10.5 Hz, CHvCH2), 4.96 (1H, d,

8194
A. Srikrishna, P. P. Kumar / Tetrahedron 56 (2000) 8189±8195
Jˆ10.5 Hz) and 4.92 (1H, d, Jˆ17.1 Hz) [CHvCH2], 2.50
(2H, s, CH2CvO), 2.05 (3H, s, CH3CvO), 1.90±1.45 (8H,
m). 13C NMR (75 MHz, DEPT, CDCl31CCl4): d 207.0 (C,
CvO), 144.8 (CH, CHvCH2), 112.1 (CH2, CHvCH2),
53.7 (CH2, CH2CvO), 47.7 (C), 37.2 (2 C, CH2), 28.8
(CH3, CH3CvO), 23.5 (2C, CH2). Mass: m/z 152 (M1,
10%), 135 (15), 109 (50), 95 (100), 94 (80). Ozonolysis of
the ketone 13a (152 mg, 1 mmol) in methanol (0.2 mL) and
CH2Cl2 (4 mL) and reductive work up with triphenyl-
phosphine (314 mg, 1.2 mmol) followed by puri®cation of
the product on a silica gel column using ethyl acetate±
hexane (1:5) as eluent furnished the keto aldehyde 14a
3.57 mmol) with 2-methoxypropene (1.54 g, 21.5 mmol)
and a catalytic amount of mercuric acetate at 1808C for
36 h followed by puri®cation of the product on a silica gel
column using ethyl acetate±hexane (1:20) as eluent
furnished the enone 13c (400 mg, 58% yield) as an oil. IR
1
(neat): nmax 1700, 1630, 910 cm21. H NMR (300 MHz,
CDCl3): d 5.79 (1H, dd, Jˆ17.5 and 11.0 Hz, CHvCH2),
5.06 (1H, d, Jˆ11.0 Hz) and 4.95 (1H, d, Jˆ17.5 Hz)
[CHvCH2], 2.40 (2H, s, CH2CvO), 2.07 (3H, s,
CH3CvO), 1.70±1.40 (14H, m). 13C NMR (75 MHz,
DEPT, CDCl3):
d
208.7 (C, CvO), 146.4 (CH,
CHvCH2), 112.6 (CH2, CHvCH2), 53.7 (CH2,
CH2CvO), 42.9 (C), 32.6 (CH3, CH3CvO), 32.3 (2C,
CH2), 28.5 (2C, CH2), 25.2 (CH2), 22.5 (2C, CH2). Mass:
m/z 194 (M1, 12%), 136 (50), 121 (30), 110 (20), 108 (32),
95 (50), 43 (100). Ozonolysis of the enone 13c (240 mg,
1.23 mmol) and reductive workup with triphenylphosphine
(388 mg, 1.48 mmol) for 8 h followed by puri®cation of the
product on a silica gel column using ethyl acetate±hexane
(1:5) as eluent furnished the keto aldehyde 14c (200 mg,
83%), which was found to form hydrate on standing. IR
(120 mg, 72%) as an oil. IR (neat): nmax 2720, 1720 cm21
.
1H NMR (90 MHz, CDCl3): d 9.58 (1H, s, H±CvO), 2.81
(2H, s, CH2CvO), 2.10 (3H, s, CH3CvO), 1.80±1.40 (8H,
m). Intramolecular aldol condensation reaction of the keto
aldehyde 14a (50 mg, 0.3 mmol) with 1 M methanolic KOH
solution (0.3 mL, 0.3 mmol) in THF (4.0 mL) for 8 h
followed by puri®cation of the product on a silica gel
column using ethyl acetate±hexane (1:9) as eluent furnished
the spiroenone 15a (40 mg, 89%).10a IR (neat): nmax 1720,
1
1
1580 cm21. H NMR (90 MHz, CDCl3): d 7.48 (1H, d,
(neat): nmax 1720 cm21. H NMR (300 MHz, CDCl3): d
Jˆ6.0 Hz, H-4), 6.01 (1H, d, Jˆ6.0 Hz, H-3), 2.22 (2H, s,
9.56 (1H, s, H±CvO), 2.73 (2H, s, CH2CvO), 2.12 (3H,
s, CH3CvO), 1.90±1.50 (14H, m). Intramolecular aldol
condensation of the keto aldehyde 14c (16 mg,
0.08 mmol) in THF (1.1 mL) with 10% methanolic KOH
solution (0.08 mL, 0.08 mmol) for 8 h followed by puri®-
cation of the product on a silica gel column using ethyl
acetate±hexane (1:9) as eluent furnished the spiroenone
H-1), 1.80±1.50 (8H, m).
Spiro[4.5]dec-3-en-2-one (15b). One-pot Claisen rearrange-
ment of the allyl alcohol 12b (1.1 g, 8.73 mmol) with
2-methoxypropene (3.14 g, 43.6 mmol) and a catalytic
amount of mercuric acetate at 1808C for 36 h and puri®-
cation of the product on a silica gel column using ethyl
acetate±hexane (1:20) as eluent furnished ketone 13b
(1.1 g, 76%) as an oil. IR (neat): nmax 1710, 1630,
1
15c (10 mg, 70%). IR (neat): nmax 1710, 1670 cm21. H
NMR (200 MHz, CDCl3): d 7.64 (1H, d, Jˆ5.7 Hz, H-4),
6.00 (1H, d, Jˆ5.5 Hz, H-3), 2.19 (2H, s, H-1), 1.70±1.60
(14H, m). 13C NMR (22.5 MHz, CDCl3): d 209.4 (s, CvO),
172.6 (d, C-4), 130.7 (d, C-3), 49.0 (t, C-1), 48.5 (s, C-5),
34.7 (2C, t, C-6 and 12), 28.1 (2C, t, C-8 and 10), 24.4 (t,
C-9), 23.3 (2C, t, C-7 and 11). Mass: m/z 178 (M1, 35%),
135 (43), 121 (43), 107 (43), 95 (80), 94 (100). HRMS: For
C12H18O, Calcd.: 178.1358. Found: 178.1361.
1
910 cm21. H NMR (300 MHz, CDCl3): d 5.81 (1H, dd,
Jˆ17.7 and 11.1 Hz, CHvCH2), 5.12 (1H, d, Jˆ11.1 Hz)
and 5.00 (1H, d, Jˆ17.7 Hz) [CHvCH2], 2.44 (2H, s,
CH2CvO), 2.08 (3H, s, CH3CvO), 1.70±1.60 (4H, m),
1.46 (6H, br s). 13C NMR (75 MHz, CDCl3): d 208.6
(CvO), 145.3 (CHvCH2), 113.5 (CHvCH2), 54.6, 39.7,
35.8 (2C), 32.8, 26.2, 22.1 (2C). Mass: m/z 166 (M1, 10%),
151 (15), 123 (50), 108 (45). Ozonolysis of the enone 13b
(200 mg, 1.2 mmol) in methanol (0.2 mL, mmol) and
CH2Cl2 (5 mL) at 2788C and reductive work up with tri-
phenylphosphine (378 mg, 1.45 mmol) followed by puri®-
cation of the product on a silica gel column using ethyl
acetate±hexane (1:5) as eluent furnished the keto aldehyde
14b (180 mg, 89%), which was found to decompose on
standing. IR (neat): nmax 2700, 1715 cm21. Intramolecular
aldol condensation of the keto aldehyde 14b (180 mg,
1.07 mmol) in THF (15 mL) with 1 M methanolic KOH
solution (1 mL, 1 mmol) at RT for 8 h followed by puri®-
cation of the product on a silica gel column using ethyl
acetate±hexane (1:20 to 1:10) as eluent furnished the
spiroenone 15b (120 mg, 75%).10b±e IR (neat): nmax 1710,
Spiro[4.11]hexadec-3-en-2-one (15d). One-pot Claisen
rearrangement of the allyl alcohol 12d (600 mg,
2.9 mmol) with 2-methoxypropene (1.03 g, 14.3 mmol)
and a catalytic amount of mercuric acetate at 1808C for
36 h followed by puri®cation of the product on a silica gel
column using ethyl acetate±hexane (1:20) as eluent
furnished the ketone 13d (450 mg, 56%) as an oil. IR
1
(neat): nmax 1700, 1640, 910 cm21. H NMR (200 MHz,
CDCl3): d 5.83 (1H, dd, Jˆ17.6 and 11.0 Hz, CHvCH2),
5.05 (1H, d, Jˆ11.0 Hz) and 4.95 (1H, d, Jˆ17.6 Hz)
[CHvCH2], 2.40 (2H, s, H-1), 2.08 (3H, s, CH3CvO),
1.60±1.20 (22H, m). 13C NMR (75 MHz, CDCl3): d 208.4
(C, CvO), 145.8 (CH, CHvCH2), 112.5 (CH2, CHvCH2),
52.9 (CH2, CH2CvO), 41.9 (C, C-10), 32.4 (CH3,
CH3CvO), 31.4 (CH2), 26.6 (2C, CH2), 26.1 (2C, CH2),
22.6 (2C, CH2), 22.1 (2C, CH2), 19.0 (2C, CH2). Mass:
m/z 250 (M1, 15%), 193 (28), 123 (20), 110 (35), 95 (36),
81 (30), 68 (30), 55 (38), 43 (100). Ozonolysis of the ketone
13d (300 mg, 1.2 mmol) in methanol (0.2 mL) and CH2Cl2
(4 mL) and reductive work up with triphenylphosphine
(367 mg, 1.4 mmol) at RT for 8 h followed by puri®cation
of the product on a silica gel column using ethyl acetate±
hexane (1:5) as eluent furnished the keto aldehyde 14d
1
1590 cm21. H NMR (300 MHz, CDCl3): d 7.45 (1H, d,
Jˆ5.5 Hz, H-4), 5.99 (1H, d, Jˆ5.5 Hz, H-3), 2.17 (2H, s,
H-1), 1.80±1.20 (10H, m). 13C NMR (75 MHz, DEPT,
CDCl31CCl4): d 208.4 (C, CvO), 172.5 (CH, C-4),
131.6 (CH, C-3), 46.9 (CH2, C-1), 46.0 (C, C-5), 36.8
(2C, CH2, C-6 and 10), 25.5 (CH2, C-8), 21.4 (2C, CH2,
C-7 and 9). Mass: m/z 150 (M1, 75%), 107 (75), 95 (100).
Spiro[4.7]dodec-3-en-2-one (15c). A one-pot Claisen
rearrangement of the allyl alcohol 12c (550 mg,
1
(220 mg, 73%) as an oil. IR (neat): nmax 1720 cm21. H

A. Srikrishna, P. P. Kumar / Tetrahedron 56 (2000) 8189±8195
8195
J. Chem. Soc., Chem. Commun. 1968, 1135; Kaiser, R.; Naegeli, P.
Tetrahedron Lett. 1972, 2009 and 2013; Tomita, B.; Hirose, H.
Tetrahedron Lett. 1970, 143; Tomita, B.; Isono, T.; Hirose, H.
Tetrahedron Lett. 1970, 1371.
NMR (300 MHz, CDCl3): d 9.67 (1H, s, H±CvO), 2.70
(2H, s, CH2CvO), 2.10 (3H, s, CH3CvO), 1.60±1.40
(4H, m), 1.26 (18H, br s). Intramolecular aldol condensation
reaction of the keto aldehyde 14d (50 mg, 0.2 mmol) in
THF (3.5 mL) with 1 M methanolic KOH solution
(0.16 mL, 0.16 mmol) at RT for 8 h followed by puri®cation
of the residue on a silica gel column using ethyl acetate±
hexane (1:20 to 1:9) as eluent furnished the spiroenone 15d
3. (a) Marx, J. N.; Norman, L. R. Tetrahedron Lett. 1973, 4375;
J. Org. Chem. 1975, 40, 1602. (b) McCrae, D. A.; Dolby, L. J. Org.
Chem. 1977, 42, 1607. (c) Martin, S. F.; Chou, T.-S. J. Org. Chem.
1978, 43, 1027. (d) Ackroyd, J.; Karpf, M.; Dreiding, A. S. Helv.
Chim. Acta 1985, 68, 338. (e) Subba Rao, G. S. R.; Pramod, K.
Indian J. Chem. 1986, 25B, 783; Biju, P. J.; Subba Rao, G. S. R.
Tetrahedron Lett. 1999, 40, 2405. (f) Mori, M.; Isono, N.; Kaneta
N.; Shibasaki, M. J. Org. Chem. 1993, 58, 2972. (g) Pinder, A. R;
Price S. J.; Rice, R. M. J. Org. Chem. 1972, 37, 2202.
4. Heathcock, C. H.; Graham, S. L.; Pirrung, M. C.; Plavac, F.;
White, C. T. In The Total Synthesis of Natural Products, Apsimon,
J., Ed.; Wiley: New York, 1983; Vol. 5, pp 284±305.
5. Srikrishna, A.; Kumar, P. P. Tetrahedron Lett. 1996, 37, 1683.
6. Tanaka, T.; Okuda, O.; Murakami, K.; Yoshino, H.;
Mikamiyama, H.; Kanda, A.; Kim, S.-W.; Iwata, C. Chem.
Pharm. Bull. 1995, 43, 1017.
(40 mg, 85%) as a solid. IR (neat): nmax 1710, 1580 cm21
.
1H NMR (200 MHz, CDCl3): d 7.60 (1H, d, Jˆ5.6 Hz,
H-4), 6.02 (1H, d, Jˆ5.7 Hz, H-3), 2.17 (2H, s, H-1),
1.50±1.30 (22H, m, H-6 to 16). 13C NMR (22.5 MHz,
CDCl3): d 208.9 (s, CvO), 172.0 (d, C-4), 131.1 (d, C-3),
47.8 (t, CH2CvO), 33.4 (2C, t, C-6 and 16), 32.2 (s, C-5),
26.3 (2C, t), 25.7 (t), 22.3 (2C, t), 21.8 (2C, t), 19.9 (2C, t).
Mass: m/z 234 (M1, 40%), 109 (70), 96 (100), 95 (80).
HRMS: For C16H26O, Calcd.: 234.1983. Found: 234.1981.
Acknowledgements
7. Claisen, L. Ber. 1912, 45, 3157; McKenzie, T. C. Org. Prep.
Proc. Int. 1987, 19, 435.
We thank the Council of Scienti®c and Industrial Research,
New Delhi for the award of a research fellowship to P. P. K.
8. Paquette, L. A. Top. Curr. Chem. 1979, 79, 41 and 1984, 119, 1;
Ramaiah, M. Synthesis 1984, 529; Mehta, G.; Srikrishna, A. Chem.
Rev. 1997, 671; Singh, V.; Thomas, B. Tetrahedron 1998, 54,
3647.
References
9. Sannigrahi, M. Tetrahedron 1999, 55, 9007 (and references
cited therein).
1. Sorm, F.; Herout, V. Collect. Czech. Chem. Commun. 1948, 13,
177; Sorm, F.; Herout, V. Collect. Czech. Chem. Commun. 1949,
14, 723; Sykora, V.; Herout, V.; Pliva, J.; Sorm, F. Collect. Czech.
Chem. Commun. 1958, 23, 1072; Sykora, V.; Herout, V.; Reiser,
A.; Sorm, F. Collect. Czech. Chem. Commun. 1959, 24, 1306;
Vrkoc, J.; Herout, V.; Sorm, F. Collect. Czech. Chem. Commun.
1962, 27, 2709; Vrkoc, J.; Jonas, J.; Herout, V.; Sorm, F. Collect.
Czech. Chem. Commun. 1964, 29, 539; McEachan, C. E.; McPhail,
A. T.; Sim, G. A. J. Chem. Soc. C 1966, 579.
10. (a) Schlosser, M.; Hartmann, J.; Stahle, M.; Kramar, J.; Walde,
A.; Mordini, A. Chimia 1986, 40, 306. (b) Corey, E. J.; Ghosh,
A. K. Tetrahedron Lett. 1987, 28, 175. (c) Karpf, M.; Dreiding,
A. S. Helv. Chim. Acta 1979, 62, 852. (d) Martin, S. F.; Chou,
T.-S.; Payne, C. W. J. Org. Chem. 1977, 42, 2520. (e) Wenkert, E.;
Buckwalter, B. L.; Craveiro, A. A.; Sanchez, E. L.; Sathe, S. S.
J. Am. Chem. Soc. 1978, 100, 1267.
2. McClure, R. J.; Schorno, K. S.; Bertrand, J. A.; Zalkow, L. H.
11. Srikrishna, A.; Kumar, P. P. J. Ind. Chem. Soc. 1999, 76, 521.