Efficient enantioselective synthesis of (+)-sclareolide and (+)-tetrahydroactinidiolide: chiral LBA-induced biomimetic cyclization

Article abstract of DOI:10.1016/j.tetasy.2009.06.020

An efficient enantioselective synthesis of the lactones (+)-sclareolide and (+)-tetrahydroactinidiolide has been achieved through Lewis acid-assisted chiral Bronsted acid-induced enantioselective cyclization of terpenic carboxylic acids. The reaction sequ

Full text of DOI:10.1016/j.tetasy.2009.06.020

Tetrahedron: Asymmetry 20 (2009) 1637–1640
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Efficient enantioselective synthesis of (+)-sclareolide and
(
+)-tetrahydroactinidiolide: chiral LBA-induced biomimetic cyclization
Kiran B. Upar, Sanjay J. Mishra, Shrikant P. Nalawade, Soni A. Singh, Reena P. Khandare, Sujata V. Bhat *
Laboratory for Advanced Research in Natural and Synthetic Chemistry, V. G. Vaze College, Mumbai University, Mithagar Road, Mulund (East), Mumbai 400 081, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient enantioselective synthesis of the lactones (+)-sclareolide and (+)-tetrahydroactinidiolide has
been achieved through Lewis acid-assisted chiral Brønsted acid-induced enantioselective cyclization of
terpenic carboxylic acids. The reaction sequence involved the [2,3] sigmatropic rearrangement of an
Received 11 March 2009
Accepted 9 June 2009
Available online 28 July 2009
0
allylic alcohol and biomimetic cyclization of terpenic acid in the presence of (R)-2-benzyloxy-2 -
0
hydroxy-1,1 -binaphthyl and tin tetrachloride as key steps. The cyclization gave lactones in good yield
and with high enantiomeric excess.
Ó 2009 Elsevier Ltd. All rights reserved.
1
. Introduction
+)-Sclareolide 1, a constituent of Arnica angustifolia, Sideritis nu-
oped to a high degree of sophistication and practical utility.20 Le-
wis acid-assisted chiral Brønsted acid (chiral LBA)-induced enan-
(
tioselective cyclization of homofarnesol with a hydroxy group as
Ò
tans, and Kyllinga erecta displays phytotoxic, antifungal, and cyto-
toxic activities against human cancer cell lines. (+)-Sclareolide 1
is obtained from oxidative degradation of more abundant labdane
a nucleophilic terminator gave (ꢀ)-ambrox in 54% yield with
1
21
Ò
42% ee. Alternatively the synthesis of (ꢀ)-ambrox (76% ee)
was achieved via the enantioselective cyclization of an (E,E)-homo-
farnesyl-triethylsilyl ether induced by chiral LBA and subsequent
diastereoselective cyclization of the resulting chiral bicyclic and
terpenes, such as (ꢀ)-sclareol, (+)-cis-abienol, (ꢀ)-labdanoic acid,
2
and manoyl oxide. It is mainly used in the perfume industry for
2
1
the synthesis of the natural ambergris substitute product (ꢀ)-amb-
monocyclic products induced by achiral LBAs. Similar enantiose-
lective cyclization of 2-(polyprenyl)-phenol derivatives gave poly-
cyclic terpenoids bearing the chroman skeleton in excellent yield
Ò
3
rox 2. (+)-Sclareolide 1 has also been employed in the synthesis
4
of various natural products such as wiedendiol, (+)-hedychilac-
tone, hispanane-like terpene derivatives, b-methylfurolabdanes,
acuminolide and 17-O-acetylacuminolide, (+)-zerumin B, onc-
eradiene analogue, austrodoral, pelorol, austrodoric acid,
5
6
7
22
and good ee %. Herein, we report the enantioselective synthesis
8
9
of (+)-sclareolide 1 and (+)-tetrahydroactinidiolide 9 through bio-
mimetic cyclization of homofarnesic acid 5 and homogeranic acid
8, respectively, in the presence of chiral LBA.
1
0
11
12
13
1
4
15
16
(
+)-coronarin-A,
(+)-puupehenone,
coscinosulfate A,
(ꢀ)-
1
7
18
yatellaquinone, and sulfircin. Actinidiolide derivatives have
been found to have insect pheromone activity and are useful as to-
bacco flavor enhancers.19
2
. Results and discussion
The present synthetic approach to (+)-sclareolide 1 and (+)-tet-
O
rahydroactinidiolide 9 from (E)-(+)-nerolidol 3 and (R)-(ꢀ)-linalool
6, respectively, involves the [2,3] sigmatropic rearrangement of an
allylic alcohol to the homologous amide followed by hydrolysis of
the amide to the acid and biomimetic enantioselective cyclization
H
O
O
O
O
SnCl4
Bn
0
0
of acid promoted by (R)-2-benzyloxy-2 -hydroxy-1,1 -binaphthyl
(-)-ambrox®
2
(R)-BINOL-Bn
Chiral LBA
[(R)-benzyl-BINOL] and SnCl (chiral LBA).
(+)-sclareolide 1
4
(E)-(+)-Nerolidol 3 and (R)-(ꢀ)-linalool 6 were heated with
N,N-dimethylformamide dimethyl acetal (DMFDMA) to achieve
one carbon homologation to the corresponding starting materials
with incorporation of a terminal amide functionality. Thus, refluxing
a mixture of (+)-(E)-nerolidol and DMFDMA in xylene for 14 h
The construction of polycyclic molecules from acyclic precur-
sors is a general theme in biosynthesis. Over the last two decades
the biomimetic cyclization of polyene molecules have been devel-
yielded an E/Z-mixture of the b,
c-unsaturated amides 4a and 4b
(
2.2:1) in 79% yield (Scheme 1), which were easily separated by
*
Corresponding author. Tel.: +91 022 21631421x113; fax: +91 022 21634262.
E-mail address: sujata8b@gmail.com (S.V. Bhat).
2
3
silica gel column chromatography. The alkaline hydrolysis of
0
957-4166/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2009.06.020

1
638
K. B. Upar et al. / Tetrahedron: Asymmetry 20 (2009) 1637–1640
O
yield and high enantiomeric excess. The method is practical and
in view of the commercial importance and wide synthetic applica-
tions of lactones 1 and 9 the present method assumes greater
significance.
NMe2
+
O
OH
NMe2
i
7
9%
4
4
. Experimental
3
(E,E)- 4a
(Z,E)- 4b
4a:4b 2.2:1 )
(
O
.1. General methods
O
OH
GC analysis of the products was performed on instrument
ii
0%
O
(
E,E)- 4a
iii
5
equipped with a flame ionization detector, using a capillary column
8
8%
(cross-linked methyl siloxane, 30 m ꢁ 0.25 m ꢁ 0.32 mm). GC–MS
l
analysis was carried out on an instrument, which was coupled with
5
a mass spectrometer with a quadrapole mass detector, using 5%
(
+)-1
phenyl-methyl siloxane column (30 m ꢁ 250
enantiomeric excess of the final lactones was obtained in GC
analysis using a chiral beta Dex 120 column (30 m ꢁ 0.25 m ꢁ
.25 mm). H NMR spectra were recorded on 400 MHz instrument
l
m ꢁ 0.25
lm). The
OH
O
R
i
l
O
6
1%
O
1
0
H
1
3
(+)-
9
and C spectra were recorded on 75 and 100 MHz instruments. IR
spectra were recorded on FTIR instrument.
6
(E)- 7 R=NMe2
ii,
iii,
0%
81%
8
4
.2. Synthesis of (E,E)-4,8,12-trimethyl-3,7,11-tridecatrienoic
(
E)- 8 R=OH
acid N,N-dimethylamide 4a
Scheme 1. Enantioselective synthesis of (+)-sclareolide and (+)-tetrahydroactinid-
iolide. Reaction conditions: (i) DMFDMA, xylene, reflux, 14 h; (ii) KOH, MeOH–
A mixture of (+)-(E)-nerolidol 3 (22.2 g, 0.1 mol), N,N-dimethyl-
formaldehyde dimethyl acetal (DMFDMA, 95.2 g, 0.8 mol), and xy-
lene (200 mL) was refluxed for 14 h with continuous removal of
methanol (Dean-Stark device). The mixture was concentrated in
vacuo to yield a residue (26.2 g) which, after silica gel column chro-
0
0
water, reflux, 12 h; (iii) 2-benzyloxy-2 -hydroxy-1,1 -binaphthyl, SnCl
4
, toluene,
ꢀ
78 °C, 3 h, and at ꢀ20 °C, 3 d.
amide 4a afforded homofarnesic acid 5,21 which was subjected to
cyclization in the presence of (R)-benzyl-BINOL and SnCl at
3E
matography, yielded D
-amide 4a (14.4 g, 55%, hexane: ethyl ace-
4
3
Z
ꢀ
78 °C for 3 h and subsequently at ꢀ20 °C for 3 d to give (+)-sclareo-
tate 92:8) and
92:8).
D -amide 4b (6.55 g, 25%, hexane–ethyl acetate
lide 1 in 58.6% yield and 88% ee (Fig. 1). A similar reaction sequence
starting from (R)-(ꢀ)-linalool 6 gave amide 7, which on hydrolysis
gave homogeranic acid 8,24 while cyclization in the presence of
4.2.1. Compound 4a
IR (Liquid) 1648 (CONMe
2
) cm 1; 1H NMR (400 MHz) d 1.58 (br s,
ꢀ
(
R)-benzyl-BINOL and SnCl
4
gave (+)-tetrahydroactinidiolide 9 in
8
0% yield and 90% ee.
6H), 1.65 (s, 3H), 1.67 (s, 3H), 2.93, 2.96 (2s, 6H), 3.04 (d, J = 6.7, 2H),
1
3
5
.04–5.10 (m, 2H), 5.30 (td, J = 6.7, 1.1, 1H); C NMR (100 MHz) d
O
172.0, 138.0, 135.1, 131.2, 124.2, 123.8, 116.8, 39.6, 39.5, 37.3,
OH
35.4, 33.7, 26.6, 26.4, 25.6, 17.6, 16.4, 15.9; MS m/z (rel. int.) 277
+
(
M , 1), 208 (8), 194 (1), 154 (2), 141 (5), 140 (7), 121 (12), 87
þ
(
21), 72 (CONMe2 , 100), 69 (26), 41 (36).
(
+)-1
4
.2.2. Compound 4b
IR (Liquid)1648 (CONMe
2
) cm 1; 1H NMR (400 MHz) d 1.55 (br s,
ꢀ
(
E,E)-5
H
6
5
H), 1.63 (s, 3H), 1.70 (s, 3H), 2.88, 2.95 (2s, 6H), 3.03 (d, J = 6.7, 2H),
.01–5.10 (m, 2H), 5.29 (td, J = 6.7, 1.3, 1H); C NMR (100 MHz) d
1
3
O
O
SnCl4
171.8, 138.0, 135.3, 131.2, 124.1, 123.6, 117.5, 39.6, 37.2, 35.3,
33.1, 32.1, 26.5, 26.0, 25.5, 23.3, 17.5, 15.8; MS m/z (rel. int.) 277
(M , 1), 208 (12), 195 (1), 154 (2), 141 (5), 140 (35), 121(15), 87
OH
(+)-9
+
Bn
O
þ
(
19), 72 (CONMe2 , 100), 69 (29), 41 (47).
Chiral LBA
8
(
E)-
4
.3. Synthesis of (E,E)-4,8,12-trimethyl-3,7,11-tridecatrienoic
H
acid 5
Chiral LBA
A mixture of amide 4a (12.5 g, 0.045 mol), KOH (3.135 g,
.055 mol), H O (3 mL), and MeOH (30 mL) was refluxed for 12 h.
After removing the solvent in vacuo the residue was fractionated
into H O–ethyl acetate. To the H O layer, 2 M HCl was added until
pH 3 and extracted with ethyl acetate (3 ꢁ 50 mL). The combined
organic extracts were dried over anhydrous MgSO and evaporated
Figure 1. Enantioselective cyclization of (E,E)-5 and (E)-8 induced by (R)-benzyl-
BINOL-SnCl
0
2
4
.
2
2
3
1
. Conclusion
4
In conclusion, a new approach to the synthesis of (+)-sclareolide
and (+)-tetrahydroactinidiolide 9 has been developed starting
to yield a yellow viscous oil (10 g), which after silica gel column
chromatography, yielded homofarnesic acid 5 (9.02 g, 80%, hex-
ꢀ1
from (E)-(+)-nerolidol 3 and (R)-(ꢀ)-linalool 6, respectively.
Interestingly, the chiral LBA-induced polyene cyclization with a
carboxylic group as a terminator resulted in lactones with good
ane–ethyl acetate 95:5). IR (Neat) 3420 (OH), 1710 (CO) cm ;
1
H NMR (400 MHz, CDCl ) d 1.50 (br s, 6H), 1.57 (s, 3H), 1.65 (s,
3
3H), 1.6–2.06 (m, 8H), 3.15 (d, J = 6.8 Hz, 2H), 5.04–5.15 (m, 2H),

K. B. Upar et al. / Tetrahedron: Asymmetry 20 (2009) 1637–1640
1639
5
2
.25 (td, J = 6.4, 1.1 Hz, 1H), 10.0–10.5 (br s, 1H); MS m/z (rel. int.)
50 (M , 1), 205 (1), 195 (4), 136 (33), 121 (56), 105 (7), 95 (14), 81
(br s, 1H); 13C NMR (75 MHz, CDCl
115.0, 39.5, 33.5, 26.5, 25.6, 17.6, 16.4. HRMS m/z calcd for
3
) 178.9, 139.7, 132.1, 123.9,
+
(
40), 69 (88), 53 (10), 41 (100). HRMS m/z calcd for C16
H
26
O
2
11 18 2
C H O 182.2627, found 182.2601.
2
50.3812, found 250.3814.
4
.7. (+)-Tetrahydroactinidiolide 9 [(3aR,7aS)-(+)-octahydro-4,4,
4.4. (+)-Sclareolide 1 {(3aR,5aS,9aS,9bR)-(+)-1,2,3a,4,5,5a,6,7,8,9,
9a,9b-dodecahydro-3a,6,6,9a-tetramethylnaptho[2,1-b]furan-
2-one}
7a-trimethyl-benzofuran-2-one]
0
0
To a solution of (R)-2-benzyloxy-2 -hydroxy-1,1 -binaphthyl
(
87 mg, 0.23 mmol) in toluene (3 mL) was added tin(IV) chloride
0
0
To a solution of (R)-2-benzyloxy-2 -hydroxy-1,1 -binaphthyl
(0.13 mL, 1.1 mmol) at ꢀ20 °C and the solution was stirred for
30 min. Subsequently this mixture was cooled to ꢀ78 °C and a solu-
tion of homogeranic acid 8 (150 mg, 0.82 mmol) in toluene (3 mL)
was added dropwise over a period of 15 min. The reaction mixture
was stirred at ꢀ78 °C for 3 h and kept at ꢀ20 °C for 3 d, quenched
with cold water, and extracted with ethyl acetate. The combined or-
(
(
3
260 mg, 0.69 mmol) in toluene (9 mL) was added tin(IV) chloride
0.4 mL, 3.37 mmol) at ꢀ20 °C and the solution was stirred for
0
0
0 min. This complex of 2-benzyloxy-2 -hydroxy-1,1 -binapthyl–
SnCl
4
prepared in situ was cooled to ꢀ78 °C and homofarnesic acid
5
(600 mg, 2.4 mmol) in toluene (9 mL) was added dropwise over a
period of 5 min. The reaction mixture was stirred at ꢀ78 °C for 3 h
4
ganic extracts were dried over anhydrous MgSO and concentrated.
The crude product was purified by column chromatography on neu-
and kept at ꢀ20 °C for 3 d, quenched with saturated aqueous NaH-
CO
3
, and extracted with ethyl acetate. The combined organic ex-
tral alumina, to yield (+)-tetrahydroactinidiolide 9 (120 mg, 80%,
2
D
5
25
25
D
tracts were dried over anhydrous MgSO
4
and concentrated. The
hexane–ethyl acetate 95:5). ½
aꢂ
¼ þ64 (c 1, hexane), Lit.
½
a
ꢂ
¼
crude product was purified by column chromatography on silica
þ71 (c 0.04 hexane); GC (initial column temperature 135 °C for
gel to yield (+)-sclareolide 1 (352 mg, 58.6 %, hexane–ethyl acetate
5 min, heat 1 °C/min, final temperature 210 °C, injection tempera-
2
25
D
9
2:8); mp 120–122 °C (hexane); (Lit. mp 121–124 °C); ½
aꢂ
¼
ture 230 °C), t
R
= 42.0 (major isomer of 9, 95%), 42.5 (minor isomer
-lactone), 1458,
3
1382 cm ; H NMR (400 MHz, CDCl ) d 0.91 (s, 3H), 1.05 (s, 3H),
2
25
D
þ42:6 (c 0.5 CHCl
3
), Lit. ½
a
ꢂ
¼ þ47:3 (c 0.9 CHCl
3
); GC (initial col-
of 9, 5%) min, ee 90%. IR (KBr) 2940, 2871, 1765 (c
ꢀ1 1
umn temperature 171 °C for 5 min, heat 1 °C/min, final temperature
2
10 °C, injection temperature 230 °C), t
R
= 37.2 (major isomer of 1,
1.32 (s, 3H), 1.6–1.4 (m, 4H), 1.84 (m, 2H), 2.07 (dd, J = 13.2, 8.8 Hz,
9
4 %), 37.8 (minor isomer of 1, 6.0%) min, ee 88%. IR (KBr) 1770
1H), 2.42 (dd, J = 8.4, 17.6 Hz, 1H), 2.53 (dd, J = 17.2, 12.8 Hz, 1H);
ꢀ1
1
13
(c
3
-lactone) cm ; H NMR (400 MHz, CDCl ) d 0.83 (s, 3H), 0.88 (s,
3
C NMR (75 MHz, CDCl ) d 175.8, 86.1, 51.9, 34.7, 33.6, 33.3, 32.2,
+
3
H), 0.90 (s, 3H), 1.04 (dd, J = 12.8, 3.7 Hz,1H), 1.21 (m, 2H), 1.32
30.1, 28.4, 26.9, 18.9. MS m/z (rel. int. %) 182 (M , 2), 167 (100),
(
s, 3H), 1.35–1.5 (m, 6H), 1.88 (dq, J = 13.2, 3.7 Hz,1H), 1.95 (dd,
J = 14.4, 6.7 Hz, 1H), 2.06 (dt, J = 12.0, 3.5 Hz,1H), 2.21 (dd, J = 16.8,
.4 Hz,1H), 2.4 (dd, J = 16.8, 14.4 Hz,1H); 13C NMR (100 MHz, CDCl
d 176.7, 86.3, 59.1, 56.6, 42.2, 39.5, 38.7, 36.1, 33.2, 33.1, 28.7, 21.6,
139 (31), 126 (7), 111 (22), 96 (29), 81 (28), 69 (43), 55 (22), 43
(40); HRMS m/z calcd for C11H O 182.2627, found 182.2618.
18 2
6
3
)
+
Acknowledgments
2
(
0.9, 20.6, 18.1, 15.1, MS m/z (rel. int. %) 250 (M , 0.7), 235 (12), 206
16), 191(13), 150 (15), 123 (49), 67 (77), 55 (66), 43 (100), HRMS
m/z calcd for C16 250.3812, found 250.3807.
We are grateful to Kelkar Education Trust, Mumbai for encour-
agement and support. We are also thankful to Department of
Chemistry and Sophisticated Analytical Instrumentation Facility,
Indian Institute of Technology, Mumbai for NMR spectral data.
26 2
H O
4
.5. Synthesis of (E)-4,8-dimethyl-3,7-nonadienoic acid
N,N-dimethylamide 7
A mixture of (R)-(ꢀ)-linalool 6 (12.0 g, 0.077 mol), DMFDMA
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H
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