(4R,6R)-6-(hydroxymethyl)-4-methyltetrahydro-2H-pyran-2-one in the synthesis of polyfunctional compounds with the methyl-branched carbon skeleton

Article abstract of DOI:10.1134/S1070428013020127

A simple and efficient asymmetrical synthesis was performed of a convenient bifunctional building block, methyl (R)-5,5-dimethoxy-3-methylpentanoate and its (S)-enantiomer. The possibility was shown of its application to the synthesis of insect pheromones.

Full text of DOI:10.1134/S1070428013020127

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 2, pp. 253−258. © Pleiades Publishing, Ltd., 2013.
Original English Text © I.V. Mineeva, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 2, pp. 262−267.
(4R,6R)-6-(Hydroxymethyl)-4-methyltetrahydro-2H-pyran-
2-one in the Synthesis of Polyfunctional Compounds
with the Methyl-Branched Carbon Skeleton
I. V. Mineeva
Belarus’State University, Minsk,220030 Belarus
e-mail: i.mineyeva@yandex.ru
Received June 27, 2012
Abstract—A simple and efficient asymmetrical synthesis was performed of a convenient bifunctional building
block, methyl (R)-5,5-dimethoxy-3-methylpentanoate and its (S)-enantiomer. The possibility was shown of its
application to the synthesis of insect pheromones.
DOI: 10.1134/S1070428013020127
The presence of several chiral centers and functional
groups is characteristic of many polyfunctional biomol-
ecules: carbohydrates, prostanoids, pheromones, mac-
rolide antibiotics, and antitumor drugs. Therefore their
synthesis is often performed with the use of versatile
chiral blocks obtained frequently basing on monoterpe-
noids, amino acids, and oxyacids [1, 2]. The application
of natural compounds is in some cases limited by the
optical purity of the initial substances, multistage and
complicate processes, the use of expensive reagents and
enzymes, and also by the availability of a single optical
isomer (antipode).
[3]. Therefore in this study an asymmetrical synthesis
was developed of a convenient bifunctional building
block, methyl (R)-5,5-dimethoxy-3-methylpentanoate
R-(I), which had been previously obtained from natu-
ral chiral compounds with a methyl-branched carbon
skeleton, (R)-(+)-pulegone [4] and L-(–)-menthol [5, 6].
Ester R-(I) was synthesized proceeding from (4R,6R)-6-
(hydroxymethyl)-4-methyltetrahydro-2H-pyran-2-one
(II) (Scheme 1), obtained by procedure [7]; at the stage
of Keck asymmetric allylation methyl-3-[(tributylstannyl)
methyl]but-3-enoate (III) was used [8] and (R)-1,1'-
bi-2-naphthol (binol) as catalyst [9]. Also a number of
useful intermediates was obtained that found applica-
tion to the synthesis of biologically active compounds
(Schemes 2–4).
Especially important for the insect pheromones syn-
thesis are the methods of preparation of bifunctional
compounds capable of selective chemical transformations
Scheme 1.
O
SnBu3
MeO
OH
OH
66% [7]
O
O
O
O
O
III
R,R-II
S,S-II
O
OMe
OMe
OMe
MeO
OMe
MeO
R-I
S-I
253

MINEEVA et al.
254
Scheme 2.
.
(1) HIO4 2H2O, EtOH
OH
O
O
(2) PPTS, acetone_H2O
LiAlH4, THF
90%
OH
HO
EtO
H
OH
70%
O
O
R,R-II
VI
V
.
HIO4 2H2O,
MeOH
85%
OMe
O
O
O
OMe
LiAlH4, Et2O
H2O2, HCl, MeOH
82%
HO
OMe
MeO
OMe
96%
MeO
OMe
VIII
VII
R-I
PPTS, acetone_H2O
94%
O
O
MeO
H
IV
particular it was used in the synthesis of all four isomers
of 4,8-dimethyldecanal (IX), aggregation pheromone of
dangerous cereal pests flour beetle (Tribolium confusum)
and red flour beetle (Tribolium castaneum) [14], of iso-
prenoid (4R)-rose oxide (X) [15], of C5–C12 block of a
cytostatic drug (–)-laulimalide (XI) [16–18].
Lactones S,S- and R,R-(II) we obtained with the
optical purity >99% in 17% yield with respect to 8 pre-
parative stages calculated on easily available initial ethyl
3,3-diethoxypropionate [7]. With respect to the C5-allyl
synthetic building block, methyl-3-[(tributylstannyl)
methyl]but-3-enoate (III), the yield in 3 stages was 66%.
The target ester R-(I) was obtained after cleavage of
lactone R,R-(II) with periodic acid in methanol and main-
taining the reaction mixture for 12 h in order to complete
the dimethylacetal protection (Scheme 2). The subsequent
hydrolysis under mild conditions furnished aldehyde
IV in a high yield. The oxidation of lactone R,R-(II) in
ethanol proceeded slower and gave a mixture of products
that was subjected to hydrolysis without purification to
provide a bifunctional block V which had been used
previously in the synthesis of the antitumor drug (–)-lauli-
malide [10, 11]. The reduction of compound R,R-(II) with
lithium aluminum hydride in tetrahydrofuran occurred
without complications affording triol VI that also had
been utilized in the synthesis of the fragment C15–C20 of
aplyronines A, C, C, antitumor drugs from the seaweeds
of Sea of Japan Aplysia kurodai [12, 13]. Ester R-(I) was
selectively oxidized to alcohol VII and reduced to diether
VIII in high yields; both compounds were also convenient
bifunctional building blocks (Scheme 2).
The reduction of aldehyde IV with sodium borohy-
dride in methanol was accompanied with the lactoniza-
tion with the formation of compound XII that had been
previously used in the synthesis of (+)-faranal (XIII), the
pheromone of the Pharaoh’s ant Monomorium pharaonis,
a dangerous infection carrier in hospitals and food stores
[19, 20], of (R)- and (S)-enantiomers of (E)-6-isopropyl-
3,9-dimethyl-5,8-decadienyl acetate (XIV), the phero-
mone of yellow scale Aonidiella citrina (Coquillett) [21].
After transesterification into a methyl ether lactone XII
was converted into silyl ether XV that could serve as a
convenient methyl-branched block in the preparation of
the key fragment of the verrucarinic acid XVI [22] and
a fragment of a cytotoxic macrolide amphidinolide H2
(XVII) [23, 24].
Alcohol VIII in several preparative stages was con-
verted into functionalized aldehydes XVIII, XIX in
moderate yields (Scheme 4). Convenient methods are
published describing conversion of these aldehydes into
insect pheromones. For instance, compound XVIII was
used in one protocol of the synthesis of the pheromone
Aldehyde IV also found application to the synthesis
of several biologically active substances (Scheme 3). In
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(4R,6R)-6-(HYDROXYMETHYL)-4-METHYLTETRAHYDRO-2H-PYRAN-
255
Scheme 3.
H
O
X
O
OMe
O
O
H
O
MeO
H
O
IX
IV
O
XI
NaBH4, MeOH
81%
O
O
O
H
O
O
XII
XIV
XIII
(1) Et3N, MeOH
(2) t-BuMe2SiCl, imidazole, DMFA
80%
O
O
HO
O
MeO
OSiMe2Bu-t
O
XVI
XV
Scheme 4.
XVII
OH
XIV
XXI
(1) AcCl, Py, CH2Cl2
(2) PPTS, acetone_H2O
O
(1) NaH, BnCl, THF
O
(2) PPTS, acetone_H2O
BnO
H
VIII
AcO
H
86%
73%
XVIII
IX
XIX
XX
O
H
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 2 2013

MINEEVA et al.
256
of yellow scale XIV, a dangerous pest of citrus plants
[21], and of flour beetles IX [1]. In its turn aldehyde XIX
proved to be a promising building block in the preparation
of (R)- and (S)-isomers of (Z)-14-methylhexadec-8-enal
(trogodermal) (XX), aggregation pheromone of Kharpa
beetle Trogoderma granarium [25], of stereoisomers
of 6,10,13-trimethyl-1-tetradecanol (XXI), aggregation
pheromone of anchor stink bug Stiretrus anchorago [26].
Methyl (3R)-3-methyl-5-oxopentanoate (IV). To a
solution of 0.89 g(4.7 mmol) of ester R-(I) in a mixture
of 10 ml of acetone and 3 ml of water was added 0.08 g
(0.3 mmol) of pyridine-p-toluenesulfonate (PPTS), and
the mixture was stirred at boiling over 3 h till the comple-
tion of the reaction (TLC monitoring).After distilling off
the solvent at a reduced pressure the residue was dissolved
in 40 ml of CHCl3, washed with saturated water solution
of NaHCO3 (25 ml), and dried with MgSO4. The solvent
was removed at a reduced pressure, the reaction product
was isolated by chromatography (eluent petroleum ether–
ethyl acetate, 60 : 1). Yield 0.63 g (94%). The spectra and
optical rotation of compound obtained were consistent
with those published in [27].
The oxidative cleavage of lactone S,S-(II) afforded
the corresponding isomeric ester S-(I) (Scheme 1) with a
high yield and a high enantiomeric purity demonstrating
the universality of the developed protocol.
Thus a simple convenient protocol is described for
the synthesis of several chiral building blocks with the
methyl-branched carbon skeleton proceeding from eas-
ily available lactone R-(II) and wide opportunities were
demonstrated of the application of these compounds to
the synthesis of versatile biologically active substances,
in particular, of the pure stereoisomers of pheromones
of insect pests.
Ethyl (3R)-3-methyl-5-oxopentanoate (V). To
a solution of 0.9 g (6.3 mmol) of lactone R,R-(II) in 10
ml of anhydrous ethanol was added 1.73 g (7.6 mmol)
of HIO4·2H2O, and the mixture was stirred for 24 h. The
alcohol was removed at a reduced pressure, the reaction
mixture was diluted with 15 ml of acetone and 2 ml of
water, 0.08 g (0.3 mmol) of PPTS was added, and the
solution was stirred at boiling for 4 h till the comple-
tion of the reaction (TLC monitoring). On removing the
solvent at a reduced pressure the residue was dissolved
in 40 ml of CHCl3, washed with saturated water solution
of NaHCO3 (25 ml), and dried with MgSO4. The solvent
was removed at a reduced pressure, the reaction prod-
uct was isolated by chromatography (eluent petroleum
ether–ethyl acetate, 50 : 1). Yield 0.69 g (70%), [α]D
–5.4° (c2.5, CHCl3). IR spectrum, cm-1: 1730, 1713, 1415,
EXPERIMENTAL
1H and 13C NMR spectra were registered from solu-
tions of compounds in deuterochloroform on a spec-
trometer Bruker AC 400 at operating frequencies 400
and 100 MHz respectively. IR spectra were recorded on
a spectrophotometer Bruker Vertex 70 from solutions in
tetrachloromethane. The chromatographic isolation of
individual compounds was performed with the use of
silica gel (70–230 mesh). All solvents before use were
dried by usual methods and distilled.
1
1360, 1238, 1182. H NMR spectrum, δ, ppm: 1.05 q
(3H, CH3, J 7.2 Hz), 1.22 t (3H, CH3CH2O, J 7.5 Hz),
2.19–2.80 m (5H, COCH2CHCH3, CHCH3, CH2CHO),
4.25 q (2H, CH3CH2O, J 7.5 Hz), 9.80 br.s (1H, CHO).
13C NMR spectrum, δ, ppm: 14.6, 20.4, 25.7, 41.4, 50.4,
60.8, 168.2, 204.0. Found, %: C60.88; H 8.84. C8H14O3.
Calculated, %: C60.74; H 8.92.
Methyl (R)-5,5-dimethoxy-3-methylpentanoate
(I). To a solution of 2 g (13.9 mmol) of lactone R,R-(II)
in 20 ml of anhydrous methanol was added 3.5 g (18.1
mmol) of HIO4·2H2O, and the mixture was stirred for
12 h. The reaction mixture was diluted with 50 ml of
ethyl ether and was treated at vigorous stirring with a
saturated water solution of NaHCO3 (50 ml). The organic
layer was separated, the reaction product was extracted
from the water layer with ethyl ether (3 × 30 ml), the
combined organic solutions were washed with brine (50
ml) and dried with MgSO4. The solvent was removed at
a reduced pressure, the reaction product was isolated by
chromatography (eluent petroleum ether–ethyl acetate,
80 : 1). Yield 2.24 g (85%), [α]D –1.5° (c 2.4, CHCl3).
The spectra of compound obtained were consistent with
those published in [4, 5].
(2R,4S)-4-Methylhexane-1,2,6-triol (VI).At cooling
to 0°C to a slurry of 0.4 g (10 mmol) of LiAlH4 in 10
ml of THF was added a solution of 0.72 g (5 mmol) of
lactone R,R-(II) in 5 ml of THF, and a vigorous stirring
was continued for 12 h. The mixture was diluted with 30
ml of ethyl ether, and 0.2 ml of water was added at cool-
ing. The reaction mixture was filtered through a thin bed
of silica gel, and the solvent was removed at a reduced
pressure. Yield 0.67 g (90%), [α]D +10.1° (c1.0, CHCl3).
The spectra of compound obtained were in agreement
with published data [13].
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(4R,6R)-6-(HYDROXYMETHYL)-4-METHYLTETRAHYDRO-2H-PYRAN-
257
product was isolated by chromatography (eluent petro-
leum ether–ethyl acetate, 70:1). Yield 2.07 g (80%). The
spectra of compound obtained were consistent with those
published in [23].
Dimethyl 3-methylpentanedioate (VII).
To a solution of 0.95 g (5 mmol) of compound
R-(I) in 10 ml of methanol cooled to 0°C was added
0.7 ml of concn. HCl, then 0.9 ml of 33% H2O2, and the
mixture was stirred for 1 h and later heated at 50–55°C
for 5 h. The large part of methanol was removed at a re-
duced pressure, the residue was diluted with ethyl acetate
(30 ml) and neutralized with sodium hydrogen carbonate,
the organic layer was separated and dried with Na2SO4.
The solvent was removed at a reduced pressure. Yield
0.71 g (82%). The spectra of compound obtained were
consistent with those published in [28].
(3S)-5-Benzyloxy-3-methylpentanal (XVIII). To
a slurry of 0.12 g (5 mmol) of NaH in 15 ml of THF
was added 0.64 g of alcohol VIII, and the mixture was
stirred for 20 min. Then a solution of 0.63 g (5 mmol) of
benzyl chloride in 3 ml of THF was added, and the reac-
tion mixture was stirred at 50°C over 8 h. The reaction
mixture was treated with 45 ml of saturated water solu-
tion of NH4Cl. The reaction product was extracted into
ethyl ether (4 × 10 ml), the combined organic solutions
were dried with Na2SO4. The solvent was removed at a
reduced pressure. The residue was diluted with 25 ml of
acetone and 3 ml of water, 0.16 g (0.6 mmol) of PPTS
was added, and the mixture was stirred at boiling for 4 h
till the completion of the reaction. The solvent was re-
moved at a reduced pressure. The residue was dissolved
in 40 ml of CHCl3, washed with saturated water solution
of NaHCO3 (25 ml), and dried with MgSO4. The solvent
was removed at a reduced pressure, the reaction product
was isolated by chromatography (eluent petroleum ether–
ethyl acetate, 60 : 1). Yield 0.71 g (86%), [α]D –4.2° (c
1.5, CHCl3). IR spectrum, cm–1: 1708, 1454, 1408, 1277,
1178, 1096, 1027. 1H NMR spectrum, δ, ppm: 0.97 q (3H,
CH3, J 6.8 Hz), 1.23–1.34 m (1H, CH2CH), 1.38–1.45 m
(1H, CH2CH), 2.02–2.09 m (CHCH3), 2.19–2.24 m (1H,
CH2CHO), 2.35–2.41 m (1H, CH2CHO), 3.42 t (2H,
CH2CH2O, J 6.8 Hz), 4.46 s (2H, OCH2Ph), 7.18–7.31 m
(5H, Ph), 9.71 br.s (1H, CHO). 13C NMR spectrum, δ,
ppm: 19.5, 26.8, 32.9, 50.5, 69.9, 72.5, 127.1, 127.2,
127.9, 138.2, 202.2. Found, %: C75.73; H 8.72. C13H18O2.
Calculated, %: C75.69; H 8.80.
(3S)-5,5-Dimethoxy-3-methylpentan-1-ol (VIII). To
a slurry of 0.76 g (5 mmol) of LiAlH4 in 20 ml of anhy-
drous ethyl ether was added a solution of 1.33 g (7 mmol)
of ester R-(I) in 3 ml of anhydrous ethyl ether at uniform
stirring while boiling. After 2 h the mixture was diluted
with 20 ml of ethyl ether and at cooling 1 ml of water was
added. The reaction mixture was filtered through a thin
bed of silica gel, and the solvent was removed at a reduced
pressure. Yield 1.09 g (96%), [α]D +5.7° (c 1.9, CHCl3).
The spectra of compound obtained were consistent with
those published in [4].
(4R)-4-Methyltetrahydro-2H-pyran-2-one (XII). To
a solution of 1.15 g (8 mmol) of aldehyde IV in 20 ml of
methanol was added 0.38 g (10 mmol) of NaBH4, and the
mixture was stirred for 12 h. The reaction mixture was
treated with 20 ml of saturated water solution of NH4Cl.
The reaction product was extracted into ethyl ether (4 ×
10 ml), the combined organic solutions were dried with
Na2SO4. On removing the solvent at a reduced pressure
compound XII was isolated by chromatography (eluent
petroleum ether–ethyl acetate, 15 : 1). Yield 0.74 g (81%).
The spectra and optical rotation of compound obtained
were consistent with those published in [20, 27].
(3S)-5-Methyl-5-oxopentyl acetate (XIX). To a
solution of 0.64 g (4 mmol) of alcohol VIII in 10 ml of
anhydrous CH2Cl2 was added at cooling in succession
0.8 g (10 mmol) of pyridine and 0.47 g (6 mmol) of
acetyl chloride in 2 ml of CH2Cl2 , and the mixture was
stirred for 12 h. The reaction mixture was treated with
40 ml of saturated water solution of NaHCO3. The reac-
tion product was extracted into CH2Cl2 (2 × 10 ml), the
combined organic solutions were dried with Na2SO4. The
solvent was removed at a reduced pressure. The residue
was diluted with 25 ml of acetone and 3 ml of water,
0.16 g (0.6 mmol) of PPTS was added, and the mixture
was stirred at boiling for 3 h till the completion of the
reaction. The solvent was removed at a reduced pressure.
The residue was dissolved in 40 ml of CHCl3, washed
Methyl (3R)-5-{[tert-butyl(dimethyl)silyl]oxy}-
3-methylpentanoate (XV). To a solution of 1.2 g
(10.5 mmol) of lactone XII in 10 ml of anhydrous metha-
nol was added 5 ml of Et3N, and the mixture was kept for
48 h. On removing the mixture of solvents at a reduced
pressure the residue was dissolved in 5 ml of DMF, in
one portion was added 0.95 g (14 mmol) of imidazole
and 1.96 g (13 mmol) of tert-butyldimethylchlorosilane
(t-BuMe2SiCl). The reaction mixture was treated with
15 ml of saturated water solution of NH4Cl. The reaction
product was extracted into ethyl ether (4×10 ml), the
combined organic solutions were dried with Na2SO4. On
removing the solvent at a reduced pressure the reaction
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 2 2013

MINEEVA et al.
258
vol. 68, p. 3036.
with saturated water solution of NaHCO3 (25 ml), and
dried with (eluent petroleum ether–ethyl acetate, 60 : 1).
Yield 0.46 g (73%). The spectra and optical rotation of
compound obtained were consistent with those published
in [26].
12. Ojika, M., Kigoshi, H., Ishigaki, T., Tsukada, I., Tsuboi, T.,
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Methyl (S)-5,5-dimethoxy-3-methylpentanoate (I)
was obtained similarly to the R-enantiomer. Yield 2.18 g
(83%), [α]D +1.5° (c1.6, CHCl3). The spectral character-
istics of compound obtained were consistent with those
of compound R-(I).
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