Synthesis of novel, simplified, C-7 substituted eleutheside analogues with potent microtubule-stabilizing activity

Article abstract of DOI:10.1016/j.tet.2004.12.039

The synthesis of a number of novel, simplified, C-7 substituted eleutheside analogues with potent tubulin-assembling and microtubule-stabilizing properties is described, using ring closing metathesis as the key-step for obtaining the 6-10 fused bicyclic r

Full text of DOI:10.1016/j.tet.2004.12.039

Tetrahedron 61 (2005) 2123–2139
Synthesis of novel, simplified, C-7 substituted eleutheside
analogues with potent microtubule-stabilizing activity
Damiano Castoldi,a Lorenzo Caggiano,a,† Pau Bayon,a,‡ Anna M. Costa,b Paolo Cappella,c
´
Ofer Sharona and Cesare Gennaria,
*
aDipartimento di Chimica Organica e Industriale, Centro di Eccellenza C.I.S.I., Universita’ di Milano,
Istituto CNR di Scienze e Tecnologie Molecolari, via Venezian 21, I-20133 Milano, Italy
b
´
Dept. Quımica Organica, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain
`
cNerviano Medical Science, viale Pasteur 10, I-20014 Nerviano, Italy
Received 20 October 2004; revised 24 November 2004; accepted 17 December 2004
Available online 13 January 2005
Abstract—The synthesis of a number of novel, simplified, C-7 substituted eleutheside analogues with potent tubulin-assembling and
microtubule-stabilizing properties is described, using ring closing metathesis as the key-step for obtaining the 6–10 fused bicyclic ring
system. The RCM precursors were synthesized starting from aldehyde 3 [prepared in six steps on a multigram scale from R-(K)-carvone in
30% overall yield] via multiple stereoselective Hafner–Duthaler allyltitanations and/or Brown allylborations. ‘Second generation’ RCM-
catalyst 15 gave the desired ring closed ten-membered carbocycles as single Z stereoisomers in good yields. The RCM stereochemical course
(100% Z) is likely to reflect thermodynamic control. Molecular mechanics and semi-empirical calculations also show that the Z stereoisomers
of these ten-membered carbocycles are consistently more stable than the E. The crucial role of the homoallylic and allylic substituents and of
their protecting groups for the efficiency of the RCM reactions is discussed. In particular, we have found that p-methoxyphenyl (PMP)
protected allylic alcohols, the products of a stereoselective oxyallylation, are compatible with the RCM reaction and give better yields than
the corresponding free allylic alcohols. One of the simplified analogues of the natural product (44, lacking inter alia the C-4/C-7 ether bridge)
retains potent microtubule-stabilizing activity. However, the cytotoxicity tests did not parallel the potent tubulin-assembling and
microtubule-stabilizing properties: limited cytotoxicity was observed against three common tumor cell lines (human ovarian carcinoma,
human colon carcinoma and human leukemia cell lines, IC50 in the mM range), approximately two orders of magnitude less than paclitaxel
(IC50 in the nM range). The mechanism of cell cycle arrest induced by compound 44 is similar to that obtained with paclitaxel.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
Sarcodictyins1,2 A (1a) and B (1b) and eleutherobin3,4 (2)
(the ‘eleutheside’ family of microtubule-stabilizing drugs,
Fig. 1) are active against paclitaxel resistant tumor cell lines
and therefore hold potential as second generation micro-
tubule-stabilizing anticancer agents.4,5 The scarce avail-
ability of 1–2 from natural sources makes their total
syntheses vital for further biological investigations.5 To
date, sarcodictyins A and B have been synthesized
successfully by Nicolaou et al.6 who have also exploited a
similar route for accessing eleutherobin.7 A subsequent
report by Danishefsky and co-workers details an elegant
Figure 1. Marine diterpenoids sarcodictyin A (1a), B (1b) and eleutherobin
(2).
alternative access to eleutherobin.8 A number of partial
syntheses and approaches have also been described.9,10
Keywords: Allylation; Antitumor compounds; Metathesis; Stereocontrol.
* Corresponding author. Tel. C39 025031 4091; fax: C39 025031 4072;
e-mail: cesare.gennari@unimi.it
† Present address: Department of Chemistry, University of Sheffield,
The total syntheses of the eleuthesides have generated very
Dainton Building, Brook Hill, Sheffield S3 7HF, UK.
‡
limited diversity in the diterpenoid core, with major
variations reported only in the C-15 functionality and C-8
´
´
`
Present address: Dept. de Quımica, Unitat Quımica Organica, Universitat
` `
Autonoma de Barcelona, 08193 Cerdanyola del Valles, Spain.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.12.039

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D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
side-chain.5–8 We previously described the synthesis of a
number of eleutheside analogues with potent tubulin-
assembling and microtubule-stabilizing activity.9h,m,n
However, the cytotoxicity assays did not parallel the potent
tubulin-polymerizing properties: limited cytotoxicity was
observed against three common tumor cell lines (human
ovarian carcinoma and human colon carcinoma cell lines,
IC50 in the mM range), two-to-three orders of magnitude less
than paclitaxel (IC50 in the nM range).9n These results were
attributed to an easy esterase-mediated hydrolytic cleavage
of the N-methylurocanic ester side-chain in living cells (it is
known that the natural eleuthesides are devoid of any
cytotoxicity when the N-methylurocanic ester side-chain is
lacking in position 8).5 The simplified analogues, in fact, had
an unsubstituted –CH2– in position 7, while natural eleuthe-
sides have a fully substituted quaternary carbon, which is
likely to hinder the hydrolysis of the adjacent ester at C-8.
R-(K)-carvone in 30% overall yield)9a,g was submitted to a
stereoselective titanium-mediated Hafner–Duthaler crotyla-
tion,11 generating alcohol 5 (Scheme 1).
The crotylation reaction proceeded in high yield (85%) and
with complete stereocontrol in favor of the desired
1
stereoisomer (diastereomeric purity O95% by H and 13C
NMR).12 After standard alcohol protection, an efficient and
well established sequence of steps8c led to the homologated
aldehyde 10, on which a Brown allylation procedure was
applied.13 Addition of the allyl borane derived from (C)-a-
pinene to aldehyde 10 gave a mixture of the two homoallylic
alcohols (11 and 12) in a 3:1 ratio.12 The use of the allyl
borane derived from (K)-a-pinene gave the opposite
stereochemical outcome (11/12Z1:6).12 Homoallylic
alcohols 11 and 12 were acetylated and the resulting dienes
(13 and 14) were subjected to ring closing metathesis14
using the ‘second generation’ RCM-catalyst15 15 (CH2Cl2,
reflux) to give the desired cyclized products 16 and 17 as
single Z stereoisomers in 71–78% yields (Scheme 2). The
stereochemistry at C-3 appears not to have a dramatic effect
on the reaction, as similar yields were achieved. The Z
stereochemistry of the double bond was unequivocally
assigned by detection of the olefinic 3Jcis coupling constant
In this paper, we describe the synthesis of a number of
eleutheside analogues substituted at C-7, using ring closing
metathesis (RCM) as the key-step for obtaining the 6–10
fused bicyclic ring. We also report the tubulin-polymerizing
activities (ED50 and ED90 values) and the cytotoxicity tests
(IC50 values) performed on these compounds using several
different tumor cell lines.
1
(10.8–10.9 Hz) in 400 MHz H NMR experiments, and by
detection of a NOE contact between these protons in
400 MHz NOESY experiments.
2. Results and discussion
The reports that describe application of the RCM reaction to
medium-sized—particularly ten-membered—rings, are still
very rare, especially when dense functionality close to the
reaction centre is involved.16 The stereochemistry of the
double bond created by our RCM reactions appears to be
2.1. Synthesis of the eleutheside analogues substituted at
C-7
Aldehyde 3 (prepared in six steps on a multigram scale from
Scheme 1. Reagents and conditions: (a) (i) 2-ButenylMgCl, (S,S)-TaddolCpTiCl [(S,S)-4], Et2O, K78 to 0 8C; (ii) solution of 3 in Et2O, K78 8C, 16 h;
(iii) NH4F (45% aqueous solution), rt, 4 h, 85% (O95% diastereomeric purity). (b) MOMCl, DIPEA, TBAI, CH2Cl2, rt, 16 h, 82%. (c) (i) LiBF4, CH3CN/H2O
(98/2), rt, 1 h; (ii) NaBH4, EtOH, rt, 20 min, 60% over two steps. (d) MsCl, Et3N, CH2Cl2, 0 8C to rt, 1 h, quant. (e) KCN, 18-crown-6, MeCN, 80 8C, 5 h, 91%.
(f) DIBAL-H, n-hexane/toluene (2/1), K78 8C, 40 min, quant. (g) (i) AllMgBr, dIpc2BOMe, Et2O-THF, 0 8C to rt; (ii) solution of 10 in Et2O, K78 8C 15 h,
K78 to K20 8C 8 h; (iii) 6 N NaOH, H2O2, rt, 16 h, 48% (11/12Z3:1). (h) (i) AllMgBr, lIpc2BOMe, Et2O–THF, 0 8C to rt; (ii) solution of 10 in Et2O, K78 8C
15 h, K78 to K20 8C 15 h; (iii) 6 N NaOH, H2O2, rt, 16 h, 54% (11/12Z1:6).

D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
2125
Scheme 2. Reagents and conditions: (a) Ac2O, cat. DMAP, Et3N, CH2Cl2, 0 8C to rt, 2 h, 91%. (b) Ac2O, cat. DMAP, Et3N, CH2Cl2, 0 8C to rt, 2 h, 80%. (c) 15
(6%), CH2Cl2, rt for 16 h, reflux for 7 h, 78% (100% Z). (d) 15 (6%), CH2Cl2, rt for 16 h, reflux for 7 h, 71% (100% Z).
controlled in the desired sense (100% Z) by the structure of
the new ten-membered carbocycles. This stereochemical
course, which was found to be common to the cyclization of
several related substrates (previously described)9h,m,n,o and
of all the substrates reported in the present manuscript (vide
infra), is likely to reflect thermodynamic control.17
Molecular mechanics and semi-empirical calculations (see
the relevant section below) also show that the Z stereo-
isomers of these ten-membered carbocycles are consistently
more stable than the E.
With the goal of synthesizing more C-7 functionalized
eleutheside analogues, aldehyde 3 was oxyallylated using
Brown’s methodology [(Z)-g-(methoxymethoxy)allyldiiso-
pinocampheylborane from (K)-a-pinene]13d in high yield
(96%) and with excellent stereoselectivity (diastereomeric
purity O95% by 1H and 13C NMR, Scheme 4).12
Compound 21 was transformed into aldehyde 22 via a
simple protection/deprotection/homologation sequence
(analogous to the sequence described in Scheme 1).
Aldehyde 22 was allylated using the allyl borane derived
from (K)-a-pinene.12,13 The protective groups were
adjusted to give 23, with a free allylic alcohol (a free
alcohol in the allylic position is known to be important for
promoting the cyclization).9o,18,19 This time, ‘second
A first simplified eleutheside analogue (20) was then
synthesized from compound 16 using standard transform-
ations (Scheme 3).
Scheme 3. Reagents and conditions: (a) p-TSA, acetone, rt, 90 h, 78%. (b) 19 (Ref. 6b), (CH2Cl)2, Et3N, DMAP, rt, 48 h, 54%.
l
Scheme 4. Reagents and conditions: (a) Ipc2BOMe, AllOMOM, sec-BuLi, BF3$Et2O, THF, K78 8C to rt, 16 h, 96% (O95% diastereomeric purity).
(b) TBDPSCl, imidazole, CH2Cl2, 0 8C to rt, 16 h, 88%. (c) (i) AcOH/THF/H2O (3/1/1), rt, 15 h, quant.; (ii) NaBH4, EtOH, rt, 20 min, 71%; (iii) MsCl, Et3N,
CH2Cl2, 0 8C to rt, 2 h, 98%; (iv) KCN, 18-crown-6, CH3CN, 80 8C, 6 h, 91%; (v) DIBAL-H, n-hexane/toluene (2/1), K78 8C, 45 min, 90%. (d) lIpc2BOMe,
AllMgBr, THF, K78 8C, 16 h, 52% (R95% diastereomeric purity). (e) t-BuCOCl (PivCl), DMAP, CH2Cl2, 40 8C, 5 h, quant. (f) BF3$Et2O, PhSH, CH2Cl2,
K78 to K20 8C, 3 h, 73%.

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D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
importance of fine tuning the allylic and homoallylic alcohol
protective groups for a successful RCM reaction.
At this point, we decided to change the stereochemistry at
C-7, C-8 from syn to anti, hoping to influence the RCM
performance20 (Scheme 6). Aldehyde 3 was oxyallylated,
using the (S,S)-TaddolCpTiCl complex (4),11 to give the
desired stereoisomer 28 in 73% isolated yield with complete
stereocontrol (C-7, C-8 anti stereochemistry).12 After
standard alcohol protection as methoxymethyl ether (29,
95%), dimethylacetal deprotection (LiBF4, CH3CN/H2O)21
and NaBH4 reduction (31, 75% over two steps), an efficient
and well established sequence of steps8c,9n led to the
homologated aldehyde 34 (95%). Using Brown allyl-
boration (70%)13 or better Hafner–Duthaler allyltitanation
chemistry (87%),11 the second olefin fragment was stereo-
selectively inserted in the south chain to give diene 35.12
Scheme 5.
generation’ RCM catalyst 1515 failed to provide the desired
ring closed product, under a variety of experimental
conditions.9o
Protective group manipulations transformed diene 35 into
the desired cyclization precursor 39 (C-7, C-8 anti)
(Scheme 7) which had the same substitution and protection
pattern as shown in compound 26 (C-7, C-8 syn). Reaction
with the robust ‘second generation’ RCM-catalyst 15 gave a
mixture of compounds, from which the cyclized product 40
could be isolated in a similarly poor yield (21%, Scheme 7).
No significant difference was observed in the reactivity of
the two diastereomers (26 and 39) in the RCM reaction.20 It
was noted, however, that if the RCM reaction was
performed with the precursor PMP-protected allylic alcohol
(38), higher yields could be obtained under similar reaction
conditions (52%, 62% considering the recovered starting
material, Scheme 8). This is, unexpectedly and unprece-
dentedly, a result in disagreement with the ‘free allylic
alcohol’ effect,9o,18,19 that is, allylic ethers are usually found
This result is striking when compared to the analogous RCM
reaction of diene 24 (Scheme 5), which proceeds smoothly
to give the ring-closed product 25 in 73% isolated yield.9n
Interconversion of the homoallylic O-protective groups of
diene 23 gave the allylic alcohol 26 which did undergo
cyclization to give 27, albeit in a disappointing 24% yield.9o
The rationale for this interconversion was that although the
substitution pattern in compound 23 is the same as that
shown by the successful cyclization precursor 24 (allylic
alcohol, homoallylic OPiv and OTBDPS, Schemes 4 and 5),
it is not the same with respect to the relationship between the
groups [OH adjacent to OTBDPS (23) versus OH adjacent
to OPiv (24)]. Again this observation demonstrates the
Scheme 6. Reagents and conditions: (a) sec-BuLi (1.3 M in cyclohexane), PMPOAllyl, (S,S)-TaddolCpTiCl [(S,S)-4], THF/Et2O (57/43), K78 to 0 8C, 73%.
(b) DIPEA, TBAI, MOMCl, CH2Cl2, 25 8C, 95%. (c) LiBF4, CH3CN/H2O (98/2), 25 8C. (d) NaBH4, EtOH, 25 8C, 75% over two steps. (e) MsCl, TEA,
CH2Cl2, 0 to 25 8C, 95%. (f) KCN, 18-crown-6, CH3CN, 80 8C, quant. (g) DIBAL-H, toluene/n-hexane (1/2), K78 8C, quant. (h) AllMgBr, dIpc2BOMe, Et2O/
THF (11/79), K78 8C, 70%. (i) AllMgBr, (R,R)-TaddolCpTiCl [(R,R)-4], Et2O, K78 8C, 87%.

D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
2127
Scheme 7. Reagents and conditions: (a) imidazole, TBDPSCl, CH2Cl2, rt, 90%. (b) Me2S, BF3$Et2O, CH2Cl2, K20 8C, 45%. (c) DMAP, PivCl, CH2Cl2, rt,
66%. (d) CAN, CH3CN/H2O (4/1), 0 8C, 67%. (e) 15 (10%), CH2Cl2, rt, 7.5 mM, 21% (100% Z).
to retard the RCM reaction while a rate acceleration is
associated with allylic alcohols. Given the success of diene
38 in the RCM reaction, attempts were made to cyclize
precursor 37. Reaction of diene 37 with a free homoallylic
alcohol and a PMP-protected allylic alcohol with the
‘second generation’ RCM-catalyst 15 gave the desired
6–10 fused bicycle 42 in 80% yield and 100% Z-selectivity
(Scheme 8).
extensive NOESY experiments also suggested formation of
the Z-olefin: a strong NOE was observed between C-7
methine and C-4 methylene protons and between H-5 and
H-6.
At present, the reasons why the allylic OPMP group
facilitates the RCM reaction are not completely understood.
Sterically, the PMP can be considered relatively small, even
smaller than a Me group (effective van der Waals radius of
PhZ1.62 A compared to MeZ1.80 A),23 but definitely not
smaller than a hydrogen. The true reason must be electronic,
but difficult to rationalise.
˚
˚
The improved results given by diene 37 compared to 38 may
be due to the use of a higher boiling solvent.22 An extensive
analysis of compounds 41 and 42 was carried out using
3
NMR spectroscopy. The olefinic Jcis coupling constants
suggested the cis configuration of the new double bonds
(3JZ11.4 Hz for 41, 3JZ11.4 Hz for 42). Furthermore,
A simplified eleutheside analogue (44) was then synthesized
from compound 42 using standard transformations
Scheme 8. Reagents and conditions: (a) 15 (10%), CH2Cl2, reflux, 11 mM, 52% (62% considering the recovered starting material) (100% Z). (b) CAN,
CH3CN/H2O (4/1), 0 8C, 80%. (c) 15 (10%), benzene, reflux, 10 mM, 80% (100% Z).
Scheme 9. Reagents and conditions: (a) 19 (Ref. 6b), (CH2Cl)2, Et3N, DMAP, 80 8C, 82%. (b) TBAF, THF, rt, 85%.

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D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
Figure 2. List of structures studied by molecular mechanics and semi-empirical PM3 calculations.
(Scheme 9). It is worth noting that the formation of the
(E)-N-methylurocanic ester in refluxing 1,2-dichloroethane
had a beneficial effect on the yield of 43 (82%).
(C2 and D2),26 OMOM into OMe. Initially, conformational
searches were carried out with MacroModel27 (MM2*,
CHCl3 GB/SA) on each of the structures represented in
Figure 2. In all cases, the Z stereoisomers of structures A–F
were found to be consistently more stable than the
corresponding E stereoisomers by ca. 1.8–12.7 kJ molK1
(Table 1). The structures generated with MacroModel were
then optimized at the PM3 level24 with the Gaussian 03
package.28 These calculations also show that the Z
stereoisomers of structures A–F are more stable than the
E stereoisomers, with energy differences ranging from 9.8 to
28.2 kJ molK1 (Table 1). It is therefore highly likely that the
selective formation of the Z ten-membered carbocycles in
the RCM reactions is due to thermodynamic control.17
2.2. Molecular mechanics and semi-empirical
calculations
Molecular mechanics and semi-empirical PM324 calcu-
lations were undertaken in order to investigate if the
stereochemical outcome of the various RCM reactions
could possibly be due to thermodynamic control. Com-
pounds 27, 40, 41, 42, 16 and 17 were simplified into
structures A–F (Z and E stereoisomers, Fig. 2) in order to
reduce the number of rotatable bonds and of low-quality
torsional parameters,25 by making the following changes in
the protective groups: OPiv into OAc, OTBDPS into
OTMS,25 OPMP into either OMe (C1 and D1) or OPh
Figure 3 shows the lowest energy conformers and relative
energies of stereoisomer (Z)-C1 (corresponding to 41) and
of stereoisomer (E)-C1, obtained at the PM3 level.
Table 1. Global minimum energy differences between the (E) and the (Z)-
stereoisomers of structures A–F
2.3. Biological assays
Structure
EE–EZ (MM2*)a
EE–EZ (PM3)a
The effect of these new eleutheside analogues on the
assembly of tubulin and on the stability of the formed
microtubules was assessed at the University of Salford
(UK), using the potent microtubule-stabilizing agent
paclitaxel as a reference (Table 2).2b,29 Eleutheside
analogue 44 was shown to be at least as potent as
paclitaxel. Microtubules were generated in the presence of
CaCl2 at 37 8C and were stable (i.e., did not depolymerize)
at 10 8C. Although there is a general agreement that the
A
B
1.8
4.3
6.6
5.0
7.4
6.2
7.7
12.7
9.8
18.0
17.4
18.6
12.3
18.6
22.4
28.2
C1
C2
D1
D2
E
F
a Energy differences in kJ molK1
.

D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
2129
However, the cytotoxicity assays did not parallel the potent
tubulin-assembling and microtubule-stabilizing properties:
limited cytotoxicity was observed for 44 (IC50 in the mM
range) against three common tumor cell lines (human
ovarian carcinoma, human colon carcinoma and human
leukemia cell lines, Table 3),30 approximately two orders of
magnitude less than paclitaxel (IC50 in the nM range).
The mechanism of cell cycle arrest was studied in the case
of compound 44.31 When tested on asynchronously
proliferating HCT116 cells, compound 44 produced cell
cycle perturbations similar to that obtained with paclitaxel:
a 2.5-fold increase in the percentage of cells in G2/M
phase (the mitotic phase) was observed with 44 at 4 mM and
a 2-fold increase was obtained with paclitaxel at 50 nM.31
Despite their excellent microtubule-stabilizing activity,
which is often superior to paclitaxel, and a mechanism of
cell cycle arrest similar to that obtained with paclitaxel, high
concentrations of our analogues (in the mM range) are
needed to inhibit tumor cell growth.9n Thus, with this new
class of eleutheside analogues, we succeeded, at least in
part, in the separation of the tubulin mechanism from the
cytostatic/cytotoxic action.32 Although the application of
these compounds as monotherapeutics in tumor indications
will be limited, they might be of value as tools and wherever
the stabilization of microtubules without other cell-toxic
effects are advantageous. One of these potential applications
might be the treatment of Alzheimer’s disease.33 It has been
demonstrated very recently that paclitaxel protects very
efficiently against b-amyloid toxicity in primary neurons.34
This will open new therapeutic areas for compounds which
are able to stabilize microtubules.
Figure 3. Lowest energy conformers and relative energies of stereoisomer
(Z)-C1 (corresponding to 41) and of stereoisomer (E)-C1, obtained at the
PM3 level.
Table 2. Tubulin polymerizing activitiesa
Compound
ED50 [mM]
ED90 [mM]
20
44
Paclitaxel
3.0
0.1
1.0
O20.0
0.5
2.5
a ED50, effective dose that induces 50% tubulin polymerization; ED90
,
effective dose that induces 90% tubulin polymerization (see Ref. 2b). ED
values may vary depending on the tubulin batch (from pig brain): the same
batch is used for the paclitaxel reference assay. For a more detailed
experimental procedure, see Ref. 9n.
3. Experimental
3.1. General procedures
(E)-N-methylurocanic side-chain, the C-4/C-7 ether bridge,
and the cyclohexene ring are important determinants of
antimitotic activity,5 it is interesting to note that this
simplified analogue of the natural product (lacking inter alia
the C-4/C-7 ether bridge) retains potent microtubule
stabilizing activity. Given the dramatic impact that the
furanose oxygen deletion is likely to have on the
conformation of the ring system, the fact that some of
these compounds retain activity comparable to paclitaxel in
the tubulin polymerization assay is remarkable.9n
All reactions were carried out in flame-dried glassware
under argon atmosphere. All commercially available
reagents were used as received. The solvents were dried
by distillation over the following drying agents and were
transferred under nitrogen: CH3CN (CaH2), CH2Cl2 (CaH2),
(CH2Cl)2 (CaH2), MeOH (CaH2), Et3N (CaH2), iPr2EtN
(CaH2), HN(TMS)2 (CaH2), THF (Na), Et2O (Na), benzene
(Na), toluene (Na), n-hexane (Na). Organic extracts were
dried over anhydrous Na2SO4. Reactions were monitored by
analytical thin-layer chromatography (TLC) using silica gel
60 F254 precoated glass plates (0.25 mm thickness) or basic
alumina supported on aluminium foils. TLC Rf values are
reported. Visualization was accomplished by irradiation
with a UV lamp and/or staining with ceric ammonium
molybdate (CAM) solution. Flash column chromatography
Table 3. Cytotoxicity assays: IC50 values on A2780, HCT116, K562 tumor
cell linesa
Compound
IC50 [mM]
(A2780)
IC50 [mM]
(HCT116)
IC50 [mM]
(K562)
20
44
10.9b
1.9b
n.d.c
0.9e
4.3d
2.3d
˚
was performed using silica gel 60 A, particle size 40–
64 mm, following the procedure by Still and co-workers.35
Proton NMR spectra were recorded on 400, 300, or
200 MHz spectrometers. Proton chemical shifts are reported
in ppm (d) with the solvent reference relative to tetra-
methylsilane (TMS) employed as the internal standard
(CDCl3, d 7.26 ppm; d6-DMSO, d 2.50 ppm). The following
abbreviations are used to describe spin multiplicity: s,
singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br,
a IC50 values: concentration inhibiting cell growth by 50%. Cell
proliferation was determined by the ATPlite assay (Perkin Elmer).
A2780: human ovarian carcinoma cell line; HCT116: human colon
carcinoma cell line; K562: human leukemia cell line.
b Paclitaxel IC50Z15 nM.
c Not determined.
d Paclitaxel IC50Z25 nM.
e Paclitaxel IC50Z7 nM.

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D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
broad signal; dd, doublet of doublet; dt, doublet of triplet;
ddd, doublet of doublet of doublet. Carbon NMR spectra
were recorded on 400 (100 MHz), 300 (75 MHz) or 200
(50 MHz) spectrometers with complete proton decoupling.
Carbon chemical shifts are reported in ppm (d) relative to
TMS with the respective solvent resonance as the internal
standard (CDCl3, d 77.0). Infrared spectra were recorded on
a standard Infrared Spectrophotometer; peaks are reported
in cmK1. Optical rotation values were measured on an
automatic polarimeter at the sodium D line. High resolution
mass spectra (HRMS) were performed on a hybrid
quadrupole time of flight mass spectrometer equipped with
an ESI ion source. A Reserpine solution 100 pg/mL (about
100 count/s), 0.1% HCOOH/CH3CN 1:1, was used as
reference compound (Lock Mass).
9.7 Hz, J2Z3.2 Hz), 3.41 (s, 3H), 3.32 (s, 3H), 3.31 (s, 3H),
2.50 (br, 1H), 2.34 (br, 1H), 2.11–1.60 (m, 9H), 1.36 (ddd,
1H, J1Z14.3 Hz, J2Z9.9 Hz, J3Z3.6 Hz), 1.04 (d, 3H, JZ
6.9 Hz), 0.91 (d, 3H, JZ6.8 Hz), 0.82 (d, 3H, JZ6.7 Hz);
13C NMR (50 MHz, CDCl3): d 141.2, 138.3, 120.2, 113.8,
107.0, 97.4, 81.4, 55.7, 55.1, 54.3, 42.0, 40.4, 36.3, 34.2,
32.1, 27.1, 24.4, 22.3, 21.3, 17.2, 14.4; FT-IR (CCl4): n
3075, 2959, 2931, 2842, 2830, 2674, 2291, 2009, 1831,
1736, 1639, 1558, 1464, 1442, 1376, 1369, 1259, 1214,
1152, 1103, 1078, 1049, 1013, 979, 914; [a]2D0ZC74.0 (cZ
0.5, EtOAc); HRMS (ESI): m/z: calculated for C21H38NaO4:
377.2668 [MCNa]C; found: 377.2667 (resolution 10,000).
3.1.3. {(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-methoxy-
methoxy-3-methyl-pent-4-enyl]-3-methyl-cyclohex-3-
enyl}-methanol (7). LiBF4 (246 mg, 2.63 mmol) was
dissolved in a mixture of CH3CN/H2O (5.2 mL, v/v: 98/2)
and added to compound 6 (932 mg, 2.63 mmol). After
stirring for 1 h, the reaction mixture was filtered through a
plug of silica gel (eluting with CH2Cl2) and the filtrate
concentrated in vacuo to give the crude aldehyde (768 mg),
which was used without further purification. To a stirred
solution of the crude aldehyde, in EtOH (28.0 mL), was
added NaBH4 (149 mg, 3.94 mmol). After stirring for
20 min, the reaction mixture was treated with NH4Cl
(1.41 g, 26.36 mmol) followed by Na2SO4 and iPr2O, and
stirred for further 20 min. The salts were removed by
filtration and washed with iPr2O. Purification by flash
chromatography (n-hexane/EtOAc, 85/15) afforded alcohol
7 (505 mg, 60% over two steps) as a colourless oil. RfZ0.25
3.1.1. (2S,3R)-1-[(1R,5R,6R)-6-Dimethoxymethyl-5-iso-
propyl-2-methyl-cyclohex-2-enyl]-3-methyl-pent-4-en-2-
ol (5). To a cold (K78 8C), stirred suspension of (S,S)-411
(1.00 g, 1.63 mmol), in Et2O (24.5 mL), was added
2-butenylmagnesium chloride (0.5 M in THF, 2.9 mL,
1.47 mmol). After stirring for 30 min, the resulting orange
solution was warmed to 0 8C and stirred for 3 h, then
recooled to K78 8C. A solution of aldehyde 39a,g (277 mg,
1.09 mmol) in Et2O (6.0 mL) was added. After stirring for
15 h, the reaction mixture was treated with a NH4F aqueous
solution (45%, 10 mL) and stirred for further 4 h at room
temperature. The organic phase was separated and the
aqueous layer was extracted with iPr2O (3!15 mL). The
organic extracts were washed with brine. Purification of the
crude by flash chromatography (n-hexane/EtOAc, 9/1)
afforded compound 5 (285 mg, 85%) as a colourless oil.
RfZ0.38 (n-hexane/EtOAc, 9/1); 1H NMR (400 MHz,
CDCl3): d 5.86–5.77 (m, 1H), 5.35 (br, 1H), 5.10–5.03
(m, 2H), 4.35 (d, 1H, JZ5.5 Hz), 3.71–3.63 (m, 1H), 3.36
(s, 6H), 2.48 (br, 1H), 2.40 (br, 1H), 2.19–2.10 (m, 1H),
2.06–1.97 (m, 2H), 1.87–1.71 (m, 4H), 1.67 (s, 3H), 1.42
(ddd, 1H, J1Z14.6 Hz, J2Z10.1 Hz, J3Z3.3 Hz), 1.03 (d,
3H, JZ6.8 Hz), 0.92 (d, 3H, JZ6.6 Hz), 0.83 (d, 3H, JZ
6.5 Hz); 13C NMR (50 MHz, CDCl3): d 141.1, 136.6, 121.3,
115.2, 106.9, 71.8, 55.1, 54.4, 45.1, 39.8, 36.1, 34.5 (2C),
27.1, 24.5, 22.2, 21.0, 17.3, 16.0; FT-IR (CCl4): n 3632,
3583, 3487, 3077, 2961, 2832, 2675, 2290, 2002, 1847,
1638, 1558, 1463, 1386, 1259, 1216, 1159, 1111, 1073,
1007, 914; [a]2D0ZC48.2 (cZ1.03, EtOAc); HRMS (ESI):
m/z: calculated for C19H34NaO3: 333.2406 [MCNa]C;
found: 333.2410 (resolution 9000).
1
(n-hexane/EtOAc, 85/15); H NMR (200 MHz, CDCl3): d
5.93–5.72 (m, 1H), 5.34 (br, 1H), 5.16–5.01 (m, 2H), 4.75
(d, 1H, JZ6.9 Hz), 4.69 (d, 1H, JZ6.9 Hz), 3.75 (dd, 1H,
J1Z11.2 Hz, J2Z5.1 Hz), 3.67–3.42 (m, 5H), 2.65–2.42
(m, 1H), 2.33 (br, 1H), 1.98–1.37 (m, 12H), 1.06 (d, 3H, JZ
6.9 Hz), 0.91 (d, 3H, JZ6.8 Hz), 0.84 (d, 3H, JZ6.7 Hz);
13C NMR (50 MHz, CDCl3): d 140.5, 137.4, 120.9, 115.1,
97.0, 81.3, 61.9, 55.9, 41.9, 41.6, 35.9, 34.2, 30.9, 24.2,
22.3, 21.1, 16.3, 14.1; FT-IR (CCl4): n 3633, 3513, 3080,
2961, 2931, 2824, 2290, 2004, 1846, 1736, 1638, 1543,
1463, 1417, 1386, 1369, 1259, 1216, 1150, 1101, 1040,
1008, 918; [a]2D0ZC73.6 (cZ0.7, EtOAc).
3.1.4. Methanesulfonic acid {(1R,2R,6R)-6-isopropyl-2-
[(2S,3R)-2-methoxymethoxy-3-methyl-pent-4-enyl]-3-
methyl-cyclohex-3-enyl}-methyl ester (8). To a cold
(0 8C), stirred solution of alcohol 7 (505 mg, 1.63 mmol),
in CH2Cl2 (12.5 mL), was added Et3N (680 mL, 4.88 mmol)
followed by MsCl (189 mL, 2.44 mmol). After stirring at
room temperature for 15 h, the solvent was evaporated
under reduced pressure. Purification of the crude by
filtration through a plug of silica gel (eluting with
CH2Cl2) afforded mesylate 8 (634 mg, quant.) as a colour-
less oil. RfZ0.72 (CH2Cl2/EtOAc, 95/5); 1H NMR
(200 MHz, CDCl3): d 5.94–5.74 (m, 1H), 5.33 (br, 1H),
5.18–5.03 (m, 2H), 4.75 (d, 1H, JZ7.0 Hz), 4.70 (d, 1H, JZ
7.0 Hz), 4.30 (dd, 1H, J1Z9.9 Hz, J2Z7.2 Hz), 4.07 (dd,
1H, J1Z9.9 Hz, J2Z8.6 Hz), 3.70–3.58 (m, 1H), 3.43 (s,
3H), 3.03 (s, 3H), 2.63 (br, 1H), 2.39 (br, 1H), 2.26–2.07 (m,
1H), 1.96 (br, 2H), 1.75–1.20 (m, 7H), 1.05 (d, 3H, JZ
6.8 Hz), 0.92 (d, 3H, JZ6.7 Hz), 0.87 (d, 3H, JZ6.6 Hz);
13C NMR (50 MHz, CDCl3): d 140.3, 136.2, 120.8, 115.3,
96.7, 80.1, 69.2, 55.9, 41.0, 38.0, 37.3, 36.7, 33.9, 30.1,
3.1.2. (4R,5R,6R)-5-Dimethoxymethyl-4-isopropyl-6-
[(2S,3R)-2-methoxymethoxy-3-methyl-pent-4-enyl]-1-
methyl-cyclohexene (6). To a stirred solution of compound
5 (993 mg, 3.20 mmol), in CH2Cl2 (8.1 mL) was added
DIPEA (1.23 mL, 7.05 mmol) followed by TBAI (237 mg,
0.64 mmol) and chloromethyl methyl ether (487 mL,
6.41 mmol). After stirring for 15 h, the resulting brown
solution was filtered through a plug of silica gel (eluting
with CH2Cl2). Purification of the crude by flash chroma-
tography (n-hexane/EtOAc, 95/5) afforded compound 6
(932 mg, 82%) as a colourless oil. RfZ0.6 (n-hexane/
EtOAc, 9/1); 1H NMR (400 MHz, CDCl3): d 5.84 (ddd, 1H,
J1Z17.4 Hz, J2Z10.3 Hz, J3Z7.1 Hz), 5.28 (br, 1H),
5.08–4.97 (m, 2H), 4.78 (d, 1H, JZ6.6 Hz), 4.70 (d, 1H,
JZ6.6 Hz), 4.29 (d, 1H, JZ5.3 Hz), 3.80 (dt, 1H, J1Z

D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
2131
27.2, 23.9, 22.1, 20.8, 17.8, 13.1; FT-IR (CCl4): n 2962,
2930, 2291, 2003, 1845, 1734, 1555, 1370, 1344, 1259,
1216, 1177, 1098, 1009; [a]2D0ZC21.0 (cZ1.4, EtOAc);
HRMS (ESI): m/z: calculated for C20H37NO5S: 406.2627
[MCNH4]C; found: 406.2622 (resolution 10,000).
combined alcohols 11 and 12 as a mixture (48%). A second
flash chromatography (CH2Cl2/iPr2O, 95/5) afforded 11
(94 mg, 36%) and 12 (31 mg, 12%) as colourless oils
(11/12Z3:1).
1
Compound 11. RfZ0.32 (CH2Cl2/iPr2O, 95/5); H NMR
(200 MHz, CDCl3): d 5.98–5.68 (m, 2H), 5.31 (br, 1H),
5.27–4.98 (m, 4H), 4.69 (s, 2H), 3.89–3.68 (m, 1H), 3.60–
3.33 (m, 4H), 2.67 (br, 1H), 2.40–1.18 (m, 16H), 1.06 (d,
3H, JZ6.9 Hz), 0.91 (d, 3H, JZ6.8 Hz), 0.82 (d, 3H, JZ
6.6 Hz); 13C NMR (50 MHz, CDCl3): d 140.3, 137.0, 134.8,
121.0, 118.3, 115.2, 96.5, 80.7, 68.2, 55.8, 42.3, 41.1, 38.4,
35.1, 34.7, 34.5, 30.5, 27.0, 24.1, 22.7, 21.0, 17.4, 14.0; FT-
IR (CCl4): n 3623, 3590, 3079, 2961, 2823, 2290, 1839,
1742, 1640, 1559, 1440, 1415, 1373, 1262, 1151, 1019, 918;
[a]2D0ZC40.9 (cZ0.98, EtOAc); HRMS (ESI): m/z:
calculated for C23H41O3: 365.3056 [MCH]C; found:
365.3065 (resolution 10,000).
3.1.5. {(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)2-methoxy-
methoxy-3-methyl-pent-4-enyl]-3-methyl-cyclohex-3-
enyl}-acetonitrile (9). To a stirred solution of mesylate 8
(634 mg, 1.63 mmol), in CH3CN (16.9 mL), was added 18-
crown-6 (1.29 g, 4.89 mmol) followed by KCN (319 mg,
4.89 mmol). After stirring for 8 h at 80 8C, the solvent was
evaporated under reduced pressure. Purification by flash
chromatography (n-hexane/EtOAc, 95/5) afforded com-
pound 9 (473 mg, 91%) as a colourless oil. RfZ0.52
1
(n-hexane/EtOAc, 85/15); H NMR (400 MHz, CDCl3): d
5.85–5.76 (m, 1H), 5.35 (br, 1H), 5.21–5.05 (m, 2H), 4.73
(s, 2H), 3.58 (dt, 1H, J1Z9.6 Hz, J2Z1.6 Hz), 3.42 (s, 3H),
2.70 (br, 1H), 2.46–1.90 (m, 6H), 1.77–1.52 (m, 6H), 1.26
(ddd, 1H, J1Z14.8 Hz, J2Z8.8 Hz, J3Z2.8 Hz), 1.08 (d,
3H, JZ7.2 Hz), 0.95 (d, 3H, JZ6.8 Hz), 0.89 (d, 3H, JZ
6.4 Hz); 13C NMR (50 MHz, CDCl3): d 140.1, 135.1, 121.0,
119.8, 115.7, 96.9, 80.2, 55.9, 41.0, 39.5, 34.9, 34.7, 29.6,
27.3, 23.6, 22.1, 20.6, 18.9, 17.3, 13.2; FT-IR (CCl4): n
3081, 2963, 2892, 2847, 2823, 2290, 2247, 2004, 1847,
1638, 1558, 1463, 1426, 1388, 1372, 1257, 1217, 1151,
1101, 1041, 1006, 980, 920; [a]2D0ZC48.2 (cZ1.33,
EtOAc); HRMS (ESI): m/z: calculated for C20H33NaNO2:
342.2409 [MCNa]C; found: 342.2419 (resolution 10,000).
1
Compound 12. RfZ0.44 (CH2Cl2/iPr2O, 95/5); H NMR
(200 MHz, CDCl3): d 5.95–5.72 (m, 2H), 5.29 (br, 1H),
5.23–5.01 (m, 4H), 4.74 (s, 2H), 3.83–3.60 (m, 2H), 3.42 (s,
3H), 2.75–2.60 (m, 1H), 2.40–1.85 (m, 6H), 1.75–1.53 (m,
6H), 1.45–1.21 (m, 4H), 1.07 (d, 3H, JZ6.8 Hz), 0.92 (d,
3H, JZ6.7 Hz), 0.87 (d, 3H, JZ6.5 Hz); 13C NMR
(50 MHz, CDCl3): d 140.7, 136.3, 134.9, 120.8, 118.1,
115.0, 97.0, 80.2, 68.0, 55.9, 42.8, 41.2, 39.3, 34.2, 34.1,
32.5, 29.5, 27.4, 24.1, 22.3, 20.8, 19.9, 13.2; FT-IR (CCl4): n
3622, 3590, 3080, 2960, 2823, 2291, 2004, 1847, 1741,
1639, 1559, 1463, 1439, 1415, 1386, 1376, 1252, 1218,
1152, 1102, 1043, 1006, 980; [a]2D0ZC19.6 (cZ0.87,
EtOAc); HRMS (ESI): m/z: calculated for C23H41O3:
365.3056 [MCH]C; found: 365.3061 (resolution 10,000).
3.1.6. {(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-methoxy-
methoxy-3-methyl-pent-4-enyl]-3-methyl-cyclohex-3-
enyl}-acetaldehyde (10). To a cold (K78 8C), stirred
solution of compound 9 (295 mg, 0.92 mmol), in toluene/
n-hexane (15.0 mL, v/v: 1/2), was slowly added DIBAL-H
(1.5 M in toluene, 6.1 mL, 9.20 mmol). After 45 min the
reaction mixture was treated with EtOAc (7.5 mL) and an
aqueous tartaric acid solution (1.0 M, 7.5 mL), and warmed
to room temperature. After 1 h the organic phase was
separated and the aqueous layer was extracted with CH2Cl2
(5!10 mL). The organic extracts were washed with
saturated NaHCO3 aqueous solution (2!10 mL). The
solvent was evaporated under reduced pressure to afford
aldehyde 10 (296 mg, quant.) as a colourless oil, which was
used without further purification. RfZ0.2 (CH2Cl2).
Following the same procedure described above and using
lIpc2BOMe13c as chiral auxiliary, the 2 epimeric alcohols
were obtained in 54% yield and in a ratio 11/12Z1:6.
3.1.8. Acetic acid (S)-1-{(1R,2R,6R)-6-isopropyl-2-
[(2S,3R)-2-methoxymethoxy-3-methyl-pent-4-enyl]-3-
methyl-cyclohex-3-enylmethyl}-but-3-enyl ester (13). To
a cold (0 8C), stirred solution of alcohol 11 (87 mg,
0.24 mmol), in CH2Cl2 (1.6 mL), was added Et3N (66 mL,
0.48 mmol), followed by DMAP (2.9 mg, 0.024 mmol) and
Ac2O (34 mL, 0.36 mmol). After stirring for 30 min, the
reaction mixture was warmed to room temperature and
stirred for further 1 h. The reaction mixture was treated with
a NaHCO3 saturated aqueous solution (3 mL) and stirred for
15 min. The organic phase was separated and the aqueous
layer was extracted with CH2Cl2 (3!5 mL). Purification by
flash chromatography (n-hexane/EtOAc, 95/5) afforded
compound 13 (89 mg, 91%) as a colourless oil. RfZ0.65
3.1.7. (R)-1-{(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-meth-
oxymethoxy-3-methyl-pent-4-enyl]-3-methyl-cyclohex-
3-enyl}-pent-4-en-2-ol (11) and (S)-1-{(1R,2R,6R)-6-iso-
propyl-2-[(2S,3R)-2-methoxymethoxy-3-methyl-pent-4-
enyl]-3-methyl-cyclohex-3-enyl}-pent-4-en-2-ol (12). To
d
a cold (0 8C), stirred solution of Ipc2BOMe13c (1.0 M in
1
THF, 2.4 mL, 2.42 mmol) was slowly added AllMgBr
(1.0 M in Et2O, 2.1 mL, 2.14 mmol). After stirring for 1 h at
room temperature, the reaction mixture was cooled to
K78 8C and aldehyde 10 (230 mg, 0.71 mmol) in Et2O
(2.8 mL) was added. After stirring for 15 h, the reaction
mixture was warmed gradually to K20 8C during 8 h, and
treated with an aqueous NaOH solution (6.0 M, 3.5 mL) and
H2O2 (35%, 2.8 mL). After stirring for 16 h at room
temperature, the organic phase was separated and the
aqueous layer was extracted with iPr2O (3!10 mL). A first
flash chromatography (n-hexane/EtOAc, 9/1) afforded
(n-hexane/EtOAc, 85/15); H NMR (200 MHz, CDCl3): d
5.90–5.73 (m, 2H), 5.29 (br, 1H), 5.21–4.97 (m, 5H), 4.70
(s, 2H), 3.58–3.35 (m, 4H), 2.62 (br, 1H), 2.41–1.20 (m,
18H), 1.06 (d, 3H, JZ6.9 Hz), 0.90 (d, 3H, JZ6.7 Hz), 0.81
(d, 3H, JZ6.6 Hz); 13C NMR (50 MHz, CDCl3): d 170.7,
140.3, 136.9, 133.8, 120.9, 117.7, 115.3, 96.5, 80.4, 71.4,
55.9, 41.1, 39.0, 38.4, 34.8, 34.4, 31.3, 30.4, 27.0, 24.0,
22.6, 21.2, 20.9, 17.6, 14.0; FT-IR (CCl4): n 3079, 2961,
2823, 2290, 2003, 1837, 1739, 1641, 1553, 1440, 1418,
1371, 1242, 1150, 1098, 1044, 918; [a]2D0ZC50.6 (cZ
1.03, EtOAc); HRMS (ESI): m/z: calculated for

2132
D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
C25H46NO4: 424.3421 [MCNH4]C; found: 424.3434
(resolution 10,000).
(17). To a stirred solution of diene 14 (20 mg,
0.049 mmol), in degassed CH2Cl2 (4.6 mL), was slowly
added a solution Grubbs catalyst 15 (2.5 mg, 3.0 mmol) in
degassed CH2Cl2 (370 mL). The reaction mixture was
stirred for 15 h at room temperature, then for 7 h at 40 8C
and then for 15 h at room temperature. Further Grubbs
catalyst 15 (1 mg) was added and then heated at 40 8C for
7 h. The reaction mixture was treated with DMSO (20 mL)
and stirred for 15 h at room temperature under argon
atmosphere. Purification by flash chromatography
(n-hexane to n-hexane/EtOAc, 95/5) afforded compound
17 (13.1 mg, 71%) as a colourless oil. RfZ0.77 (n-hexane/
EtOAc, 9/1, TLC runs twice); 1H NMR (400 MHz, CDCl3):
d 5.46–5.40 (m, 2H), 5.33 (br, 1H), 5.24–5.15 (m, 1H), 4.72
(d, 1H, JZ6.9 Hz), 4.60 (d, 1H JZ6.9 Hz), 3.89–3.82 (m,
1H), 3.42 (s, 3H), 3.02–2.93 (m, 1H), 2.81–2.71 (m, 1H),
2.34–2.21 (m, 2H), 2.06 (s, 3H), 2.00–1.75 (m, 6H), 1.71–
1.50 (m, 4H), 1.46–1.37 (m, 1H), 1.13 (d, 3H JZ6.6 Hz),
0.87 (d, 3H, JZ6.8 Hz), 0.67 (d, 3H, JZ6.7 Hz); 13C NMR
(50 MHz, CDCl3): d 170.4, 138.7, 133.6, 124.9, 120.9, 95.8,
81.4, 72.7, 55.8, 37.5, 37.0, 35.1, 34.5, 33.6, 32.4, 26.9,
26.4, 24.5, 24.4, 21.2, 21.0, 18.0, 14.7; FT-IR (CCl4): n
2961, 2930, 2290, 2003, 1847, 1740, 1558, 1458, 1369,
1246, 1149, 1098, 1042, 1008, 930; [a]2D0ZC86.4 (cZ
0.56, EtOAc); HRMS (ESI): m/z: calculated for
C23H38NaO4: 401.2662 [MCNa]C; found: 401.2657
(resolution 10,000).
3.1.9. Acetic acid (R)-1-{(1R,2R,6R)-6-isopropyl-2-
[(2S,3R)-2-methoxymethoxy-3-methyl-pent-4-enyl]-3-
methyl-cyclohex-3-enylmethyl}-but-3-enyl ester (14). To
a cold (0 8C), stirred solution of alcohol 12 (92 mg,
0.25 mmol), in CH2Cl2 (1.7 mL) was added Et3N (70 mL,
0.50 mmol) followed by DMAP (3.1 mg, 0.025 mmol) and
Ac2O (36 mL, 0.38 mmol). After stirring for 30 min at 0 8C,
the reaction was warmed to room temperature. After further
1 h, the reaction mixtures was filtered through a plug of
silica gel (eluting with CH2Cl2). Purification by flash
chromatography (n-hexane/EtOAc, 95/5) afforded com-
pound 14 (81 mg, 80%) as a colourless oil. RfZ0.50
(n-hexane/EtOAc, 9/1); 1H NMR (200 MHz, CDCl3): d
5.93–5.64 (m, 2H), 5.27 (br, 1H), 5.20–4.94 (m, 5H), 4.73
(s, 2H), 3.64 (dt, 2H, J1Z10.2 Hz, J2Z2.8 Hz), 3.41 (s,
3H), 2.75 (br, 1H), 2.42–2.20 (m, 3H), 2.06–1.20 (m, 15H),
1.09 (d, 3H, JZ6.8 Hz), 0.87 (d, 3H, JZ6.3 Hz), 0.84 (d,
3H, JZ5.8 Hz); 13C NMR (50 MHz, CDCl3): d 170.5,
140.6, 135.6, 133.6, 120.7, 117.7, 114.9, 97.3, 80.1, 71.0,
55.8, 41.3, 39.7, 39.5, 33.1, 31.3, 30.6, 29.1, 27.4, 23.9,
22.8, 22.1, 21.1, 20.6, 12.7; FT-IR (CCl4): n 3080, 2962,
2823, 2290, 2008, 1836, 1739, 1641, 1558, 1462, 1439,
1417, 1373, 1242, 1151, 1130, 1101, 1044, 940; [a]2D0Z
C9.6 (cZ0.83, EtOAc); HRMS (ESI): m/z: calculated
for C25H43O4: 424.3421 [MCH]C; found: 424.3439
(resolution 10,000).
3.1.12. Acetic acid (Z)-[(4R,4aR,6S,10R,11S,12aR)-11-
hydroxy-4-isopropyl-1,10-dimethyl-3,4,4a,5,6,7,10,11,
12,12a-decahydro-benzocyclodecen-6-yl] ester (18). To a
stirred solution of compound 16 (6.4 mg, 0.017 mmol), in
acetone (390 mL), was added p-TSA monohydrate (8.0 mg,
0.042 mmol). After stirring for 90 h at room temperature,
the reaction mixture was filtered through a plug of silica gel
(eluting with CH2Cl2). Purification by flash chromatography
(n-hexane/EtOAc, 85/15) afforded alcohol 18 (4.4 mg,
78%) as an amorphous white solid. RfZ0.38 (n-hexane/
EtOAc, 85/15); 1H NMR (400 MHz, CDCl3): d 5.64 (dt, 1H,
J1Z11.0 Hz, J2Z4.8 Hz), 5.52 (dd, 1H, J1ZJ2Z11.0 Hz),
5.31 (br, 1H), 5.11–5.04 (m, 1H), 3.92–3.84 (m, 1H), 2.84
(br, 1H), 2.76–2.67 (m, 1H), 2.29–2.22 (m, 1H), 2.07 (s,
3H), 2.03–1.93 (m, 1H), 1.88–1.48 (m, 11H), 1.39 (br, 1H),
1.17 (d, 3H, JZ6.7 Hz), 0.87 (d, 3H, JZ6.8 Hz), 0.78 (d,
3H, JZ6.7 Hz); 13C NMR (50 MHz, CDCl3): d 170.8,
138.4, 133.3, 125.6, 121.3, 76.3, 75.0, 38.4, 38.0, 37.8, 37.0,
35.0, 32.6, 29.7, 27.6, 24.9, 24.4, 21.9, 21.4, 18.5, 15.9;
FT-IR (CCl4): n 3631, 3455, 3015, 2961, 2931, 2847, 2290,
2003, 1847, 1734, 1558, 1452, 1370, 1245, 1218, 1102,
1010; [a]2D0ZC88.4 (cZ0.74, CHCl3).
3.1.10. Acetic acid (Z)-[(4R,4aR,6S,10R,11S,12aR)-4-iso-
propyl-11-methoxymethoxy-1,10-dimethyl-3,4,4a,5,6,
7,10,11,12,12a-decahydro-benzocyclodecen-6-yl] ester
(16). To a stirred solution of diene 13 (35 mg,
0.086 mmol), in degassed CH2Cl2 (8.0 mL), was added a
solution of Grubbs catalyst 15 (4.4 mg, 5.2 mmol) in
degassed CH2Cl2 (650 mL). After stirring for 15 h at room
temperature, the reaction mixture was heated at 40 8C for
7 h. The reaction mixture was treated with DMSO (31 mL)
and stirred for 15 h at room temperature under argon
atmosphere. Purification by flash chromatography (n-hex-
ane/EtOAc, 95/5) afforded compound 16 (25 mg, 78%) as a
colourless oil. RfZ0.77 (n-hexane/EtOAc, 9/1, TLC runs
twice); 1H NMR (400 MHz, CDCl3): d 5.61 (dt, 1H,
J1Z10.8 Hz, J2Z5.0 Hz), 5.52 (dd, 1H, J1Z10.8 Hz,
J2Z10.3 Hz), 5.30 (br, 1H), 5.13–5.05 (m, 1H), 4.73 (d,
1H, JZ6.9 Hz), 4.61 (d, 1H, JZ6.9 Hz), 3.79–3.72 (m,
1H), 3.42 (s, 3H), 2.94–2.84 (m, 1H), 2.70 (ddd, 1H,
J1Z14.8 Hz, J2Z10.3 Hz, J3Z4.0 Hz), 2.24 (dt, 1H,
J1Z14.8 Hz, J2Z4.3 Hz), 2.09–1.50 (m, 15H), 1.38 (br,
1H), 1.15 (d, 3H, JZ6.6 Hz), 0.88 (d, 3H, JZ6.8 Hz),
0.77 (d, 3H, JZ6.7 Hz); 13C NMR (50. MHz, CDCl3): d
170.4, 138.1, 134.1, 124.5, 120.8, 95.9, 81.6, 74.5, 55.8,
38.0, 37.4, 36.6, 34.3, 34.1, 32.1, 29.2, 27.1, 24.5, 24.0,
21.4, 21.0, 18.3, 15.5; FT-IR (CCl4): n 2961, 2931,
2290, 2004, 1847, 1735, 1558, 1464, 1370, 1245, 1218,
1150, 1099, 1042, 1008, 980; [a]2D0ZC102.0 (cZ0.83,
EtOAc); HRMS (ESI): m/z: calculated for C23H38NaO4:
401.2662 [MCNa]C; found: 401.2659 (resolution 10,000).
3.1.13. (E)-3-(1-Methyl-1H-imidazol-4-yl)-acrylic acid
(Z)-[(1R,4aR,6S,7R,11S,12aR)-11-acetoxy-1-isopropyl-
4,7-dimethyl-1,2,4a,5,6,7,10,11,12,12a-decahydro-benzo-
cyclodecen-6-yl] ester (20). To the mixed anhydride 19
(prepared according to Ref. 6b; 155 mg, 0.66 mmol) were
added a solution of alcohol 18 (7.4 mg, 0.022 mmol) in
(CH2Cl)2 (1.3 mL), followed by Et3N (40 mg, 55 mL,
0.40 mmol) and DMAP (2.7 mg, 0.022 mmol). After
stirring for 48 h at room temperature, the solvent was
evaporated under reduced pressure. Purification by flash
chromatography (n-hexane/EtOAc, 2/8) afforded compound
20 (5.6 mg, 54%) as a colourless oil. RfZ0.35 (n-hexane/
3.1.11. Acetic acid (Z)-[(4R,4aR,6R,10R,11S,12aR)-4-iso-
propyl-11-methoxymethoxy-1,10-dimethyl-3,4,4a,5,6,7,
10,11,12,12a-decahydro-benzocyclodecen-6-yl] ester

D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
2133
1
EtOAc, 1/9); H NMR (400 MHz, CDCl3): d 7.55 (d, 1H,
stirred solution of alcohol 28 (598 mg, 1.43 mmol) in
CH2Cl2 (4.0 mL), was added DIPEA (1.5 mL, 8.58 mmol),
TBAI (106 mg, 0.29 mmol) and MOMCl (543 mL,
7.15 mmol). After stirring for 7 h, the reaction mixture
was treated with a saturated NaHCO3 aqueous solution
(10 mL). The organic phase was separated and the aqueous
layer was extracted with CH2Cl2 (3!10 mL). Purification
of the crude by flash chromatography (petroleum ether/
EtOAc, 9/1) afforded compound 29 (628 mg, 95%) as a
colourless oil. RfZ0.28 (basic alumina plate, iPr2O/toluene,
JZ15.6 Hz), 7.47 (s, 1H), 7.09 (s, 1H), 6.58 (d, 1H, JZ
15.6 Hz), 5.67 (dt, 1H, J1Z10.8 Hz, J2Z5.0 Hz), 5.59 (dd,
1H, J1ZJ2Z10.8 Hz), 5.31 (br, 1H), 5.21 (dt, 1H, J1Z
11.5 Hz, J2Z3.0 Hz), 5.15–5.08 (m, 1H), 3.72 (s, 3H),
3.05–2.95 (m, 1H), 2.73 (ddd, 1H, J1Z14.6 Hz, J2Z
10.8 Hz, J3Z4.0 Hz), 2.28 (dt, 1H, J1Z14.6 Hz, J2Z
4.5 Hz), 2.14–1.25 (m, 16H) 1.06 (d, 3H, JZ6.6 Hz), 0.87
(d, 3H, JZ6.8 Hz), 0.78 (d, 3H, JZ6.7 Hz); 13C NMR
(50 MHz, CDCl3): d 170.4, 167.2, 138.6, 137.6, 135.9,
133.6, 125.1, 122.4, 120.8, 116.3, 77.7, 74.3, 37.7, 37.5,
36.5, 33.7, 33.6, 32.0, 27.1, 24.5, 23.9, 22.7, 21.5, 21.0,
17.8, 14.1; FT-IR (CCl4): n 3016, 2961, 2929, 2873, 2856,
2291, 2003, 1847, 1734, 1708, 1645, 1548, 1458, 1387,
1370, 1297, 1245, 1218, 1162, 1103, 1008, 933; [a]2D0Z
C28.9 (cZ0.56, EtOAc); HRMS (ESI): m/z: calculated for
C28H41N2O4: 469.3061 [MCH]C; found: 469.3070
(resolution 10,000).
1
5/95); H NMR (400 MHz, CDCl3): d 6.92–6.75 (m, 4H),
5.91 (ddd, 1H, J1Z17.1 Hz, J2Z10.7 Hz, J3Z6.3 Hz),
5.34–5.22 (m, 3H), 4.86 (s, 3H), 4.67 (br, 1H), 4.33 (d, 1H,
JZ5.3 Hz), 4.22–4.15 (m, 1H), 3.75 (s, 3H), 3.37 (s, 3H),
3.33 (s, 3H), 3.29 (s, 3H), 2.43 (br, 1H), 2.05–1.52 (m, 9H),
0.91 (d, 3H, JZ6.8 Hz), 0.84 (d, 3H, JZ6.8 Hz); 13C NMR
(100 MHz, CDCl3): d 153.7, 152.6, 137.9, 135.1, 120.3,
117.9, 117.3, 114.3, 107.0, 97.8, 83.3, 79.5, 55.6, 55.3, 54.3,
40.3, 36.3, 34.0, 31.8, 26.9, 24.4, 22.2, 21.2, 17.3; FT-IR
(CCl4): n 2932, 2833, 2289, 2007, 1848, 1742, 1544, 1510,
1466, 1442, 1369, 1230, 1153, 1040, 926; [a]2D0ZC59.7
(cZ0.47, EtOAc); HRMS (ESI): calculated for C27H46NO6:
480.3325 [MCNH4]C; found: 480.3318 (resolution
10,000).
3.1.14. (2S,3R)-1-[(1R,5R,6R)-6-Dimethoxymethyl-5-iso-
propyl-2-methyl-cyclohex-2-enyl]-3-(4-methoxy-
phenoxy)-pent-4-en-2-ol (28). To a cold (K60 8C), stirred
solution of 1-allyloxy-4-methoxy-benzene36 (575.5 mg,
3.5 mmol) in THF (27.9 mL), was added sec-butyllithium
(2.5 mL, 3.5 mmol, 1.3 M in cyclohexane). After stirring for
1.5 h, the resulting orange solution (colour is important) was
transferred, via cannula, to a cold (K78 8C) suspension of
(S,S)-411 (3.5 mmol, based on the amount of CpTiCl3) in
Et2O (25.0 mL). The reaction mixture was stirred for 3 h
(colour changed from yellow to orange and finally dark
brown), and then was treated with a solution of aldehyde 3
(495 mg, 1.95 mmol) in THF (5.0 mL). After 16 h, the
reaction mixture was warmed to 0 8C and then stirred for
8 h. The mixture was then treated with a NH4F aqueous
solution (45%, 100 mL) and stirred for further 16 h. After
filtration through a pad of Celitew the organic phase was
separated and the aqueous layer was extracted with iPr2O
(3!50 mL). Purification of the crude by flash chromato-
graphy on silica gel (petroleum ether/EtOAc, 9/1) gave a
white foam (2.0 g) which was subjected to crystallization of
Taddol from CCl4. The solid was accurately washed and the
mother liquors combined and concentrated, affording
compound 28 (809 mg, impure of Taddol). A second
purification by flash chromatography on basic alumina
(toluene/CH2Cl2, 95/5) finally afforded pure 28 (598 mg,
73%) as colourless oil. RfZ0.40 (basic alumina plate,
toluene/CH2Cl2, 95/5); 1H NMR (200 MHz, CDCl3): d
6.94–6.75 (m, 4H), 6.04–5.79 (m, 1H), 5.44–5.21 (m, 3H),
4.50–4.36 (m, 2H), 4.28–4.03 (m, 1H), 3.75 (s, 3H), 3.35 (s,
6H), 2.88 (d, 1H, JZ4.5 Hz), 2.61–2.47 (m, 1H), 2.17–1.49
(m, 10H), 0.93 (d, 3H, JZ6.3 Hz), 0.84 (d, 3H, JZ6.3 Hz);
13C NMR (50.3 MHz, CDCl3): d 153.9, 152.3, 136.4, 134.6,
121.4, 118.5, 117.4, 114.4, 106.9, 83.9, 70.5, 55.6, 55.3,
39.9, 36.0, 34.4, 32.4, 27.0, 24.4, 22.1, 21.0, 17.2; FT-IR
(CCl4): n 3602, 3468, 2960, 2834, 2289, 1848, 1730, 1558,
1504, 1465, 1386, 1227, 1111, 929; [a]2D0ZC51.8 (cZ
0.48, EtOAc); HRMS (ESI): calculated for C25H42NO5:
436.3063 [MCNH4]C; found: 436.3066 (resolution
10,000).
3.1.16. (1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-methoxy-
methoxy-3-(4-methoxy-phenoxy)-pent-4-enyl]-3-methyl-
cyclohex-3-enecarbaldehyde (30). To a stirred solution of
compound 29 (602 mg, 1.30 mmol) in CH3CN/H2O
(7.6 mL, v/v: 98/2), was added LiBF4 (122 mg,
1.30 mmol). After stirring for 6 h, the reaction mixture
was treated with a saturated NaHCO3 aqueous solution
(15 mL) and CH2Cl2 (10 mL). The organic phase was
separated and the aqueous layer was extracted with CH2Cl2
(3!10 mL) to give crude 30 (540 mg), which was used
without further purification. Purification of the crude by
flash chromatography (petroleum ether/EtOAc, 9/1), for
analytical purposes, afforded pure 30 as a colourless oil.
RfZ0.47 (petroleum ether/EtOAc, 8/2); 1H NMR
(200 MHz, CDCl3): d 9.81 (d, 1H, JZ3.9 Hz), 6.92–6.70
(m, 4H), 5.90–5.70 (m, 1H), 5.49–5.19 (m, 3H), 4.85–4.62
(m, 3H), 3.75 (s, 3H), 3.65 (dt, 1H, J1Z9.5 Hz, J2Z3.8 Hz),
3.31 (s, 3H), 2.72–2.45 (m, 2H) 2.15–1.65 (m, 9H), 0.94 (d,
3H, JZ6.4 Hz), 0.84 (d, 3H, JZ6.4 Hz); 13C NMR
(50 MHz, CDCl3): d 206.9, 135.7, 134.4, 121.5, 118.8,
117.0, 114.4, 97.4, 81.9, 79.0, 55.6, 51.8, 37.5, 34.0, 30.1,
28.1, 24.2, 21.7, 20.7, 18.2; FT-IR (CCl4): n 2962, 2290,
1719, 1558, 1508, 1261, 1225, 1103, 1008, 980, 823;
[a]2D0ZC36.6 (cZ0.13, EtOAc); HRMS (ESI): calculated
for C25H40NO5: 434.2906 [MCNH4]C; found: 434.2914
(resolution 10,000).
3.1.17. {(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-methoxy-
methoxy-3-(4-methoxy-phenoxy)-pent-4-enyl]-3-methyl-
cyclohex-3-enyl}-methanol (31). To a stirred solution of
crude 30, in EtOH (13.6 mL), was added NaBH4 (74 mg,
1.95 mmol). After stirring for 20 min, the reaction mixture
was treated with solid NH4Cl (696 mg, 13.0 mmol), stirred
for further 30 min, diluted with iPr2O and dried over
Na2SO4. Purification by flash chromatography (petroleum
ether/EtOAc, 8/2) afforded compound 31 (408 mg, 75%,
over two steps) as a colourless oil. RfZ0.15 (petroleum ether/
EtOAc, 8/2); 1H NMR (200 MHz, CDCl3): d 6.88–6.75 (m,
3.1.15. 1-{(R)-1-[(S)-2-((1R,5R,6R)-6-Dimethoxymethyl-
5-isopropyl-2-methyl-cyclohex-2-enyl)-1-methoxy-
methoxy-ethyl]-allyloxy}-4-methoxy-benzene (29). To a

2134
D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
4H), 5.91 (ddd, 1H, J1Z16.8 Hz, J2Z10.2 Hz, J3Z6.3 Hz),
5.33–5.27 (m, 3H), 4.88 (d, 1H, JZ6.8 Hz), 4.76 (d, 1H, JZ
6.8 Hz), 4.67–4.61 (m, 1H), 3.93 (dt, 1H, J1Z9.6 Hz, J2Z
3.3 Hz), 3.82–3.71 (m, 4H), 3.63–3.54 (m, 1H), 3.39 (s, 3H),
2.43 (br, 1H), 2.07 (br, 1H), 2.00–1.47 (m, 10H), 0.91 (d,
3H, JZ6.8 Hz), 0.84 (d, 3H, JZ6.8 Hz); 13C NMR
(100 MHz, CDCl3): d 154.3, 152.1, 137.1, 134.8, 121.0,
118.8, 117.2, 114.4, 97.6, 82.7, 79.8, 62.0, 56.0, 55.6, 41.3,
36.3, 34.2, 30.9, 27.0, 24.2, 22.2, 21.0, 16.6; FT-IR (CCl4): n
3514, 2961, 2933, 2896, 2290, 2003, 1857, 1544, 1507, 1259,
1228, 1105, 1041, 1008, 930; [a]2D0ZC61.2 (cZ0.57,
EtOAc); HRMS (ESI): calculated for C25H42NO5: 436.3063
[MCNH4]C; found: 436.3060 (resolution 10,000).
1182, 1152, 1106, 1066, 1041, 1006, 980; [a]2D0ZC23.9
(cZ1.02, EtOAc); HRMS (ESI): calculated for C26H38NO4:
428.2801 [MCH]C; found: 428.2811 (resolution 10,000).
3.1.20. {(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-methoxy-
methoxy-3-(4-methoxy-phenoxy)-pent-4-enyl]-3-methyl-
cyclohex-3-enyl}-acetaldehyde (34). To a cold (K78 8C),
stirred solution of compound 33 (67 mg, 0.16 mmol) in
toluene/n-hexane (2.55 mL, v/v: 1/2), was added DIBAL-H
(1.5 M in toluene, 1.1 mL, 1.56 mmol). After stirring for
1 h, the reaction mixture was treated with EtOAc (1.3 mL)
and an aqueous tartaric acid solution (1.0 M, 1.3 mL), then
warmed to room temperature and stirred for further 1 h. The
organic phase was separated and the aqueous layer was
extracted with CH2Cl2 (5!5 mL). The organic extracts
were washed with a saturated NaHCO3 aqueous solution
(2!5 mL) to give crude 34 (68 mg), which was used
without further purification. Purification of the crude by
flash chromatography (petroleum ether/EtOAc, 14/1), for
analytical purposes, afforded pure 34 (67 mg, quant.) as a
3.1.18. Methanesulfonic acid (1R,2R,6R)-6-isopropyl-2-
[(2S,3R)-2-methoxymethoxy-3-(4-methoxy-phenoxy)-
pent-4-enyl]-3-methyl-cyclohex-3-enylmethyl ester (32).
To a cold (0 8C), stirred solution of alcohol 31 (367 mg,
0.88 mmol) in CH2Cl2 (7.0 mL), was added TEA (367 mL,
2.63 mmol) followed by MsCl (102 mL, 1.30 mmol). After
1 h, the reaction mixture was warmed to room temperature
and stirred for 2 h. The solution was concentrated under
reduced pressure and filtered through a plug of silica gel.
Purification of the crude by flash chromatography
(petroleum ether/EtOAc, 8/2) afforded mesylate 32
(414 mg, 95%) as a colourless oil. RfZ0.20 (petroleum
1
colourless oil. RfZ0.39 (petroleum ether/EtOAc, 8/2); H
NMR (400 MHz, CDCl3): d 9.79 (t, 1H, JZ2.2 Hz), 6.89–
6.74 (m, 4H), 5.87 (ddd, 1H, J1Z17.1 Hz, J2Z10.7 Hz,
J3Z6.0 Hz), 5.38–5.24 (m, 3H), 4.86–4.70 (m, 3H), 3.80–
3.67 (m, 4H), 3.31 (s, 3H), 2.53–2.29 (m, 4H), 2.07–1.85
(m, 3H), 1.73–1.60 (m, 4H), 1.60–1.46 (m, 1H), 1.35–1.23
(m, 1H), 0.95 (d, 3H, JZ6.7 Hz), 0.84 (d, 3H, JZ6.7 Hz);
13C NMR (100 MHz, CDCl3): d 203.2, 154.0, 152.2, 135.8,
134.9, 121.0, 118.7, 117.1, 114.4, 99.6, 82.1, 79.3, 55.8,
55.6, 43.3, 40.1, 34.7, 32.5, 29.8, 27.5, 23.9, 22.1, 20.8,
19.0; FT-IR (CCl4): n 2961, 2910, 2834, 2713, 2003, 1857,
1727, 1559, 1507, 1466, 1442, 1388, 1370, 1259, 1226, 1152,
1105, 1068, 1042, 1008, 980; [a]2D0ZC27.6 (cZ0.46,
EtOAc); HRMS (ESI): calculated for C26H38O5: 448.3063
[MCNH4]C; found: 448.3048 (resolution 10,000).
1
ether/EtOAc, 8/2); H NMR (200 MHz, CDCl3): d 6.89–
6.76 (m, 4H), 5.87 (ddd, 1H, J1Z16.2 Hz, J2Z10.4 Hz,
J3Z5.8 Hz), 5.37–5.29 (m, 3H), 4.85 (d, 1H, JZ6.9 Hz),
4.78–4.70 (m, 2H), 4.34–4.13 (m, 2H), 3.85 (dt, J1Z
10.4 Hz, J2Z2.6 Hz, 1H), 3.75 (s, 3H), 3.33 (s, 3H), 3.01 (s,
3H), 2.47 (br, 1H), 2.27–2.13 (m, 1H), 2.07–1.50 (m, 9H),
0.92 (d, 3H, JZ6.9 Hz), 0.89 (d, 3H, JZ6.9 Hz); 13C NMR
(100 MHz, CDCl3): d 154.0, 152.2, 135.8, 134.8, 120.9,
118.7, 117.1 (2C), 114.4 (2C), 97.5, 82.2, 79.1, 69.4, 55.8,
55.6, 37.7, 37.3, 37.1, 33.8, 30.0, 27.2, 23.9, 22.0, 20.7,
18.1; FT-IR (CCl4): n 2962, 2898, 2291, 2004, 1857, 1742,
1544, 1507, 1370, 1345, 1229, 1178, 1106, 1041, 1007, 979;
[a]2D0ZC64.0 (cZ0.48, EtOAc); HRMS (ESI): calculated
for C26H44NO7S: 514.2839 [MCNH4]C; found: 514.2831
(resolution 10,000).
3.1.21. (S)-1-{(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-
methoxymethoxy-3-(4-methoxy-phenoxy)-pent-4-enyl]-
3-methyl-cyclohex-3-enyl}-pent-4-en-2-ol (35). To a cold
(0 8C), stirred solution of AllMgBr (1.0 M in Et2O, 3.8 mL,
3.80 mmol) was added dIpc2BOMe13c (1.0 M in THF,
4.2 mL, 4.18 mmol). The reaction mixture was warmed to
room temperature and stirred for 1 h, cooled to K78 8C and
treated with a solution of aldehyde 34 (545 mg, 1.27 mmol)
in THF (10.0 mL). After stirring for 48 h, the reaction
mixture was warmed to 0 8C and treated with a NaOH
aqueous solution (6.0 M, 6.4 mL) and H2O2 (35%, 4.4 mL).
After 3 h at room temperature, the mixture was heated to
50 8C and stirred for further 2 h. The organic phase was
separated and the aqueous layer was extracted with EtOAc
(3!10 mL). Purification of the crude by flash chromato-
graphy (petroleum ether/EtOAc, 85/15) afforded compound
35 (420 mg, 70%) as a colourless oil. For characterization
and analytical data, see below.
3.1.19. {(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-methoxy-
methoxy-3-(4-methoxy-phenoxy)-pent-4-enyl]-3-methyl-
cyclohex-3-enyl}-acetonitrile (33). To a stirred solution of
mesylate 32 (410 mg, 0.83 mmol) in CH3CN (8.0 mL), was
added 18-crown-6 (1.09 g, 4.13 mmol) and KCN (269 mg,
4.13 mmol). After stirring for 2.5 h at 80 8C, the red solution
was diluted with CH2Cl2 and filtered through a plug of silica
gel. Purification of the crude by flash chromatography
(petroleum ether/EtOAc, 9/1) afforded compound 33
(353 mg, quant.) as a colourless oil. RfZ0.31 (petroleum
1
ether/EtOAc, 8/2); H NMR (200 MHz, CDCl3): d 6.92–
6.75 (m, 4H), 5.87 (ddd, 1H, J1Z16.3 Hz, J2Z10.4 Hz,
J3Z5.9 Hz), 5.43–5.30 (m, 3H), 4.88–4.75 (m, 3H), 3.80–
3.69 (m, 4H), 3.32 (s, 3H), 2.53 (br, 1H), 2.41–2.30 (m, 2H),
2.30–2.12 (m, 1H), 2.12–1.88 (m, 3H), 1.77–1.40 (m, 6H),
0.93 (d, 3H, JZ6.3 Hz), 0.89 (d, 3H, JZ6.3 Hz); 13C NMR
(50 MHz, CDCl3): d 153.9, 152.0, 134.8, 134.7, 121.0,
119.8, 119.0, 117.0, 114.4, 97.7, 81.7, 79.2, 55.8, 55.6, 39.7,
34.4, 29.4, 27.3, 26.5, 23.6, 22.0, 20.5, 19.2, 17.3; FT-IR
(CCl4): n 2961, 2934, 2896, 2847, 2834, 2290, 2003, 1857,
1558, 1507, 1465, 1441, 1427, 1388, 1370, 1250, 1228,
3.1.22. (S)-1-{(1R,2R,6R)-6-Isopropyl-2-[(2S,3R)-2-
methoxymethoxy-3-(4-methoxy-phenoxy)-pent-4-enyl]-
3-methyl-cyclohex-3-enyl}-pent-4-en-2-ol (35). To a cold
(0 8C), stirred suspension of (R,R)-411 (0.53 mmol, based on
the amount of CpTiCl3) in Et2O (6.0 mL), was added a
solution of AllMgBr (1.0 M in Et2O, 444 mL, 0.44 mmol).
After stirring the brown-green solution for 1.5 h, the
reaction mixture was cooled to K78 8C. To this solution

D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
2135
was added, via cannula, a solution of aldehyde 34 (96 mg,
0.22 mmol) in Et2O (2.0 mL). The reaction mixture was
stirred for 3 h, treated with a NH4F aqueous solution (45%,
5 mL) and stirred for further 15 h at room temperature. The
organic phase was separated and the aqueous layer was
extracted with iPr2O (3!10 mL). Purification of the crude
by flash chromatography (petroleum ether/EtOAc, 85/15)
afforded compound 35 (92 mg, 87%) as a colourless oil.
RfZ0.38 (petroleum ether/EtOAc, 8/2); 1H NMR
(400 MHz, CDCl3): d 6.90–6.78 (m, 4H), 5.96–5.79 (m,
2H), 5.39–5.30 (m, 3H), 5.20–5.11 (m, 2H), 4.87 (d, 1H, JZ
6.8 Hz), 4.77 (d, 1H, JZ6.8 Hz), 4.75–4.70 (m, 1H), 3.89–
3.73 (m, 5H), 3.36 (s, 3H), 2.42–2.25 (m, 2H), 2.17–1.99
(m, 2H), 1.99–1.67 (m, 7H), 1.67–1.48 (m, 3H), 1.43–1.25
(m, 2H), 0.93 (d, 3H, JZ6.7 Hz), 0.85 (d, 3H, JZ6.6 Hz);
13C NMR (50 MHz, CDCl3): d 153.9, 152.2, 136.5, 134.9,
134.7, 121.0, 118.7, 118.4, 117.2, 114.4, 97.4, 82.5, 79.4, 68.3,
55.8, 55.6, 42.2, 38.8, 34.7, 34.3, 34.1, 30.4, 27.2, 24.2, 22.5,
20.9, 18.0; FT-IR (CCl4): n 3585, 3403, 3028, 2961, 2290,
2004, 1855, 1548, 1506, 1465, 1441, 1386, 1368, 1260, 1227,
1150, 1103, 1010, 927; [a]2D0ZC77.0 (cZ1.04, EtOAc);
HRMS (ESI): calculated for C29H44NaO5: 495.30809 [MC
Na]C; found: 495.30596 (resolution 23,400).
(CCl4): n 3400, 3072, 2963, 2905, 2290, 2001, 1854, 1558,
1442, 1413, 1296, 1219, 1018, 823; [a]2D0ZC30.1 (cZ0.77,
EtOAc).
3.1.25. 2,2-Dimethyl-propionic acid (1S,2R)-1-
{(1R,5R,6R)-6-[(S)-2-(tert-butyl-diphenyl-silanyloxy)-
pent-4-enyl]-5-isopropyl-2-methyl-cyclohex-2-enyl-
methyl}-2-(4-methoxy-benzyl)-but-3-enyl ester (38). To a
stirred solution of compound 37 (87 mg, 0.13 mmol),
pyridine (1.0 mL) and DMAP (3.2 mg, 0.026 mmol) in
CH2Cl2 (2.0 mL), was added PivCl (32 mL, 0.26 mmol).
After stirring for 16 h at 40 8C, the reaction mixture was
treated with a saturated NH4Cl aqueous solution (5.0 mL).
The organic phase was separated and the aqueous layer was
extracted with EtOAc (3!5 mL). The combined organic
extracts were washed with water and brine. Purification of
the crude by flash chromatography (petroleum ether/EtOAc,
9/1) afforded compound 38 (65 mg, 66%) as a colourless oil.
RfZ0.45 (petroleum ether/EtOAc, 8/2); 1H NMR
(400 MHz, CDCl3): d 7.76–7.64 (m, 4H), 7.48–7.31 (m,
6H), 6.90–6.76 (m, 4H), 6.08–5.96 (m, 1H), 5.85 (ddd, 1H,
J1Z17.1 Hz, J2Z10.6 Hz, J3Z6.4 Hz), 5.41–5.32 (m, 2H),
5.19–5.03 (m, 3H), 4.56 (dd, 1H, J1ZJ2Z5.3 Hz), 3.94 (br,
1H), 3.77 (s, 3H), 2.37–2.27 (m, 1H), 2.21–2.11 (m, 1H),
2.06–1.97 (m, 1H), 1.96–1.84 (m, 1H), 1.75–1.41 (m, 6H),
1.41–1.26 (m, 3H), 1.13 (s, 9H), 1.07 (s, 9H), 0.79 (d, 3H,
JZ7.1 Hz), 0.77 (d, 3H, JZ6.8 Hz); [a]2D0ZC6.0 (cZ
0.95, EtOAc); HRMS (ESI): calculated for C48H67O5Si:
751.4758 [MCH]C; found: 751.4761 (resolution 12,000).
3.1.23. tert-Butyl-((S)-1-{(1R,2R,6R)-6-isopropyl-2-
[(2S,3R)-2-methoxymethoxy-3-(4-methoxy-phenoxy)-
pent-4-enyl]-3-methyl-cyclohex-3-enylmethyl}-but-3-
enyloxy)-diphenyl-silane (36). To a stirred solution of
alcohol 35 (500 mg, 1.06 mmol) in CH2Cl2 (12.0 mL), was
added imidazole (360 mg, 5.29 mmol) followed by
TBDPSCl (581 mg, 2.11 mmol). After stirring for 16 h at
room temperature, the solvent was removed under reduced
pressure and the crude was purified by flash chromato-
graphy (petroleum ether/EtOAc, 25/1) to give compound 36
(677 mg, 90%) as a colourless oil. RfZ0.59 (petroleum
ether/EtOAc, 8/2); HRMS (ESI): calculated for
C45H66NO5Si: 728.4710 [MCNH4]C; found: 728.4700
(resolution 10,000).
3.1.26. 2,2-Dimethyl-propionic acid (1S,2R)-1-((1R,
5R,6R)-6-[(S)-2-(tert-butyl-diphenyl-silanyloxy)-pent-4-
enyl]-5-isopropyl-2-methyl-cyclohex-2-enylmethyl)-2-
hydroxy-but-3-enyl ester (39). To a cold (0 8C), stirred
solution of compound 38 (20 mg, 0.03 mmol) in CH3CN/
H2O (328 mL, v/v: 4/1), was added ceric ammonium nitrate
(36 mg, 0.07 mmol).38 After stirring for 1 h, the reaction
mixture was filtered through a plug of silica (eluting with
EtOAc). Purification of the crude by flash chromatography
(toluene/iPr2O, 95/5) afforded 39 (11 mg, 67%) as a
colourless oil. RfZ0.31 (toluene/iPr2O, 95/5); 1H NMR
(200 MHz, CDCl3): d 7.74–7.65 (m, 4H), 7.47–7.32 (m,
6H), 6.07–5.72 (m, 2H), 5.38–4.84 (m, 6H), 4.14 (br, 1H),
3.88 (br, 1H), 2.40–1.80 (m, 4H), 1.73–1.05 (m, 29H), 0.78
(d, 3H, JZ6.7 Hz), 0.76 (d, 3H, JZ6.5 Hz).
3.1.24. (2S,3R)-1-{(1R,5R,6R)-6-[(S)-2-(tert-Butyl-di-
phenyl-silanyloxy)-pent-4-enyl]-5-isopropyl-2-methyl-
cyclohex-2-enyl}-3-(4-methoxy-phenoxy)-pent-4-en-2-ol
(37). To a cold (K20 8C), stirred solution of compound 36
(520 mg, 0.73 mmol) in CH2Cl2 (22.0 mL), was added
Me2S (209 mg, 3.36 mmol) and BF3$OEt2 (550 mg,
3.88 mmol).37 After 30 min (time control is essential), the
reaction mixture was treated with a saturated NaHCO3
aqueous solution (4.0 mL) and warmed to room temperature
under vigorous stirring. The organic phase was separated
and the aqueous layer was extracted with CH2Cl2 (3!
5 mL). Purification of the crude by flash chromatography
(toluene/iPr2O, 8/2) afforded compound 37 (219 mg, 45%)
as a colourless oil. RfZ0.31 (toluene/iPr2O, 8/2); 1H NMR
(400 MHz, CDCl3): d 7.74–7.69 (m, 4H), 7.47–7.35 (m,
6H), 6.91–6.81 (m, 4H), 5.94–5.81 (m, 2H), 5.39–5.29 (m,
2H), 5.17 (br, 1H), 5.01–4.94 (m, 2H), 4.38 (dd, 1H, J1Z
6.7 Hz, J2Z4.1 Hz), 3.92–3.78 (m, 5H), 2.33–2.24 (m, 2H),
2.20–2.12 (m, 1H), 2.01–1.84 (m, 2H), 1.70–1.32 (m, 9H),
1.07 (s, 9H), 0.88 (d, 3H, JZ6.7 Hz), 0.80 (d, 3H, JZ
6.5 Hz); 13C NMR (100 MHz, CDCl3): d 154.1, 152.0, 136.0,
135.6, 135.3, 135.0, 134.6, 134.3, 129.5, 127.5, 121.1, 119.5,
117.4, 117.1, 114.5, 83.8, 70.9, 70.6, 55.7, 40.9, 38.8, 34.2,
33.4, 32.3, 31.2, 27.3, 27.0, 23.9, 22.3, 20.7, 19.4; FT-IR
3.1.27. 2,2-Dimethyl-propionic acid (Z)-(1R,4aR,
6S,7R,11S,12aR)-11-(tert-butyl-diphenylsilanyloxy)-7-
hydroxy-1-isopropyl-4-methyl-1,2,4a,5,6,7,10,11,12,12a-
decahydro-benzocyclodecen-6-yl ester (40). To a stirred
solution of diene 39 (11 mg, 0.017 mmol) in degassed
CH2Cl2 (2.1 mL), was slowly added a solution of Grubbs
catalyst 15 (1.5 mg, 0.002 mmol) in CH2Cl2 (166 mL) and
stirred for 24 h. Purification of the crude by flash
chromatography (petroleum ether/EtOAc, 9/1) afforded 40
(2.2 mg, 21%) as a colourless oil. For characterization and
analytical data, see below.
3.1.28. 2,2-Dimethyl-propionic acid (Z)-(1R,4aR,6S,
7R,11S,12aR)-11-(tert-butyl-diphenyl-silanyloxy)-1-iso-
propyl-7-(4-methoxy-phenoxy)-4-methyl-1,2,4a,5,6,7,
10,11,12,12a-decahydro-benzocyclodecen-6-yl ester (41).
To stirred a solution of diene 38 (50 mg, 0.066 mmol) in

2136
D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
CH2Cl2 (5.5 mL), was added, via syringe pump (during
45 min), a freshly prepared solution of Grubbs catalyst 15
(5.7 mg, 0.0066 mmol) in CH2Cl2 (0.5 mL). After stirring
for 15 h, the reaction mixture was heated to 40 8C for 24 h.
Purification of the crude by flash chromatography
(petroleum ether/CH2Cl2, 4/6) afforded the starting material
38 (7.7 mg) and the RCM product 41 (25 mg, 52%; 62%
considering the recovered starting material) as a colourless
oil. RfZ0.50 (petroleum ether/EtOAc, 9/1); 1H NMR
(400 MHz, CDCl3): d 7.74–7.63 (m, 4H), 7.51–7.33 (m,
6H), 6.80–6.63 (m, 4H), 6.12 (dt, 1H, J1Z11.0 Hz, J2Z
5.3 Hz), 5.71 (dd, 1H, J1Z11.0 Hz, J2Z9.6 Hz), 5.44 (dt,
1H, J1Z10.6 Hz, J2Z3.5 Hz), 5.23 (br, 1H), 4.97 (dd, 1H,
J1Z9.6 Hz, J2Z2.7 Hz), 4.01 (br, 1H), 3.76 (s, 3H), 2.64–
2.54 (m, 1H), 2.43–2.34 (m, 1H), 1.87–1.59 (m, 10H), 1.52–
1.35 (m, 2H), 1.26 (s, 9H), 1.17–1.08 (m, 10H), 0.81 (d, 3H,
JZ6.8 Hz), 0.55 (d, 3H, JZ6.7 Hz); 13C NMR (100 MHz,
CDCl3): d 177.8, 153.9, 151.6, 137.2, 135.9, 134.1, 133.9,
130.6, 129.7, 127.6, 121.0, 117.1, 114.4, 74.9, 74.1, 72.8,
55.6, 39.0, 37.6, 37.3, 36.2, 36.1, 33.2, 31.8, 27.2, 27.0,
26.9, 24.3, 23.8, 21.0, 19.2, 15.7; FT-IR (CCl4): n 3072,
2962, 2932, 2859, 2291, 2003, 1847, 1730, 1551, 1507,
1480, 1463, 1442, 1428, 1389, 1367, 1260, 1229, 1158,
1106, 1065, 1008, 980; [a]2D0ZC137.7 (cZ0.74, EtOAc);
HRMS (ESI): calculated for C39H55O3Si: 599.3921 [M-
PMPOHCH]C; found: 599.3918 (resolution 10,000).
0.0018 mmol) in benzene (0.14 mL). After 19 h at 80 8C,
the reaction mixture was cooled at room temperature,
treated with DMSO (5 mL) and stirred for 12 h. Purification
of the crude by flash chromatography (petroleum ether/
EtOAc, 9/1) afforded compound 42 (9.2 mg, 80%) as a
1
colourless oil. RfZ0.78 (petroleum ether/EtOAc, 8/2); H
NMR (400 MHz, CDCl3): d 7.72–7.66 (m, 4H), 7.48–7.33
(m, 6H), 6.79 (s, 4H), 6.11 (dt, 1H, J1Z11.4 Hz, J2Z
5.1 Hz), 5.74 (dd, 1H, J1Z11.4 Hz, J2Z9.9 Hz), 5.23 (br,
1H), 4.90 (dd, 1H, J1Z9.9 Hz, J2Z2.6 Hz), 4.32–4.21 (m,
1H), 4.04–3.96 (m, 1H), 3.78 (s, 3H), 2.75 (s, 1H), 2.60–
2.50 (m, 1H), 2.41–2.29 (m, 1H), 1.92–1.73 (m, 3H), 1.73–
1.53 (m, 8H), 1.42–1.31 (m, 1H), 1.21–1.03 (m, 10H), 0.80
(d, 3H, JZ6.8 Hz), 0.57 (d, 3H, JZ6.7 Hz); 13C NMR
(100 MHz, CDCl3): d 154.3, 151.3, 137.2, 135.9, 134.2,
134.1, 130.8, 129.6, 127.6, 127.5, 127.0, 121.1, 117.3,
114.6, 77.6, 73.5, 72.6, 55.6, 38.0, 37.0, 35.9, 35.7, 33.3,
33.0, 27.2, 27.0, 24.3, 23.9, 19.2, 16.5, 14.0; FT-IR (CCl4): n
3400, 3072, 2962, 2859, 2290, 2003, 1852, 1742, 1558,
1428, 1389, 1258, 1219, 1105, 1066, 1007, 980; [a]2D0Z
C94.0 (cZ0.92, EtOAc); HRMS (ESI): calculated for
C41H54NaO4Si: 661.36835 [MCNa]C; found: 661.36917
(resolution 17,600).
3.1.31. (E)-3-(1-Methyl-1H-imidazol-4-yl)-acrylic acid
(Z)-(1R,4aR,6S,7R,11S,12aR)-11-(tert-butyl-diphenyl-
silanyloxy)-1-isopropyl-7-(4-methoxy-phenoxy)-4-
methyl-1,2,4a,5,6,7,10,11,12,12a-decahydro-benzocyclo-
decen-6-yl ester (43). To a stirred suspension of the mixed
anhydride 19 (prepared according to Ref. 6b, 102 mg,
0.43 mmol) and of alcohol 42 (9.2 mg, 0.014 mmol) in
(CH2Cl)2 (0.9 mL), was added DMAP (1.8 mg,
0.014 mmol) followed by TEA (40 mL, 0.29 mmol). After
stirring for 1 h, the suspension (slightly more soluble) was
heated to 80 8C for 2 h, cooled to room temperature
overnight and heated to 80 8C for further 4 h. Purification
by flash chromatography (petroleum ether/EtOAc, 1/9)
afforded compound 43 (9.2 mg, 82%) as a clear yellowish
oil. RfZ0.3 (petroleum ether/EtOAc, 2/8); 1H NMR
(400 MHz, CDCl3): d 7.73–7.64 (m, 4H), 7.58 (d, 1H, JZ
15.7 Hz), 7.52 (s, 1H), 7.48–7.32 (m, 6H), 7.10 (s, 1H),
6.78–6.67 (m, 4H), 6.61 (d, 1H, JZ15.7 Hz), 6.14 (dt, 1H,
J1Z11.1 Hz, J2Z5.1 Hz), 5.81 (dd, 1H, J1Z11.1 Hz, J2Z
10.5 Hz), 5.62–5.52 (m, 1H), 5.22 (br, 1H), 5.05–4.96 (m,
1H), 4.01 (br, 1H), 3.75 (s, 3H), 3.73 (s, 3H), 2.66–2.54 (m,
1H), 2.44–2.33 (m, 1H), 1.91–1.02 (m, 22H), 0.78 (d, 3H,
JZ6.7 Hz), 0.54 (d, 3H, JZ6.7 Hz); 13C NMR (50 MHz,
CDCl3): d 166.9, 154.1, 151.8, 138.6, 137.0, 136.0, 135.9,
134.2, 134.0, 130.4, 129.6, 127.7, 127.6, 127.5, 122.2,
121.0, 117.7, 116.5, 114.4, 75.4, 74.3, 72.7, 55.6, 37.9, 37.1,
36.1, 36.0, 33.6, 33.1, 32.0, 27.0, 26.5, 24.3, 23.7, 21.0,
19.3, 16.1; FT-IR (CCl4): n 2963, 2291, 2002, 1847, 1709,
1646, 1558, 1413, 1260, 1219, 1160, 1099, 1012; [a]2D0Z
C71.6 (cZ0.92, EtOAc); HRMS (ESI): calculated for
C48H61N2O5Si: 773.43443 [MCH]C; found: 773.43474
(resolution 15,100); calculated for C48H60N2NaO5Si:
795.41637 [MCNa]C; found: 795.41775 (resolution
15,100).
3.1.29. 2,2-Dimethyl-propionic acid (Z)-(1R,4aR,6S,
7R,11S,12aR)-11-(tert-butyl-diphenylsilanyloxy)-7-
hydroxy-1-isopropyl-4-methyl-1,2,4a,5,6,7,10,11,12,12a-
decahydro-benzocyclodecen-6-yl ester (40). To a cold
(0 8C), stirred solution of compound 41 (22 mg, 0.03 mmol)
in CH3CN/H2O (1.0 mL, v/v: 4/1), was added ceric
ammonium nitrate (35 mg, 0.064 mmol) in one portion.38
After 15 min, the reaction mixture was diluted with CH3CN
and filtered through a plug of silica gel. Purification of
the crude by flash chromatography (petroleum ether/EtOAc,
8/2) afforded compound 40 (14.8 mg, 80%) as a colourless
oil. RfZ0.45 (petroleum ether/EtOAc, 8/2); 1H NMR
(400 MHz, CDCl3): d 7.74–7.61 (m, 4H), 7.49–7.35 (m,
6H), 6.01 (dt, 1H, J1Z11.1 Hz, J2Z5.2 Hz), 5.62 (dd, 1H,
J1Z11.1 Hz, J2Z9.6 Hz), 5.27–5.17 (m, 2H), 4.60 (dd, 1H,
J1Z9.6 Hz, J2Z2.9 Hz), 3.93 (br, 1H), 2.53–2.42 (m, 1H),
2.32–2.23 (m, 1H), 1.92–1.58 (m, 9H), 1.53–1.32 (m, 2H),
1.31–1.20 (m, 10H), 1.09 (s, 9H), 0.81 (d, 3H, JZ6.8 Hz),
0.58 (d, 3H, JZ6.6 Hz); 13C NMR (100 MHz, CDCl3): d
178.6, 137.0, 135.9, 135.8, 134.3, 134.1, 129.6, 129.2,
129.1, 127.6, 127.5, 121.4, 76.6, 72.7, 68.5, 39.0, 37.9, 37.0,
35.9, 35.6, 32.9, 31.8, 27.2, 27.0, 24.3, 23.7, 21.0, 19.2,
16.2; FT-IR (CCl4): n 3448, 3072, 3051, 2962, 2931, 2859,
2291, 2003, 1847, 1731, 1558, 1480, 1462, 1428, 1389,
1368, 1262, 1218, 1156, 1104, 1009, 980; [a]2D0ZC71.3
(cZ0.94, EtOAc); HRMS (ESI): calculated for C39H56-
NaO4Si: 639.38400 [MCNa]C; found: 639.38421
(resolution 17,000).
3.1.30. (Z)-(1R,4aR,6S,7R,11S,12aR)-11-(tert-Butyl-
diphenyl-silanyloxy)-1-isopropyl-7-(4-methoxy-
phenoxy)-4-methyl-1,2,4a,5,6,7,10,11,12,12a-decahydro-
benzocyclodecen-6-ol (42). To a stirred solution of
compound 37 (12 mg, 0.018 mmol) in degassed benzene
(1.66 mL), was added, via syringe pump (during 30 min), a
freshly prepared solution of Grubbs catalyst 15 (1.5 mg,
3.1.32. (E)-3-(1-Methyl-1H-imidazol-4-yl)-acrylic acid
(Z)-(1R,4aR,6S,7R,11S,12aR)-11-hydroxy-1-isopropyl-7-
(4-methoxy-phenoxy)-4-methyl-1,2,4a,5,6,7,10,11,12,
12a-decahydro-benzocyclodecen-6-yl ester (44). To a

D. Castoldi et al. / Tetrahedron 61 (2005) 2123–2139
2137
stirred solution of compound 43 (10 mg, 0.013 mmol) in
THF (0.5 mL), was added TBAF (1.0 M in THF, 52 mL,
0.057 mmol). After stirring for 19 h, the solvent was
removed under reduced pressure. Purification of the crude
product by flash chromatography (petroleum ether/EtOAc,
1/9) afforded compound 44 (5.9 mg, 85%) as a clear
gratefully acknowledge the Spanish ‘Ministerio de Ciencia
y Tecnologia’ for a ‘Ramon y Cajal’ fellowship to A. M. C.,
‘Merck Research Laboratories’ (Merck’s Academic Devel-
`
opment Program Award to C. G.) and Universita degli Studi
di Milano for financial support and for a graduate fellowship
to D. C. We thank Dr. Raphael Beumer, Dr. Joachim Telser
for preliminary experiments related to this work, and Dr.
Nicola Mongelli (Nerviano Medical Science, Italy) for
inspiring discussions. We thank Dr. Marina Ciomei and Dr.
Aurelio Marsiglio (Biology, R&D Unit, Nerviano Medical
Science, Italy) for assistance in the cytotoxicity assays on
the human tumor cell lines. We thank Dr. Sylvie Ducki
(Centre for Molecular Drug Design, Kidscan Laboratories,
University of Salford, UK) for the tubulin polymerization
assays.
1
yellowish oil. RfZ0.15 (petroleum ether/EtOAc, 1/9); H
NMR (400 MHz, CDCl3): d 7.59 (d, 1H, JZ15.7 Hz), 7.48
(s, 1H), 7.10 (s, 1H), 6.84–6.74 (m, 4H), 6.62 (d, 1H, JZ
15.7 Hz), 6.01 (dt, 1H, J1Z11.4 Hz, J2Z4.9 Hz), 5.86 (dd,
1H, J1Z11.4 Hz, J2Z9.5 Hz), 5.71–5.64 (m, 1H), 5.33 (br,
1H), 5.17 (dd, 1H, J1Z9.5 Hz, J2Z2.7 Hz), 4.05 (br, 1H),
3.76 (s, 3H), 3.72 (s, 3H), 2.83–2.74 (m, 1H), 2.54–2.44 (m,
1H), 2.17–1.26 (m, 14H), 0.88 (d, 3H, JZ6.8 Hz), 0.79 (d,
3H, JZ6.7 Hz); 13C NMR (100 MHz, CDCl3): d 166.9,
154.3, 151.8, 138.9, 137.1, 136.1, 129.2, 128.4, 122.3,
121.1, 117.7, 116.4, 114.5, 75.4, 74.1, 71.7, 55.6, 37.9, 37.6,
36.2, 35.7, 33.6, 32.9, 32.3, 27.1, 24.5, 23.9, 21.0, 16.1; FT-
IR (CCl4): n 3468, 2963, 2928, 2855, 2290, 2002, 1847,
1709, 1559, 1414, 1261, 1219, 1099, 1013; [a]2D0ZC79.3
(cZ0.30, EtOAc); HRMS (ESI): calculated for
C32H43N2O5: 535.3166 [MCH]C; found: 535.3165
(resolution 10,000).
References and notes
1. Isolation: (a) D’Ambrosio, M.; Guerriero, A.; Pietra, F. Helv.
Chim. Acta 1987, 70, 2019–2027. (b) D’Ambrosio, M.;
Guerriero, A.; Pietra, F. Helv. Chim. Acta 1988, 71, 964–976.
2. Antitumor activity and paclitaxel-like mechanism of action:
(a) Ciomei, M.; Albanese, C.; Pastori, W.; Grandi, M.; Pietra,
F.; D’Ambrosio, M.; Guerriero, A.; Battistini, C. Proc. Am.
Assoc. Cancer Res. 1997, 38, 5(Abstract 30). (b) Battistini, C.;
Ciomei, M.; Pietra, F.; D’Ambrosio, M.; Guerriero, A.
(Pharmacia S.p.A.), PCT Int. Appl. WO 9636335, 1996
[Chem. Abstr. 1997, 126, P54863x].
3.1.33. Molecular mechanics and semi-empirical calcu-
lations. The potential energy surface of structures A–F (Z
and E stereoisomers, Fig. 2) was searched using Monte
Carlo27b conformational searches with MacroModel
(v8.5)27a running on a 3.0 GHz Intel Pentium 4 with
LINUX Red Hat 9 operating system. The calculations were
performed with the MM2* force field using the GB/SA
continuum solvent model for CHCl3.27c Interconversion of
ring structures was enabled using the ring-opening method
of Still.39 Ring closure bonds were defined for both the six
and ten-membered rings present in structures A–F. Each
search was run in blocks of 15,000 steps until convergence
was reached, that is, no new structures were found and the
global minimum energy remained constant throughout the
search. Typically, 50,000–60,000 steps were enough to
ensure convergence. Each new cycle used as input the
results of the previous cycle and different ring-closure bond
choices were used. During the search, structures with energy
20 kJ molK1 higher than the current global minimum were
discarded. Structures were fully minimized for up to 5000
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˚
the Polak Ribiere conjugate gradient method.40 Redundant
conformations were removed after heavy atom super-
˚
imposition (RMSD cutoffZ0.25 A). The lowest energy
conformers obtained with MacroModel for the Z and the
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package.28
Acknowledgements
We thank the European Commission for financial support
(IHP Network grant ‘Design and synthesis of microtubule
stabilizing anticancer agents’ HPRN-CT-2000-00018) and
for postdoctoral fellowships to L. C. (HPRN-CT-2000-
00018), P. B. (‘Marie Curie’ HPMF-CT-2000-00838) and
O. S. (‘Marie Curie’ MEIF-CT-2003-500880). We also
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