Synthesis of functionalized pentalenes via carbonyl-ene reaction and enzymatic kinetic resolution

Article abstract of DOI:10.1055/s-2008-1067012

The synthesis of functionalized pentalene derivatives is described. Bicyclo[3.3.0]octane-3,7-dione 5 (Weiss diketone) was converted in six steps into the silyl-protected 3-methylbicyclo[3.3.0]octenol 6, which was submitted to Lewis acid catalyzed carbonyl

Full text of DOI:10.1055/s-2008-1067012

PAPER
1619
Synthesis of Functionalized Pentalenes via Carbonyl-Ene Reaction and
Enzymatic Kinetic Resolution
S
T
ynthesis of Fu
i
nctiona
m
lized Pentalenes o Anderl, Marc Emo, Sabine Laschat,* Angelika Baro, Wolfgang Frey
Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
Fax +49(711)68564285; E-mail: sabine.laschat@oc.uni-stuttgart.de
Received 5 February 2008
Dedicated to Prof. Larry E. Overman on the occasion of his 65 birthday
th
H
H
H
Abstract: The synthesis of functionalized pentalene derivatives is
described. Bicyclo[3.3.0]octane-3,7-dione 5 (Weiss diketone) was
converted in six steps into the silyl-protected 3-methylbicyc-
lo[3.3.0]octenol 6, which was submitted to Lewis acid catalyzed
carbonyl-ene reactions with trioxane yielding the primary alcohol 7
with exocyclic double bond in high yield. By subsequent kinetic
resolution with lipases compound 7 was enantiomerically enriched
O
O
TBSO
H
5
6
H
H
carbonyl-ene
reaction
O
Lewis acid
OH
(up to 94% ee). It was also demonstrated that compound 7 could be
OR
H
H
H
functionalized by hydroboration and oxidative workup to give the
trihydroxy pentalene 8 as well as by chain extension to the pental-
ene 23.
*
TBSO
TBSO
*
OH
H
8
Key words: bicyclo[3.3.0]octanedione, hydroboration, lipases, pri-
mary alcohols, pentalene
7
Scheme 1
A variety of natural products and pharmaceutical com-
pounds contain a substituted pentalene, in the form of a bi-
cyclo[3.3.0]octane system, as a common structural
feature. Typical examples are carbacyclin (1), triquinanes
such as silphiperfolene (2) and hirsutane (3), and the mac-
10
readily available Weiss diketone 5 as a suitable precur-
sor to functionalized pentalenes (Scheme 1).
Diketone 5 may be converted into the alkene 6, followed
by Lewis acid catalyzed carbonyl-ene reaction1 as the
key step towards pentalene derivative 7, which should
then be further functionalized to the pentalene 8.
1
1
,2
rolactam cylindramide (4) (Figure 1).
CO2H
O
The carbonyl-ene reaction of the regioisomer of 6 with
H
exocyclic double bond and glyoxylate was performed by
HN
HO
HO
12
Mikami in a highly stereoselective manner, and White-
sell reported an auxiliary-controlled ene reaction of gly-
H
13
oxylate with bicyclo[3.3.0]octa-1,5-diene. However, to
the best of our knowledge, the ene reaction of endocyclic
alkene 6 with aldehydes has not been reported. It was par-
ticularly envisaged to utilize the exocyclic double bond in
derivative 7 for hydroboration and enzymatic resolution,
and furthermore, to use the alcohol side chain for chain
extension. The results towards this goal are reported be-
low.
O
H
H
HO
NH
C5H11
1
O
OH
4
H
H
2
3
Figure 1 Natural products containing the bicyclo[3.3.0]octane
system
The synthesis of the ene component 6 commenced with
the diketone 5 (Scheme 2), which was prepared in 69%
yield from dimethyl acetone-1,3-dicarboxylate (9) and
Consequently, several different synthetic routes to the
pentalene system were reported: cationic, anionic, radical
1
0a
3
–5
6
glyoxal according to the procedure by Weiss. Follow-
or metal-mediated cyclizations, Diels–Alder reactions
14
7
ing a method by Piers, diketone 5 was treated with 2,2-
dimethylpropane-1,3-diol in the presence of TsOH to
yield the monoacetal 10 in 52% yield after chromato-
as well as intermolecular Pauson–Khand reactions. Al-
though the last reaction opens access to different substitu-
8
,9
tion patterns, the use of stoichiometric amounts of
Co (CO) is a major limitation. Thus, we considered the
graphic separation on SiO , and the diacetal 11 in 17% to-
2
2
8
gether with 21% of unreacted starting material 5. When
the mixture of diacetal 11 and diketone 5 was resubmitted
1
4
to TsOH in toluene at reflux for two hours, transacetal-
ization took place and the desired monoacetal 10 was iso-
lated in 32% yield. In this manner, the total yield of 10
SYNTHESIS 2008, No. 10, pp 1619–1627
x
x.
x
x
.
2
0
0
8
Advanced online publication: 11.04.2008
DOI: 10.1055/s-2008-1067012; Art ID: Z04108SS
Georg Thieme Verlag Stuttgart · New York
©

1
620
T. Anderl et al.
PAPER
TsOH, toluene
reflux, 2 h, 32%
The carbonyl-ene reaction of the alkene 6 with 1,3,5-tri-
19
oxane (1 equiv) and Lewis acids (3 equiv) in CH Cl was
2
2
performed under various conditions, and after aqueous
workup, the regioisomeric products rac-7 and rac-15
were isolated (Table 1).
O
O
O
O
O
CO2Me
HO
OH
(
CHO)2
O
5
H
H + H
H
Table 1 Carbonyl-Ene Reaction of Pentalene 6 with 1,3,5-Trioxane
in the Presence of Various Lewis Acids
69%
TsOH, toluene
reflux, 3 h
CO2Me
O
O
6
9
1
,3,5-trioxane (1 equiv)
CH2Cl2
OH
Lewis acid (3 equiv)
1
0 (52%)
11 (17%)
5 (21%)
OH
H
H
+
NaBH4, MeOH, 99%
TBSO
+
TBSO
H
H
PPTS
O
O
H
H
acetone, H2O
RO
O
HO
rac-7
rac-15
reflux, 4 h
1%
8
Entry Lewis acid Temp Time Conv. 7:15a
H
H
Yield
(%)
(%)a
100
100
95
b
1
1
3 R = H
12 dr 97:3
(°C)
(h)
TBSCl, imidazole, DMF
r.t., 1 h, 99%
4 R = TBS
1
2
3
4
5
6
BF ·OEt
0
8
–
–
3
2
92% MePPh3 Br , KOt-Bu, THF, r.t., 3 h
SnCl4
AlCl3
0
8
–
–
H
–78
20
5
1:99
8:92
20:80
99:1
3 (15)
10 (15)
TsOH, toluene
6
TBSO
reflux, 1 h
AlMe
AlMe3
MAPH
2
Cl
24
96
3
82
87%
H
6
c
20
89
47 (7 + 15)
a
–78
100
91 (7)
Scheme 2
a
b
c
Determined by capillary GC.
Isolated yield.
Combined yield.
was improved to 84%. Reduction of 10 with NaBH in
4
1
5
MeOH gave the alcohol 12 as a diastereomeric mixture
dr 97:3) in 99% yield. Cleavage of the acetal 12 with
(
PPTS in aqueous acetone afforded the ketone 13. The ma-
jor diastereomer of 13 could be separated by recrystalliza-
Despite complete consumption, no trace of the desired
products rac-7 and rac-15 were found with BF ·OEt and
3
2
tion from Et O. An X-ray crystal structure analysis
2
SnCl (entries 1 and 2). With AlCl , AlMe Cl, and AlMe
4 3 2 3
confirmed the endo-configuration of the alcohol moiety
the formation of product rac-15 clearly dominated (en-
tries 3–5). However, by using the sterically demanding
Lewis acid methylaluminum bis(2,6-diphenylphenoxide)
1
6
(Figure 2).
1
7
Compound 13 was protected with TBSCl in the presence
of imidazole in DMF to give the silyl ether 14 in 99%
yield. Wittig reaction of the derivative 14 with methyl-
(
MAPH) originally developed by Maruoka and Yamamo-
2
0
to, the desired regioisomer rac-7 was strongly favored
1
8a
(
entry 6), and on a preparative scale we succeeded in iso-
triphenylphosphonium bromide produced the exocyclic
lating rac-7 in 91% yield.
alkene 6a, which was finally isomerized under acid
1
8b
catalysis to give the desired alkene 6 in 87% yield
Scheme 2).
In order to obtain enantiomerically pure pentalenes, the
alcohol rac-7 was submitted to lipase-catalyzed kinetic
resolution (Scheme 3). An empirical primary alcohol rule
by Kazlauskas is based on the size of substituents, and the
general structure 16 represents the favored enantiomer
that is acylated by the lipase.21 We anticipated that the
(
(
1R,3aR,5S,6aS)-pentalene isomer 7 with comparable
shape should fit this rule. The first screening of various
lipases and solvents at 40 °C is summarized in Table 2.
As shown in Table 2, most lipases were active in various
solvents, however, with regard to selectivity (E-value)
and activity, that is, short reaction times, lipase PS-D in n-
hexane seemed to work best (entry 9). Thus, this system
was chosen for further optimization (Table 3).
Figure 2 ORTEP presentation of (3aR,6aS)-5-hydroxyhexahydro-
pentalen-2(1H)-one (13)
Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York

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Synthesis of Functionalized Pentalenes
1621
Table 2 Enzymatic Kinetic Resolution of Pentalene rac-7 at 40 °C under Various Conditions
Entry
Solvent
toluene
Lipasea
Time (h)
3.5
8
Conv. (%)
53
ee of 7 (%)b
E-value
23
4
1
2
3
4
5
6
7
8
9
Chirazym L-1
88
44
78
80
78
46
44
64
84
82
84
42
–
Novozym 435
49
Lipase AY Amano
Lipase PS-D Amano I
Lipase AK Amano 20
Chirazym L-1
7
54
11
14
19
3
3.5
5.5
0.5
3
53
50
n-hexane
57
Novozym 435
52
4
Lipase AY Amano
Lipase PS-D Amano I
Lipase AK Amano 20
Chirazym L-1
44.5
4
47
12
30
32
17
4
50
1
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
9
0
19
23
26
48
26
48
1
49
MeCN
54
Novozym 435
49
Lipase AY Amano
Lipase PS-D Amano I
Lipase AK Amano 20
Chirazym L-1
–
–
51
70
–
10
–
–
MTBE
57
90
14
60
78
74
16
1
Novozym 435
2.5
150
31
7
53
Lipase AY Amano
Lipase PS-D Amano I
Lipase AK Amano 20
47
9
52
14
17
2
49
a
Chirazym L-1 and Lipase PS-D Amano I from Burkholderia cepacia, Novozym 435 from Candida antarctica B, Lipase AY Amano from
Candida rugosa, and Lipase AK Amano 20 from Pseudomonas fluorescens.
b
Determined by capillary GC on a chiral stationary phase. The optical antipodes of acetates 17, however, could not be resolved.
OH
OH
H
Table 3 Enzymatic Kinetic Resolution of Pentalene rac-7 with
Lipase PS-D in n-Hexane at Various Temperatures
OH
H
RM
TBSO
RL
Entry
Temp (°C) Time (h) Conv. (%) ee (%)
E-value
30
H
H
1
2
3
4
40
20
4
50
49
48
51
84
82
82
94
16
OTBS
(1R,3aR,5S,6aS)-7
4.5
6
32
OH
OAc
OAc
H
H
H
0
43
MS 4 Å
lipase
rac-7
TBSO
+ TBSO
–20
27.5
70
H
(
1R,3aR,5S,6aS)-17 and 46% of alcohol (1S,3aS,5R,6aR)-
(
1S,3aS,5R,6aR)-7
(1R,3aR,5S,6aS)-17
7
were obtained with only 70% ee each (E = 12). The
Scheme 3
enantiomeric excess of the acetate (1R,3aR,5S,6aS)-17
was determined after saponification with K CO3 in
2
As can be seen from Table 3, upon decreasing the reaction MeOH–H
O
to give the corresponding alcohol
2
temperature the E-value increased, and the best result was (1R,3aR,5S,6aS)-7 and subsequent GC analysis.
obtained at –20 °C with 94% ee and an E-value of 70,
albeit with long reaction time (entry 4). Unfortunately,
scaling up resulted in a dramatic reduction of the enantio-
selectivity, and on a 2 mmol scale, 48% of the acetate
Next, the functionalization of the exocyclic methylene
group in rac-7 was explored (Scheme 4). Following a
22
method by Maezaki and Tanaka, the racemic pentalene
7
was converted into the MOM-protected derivative 18,
Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York

1
622
T. Anderl et al.
PAPER
2
3
which was submitted to hydroboration. Final oxidative In conclusion, Weiss diketone 5 was found to be a useful
workup gave the terminal alcohols 8a and 8b as a diaste- precursor for the formation of functionalized pentalene
reomeric mixture (dr 81:19), which was separated by derivatives such as 7 by utilizing a Lewis acid catalyzed
chromatography on SiO to yield 8a as the major diaste- carbonyl-ene reaction as a key step. Enantiomerically en-
2
reoisomer (66%) and 18% of a diastereomeric mixture (dr riched pentalenes (1S,3aS,5R,6aR)- and (1R,3aR,5S,6aS)-
9
5:5) (Scheme 4).
7 were available by lipase-catalyzed kinetic resolution.
The primary alcohol moiety and the exocyclic double
bond in compound 7 provided entries into further func-
tionalization such as chain elongation to alcohol 23 and
hydroboration to derivative 8, respectively. Progress to-
wards the use of pentalenes in natural product synthesis is
currently under way.
OMOM
OH
H
TBSO
OR
H
H
H
8
8
a (66%)
1
) 9-BBN, THF, r.t., 4 h
) H2O2, NaOH, r.t., 20 min
TBSO
+
2
OMOM
H
Melting points were measured on a Mettler-Toledo DSC822e calo-
rimeter and are uncorrected. IR spectra were recorded on a Bruker
rac-7 R = H
MOMCl, i-Pr NEt
CH2Cl2, 0°C to r.t.
TBSO
2
1
13
Vector 22 FT-IR spectrometer. H and C NMR spectra were re-
corded on a Bruker Avance 300 or a Bruker Avance 500 spectro-
meter with TMS as an internal standard. Mass spectra were obtained
using a Finnigan MAT 95 or a Varian MAT 711 spectrometer. Op-
tical rotations were measured using a Perkin-Elmer Polarimeter 241
at 20 °C. Flash chromatography was performed using Kieselgel 60,
OH
20 h, 78%
H
rac-18 R = MOM
b dr 95:5 (18%)
Scheme 4
4
0–63 mm (Fluka). GC was performed on a Thermo-Finnigan Trace
In order to probe the versatility of rac-7 as a building
GC Ultra using an Optima-5 column (30 m × 0.25 mm) (Macherey-
Nagel) with H as carrier gas; temperature program: 16 °C min
gradient from 80 to 300 °C. All solvents were dried, and reactions
were performed in dried glassware. PE = hexanes (bp 30–75 °C).
block for chain extension, it was converted into bromide
–
1
2
4
2
1
9 in 48% yield by Mukaiyama redox condensation with
Ph PBr and imidazole in CH Cl at –40 °C (Scheme 5,
3
2
2
2
Method A). The yield could be improved to 82% by using
The following compounds were prepared according to literature
procedures: 5, 10, 11, and 12.
2
5
a method developed by Iranpoor, utilizing PPh , DDQ,
10
14
15
3
and tetrabutylammonium bromide in CH Cl at room tem-
2
2
perature (Scheme 5, Method B).
(3aR,5sr,6aS)-5-Hydroxyhexahydropentalen-2(1H)-one (13)
PPTS (2.28 g, 9.10 mmol) was added to a solution of the acetal 12
As chain elongation of bromide 19 by treatment of the
corresponding Grignard reagent with formaldehyde was
insufficient, an alternative route was developed
(
8.20 g, 36.2 mmol) in acetone (400 mL), and the mixture was heat-
ed at reflux for 4 h. After cooling to r.t., the mixture was hydrolyzed
with aq sat NaHCO (200 mL). The aqueous layer was separated
3
2
6
(
Scheme 5). Tosylation of rac-7 gave derivative 20 in and extracted with CH Cl (5 × 40 mL). The combined organic ex-
2
2
2
7
7
4% yield. Subsequent Kolbe synthesis provided the ni- tracts were dried (MgSO
4
), and the solvent removed under vacuum
to give a colorless solid (4.80 g). Recrystallization from hexane–
trile 21 in 60% yield without any problem. Nitrile 21 was
converted into aldehyde 22 by reaction with DIBAL-H in
CH Cl followed by hydrolysis. Finally, aldehyde 22 was
Et O (2:1) gave 13 as colorless plates; yield: 4.13 g (81%); mp
2
4
7 °C; R = 0.28 (PE–EtOAc, 1:2). The spectroscopic data were in
f
2
2
17
accordance with those given in the literature.
reduced with NaBH in MeOH to yield the desired alcohol
4
Anal. Calcd for C H O : C, 68.54; H, 8.63. Found: C, 68.73; H,
8
12
2
2
3 in 79%.
8
.66.
Br
(
3aRS,5sr,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}hexahydro-
H
H
pentalen-2(1H)-one (14)
Method A (48%)
Method B (82%)
rac-7
TBSO
A solution of 13 (3.04 g, 21.7 mmol), TBSCl (3.92 g, 26.0 mmol),
and imidazole (3.69 g, 54.2 mmol) in DMF (30 mL) was stirred at
r.t. for 1 h. The solvent was removed and the residue was purified
19
TsCl, Et3N, DMAP
CH2Cl2, r.t., 7 h, 74%
1) Mg, Et2O
2) HCHO, 0.5 h
by flash chromatography on SiO with PE–EtOAc (10:1) to give 14
2
9%
OH
as a colorless oil; yield: 5.48 g (99%); R = 0.52 (PE–EtOAc, 10:1).
f
X
FT-IR (ATR): 2951 (m), 2928 (m), 2856 (m), 1739 (s), 1252 (m),
H
H
H
–
1
1
103 (m), 1029 (m), 831 (s), 772 cm (s).
NaBH4, MeOH
20 °C, 1 h
9%
TBSO
TBSO
1
H NMR (500 MHz, CDCl ): d = 0.04 [s, 6 H, Si(CH ) ], 0.86 [s, 9
–
3
3 2
7
H, SiC(CH ) ], 1.58 (d, J = 13.3 Hz, 2 H, H -4, H -6), 2.03–2.08 (m,
3
3
a
a
H
23
2
H, H -4, H -6), 2.30 (dd, J = 19.3, 2.9 Hz, 2 H, H -1, H -3), 2.51
b b a a
2
2
2
0 X = OTs
1 X = CN
2 X = CHO
KCN, DMF, 40 °C, 2 h, 60 °C, 16 h, 60%
DIBAL-H, CH2Cl2, –78 °C, 4 h, 54%
(
dd, J = 19.3, 10.0 Hz, 2 H, H -1, H -3), 2.75–2.81 (m, 2 H, H-3a,
b b
H-6a), 4.33 (tt, J = 5.0, 3.9 Hz, 1 H, H-5).
13C NMR
(125 MHz, CDCl3): d = –4.9 [Si(CH3)2], 18.0
SiC(CH ) ], 25.8 [SiC(CH ) ], 37.8 (C-3a, C-6a), 43.5 (C-4, C-6),
Method A: Ph3PBr2, imidazole, CH2Cl2, –40°C to r.t., 18 h
Method B: Ph3P, DDQ, Bu4NBr, CH2Cl2, r.t., 2 h
[
3
3
3 3
4
5.8 (C-1, C-3), 75.5 (C-5), 221.0 (C-2).
Scheme 5
+
+
MS (CI): m/z (%) = 272.2 (12, [M + NH ] ), 255.2 (20, [MH ]),
4
+
+
1
97.1 (100, [M – t-Bu]), 105 (11), 75 (10, [HOSiMe ] ).
2
Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York

PAPER
Synthesis of Functionalized Pentalenes
1623
Anal. Calcd for C H O Si: C, 66.09; H, 10.30. Found: C, 66.07;
H, 10.34.
by chromatography on SiO with PE–EtOAc (50:1 → 10:1) to give
14
26
2
2
the alcohols 7 and 15 as colorless oils.
tert-Butyl(dimethyl){[(3aR,6aS)-5-methyleneoctahydropental-
en-2-yl]oxy}silane (6a)
t-BuOK (0.23 g, 2.00 mmol) was added in one portion to a solution
of methyltriphenylphosphonium bromide (0.72 g, 2.00 mmol) in
freshly distilled THF (10 mL), and the mixture was stirred for 30
min. Then a solution of 14 (0.26 g, 1.00 mmol) in THF (10 mL) was
slowly added. After stirring for 2.5 h, the mixture was diluted with
((1RS,3aRS,5SR,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}-
2-methyleneoctahydropentalen-1-yl)methanol (rac-7)
Rf = 0.22 (PE–EtOAc, 10:1).
FT-IR (ATR): 2950 (s), 2928 (s), 2857 (s), 1462 (m), 1374 (m),
–1
1
252 (s), 1110 (vs), 1039 (s), 891 (s), 833 (vs), 772 cm (vs).
1
H NMR (500 MHz, CDCl ): d = 0.03 [s, 6 H, Si(CH ) ], 0.87 [s, 9
3
3 2
H, SiC(CH ) ], 1.30 (ddd, J = 12.6, 8.2, 8.2 Hz, 1 H, H -4), 1.38
H O (10 mL). The layers were separated, and the aqueous layer was
3 3
a
2
(
ddd, J = 15.1, 6.3, 6.3 Hz, 1 H, H -6), 1.50 (br t, J = 5.5 Hz, 1 H,
extracted with PE (4 × 15 mL). The combined organic layers were
a
OH), 1.99–2.05 (m, 1 H, H -4), 2.05–2.11 (m, 1 H, H -6), 2.14–2.21
dried (MgSO ) and concentrated. The crude product was purified by
b
b
4
(
m, 2 H, H -3, H-6a), 2.40 (ddddd, J = 8.9, 8.9, 8.9, 8.9, 3.8 Hz, 1
flash chromatography with PE to give 6a as a colorless oil; yield:
a
H, H-3a), 2.44–2.49 (m, 1 H, H-1), 2.53–2.59 (m, 1 H, H -3), 3.43–
0
.23 g (92%); R = 0.27 (PE).
b
f
3
.47 (m, 1 H, CH H OH), 3.55–3.61 (m, 1 H, CH H OH), 4.10
1
a
b
a
b
H NMR (300 MHz, CDCl ): d = 0.00 [s, 6 H, Si(CH ) ], 0.84 [s, 9
3
3 2
(
dddd, J = 7.9, 7.9, 6.0, 6.0 Hz, 1 H, H-5), 4.90 (m, 1 H, =CH H ),
a b
H, SiC(CH ) ], 1.17–1.27 (m, 2 H, H -4, H -6), 1.93–2.03 (m, 2 H,
3
3
a
a
4
.97 (m, 1 H, =CH H ).
a b
H -4, H -6), 2.03–2.10 (m, 2 H, H -1, H -3), 2.29–2.46 (m, 4 H, H -
b
b
a
a
b
13C NMR
(125 MHz, CDCl3): d = –4.8 [Si(CH3)2], 18.2
1
, H -3, H-3a, H-6a), 4.03 (tt, J = 8.4, 6.1 Hz, 1 H, H-5), 4.74–4.77
b
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 38.8 (C-3a), 39.3 (C-3), 42.0 (C-6),
(m, 2 H, =CH2).
3 3 3 3
4
1
2.5 (C-4), 43.4 (C-6a), 54.7 (C-1), 64.2 (CH OH), 74.5 (C-5),
13C NMR
2
(125 MHz, CDCl ): d = –4.8 [Si(CH3)2], 18.2
3
07.7 ( =CH ), 152.9 (C-2).
2
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 39.6 (C-3a, C-6a), 40.2 (C-1, C-3),
3 3 3 3
+
+
MS (CI): m/z (%) = 282.2 (4, [M ]), 266.2 (22), 265.2 (100, [MH
4
2.5 (C-4, C-6), 74.5 (C-5), 105.7 (=CH ), 152.8 (C-2).
2
+
–
H O]), 225.1 (8, [M – t-Bu] ), 207.1 (8), 133.1 (42).
2
tert-Butyl(dimethyl){[(2SR,3aRS,6aSR)-5-methyl-1,2,3,3a,4,6a-
hexahydropentalen-2-yl]oxy}silane (6)
A solution of 6a (4.90 g, 19.4 mmol) and TsOH hydrate (0.18 g,
Anal. Calcd for C H O Si: C, 68.03; H, 10.70. Found: C, 68.18;
H, 10.69.
1
6
30
2
1
.0 mmol) in toluene (400 mL) was heated at reflux for 1 h. After
(
(1RS,3aRS,5SR,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}-
2-methyl-1,3a,4,5,6,6a-hexahydropentalen-1-yl)methanol
rac-15)
cooling to r.t., aq sat. NaHCO (40 mL) was added. The aqueous
layer was separated and extracted with PE (3 × 40 mL). The com-
bined extracts were dried (MgSO ) and concentrated. The residue
was chromatographed on SiO with PE to give 6 as a colorless oil;
yield: 4.27 g (87%); R = 0.19 (PE).
3
(
4
Rf = 0.21 (PE–EtOAc, 10:1).
2
FT-IR (ATR): 2951 (s), 2928 (s), 2857 (s), 1471 (m), 1373 (m),
1
1H NMR (500 MHz, CDCl
H, SiC(CH ) ], 1.19 (br s, 1 H, OH), 1.28 (ddd, J = 12.5, 7.0, 7.0 Hz,
1 H, H -4), 1.40 (ddd, J = 12.0, 8.0, 8.0 Hz, 1 H, H -6), 1.66 (s, 3 H,
CH at C-2), 1.98 (dddd, J = 12.5, 7.6, 6.3, 1.2 Hz, 1 H, H -4), 2.03–
3 b
2.10 (m, 1 H, H -6), 2.43–2.50 (m, 2 H, H-1, H-6a), 2.95–3.01 (m,
1 H, H-3a), 3.60 (dd, J = 10.4, 5.2 Hz, 1 H, CH H OH), 3.63–3.68
(m, 1 H, CH H OH), 4.10 (dddd, J = 7.6, 7.6, 6.0, 6.0 Hz, 1 H, H-
f
–1
251 (s), 1107 (vs), 1044 (s), 891 (s), 832 (vs), 772 cm (vs).
FT-IR (ATR): 2951 (m), 2928 (m), 2885 (m), 2856 (m), 1252 (s),
1
–
1
): d = 0.03 [s, 6 H, Si(CH ) ], 0.86 [s, 9
3 3 2
107 (vs), 1036 (s), 897 (s), 833 (vs), 771 cm (vs).
3
3
1
H NMR (500 MHz, CDCl ): d = 0.03 [s, 6 H, Si(CH ) ], 0.86 [s, 9
3
3
2
a
a
H, SiC(CH ) ], 1.27 (ddd, J = 12.1, 8.0, 6.8 Hz, 1 H, H -1), 1.32
3
3
a
(
ddd, J = 11.9, 8.8, 8.6 Hz, 1 H, H -3), 1.66 (dddd, J = 1.8, 1.7, 1.3,
a
b
1
.3 Hz, 1 H, CH at C-5) , 1.98–2.05 (m, 3 H, H -1, H -3, H -4), 2.48
3 b b a
a
b
(
dd, J = 16.0, 9.2 Hz, 1 H, H -4), 2.55 (ddddd, J = 9.1, 9.0, 8.6, 8.5,
b
a b
2
8
.8 Hz, 1 H, H-3a), 2.93–3.00 (m, 1 H, H-6a), 4.07 (dddd, J = 8.6,
.0, 6.0, 5.7 Hz, 1 H, H-2), 5.22 (dddq, J = 1.8, 1.8, 1.7, 1.7 Hz, 1
5
1
), 5.42 (m, 1 H, H-3).
3
C NMR (125 MHz, CDCl ): d = –4.76, –4.81 [Si(CH ) ], 14.9
3 3 3 3 3
3
3 2
H, H-6).
(
CH at C-2), 18.1 [SiC(CH ) ], 25.9 [SiC(CH ) ], 40.6 (C-4), 42.7
1
3
C NMR (125 MHz, CDCl ): d = –4.7, –4.8 [Si(CH ) ], 16.5 (CH
3
3 2
3
(C-6), 43.2 (C-6a), 46.8 (C-3a), 58.9 (C-1), 64.5 (CH OH), 74.2 (C-
5), 132.7 (C-3), 136.1 (C-2).
2
at C-5), 18.1 [SiC(CH ) ], 25.9 [SiC(CH ) ], 38.6 (C-3a), 41.1 (C-
1
1
3
3
3 3
), 43.5 (C-3), 44.2 (C-4), 48.0 (C-6a), 74.4 (C-2), 128.8 (C-6),
37.4 (C-5).
+
+
MS (CI): m/z (%) = 283.2 (4, [MH ]), 282.2 (4, [M ]), 266.2 (22),
2
+
65.2 (100, [MH – H O]), 207.1 (26, [M – t-Bu – H O]), 133.1
2
2
+
MS (CI): m/z (%) = 253.2 (39, [MH ]), 237.2 (26), 212.1 (46),
1
(
50).
HRMS (CI): m/z calcd for C16
83.2098.
+
+
95.1 (100, [M – t-Bu] ), 121.1 (28, [MH – OSiMe t-Bu]), 119.1
2
+
+
H O Si [MH ]: 283.2093; found:
31 2
(
34), 75 (22, [HOSiMe ]).
2
2
Anal. Calcd for C H OSi: C, 71.36; H, 11.18. Found: C, 71.59; H,
15
28
1
1.03.
rac-7 on a Preparative Scale
Me Al (8.4 mL, 8.4 mmol, 2 M in toluene) was rapidly added to a
3
Carbonyl-Ene Reaction of 6 to Alcohols 7 and 15; General Pro-
cedure
solution of 2,6-diphenylphenol (4.09 g, 16.6 mmol) in CH Cl (50
2
2
mL) at –30 °C, and the resulting solution was allowed to warm to
r.t. over 1 h. A solution of 1,3,5-trioxane (0.22 g, 2.40 mmol) in
CH Cl (1 mL) was subsequently added at 0 °C, and the mixture
A solution of 1,3,5-trioxane (36 mg, 0.40 mmol) in anhyd CH Cl
2
2
(
1 mL) was added dropwise to a solution of the appropriate Lewis
2
2
acid (3 equiv) in anhyd CH Cl (5 mL) in a Schlenk flask at 0 °C un-
2
2
was stirred for 1 h. After cooling again to –78 °C, a solution of 6
der N , and the mixture stirred for 1 h. At the given temperature
2
(0.51 g, 2 mmol) in CH Cl (1 mL) was slowly added dropwise and
2
2
(
Table 1), a solution of 6 (100 mg, 0.40 mmol) in anhyd CH Cl (1
2 2
the mixture stirred for 3 h. The mixture was then quenched with aq
mL) was added dropwise, and the mixture was stirred for the given
sat. NaHCO (40 mL). The aqueous layer was separated and extract-
3
time. After warming to r.t., aq sat. NaHCO (10 mL) was added, the
3
ed with CH Cl (3 × 60 mL). The combined organic layers were
2
2
aqueous layer separated and extracted with CH Cl (3 × 10 mL).
2
2
washed with brine (60 mL), dried (MgSO ), and the solvent was re-
4
The combined organic layers were washed with brine (15 mL),
moved under vacuum. The crude product was purified by flash
dried (MgSO ), and concentrated. The crude product was purified
4
Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York

1
624
T. Anderl et al.
PAPER
chromatography with PE–EtOAc (10:1) to give rac-7 as a colorless
oil; yield: 0.51 g (91%).
mL) was added, the aqueous layer separated, and extracted with
EtOAc (3 × 10 mL). The combined organic layers were washed suc-
cessively with H O (10 mL) and brine (10 mL), dried (MgSO ), and
2
4
Lipase Screening of rac-7; General Procedure
Vinyl acetate (4.0 mL, 3.7 mg, 42 mmol), molecular sieves (4 Å, 4
beads) and the respective lipase Chirazym L-1 (0.1 mg), Novozym
concentrated. The residue was chromatographed on SiO with PE–
EtOAc (50:1) to give 18 as a colorless oil; yield: 0.13 g (78%);
Rf = 0.58 (PE–EtOAc, 10:1).
2
4
35 (2 mg), AY Amano (5 mg), PS-D Amano I (0.3–2 mg), or AK
Amano 20 (1–2.5 mg) were added to a solution of rac-7 (4.0 mg,
4 mmol) in the appropriate solvent (1.4 mL) at the given tempera-
ture (Tables 2, 3). The mixture was stirred for the given time
Tables 2, 3), and the reaction was followed by TLC to almost iden-
tical intensities of rac-7 [R = 0.22 (PE–EtOAc)] and product 17
FT-IR (ATR): 2949 (m), 2928 (m), 2856 (m), 1471 (m), 1462 (m),
1
375 (m), 1252 (s), 1150 (s), 1107 (vs), 1043 (vs), 834 (vs), 772
1
–1
cm (vs).
1
H NMR (500 MHz, CDCl ): d = 0.04 [s, 6 H, Si(CH ) ], 0.87 [s, 9
(
3
3 2
H, SiC(CH ) ], 1.33 (ddd, J = 12.4, 7.6, 7.6 Hz, 1 H, H -4), 1.42
3 3
a
f
(
ddd, J = 12.4, 6.9, 6.9 Hz, 1 H, H -6), 1.98–2.03 (m, 1 H, H -4),
[
Rf = 0.57 (PE–EtOAc)]. Then aliquots (50 mL) were taken in inter-
a
b
2
2
.03–2.09 (m, 1 H, H -6), 2.20–2.26 (m, 2 H, H -3, H-6a), 2.38–
b a
vals of 30 min and filtered through SiO with CH Cl (10 mL) as
2
2
2
.42 (m, 1 H, H-3a), 2.53–2.59 (m, 2 H, H-1, H -3), 3.57 (s, 3 H,
eluent. Conversion and enantioselectivity of alcohol 7 was directly
determined from the filtrate by GC. This procedure was repeated
until the conversion exceeded 50%.
b
OCH ), 3.45 (dd, J = 9.7, 6.7 Hz, 1 H, CCH H O), 3.55 (dd, J = 9.7,
3
a
b
6
.3 Hz, 1 H, CCH H O), 4.11–4.16 (m, 1 H, H-5), 4.63 (s, 2 H,
a b
OCH OMe), 4.85 (m, 1 H, =CH H ), 4.87 (m, 1 H, =CH H ).
2
a
b
a
b
Enzymatic Kinetic Resolution of rac-7 on a Preparative Scale
Vinyl acetate (0.50 mL, 0.46 g, 5.31 mol), molecular sieves (4 Å,
13C NMR
(125 MHz, CDCl3): d = –4.8 [Si(CH3)2], 18.2
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 38.9 (C-3a), 40.0 (C-3), 42.0 (C-6),
3 2 3 3
0
.05 g) and Lipase PS-D Amano I (0.07 g) were added to a solution
of rac-7 (0.49 g, 1.77 mmol, 20 mM) in n-hexane (88 mL) at
20 °C, and the mixture was stirred for 12 h (conversion determined
4
7
2.4 (C-4), 44.5 (C-6a), 51.6 (C-1), 55.2 (OCH ), 70.4 (CCH O),
4.9 (C-2), 96.5 (OCH O), 106.4 ( =CH ), 153.4 (C-2).
3
2
2
2
–
+
+
MS (CI): m/z (%) = 344.3 (3, [M + NH ] ), 327.3 (3, [MH ]), 265.2
4
as described above). Then the mixture was filtered through SiO2
with CH Cl (300 mL) as eluent and the filtrate concentrated. The
+
(
100, [MH – OCH OMe]), 207.2 (15), 133.1 (20).
2
2
2
residue was purified by chromatography on SiO with PE–EtOAc
Anal. Calcd for C15
10.51.
H28OSi: C, 66.21; H, 10.49. Found: C, 66.44; H,
2
(
50:1 → 5:1) as eluent to give the acetate (1R,3aR,5S,6aS)-17 in the
first fraction [R = 0.57 (PE–EtOAc, 10:1)] as a colorless oil (0.28 g,
f
4
8%), and the alcohol (1S,3aS,5R,6aR)-7 in the second fraction
{(1RS,2RS,3aRS,5SR,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}-
1-[(methoxymethoxy)methyl]octahydropentalen-2-yl}meth-
anol (8)
[
[
R = 0.22 (PE–EtOAc, 10:1)] as a colorless oil (0.23 g, 46%);
a]D +4.8 (c 1.00, CH Cl ).
f
20
2
2
2
3
Analogous to a literature procedure, 9-BBN (112 mg, 0.92 mmol)
was added with caution to a solution of 18 (60 mg, 0.18 mmol) in
anhyd THF (1 mL) at 0 °C, and the mixture was warmed slowly to
r.t. and then stirred for 4 h. At 0 °C, aq 2 M NaOH (0.5 mL) and
H O (30 wt%, 0.5 mL) were slowly added. After sonification at r.t.
(
1R,3aR,5S,6aS)-5-{[tert-Butyl(dimethyl)silyl]oxy}-2-methyl-
eneoctahydropentalen-1-yl)methyl Acetate (17)
20
[
a]D –0.4 (c 1.00, CH Cl ).
2 2
2
2
FT-IR (ATR): 2951 (m), 2929 (m), 2856 (m), 1741 (vs), 1462 (m),
for 20 min, the mixture was acidified with aq 2 M HCl, diluted with
1
8
1
379 (m), 1371 (m), 1363 (m), 1230 (vs), 1111 (s), 1034 (s), 893 (s),
34 (vs), 773 cm–1 (vs).
H O (10 mL), and extracted with EtOAc (3 × 10 mL). The com-
2
bined organic layers were dried (MgSO ) and concentrated. The
4
H NMR (500 MHz, CDCl ): d = 0.03 [s, 6 H, Si(CH ) ], 0.87 [s, 9
3
3
2
residue with dr 81:19 (determined by GC) was chromatographed on
H, SiC(CH ) ], 1.34 (ddd, J = 12.6, 7.9, 7.4 Hz, 1 H, H -4), 1.42
3
3
a
SiO with PE–EtOAc (5:1) as eluent to give 8a in the first fraction
2
(
ddd, J = 12.8, 6.7, 6.7 Hz, 1 H, H -6), 1.97–2.06 (m, 2 H, H -4, H -
a
b
b
[R = 0.71 (PE–EtOAc, 1:1)] as a colorless oil (41 mg, 66%), and 8b
f
6
), 2.05 (s, 3 H, CH ), 2.14–2.20 (m, 1 H, H-6a), 2.23 (dddd,
3
in the second fraction [R = 0.68 (PE–EtOAc, 1:1)] as a colorless oil
f
J = 15.6, 4.7, 1.9, 1.9 Hz, 1 H, H -3), 2.42 (ddddd, J = 8.9, 8.7, 8.7,
7
1
CH H O), 4.11 (dd, J = 10.8, 6.8 Hz, 1 H, CH H O), 4.14 (dddd,
J = 7.4, 7.2, 6.7, 6.0 Hz, 1 H, H-5), 4.82 (dddd, J = 2.0, 2.0, 1.9, 1.3
Hz, 1 H, =CH H ), 4.88 (dddd, J = 1.9, 1.9, 1.9, 1.3 Hz, 1
a
(11 mg, 18%, dr = 5:95).
.9, 4.7 Hz, 1 H, H-3a), 2.57 (ddddd, J = 15.6, 8.9, 2.0, 2.0, 1.3 Hz,
H, H -3), 2.64 (m, 1 H, H-1), 3.99 (dd, J = 10.8, 7.4 Hz, 1 H,
b
Alcohol 8a
a
b
a
b
FT-IR (ATR): 3433 (m), 2927 (s), 2856 (s), 2363 (m), 1463 (m),
–1
1
252 (s), 1106 (s), 1037 cm (vs).
a
b
1
H NMR (500 MHz, CDCl ): d = 0.04 [s, 6 H, Si(CH ) ], 0.87 [s, 9
3
3 2
H, =CH H ).
13C NMR
a
b
H, SiC(CH ) ], 1.38 (ddd, J = 12.1, 12.1, 9.3 Hz, 1 H, H -3), 1.47
3
3
a
(125 MHz, CDCl ): d = –4.8 [Si(CH3)2], 18.1
3
3 3 3 3 3
(dddd, J = 13.1, 4.5, 4.3, 1.7 Hz, 1 H, H -4), 1.53 (dddd, J = 13.1,
a
[
SiC(CH ) ], 21.0 (CH ), 25.9 [SiC(CH ) ], 39.0 (C-3a), 39.8 (C-3),
4.3, 4.0, 1.7 Hz, 1 H, H -6), 1.80–1.88 (m, 3 H, H -4, H -6, H-2),
a
b
b
4
1.9 (C-6), 42.4 (C-4), 44.6 (C-6a), 50.4 (C-1), 66.6 (CH O), 74.9
2
1.92 (dddd, J = 9.4, 9.0, 8.9, 3.7 Hz, 1 H, H-1), 1.98 (ddd, J = 12.1,
(
C-5), 106.9 (=CH ), 171.2 (C-2).
2
8.5, 6.3 Hz, 1 H, H -3), 2.05 (dddd, J = 10.4, 8.9, 8.8, 4.1 Hz, 1 H,
b
+
+
H-6a), 2.41 (ddddd, J = 10.4, 9.3, 8.8, 8.5, 4.3 Hz, 1 H, H-3a), 3.36–
3.40 (m, 1 H, CH H OCH ), 3.38 (s, 3 H, OCH ), 3.43 (dd, J = 11.1,
MS (CI): m/z (%) = 325.2 (10, [MH ]), 307.2 (10, [MH – H O]),
2
2
+
65.2 (84), 207.1 (20), 133.1 (100, [C H13 ]), 117 (18).
a
b
2
3
8
8
.6 Hz, 1 H, CH H OH), 3.62 (ddd, J = 11.1, 10.2, 3.5 Hz, 1 H,
a b
Anal. Calcd for C H O Si: C, 66.62; H, 9.94. Found: C, 66.59; H,
9
18
32
3
CH H OH), 3.69 (dd, J = 9.7, 3.8 Hz, 1 H, CH H OCH ), 3.81 (br
a
b
a
b
2
.89.
d, J = 10.2 Hz, 1 H, OH), 4.26 (dddd, J = 5.2, 5.2, 4.3, 4.3 Hz, 1 H,
H-5), 4.67 (s, 2 H, OCH OMe).
2
tert-Butyl({(2SR,3aSR,4RS,6aRS)-4-[(methoxymethoxy)meth-
yl]-5-methyleneoctahydropentalen-2-yl}oxy)dimethylsilane
1
3
C NMR (125 MHz, CDCl ): d = –4.85, –4.88 [Si(CH ) ], 18.0
3
3 2
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 38.2 (C-3), 39.7 (C-3a), 41.2 (C-6),
(
18)
3 3 3 3
2
2
42.2 (C-4), 46.5 (C-6a), 51.5 (C-2), 53.2 (C-1), 55.6 (OCH ), 66.5
Analogous to a literature procedure, i-Pr NEt (0.34 g, 2.65 mmol)
3
2
(
CH OH), 71.3 (CH OCH OMe), 76.4 (C-5), 96.3 (OCH OMe).
2 2 2 2
and MOMCl (0.13 g, 1.59 mmol) were added at 0 °C to a stirred so-
lution of rac-7 (0.15 g, 0.53 mmol) in CH Cl (10 mL). The mixture
+
2
2
MS (CI): m/z (%) = 345.2 (52, [M ]), 313.2 (32), 225.1 (44), 133.1
(100).
was allowed to warm to r.t. and stirred for 24 h. Aq sat. NH Cl (10
4
Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York

PAPER
Synthesis of Functionalized Pentalenes
1625
+
+
Anal. Calcd for C H O Si: C, 62.74; H, 10.53. Found: C, 62.90;
H, 10.50.
MS (Cl): m/z (%) = 347.1 (12, [MH ]), 345.1 (12, [MH ]), 289.0 (5,
18
36
4
+
+
+
[M – t-Bu] ), 287 (5, [M – t-Bu] ), 265.2 (14, [M – Br]), 133.1
100), 105.1 (13), 91.1 (16).
(
Alcohol 8b
Anal. Calcd for C H BrOSi: C, 55.64; H, 8.46; Br, 23.13. Found:
C, 55.71; H, 8.49; Br, 22.90.
1
6
29
FT-IR (ATR): 3429 (m), 2927 (s), 2856 (s), 2362 (m), 1462 (m),
–
1
1
253 (m), 1107 (vs), 1042 cm (vs).
1
H NMR (500 MHz, CDCl ): d = 0.04 [s, 6 H, Si(CH ) ], 0.87 [s, 9
((1RS,3aRS,5SR,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}-2-
methyleneoctahydropentalen-1-yl)methyl-4-methylbenzene-
sulfonate (20)
3
3 2
H, SiC(CH ) ], 1.25–1.36 (m, 2 H, H -1, H -3), 1.51 (ddd, J = 12.6,
6
3
3
a
a
.9, 3.8 Hz, 1 H, H -6), 1.58–1.62 (m, 1 H, H -6), 1.97–2.10 (m, 3
a
b
H, H -1, H -3, H-5), 2.22 (dddd, J = 10.1, 8.2, 4.5, 2.0 Hz, 1 H, H-
A solution of rac-7 (74 mg, 0.26 mmol), Et N (56 mg, 0.08 mL,
b
b
3
4
1
), 2.37 (ddddd, J = 8.6, 8.6, 8.6, 8.6, 3.8 Hz, 1 H, H-6a), 2.52 (m,
0.55 mmol) and DMAP (4 mg, 0.03 mmol) in CH Cl (2.8 mL) was
stirred at r.t. for 15 min prior to the addition of TsCl (106 mg, 0.56
mmol) in small portions. The mixture was stirred at r.t. for 7 h and
2
2
H, H-3a), 2.73 (br s, 1 H, OH), 3.38 (s, 3 H, OCH ), 3.45 (dd,
3
J = 9.7, 4.5 Hz, 1 H, CH H OCH ), 3.54 (dd, J = 10.1, 9.7, 1 H,
a
b
2
CH H OCH ), 3.61 (br d, J = 7.9 Hz, 2 H, CH OH), 4.04 (dddd,
then quenched with H O (2 mL). The layers were separated, and the
a
b
2
2
2
J = 7.9, 7.9, 5.7, 5.7 Hz, 1 H, H-2), 4.63 (s, 2 H, OCH OMe).
aqueous layer was extracted with Et O (3 × 10 mL). The combined
2
2
13C NMR
organic layers were washed with brine (10 mL), dried (MgSO ), and
4
(125 MHz, CDCl ): d = –4.8 [Si(CH3)2], 18.1
3
concentrated. The residue was purified by flash chromatography
with PE–EtOAc (10:1) to give 20 as a colorless solid; yield: 94 mg
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 34.6 (C-6), 38.5 (C-6a), 42.2 (C-3),
3 3 3 3
4
2.9 (C-1), 43.5 (C-5), 43.5 (C-3a), 47.6 (C-4), 55.6 (OCH ), 63.4
3
(
83%); mp 59–60 °C; R = 0.19 (PE–EtOAc, 30:1).
f
(
CH OH), 68.5 (CH OCH OMe), 74.6 (C-2), 96.7 (OCH OMe).
2
2
2
2
+
+
FT-IR (ATR): 2951 (m), 2926 (m), 1357 (s), 1250 (m), 1189 (m),
166 (s), 1096 (s), 1031 (s), 1006 (m), 952 (s), 906 (s), 891 (s), 829
MS (CI): m/z (%) = 362.3 (100, [M + NH ] ), 345.2 (20, [MH ]),
4
1
3
30.2 (48), 255.1 (16), 133.1 (20).
–
1
(s), 769 cm (s).
+
HRMS (CI): m/z calcd for C H NO Si [M + NH ] : 362.2727;
1
8
40
4
4
1
H NMR (500 MHz, CDCl ): d = 0.00 [s, 6 H, Si(CH ) ] 0.83 [s, 9
3
3 2
found: 362.2731.
H, SiC(CH ) ], 1.26–1.33 (m, 1 H, H -4), 1.33–1.39 (m, 1 H, H -6),
3
3
a
a
1
2
.90–1.99 (m, 2 H, H -4, H -6), 2.14–2.23 (m, 2 H, H -3, H-6a),
b
b
a
{
[(2SR,3aSR,4RS,6aRS)-4-(Bromomethyl)-5-methyleneocta-
.31–2.40 (m, 1 H, H-3a), 2.43–2.49 (m, 1 H, H -3), 2.44 (t, J = 0.9
b
hydropentalen-2-yl]oxy}(tert-butyl)dimethylsilane (19)
Method A: Analogous to a literature procedure, a solution of
Ph PBr (1.47 g, 3.48 mmol) in anhyd CH Cl (20 mL) under N
was cooled to –40 °C and a solution of rac-7 (0.89 g, 3.16 mmol)
2
4
Hz, 3 H, ArCH
1
3
), 2.60–2.66 (m, 1 H, H-1), 3.89 (dd, J = 9.5, 7.9 Hz,
H, CH H OTs), 4.02 (dd, J = 9.5, 6.0 Hz, 1 H, CH H OTs), 4.10
a
b
a
b
3
2
2
2
2
(
1
dddd, J = 6.7, 6.7, 6.0, 6.0 Hz, 1 H, H-5), 4.70 (dddd, J = 1.9, 1.9,
.8, 0.8 Hz, 1 H, =CH H ), 4.83 (dddd, J = 1.9, 1.9, 1.8, 0.8 Hz, 1
a
b
and imidazole (0.32 g, 4.74 mmol) in anhyd CH Cl (5 mL) was
2
2
H, =CH H ), 7.31–7.34 (m, 2 H, ArHmeta), 7.76–7.79 (m, 2 H, Ar-
Hortho).
13C NMR (125 MHz, CDCl3): d = –4.8 [Si(CH3)2], 18.1
[SiC(CH ) ], 21.7 (ArCH ), 25.9 [SiC(CH ) ], 39.1 (C-3a), 39.9 (C-
a
b
added dropwise. The mixture was slowly warmed to r.t. and then
stirred for 15 h. The solvent was removed, the remaining solid taken
up in n-hexane (10 mL) and stirred at r.t. for a further 5 h. The mix-
ture was filtered through SiO with PE–EtOAc (50:1) as eluent. The
2
3
3
3
3 3
filtrate was concentrated and the residue dried under high vacuum
3), 41.8 (C-6), 42.3 (C-4), 44.5 (C-6a), 50.4 (C-1), 72.4 (CH OTs),
2
–3
(
10 mbar) to give 19 as a colorless oil; yield: 0.71 g (48%).
74.9 (C-5), 107.6 (=CH ), 127.9 (Cortho-Ar), 129.8 (Cmeta-Ar), 133.2
2
(
C -Ar), 144.7 (CSO ), 151.3 (C-2).
q
2
Method B: To a solution of PPh (69 mg, 0.26 mmol) and DDQ (64
3
–1
mg, 0.28 mmol) in CH Cl (2 mL) at r.t. was added Bu NBr (87 mg,
UV-Vis (hexane, 5·10–6 mol L ): l (log e) = 273 (0.15), 222 nm
(0.19).
2
2
4
max
0
.27 mmol), and the mixture stirred for 15 min. Then a solution of
rac-7 (50 mg, 0.18 mmol) in CH Cl (0.2 mL) was added and the
mixture stirred for 2 h. The solvent was removed under vacuum and
the crude product purified by flash chromatography with PE–
2
2
Anal. Calcd for C H O SSi: C, 63.26; H, 8.31; S, 7.39. Found: C,
2
3
36
4
6
3.01; H, 8.28; S, 7.34.
EtOAc (5:1) as eluent to give 19; yield: 54 mg (82%); R = 0.86
f
(
(1RS,3aRS,5SR,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}-2-
(
PE–EtOAc, 10:1).
methyleneoctahydropentalen-1-yl)acetonitrile (21)
FT-IR (ATR): 2989 (m), 2928 (m), 2856 (m), 1471 (m), 1462 (m),
KCN (51 mg, 0.78 mmol) was added in small portions to a solution
of 20 (66.0 mg, 0.15 mmol) in DMF (0.82 mL), and the mixture
heated at 40 °C for 2 h, then stirred at r.t. for 8 h, and for a further
–
1
1
251 (s), 1109 (s), 1041 (s), 894 (s), 833 (vs), 772 cm (vs).
1
H NMR (500 MHz, CDCl ): d = 0.03 [s, 6 H, Si(CH ) ], 0.87 [s, 9
3
3 2
1
2 h at 60 °C. The mixture was quenched with H O (5 mL), and the
2
H, SiC(CH ) ], 1.30 (ddd, J = 13.2, 5.8, 5.6 Hz, 1 H, H -4), 1.42
3
3
a
solvent was removed under vacuum. The residue was diluted in
(
ddd, J = 13.9, 7.9, 6.9 Hz, 1 H, H -6), 1.95 (dddd, J = 13.2, 8.0, 5.8,
a
H O (5 mL) and extracted with EtOAc (3 × 10 mL). The combined
2
1
6
.3 Hz, 1 H, H -4), 2.05 (dddd, J = 13.9, 7.0, 6.2, 1.3 Hz, 1 H, H -
b b
organic layers were washed with brine (10 mL), dried (MgSO ), and
4
), 2.22 (dddd, J = 15.1, 4.8, 2.0, 1.9 Hz, 1 H, H -3), 2.28 (dddd,
a
concentrated. The crude product was purified by flash chromatog-
J = 8.8, 7.9, 6.2, 5.0 Hz, 1 H, H-6a), 2.39 (ddddd, J = 8.8, 8.7, 8.4,
raphy on SiO with PE–EtOAc (30:1) to give 21 as a colorless oil;
2
8
1
.0, 4.8 Hz, 1 H, H-3a), 2.55 (ddddd, J = 15.1, 8.7, 2.1, 2.0, 1.4 Hz,
yield: 26.0 mg (60%); R = 0.24 (PE–EtOAc, 30:1).
f
H, H -3), 2.69–2.75 (m, 1 H, H-1), 3.29 (dd, J = 9.8, 8.6 Hz, 1 H,
b
CH H Br), 3.47 (dd, J = 9.8, 5.5 Hz, 1 H, CH H Br), 4.12 (dddd,
FT-IR (ATR): 2951 (s), 2927 (s), 2855 (s), 1472 (m), 1463 (m),
1253 (s), 1107 (s), 1042 (s), 1024 (m), 1006 (m), 895 (s), 835 cm
(s).
a
b
a
b
–
1
J = 7.0, 6.9, 5.8, 5.8 Hz, 1 H, H-5), 4.82 (dddd, J = 2.0, 2.0, 2.0, 0.9
Hz, 1 H, =CH H ), 4.89 (dddd, J = 2.1, 1.9, 1.9, 0.9 Hz, 1
a
b
H, =CH H ).
1
a
b
H NMR (500 MHz, CDCl ): d = 0.00 [s, 6 H, Si(CH ) ], 0.82 [s, 9
3
3 2
1
3
C NMR (125 MHz, CDCl ): d = –4.79, –4.81 [Si(CH ) ], 18.1
H, SiC(CH ) ], 1.35–1.41 (m, 1 H, H -4), 1.49–1.55 (m, 1 H, H -6),
1.93 (dddd, J = 13.1, 8.4, 5.7, 1.1 Hz, 1 H, H -4), 2.00 (dddd,
3
3 2
3
3
a
a
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 37.4 (CH Br), 38.9 (C-3a), 39.8 (C-
3
3
3 3
2
b
3
), 42.3 (C-4), 42.3 (C-6), 46.9 (C-6a), 53.5 (C-1), 74.8 (C-5), 107.6
J = 13.1, 8.4, 5.7, 1.1 Hz, 1 H, H -6), 2.16–2.22 (m, 1 H, H-6a),
b
(
=CH ), 153.2 (C-5).
2.27–2.32 (m, 1 H, H -3), 2.36 (dd, J = 16.7, 7.5 Hz, 1 H, CH H -
2
a
a
b
CN), 2.41–2.51 (m, 1 H, H-3a), 2.49 (dd, J = 16.7, 5.9 Hz, 1 H,
CH H CN), 2.53–2.60 (m, 1 H, H -3), 2.64–2.70 (m, 1 H, H-1), 4.19
a
b
b
Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York

1
626
T. Anderl et al.
PAPER
(
dddd, J = 5.6, 5.6, 5.6, 5.6 Hz, 1 H, H-5), 4.75 (ddd, J = 1.9, 1.9,
Anal. Calcd for C H O Si: C, 68.86; H, 10.88. Found: C, 68.78;
1
7
32
2
1
.9 Hz, 1 H, =CH H ), 4.87 (ddd, J = 1.9, 1.9, 1.9 Hz, 1
H, 10.80.
a
b
H, =CH H ).
a
b
13C NMR
(125 MHz, CDCl ): d = –4.8 [Si(CH3)2], 18.1
3
Acknowledgment
[
(
1
SiC(CH ) ], 21.1 (CH CN), 25.9 [SiC(CH ) ], 39.2 (C-3a), 39.8
C-3), 41.5 (C-6), 42.3 (C-4), 46.8 (C-1), 47.7 (C-6a), 75.3 (C-5),
06.1 (=CH ), 118.9 (CN), 153.3 (C-2).
3 3 2 3 3
We gratefully acknowledge the Deutsche Forschungsgemeinschaft,
the Ministerium für Wissenschaft, Forschung und Kunst des Landes
Baden-Württemberg, the European Union (ERASMUS/Sokrates
fellowship for M.E.), and the Fonds der Chemischen Industrie for
generous financial support. We would like to thank Dr. Michael
Schwarm (Degussa AG) for kind donation of lipases.
2
Anal. Calcd for C H NOSi: C, 70.04; H, 10.03; N, 4.80. Found: C,
1
7
29
7
0.08; H, 9.90; N, 4.58.
(
2
(1RS,3aRS,5SR,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}-
-methyleneoctahydropentalen-1-yl)acetaldehyde (22)
To a solution of 21 (31 mg, 0.11 mmol) in CH Cl (1.2 mL) was
2
2
References
slowly added a 1 M solution of DIBAL-H in hexane (0.32 mL, 0.32
mmol) at –78 °C, and the mixture stirred for 4 h. Then it was
quenched with aq sat. NH Cl (2 mL) and diluted with H O (2 mL).
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A. Top. Curr. Chem. 1998, 196, 137. (b) Ghatak, U. R.
Proc. Indian Nat. Sci. Acad. A 1995, 61, 21. (c) Negishi, E.
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Zingde, G.; Natchus, M. G.; Ranu, B. C.; Papadopolous, P.
Tetrahedron 1987, 43, 5685. (e) Demuth, M. In Modern
Synthetic Methods, Vol. 4; Scheffold, R., Ed.; Springer:
Berlin, 1986, 89–124. (f) Ley, S. V. Chem. Ind. (London)
4
2
The aqueous layer was extracted with CH Cl (3 × 10 mL), and the
2
2
combined organic layers were washed with brine (10 mL), dried
MgSO ), and concentrated under vacuum. The residue was puri-
(
4
fied by flash chromatography with PE–EtOAc (30:1) as eluent to
give 22 as a colorless oil; yield: 17 mg (54%); R = 0.33 (PE–
EtOAc, 30:1).
f
1
985, 101.
FT-IR (ATR): 2950 (m), 2928 (m), 2856 (m), 1726 (s), 1253 (m),
–
1
(2) Reviews on polyquinanes: (a) Mehta, G.; Srikrishna, A.
Chem. Rev. 1997, 97, 671. (b) Paquette, L. A. Top. Curr.
Chem. 1984, 119, 1. (c) Ramaiah, M. Synthesis 1984, 529.
(d) Trost, B. M. Chem. Soc. Rev. 1982, 11, 141.
1
110 (s), 1039 (m), 897 (m), 835 cm (s).
1
H NMR (500 MHz, CDCl ): d = 0.00 [s, 6 H, Si(CH ) ], 0.83 [s, 9
3
3 2
H, SiC(CH ) ], 1.32–1.38 (m, 1 H, H -4), 1.38–1.44 (m, 1 H, H -6),
3
3
a
a
1
2
.92–2.00 (m, 2 H, H -4, H -6), 2.00–2.08 (m, 1 H, H-6a), 2.22–
b b
(e) Paquette, L. A. Top. Curr. Chem. 1979, 79, 41. For
macrolactams such as cylindramide, see: (f) Kanazawa, S.;
Fusetani, N.; Matsunaga, S. Tetrahedron Lett. 1993, 34,
1065. (g) Cramer, N.; Laschat, S.; Baro, A.; Schwalbe, H.;
Richter, C. Angew. Chem. Int. Ed. 2005, 44, 820; Angew.
Chem. 2005, 117, 831. (h) Cramer, N.; Buchweitz, M.;
Laschat, S.; Frey, W.; Baro, A.; Mathieu, D.; Richter, C.;
Schwalbe, H. Chem. Eur. J. 2006, 12, 2488; and references
cited therein.
.28 (m, 1 H, H -3), 2.40 (ddd, J = 16.1, 7.4, 2.5 Hz, 1 H, CH H -
a
a
b
CHO, H-3a), 2.50–2.57 (m, 1 H, H -3), 2.54 (ddd, J = 16.1, 6.6, 2.3
b
Hz, 1 H, CH H CHO), 2.80–2.86 (m, 1 H, H-1), 4.13 (dddd, J = 6.6,
a
b
6
.6, 5.8, 5.8 Hz, 1 H, H-5), 4.66 (dddd, J = 1.9, 1.9, 1.9, 0.7 Hz, 1
H, =CH H ), 4.79 (dddd, J = 1.9, 1.9, 1.9, 0.7 Hz, 1 H, =CH H ),
a
b
a
b
9
.74 (t, J = 2.4 Hz, 1 H, CHO).
13C NMR
(125 MHz, CDCl ): d = –4.8 [Si(CH3)2], 18.1
3
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 38.9 (C-3a), 39.9 (C-3), 41.5 (C-6),
3 3 3 3
4
1
2.4 (C-4), 45.4 (C-1), 47.5 (C-6a), 47.8 (CH H CHO), 75.1 (C-5),
(3) Triquinane synthesis: Son, S. U.; Park, K. H.; Lee, S. J.;
Kim, B. M.; Chung, Y. K. Synlett 2003, 1101.
a
b
05.3 (=CH ), 155.0 (C-2), 202.6 (CH H CHO).
2
a
b
(
4) (a) Harrington-Frost, N. M.; Pattenden, G. Tetrahedron Lett.
000, 41, 403. (b) Devin, P.; Fensterbank, L.; Malacria, M.
+
MS (ESI-TOF): m/z (%) = 317.2 (100, [M + Na] ), 295.2 (37, [M +
H] ], 277.2 (34), 177.1 (70), 163.1 (75), 145.1 (90).
2
+
J. Org. Chem. 1998, 63, 6764. (c) Sha, C.-K.; Santhosh, K.
C.; Lih, S.-H. J. Org. Chem. 1998, 63, 2699. (d) Enholm, E.
J.; Jia, Z. J. J. Org. Chem. 1997, 62, 174. (e) Jasperse, C. P.;
Curran, D. P.; Fevig, T. L. Chem. Rev. 1991, 91, 1237.
5) (a) Renaud, J.-L.; Aubert, C.; Malacria, M. Tetrahedron
(
2
(1RS,3aRS,5SR,6aSR)-5-{[tert-Butyl(dimethyl)silyl]oxy}-
-methyleneoctahydropentalen-1-yl)ethanol (23)
NaBH (10 mg, 0.26 mmol) was added in small portions to a solu-
tion of 22 (34 mg, 0.12 mmol) in freshly distilled MeOH (1 mL) at
–
4
(
1
999, 55, 5113. (b) Seo, J.; Fain, H.; Blanc, J.-B.;
20 °C. After stirring for 1 h at –20 °C, the mixture was diluted with
Montgomery, J. J. Org. Chem. 1999, 64, 6060. (c) Tormo,
Et O (15 mL) and successively washed with aq sat. NH Cl (3 × 10
2
4
J.; Moyano, A.; Pericas, M. A.; Riera, A. J. Org. Chem.
mL) and brine (3 × 10 mL). The aqueous layers were extracted with
1
997, 62, 4851. (d) Meyer, C.; Marek, I.; Normant, J.-F.
Et O (3 × 10 mL), and the combined organic layers were dried
2
Tetrahedron Lett. 1996, 37, 857. (e) Tormo, J.; Verdaguer,
X.; Moyano, A.; Pericas, M. A.; Riera, A. Tetrahedron 1996,
(
MgSO ), and concentrated. The residue was purified by flash chro-
4
matography on SiO with PE–EtOAc (5:1) to give 23 as a colorless
oil; yield: 27 mg (79%); R = 0.34 (PE–EtOAc, 5:1).
2
52, 14021. (f) Saitoh, F.; Mori, M.; Okamura, K.; Date, T.
f
Tetrahedron 1995, 51, 4439. (g) Piers, E.; Orellana, A.
Synthesis 2001, 2138.
FT-IR (ATR): 3314 (br), 2949 (s), 2927 (s), 2856 (s), 1472 (m),
1
462 (m), 1254 (s), 1111 (s), 1042 (m), 835 (s), 774 cm–1 (s).
(6) Bahu, G.; Sridar, V. Indian J. Chem., Sect. B: Org. Chem.
Incl. Med. Chem. 1996, 35, 711.
1
H NMR (500 MHz, CDCl ): d = 0.00 [s, 6 H, Si(CH ) ], 0.83 [s, 9
3
3 2
(
7) (a) Laschat, S.; Becheanu, A.; Bell, T.; Baro, A. Synlett
H, SiC(CH ) ], 1.28–1.35 (m, 2 H, H -4, H -6), 1.48–1.56 (m, 1 H,
3
3
a
a
2
005, 2547. (b) Park, K. H.; Chung, Y. K. Synlett 2005,
CH H CH OH), 1.69–1.77 (m, 1 H, CH H CH OH), 1.95–2.05 (m,
3
H, H-1), 2.33–2.40 (m, 1 H, H-3a), 2.50–2.56 (m, 1 H, H -3), 3.65–
3
H, =CH H ), 4.78–4.80 (m, 1 H, =CH H ).
13C NMR
a
b
2
a
b
2
545. (c) Rodriguez Rivero, M.; Adrio, J.; Carretero, J. C.
H, H -4, H -6, H-6a), 2.08–2.14 (m, 1 H, H -3), 2.28–2.33 (m, 1
b
b
a
Synlett 2005, 26. (d) Gibson, S. E.; Mainolfi, N. Angew.
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b
.71 (m, 2 H, CH OH), 4.02–4.11 (m, 1 H, H-5), 4.74–4.77 (m, 1
2
3082. (e) Bonaga, L. V. R.; Krafft, M. E. Tetrahedron 2004,
a
b
a
b
60, 9795. (f) Gibson, S. E.; Stevenazzi, A. Angew. Chem.
(125 MHz, CDCl ): d = –4.8 [Si(CH3)2], 18.2
3
Int. Ed. 2003, 42, 1800; Angew. Chem. 2003, 115, 1844.
[
SiC(CH ) ], 25.9 [SiC(CH ) ], 37.1 (CH CH OH), 38.3 (C-3a),
3 3 3 3 2 2
(
(
g) Hanson, B. E. Comments Inorg. Chem. 2002, 23, 289.
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3
9.5 (C-3), 42.1 (C-6), 42.5 (C-4), 47.1 (C-6a), 48.2 (C-1), 61.8
(
CH OH), 74.7 (C-5), 105.5 (=CH ), 155.9 (C-2).
2
2
Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York

PAPER
Synthesis of Functionalized Pentalenes
1627
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(16) CCDC-676656 contains all crystallographic details of this
publication and is available free of charge at
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Synthesis 2008, No. 10, 1619–1627 © Thieme Stuttgart · New York