A short and facile stereoselective total synthesis of cryptocarya diacetate

Article abstract of DOI:10.1007/s00706-013-1013-8

A short, simple, and efficient stereoselective total synthesis of cryptocarya diacetate using benzylidene acetal as a key intermediate is described. The synthesis proceeded with overall yield of 10 % starting from commercially available (S)-ethyl lactate.

Full text of DOI:10.1007/s00706-013-1013-8

Monatsh Chem
DOI 10.1007/s00706-013-1013-8
ORIGINAL PAPER
A short and facile stereoselective total synthesis of cryptocarya
diacetate
•
Jhillu S. Yadav P. Murali Krishna Reddy
•
•
Manoj K. Gupta Basi V. Subba Reddy
Received: 15 November 2012 / Accepted: 6 May 2013
Ó Springer-Verlag Wien 2013
Abstract A short, simple, and efficient stereoselective
total synthesis of cryptocarya diacetate using benzylidene
acetal as a key intermediate is described. The synthesis
proceeded with overall yield of 10 % starting from com-
mercially available (S)-ethyl lactate.
biological properties of structurally related 1,3-diol-con-
taining polyketides, we have been interested in the
development of practical and concise stereoselective
approaches for construction of 1,3-diol functionalities
[18, 19].
Keywords Ethyl lactate Á Benzylidene acetal Á
Lactonization Á Chiral allylation Á Homologation Á
Cross-metathesis
Results and discussion
Our retrosynthetic strategy for synthesis of cryptocarya
diacetate (1) is outlined in Scheme 1. We envisioned that
the lactone moiety could be constructed by lactonization of
(Z)-a,b-unsaturated ester 13, which in turn could be
obtained from the benzylidene protected ester 11. The
intermediate 11 could be prepared from homoallylic alco-
Introduction
Lactone-containing natural products have attracted
remarkable synthetic interest due to their unique structural
features and potent biological activities [1–5]. Cryptocarya
diacetate (1), cryptocarya triacetate (2), cryptocaryolone
(3), and cryptocaryolone diacetate (4) along with several
other compounds have been isolated from the leaves and
bark of Cryptocarya latifolia, which has long been known
for its medicinal properties (Fig. 1) [6]. These molecules
are used for treatment of headaches and morning sickness,
and treatment of cancer, pulmonary diseases, and various
bacterial and fungal infections [7]. Consequently, several
approaches have been reported for synthesis of cryptocarya
diacetate (1) [8–17]. However, synthesis involving inex-
pensive and readily available raw materials by a short and
efficient route continues to be a challenging endeavor in
synthetic organic chemistry. Owing to the broad range of
hol
9 via stereoselective oxyanion-assisted Michael
addition of a conjugated ester derived via cross-metathesis
with ethyl acrylate. The precursor 9 could be accessed
readily from commercially available (S)-ethyl lactate 5
through reduction, asymmetric allylation, and appropriate
functional group manipulation.
O
O
OAc OAc OAc O
OAc OAc O
2
Cryptocarya triacetate ( )
1
Cryptocarya diacetate ( )
O
O
OAc OAc O
O
OH OH
O
O
J. S. Yadav (&) Á P. M. K. Reddy Á M. K. Gupta Á
B. V. S. Reddy
4
Cryptocaryolone diacetate ( )
3
CSIR-Natural Product Chemistry, Indian Institute of Chemical
Technology, Hyderabad 500 607, India
e-mail: yadavpub@iict.res.in
Cryptocaryolone ( )
Fig. 1 Representative examples of cryptocarya natural products
123

J. S. Yadav et al.
Ph
Ph
Scheme 1
O
TBDPSO
O
O
TBDPS
O
O
O
OAc OAc O
CO2Et
CO2Me
13
11
Cryptocarya diacetate (1)
OH
TBDPSO
OH
CO2Et
5
9
We began our synthesis with commercially available
(S)-ethyl lactate 5. Accordingly, compound 5 was protected
as its silyl ether using imidazole and tert-butyl-
chlorodiphenylsilane (TBDPSCl) in dichloromethane to
give the (S)-ethyl 2-(tert-butyldiphenylsilyloxy)propanoate
6 in 82 % yield. The ester 6 was then subjected to partial
reduction using diisobutylaluminum hydride (DIBAL-H) in
dichloromethane at -78 °C to afford the corresponding
aldehyde 7 in 78 % yield. Sequential homologation of
aldehyde 7 using sodium hexamethyldisilazide (NaHMDS)
and MeOCH2PPh3Cl in tetrahydrofuran (THF) followed by
treatment with pyridinium p-toluenesulfonate (PPTS) in
dioxane-H2O [20, 21] gave the aldehyde 8 in 76 % yield
[4f]. The crude aldehyde 8 was then subjected to chiral
allylation using (?)-allyldiisopinocamphenyl borane [22,
23] at -78 °C in anhydrous ether. The resulting boron
complex was quenched with triethylamine and 2 equiv.
H2O2 to afford the homoallyl alcohol 9 [4f] in 75 % yield
with 9:1 diastereomeric ratio. The chiral allylating agent
(?)-allyldiisopinocamphenyl borane was readily prepared
from (-)-a-pinene using literature procedure [24, 25].
A transition-metal-mediated cross-metathesis reaction
of homoallylic alcohol 9 with ethyl acrylate gave the trans-
d-hydroxy-1-enoate 10 in 83 % yield [26–28]. C–O bond
formation with a concomitant new stereocenter was
achieved via oxyanion-assisted Michael addition [29] using
KO-t-Bu and benzaldehyde in THF at 0 °C, leading to the
formation of benzylidene protected 3,5-dihydroxycarb-
oxylic ester 11 in 81 % yield as a single diastereomer [4i]
(Scheme 2).
was successfully achieved in one pot using p-toluenesul-
fonic acid (p-TSA) in benzene to furnish the desired
lactone, which was subsequently acylated with acetic
anhydride in the presence of 4-dimethylaminopyridine
(DMAP) and pyridine to afford cryptocarya diacetate (1) in
74 % yield (over two steps).
In summary, we have demonstrated a short, simple, and
efficient route for total synthesis of cryptocarya diacetate
(1), starting from commercially available (S)-ethyl lactate
using lactonization with benzylidene acetal moiety. This
route is amenable and modular, and utilizes easily handled
reagents to synthesize cryptocarya diacetate (1).
Experimental
All solvents and reagents were purified by standard tech-
niques. Column chromatography was performed using
silica gel 60–120 mesh. All solvents were dried and dis-
tilled prior to use. Infrared (IR) spectra were recorded on a
PerkinElmer infrared spectrophotometer as KBr wafers,
1
neat or in CHCl3 as a thin film. H and 13C nuclear mag-
netic resonance (NMR) spectra were recorded on a Varian
Gemini 200, Bruker Avance 300, or Varian Unity 400
instrument (1H operating frequencies of 300 and 400 MHz,
respectively) using tetramethylsilane (TMS) as internal
standard. Mass spectroscopy (MS) spectra were obtained
on an Agilent Technologies LC/MSD Trap SL. High-res-
olution mass spectroscopy (HRMS) was carried out on a
Varian MAT-711 and MAT-95. Optical rotations were
recorded on a JASCO DIP-360 digital polarimeter at
25 °C.
Partial reduction of ester 11 with 1.1 equiv. DIBAL-H in
THF at -78 °C gave the aldehyde 12 [4j]. Upon treatment
of aldehyde 12 with methyl (bistrifluoroethyl)phosphono-
acetate in the presence of sodium hydride in THF under
modified Wadsworth–Emmons conditions gave the (Z)-
unsaturated ester 13 in 82 % yield. Next, we attempted
sequential deprotection and lactonization to convert the
enoate 13 into the target lactone 1. Accordingly, depro-
tection of both benzylidene acetal and TBDPS ether of 13
(S)-Ethyl 2-(tert-butyldiphenylsilyloxy)propanoate
(6, C21H28O3Si)
To a solution of 2 g (S)-ethyl 2-hydroxypropanoate (5,
16.95 mmol) and 2.30 g imidazole (33.78 mmol) in
80 cm3 CH2Cl2 at 0 °C was added 4.76 cm3 TBDPSCl
(17.32 mmol) portionwise. The mixture was stirred
123

A short and facile stereoselective total synthesis
Scheme 2
OH
COOEt
OTBDPS
COOEt
OTBDPS
CHO
OTBDPS
TBDPSO
OH
a
b
c
d
CHO
5
8
9
6
7
Ph
g
O
O
TBDPSO
Ph
O
OH
TBDPS
e
f
CO2Et
CO2Et
11
10
O
Ph
O
O
TBDPSO
OAc O
OAc
i
h
O
O
TBDPSO
CHO
CO2Me
1
13
12
a TBDPSCl, imidazole, CH2Cl2, 0 °C – r.t., 12 h, 82 %. b DIBAL-H,
CH2Cl2, -78 °C, 2 h, 78 %. c (i) MeOCH2PPh3Cl, NaHMDS, THF;
-40 to 0 °C, 3 h. (ii) PPTS, dioxane/H2O (9:1), 50 °C, 10 h, 76 %;
d (?)-allyldiisopinocamphenyl borane, Et3N, H2O2, -78 °C, 1 h,
75 %. e 1 mol % (Cy3P)2Cl2Ru = CHPh, ethyl acrylate, CH2Cl2, r.t.,
12 h, 83 %. f PhCHO, t-BuOK, THF, 0 °C, 2 h, 81 %. g DIBAL-H,
CH2Cl2, -78 °C, 2 h, 68 %. h NaH, MeO2CCH2P(O)(OCH2CF3)2,
THF, -78 to 0 °C; 1 h, 82 %. i (i) p-TSA, benzene, r.t. (ii) Ac2O, Py,
DMAP, 74 %
overnight at room temperature and then quenched with
20 cm3 saturated aq. NaHCO3 solution. The aqueous phase
was separated and further extracted with CH2Cl2
(2 9 25 cm3). The combined organic phases were dried
over anhydrous Na2SO4 and concentrated in vacuo to give
the crude residue, which was then purified by column
chromatography (EtOAc:hexane, 0.5:9.5). Colorless oil,
yield 4.94 g (82 %). Analytical data of compound 6 were
identical to those described in Refs. [30, 31].
(S)-3-(tert-Butyldiphenylsilyloxy)butanal
(8, C20H26O2Si)
To a suspension of 8.82 g MeOCH2PPh3Cl (25.73 mmol)
in 20 cm3 THF at 0 °C was added 24.2 cm3 NaHMDS
(24.2 mmol, 1 M in THF) dropwise. The resulting red-
colored mixture was stirred at 0 °C for 1 h and then cooled
to -40 °C. A solution of 2.70 g (S)-2-(tert-butyldiphenyl-
silyloxy)propanal (7, 8.64 mmol) in 7 cm3 THF was added,
and the mixture was allowed to stir at 0 °C over 2 h. The
reaction mixture was then quenched with 15 cm3 satd.
NH4Cl, and then phases were separated. The aqueous phase
was extracted with EtOAc (2 9 50 cm3). The combined
organic extracts were dried over Na2SO4 and evaporated
in vacuo. The resulting residue was purified by flash
chromatography (hexane/EtOAc, 5 %) to yield enol ether
as colorless viscous oil (2.0 g, 68 %), which was used
immediately for the next step.
(S)-2-(tert-Butyldiphenylsilyloxy)propanal
(7, C19H24O2Si)
To a stirred solution of 4.50 g (S)-ethyl 2-(tert-butyldiphen-
ylsilyloxy)propanoate (6, 12.62 mmol) in 50 cm3 CH2Cl2
under nitrogen atmosphere was added 15.12 cm3 DIBAL-H
(1 M in CH2Cl2, 15.12 mmol) dropwise along the walls of
the flask. The reaction was stirred at the same temperature
while monitoring the progress of the reaction. After
completion of the reaction (*2 h), the mixture was
quenched by addition of 15 cm3 methanol at -78 °C, and
the reaction mixture was allowed to reach room temperature.
The solvent was evaporated under vacuum, and the residue
was treated with saturated solution of sodium–potassium
tartrate. The residue dissolved in the aqueous layer, and the
product was extracted with ethyl acetate (4 9 50 cm3). The
combined organic layers were washed with brine and dried
over anhydrous Na2SO4. Upon concentration under reduced
pressure, the crude mass was purified by silica gel column
chromatography (EtOAc:hexane, 1:9). Colorless oil, yield
3.07 g (78 %). Analytical data of compound 7 were identical
to those described in Ref. [31].
To a solution of 1.9 g enol ether (5.58 mmol) in diox-
ane:water (9:1, 30 cm3) was added 11.2 g pyridinium p-
toluenesulfonate (44.57 mmol), and the mixture was stirred
at 50 °C until thin-layer chromatography (TLC) indicated
completion of the reaction (10 h). The reaction was then
quenched with 15 cm3 satd. NaHCO3, and the mixture was
extracted with EtOAc (3 9 50 cm3). The combined
extracts were dried over anhydrous Na2SO4. The solvent
was removed under reduced pressure, and the residue was
purified on silica gel column chromatography
(EtOAc:hexane, 2:8). Colorless oil, yield 1.38 g (76 %).
Analytical data of compound 8 were identical to those
described in Ref. [32].
123

J. S. Yadav et al.
(4R,6S)-6-(tert-Butyldiphenylsilyloxy)hept-1-en-4-ol
(9, C23H32O2Si)
(75 MHz, CDCl3): d = 14.2, 19.1, 22.3, 24.1, 26.9, 40.2,
45.5, 60.2, 69.6, 70.6, 123.6, 127.4, 127.7, 129.6, 129.8,
133.1, 134.1, 135.7, 145.0, 166.3 ppm; HR-MS (ESI):
m/z [M?Na]? calcd. for C26H36NaO4Si 463.2280, found
463.2293.
A solution of 1.13 g (?)-allyldiisopinocamphenyl borane
(3.50 mmol) in 20 cm3 anhydrous diethyl ether was cooled
to -78 °C, and 1.20 g (S)-3-(tert-butyldiphenylsilyl-
oxy)butanal (8, 3.68 mmol) in 5 cm3 anhydrous diethyl
ether was added dropwise over 5 min under nitrogen
atmosphere. The resulting mixture was stirred at the same
temperature for 1 h and then brought to room temperature
(*1 h). The above mixture was then treated with slow
addition of 2.05 cm3 triethylamine (14.73 mmol) and
0.80 cm3 hydrogen peroxide (30 % w/v dispersion in
water, 7.36 mmol) successively, maintaining the tempera-
ture at 0 °C. The mixture was allowed to warm to room
temperature and then stirred for 12 h. The organic layer
was separated and washed with 10 cm3 water and 10 cm3
brine, and dried over Na2SO4. The solvent was removed,
and the crude residue was purified by column chromatog-
raphy (EtOAc:hexane, 2:8). Colorless liquid, yield 1.02 g
(75 %); [a]2D5 = ?4.1° cm3 g-1 dm-1 (c = 0.6, CHCl3);
IR (KBr): m = 3,448, 3,383, 3,076, 3,026, 2,978, 2,905,
Ethyl 2-((4S,6R)-6-((S)-2-(tert-butyldiphenylsilyloxy)pro-
pyl)-2-phenyl-1,3-dioxan-4-yl)acetate (11, C33H42O5Si)
To
a solution of 0.80 g a,b-unsaturated ester 10
(1.81 mmol) in 20 cm3 THF at 0 °C was added 0.19 cm3
freshly distilled benzaldehyde (1.86 mmol), followed by
0.02 g t-BuOK (0.18 mmol). The resulting yellow solution
was stirred for 15 min at 0 °C. Addition of benzaldehyde/t-
BuOK was repeated three times, and the mixture was
quenched with 10 cm3 saturated NH4Cl solution. The
layers were separated, and the aqueous layer was extracted
with ether (3 9 30 cm3). The combined organic layers
were washed with brine (2 9 10 cm3), dried over anhy-
drous Na2SO4, and concentrated in vacuo. The crude
product was purified by silica gel chromatography
(EtOAc:hexane, 1:9). Colorless oil, yield 0.8 g (81 %);
[a]2D5 = -10.2° cm3 g-1 dm-1 (c = 1.1, CHCl3); IR
(KBr): m = 3,030, 2,922, 2,854, 1,747, 1,628, 1,452,
1,372, 1,338, 1,306, 1,261, 1,213, 1,161, 1,099, 1,020,
1,641, 1,493, 1,444, 1,312, 1,029, 916, 749, 693 cm-1; H
1
NMR (200 MHz, CDCl3): d = 7.70 (m, 4H), 7.39–7.36
(m, 6H), 5.88–5.67 (m, 1H), 5.02 (d, J = 12.5 Hz, 2H),
4.17–4.02 (m, 1H), 3.91–3.84 (m, 1H), 2.92 (brs, OH, 1H),
2.16 (t, J = 6.2 Hz, 2H), 1.76–1.50 (m, 2H), 1.02 (s, 9H),
0.96 (d, J = 6.2 Hz, 3H) ppm; 13C NMR (75 MHz,
CDCl3): d = 19.1, 23.9, 26.5, 26.9, 42.0, 45.6, 69.6,
70.1, 117.5, 127.4, 127.6, 129.5, 129.7, 133.5, 134.4,
134.7, 135.7 ppm; HR-MS (ESI): m/z [M?Na]? calcd. for
C23H32NaO2Si 391.2069, found 391.2081.
967,752, 698 cm-1
;
1H NMR (200 MHz, CDCl3):
d = 7.73–7.62 (m, 5H), 7.39–7.34 (m, 10H), 5.48 (s,
1H), 4.53–4.05 (m, 5H), 2.62–2.25 (m, 2H), 1.62–1.41 (m,
4H), 1.25 (t, J = 7.0 Hz, 3H), 1.09 (s, 9H), 1.07 (d,
J = 7.8 Hz, 3H) ppm; HR-MS (ESI): m/z: [M?Na]?
calcd. for C33H42NaO5Si 569.2699, found 569.2706.
2-((4S,6R)-6-((S)-2-(tert-Butyldiphenylsilyloxy)propyl)-2-
phenyl-1,3-dioxan-4-yl)acetaldehyde (12, C31H38O4Si)
To a stirred solution of 0.60 g benzylidene ester 11
(1.09 mmol) in 20 cm3 THF in a 50-cm3 two-neck
round-bottom flask equipped with a magnetic bar and a
nitrogen inlet was added 1.2 cm3 DIBAL-H (1.2 mmol,
1 M in THF) dropwise along the walls of the flask. The
reaction was stirred at the same temperature over 2 h until
complete consumption of the starting material. The reac-
tion mixture was then quenched by addition of 10 cm3
methanol at -78 °C, and the reaction mixture was allowed
to reach room temperature. The solvent was evaporated
under vacuum, and the residue was treated with 5 cm3
saturated solution of sodium–potassium tartrate. The
product was extracted with ethyl acetate (4 9 20 cm3).
The combined organic layers were washed with brine and
then dried over Na2SO4. Upon concentration under reduced
pressure, the crude aldehyde was purified using a small
plug of silica pad (EtOAc:hexane, 1:9) and used immedi-
ately in the next step. Colorless liquid, yield 0.375 g
(68 %); LC–MS: m/z = 525 ([M?Na]?).
(5R,7S,E)-Ethyl 7-(tert-butyldiphenylsilyloxy)-5-
hydroxyoct-2-enoate (10, C26H36O4Si)
(4R,6S)-6-(tert-Butyldiphenylsilyloxy)hept-1-en-4-ol 9
(0.95 g, 2.58 mmol) was dissolved in 3 cm3 CH2Cl2 under
nitrogen, to which was added 0.55 cm3 ethyl acrylate
(5.12 mmol) followed by Grubb’s catalyst 2nd generation
(1 mol %). The reaction was allowed to stir overnight at
room temperature and then quenched by exposing to air.
The solvent was removed under reduced pressure, and the
crude product was purified by silica gel chromatography
(EtOAc:hexane, 1:9) to afford exclusively the E-isomer.
Colorless liquid, yield 0.94 g (83 %); [a]2D5 = -3.2° cm3
g-1 dm-1 (c = 0.8, CHCl3); IR (KBr): m = 3,486, 3,027,
2,982, 2,933, 1,718, 1,653, 1,448, 1,272, 1,203, 1,166,
1,039, 970, 751 cm-1 1H NMR (200 MHz, CDCl3):
;
d = 7.75–7.66 (m, 4H), 7.43–7.36 (m, 6H), 7.04–6.88
(m, 1H), 5.86 (d, J = 15.3 Hz, 1H), 4.15 (q, J = 7.3 Hz,
2H), 4.06–3.97 (m, 1H), 3.36–3.25 (m, 1H), 2.31 (t,
J = 5.8 Hz, 2H), 1.79–1.50 (m, 2H), 1.27 (t, J = 7.3 Hz,
3H), 1.04 (s, 9H), 0.97 (d, J = 5.8 Hz, 3H) ppm; 13C NMR
123

A short and facile stereoselective total synthesis
(Z)-Methyl 4-((4R,6R)-6-((S)-2-(tert-butyldiphenylsilyl-
oxy)propyl)-2-phenyl-1,3-dioxan-4-yl)but-2-enoate
(13, C34H42O5Si)
References
1. Casiraghi G, Zanardi F, Rassu G, Pinna L (1996) Org Prep Proced
Int 28:641
2. Hartmann T, Witte L (1995) In: Pelletier SW (ed) Alkaloids:
chemical and biological perspectives. Pergamon, New York, chap
4, p 155
To
a stirred solution of 0.16 g bis(2,2,2-trifluoro-
ethyl)(methoxycarbonylmethyl)phosphonate (0.503 mmol)
in 10 cm3 anhydrous THF was added 24 mg NaH (60 %
dispersion in mineral oil; 0.99 mmol) at 0 °C. After
30 min, a solution of 0.25 g 2-((4S,6R)-6-((S)-2-(tert-
butyldiphenylsilyloxy)propyl)-2-phenyl-1,3-dioxan-4-yl)
acetaldehyde (12, 0.497 mmol) in 5 cm3 anhydrous THF
was added dropwise at -78 °C. After completion, the
reaction mixture was diluted with 20 cm3 water and
extracted with EtOAc (3 9 20 cm3). The combined
organic layers were washed with water (2 9 20 cm3) and
brine (2 9 20 cm3) and dried over anhydrous Na2SO4.
Removal of the solvent followed by purification on silica
gel column chromatography (EtOAc-hexane, 2:8) gave the
pure product. Colorless liquid, yield 0.233 g (82 %);
[a]2D5 = ?15.9° cm3 g-1 dm-1 (c = 0.5, CHCl3); IR
(KBr): m = 3,029, 2,922, 2,852, 2,362, 1,725, 1,644,
1,438, 1,401, 1,334, 1,196, 1,172, 1,134, 1,101, 1,011,
3. Yadav JS, Reddy PMK, Gupta MK, Chary CJ (2007) Synthesis
2007:3639
4. Yadav JS, Gupta MK, Pratahp I (2007) Synthesis 2007:1343
5. Smith AB III, Freeze BS, LaMarche MJ, Hirose T, Brouard I,
Rucker PV, Xian M, Sundermann KF, Shaw SJ, Burlingame MA,
Horwitz SB, Myles DC (2005) Org Lett 7:311
6. Drewes SE, Sehlapelo BM, Horn MM, Scott-Shaw R, Sandor P
(1995) Pytochemistry 38:1427
7. Sam TW, Yeu CS, Jodynis-Liebert J, Murias M, Bloszyk E
(2000) Planta Med 66:199
8. Sabitha G, Reddy NM, Prasad MN, Yadav JS (2009) Helv Chim
Acta 92:967
9. Gurjar MK, Raghupathi N, Chorghade MS (2009) Heterocycles
77:945
10. Yadav JS, Rao PP, Reddy MS, Rao NV, Prasad AR (2007)
Tetrahedron Lett 48:1469
11. Umarye JD, Leßmann T, Ana B, Garcia AB, Mamane B, Sommer
S, Waldmann H (2007) Chem Eur J 13:3305
12. Boxer MB, Yamamoto H (2007) J Am Chem Soc 129:2762
13. Garcia AB, Leßmann T, Umarye JD, Mamane B, Sommer S,
Waldmann H (2006) Chem Commun 42:3869
14. Kumar P, Gupta P, Naidu SV (2006) Chem Eur J 12:1397
15. Krishna RP, Reddy VVR (2005) Tetrahedron Lett 46:3905
16. Hunter TJ, O’Doherty GA (2001) Org Lett 3:2777
17. Jorgensen KB, Suenaga T, Nakata T (1999) Tetrahedron Lett
40:8855
1
966, 817, 750, 695 cm-1; H NMR (300 MHz, CDCl3):
d = 7.63–7.61 (m, 5H), 7.43–7.25 (m, 10H), 6.42–6.34
(ddd, J = 11.0, 7.9, 6.2 Hz, 1H), 5.84 (d, J = 13.5 Hz,
1H), 5.42 (s, 1H), 4.32–3.97 (m, 3H), 3.69 (s, 3H),
2.91–2.00 (m, 8H), 1.07 (s, 9H), 1.03 (d, J = 7.8 Hz, 3H)
ppm; LC–MS: m/z = 581.1 ([M?Na]?).
18. Yadav JS, Reddy MS, Rao PP, Prasad AR (2006) Tetrahedron
Lett 47:4397
19. Yadav JS, Reddy MS, Prasad AR (2006) Tetrahedron Lett
47:4937
(R)-6-[(2S,4S)-2,4-(Diacetyloxy)pentyl]-5,6-dihydro-
2H-pyran-2-one (1, C14H20O6)
To a stirred solution of 0.18 g compound 13 (0.314 mmol)
in 2 cm3 benzene at 0 °C was added p-TsOH (catalyst).
After stirring for 6 h at r.t., the reaction mixture was
quenched with solid NaHCO3 and the solvent was removed
under reduced pressure. The resulting crude product was
then dissolved in CH2Cl2 and cooled to 0 °C. To this
solution 0.4 cm3 pyridine, 0.2 cm3 acetic anhydride, and a
catalytic amount of DMAP were added successively. The
resulting mixture was allowed to stir overnight, then
quenched with solid NaHCO3 and filtered through glass
wool using EtOAc. The solvent was removed under
reduced pressure, and the product was purified by column
chromatography (EtOAc:hexane, 2:8). Colorless oil, yield
66 mg (74 %). Analytical data of compound 1 were
identical to those described in Ref. [8–17].
20. Saibaba V, Das P, Mukkanti K, Iqbal J (2006) Tetrahedron Lett
47:7927
21. Nicolaou KC, Ritzen A, Namoto K, Buey RM, Fernando Diaz J,
Andreu JM, Wartmann M, Altmann KH, OBrate A, Giannakakou
P (2002) Tetrahedron 58:6413
22. Brown HC, Jadhav PK (1983) J Am Chem Soc 105:2092
23. Brown HC, Ramachandran PVJ (1995) Organomet Chem 1:500
24. Jadav KP, Bhat KS, Perumal T, Brown HC (1986) J Org Chem
15:432
25. Brown HC, Desai MC, Jadhav PK (1982) J Org Chem 47:5065
26. BouzBouz S, Cossy J (2001) Org Lett 3:1451
27. Cossy J, Bargiggia F, BouzBouz S (2003) Org Lett 5:459
28. Reher SD, Leighton JL (2001) J Am Chem Soc 123:341
29. Evans DA, Gauchet-Prunet JA (1993) J Org Chem 58:2446
30. Krishna PR, Alivelu M, Rao TP (2012) Eur J Org Chem 10:616
31. Takashima Y, Kaneko Y, Kobayashi Y (2010) Tetrahedron
66:197
32. Germay O, Kumar N, Moore CG, Thomas EJ (2012) Org Biomol
Chem 10:9709
Acknowledgments P.M.K.R. thanks UGC, New Delhi and M.K.G.
thanks CSIR, New Delhi for research fellowships.
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