Straightforward Synthesis of a Vicinal Double-Bridgehead Iodo Trimethylsilyl Octacycle: Unprecedented Lack of Reactivity of the Silyl Group in the Presence of Fluoride Anions

Article abstract of DOI:10.1002/ejoc.201601618

A convenient synthesis of an octacyclic compound containing an iodo and a trimethylsilyl group in vicinal double-bridgehead positions, as a possible precursor of a pyramidalized alkene, is described. The key step of the synthesis consists of a double nucl

Full text of DOI:10.1002/ejoc.201601618

DOI: 10.1002/ejoc.201601618
Full Paper
Polycycle Synthesis
Straightforward Synthesis of a Vicinal Double-Bridgehead Iodo
Trimethylsilyl Octacycle: Unprecedented Lack of Reactivity of
the Silyl Group in the Presence of Fluoride Anions
Pelayo Camps,*[a] David Lozano,[a] Enrique Guitián,[b] Diego Peña,[b] Dolores Pérez,[b]
Mercè Font-Bardia,[c,d] and Antonio L. Llamas-Saíz[e]
Dedicated to Professor Alejandro F. Barrero[‡]
Abstract: A convenient synthesis of an octacyclic compound tion with different sources of fluoride failed. This octacyclic
containing an iodo and a trimethylsilyl group in vicinal double- compound, which contains two disubstituted C=C bonds, un-
bridgehead positions, as a possible precursor of a pyramidalized derwent a chemo- and stereoselective Pd0-catalyzed co-cyclo-
alkene, is described. The key step of the synthesis consists of a trimerization with dimethyl acetylenedicarboxylate to give a
double nucleophilic substitution of two neopentyl-type iodides nonacyclic cyclohexadiene derivative that can be aromatized
by cyclopentadienide anions followed by two intramolecular upon reaction with CsF or transformed into a related fluoride
Diels–Alder cycloadditions. All attempts to generate the ex- upon reaction with AgF.
pected pyramidalized alkene from the above precursor on reac-
Introduction
trapped as Diels–Alder adducts with different dienes and, in the
absence of dienes, they usually dimerize to form cyclobutane
derivatives (Figure 1).
The generation and reactions of highly pyramidalized alkenes
have been the subject of many publications and several re-
views[1] since the first alkene of this type, 9,9′-dehydrodianthra-
cene was reported by Weinshenker and Greene in 1968.[2]
Worthy of mention are 1,2-dehydrocubane (cubene),[3] 1,5-
dehydroquadricyclane,[4] tricyclo[3.3.1.03,7]non-3(7)-ene,[5] tri-
cyclo[3.3.0.03,7]oct-1(5)-ene and derivatives,[6] pentacyclo-
[4.3.0.02,4.03,8.05,7]non-4-ene,[7] and 3,4,8,9-tetramethyltetra-
cyclo[4.4.0.03,9.04,8]dec-1(6)-ene.[8] These alkenes can be easily
[a] Laboratori de Química Farmacèutica (Unitat Associada al CSIC), Facultat
de Farmàcia i Ciències de la Alimentació and Institut de Biomedicina
(IBUB), Universitat de Barcelona,
Av. Joan XXIII 27–31, 08028 Barcelona, Spain
E-mail: camps@ub.edu
http://www.ub.edu/farmaco/ca/farmaceutica/llistat_recerca/
[b] Centro Singular de Investigación en Química Biolóxica e Materiais
Moleculares (CIQUS) and Departamento de Química Orgánica,
Universidade de Santiago de Compostela,
15782 Santiago de Compostela, Spain
Homepage: http://www.usc.es/ciqus/es/grupos/commo
[c] Departament de Cristal·lografia, Mineralogia I Dipòsits Minerals,
Universitat de Barcelona,
Martí Franquès s/n, 08028 Barcelona, Spain
[d] Unitat de Difracció de RX, Centres Científics I Tecnològics de la Universitat
de Barcelona (CCiTUB),
Figure 1. Structures of significant pyramidalized alkenes.
The more highly pyramidalized alkenes are usually generated
by reaction of a vicinal double-bridgehead diiodide or dibro-
mide with an organolithium reagent in THF, sodium/potassium
alloy, or with molten sodium in boiling 1,4-dioxane. However,
these conditions are drastic and sometimes it is desirable to
apply milder conditions. For instance, when cubene was gener-
Solé i Sabarís 1–3, 08028 Barcelona, Spain
[e] Unidade de Raios X. RIAIDT, Edificio CACTUS, Campus Vida, Universidade
de Santiago de Compostela,
15782 Santiago de Compostela, Spain
[‡] Organic Chemistry Department, University of Granada
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejoc.201601618.
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ated from 1,2-diiodocubane by reaction with an organolithium and the starting diene, which could not be separated by silica
reagent, it reacted very rapidly with any of the organolithiums gel column chromatography, were always obtained.
present at its generation.[3a] This fact restricted the study of the
behavior of cubene towards other reagent probes. Only 11,12-
dimethylene-9,10-dihydro-9,10-ethanoanthracene was found to
be a moderate organolithium-compatible trap able to compete
with the organolithium addition process, and the correspond-
ing Diels–Alder adduct could be isolated. Lukin and Eaton de-
veloped a milder procedure to generate cubene by reaction of
a vicinal iodo- or bromo-trimethylsilyl precursor with fluoride
(Scheme 1).[3c]
Scheme 2. Preparation of octacycle 2 from cyclopentadiene 1.
Basic methanolysis of diacetate 6 gave diol 7 in 77 % yield,
which was mesylated under standard conditions to give di-
mesylate 8 in 89 % yield. The reaction of 8 with sodium iodide
in acetone at reflux gave triiodide 9 in 79 % yield. Finally, the
reaction of a solution of 9 in anhydrous DMF with potassium
Scheme 1. Previously described generation of cubene[3c] and planned prepa-
cyclopentadienide, prepared from freshly distilled cyclopentadi-
ration of pyramidalized alkene 3 from octacycle 2.
ene and 30 % KH in mineral oil in THF, in the presence of 18-
crown-6 (5 mol-%) gave octacycle 2 in 58 % yield. This transfor-
mation consists of two nucleophilic substitutions of neopentyl-
type iodides by the cyclopentadienide anion followed by two
intramolecular Diels–Alder reactions. The obtained yield corre-
sponds to an average 87 % per synthetic stage. Although the
intramolecular Diels–Alder reaction with the less substituted
alkene moiety was to be expected,[9] this was not the case for
the more substituted, non-electron-deficient, and hindered
alkene. Although octacycle 2 was fully characterized by spectro-
scopic means as well as by elemental analysis and accurate
mass measurement, its structure was confirmed by X-ray diffrac-
tion analysis (Figure 2).
Moreover, the preparation of the diiodide precursor in the
series of tricyclo[3.3.0.03,7]oct-1(5)-ene derivatives implies a
long sequence of transformations, the key step consisting of a
double iododecarboxylation of a not easily available 1,2-dicarb-
oxylic acid upon reaction with iodosobenzene diacetate (IBDA)
and iodine under photochemical conditions.[6] Also, the prepa-
ration of 1-iodo- or 1-bromo-2-(trimethylsilyl)cubane requires a
long sequence of transformations, the trimethylsilyl group be-
ing introduced by the reaction of a carbanion with trimethylsilyl
chloride.[3a,3b]
We planned the preparation of the vicinal double-bridge-
head iodo-trimethylsilyl polycycle 2 from the recently de-
scribed[9] 1,1-disubstituted cyclopentadiene 1 in a process not
requiring any iododecarboxylation step or reaction of a carb-
anion with trimethylsilyl chloride, as well as the generation of
the pyramidalized alkene 3 by a procedure similar to that used
by Lukin and Eaton to generate cubene to study its reactivity
(Scheme 1).
Results and Discussion
Octacycle 2 was prepared according to Scheme 2. Cyclopenta-
diene 1 was fully transformed into the corresponding Diels–
Alder adduct 5 upon reaction with the known[10] phenyl[(tri-
methylsilyl)ethynyl]iodonium triflate 4 in anhydrous acetonitrile
at reflux for 64 h. This adduct was directly treated with NaI and
CuI[11] at room temperature for 17 h to give the substituted
norbornadiene 6 in 32 % overall yield. By contrast, when diene
1 was treated with (iodoethynyl)trimethylsilane in o-dichloro-
Figure 2. ORTEP representation of octacycle 2.
All attempts to generate pyramidalized alkene 3 from octacy-
benzene at 180 °C for different reaction times, mixtures of 6 cle 2 and trap it as a Diels–Alder adduct with different dienes
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left the starting compound unchanged, in spite of using excess
of CsF, alone or in combination with AgF, or tetrabutylammo-
nium fluoride as fluoride source in the presence of excess of
furan, 1,3-diphenylisobenzofuran, tetraphenylcyclopentadi-
enone, or anthracene as dienes. To the best of our knowledge,
there is no precedent for this lack of reactivity of the trimethyl-
silyl group in the presence of fluoride anions and it might be
due to the steric hindrance experienced by the silyl group.
Bearing in mind that strained cyclic intermediates can be
stabilized by coordination to transition metals,[12] we consid-
ered the possibility of generating a transient palladium complex
of alkene 3 initiated by the oxidative addition of palladium(0)
to iodo-octacycle 2. Subsequent reaction of the plausible palla-
dium–alkene complex with two molecules of dimethyl acety-
lenedicarboxylate (DMAD) could lead to the formation of the
corresponding co-cyclotrimerization product, similarly to the
palladium-catalyzed [2+2+2] co-cycloaddition of arynes or cy-
clic alkynes with DMAD.[13] However, the reaction of 2 with an
excess of DMAD in the presence of CsF, AgF, and a catalytic
amount of tris(dibenzylideneacetone)dipalladium(0)·CHCl3
([Pd2(dba)3·CHCl3], 6 mol-%) in 1,4-dioxane at reflux gave in
34 % yield nonacycle 10, a compound that contains the vicinal
iodo and trimethylsilyl groups of the starting compound and a
new benzene ring, fused to polycycle 2 at the C=C bond more
remote from the iodine and trimethylsilyl substituents and
hence less affected by the steric effect of the trimethylsilyl
group (Scheme 3). The structure of this compound was clearly
established by X-ray diffraction analysis (Figure 3) and was fully
characterized on the basis of its spectroscopic data and elemen-
tal analysis. Once again, the trimethylsilyl group remained un-
affected under these conditions. Thus, the palladium catalyst
does not seem to promote the formation of pyramidalized
alkene 3 or a palladium complex derivative.
Figure 3. ORTEP representation of nonacycle 10.
DMAD in the presence of a catalytic amount of tetrakis(meth-
oxycarbonyl)palladiacyclopentadiene to give stereoselectively a
cyclohexadiene derivative.[15] When compound 2 was treated
with DMAD in the presence of [Pd2(dba)3] (10 mol-%) in 1,4-
dioxane at reflux, nonacycle 11 was obtained in high yield. As
before, the structure and configuration of this compound was
clearly established by X-ray diffraction analysis (Figure 4). It was
also fully characterized on the basis of its spectroscopic data
and elemental analysis. As before, the more remote C=C bond
in 2 with respect to the trimethylsilyl and iodine substituents is
the only one that reacts, in spite of using an excess of DMAD,
a fact reasonably associated with the steric hindrance of the
trimethylsilyl group, which includes not only the carbocyclic
skeleton but also the vicinal iodide substituent.
Figure 4. ORTEP representation of nonacycle 11.
Taking into account the fact that the conversion of 11 into
10 might require an oxidant, compound 11 was treated with
an excess of AgF (3 equiv.) under similar reaction conditions to
those used before. Worthy of note, compound 13, which still
contains the cyclohexadiene subunit and with the iodine atom
having been replaced by fluorine, was the only isolated product
(47 % yield) from this reaction, the formation of compound 10
not being observed. The structure and configuration of com-
Scheme 3. Several transformations of octacycle 2.
It is known that palladium(0) catalyzes the co-cyclotrimeriza- pound 13 was also established by X-ray diffraction analysis (Fig-
tion of acetylenes with electron-deficient or some bicyclic ole- ure 5) and fully characterized on the basis of its spectroscopic
fins.[14] In particular, norbornene reacts with 2 equivalents of data and elemental analysis. Compound 13 was also obtained,
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although in only 31 % yield, upon reaction of octacycle 2 with
excess DMAD in the presence of [Pd2(dba)3] (10 mol-%) and
AgF (3 equiv.) in 1,4-dioxane at reflux. As expected, when com-
pound 2 was treated with excess AgF in 1,4-dioxane at reflux,
octacycle fluoride 12 was obtained in 46 % yield. Bridgehead
iodides have previously been transformed into the correspond-
ing fluorides upon reaction with different reagents, such as
XeF2,[16] elemental fluorine,[17] nitronium tetrafluoroborate/pyr-
idine polyhydrogen fluoride or sodium nitrate/pyridine poly-
hydrogen fluoride,[18] and HgF2,[19] the last reagent giving better
results than AgF for the studied halogenated adamantanes. It
seems reasonable that the conversion of compounds 11 and 2
into 13 and 12, respectively, takes place through an SN1-type
mechanism,[19] the ꢀ-silicon syn effect helping to stabilize the
pyramidalized intermediate carbocation.[20]
Scheme 4. Mechanistic proposals for the CsF-promoted conversion of nona-
cycle 11 into compound 10.
the starting 2 was recovered, and some degradation products
were also detected.
CCDC 1522945 (for 2), 1522948 (for 10), 1522946 (for 11),
and 1522947 (for 13) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre.
Conclusions
Pyramidalized alkene 3 could not be generated from polycycle
2 upon reaction with different sources of fluoride under differ-
ent reaction conditions. Work is in progress to prepare a polycy-
cle with the same skeleton as 2 but containing a second iodine
atom instead of the trimethylsilyl group. Based on our previous
experience, the desired pyramidalized alkene 3 might be gener-
ated from this diiodide.
Figure 5. ORTEP representation of nonacycle 13.
Worthy of note, the reaction of nonacycle 11 with excess CsF
in 1,4-dioxane at reflux gave compound 10 in 89 % yield as the
only isolated product. A possible explanation of this transforma-
tion is given in Scheme 4. The fluoride could catalyze the tau-
tomerizaton of 11 to a cis-1,4-dihydrobenzene derivative, which
might lose hydrogen in a concerted (4q+2)-allowed process, as
recently proposed in a related dehydrogenation.[21] An alterna-
tive ionic mechanism for the dehydrogenation of 11 is also
shown in Scheme 4. Alternatively, although this transformation
was carried out under Ar, we cannot exclude the possibility of
an autoxidation process.[22]
Experimental Section
General: Melting points were determined in open capillary tubes
with an MFB 595010M Gallenkamp melting-point apparatus. All
new compounds were fully characterized by their analytical (melt-
ing point, elemental analysis, and/or accurate mass measurement)
and spectroscopic data (IR, 1H, 13C, and 19F NMR) and, in several
cases, X-ray diffraction analysis. Assignments given for the NMR
spectra are based on DEPT, COSY, NOESY, 1H/13C single quantum
correlation (gHSQC sequence) and 1H/13C multiple bond correlation
The inability to generate pyrimidalized alkene 3 from 2 upon
reaction with different sources of fluoride under different condi-
tions, including the presence of AgF to increase the leaving
1
(gHMBC sequence) spectra. H and 13C NMR spectra were recorded
1
with a Varian Mercury 400 (400 MHz for H, 100.6 MHz for 13C, and
group capacity of the iodide group, is in striking contrast to 376.28 MHz for 19F) spectrometer. Unless otherwise stated, the NMR
spectra were recorded in CDCl3. Chemical shifts (δ) are reported in
parts per million relative to internal TMS or CDCl3 (for 1H and 13C
NMR) and to external CFCl3 (δ = 0 ppm, for 19F NMR). Multiplicities
are reported by using the following abbreviations: s, singlet; d, dou-
blet; t, triplet; m, multiplet; br., broad, or combinations thereof. IR
spectra were recorded with an FTIR Perkin–Elmer Spectrum RX1
spectrometer using the attenuated total reflectance (ATR) technique
or a Nicolet Avantar 320 FT-IR spectrometer; the intensities of the
absorptions are denoted as strong (s), medium (m), or weak (w).
HRMS was carried out at the Mass Spectrometry Unit of the Centres
previous works in which vicinal halo-trimethylsilyl compounds
were transformed into reactive intermediates such as pyr-
amidalized alkenes[3c] or benzynes[23] upon reaction with di-
verse fluoride sources. The steric hindrance of the trimethylsilyl
group in this compound might be responsible of this lack of
reactivity. In accord with the indications of the referees, a mix-
ture of compound 2 and a great excess of tetrabutylammonium
fluoride (TBAF, from a 1
M solution in THF) was heated at 150 °C
for 19 h, after the solvent had been distilled off. The partial
degradation of TBAF to tributylamine was observed, most of Científics i Tecnològics of the Universitat de Barcelona (CCiTUB) by
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using an LC/MSD-TOF spectrometer with electrospray ionization
CH3COO), 3.48 [overlapped pseudo-dt, 4J(H,H) = 0.9, 3J(H,H) =
(ESI-TOF-MS) from Agilent Technologies. Elemental analyses were 4J(H,H) = 2.8 Hz, 1 H, 1-H], 3.50 [overlapped pseudo-dt, 4J(H,H) =
3
4
2
carried out at the IIQAB (CSIC) of Barcelona, Spain, in Thermofinni- 0.9, J(H,H) = J(H,H) = 2.8 Hz, 1 H, 4-H], 4.15 [d, J(H,H) = 11.6 Hz,
gan model Flash 1112 series elemental microanalyzers (A5) for C,
1 H, anti-CHaOAc], 4.20 [overlapped d, 2J(H,H) = 11.6 Hz, 1 H, syn-
H, and N determinations and in a Methrom model 808 titroproces- CHaOAc], 4.21 [overlapped d, 2J(H,H) = 11.6 Hz, 1 H, syn-CHbOAc],
sor for halogen determination. For flash column chromatography, 4.24 [d, 2J(H,H) = 11.6 Hz, 1 H, anti-CHbOAc], 6.66 [ddd, 3J(H,H) =
silica gel 60 AC (35–70 μm, SDS, ref. 2000027) was used. The eluents
employed are reported as volume/volume percentages. Automa- 5.6, 3J(H,H) = 3.2 Hz, 4J(H,H) = 0.9 Hz, 1 H, 6-H]. 13C NMR (100.6 MHz,
5.6, 3J(H,H) = 3.2, 4J(H,H) = 0.9 Hz, 1 H, 5-H], 6.77 ppm [ddd, 3J(H,H) =
tized chromatography was carried out with a Combiflash RF 150 psi
from Teledyne Isco. TLC was performed on aluminium-backed
sheets with silica gel 60 F254 (Merck, ref. 1.05554) and the spots
were visualized with UV light or a 1 % aqueous solution of KMnO4.
X-ray diffraction analyses of compounds 2, 11, and 13 were per-
formed with a D8 Venture diffractometer at the CCiTUB of the Uni-
versity of Barcelona and that of compound 10 was performed with
a Bruker X8 APEXII CCD at Unidade de Raios X, RIAIDT, Universidade
CDCl3): δ = –1.9 [CH3, Si(CH3)3], 20.79 (anti-CH3COO), 20.85 (syn-
CH3COO), 59.7 (CH, C-4), 64.5 (CH2, anti-CH2OAc), 64.7 (CH2, syn-
CH2OAc), 68.4 (CH, C-1), 84.1 (C, C-7), 115.9 (C, C-2), 139.2 (CH, C-6),
141.0 (CH, C-5), 154.2 (C, C-3), 170.6 (syn-CH3COO), 170.7 ppm (anti-
CH3COO). IR (ATR): ν = 2950 (w), 1541 (m), 1739 (s), 1537 (w), 1374
˜
(m), 1361 (m), 1232 (s), 1028 (s), 1000 (m), 977 (m), 860 (m), 837 (s),
754 (m), 734 (m), 692 cm–1 (m). HRMS: calcd. for C16H23IO4Si + NH4
+
452.0749; found 452.0747. C16H23IO4Si (434.35): calcd. C 44.24, H
de Santiago de Compostela. DMAD, iodosobenzene diacetate, tetra- 5.34, I 29.22; found C 44.05, H 5.27, I 29.53.
butylammonium fluoride, and CuI were purchased from Sigma–
[(1R*,4S*)-2-Iodo-3-(trimethylsilyl)bicyclo[2.2.1]hepta-2,5-di-
Aldrich, bis(trimethylsilyl)acetylene, methanesulfonyl chloride, 18-
crown-6, and NaI from ACROS Organics, trifluoromethanesulfonic
acid, CsF, and AgF from Fluorochem, [Pd2(dba)3] from Alfa Aesar,
1,3-diphenylisobenzofuran from Fluka, tetraphenylcyclopentadi-
enone from ABCR chemicals, and anthracene from Merck. All of
them were used without further purification. An anhydrous stock
ene-7,7-diyl]dimethanol (7): K2CO3 (22 mg, 0.16 mmol) was added
to a solution of diacetate 6 (271 mg, 0.62 mmol) in anhydrous
MeOH (6.3 mL) and the mixture was heated at reflux for 2 h. A
saturated aqueous solution of NaHCO3 (0.1 mL) was added. The
mixture was cooled to 0 °C with an ice/water bath and filtered. The
solid was washed with MeOH (4 × 5 mL). The combined filtrate and
washings were concentrated in vacuo, the oily residue was taken in
CH2Cl2 (5 mL), and the solution was dried with anhydrous Na2SO4
solution of TBAF (1
M in acetonitrile) was prepared as described
previously.[24]
[(1R*,4S*)-2-Iodo-3-(trimethylsilyl)bicyclo[2.2.1]hepta-2,5-di- and concentrated in vacuo to give diol 7 as a brown oil (201 mg).
ene-7,7-diyl]bis(methylene) Diacetate (6): Trifluoromethane- This crude product was subjected to column chromatography (35–
sulfonic acid (5.16 mL, 58.7 mmol) was added through a glass pi- 70 μm silica gel, 5.0 g, hexane/EtOAc mixtures). On elution with
pette to a cold solution (0 °C, ice/water bath) of iodosobenzene
diacetate (IBDA; 10.02 g, 31.1 mmol) in anhydrous CH2Cl2 (50 mL),
and the mixture was stirred for 30 min at this temperature. Bis(tri-
methylsilyl)acetylene (5.00 g, 29.3 mmol) was added and stirring at
0 °C was continued for 2 h. The solution was concentrated in vacuo
at room temperature, hexane (120 mL) was added to the white oily
residue, and the mixture was stirred for 10 min. The solid formed
was filtered, washed with Et2O (3 × 10 mL), and dried in vacuo to
give iodonium triflate 4 (9.28 g). The combined filtrate and wash-
ings were concentrated in vacuo at room temperature to give an
oily residue. Hexane (70 mL) was added to this residue and the
solid formed was filtered, washed with Et2O (3 × 8 mL), and dried
hexane/EtOAc (95:5), diol 7 (168 mg, 77 % yield) was obtained as a
yellow oil. Crystallization of the above product from pentane (1 mL)
gave the analytical sample of 7 as a white solid. Rf (silica gel, 10 cm,
hexane/EtOAc, 3:7) = 0.38; m.p. 55–56 °C (pentane). 1H NMR
(400 MHz, CDCl3): δ = 0.18 [s, 9 H, Si(CH3)3], 2.05–2.10 (br. s, 1 H)
and 2.10–2.15 (br. s, 1 H, 2 OH), 3.50 [pseudo-dt, 4J(H,H) = 0.8,
4
4
3J(H,H) = J(H,H) = 2.8 Hz, 1 H, 1-H], 3.54 [pseudo-dt, J(H,H) = 0.8,
4
3J(H,H) = J(H,H) = 2.8 Hz, 1 H, 4-H], 3.86 (s, 2 H, anti-CH2OH), 3.88
[overlapped d, 2J(H,H) = 10.8 Hz, 1 H] and 3.92 [d, 2J(H,H) = 10.8 Hz,
1 H, syn-CH2OH), 6.65 [ddd, 3J(H,H) = 5.2, 4J(H,H) = 3.2, 3J(H,H) =
0.8 Hz, 1 H, 5-H], 6.79 ppm [ddd, 3J(H,H) = 5.2, 4J(H,H) = 3.2, 3J(H,H) =
1.1 Hz, 1 H, 6-H]. 13C NMR (100.6 MHz, CDCl3): δ = –1.8 [CH3,
in vacuo to give more triflate 4 (1.23 g, altogether 10.51 g, 80 % Si(CH3)3], 59.3 (CH, C-4), 66.2 (CH2, CH2OH), 66.6 (CH2, CH2OH), 68.1
yield), some of which was used as such in the next step.
(CH, C-1), 88.8 (C, C-7), 116.0 (C, C-2), 139.5 (CH, C-6), 140.9 (CH, C-
5), 154.7 ppm (C, C-3). IR (ATR): ν = 3100–3600 (br, m), 2952 (m),
˜
A solution of cyclopentadiene 1 (284 mg, 1.35 mmol) in anhydrous
acetonitrile (3 mL) was added dropwise to a magnetically stirred
and cold solution (–35 °C, cryocool) of phenyl[(trimethylsilyl)-
ethynyl]iodonium trifluoromethanesulfonate (4; 790 mg,
1.75 mmol) in anhydrous acetonitrile (3 mL) under Ar, and the mix-
ture was heated at reflux for 64 h. The solvent was distilled in vacuo
and the black oily residue was taken in acetonitrile (1.7 mL). This
solution was added dropwise to a cold mixture (–35 °C, cryocool) of
NaI (206 mg, 1.37 mmol) and CuI (263 mg, 1.38 mmol) in anhydrous
acetonitrile (3.8 mL). The reaction mixture was allowed to warm to
room temperature and then it was stirred at this temperature for
17 h. The solvent was distilled in vacuo and the black solid residue
was extracted with CH2Cl2 (3 × 20 mL). The solvent and the formed
iodobenzene were eliminated in vacuo from the combined extracts.
The brown oily residue (443 mg) was subjected to automated col-
1541 (m), 1247 (m), 1008 (s), 836 (vs), 755 (m), 727 (m), 691 cm–1
(m). HRMS: calcd. for C12H19IO2Si + Na+ 373.0091; found 373.0106.
C12H19IO2Si (350.27): calcd. C 41.15, H 5.47, I 36.23; found C 41.17,
H 5.45, I 36.15.
[(1R*,4S*)-2-Iodo-3-(trimethylsilyl)bicyclo[2.2.1]hepta-2,5-di-
ene-7,7-diyl]bis(methylene) Dimethanesulfonate (8): Methane-
sulfonyl chloride (50 μL, 0.60 mmol) was added dropwise to a cold
(0 °C, ice/water bath) and magnetically stirred solution of a mixture
of diol 7 (87 mg, 0.25 mmol) and Et3N (0.14 mL, 1.0 mmol) in anhy-
drous CH2Cl2 (2 mL) under Ar, and the mixture was stirred at this
temperature for 1.5 h. A saturated aqueous solution of NaHCO3
(0.1 mL) was added. The organic phase was separated and was
washed with a saturated aqueous solution of NaHCO3 (3 × 2 mL).
The combined aqueous phases were extracted with CH2Cl2 (3 ×
umn chromatography (35–70 μm silica gel, 12 g, hexane/EtOAc mix- 5 mL). The combined organic phases and extracts were washed
tures). On elution with hexane/EtOAc (9:1, 3 min), diacetate 6
(186 mg, 32 % yield) was obtained as a yellow oil. Rf (silica gel,
10 cm, hexane/EtOAc, 8:2) = 0.43. 1H NMR (400 MHz, CDCl3): δ =
with water (3 mL) and brine (3 mL), dried (anhydrous Na2SO4), and
concentrated in vacuo to give dimesylate 8 as a brown oil (140 mg).
This crude product was subjected to automated column chroma-
0.16 [s, 9 H, Si(CH3)3], 2.02 (s, 3 H, anti-CH3COO), 2.03 (s, 3 H, syn- tography (35–70 μm silica gel, 4.0 g, hexane/EtOAc mixtures). On
Eur. J. Org. Chem. 2017, 1594–1603
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elution with hexane/EtOAc (4:1) to hexane/EtOAc (1:9; 4 min),
dimesylate 8 (112 mg, 89 % yield) was obtained as a yellow oil.
Crystallization of the above product from EtOAc/pentane (1:3, 2 mL)
gave the analytical sample of 8 as a white solid. Rf (silica gel, 10 cm,
hexane/EtOAc, 3:7) = 0.76; m.p. 82–83 °C. 1H NMR (400 MHz, CDCl3):
δ = 0.20 [s, 9 H, Si(CH3)3], 3.00 (s, 3 H) and 3.02 (s, 3 H, 2 CH3SO3),
mixture was stirred for 10 min. Then EtOAc (5 mL) and water (5 mL)
were added and the organic phase was separated. The aqueous
phase was extracted with EtOAc (3 × 10 mL) and the combined
organic phases were washed with a saturated aqueous solution of
NaHCO3 (3 × 10 mL), water (2 × 10 mL), and brine (10 mL), dried
(anhydrous Na2SO4), and concentrated in vacuo to give a crude
3.55–3.58 (m, 1 H, 1-H), 3.57–3.60 (m, 1 H, 4-H), 4.38 [d, 2J(H,H) = brown oily residue (339 mg), which was subjected to column chro-
10.4 Hz, 1 H] and 4.39 [d, 2J(H,H) = 9.6 Hz, 1 H, syn- and anti-
CHaOMs), 4.43 [d, 2J(H,H) = 9.6 Hz, 2 H, syn- and anti-CHbOMs), 6.71
[dd, 3J(H,H) = 5.2, 4J(H,H) = 3.2 Hz, 1 H, 5-H], 6.85 ppm [pseudo-t,
3J(H,H) = 4J(H,H) = 4.0 Hz, 1 H, 6-H]. 13C NMR (100.6 MHz, CDCl3):
δ = –2.0 [CH3, Si(CH3)3], 37.20 (CH3, CH3SO3), 37.21 (CH3, CH3SO3),
59.2 (CH, C-4), 67.6 (CH, C-1), 69.4 (CH2) and 69.6 (CH2, syn- and
anti-CH2OMs), 83.2 (C, C-7), 115.0 (C, C-2), 139.4 (CH, C-6), 141.0 (CH,
matography [35–70 μm silica gel (20 g) pentane/EtOAc mixtures] to
give, on elution with pentane, octacycle 2 (188 mg, 58 % yield) as
a white solid. An analytical sample of 2 (136 mg) was obtained as
a white solid by crystallization of the above product from CH2Cl2/
MeOH (1:3; 2 mL). Rf (silica gel, 10 cm, hexane/EtOAc, 9:1) = 0.74;
1
m.p. 108.7–109.5 °C (CH2Cl2/MeOH). H NMR (400 MHz, CDCl3): δ =
2
3
0.19 [s, 9 H, Si(CH3)3], 1.33 [dd, J(H,H) = 14.2, J(H,H) = 2.6 Hz, 1 H,
2
C-5), 154.8 ppm (C, C-3). IR (ATR): ν = 3028 (w), 2949 (w), 1349 (s),
12-Ha], 1.43 (overlapped s, 1 H, 9-H), 1.45 [overlapped dd, J(H,H) =
˜
1328 (s), 1245 (m), 1170 (s), 940 (s), 840 (s), 822 (s), 775 (m), 754 14.2, 3J(H,H) = 2.6 Hz, 1 H, 12-Hb], 1.53 [overlapped dd, 2J(H,H) =
(m), 729 cm–1 (m). HRMS: calcd. for C14H23IO6S2Si + NH4 524.0088; 14.8, 3J(H,H) = 2.8 Hz, 1 H, 10-Ha], 1.57 [overlapped dd, 2J(H,H) =
+
3
found 524.0104. C14H23O6S2Si (379.54): calcd. C 33.20, H 4.58, S
12.66; found C 33.64, H 4.61, S 12.17.
14.8, J(H,H) = 3.2 Hz, 1 H, 10-Hb], 1.74–1.78 (br. s, 1 H, 11-H), 1.88–
3
1.92 (br. s, 1 H, 10a-H), 1.96 (s, 1 H, 4a-H), 2.01 [d, J(H,H) = 6.4 Hz,
3
1 H, 8a-H], 2.07 [d, J(H,H) = 6.4 Hz, 1 H, 4b-H], 2.31–2.35 (br. s, 1 H,
[(1R*,4S*)-2-Iodo-7,7-bis(iodomethyl)bicyclo[2.2.1]hepta-2,5-
dien-2-yl]trimethylsilane (9): Powdered NaI (365 mg, 2.43 mmol)
was added to a solution of dimesylate 8 (103 mg, 0.20 mmol) in
anhydrous acetone (2 mL) under Ar and the mixture was heated at
reflux for 17 h. The reaction mixture was concentrated in vacuo and
the yellow solid residue was subjected to column chromatography
(35–70 μm silica gel, 1.0 g, hexane/EtOAc mixtures). On elution with
hexane/EtOAc (90:10), diiodide 9 (92 mg, 79 % yield) was obtained
as a light-yellow oil. Rf (silica gel, 10 cm, hexane/EtOAc, 1:1) = 0.84.
1H NMR (400 MHz, CDCl3): δ = 0.22 [s, 9 H, Si(CH3)3], 3.54 [over-
8-H), 2.40–2.44 (br. s, 1 H, 5-H), 2.47–2.51 (br. s, 1 H, 1-H), 3.00–3.04
3
3
(br. s, 1 H, 3a-H), 5.98 [dd, J(H,H) = 5.6, J(H,H) = 3.2 Hz, 1 H, 3-H],
6.05 [dd, 3J(H,H) = 6.0, 3J(H,H) = 2.8 Hz, 1 H, 7-H], 6.10 [dd, 3J(H,H) =
6.0, 3J(H,H) = 2.8 Hz, 1 H, 6-H], 6.33 ppm [dd, 3J(H,H) = 5.6, 3J(H,H) =
3.2 Hz, 1 H, 2-H]. 13C NMR (100.6 MHz, CDCl3): δ = 4.0 [CH3, Si(CH3)3],
35.0 (CH2, C-10), 35.4 (CH2, C-12), 42.6 (C, C-9a), 43.0 (CH, C-8a), 46.3
(C, C-13), 48.4 (CH, C-4b), 49.0 (CH, C-8), 49.7 (CH, C-5), 52.3 (CH, C-
11), 52.5 (CH, C-1), 53.1 (CH, C-9), 55.0 (CH, C-10a), 63.2 (CH, C-4a),
63.4 (CH, C-3a), 72.2 (C, C-4), 137.2 (CH, C-7), 137.3 (CH, C-6), 139.4
(CH, C-3), 140.7 ppm (CH, C-2). IR (ATR): ν = 3055 (w), 2944 (m),
˜
4
3
4
lapped pseudo-dt, J(H,H) = 1.2, J(H,H) = J(H,H) = 2.8 Hz, 1 H, 4-
2910 (m), 2893 (m), 2833 (w), 1326 (w), 1245 (m), 937 (m), 921
(m), 856 (m), 842 (s), 829 (s), 810 (m), 794 (m), 724 (m), 708 (s),
680 cm–1 (m). HRMS: calcd. for C22H27ISi + H+ 447.0999; found
447.0991; calcd. for C22H27ISi – I+ 319.1877; found 319.1873.
C22H27ISi (446.45): calcd. C 59.19, H 6.10, I 28.43; found C 59.18, H
5.98, I 28.58.
H], 3.56 [overlapped pseudo-dt, 4J(H,H) = 1.2, 3J(H,H) = 4J(H,H) =
2
2
2.8 Hz, 1 H, 1-H], 3.65 [d, J(H,H) = 10.0 Hz, 1 H], 3.70 [d, J(H,H) =
10.8 Hz, 1 H] and 3.71–3.76 (complex signal, 2 H, anti- and syn-
CH2I), 6.68 [ddd, 3J(H,H) = 5.6, 3J(H,H) = 3.2, 4J(H,H) = 1.2 Hz, 1 H, 5-
H], 6.85 ppm [ddd, 3J(H,H) = 5.2, 3J(H,H) = 3.2, 4J(H,H) = 1.4 Hz, 1 H,
6-H]. 13C NMR (100.6 MHz, CDCl3): δ = –1.7 [CH3, Si(CH3)3], 13.88
(CH2, CH2I), 13.95 (CH2, CH2I), 63.8 (CH, C-4), 71.9 (CH, C-1), 85.6 (C,
C-7), 115.9 (C, C-2), 139.9 (CH, C-6), 141.2 (CH, C-5), 155.6 ppm (C,
Attempts to Generate and Trap Pyramidalized Alkene 3
General: All of the following reactions were performed under argon
in a 10 mL Schlenk tube equipped with a magnetic stirrer. The
reactions were followed by TLC and GC. In all cases, no evolution
of the reaction mixtures was observed. At the end of the reactions,
the solutions were concentrated in vacuo and the products were
submitted to column chromatography (silica gel, 35–70 μm, hex-
ane/EtOAc mixtures). On elution with hexane, the starting com-
pound 2 was recovered unchanged. No products derived from 2
were detected.
C-3). IR (ATR): ν = 2949 (w), 1567 (w), 1536 (m), 1418 (m), 1281 (m),
˜
1245 (m), 1198 (m), 1006 (m), 867 (m), 834 (s), 791 (m), 751 (m), 727
(m), 637 (m), 626 cm–1 (m). C12H17I3Si (570.07): calcd. C 25.28, H
3.01, I 66.78; found C 25.38, H 2.93, I 66.94.
(1R*,3aS*,4R*,4aR*,4bS*,5R*,8S*,8aR*,9S*,9aS*,10aR*,
11S*,13S*)-4-Iodo-13-(trimethylsilyl)-3a,4,4a,4b,5,8,8a,9,
10,10a-decahydro-1H-5,8,9a-(epiethane[1,1,2]triyl)-1,4,9-(epi-
methanetriyl)cyclopenta[b]fluorene (2): In a 10 mL flask, KH
(30 % in mineral oil, 267 mg, 2.00 mmol) was washed with anhy-
drous THF (5 × 10 mL) under Ar. Anhydrous THF (10 mL) was added
to the washed KH and the suspension was cooled to 0 °C in an
ice/water bath. Freshly distilled cyclopentadiene (0.25 mL, 198 mg,
3.0 mmol) was added and the mixture was stirred at this tempera-
ture for 10 min. 18-Crown-6 (26 mg, 0.10 mmol, 5 % with respect
to KH) was added and the mixture was stirred at 0 °C for 10 min
and at room temperature for 15 min.
Reaction with CsF in the Presence of Furan: Anhydrous CsF
(54 mg, 0.36 mmol) was added to a solution of octacycle 2 (50 mg,
0.11 mmol) and furan (40 μL, 0.55 mmol) in anhydrous acetonitrile
(3 mL), and the mixture was stirred at room temperature for 18 h.
Then, the mixture was heated at 45 °C for 5 h. Finally, 18-crown-6
(6 mg, 23 μmol) was added and the mixture was heated at 45 °C
for 16 h.
Reaction with CsF and AgF in the Presence of 1,3-Diphenyliso-
benzofuran: Anhydrous CsF (85 mg, 0.56 mmol) and AgF (43 mg,
0.34 mmol) were added to a solution of octacycle 2 (50 mg,
0.11 mmol) and 1,3-diphenylisobenzofuran (45 mg, 0.17 mmol) in
anhydrous acetonitrile (3 mL), and the mixture was heated at reflux
for 20 h.
A solution of diiodide 9 (415 mg, 0.73 mmol) in anhydrous DMF
(4.1 mL) was prepared in a 25 mL flask equipped with a magnetic
stirrer and reflux condenser under Ar. The solution was cooled to
0 °C in an ice/water bath and then part of the above potassium
cyclopentadienide solution (8.0 mL, 1.6 mmol) was added dropwise.
The mixture was stirred at 0 °C for 5 min, at room temperature for
10 min, and then it was heated at 90 °C for 17 h. The mixture was
cooled to room temperature, MeOH (0.1 mL) was added, and the
Reaction with CsF and AgF in the Presence of Tetraphenylcyclo-
pentadienone: Anhydrous CsF (85 mg, 0.56 mmol) and AgF (43 mg,
Eur. J. Org. Chem. 2017, 1594–1603
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0.34 mmol) were added to a solution of octacycle 2 (50 mg,
0.11 mmol) and tetraphenylcyclopentadienone (65 mg, 0.17 mmol)
in a mixture of anhydrous THF (1.5 mL) and acetonitrile (1.5 mL),
and the mixture was heated at 60 °C for 17 h.
C34H37IO8Si (728.65): calcd. C 56.05, H 5.12, I 17.42; found C 55.97,
H 5.17, I 17.54.
Tetramethyl (1R*,3aS*,4R*,4aR*,4bS*,5R*,5aR*,9aR*,
10S*,10aS*,11R*,11aS*,12aR*,14S*,15S*)-3a,4,4a,4b,5,5a,9a,
10,10a,11,12,12a-Dodecahydro-4-iodo-15-(trimethylsilyl)-1H-
5,10,11a-(epiethane[1,1,2]triyl)-1,4,11-(epimethanetriyl)-
benzo[b]cyclopenta[h]fluorene-6,7,8,9-tetracarboxylate (11):
DMAD (0.1 mL, 0.79 mmol) and tris(dibenzylideneacetone)di-
palladium(0) (18 mg, 20 μmol) were added to a solution of octacy-
cle 2 (88 mg, 0.20 mmol) in anhydrous 1,4-dioxane (4.4 mL) and
the mixture was stirred and heated at 100 °C for 17 h. The reaction
mixture was cooled to room temperature and concentrated in
vacuo to give a brown solid (190 mg), which was submitted to
automated column chromatography [35–70 μm silica gel (4 g), hex-
ane/EtOAc mixtures]. On elution with hexane/AcOEt (3:1) to hex-
ane/AcOEt (7:3, 4 min), adduct 11 (117 mg, 81 % yield) was ob-
tained as a white solid. An analytical sample of 11 (93 mg) was
obtained as a white solid by crystallization of the above product
from CH2Cl2/pentane (1:3, 1.5 mL). Rf (silica gel, 10 cm, hexane/
EtOAc, 3:2) = 0.19; m.p. 117–118 °C (CH2Cl2/pentane). 1H NMR
(400 MHz, CDCl3): δ = 0.22 [s, 9 H, Si(CH3)3], 1.43 (overlapped s, 1
Reaction with Tetrabutylammonium Fluoride in the Presence of
Tetraphenylcyclopentadienone: Procedure 1: Tetraphenylcyclo-
pentadienone (65 mg, 0.17 mmol) was added to a cold (0 °C) sus-
pension of tetrabutylammonium fluoride (1
M in acetonitrile,
0.34 mL, 0.34 mmol). Then octacycle 2 (50 mg, 0.11 mmol) in anhy-
drous THF (50 μL) was added and the mixture was stirred at 0 °C
for 1 h.
Procedure 2: A suspension of tetrabutylammonium fluoride (1
M in
acetonitrile, 70 μL, 70 μmol) was added to a solution of octacycle
2 (10 mg, 22 μmol) and tetraphenylcyclopentadienone (17 mg,
44 μmol) in anhydrous 1,4-dioxane (0.5 mL), and the mixture was
heated at 100 °C for 19 h.
Reaction with CsF and AgF in the Presence of Anthracene: Anhy-
drous CsF (85 mg, 0.56 mmol) and AgF (43 mg, 0.34 mmol) were
added to a solution of octacycle 2 (50 mg, 0.11 mmol) and anthra-
cene (40 mg, 0.22 mmol) in a mixture of anhydrous 1,4-dioxane
(2.5 mL) and acetonitrile (1 mL), and the mixture was heated at
100 °C for 20 h.
2
3
H, 11-H), 1.46 [overlapped dd, J(H,H) = 10.2, J(H,H) = 2.8 Hz, 1 H,
13-Hb], 1.51–1.60 [complex signal, 3 H, 12-Ha, 12-Hb, 13-Ha], 1.82–
1.84 (m, 1 H, 12a-H), 1.94–1.96 (br. s, 2 H, 4a-H, 10-H), 2.00–2.02 (m,
Tetramethyl (1R*,3aS*,4R*,4aR*,4bR*,5R*,10S*,10aS*,
11S*,11aS*,12aR*,14S*,15S*)-3a,4,4a,4b,5,10,10a,11,12,12a-
Decahydro-4-iodo-15-(trimethylsilyl)-1H-5,10,11a-(epiethane-
[1,1,2]triyl)-1,4,11-(epimethanetriyl)benzo[b]cyclopenta[h]-
fluorene-6,7,8,9-tetracarboxylate (10): A 10 mL Schlenk tube
equipped with a reflux condenser and magnetic stirrer was charged
with a solution of octacycle 2 (50 mg, 0.11 mmol) in anhydrous
1,4-dioxane (2.5 mL) under Ar. Then DMAD (0.03 mL, 0.24 mmol),
tris(dibenzylideneacetone)dipalladium(0)·CHCl3 (6 mg, 6 μmol), an-
hydrous CsF (85 mg, 0.56 mmol), and AgF (43 mg, 0.34 mmol) were
successively added and the mixture was stirred and heated at
100 °C for 17 h. The reaction mixture was cooled to room tempera-
ture and concentrated in vacuo to give a brown solid (196 mg),
which was submitted to column chromatography [35–70 μm silica
gel (7 g), hexane/EtOAc mixtures] to give, on elution with hexane/
EtOAc (8:2), adduct 10 (28 mg, 34 % yield) as a white solid. An
analytical sample of 10 (20 mg) was obtained as a white solid by
crystallization of the above product from CH2Cl2/pentane (1:4,
1 mL). Rf (silica gel, 10 cm, hexane/EtOAc, 8:2) = 0.22; m.p. 117–
118 °C (CH2Cl2/pentane). 1H NMR (400 MHz, CDCl3): δ = 0.14 [s, 9
H, Si(CH3)3], 1.48 [dd, 2J(H,H) = 14.4, 3J(H,H) = 2.8 Hz, 1 H, 13-Hb],
1.60 [overlapped dd, 2J(H,H) = 14.8, 3J(H,H) = 3.2 Hz, 1 H, 13-Ha],
1.65 [overlapped d, 4J(H,H) = 0.8 Hz, 1 H, 11-H], 1.62–1.68 [complex
signal, 2 H, 12-Ha, 12-Hb], 1.90–1.93 (br. s, 1 H, 12a-H), 2.14–2.18 (br.
s, 2 H, 14-H, 4a-H), 2.24–2.28 (m, 2 H, 10a-H, 4b-H), 2.52–2.55 (br. s,
1 H, 1-H), 3.02–3.05 (br. s, 1 H, 3a-H), 3.26–3.28 (br. s, 1 H, 10-H),
3.48–3.50 (br. s, 1 H, 5-H), 3.86 (s, 3 H, OCH3), 3.88 (s, 3 H, OCH3),
3.90 (s, 3 H, OCH3), 3.93 (s, 3 H, OCH3), 5.99 [dd, 3J(H,H) = 6.0,
3J(H,H) = 3.2 Hz, 1 H, 3-H], 6.33 ppm [dd, 3J(H,H) = 6.0, 3J(H,H) =
3.2 Hz, 1 H, 2-H]. 13C NMR (100.6 MHz, CDCl3): δ = 3.9 [CH3, Si(CH3)3],
34.1 (CH2, C-13), 34.8 (CH2, C-12), 42.9 (C, C-11a), 43.2 (CH, C-10a),
45.9 (C, C-15), 48.6 (CH, C-4b), 50.5 (CH, C-10), 51.0 (CH, C-5), 52.0
(CH, C-14), 52.59 (CH, C-1), 52.61 (CH3), 52.8 (CH3), 52.91 (CH3), 52.94
(CH3, 4 COOCH3), 53.4 (CH, C-11), 54.6 (CH, C-12a), 63.2 (CH, C-4a),
63.4 (CH, C-3a), 68.8 (C, C-4), 126.6 (C) and 126.8 (C, C-7, C-8), 129.8
(C) and 130.4 (C, C-6, C-9), 139.5 (CH, C-3), 140.7 (CH, C-2), 150.8 (C,
C-9a), 151.3 (C, C-5a), 166.2 (C), 166.3 (C), 166.9 (C), 167.4 ppm (C,
3
1 H, 5-H), 2.22–2.26 (br. s, 1 H, 14-H), 2.36 [d, J(H,H) = 6.0 Hz, 1 H,
10a-H], 2.46 (overlapped br. s, 1 H, 1-H), 2.47 [overlapped d,
3J(H,H) = 6.0 Hz, 1 H, 4b-H], 2.90 [d, 3J(H,H) = 12.4 Hz, 1 H, 9a-H],
3
3
2.97 [d, J(H,H) = 2.4 Hz, 3aH], 3.08 [d, J(H,H) = 12.4 Hz, 1 H, 5a-H],
3.74 (s, 3 H, OCH3), 3.75 (s, 3 H, OCH3), 3.76 (s, 3 H, OCH3), 3.79 (s,
3 H, OCH3), 5.95 [dd, 3J(H,H) = 6.0, 3J(H,H) = 3.2 Hz, 1 H, 3-H],
6.29 ppm [dd, 3J(H,H) = 5.8, 3J(H,H) = 3.0 Hz, 1 H, 2-H]. 13C NMR
(100.6 MHz, CDCl3): δ = 4.0 [CH3, Si(CH3)3], 33.0 (CH2, C-13), 34.6
(CH2, C-12), 40.2 (CH, C-14), 43.60 (CH) and 43.64 (CH, C-5a, C-9a),
45.1 (C, C-15), 46.3 (CH, C-10a), 51.1 (CH, C-4b), 52.46 (CH, C-1),
52.47 (CH3), 52.59 (CH3), 52.62 (CH3), (4 COOCH3), 53.0 (CH, C-10),
53.2 (CH, C-5), 54.60 (CH) and 54.62 (CH, C-11, C-12a), 63.3 (CH, C-
3a), 64.4 (CH, C-4a), 69.5 (C, C-4), 130.6 (C, C-7), 131.6 (C, C-8), 133.1
(C, C-9), 134.7 (C, C-6), 139.2 (CH, C-3), 140.4 (CH, C-2), 166.5 (C) and
166.6 (C, 8-COOMe, 9-COOMe), 166.9 (C) and 167.0 ppm (C, 6-
COOMe, 7-COOMe); according to the gHMBC spectrum, C-11a
might be under the signals at δ = 43.60 and 43.64 ppm. IR (NaCl):
ν = 2949 (m), 2916 (m), 2840 (w), 1732 (s), 1644 (w), 1591 (w), 1434
˜
(s), 1342 (m), 1243 (s), 1117 (m), 993 (m), 849 (m), 836 (m), 727 cm–1
(m). HRMS: calcd. for C34H39IO8Si + NH4+ 748.1797; found 748.1801.
C34H39IO8Si·0.75CH2Cl2: calcd. C 52.54, H 5.14; found C 52.55, H 5.11.
Preparation of Compound 10 from 11: A solution of nonacycle 11
(51 mg, 0.07 mmol) in anhydrous 1,4-dioxane (1.5 mL) was placed
in a 10 mL flask equipped with a reflux condenser and magnetic
stirrer under Ar. Then anhydrous CsF (32 mg, 0.21 mmol) was added
and the mixture was stirred and heated at 100 °C for 16 h. The
reaction mixture was cooled to room temperature and concen-
trated in vacuo to give a white solid (87 mg), which was submitted
to column chromatography [35–70 μm silica gel (2 g), hexane/
EtOAc mixtures] to give, on elution with hexane/EtOAc (8:2), adduct
10 (45 mg, 89 % yield) as a white solid.
(1R*,3aS*,4R*,4aR*,4bS*,5R*,8S*,8aR*,9S*,9aS*,10aR*,11S*,
13S*)-4-Fluoro-13-(trimethylsilyl)-3a,4,4a,4b,5,8,8a,9,10,10a-
decahydro-1H-5,8,9a-(epiethane[1,1,2]triyl)-1,4,9-(epimeth-
anetriyl)cyclopenta[b]fluorene (12): A solution of octacycle 2
(63 mg, 0.14 mmol) in anhydrous dioxane (3 mL) was added to a
10 mL flask equipped with a reflux condenser and magnetic stirrer
under Ar. Then anhydrous AgF (54 mg, 0.43 mmol) was added and
4 COOCH3). IR (NaCl): ν = 2951 (m), 2918 (m), 1733 (s), 1444 (m),
˜
1361 (m), 1321 (m), 1249 (s), 1212 (s), 1166 (m), 1143 cm–1 (m).
+
HRMS: calcd. for C34H37IO8Si + NH4 746.1641; found 746.1635.
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the mixture was stirred and heated at 100 °C for 15 h. The reaction
mixture was cooled to room temperature and concentrated in
vacuo to give a residue (130 mg), which was submitted to column
C-10), 53.7 [d, 3J(C,F) = 3.0 Hz, CH, C-1], 55.7 [d, 2J(C,F) = 21.4 Hz,
CH, C-3a], 56.9 [d, 3J(C,F) = 2.3 Hz, CH, C-11], 58.0 [d, 3J(C,F) = 3.7 Hz,
CH, C-12a], 58.8 [d, 2J(C,F) = 20.6 Hz, CH, C-4a], 113.5 [d, 1J(C,F) =
chromatography [35–70 μm silica gel (1.0 g), hexane/EtOAc mix- 206.6 Hz, C, C-4], 130.9 (C, C-7), 131.7 (C, C-8), 132.3 [d, 3J(C,F) =
tures] to give, on elution with hexane, product 12 (22 mg, 46 %
yield) as a colorless oil. Rf (silica gel, 10 cm, hexane/EtOAc, 9:1) =
3.0 Hz, CH, C-3], 133.1 (C, C-9), 134.5 (C, C-6), 142.1 (CH, C-2), 166.55
(C), 166.61 (C), 166.89 (C) and 166.90 ppm (C, 6-COOMe, 7-COOMe,
0.63. 1H NMR (400 MHz, CDCl3): δ = 0.05 [s, 9 H, Si(CH3)3], 1.37–1.44 8-COOMe and 9-COOMe). 19F NMR (376.28 MHz, CDCl3): δ =
2
(complex signal, 3 H, 10-Ha, 10-Hb, 12-Ha), 1.48 [dd, J(H,H) = 14.2,
–173.8 ppm. IR (NaCl): ν = 3064 (w), 2950 (s), 2918 (s), 2844 (m),
˜
3J(H,H) = 3.0 Hz, 1 H, 12-Hb], 1.55–1.57 (br. s, 1 H, 9-H), 1.81–1.84
1739 (s), 1733 (s), 1645 (w), 1686 (w), 1435 (s), 1343 (m), 1243 (s),
(br. s, 1 H, 11-H), 1.88–1.90 (br. s, 1 H, 4a-H), 2.00–2.04 (br. s, 1 H, 1115 (s), 994 (m), 860 (s), 839 (s), 734 cm–1 (s). HRMS: calcd. for
+
10a-H), 2.10 (s, 2 H, 4b-H, 8a-H), 2.32–2.35 (br. s, 1 H, 8-H), 2.39–2.42
(br. s, 1 H, 5-H), 2.45–2.48 (br. s, 1 H, 1-H), 2.63–2.66 (br. s, 1 H, 3a-
H), 6.05–6.10 (complex signal, 3 H, 3-H, 6-H, 7-H), 6.43 ppm [dd,
3J(H,H) = 5.8, 3J(H,H) = 3.0 Hz, 1 H, 2-H]. 13C NMR (100.6 MHz, CDCl3):
C
34H39FO8Si + NH4 640.2736; found 640.2727. C34H39FO8Si
(622.76): calcd. C 65.57, H 6.31, F 3.05; found C 65.51, H 6.38.
Preparation of Compound 13 from 2: A solution of octacycle 2
(50 mg, 0.11 mmol) in anhydrous 1,4-dioxane (2.5 mL) was added
to a 10 mL flask equipped with a reflux condenser and magnetic
stirrer under Ar. Then DMAD (0.06 mL, 0.45 mmol), tris(dibenzyl-
ideneacetone)dipalladium(0) (10 mg, 11 μmol), and AgF (43 mg,
0.34 mmol) were successively added and the mixture was stirred
and heated at 100 °C for 16 h. The reaction mixture was cooled to
room temperature and concentrated in vacuo to give a gray solid
(117 mg), which was submitted to automated column chromatogra-
phy [35–70 μm silica gel (12 g), hexane/EtOAc mixtures]. On elution
with hexane/EtOAc (3:1) to hexane/EtOAc (3:2, 3 min), adduct 13
(21 mg, 31 % yield) was obtained as a white solid.
4
4
δ = 3.1 [d, J(C,F) = 2.2 Hz, CH3, Si(CH3)3], 34.7 [d, J(C,F) = 2.3 Hz,
CH2, C-10], 35.4 (CH2, C-12), 38.7 [d, 3J(C,F) = 4.6 Hz, CH, C-4b], 44.7
[d, 3J(C,F) = 4.5 Hz, C, C-9a], 44.8 (CH, C-8a), 46.9 [d, 2J(C,F) = 25.1 Hz,
C, C-13], 49.0 (CH, C-5), 49.4 (CH, C-8), 52.5 (CH, C-11), 53.7 [d,
3J(C,F) = 3.0 Hz, CH, C-1], 55.4 [d, J(C,F) = 3.3 Hz, CH, C-9], 55.8 [d,
3
2J(C,F) = 22.1 Hz, CH, C-3a], 57.4 [d, 2J(C,F) = 20.5 Hz, CH, C-4a], 58.4
3
1
[d, J(C,F) = 3.0 Hz, CH, C-10a], 114.5 [d, J(C,F) = 207.6 Hz, C, C-4],
3
132.5 [d, J(C,F) = 3.1 Hz, CH, C-3], 137.0 (CH, C-7), 137.3 (CH, C-6),
142.3 ppm (CH, C-2). 19F NMR (376.28 MHz, CDCl3): δ = –174.0 ppm.
IR (NaCl): ν = 3062 (w), 2950 (m), 2916 (m), 2838 (w), 1329 (w), 1249
˜
(m), 1135 (w). 858 (m), 836 (s), 721 (m), 712 (s), 627 cm–1 (m). HRMS:
+
calcd. for C22H27FSi + NH4 356.2204; found 356.2191; calcd. for
X-ray Crystal Structure Determination of Compound 2: A color-
less prism-like specimen of C22H27ISi, approximate dimensions
0.143 mm × 0.177 mm × 0.568 mm, was used for the X-ray crystallo-
graphic analysis. The X-ray intensity data were measured with a D8
Venture system equipped with a multilayer monochromator and a
Mo microfocus (λ = 0.71073 Å). The frames were integrated by using
the Bruker SAINT software package[25] using a narrow-frame algo-
rithm. The integration of the data using a monoclinic unit cell
yielded a total of 50804 reflections to a maximum θ angle of 30.62
(0.70 Å resolution), of which 5778 were independent (average re-
dundancy 8.793, completeness = 99.4 %, Rint = 3.13 %, Rsig = 1.76 %)
and 5168 (89.44 %) were greater than 2σ(F2). The final cell constants
of a = 10.6974(5), b = 11.8520(5), c = 15.1773(7) Å, ꢀ = 101.230(2)°,
V = 1887.42(15) Å3 are based upon the refinement of the XYZ
centroids of reflections above 20σ(I). Data were corrected for
absorption effects by using the multiscan method (SADABS).[26] The
calculated minimum and maximum transmission coefficients (based
on crystal size) are 0.5839 and 0.7461. The structure was solved and
refined by using the Bruker SHELXTL software package using the
space group P21/n with Z = 4 for the formula unit C22H27ISi. The
final anisotropic full-matrix least-squares refinement on F2 with 220
variables converged at R1 = 2.12 % for the observed data and wR2 =
5.18 % for all data. The goodness-of-fit was 1.090. The largest peak
in the final difference electron density synthesis was 0.606 e Å–3
C22H27FSi – F+ 319.1877; found 319.1875. C22H27FSi (338.54): calcd.
C 78.05, H 8.04; found C 78.08, H 8.07.
Tetramethyl (1R*,3aS*,4R*,4aR*,4bS*,5R*,5aR*,9aS*,10S*,
10aR*,11S*,11aR*,12aS*,14R*,15S*)-4-Fluoro-3a,4,4a,4b,5,5a,
9a,10,10a,11,12,12a-dodecahydro-15-(trimethylsilyl)-1H-
5,10,11a-(epiethane[1,1,2]triyl)-1,4,11-(epimethanetriyl)-
benzo[b]cyclopenta[h]fluorene-6,7,8,9-tetracarboxylate (13): A
solution of iodo nonacycle 11 (90 mg, 0.12 mmol) in anhydrous 1,4-
dioxane (2.6 mL) was placed in a 10 mL flask equipped with a reflux
condenser and magnetic stirrer under Ar. Then anhydrous AgF
(47 mg, 0.37 mmol) was added and the mixture was stirred and
heated at 100 °C for 16 h. The reaction mixture was cooled to room
temperature and concentrated in vacuo to give a gray residue
(145 mg), which was submitted to automated column chromatogra-
phy [35–70 μm silica gel (12 g), hexane/EtOAc mixtures]. On elution
with hexane/EtOAc (4:1) to hexane/EtOAc (7:3, 4 min), product 13
(36 mg, 47 % yield) was obtained as a white solid. An analytical
sample of 13 (30 mg) was obtained as a white solid by crystalliza-
tion of the above product from CH2Cl2/pentane (1:3, 1.2 mL). Rf
(silica gel, 10 cm, hexane/EtOAc, 6:4) = 0.37; m.p. 192–193 °C
(CH2Cl2/pentane). 1H NMR (400 MHz, CDCl3): δ = 0.09 [s, 9 H,
Si(CH3)3], 1.38–1.48 (complex signal, 2 H, 12-Ha, 12-Hb), 1.54 [over-
lapped pseudo-dt, 2J(H,H) = 14.0, 3J(H,H) = 5J(H,F) = 2.8 Hz, 1 H, 13-
Ha], 1.56–1.58 (br. s, 1 H, 11-H), 1.62 [dd, 2J(H,H) = 14.0, 3J(H,H) =
2.8 Hz, 1 H, 13-Hb], 1.88–1.90 (br. s, 1 H, 4a-H), 1.94–1.98 (br. s, 2 H,
10-H, 12a-H), 1.98–2.00 (br. s, 1 H, 5-H), 2.30–2.34 (br. s, 1 H, 14-H),
2.43–2.45 (overlapped br. s, 1 H, 1-H), 2.45 (overlapped d, 1 H, 10a-
H), 2.48 [d, 3J(H,F) = 6.4 Hz, 1 H, 4b-H], 2.60–2.63 (br. s, 1 H, 3aH),
andthelargestholewas–0.546e Å–3withanRMSdeviationof0.095e Å–3
.
On the basis of the final model, the calculated density was
1.571 g cm–3 and F(000) = 904 e (Table 1).
X-ray Crystal Structure Determination of Compound 10: A color-
less prism-like specimen of C34H37IO8Si, approximate dimensions
0.41 mm × 0.20 mm × 0.17 mm, was used for the X-ray crystallo-
graphic analysis. The X-ray intensity data were measured with a
Bruker X8 APEXII CCD system equipped with a graphite monochro-
3
2.94 [d, 3J(H,H) = 12.6 Hz, 1 H, 9a-H], 3.06 [d, J(H,H) = 12.6 Hz, 1 H,
5a-H], 3.74 (s, 3 H, OCH3), 3.76 (s, 3 H, OCH3), 3.77 (s, 3 H, OCH3),
3
3
3.78 (s, 3 H, OCH3), 6.05 [dd, J(H,H) = 5.8, J(H,H) = 3.0 Hz, 1 H, 3-
H], 6.41 ppm [dd, J(H,H) = 5.8, J(H,H) = 3.0 Hz, 1 H, 2-H]. 13C NMR mator and Mo-Kα (λ = 0.71073 Å) sealed tube. The frames were
3
3
4
(100.6 MHz, CDCl3): δ = 3.1 [d, J(C,F) = 2.2 Hz, CH3, Si(CH3)3], 32.9
integrated by using the Bruker SAINT V8.37A software package[25]
using a narrow-frame algorithm. The integration of the data using
(CH2, C-13), 34.2 (CH2, C-12), 40.3 (CH, C-14), 42.0 [d, 3J(C,F) = 4.6 Hz,
CH, C-4b], 43.6 (CH) and 43.7 (CH, C-5a, C-9a), 45.7 [d, 2J(C,F) = a triclinic unit cell yielded a total of 176875 reflections to a maxi-
24.4 Hz, C, C-15], 45.8 [d, 3J(C,F) = 4.6 Hz, C, C-11a], 48.1 (CH, C-
10a), 52.5 (CH3) and 52.6 (3 CH3, 4 COOCH3), 52.6 (CH, C-5), 53.5 (CH,
mum θ angle of 35.1° and a minimum θ angle of 1.6° (0.62 Å resolu-
tion), of which 13773 were independent (average redundancy
Eur. J. Org. Chem. 2017, 1594–1603
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1601
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Table 1. Experimental data[a] from the X-ray crystal-structure determinations of compounds 2, 10, 11, and 13.
Compound
2
10
11
13
Molecular formula
Molecular mass
C22H27ISi
446.42
C34H37IO8Si
728.62
C34H39IO8Si·CH2Cl2
815.57
C34H39FO8Si
622.74
Wavelength [Å]
Crystal system
Space group
Unit cell dimensions
0.71073
monoclinic
P21/n
0.71073
triclinic
P1
¯
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21
a [Å]
b [Å]
c [Å]
α [°]
10.6974(5)
11.8520(5)
15.1773(7)
90
9.4212(4)
13.492(2)
7.9880(14)
31.941(5)
90
13.5766(8)
7.8653(4)
14.9087(8)
90
12.9967(6)
13.3746(5)
76.241(2)
ꢀ [°]
101.230(2)
90°
1887.42(3)
4
1.571
1.761
82.033(2)
84.308(3)
1571.56(12)
2
1.540
98.032(5)
90
3408.7(10)
4
1.589
1.183
108.082(2)
90
1513.39(14)
2
1.367
0.137
γ [°]
V [Å3]
Z
Density [Mg/m3]
Absorption coefficient [mm–1
F(000)
]
1.109
744
904
1664
660
Crystal size [mm3]
0.568 × 0.177 × 0.143
2.196–30.618
–15 ≤ h ≤ 15
–16 ≤ k ≤ 16
–21 ≤ l ≤ 21
50804
0.410 × 0.200 × 0.170
1.579–35.056
–15 ≤ h ≤ 15
–20 ≤ k ≤ 20
–21 ≤ l ≤ 21
176875
0.258 × 0.095 × 0.075
2.129–26.446
–16 ≤ h ≤ 16
–9 ≤ k ≤ 9
–40 ≤ l ≤ 39
58589
0.451 × 0.096 × 0.059
2.442–26.417
–16 ≤ h ≤ 16
–9 ≤ k ≤ 9
–18 ≤ l ≤ 18
16671
θ range for data collection [°]
Index ranges
Reflections collected
Independent reflections
5778
13773
6901
6171
[Rint = 0.0313]
25.242 (99.9 %)
semi-empirical
from equivalents
0.7461 and 0.5839
5778/0/220
1.090
R1 = 0.0212
wR2 = 0.0498
R1 = 0.0266
wR2 = 0.0518
0.606 and –0.546
[Rint = 0.0626]
25.242 (100.0 %)
semi-empirical
from equivalents
0.7190 and 0.8138
13773/0/404
1.084
R1 = 0.0346
wR2 = 0.0750
R1 = 0.0523
wR2 = 0.0795
1.873 and –1.486
[Rint = 0.1058]
25.242 (99.0 %)
multiscan
[Rint = 0.0317]
25.242 (99.8 %)
semi-empirical
from equivalents
0.7454 and 0.7188
6171/1/404
1.047
R1 = 0.0338
wR2 = 0.0765
R1 = 0.0414
wR2 = 0.0806
0.229 and –0.230
Completeness to θ [°]
Absorption
correction
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
0.7454 and 0.5356
6901/0/425
1.118
R1 = 0.0686
wR2 = 0.1369
R1 = 0.0966
wR2 = 0.1490
1.874 and –1.610
[I > 2σ(I)]
R indices (all data)
Largest diff. peak and hole [e Å–3
]
[a] Temperature: 100(2) K; refinement method: full-matrix least-squares on F2; extinction coefficient: n/a; absolute structure parameter for compound 13:
–0.02(5).
12.72, completeness = 99.1 %, Rint = 6.26 %, Rsig = 4.33 %) and
10896 (79.11 %) were greater than 2σ(F2). The final cell constants of
a = 9.4212(4), b = 12.9967(6), c = 13.3746(5) Å, α = 76.241(2), ꢀ =
tor and a Mo microfocus (λ = 0.71073 Å). The frames were inte-
grated by using the Bruker SAINT software package[25] using a nar-
row-frame algorithm. The integration of the data using a monoclinic
82.033(2), γ = 84.308(3)°, V = 1571.56(12) Å3 are based upon the unit cell yielded a total of 58589 reflections to a maximum θ angle
refinement of the XYZ centroids of 9157 reflections between θ an-
gular values of 2.5 and 30.9°. Data were corrected for absorption
effects by using the multiscan method (SADABS2014/5),[26] Bruker
AXS area detector, and absorption correction. The calculated mini-
mum and maximum transmission coefficients are 0.7190 and
0.8138. The structure was solved and refined by using the Bruker
of 26.45° (0.80 Å resolution) of which 6901 were independent (aver-
age redundancy 8.490, completeness = 98.4 %, Rint = 10.58 %, Rsig
=
7.23 %) and 5378 (77.93 %) were greater than 2σ(F2). The final cell
constants of a = 13.492(2), b = 7.9880(14), c = 31.941(5) Å, ꢀ =
98.032(5)°, V = 3408.6(10) Å3 are based upon the refinement of the
XYZ centroids of reflections above 20σ(I). Data were corrected for
absorption effects by using the multiscan method (SADABS).[25] The
calculated minimum and maximum transmission coefficients (based
on crystal size) are 0.5356 and 0.7454. The structure was solved
and refined by using the Bruker SHELXTL software package[26] by
using the space group P21/c with Z = 4 for the formula unit
C34H39IO8Si·CH2Cl2. The final anisotropic full-matrix least-squares re-
finement on F2 with 425 variables converged at R1 = 6.86 % for the
observed data and wR2 = 14.90 % for all data. The goodness-of-fit
was 1.118. The largest peak in the final difference electron density
synthesis was 1.874 e Å–3 and the largest hole was –1.610 e Å–3 with
an RMS deviation of 0.153 e Å–3. On the basis of the final model, the
calculated density was 1.589 g cm–3 and F(000) = 1664 e (Table 1).
SHELX-2014 software package[15] using the space group P1 with Z =
¯
2 for the formula unit C34H37IO8Si. The final anisotropic full-matrix
least-squares refinement on F2 with 404 variables converged at R1 =
3.46 % for the observed data and wR2 = 7.95 % for all data. The
goodness-of-fit was 1.084. The largest peak in the final difference
electron density synthesis was 1.783 e Å–3 and the largest hole was
–1.486 e Å–3 with an RMS deviation of 0.110 e Å–3. On the basis of
the final model, the calculated density was 1.540 g cm–3 and
F(000) = 744 e (Table 1).
X-ray Crystal Structure Determination of Compound 11: A color-
less prism-like specimen of C34H39IO8Si·CH2Cl2, approximate dimen-
sions 0.075 mm × 0.095 mm × 0.258 mm, was used for the X-ray
crystallographic analysis. The X-ray intensity data were measured
X-ray Crystal Structure Determination of Compound 13: A color-
with a D8 Venture system equipped with a multilayer monochroma- less prism-like specimen of C34H39FO8Si, approximate dimensions
Eur. J. Org. Chem. 2017, 1594–1603
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1602 © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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0.059 mm × 0.096 mm × 0.451 mm, was used for the X-ray crystallo-
graphic analysis. The X-ray intensity data were measured on a D8
Venture system equipped with a multilayer monochromator and a
Mo microfocus (λ = 0.71073 Å). The frames were integrated by using
the Bruker SAINT software package[25] using a narrow-frame algo-
rithm. The integration of the data by using a monoclinic unit cell
yielded a total of 16671 reflections to a maximum θ angle of 26.42°
(0.80 Å resolution), of which 6171 were independent (average re-
dundancy 2.702, completeness = 99.7 %, Rint = 3.17 %, Rsig = 3.74 %)
and 5537 (89.73 %) were greater than 2σ(F2). The final cell constants
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on crystal size) are 0.7188 and 0.7454. The structure was solved and
refined by using the Bruker SHELXTL software package[26] and the
space group P21 with Z = 2 for the formula unit C34H39FO8Si. The
final anisotropic full-matrix least-squares refinement on F2 with 404
variables converged at R1 = 3.38 % for the observed data and wR2 =
8.06 % for all data. The goodness-of-fit was 1.047. The largest peak
in the final difference electron density synthesis was 0.229 e Å–3
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0.047 e Å–3. On the basis of the final model, the calculated density
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Acknowledgments
We thank the Ministerio de Economía y Competitividad
(MINECO: SAF2014-57094-R, CTQ2013-44142-P, MAT2013-
46593-C6-6-P) and the Generalitat de Catalunya (2014SGR1189)
for financial support, CCiTUB for NMR and MS facilities, and the
Institut de Química Avançada de Catalunya for elemental analy-
ses. Financial support from the Consellería de Cultura, Educa-
ción e Ordenación Universitaria (Centro singular de investiga-
ción de Galicia accreditation 2016-2019, ED431G/09) and the
European Regional Development Fund (ERDF) is gratefully ac-
knowledged. We thank all members of the P1L1 Laboratory
from CIQUS Universidade de Santiago de Compostela for their
helpful advice.
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Keywords: Domino reactions · X-ray diffraction · Polycycles ·
Cycloaddition · Nucleophilic substitution
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Received: December 19, 2016
Eur. J. Org. Chem. 2017, 1594–1603
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