Versatile approach for the asymmetric synthesis of (R)- and (S)-massoialactones

Article abstract of DOI:10.1080/00397910701229107

A general synthetic approach to both enantiomers, (R)- and (S)-massoialactones, has been devised from commercially available (S)-butane-1,2,4-triol. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701229107

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Versatile Approach for the Asymmetric
Synthesis of (R)‐ and (S)‐Massoialactones
Gowravaram Sabitha a , P. Gopal a & J. S. Yadav a
a Organic Division I , Indian Institute of Chemical Technology , Hyderabad,
India
Published online: 11 May 2007.
To cite this article: Gowravaram Sabitha , P. Gopal & J. S. Yadav (2007) Versatile Approach for the
Asymmetric Synthesis of (R)‐ and (S)‐Massoialactones , Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 37:9, 1495-1502, DOI: 10.1080/00397910701229107
To link to this article: http://dx.doi.org/10.1080/00397910701229107
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Synthetic Communicationsw, 37: 1495–1502, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701229107
Versatile Approach for the Asymmetric
Synthesis of (R)- and (S)-Massoialactones
Gowravaram Sabitha, P. Gopal, and J. S. Yadav
Organic Division I, Indian Institute of Chemical Technology,
Hyderabad, India
Abstract: A general synthetic approach to both enantiomers, (R)- and (S)-massoialac-
tones, has been devised from commercially available (S)-butane-1,2,4-triol.
Keywords: chiral lactones, enantiomers, massoialactone, natural products
INTRODUCTION
The 6-substituted chiral d-lactone moiety is present in a number of natural
products and exhibits significant bioactivities.[1] Massoialactone (1) belongs
to this family, first isolated from the bark oil of Cryptocarya massoia by
Abe in 1937.[2] Later this lactone was also isolated as a flavor substance
from cane molasses[3] and jasmine flowers.[4] The R enantiomer has been
identified as the defense secretion of two species of formicin ants of the
genus Camponotus.[5]
Several methods for the synthesis of (R)-massoialactone have been
reported[6] either from a chiral pool starting material,[7] hydrolytic kinetic
resolution,[8] or the resolution of racemic mixtures of the lactone
precursor,[9] whereas methods for the synthesis of (S)-massoialactone are
rare.[10] The lactone 1 has been used for many centuries as a constituent of
native medicines. A general synthetic route to the enantiomerically pure
lactones would be of value because these lactones are synthetically versatile
Received September 27, 2006
IICT Communication No. 060319.
Address correspondence to Gowravaram Sabitha, Organic Division I, Indian
Institute of Chemical Technology, Hyderabad 500 007, India. E-mail:
gowravaramsr@yahoo.com
1495

1496
G. Sabitha, P. Gopal, and J. S. Yadav
precursors to other chiral molecules of considerable interest. Recently we have
been interested in the development of practical and concise enantioselective
approaches to naturally occurring biologically important lactones.[11] As a
consequence, we herein describe a general synthetic approach that affords
both isomers, natural (R)-1 and unnatural (S)-1 massoialactones. The
synthesis of both natural (R)- and (S)-1 massoialactones started from
commercially available (S)-butane-1,2,4-triol (2) by manipulating the
reactions. The retrosynthetic plan for the synthesis of both isomers is illus-
trated in Scheme 1.
RESULTS AND DISCUSSION
The known (S)-epoxide 3[12] (Scheme 2) could be derived from (S)-butane-
1,2,4-triol 2. Selective opening of epoxide (S)-3 with CuI and n-BuLi[12]
furnished (R)-4 in 87% yield. The secondary hydroxyl group in compound
4 was protected as tert-butyldimethylsilyl (TBDMS) ether (R)-5 using
TBDMSCl, imidazole in CH2Cl2 (74%). Oxidative deprotection of the para-
methoxybenzyl (PMB) group using 2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none (DDQ) in aq. CH2Cl2 gave the primary alcohol (R)-6 in 80% yield,
which on oxidation with iodoxybenzoic acid (IBX) in dimethylsulphoxide
(DMSO) furnished the corresponding aldehyde (R)-7 (68%).[6e,6g,13]
A
modified Still’s Horner–Wadsworth–Emmons reaction of (R)-7 using
methyl(bistrifluoroethyl) phosphonoacetate in the presence of NaH in THF
gave Z-unsaturated ester (R)-8, exclusively. Subsequent cyclization of
Z-ester using a catalytic amount of p-TsOH in methanol and benzene
furnished the target molecule, (R)-1, in 76% yield by in situ deprotection of
1
TBDMS group. The H and 13C NMR data and optical rotation value of
synthetic (R)-1, [a]D 2113.5 (c 1, CHCl3), lit.[8] [a]D 2115.2 (c 1, CHCl3),
were in good accordance with the literature data.
Similarly, the synthesis of (S)-massoialactone began with the known (R)-
epoxide 3[12] with the required stereogenic center, derived from (S)-butane-
1,2,4-triol 2. The same set of reactions were carried out as shown in
Scheme 2. Thus, selective opening of epoxide (R)-3 with CuI and n-BuLi
furnished (S)-4 in 86% yield, which was protected as its TBDMS ether
(S)-5. The deprotection of the PMB group in (S)-5 using DDQ (84%) and
Scheme 1. Retrosynthetic analysis.

Asymmetric Synthesis of Massoialactones
1497
Scheme 2. Reagents and conditions: a) CuI, n BuLi, dry ether, 2208C, 1.5 h, 87%;
b) TBDMSCl, imidazole, DCM, 08C, 2 h, 74%; c) DDQ, DCM:H2O rt, 3 h, 80%; d)
IBX, DMSO, DCM, 2 h, 68%; e) H3COOCCH2P(O)(OCH2CF3)2, NaH, THF, 1 h,
85%; f) PTSA/MeOH, 30 min, benzene, 1 h, 76%.
subsequent oxidation with IBX afforded the aldehyde (S)-7 in 67% yield.
Homologation of (S)-7 with methyl(bistrifluoroethyl) phosphonoacetate in
the presence of NaH in THF gave Z-unsaturated ester (S)-8 (89%). Finally,
the deprotection of TBDMS group and lactonization was effected in one
step by treatment with p-TSOH in methanol to give unnatural (S)-1 in 74%
yield. The physical and spectroscopic data of (S)-1 were in full agreement
with the literature data.[9]
In conclusion, we have developed a simple and new synthetic route
for both isomers, (R)- and (S)-massoialactones 1, from (S)-2, employing a
divergent strategy. A general and simple reaction sequence and high-yielding
steps to provide the targets from the same starting material, (S)-butane-1,2,4-
triol, renders our strategy a good alternative to the known methods.
EXPERIMENTAL
All solvents were distilled before use. Dry solvents were prepared according
to the standard procedures. All reactions were carried out under an N2
atmosphere and monitored by thin-layer chromatography (TLC) on silica
gel (60–120 mesh, Merck). NMR spectra were recorded on Bruker
1
1
(300 MHz H, 75 MHz 13C) and Varian (200 MHz H, 50 MHz 13C) NMR
spectrometers using CDCl3 as solvent. ESI-mass spectra were recorded with
LC-MSD-Trap-SL (Agilent technologies). IR spectra were recorded
with Fourier Transform Infra Red (FTIR) (Thermo Nicolet Nexus 670
spectrometer). Optical rotations were measured with Jasco DIP-370 Polari-
meter at 208C.

1498
G. Sabitha, P. Gopal, and J. S. Yadav
(3R)-1-[(4-Methoxybenzyl)oxy]octan-3-ol ((R)-4)
To a stirred mixture of copper (I) iodide (9.13 g, 48.08 mmol) in dry ether
(40 mL), n-butyllithium (37.56 mL, 60.09 mmol, 1.6 M solution in n-hexane)
was added at 2208C and stirred for 0.5 h. Then, a solution of epoxide (S)-3
(5 g, 24.03 mmol) in dry ether (20 mL) was added and stirred at the same temp-
erature for 1 h. The reaction mixture was quenched with aq. NH4Cl solution
(20 mL) and allowed to stir for 15 min. The organic layer was separated, and
aq. layer was washed with ethyl acetate (2 ꢀ 40 mL). The combined organic
layers were washed with water (2 ꢀ 20 mL) and brine (20 mL), dried
(Na2SO4), and concentrated under reduced pressure. The crude product was
purified by silica-gel column chromatography to afford (R)-4 (5.53 g, 87%)
as a liquid. [a]D þ3.79 (c 1, CHCl3). IR (neat): 3459, 2931, 2860, 1093, 822,
1
770 cm21; H NMR (300 MHz, CDCl3): d 7.20 (d, 2H, J ¼ 8.3 Hz), 6.82
(d, 2H, J ¼ 8.3 Hz), 4.43 (s, CH2-O, -PMB), 3.79 (s, 3H, -O-Me), 3.53–3.76
(m, 3H, CH-OH, CH2-OPMB), 2.74 (brs, 1H, -OH), 1.68 (q, 2H, J ¼ 6.0 Hz,
HO-CH2-CH2-CH2-OPMB), 1.24–1.49 (m, 8H, aliphatic), 0.89 (t, 3H,
J ¼ 6.0 Hz); 13C NMR (50 MHz, CDCl3): 159.15, 129.96, 129.23, 113.78,
72.91, 71.52, 68.94, 55.16, 37.35, 36.29, 31.86, 25.21, 22.61, 13.99; LCMS:
289 (M þ Na).
(3S)-1-[(4-Methoxybenzyl)oxy]octan-3-ol ((S)-4)
Compound (S)-4 was similarly obtained in 86% yield from epoxide (R)-3:
liquid, [a]D 23.72 (c 1, CHCl3).
Tert-butyl[((1R)-1-2-[(4-methoxybenzyl)oxy]ethylhexyl)oxy]
dimethyl silane ((R)-5)
To a stirred solution of alcohol (R)-4 (5.0 g, 18.79 mmol) and imidazole
(2.5 g, 37.59 mmol) in dry DCM (35 mL), TBDMSCl (3.399 g,
22.55 mmol) was added portionwise at 08C. The reaction mixture was
stirred at the same temperature for 2 h and then quenched with water
(20 mL). The dichloromethane (DCM) layer was separated, and the aqueous
layer was extracted with additional DCM (2 ꢀ 20 mL). Combined organic
layers were washed with water and brine solution and dried over anhydrous
Na2SO4. Solvent was removed in vacuo, and the residue was purified by
silica-gel column chromatography to afford (R)-5 (5.3 g, 74%) as a
colorless liquid. [a]D 28.33 (c 0.85, CHCl3); IR (neat): 2931, 2857, 1249,
1093, 835, 773 cm21 1H NMR (300 MHz, CDCl3): d 7.19 (d, 2H,
;
J ¼ 8.3 Hz), 6.82 (d, 2H, J ¼ 8.3 Hz), 4.37 (Abq, 2H, J ¼ 11.3 Hz, O-CH2-
O-PMB), 3.79 (s, 3H, -OMe), 3.76–3.83 (m, 1H, CH-O-TBS), 3.45 (dt, 2H,
J ¼ 3.0 Hz, CH2-O-PMB), 1.6–1.74 (m, 2H, TBS-O-CH-CH2-CH2-O-PMB),

Asymmetric Synthesis of Massoialactones
1499
1.23–1.43 (m, 8H, aliphatic), 0.89 (t, 3H, J ¼ 6.0 Hz terminal CH3), 0.87
(s, 9H), 0.03 (s, 6H, 2 ꢀ CH3); 13C NMR (75 MHz, CDCl3): 158.98, 129.13,
113.5, 72.46, 69.34, 66.87, 55.13, 37.44, 36.81, 31.95, 25.78, 24.57, 22.49,
17.93, 13.89, 24.51, 24.76; LCMS: 403 (M þ Na).
Tert-butyl[((1S)-1-2-[(4-methoxybenzyl)oxy]ethylhexyl)oxy]
dimethyl silane ((S)-5)
Compound (S)-5 was similarly obtained in 77% yield from (S)-4: liquid, [a]D
þ8.83 (c 0.85, CHCl3).
(3R)-3-[1-(Tert-butyl)-1,1-dimethylsilyl]oxyoctan-1-ol ((R)-6)
To a stirred solution of compound (R)-5 (5.0 g, 13.15 mmol) in 36 mL of aq.
DCM (DCM–H2O, 9:1), DDQ (5.97 g, 26.31 mmol) was added, and the
reaction mixture was stirred for 3 h at room temperature. The reaction
mixture was washed with 5% aq. NaHCO3 solution (35 mL). The layers
were separated, and the aqueous layer was extracted twice with DCM. The
combined organic extracts were washed with water, dried over anhydrous
Na2SO4, and concentrated in vacuo. The crude product was purified by
column chromatography using silica gel to give alcohol (R)-6 (2.75 g, 80%
yield) as a liquid. [a]D 217.09 (c 1, CHCl3); IR (neat): 3464, 2929, 2858,
1
1059 cm21; H NMR (300 MHz, CDCl3): d 3.6–3.94 (m, 3H, -CH-O-TBS,
-CH2-OH), 2.15 (brs, 1H, -OH), 1.69–1.89 (m, 2H), 1.56–1.68 (m, 2H),
1.21–1.55 (m, 6H), 0.90 (s, 9H), 0.88 (t, 3H, J ¼ 6.0 Hz), 0.09 (s, 6H,
2 ꢀ CH3); 13C NMR (75 MHz, CDCl3): 72.00, 60.28, 37.62, 36.74, 31.91,
25.78, 24.99, 22.58, 17.92, 13.96, 24.45, 24.77; LCMS: 261 (M þ 1).
(3S)-3-[1-(Tert-butyl)-1,1-dimethylsilyl]oxyoctan-1-ol ((S)-6)
Compound (S)-6 was similarly obtained in 84% yield from (S)-5: liquid, [a]D
þ17.82 (c 1, CHCl3).
(3R)-3-[1-(Tert-butyl)-1,1-dimethylsilyl]oxyoctanal ((R)-7)
To a stirred solution of IBX (4.56 g, 16.92 mmol) in DMSO (2.2 mL), alcohol
(R)-6 (2.2 g, 8.46 mmol) was added in dry DCM (15 ml). The reaction mixture
was allowed to stir at room temperature for 2 h. DCM was removed from the
reaction mixture under reduced pressure, then diethylether (20 ml) was added
to reaction mixture and filtered through Celitew. The filter cake was washed
with DCM and water. The layers were separated, and the aqueous phase was

1500
G. Sabitha, P. Gopal, and J. S. Yadav
extracted with DCM. The combined organic phase was dried over anhydrous
Na2SO4, and concentrated in vacuo. The crude product was purified by
column chromatography using silica gel to give the aldehyde (R)-7 (1.48 g,
68%). [a]2D5 25.0 (c 1, CHCl3), lit.[6g] 25.83 (c 1, CHCl3); IR (neat): 2929,
1
1714, 772 cm21; H NMR (300 MHz, CDCl3): d 9.78 (t, -CHO, J ¼ 2.2 Hz),
4.07–4.20 (m, 1H, -CH-O-TBS), 2.45–2.52 (m, 2H, CH2-CHO), 1.22–1.56
(m, 8H, aliphatic), 0.91 (t, 3H, CH3, J ¼ 6.0 Hz), 0.87 (s, 9H, tBu), 0.07
(s, 6H, 2 ꢀ CH3); 13C NMR (50 MHz, CDCl3): 202.43, 68.24, 50.75, 37.82,
31.75, 25.68, 24.76, 22.56, 17.95, 13.94, 24.46, 24.47.
(3S)-3-[1-(Tert-butyl)-1,1-dimethylsilyl]oxyoctanal ((S)-7)
Compound (S)-7 was similarly obtained in 62% yield from (S)-6: liquid, [a]D25
þ5.9 (c 1, CHCl3), lit.[14] 26.7 (c 1, CHCl3).
Methyl (Z, 5R)-5-[1-(Tert-butyl)-1,1-dimethylsilyl]oxy-2-decenoate
((R)-8)
To a stirred suspension of NaH (0.11 g, 4.58 mmol) in dry THF (10 mL), a
solution of methyl(bistrifluoroethyl) phosphonoacetate (1.602 g, 5.03 mmol)
in THF (5 mL) was added at 08C. After 0.5 h, a solution of aldehyde (1 g,
3.87 mmol) in dry THF (10 mL) was added and stirred. After 2 h, EtOAc
(15 ml) and water (20 ml) were added to the reaction mixture and stirred for
a few min; the organic layer was separated and the aq. layer was washed
with ethyl acetate (2 ꢀ 10 mL). The combined organic layers were washed
with water (10 mL), dried (Na2SO4), and concentrated under reduced
pressure. The crude product was purified by column chromatography using
silica gel to get Z-unsaturated ester (1.03 g, 85% yield). [a]D þ7.35 (c 0.85,
CHCl3); IR (neat): 1722, 1685, 1083, 823 cm21 1H NMR (300 MHz,
;
CDCl3): d 6.30–6.40 (m, 1H), 5.78–5.84 (dt, 1H), 3.69 (s, 3H, -COOMe),
3.71–3.82 (m, 1H, CH-O-TBS), 2.7–2.93 (m, 2H, allylic), 1.22–1.47
(m, 8H, aliphatic), 0.88 (t, 3H, J ¼ 6.0 Hz), 0.90 (s, 9H, tBu), 0.04 (s, 6H,
2 ꢀ CH3); 13C NMR (50 MHz, CDCl3): 166.79, 147.31, 120.22, 71.46,
50.96, 37.15, 36.35, 31.89, 25.81, 25.0, 22.61, 18.0, 14.0, 24.6; LCMS:
315 (M þ 1).
Methyl (Z, 5S)-5-[1-(Tert-butyl)-1,1-dimethylsilyl]oxy-2-decenoate
((S)-8)
Compound (S)-8 was similarly obtained in 89% yield from (S)-7: liquid [a]D
29.21 (c 0.85, CHCl3).

Asymmetric Synthesis of Massoialactones
1501
(6R)-6-Pentyl-5,6-dihydro-2H-2-pyranone ((R)-1)
To a stirred solution of ester (R)-8 (0.92 g, 2.93 mmol) in MeOH (15 mL), a
pinch of PTSA was added. The reaction mixture was allowed to stir for
30 min at room temperature. Methanol was removed in vacuum, and then
benzene (15 ml) was added to the reaction mixture and stirred for 1 h at
room temperature. Followed by TLC, the reaction mixture was concentrated
under reduced pressure. The crude product was purified by column chromato-
graphy using silica gel to give a lactone (R)-1 (0.372 g, 76%). [a]D 2113.5 (c
1, CHCl3), lit.[6e] [a]D 2110.7 (c 1, CHCl3); IR (neat): 2933, 1725, 1617,
1
1039 cm21; H NMR (300 MHz, CDCl3): d 6.80–6.87 (m, 1H), 5.96–6.02
(m, 1H), 4.33–4.44 (m, 1H), 2.27–2.35 (m, 2H), 1.25–1.86 (m, 8H), 0.91
(t, J ¼ 6.0 Hz, 3H); 13C NMR (75 MHz, CDCl3): 164.57, 144.99, 121.43,
78.0, 34.79, 31.54, 29.35, 24.47, 22,46, 13.94; LCMS: 191 (M þ Na).
(6S)-6-Pentyl-5,6-dihydro-2H-2-pyranone ((S)-1)
Compound (S)-1 was similarly obtained in 74% yield from (S)-8: liquid, [a]D
þ104.8 (c 0.41, CHCl3), lit.[9] [a]D þ109.6 (c 2.0, CHCl3).
ACKNOWLEDGMENT
P. G. thanks Council of Scientific and Industrial Research (CSIR), New Delhi,
for the award of a fellowship.
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