Convenient synthesis of volatile Streptomyces lactones

Article abstract of DOI:10.1055/s-2005-870025

A convenient three-step synthetic approach towards 3-alkyl-5-methyl-2[5H] furanones is described. The steps involved in the synthesis are domino primary alcohol oxidation-Wittig reaction, acid-catalysed lactonisation and isomerisation. This synthetic appr

Full text of DOI:10.1055/s-2005-870025

PAPER
2341
Convenient Synthesis of Volatile Streptomyces Lactones
ConvenientSynth
h
esisof
V
ola
a
tile Strepto
n
m
yces Lacton
d
es an P. Amonkar,a Santosh G. Tilve,*a P. S. Parameswaranb
a
Department of Chemistry, Goa University, Taleigao Plateau, Goa 403 206, India
Fax +91(832)245184; E-mail: santoshtilve@yahoo.com
b
Chemical Oceanography Division, National Institute of Oceanography (CSIR), Dona-Paula-Goa 403 004, India
Received 20 January 2005; revised 11 April 2005
Dedicated to Prof. Ian Blair on the occasion of his 60th birthday
tion conditions (Scheme 1). Thus, butanol was subjected
to the domino primary alcohol oxidation–Wittig reaction,
after three hours the alcohol was found to be consumed
(TLC). On usual work-up, only one product was obtained.
Abstract: A convenient three-step synthetic approach towards 3-
alkyl-5-methyl-2[5H]furanones is described. The steps involved in
the synthesis are domino primary alcohol oxidation–Wittig reac-
tion, acid-catalysed lactonisation and isomerisation. This synthetic
approach has been exploited to synthesise four Streptomyces lac- As the product could be E or Z, it was necessary to know
tones.
the geometry of the product. As the product was a trisub-
1
stituted olefin it was necessary to compare the H NMR
chemical shift values with syn and anti protons attached at
the b-carbon of the unsaturated system. To do this, stable
phosphorane 5 was condensed with formaldehyde to give
6a (Figure 2). The protons at the b-carbon appeared at
5.77 and 6.20 ppm. The signal at 5.77 ppm was due to the
anti proton and the signal at 6.20 ppm was due to the syn
proton with respect to carboethoxy group and thus 6c was
confirmed to be the E-isomer. Prolonging the reaction
time (> 4 h) resulted in a decrease in yield showing just
how sensitive the product was to reaction conditions. The
E-ester 6c was then subjected to acid-catalysed lactonisa-
tion followed by isomerisation using RhCl3·3H2O as de-
picted (Scheme 1), to yield racemic 3-butyl-5-methyl-
2[5H]furanone (1c), a naturally occurring butenolide. Op-
tically active compound 1c is a precursor9 to (+)-blastmy-
cinone and (–)-3-epi-blastmycinone. Similarly, hexanol
and 3-methyl butanol were subjected to the above proto-
col to obtain ( )-butenolides 1d,e. For volatile aldehydes
direct condensation of phosphorane 5 with 37% formalin
and 20% aqueous acetaldehyde was necessary to obtain
6a,b. In our hands, pure butenolide 1a was not obtained
by the isomerisation of 7a. Incidentally all the ( )-g-
methyl-a-alkylidene-g-lactones (7b–e) have exclusive E-
geometry.10
Key words: domino reaction, Wittig reaction, isomerisation, lac-
tone, oxidation
Butenolide (3-alkyl-5-methyl-2[5H]furanone), a five-
membered unsaturated lactone, is widely encountered in
many natural products.1 Butenolides are of interest2 due to
their broad range of biological activities e.g. butenolide 1a
is a component of mushroom flavour,3 1b has fungicidal
activity,4 1c–g are metabolites from Streptomyces gri-
seus,1b,5 while 2 and 3 isolated from leaves of Hortonia
exhibited mosquito larvicidal activities (Figure 1).6 3-
Substituted-5-methyl-2[5H]furanone is believed to be one
of the essential subunits responsible for the cytotoxicity of
acetogenins.2g
O
O
O
R
(
)
8
(
)
8
O
O
O
1a–e
2
3
1a R = CH3
b R = CH2CH3
c R = CH2CH2CH2CH3
d R = CH2CH2CH2CH2CH2CH3
e R = CH2CH2CH(CH3)2
In conclusion, we have demonstrated that functionalised
Wittig reagent 5 can also be used for the domino primary
alcohol oxidation–Wittig reaction. Using this protocol,
four volatile Streptomyces lactones were synthesized as
racemates in just three steps in a convenient manner. Syn-
thesis of two of them (1d and 1e) is reported for the first
time.
f R = CH2CH2CH2CH(CH3)2
g R = CH2CH2CH2CH2CH(CH3)2
Figure 1
Domino reactions have attracted considerable attention7
as they result in the reduction in the amount of by-prod-
ucts, solvents, eluents, time and energy used. In continua-
tion of our research work dealing with the use of domino
primary alcohol oxidation–Wittig reactions,8 we were in-
terested in testing functionalised Wittig reagent 5 for its
own and its products’ stability towards the domino reac-
δ 6.20
H
H
COOEt
δ 5.77
SYNTHESIS 2005, No. 14, pp 2341–2344
x
x.
x
x
.
2
0
0
5
6a
Advanced online publication: 14.07.2005
DOI: 10.1055/s-2005-870025; Art ID: Z01705SS
© Georg Thieme Verlag Stuttgart · New York
Figure 2

2342
C. P. Amonkar et al.
PAPER
O
H
O
H
R
COOEt
PCC-NaOAc
COOEt
Ph3P
R
H+
R
R-CH2OH
O
O
RhCl3⋅3H2O
4
5
6
7
1
Scheme 1
Table 1 Yields for the Three-Step Synthesis
7.1 Hz, 2 H, OCH2CH3), 5.11 (m, 2 H, CH2CH=CH2), 5.57 (br s, 1
H, HCH=C), 5.84 (m, 1 H, CH2CH=CH2), 6.20 (br s, 1 H, HCH=C).
13C NMR (75 MHz, CDCl3): d = 14.10 (CH3), 35.82 (CH), 60.60
(OCH2), 116.65 (CH=CH2), 125.08 (=CH2), 135.10 (=CH), 139.18
(C), 166.86 (C=O).
MS: m/z (%) = 141 (28, M+ + 1), 113 (100), 112 (12), 95 (48),
67(36).
Compound
R
Yield (%)
6
7
1
a
H
50a
50a
57
87
85
92
89
90
–
b
cb
d
e
CH3
92
77
93
94
CH2CH2CH3
CH2(CH2)3CH3
CH2CH(CH3)2
(E)-Ethyl-2-ethylidenepent-4-enoate (6b)
Yield: 50%.
IR (neat):1722 (C=O), 1660 (C=C), 1643 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 1.28 (t, J = 7.2 Hz, 3 H,
OCH2CH3), 1.79 (d, J = 6.9 Hz, 3 H, CH3), 3.08 (d, J = 6.0 Hz, 2 H,
CH2CH=CH2), 4.19 (q, J = 7.2 Hz, 2 H, OCH2CH3), 5.00 (m, 2 H,
CH2CH=CH2), 5.81 (m, 1 H, CH2CH=CH2), 6.95 (q, J = 6.9 Hz, 1
H, =CHCH3).
60
65
a Yield based on phosphorane consumed.
b Yield: 49%, obtained using IBX.11
13C NMR (75 MHz, CDCl3): d = 14.12 (CH3), 14.21 (CH3), 30.45
(CH2), 60.36 (OCH2), 114.91 (CH=CH2), 130.96 (C), 135.19
(CH=CH2), 138.28 (=CH), 167.45 (C=O).
MS: m/z (%) = 155 (22, M+ + 1), 127 (100), 109 (54), 99 (48), 81
(39), 79 (11).
Column chromatography was performed on silica gel (60–120
mesh) and TLC on silica gel (13% CaSO4 as binder). IR spectra
were recorded on Shimadzu FT-IR spectrophotometer (KBr pellet
or neat sample). 1H NMR and 13C NMR were recorded on a Bruker-
300 MHz instrument. The multiplicities of carbon signals were ob-
tained from DEPT experiments. Low resolution mass spectra were
recorded on triple quadrapole MS/MS instrument (Applied Biosys-
tem Inc.) and high resolution mass spectra (HRMS) were recorded
on a MicroMass ES-QTOF Mass spectrometer.
Esters 6c–e; General Procedure
To a magnetically stirred suspension of PCC (1.5 mmol) and
NaOAc (1.5 mmol) in anhyd CH2Cl2 (10 mL), alcohol 4 (1 mmol)
in anhyd CH2Cl2 (5 mL) was added followed by phosphorane 5 (1
mmol) in one portion. After 3 h, Et2O (5 mL) was added and the su-
pernatant solution was decanted from the black granular solid. The
combined organic layers were filtered through a short pad of celite.
The residue obtained after evaporation of the solvent was further
purified by column chromatography using hexanes as the eluent to
afford a pleasant-smelling liquid.
Phosphorane 5
A mixture of carboethoxymethylenetriphenylphosphorane (10 g,
2.87 mmol) and allyl bromide (4.16 g, 3.44 mmol) was refluxed in
CHCl3 (25 mL) for 5 h. The solvent was evaporated under vacuum.
H2O (100 mL) was added and the reaction mixture was washed with
benzene (2 × 20 mL). Benzene (50 mL) and phenolphthalein (2
drops) were added to the aqueous layer and 2 N NaOH was added
dropwise with vigorous shaking till a pink colour persisted. The
benzene layer was separated, washed with H2O (20 mL), brine (10
mL), dried over Na2SO4 and concentrated to get a thick syrupy liq-
uid which on scratching after addition of anhyd hexane (15 mL) re-
sulted in a solid product. The solid, on recrystallisation (benzene–
hexane), yielded phosphorane 5 (7.8 g, 70%); mp 122 °C.12
(E)-Ethyl-2-(prop-2-enyl)hex-2-enoate (6c)
Yield: 57%.
IR (neat): 1716 (C=O), 1654 (C=C), 1643 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 0.95 (t, J = 7.5 Hz, 3 H, CH2CH3),
1.29 (t, J = 7.2 Hz, 3 H, OCH2CH3), 1.49 (q, J = 7.5 Hz, 2 H,
CH2CH3), 2.17 (q, J = 7.5 Hz, 2 H, CH2CH2CH3), 3.07 (d, J = 6.0
Hz, 2 H, CH2CH=CH2), 4.19 (q, J = 7.2 Hz, 2 H, OCH2CH3), 4.99
(m, 2 H, CH2CH=CH2), 5.80 (m, 1 H, CH2CH=CH2), 6.84 (t, J = 7.5
Hz, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 13.80 (CH3), 14.15 (CH3), 21.89
(CH2), 30.46 (CH2), 30.75 (CH2), 60.30 (CH2), 114.00 (CH=CH2),
130.02 (C), 135.55 (CH=CH2), 143.45 (CH), 167.52 (C=O).
Esters 6a,b; General Procedure
To a solution of phosphorane 5 (1 mmol) in MeOH (10 mL) was
added an aq solution of aldehyde (2 mL, 5 mmol) and the reaction
mixture was refluxed for 2 h. After the completion of reaction, hex-
anes (20 mL) was added and the reaction mixture was shaken vig-
orously. The upper layer was separated, evaporated and the
resulting crude product was purified by silica gel column chroma-
tography (hexanes) to afford a pleasant-smelling volatile liquid.
MS: m/z (%) = 183 (6, M+ + 1), 155 (3), 137 (73), 109 (100), 67
(43).
Ethyl-2-methylidenepent-4-enoate (6a)
Yield: 50%.
IR (neat):1727 (C=O), 1640 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 1.31 (t, J = 7.2 Hz, 3 H,
OCH2CH3), 3.07 (br d, J = 6.6 Hz, 2 H, CH2CH=CH2), 4.22 (q, J =
(E)-Ethyl-2-(prop-2-enyl)oct-2-enoate (6d)
Yield: 60%.
IR (neat): 1722 (C=O), 1653 (C=C), 1643 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 0.82 (t, J = 7.5 Hz, 3 H, CH2CH3),
1.11–1.35 (m, 9 H, OCH2CH3 and 3 × CH2), 2.11 (m, 2 H, =CCH2),
3.00 (d, J = 6 Hz, 2 H, CH2CH=CH2), 4.12 (q, J = 7.2 Hz, 2 H,
Synthesis 2005, No. 14, 2341–2344 © Thieme Stuttgart · New York

PAPER
Convenient Synthesis of Volatile Streptomyces Lactones
2343
OCH2CH3), 4.91 (m, 2 H, CH2CH=CH2), 5.74 (m, 1 H,
CH2CH=CH2), 6.77 (t, J = 7.5 Hz, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 13.97 (CH3), 14.28 (CH3), 22.49
(CH2), 28.40 (CH2), 28.54 (CH2), 30.84 (CH2), 31.62 (CH2), 60.44
(OCH2), 114.96 (CH=CH2), 129.86 (C), 135.66 (CH=CH2), 143.92
(=CH), 167.69 (C=O).
IR (neat): 1753 (C=O), 1690 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 0.95 (t, J = 7.5 Hz, 3 H, CH2CH3),
1.42 (d, J = 6.3 Hz, 3 H, CHCH3), 1.51 (m, 2 H, CH2CH3), 2.16 (m,
2 H, =CHCH2), 2.44 (m, 1 H, HCHCH), 3.01 (m, 1 H, HCHCH),
4.66 (m, 1 H, CH), 6.73 (m, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 13.78 (CH3), 21.47 (CH2), 22.26
(CH3), 32.16 (CH2), 32.91 (CH2), 73.94 (CH), 126.67 (C), 140.55
(=CH), 170.72 (C=O).
HRMS: m/z calcd for C13H23O2 (M + H+): 211.1698; found:
211.1696.
MS: m/z (%) = 155 (6, M+ + 1), 137 (50), 109 (100), 95 (26), 81
(28), 67 (96), 65 (10), 43 (8).
(E)-Ethyl-5-methyl-2-(prop-2-enyl)hex-2-enoate (6e)
Yield: 65%.
IR (neat): 1720 (C=O), 1650 (C=C) cm–1.
5-Methyl-3-[(E)-hexylidene]dihydrofuran-2(5H)-one (7d)
Yield: 89%.
IR (neat): 1753 (C=O), 1685 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 0.90 [d, J = 6.6 Hz, 6 H,
CH(CH3)2], 1.22 (t, J = 7.2 Hz, 3 H, OCH2CH3), 1.69 [m, 1 H,
CH(CH3)2], 2.01 (m, 2 H, CH2), 2.99 (d, J = 6.0 Hz, 2 H,
CH2CH=CH2), 4.11 (q, J = 7.2 Hz, 2 H, OCH2CH3), 4.91 (m, 2 H,
CH2CH=CH2), 5.73 (m, 1 H, CH2CH=CH2), 6.79 (t, J = 7.2 Hz, 1
H, CH2CH=C).
13C NMR (75 MHz, CDCl3): d = 14.23 (CH3), 22.32 (CH3), 22.66
(CH3), 29.08 (CH), 31.58 (CH2), 37.58 (CH2), 60.38 (OCH2),
114.98 (CH=CH2), 130.48 (C), 135.56 (CH=CH2), 148.13 (=CH),
167.58 (C=O).
1H NMR (300 MHz, CDCl3): d = 0.90 (t, J = 6.6 Hz, 3 H, CH2CH3),
1.25–1. 50 (m, 6 H, 3 × CH2), 1.42 (d, J = 6.3 Hz, 3 H, CH3), 2.18
(q, J = 7.2 Hz, 2 H, =CHCH2), 2.40 (m, 1 H, HCHCH), 3.00 (br dd,
J = 16.8, 7.8 Hz, 1 H, HCHCH), 4.65 (m, 1 H, CH), 6.72 (t, J = 7.5
Hz, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 13.91 (CH3), 22.25 (CH3), 22.40
(CH2), 27.80 (CH2), 30.13 (CH2), 31.43 (CH2), 32.88 (CH2), 73.94
(CH), 126.45 (C), 140.87 (=CH), 170.96 (C=O).
HRMS: m/z calcd for C12H20O2 + Na (M + Na+): 219.1361; found:
219.1361.
HRMS: m/z calcd for C11H19O2 (M + H+): 183.1385; found:
183.1376.
7a–e; General Procedure
5-Methyl-3-[(E)-3-methylbutylidene]dihydrofuran-2(5H)-one
To a flask containing ice-cold ester 6 (1 mmol) was added ice-cold
concd H2SO4 (2 mL) and the reaction mixture was stirred in an ice
bath for 1 h. After the completion of reaction sufficient crushed ice
(10 mL) was added to the reaction mixture and the reaction mixture
was extracted with Et2O (3 × 5 mL). The combined organic extracts
were dried over anhyd Na2SO4 and the crude product was purified
by silica gel column chromatography (EtOAc–hexanes, 1:9) to
yield liquid lactone.
(7e)
Yield: 90%.
IR (neat): 1752 (C=O), 1680 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 0.94 [d, J = 6.6 Hz, 6 H,
CH(CH3)2], 1.41 (d, J = 6.0 Hz, 3 H, CHCH3), 1.81 (m, 1 H,
CHCH3), 2.06 (t, J = 6.6 Hz, 2 H, =CHCH2), 2.40 (m, 1 H, HCH
CH), 3.00 (br dd, J = 16.8, 7.8 Hz, 1 H, HCHCH), 4.66 (m, 1 H,
CH), 6.76 (t, J = 7.8 Hz, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 22.25 (CH3), 22.39 (CH3), 28.09
(CH3), 33.05 (CH2), 39.28 (CH2), 73.93 (CH), 127.17 (C), 139.68
(=CH), 170.86 (C=O).
5-Methyl-3-(methylidene)dihydrofuran-2(5H)-one (7a)
Yield: 87%.
IR (neat): 1765 (C=O), 1665 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 1.43 (d, J = 6.3 Hz, 3 H, CHCH3),
2.56 (ddt, J = 16.8, 5.7, 2.7 Hz, 1 H, HCHCH), 3.10 (ddt, J = 16.8,
7.2, 2.7 Hz, 1 H, HCHCH), 4.66 (m, 1 H, CHCH3), 5.63 (t, J = 2.7
Hz, 1 H, HCH=C), 6.23 (t, J = 2.7 Hz, 1 H, HCH=C).
HRMS: m/z calcd for C10H17O2 (M + H+): 169.1228; found:
169.1219.
1b–e; General Procedure
13C NMR (75 MHz, CDCl3): d = 21.88 (CH3), 35.10 (CH2), 73.82
(CH), 121.91(CH2), 134.80 (C), 176.20 (C=O).
MS: m/z (%) = 113 (8, M+ + 1), 95 (17), 67 (100), 65 (20), 43 (13).
To a solution of lactone 7 (1 mmol) in degassed EtOH (10 mL) was
added RhCl3·3H2O (0.01 mmol) and the reaction mixture was re-
fluxed for 15 h. The crude product was purified by silica gel column
chromatography (EtOAc–hexanes, 1:9) to yield liquid butenolide.
5-Methyl-3-[(E)-ethylidene]dihydrofuran-2(5H)-one (7b)
Yield: 85%.
IR (neat): 1756 (C=O), 1680 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 1.35 (d, J = 6.3 Hz, 3 H, CHCH3),
1.84 (dt, J = 6.9, 2.1, 1.8 Hz, 3 H, =CHCH3), 2.35 (ddt, J = 16.8,
5.2, 1.8 Hz, 1 H, HCH CH), 3.01 (ddt, J = 16.8, 7.8, 2.1 Hz, 1 H,
HCHCH), 4.61 (ddq, J = 7.8, 6.3, 5.2 Hz, 1 H, CHCH3), 6.78 (m, 1
H, =CH).
13C NMR (75 MHz, CDCl3): d = 15.55 (CH3), 22.20 (CH3), 32.65
(CH2), 73.85 (CH), 127.55 (C), 135.38 (CH), 170.64 (C=O)
3-Ethyl-5-methyl-2[5H]furanone (1b)
Yield: 92%.
IR (neat): 1750 (C=O), 1650 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 1.19 (t, J = 7.2 Hz, 3 H, CH2CH3),
1.34 (d, J = 6.6 Hz, 3 H, CHCH3), 2.22 (q, J = 7.2 Hz, 2 H,
CH2CH3), 4.94 (m, 1 H, CH), 6.93 (br s, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 11.43 (CH3), 18.24 (CH3), 18.98
(CH2), 77.23 (CH), 134.86 (C), 148.54 (=CH), 173.57 (C=O).
MS: m/z (%) = 127 (88, M+ + 1), 109 (100), 99 (26), 69 (34).
MS: m/z (%) = 127 (7, M+ + 1), 109 (29), 81 (100), 79 (37), 77 (6),
43 (5).
3-Butyl-5-methyl-2[5H]furanone (1c)
Yield: 77%.
IR (neat): 1750 (C=O), 1650 (C=C) cm–1.
5-Methyl-3-[(E)-butylidene]dihydrofuran-2(5H)-one (7c)
1H NMR (300 MHz, CDCl3): d = 0.87 (t, J = 7.5 Hz, 3 H, CH2CH3),
1.19–1.53 (m, 4 H, 2 × CH2), 1.34 (d, J = 6.0 Hz, 3 H, CHCH3), 2.22
Yield: 92%.
Synthesis 2005, No. 14, 2341–2344 © Thieme Stuttgart · New York

2344
C. P. Amonkar et al.
PAPER
(t, J = 7.5 Hz, 2 H, =CCH2), 4.95 (q, J = 7.5 Hz, 1 H, CH), 6.90 (m,
1 H, =CH).
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13C NMR (75 MHz, CDCl3): d = 13.68 (CH3), 19.13 (CH3), 22.18
(CH2), 24.78 (CH2), 29.43 (CH2), 75.45 (CH), 134.24 (C), 148.73
(=CH), 173.60 (C=O).
MS: m/z (%) = 155 (32, M+ + 1), 137 (47), 109 (100), 67 (20).
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3-Hexyl-5-methyl-2[5H]furanone (1d)
Yield: 93%.
IR (neat): 1750 (C=O), 1650 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 0.88 (d, J = 6.3 Hz, 3 H, CH2CH3),
1.26–1.60 (m, 8 H, 4 × CH2), 1.47 (d, J = 6.6 Hz, 3 H, CHCH3), 2.27
(t, J = 7.5 Hz, 2 H, =CCH2), 5.00 (m, 1 H, CH), 6.99 (br d, J = 0.9
Hz, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 14.01 (CH3), 19.12 (CH3), 22.51
(CH2), 22.16 (CH2), 27.35 (CH2), 28.82 (CH2), 31.48 (CH2), 73.87
(CH), 134.35 (C), 148.83 (=CH), 173.87 (C=O).
HRMS: m/z calcd for C11H19O2 (M + H+): 183.1385; found:
183.1393.
3-(3-Methyl-butyl)-5-methyl-2[5H]furanone (1e)
Yield: 94%.
IR (neat): 1750 (C=O), 1650 (C=C) cm–1.
1H NMR (300 MHz, CDCl3): d = 0.93 [d, J = 6.6 Hz, 6 H,
CH(CH3)2], 1.18–1.65 (m, 3 H, CH2, CH), 1.42 (d, J = 6.3 Hz, 3 H,
CHCH3), 2.28 (t, J = 7.8 Hz, 2 H, =CCH2), 4.99 (m, 1 H, CH), 6.98
(d, J = 1.2 Hz, 1 H, =CH).
13C NMR (75 MHz, CDCl3): d = 19.22 (CH3), 22.36 (CH3), 23.12
(CH3), 27.74 (CH2), 29.69 (CH), 36.41 (CH2), 77.02 (CH), 134.59
(C), 148.65 (=CH), 170.01 (C=O).
(7) Tietze, L. F. Chem. Rev. 1996, 96, 195.
(8) Shet, J. B.; Desai, V. G.; Tilve, S. G. Synthesis 2004, 1859.
(9) (a) Nishide, K.; Aramat, A.; Kamanaka, T.; Inoue, T.; Node,
M. Tetrahedron 1994, 50, 8337. (b) Nishide, K.; Aramat,
A.; Kamanaka, T.; Node, M. Heterocycles 1993, 36, 2237.
(10) Matsui, S. Bull. Chem. Soc. Jpn. 1987, 60, 1853.
(11) Crich, D.; Mo, X.-S. Synlett 1999, 67.
HRMS: m/z calcd for C10H17O2 (M + H+): 169.1228; found:
169.1232.
Acknowledgment
(12) Mali, R. S.; Tilve, S. G.; Yeola, S. N.; Manekar, A. R.
Heterocycles 1987, 26, 121.
We wish to thank CSIR, New Delhi for a grant and for the award of
a research fellowship (to CPA, NET), NIO, Goa, for spectral analy-
sis and Dept. of Organic Chemistry, IISc, Bangalore, for (HRMS)
data.
Synthesis 2005, No. 14, 2341–2344 © Thieme Stuttgart · New York