Cycloisomerization of dienes and enynes catalysed by a modified ruthenium carbene species

Article abstract of DOI:10.1039/c2ob07185a

Cycloisomerization is a totally atom economic procedure which converts dienes and enynes into cyclic molecules. Modification of Grubbs' 2nd generation catalysts by reaction with dimethylformamide provides a new species able to catalyse this transformation

Full text of DOI:10.1039/c2ob07185a

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PAPER
Cycloisomerization of dienes and enynes catalysed by a modified ruthenium
carbene species†
Álvaro Mallagaray, Kazem Mohammadiannejad-Abbasabadi,‡ Sandra Medina, Gema Domínguez and
Javier Pérez-Castells*
Received 28th December 2011, Accepted 19th June 2012
DOI: 10.1039/c2ob07185a
Cycloisomerization is a totally atom economic procedure which converts dienes and enynes into cyclic
molecules. Modification of Grubbs’ 2nd generation catalysts by reaction with dimethylformamide
provides a new species able to catalyse this transformation. Selection of suitable conditions allowed high
yields and selectivity. Studies performed in order to identify the catalytic species point to a non-carbenic
ruthenium complex that has lost the phosphine. No hydride signals appeared. In addition, the reaction
works with enynes and the new species catalyses efficiently crossed cyclotrimerizations of alkynes with
diynes.
devoted to identify the catalytic species and the mechanism of
the tandem RCM-isomerization-cyclopropanation transform-
ation, we have found that when heated in dimethylformamide
Introduction
Non-metathetic transformations1 are side reactions observed fre-
quently when developing metathesis reactions catalysed by
ruthenium alkylidene catalysts.2 However, these alternative reac-
tions, if optimized, may be useful transformations. Examples
include oxidations, hydrosilylations of alkynes, hydrogenation of
olefins, cyclopropanations, cycloaddition reactions and olefin
isomerizations. We have shown recently the ability of second
generation Grubbs’ catalyst to mediate in a concurrent tandem
catalysed triple process including RCM-isomerization and cyclo-
propanation.3 This transformation is achieved by heating the
reaction after the completion of the RCM. Upon heating, the
catalyst is presumably transformed into another species, possibly
a ruthenium hydride able to produce a shift of the double bond
formed in the RCM and to mediate in the final cyclopropanation
step with ethyl diazoacetate. Many times the key issue in
directing a particular process either to a metathesis or to a differ-
ent transformation is to modify the ruthenium species before or
during the reaction. Thus, various groups have reported on
thermal transformations of [Ru]-I and [Ru]-II leading to species
able to produce olefin isomerization.4 In addition, ruthenium
hydrides can be obtained from [Ru]-II by reaction with meth-
oxide or other additives. These hydrides mediate in double bond
shifts,5 reductions6 and hydrovinylations.7 During our studies
(DMF), [Ru]-II can be transformed into a new species that pro-
duces cycloisomerization of dienes. Recently, Arisawa and
Nishida developed the selective cycloisomerization of dienes by
a combination of [Ru]-II and vinyloxytrimethylsilane. They
identified hydride A as the catalytic species and applied this
methodology to the synthesis of indoles (Fig. 1).8
Cycloisomerizations can be catalyzed by various transition
metals, such as palladium, nickel, rhodium and some ruthenium
10
complexes9 like [RuCl2(p-cymene)]2
or [Ru(cod)Cl2]2.11
Development of convenient selective methodologies based on
efficient and easy to handle catalysts for the cycloisomerization
of dienes is highly desirable and herein we present our results in
Universidad San Pablo-CEU, Departamento de Química, Facultad de
Farmacia, Urb. Montepríncipe, 28668 Boadilla del Monte (Madrid),
Spain. E-mail: jpercas@ceu.es
†Electronic supplementary information (ESI) available: Kinetics exper-
iments, synthesis and isolation of modified carbene species and NMR
spectra for new compounds. See DOI: 10.1039/c2ob07185a
‡Present address: Catalysis Division, Department of Chemistry, Univer-
sity of Isfahan, Isfahan 81746-73441, Iran.
Fig. 1 Catalytic ruthenium species.
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the use of ruthenium species obtained by reaction of Grubb’s
catalysts and DMF in cycloisomerization reactions.
decomposition of starting material (entry 10). On the other hand,
[Ru]-III gave a mixture of RCM and RCM-isomerization
products along with a small amount of cycloisomerization
(entry 11). In an attempt to improve further the yields of this
reaction avoiding the presumable decomposition of starting
materials due to the high temperatures and with the aim to
decrease the amount of DMF needed, we studied the possibility
of carrying out the second part of the reaction in toluene. Thus,
after modifying the complex in DMF (5 mL per mmol) a solu-
tion of the diene in toluene was added, reaching the optimized
concentration, and reacted at reflux temperature (entry 12). To
our delight the yield of 2a became excellent under these con-
ditions (91%) and the reaction was completed after 30 min.
Once the feasibility of performing a selective cyloisomeriza-
tion was proved, we studied the scope of the reaction with
different 1,5-dienes using the conditions of entry 12 in Table 1.
Results are summarized in Table 2.
The reaction gave excellent results with dienes 1b–d (entries
1–3). Protected amino groups were tolerated, giving tosyl deriva-
tive 1e good yields of cycloisomerization product 2e with a
small amount of its thermodynamically stable isomer 2e′ (90%
yield jointly, entry 4). However, the parent BOC derivative 1f
produced only 36% yield of 2f, and a double bond isomerization
reaction was the major process and a (7 : 3) mixture of 5f + 5f′
was isolated in 40% yield (entry 5). The cycloisomerization of
amide 1g gave a mixture of the two possible lactams 2g and 2g′
in good global yield (57%, entry 6). On the other hand, a double
bond shift was the only process observed with sulfone 1h
(entry 7).
Results and discussion
Our initial aim was exploring different reaction conditions with
diene 1a (Table 1). Searching for RCM-isomerization products
we explored the use of DMF as solvent. When performing a
reaction at r.t., the metathesis product 3a was isolated in 89%
yield as the only reaction product detectable in the 1H NMR
spectrum (entry 1). Heating the reaction to 120 °C, after mixing
all the components, provided a mixture of 3a, its isomer 4a and
the cycloisomerization product 2a (entry 2). In view of this
result we decided to heat [Ru]-II for a short period of time and
then add the diene continuing the reaction for 3 additional hours.
Under these conditions (entry 3) conversion was low, but the
major product was 2a albeit in low yield (17%) jointly with 5%
of 3a. The finding of optimum conditions to obtain 2a was
achieved with a subtle combination of time for the modification
of the catalyst, catalyst loading and concentration. Finally, the
best conditions were those of entry 6, with 10 mol% of catalyst,
10 min. for the modification of the complex and a concentration
of 0.27 mM. Under these conditions total conversion was
achieved and a 72% of cycloisomerization product 2a was iso-
lated along with 7% of RCM product 3a. A slight variation of
these conditions (entry 7) allowed total selectivity towards 2a
(62% isolated yield) and a lower catalyst loading although
without total conversion.
The extension of the reaction to larger rings seem to be pre-
cluded as compound 6 gave only a 38% of a isomerization–
cycloisomerization 5 membered-ring product 9. In addition, we
The ability of [Ru]-I and [Ru]-III to catalyse this reaction
was checked next. As expected, due to its thermal instability
[Ru]-I did not produce any identifiable product but an extensive
Table 1 Study of the cycloisomerization conditionsa
Yieldb (%)
Entry
Cat. (mol%)
Conc 1a (mM)
t1 (min)
t2 (h)
Conv.
2a
3a
4a
1
2
3
4
5
6
7
8
5 [Ru]-II
10 [Ru]-II
5 [Ru]-II
0.10
0.10
0.10
0.27
0.15
0.27
0.27
0.44
0.36
0.27
0.27
0.27
3 h at r.t.
3 h at 120 °C
3
30
5
10
5
5
7.5
7.5
7.5
12
100
100
15
n.d.
10
17
26
40
72
62
59
57
n.d.
4
89
50
5
n.d.
15
7
n.d.
7
15
n.d.
47
6
n.d.
16
n.d.
n.d.
32
n.d.
n.d.
n.d.
6
n.d.
44
3
3
3
3
3
3
3
3
5 [Ru]-II
37
10 [Ru]-II
10 [Ru]-II
7.5 [Ru]-II
10 [Ru]-II
10 [Ru]-II
10 [Ru]-I
10 [Ru]-III
10 [Ru]-II
100
100
85
95
9
100
100
100
100
10
11
12
3
0.5(tol)
91
n.d.
a Reactions were carried out in anhydrous DMF (except entry 12, see text) at 120 °C except otherwise indicated and under inert atmosphere. b Yields
in pure products. n.d. = not detected.
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Table 2 Cycloisomerization reactions of dienes 1b–h, 6 and enynes 10a–ba
No.
1
Reagents
t2
Products and yieldsb (%)
16 h
2
25 min
3
45 min
4
5
6
20 min
1 h
16 h
7
8
3 h
16 h
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Table 2 (Contd.)
No.
Reagents
t2
Products and yieldsb (%)
9
20 min
10
20 min
a Reaction conditions: Ru-[II] (10 mol%) in DMF at 120 °C for 12 min then a solution of the substrate in toluene was added and refluxed. b Yields in
pure products. Bn = benzyl; Dmob = 2,4-dimethoxybenzyl.
Fig. 2 1H NMR spectra of the reaction of [Ru]-II in DMF-d7.14
obtained mixtures of two isomers of the starting material, 7 and
8, that were separated and are formed upon one or two double
bond shifts respectively. On the other hand, we studied the be-
havior of enynes 10a–b under the same reaction conditions.
Interestingly, these substrates were transformed into 11a–b as the
only reaction products (80 and 63% respectively).12
appeared corresponding to an imidazolinium salt. No ruthenium
hydride species were detected. NMR measurements were con-
ducted down to −35 ppm to check the possible presence of
ruthenium hydrides which were not detected. In addition, the
31P spectra showed the loss of the 31P signal at 30 ppm while a
signal at 50 ppm corresponding to P(O)Cy3 appeared (see ESI†).
From these data it can be presumed that the catalyst suffers suc-
cessive loss of the phosphine and the benzylidene moieties. It is
possible that the vacancies left are occupied by DMF molecules
creating complexes similar to those described in the literature.15
At the end of the process the species is totally decomposed and
the only product isolated is an imidazolinium salt (9.18 ppm),16
produced from the NHC ligand. The catalytic species could be
an unstable complex formed along the process. Upon extraction
of aliquots after 7 and 15 min of the catalyst modification
Next we dedicated our efforts to try to identify the catalytic
species formed upon the reaction of [Ru]-II with DMF. Thus,
1
we performed 31P, H and 13C NMR spectra of the ruthenium
species before and after reaction with DMF and we also followed
1
the transformation of the complex by H NMR (Fig. 2).13 From
these spectra,14 we observed the disappearance of the carbenic
signal at 19.4 ppm as well as the signals corresponding to the
phenyl group. At the same time (E)-stilbene appeared in the
spectrum. After 15 min a new broad singlet at 9.18 ppm
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process we recorded sluggish 1H- and 13C-NMR spectra
(see Fig. 2 and ESI†) and the IR spectra showed absorptions
around 1630 cm−1 plus one absorption at 1947 cm−1 which may
correspond to a CO ligand bonded to ruthenium15 which would
come from thermal decomposition of DMF into CO and
dimethylamine. MS spectra at 7 min showed a peak at 1002
which suggests a dimeric nature of an intermediate complex.
This hypothetical structure could be similar to the ones
described by Grubbs in the studies on the thermal decomposi-
tion of [Ru]-II and other ruthenium-based carbenic catalysts.17
If the mixture is analysed after 15 min it becomes more complex
and we can see peaks at 1298, 1669 and 1882. Unfortunately,
we were not able to isolate a pure sample of the active species.
Attempts to separate it from imidazolinium salts phosphine
oxides and other subproducts led to extensive decomposition.
The inability of the new species to catalyse metathesis
whereas it is capable to produce both cycloisomerization and
double bond shifts means a transformation into one or more
active catalysts possibly with a short life. The preference for
each process seems to be related mainly to the structure of the
substrate.
Experimental section
General procedures
1H NMR, 13C NMR and 31P NMR spectra were acquired on
Bruker AM-300, Bruker AV400 and Bruker AVIII 700 specto-
meters. Chemical shifts(TM) are in parts per million relative to
tetramethylsilane at 0.00 ppm. IR spectra were determined by a
FT-IR Perkin-Elmer 2000 spectrometer. TLC analyses were per-
formed on commercial aluminium sheets bearing 0.25 mm layer
of Silica gel. Silica gel 0.035–0.070 mm, 60 Å was used for
column chromatography. Anhydrous N,N-dimethylformamide
(DMF) was purchased and used without further purification.
Hexane and toluene were refluxed over calcium hydride.
All reactions were conducted under argon atmosphere.
Preparation of starting materials
Products 1a,19 1b,19 1c,20 1d,20 1e,21 1f,21 1g,3 1h,22 6,3 10a,23
and 12a24 were prepared according to the reported procedures.
Compounds 3a,25 4a,26 5e27 have already been described and
matched with the bibliography data.
Following our recent results in the use of ruthenium carbenes
in cyclotrimerization reactions of alkynes,18 we checked the
ability of the new species to promote this transformation. In
Scheme 1 three crossed-cyclotrimerization reactions are shown
between diynes 12a–b and phenylacetylene or 1-phenylpropyne.
The reaction was highly efficient even when constructing steri-
cally crowded products as 13c. As the cyclotrimerization reaction
catalysed by ruthenium complexes is presumed to proceed
through a cascade metathesis mechanism, this result opens the
possibility of a different reaction pathway with this complex,
possibly related with that observed with other metal complexes
used in cyclotrimerization reactions.
Preparation of 6-allyl-2,2,3,3,9,9,10,10-octamethyl-6-(prop-
2-ynyl)-4,8-dioxa-3,9-disilaundecane
(10b). 2-Allyl-2-(prop-
2-ynyl)propane-1,3-diol28 (400.0 mg, 2.6 mmol), TBSCl
(1.70 g, 10.4 mmol) and imidazol (884.0 mg, 13.0 mmol) were
dissolved in anhydrous DMF (13 mL) and the reaction was con-
ducted under argon for 2 h at r.t. A mixture of water–ice
(30 mL) and diethyl ether (30 mL) was added and the organic
layer was extracted, washed with water (5 × 10 mL), brine
(3 × 10 mL), dried with MgSO4 and the solvent was evaporated.
The resulting oil was purified by performing a silica gel chrom-
atography (hexane, Rf = 0.88 in hexane) obtaining 10b (862 mg,
2.25 mmol, 87%) as a colorless oil. 1H NMR (300 MHz,
CDCl3) δ 5.84–5.60 (m, 1H, CHvCH2), 5.08–5.01 (m, 2H,
CHvCH2), 3.41–3.34 (m, 4H, 2 × CH2O), 2.08–2.06 (m, 4H,
2 × CH2), 1.89 (t, J = 2.6 Hz, 1H, CuCH), 0.85 (s, 18H, 2 ×
C(CH3)3), 0.00 (s, 12H, 2 × (CH3)2Si)); 13C NMR (75 MHz,
CDCl3) δ 134.2, 117.8, 81.7, 69.8, 63.6, 43.3, 35.1, 25.9, 21.0,
18.3, −5.6; IR (neat) 3077, 2955, 2930, 2858, 1640 cm−1
;
Anal. Calcd for C21H42O2Si2: C, 65.90; H, 11.06. Found:
C, 66.04; H, 11.18.
Preparation of dibenzyl 2,2-di(but-2-ynyl)malonate (12b).
Over a suspension of NaH (288.2 mg, 12.0 mmol) in anhydrous
THF (20 mL) at 0 °C and under argon, a solution of dibenzyl
malonate29 (1.36 g, 4.80 mmol) in anhydrous THF (5 mL) was
added and the mixture was heated to r.t. and stirred for 30 min.
1-Bromobut-2-yne (1.40 g, 10.6 mmol, 0.95 mL) was added and
the reaction was stirred at r.t. until no more starting material was
observed (TLC). Water (20 mL) was slowly added and the crude
was extracted with DCM (3 × 40 mL). The organic layers were
dried with MgSO4, organic solvents were evaporated and the
resulting oil was purified by performing a silica gel chromato-
graphy (Hex–AcOEt 9 : 1, Rf = 0.57 in Hex–AcOEt 4 : 1) obtain-
Scheme 1 Crossed-ciclotrimerization reactions of 12a–b catalysed by
the modified ruthenium species.
Conclusions
In summary, second generation Grubb’s catalyst has been
modified by reaction with DMF. We have shown the ability of
the new species to catalyse several isomerization reactions with
dienes, enynes and diynes. Extension of this methodology to
more substrates and further studies on this topic are currently
underway. Funding of this project by Spanish MEC (No.
CTQ2009-07738/BQU) is acknowledged. A.M. and S.M. thank
FUSP-CEU for a pre-doctoral fellowship.
1
ing 12b (1.27 g, 3.26 mmol, 68%) as a colorless oil. H NMR
(300 MHz, CDCl3) δ 7.33–7.25 (m, 10H, 2 × Ar), 5.13 (s, 4H,
2 × Ar–CH2O), 2.94 (d, J = 2.5 Hz, 4H, 2 × CH2CuCCH3),
1.67 (t, J = 2.5 Hz, 6H, 2 × CH2CuCCH3); 13C NMR
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(75 MHz, CDCl3) δ 169.0, 135.4, 128.5, 128.2, 128.1, 79.2,
73.1, 67.3, 57.3, 23.0, 3.5; IR (neat) 3034, 2957, 2921, 1740,
1607, 1587, 1498 cm−1; Anal. Calcd for C25H24O4: C, 77.30;
H, 6.23. Found: C, 77,13; H, 6.16.
12.8 Hz, J2 = 10.5 Hz, 1H, CH2CHCH3); Anal. Calcd for
C12H20O2: C, 73.43; H, 10.27. Found: C, 73.61; H, 10.12.
(3-Methyl-4-methylenecyclopentane-1,1-diyl)bis(methylene)bis-
(oxy)bis(tert-butyldimethylsilane) (2d).20 Following general pro-
cedure for cycloisomerization, starting with 1d (100 mg,
0.26 mmol) after 45 min 2d was obtained after silica gel chrom-
atography (hexane, Rf = 0.50 in hexane) as a colorless oil
(88 mg, 0.23 mmol, 88%). 1H NMR (300 MHz, CDCl3) δ
1H NMR (300 MHz, CDCl3) δ 4.77 (s, 1H, CvCH2), 4.69 (s,
1H, CvCH2), 3.41–3.33 (m, 4H, 2 × CH2O), 2.49–2.45 (m, 1H,
CHCH3), 2.14 (s, 2H, CH2CvCH2), 1.79 (dd, 1H, J1 = 12.9 Hz,
J2 = 8.3 Hz, CH2CHCH3), 1.08 (d, J = 6.7 Hz, 3H, CH3CH),
0.97 (dd, J1 = 12.8 Hz, J2 = 10.5 Hz, 1H, CH2CHCH3), 0.86 (s,
18H, 2 × C(CH3)3), 0.00 (s, 12H, 2 × (CH3)2Si)); Anal. Calcd
for C21H44O2Si2: C, 65.56; H, 11.53. Found: C, 65.69; H, 11.64.
General procedure for cycloisomerization reaction
Catalyst [Ru]-II (36 mg, 0.042 mmol) was placed in a flame-
dried two-necked flask equipped with a condenser, and two
cycles of vacuum-argon were performed. Anhydrous DMF
(0.2 mL) was added and the suspension was heated at 120 °C for
12 min. The dark solution was cooled to r.t., anhydrous toluene
(0.9 mL) was added followed by the addition of diene
(0.42 mmol) in anhydrous toluene (1 mL). The mixture was
gently refluxed until no more starting material was detected
(TLC), cooled to r.t., filtered through Celite and solvents were
removed under reduced pressure. The resulting dark-brown oil
was purified by flash chromatography.
3-Methyl-4-methylene-1-[(4-methylphenyl)sulfonyl]pyrroli-
dine (2e).30 Following general procedure for cycloisomerization,
starting with 1e (100 mg, 0.398 mmol) after 20 min and purifi-
cation through silica gel chromatography (Hex–AcOEt 20 : 1,
Rf = 0.29 for 2e and Rf = 0.24 for 2e′, both in Hex–AcOEt 9 : 1)
2e (71 mg, 0.282 mmol, 71%) was obtained as a white solid
(Mp: 60–63 °C) and 2e′ (19 mg, 0.075 mmol, 19%) as a white
Diethyl 3-methyl-4-methylenecyclopentane-1,1-dicarboxylate
(2a).29 Following general procedure for cycloisomerization,
starting with 1a (100 mg, 0.416 mmol) after 25 min 2a was
obtained after silica gel chromatography (Hex–AcOEt 49 : 1,
Rf = 0.63 in Hex–AcOEt 9 : 1) as a colorless oil (91 mg,
1
solid (Mp: 152–156 °C). H NMR (300 MHz, CDCl3) δ 7.71
1
(d, J = 7.8 Hz, 2H, Ar), 7.34 (d, J = 8.3 Hz, 2H, Ar), 4.91 (d,
J = 1.5 Hz, 1H, CvCHa), 4.85 (d, J = 1.9 Hz, 1H, CvCHb),
3.96 (d, J = 13.7 Hz, 1H, NCHaCvCH2), 3.73 (d, J = 14.2 Hz,
1H, NCHbCvCH2), 3.58 (m, 1H, NCH2CH), 2.72–2.67 (m,
2H, NCH2CH), 2.44 (s, 3H, CH3–Ar), 1.04 (d, J = 5.9 Hz, 3H,
CH3); Anal. Calcd for C13H17NO2S: C, 62.12; H, 6.82; N, 5.57.
Found: C, 62.00; H, 6.93; N, 5.41.
0.38 mmol, 91%). H NMR (300 MHz, CDCl3) δ 4.91 (d, J =
2.0 Hz, 1H, CvCHa), 4.80 (d, J = 2.1 Hz, 1H, CvCHb),
4.19 (q, J = 7.2 Hz, 2H, CO2CH2CH3), 4.18 (q, J = 7.0 Hz,
2H, CO2CH2CH3), 3.08–2.90 (m, 2H, CO2CCH2CvCH2),
2.57–2.51 (m, 2H, CO2CCH2CH), 1.80–1.70 (m, 1H, CO2CCH2-
CH), 1.25 (t, J = 7.0 Hz, 3H, CO2CH2CH3), 1.24 (t, J = 7.2 Hz,
3H, CO2CH2CH3), 1.11 (d, J = 6.1 Hz, 3H, CCH3); Anal. Calcd
for C13H20O4: C, 64.98; H, 8.39. Found: C, 65.14; H, 8.47.
3,4-Dimethyl-1-[(4-methylphenyl)sulfonyl]-2,5-dihydro-1H-
pyrrole (2e′).31 1H NMR (300 MHz, CDCl3) δ 7.72 (d, J =
8.3 Hz, 2H, Ar), 7.31 (d, J = 8.0 Hz, 2H, Ar), 3.97 (s, 4H,
2 × NCH2C), 2.42 (s, 3H, CH3–Ar), 1.54 (s, 6H, 2 × CH3);
Anal. Calcd for C13H17NO2S: C, 62.12; H, 6.82; N, 5.57.
Found: C, 62.03; H, 6.65; N, 5.44.
Dibenzyl 3-methyl-4-methylenecyclopentane-1,1-dicarboxylate
(2b). Following general procedure for cycloisomerization, start-
ing with 1b (100 mg, 0.27 mmol) after 16 h 2b was obtained
after silica gel chromatography (Hex–AcOEt 20 : 1, Rf = 0.53 in
Hex–AcOEt 9 : 1) as a colorless oil (93 mg, 0.25 mmol, 93%).
1H NMR (300 MHz, CDCl3) δ 7.31–7.22 (m, 10H, Ar), 5.11 (s,
2H, Ar–CH2O), 5.11 (s, 2H, Ar–CH2O), 4.90 (d, J = 2.1 Hz,
1H, CvCHa), 4.79 (d, J = 2.2 Hz, 1H, CvCHb), 3.11–2.93 (m,
2H, CO2CCH2CvCH2), 2.63–2.53 (m, 2H, CO2CCH2CH),
1.83–1.74 (m, 1H, CO2CCH2CH), 1.09 (d, J = 6.3 Hz, 3H,
CCH3); 13C NMR (75 MHz, CDCl3) δ 172.0, 171.9, 153.5,
135.9, 128.9, 128.6, 128.3, 106.1, 67.6, 67.5, 58.8, 42.5, 41.0,
37.6, 18.4; IR (neat) 3067, 3034, 2961, 2932, 2873, 1733,
1659 cm−1; Anal. Calcd for C23H24O4: C, 75.80; H, 6.64.
Found: C, 75.72; H, 6.54.
tert-Butyl 3-methyl-4-methylenepyrrolidine-1-carboxylate (2f)21.
Following general procedure for cycloisomerization, starting
with 1f (100 mg, 0.398 mmol) after 1 h and purification through
silica gel chromatography (Hex–AcOEt 20 : 1, Rf = 0.36 for 2f
and Rf = 0.67 for 5f + 5f′, both in Hex–AcOEt 4 : 1) 2f (36 mg,
0.18 mmol, 36%) and 5f + 5f′ (70 : 30, 40 mg, 0.202 mmol,
40%) were obtained as colorless oils. Data for 2f: 1H NMR
(300 MHz, CDCl3) δ 4.95 (bs, 1H, CvCHa), 4.89 (q, 1H,
J = 2.3 Hz, CvCHb), 3.98 (q, J = 9.6 Hz, 2H, NCH2CvCH2),
3.78–3.61 (m, 1H, NCH2CH), 2.91 (t, J = 9.2 Hz, 1H,
NCHaCH), 2.79–2.63 (m, 1H, NCHbCH), 1.47 (s, 9H,
3 × CH3), 1.12 (d, J = 6.7 Hz, 3H, CHCH3); Anal. Calcd for
C11H19NO2: C, 66.97; H, 9.71; N, 7.10. Found: C, 67.05; H,
9.58; N, 7.01.
2,8,8-Trimethyl-3-methylidene-7,9-dioxaspiro[4.5]decane (2c).20
Following general procedure for cycloisomerization, starting
with 1c (100 mg, 0.509 mmol) after 25 min 2c was obtained
after silica gel chromatography (Hex–AcOEt 49 : 1, Rf = 0.45 in
Hex–AcOEt 9 : 1) as a colorless oil (66 mg, 0.33 mmol, 66%).
1H NMR (300 MHz, CDCl3) δ 4.86 (s, 1H, CvCH2), 4.78 (s,
1H, CvCH2), 3.64–3.55 (m, 4H, 2 × CH2O), 2.54–2.46 (m, 1H,
CHCH3), 2.42–2.17 (m, 2H, CH2CvCH2), 1.99 (dd, 1H, J1 =
13.0 Hz, J2 = 8.2 Hz, CH2CHCH3), 1.43 (s, 3H, CH3C), 1.42 (s,
3H, CH3C), 1.08 (d, J = 6.7 Hz, 3H, CH3CH), 1.03 (dd, J1 =
Data for (E)-tert-butyl allyl(prop-1-enyl)carbamate, (5f) and
tert-butyl
di(E)-prop-1-enylcarbamate,
(5f′). 1H
NMR
(300 MHz, CDCl3) δ: 5f, 6.70 (d, J = 13.6 Hz, 1H,
CHvCHCH3), 5.75–5.62 (m, 1H, CH2CHvCH2), 5.06–4.99
(m, 2H, CH2CHvCH2), 4.83–4.69 (m, 1H, CHvCHCH3), 4.00
(bs, 2H, CH2CHvCH2), 1.63 (dd, J1 = 6.7 Hz, J2 = 1.6 Hz, 3H,
6670 | Org. Biomol. Chem., 2012, 10, 6665–6672
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CHvCHCH3), 1.41 (s, 9H, C(CH3)3); 5f′, 6.22 (d, J = 14.1 Hz,
2H, 2 × CHvCHCH3), 5.31–5.19 (m, 2H, 2 × CHvCHCH3),
1.60 (d, J = 6.6 Hz, 6H, 2 × CHvCHCH3), 1.41 (s, 9H,
C(CH3)3); 13C NMR (75 MHz, CDCl3) δ 152.4, 133.1, 127.8,
127.0, 115.7, 115.2, 103.6, 81.0, 80.8, 46.5, 28.3, 15.4, 15.2.
2H, NCH2CvCH2), 3.80 (s, 3H, OMe), 3.79 (s, 3H, OMe),
3.03 (bs, 1H, COCH), 1.93–1.72 (m, 2H, CHCH2CH3), 0.89
(t, J = 7.3 Hz, 3H, CHCH2CH3); 13C NMR (75 MHz, CDCl3)
δ 174.8, 160.6, 158.7, 142.1, 130.9, 116.9, 108.3, 104.3, 98.4,
55.4 (2 × C), 51.6, 47.7, 40.4, 24.0, 9.7; IR (neat) 2962, 2930,
2854, 1693, 1663, 1613, 1589 cm−1
; Anal. Calcd for
1-(2,4-Dimethoxybenzyl)-3-methyl-4-methylidenepyrrolidin-2-
one (2g). Following general procedure for cycloisomerization,
starting with 1g (100 mg, 0.383 mmol) after 16 h and purifi-
cation through silica gel chromatography (Hex–AcOEt 4 : 1,
Rf = 0.60 for 2g and Rf = 0.55 for 2g′, both in Hex–AcOEt 1 : 1)
2g (45 mg, 0.17 mmol, 45%) and 2g′ (12 mg, 0.045 mmol,
C16H21NO3: C, 69.79; H, 7.69; N, 5.09. Found: C, 69.89; H,
7.72; N, 5.03.
Data for (E)-N-allyl-N-(2,4-dimethoxybenzyl)but-2-enamide,
(7). 1H NMR (300 MHz, DMSO-d6, 80 °C) δ 6.99 (d, J =
8.4 Hz, 1H, Ar), 6.75–6.65 (m, 1H, CHvCHCH3), 6.56 (d, J =
2.3 Hz, 1H, Ar), 6.49 (dd, J1 = 8.4 Hz, J2 = 2.3 Hz, 1H, Ar),
6.36 (dd, J1 = 14.9 Hz, J2 = 1.5 Hz, 1H, CHvCHCH3),
5.78–5.71 (m, 1H, CH2CHvCH2), 5.11–5.04 (m, 2H,
CH2CHvCH2) 4.44 (s, 2H, ArCH2N), 3.92 (AB system, 2H,
CH2CHvCH2), 3.79 (s, 3H, OMe), 3.76 (s, 3H, OMe),
1.83 (dd, J1 = 6.8 Hz, J2 = 1.6 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3) 2 conformers δ 167.1, 160.4, 160.2, 158.0,
141.8, 141.8, 133.5, 133.4, 130.6, 127.9, 122.1, 117.5, 117.0,
116.3, 104.3, 103.9, 98.6, 98.3, 55.4, 55.2, 49.6, 48.2, 45.4,
43.2, 18.2;
1
12%) were obtained as pale yellow oils. H NMR (300 MHz,
CDCl3) δ 7.13 (d, J = 8.8 Hz, 1H, Ar), 6.46–6.44 (m, 2H, Ar),
5.03–5.00 (m, 2H, CvCH2), 4.48 (s, 2H, CH2Ar), 3.90–3.77
(m, 2H, NCH2CvCH2), 3.81 (s, 3H, OMe), 3.80 (s, 3H, OMe),
3.05 (q, J = 7.3 Hz, 1H, CHCH3), 1.32 (d, J = 7.3 Hz, 3H,
CHCH3); 13C NMR (75 MHz, CDCl3) δ 175.7, 160.8, 159.0,
144.6, 131.2, 117.1, 108.0, 104.5, 98.7, 55.7, 55.7, 51.6, 41.8,
40.7, 15.8; IR (neat) 2924, 2851, 1711, 1649, 1615, 1589 cm−1
;
Anal. Calcd for C15H19NO3: C, 68.94; H, 7.33; N, 5.36. Found:
C, 69.03; H, 7.24; N, 5.33.
1-(2,4-Dimethoxybenzyl)-4-methyl-3-methylidenepyrrolidin-2-
one (2g′). 1H NMR (300 MHz, CDCl3) δ 7.16 (d, J = 8.8 Hz,
1H, Ar), 6.47–6.43 (m, 2H, Ar), 6.00 (d, J = 2.4 Hz, 1H,
CvCHa), 5.27 (d, J = 2.4 Hz, 1H, CvCHb), 4.56 (d, J =
14.6 Hz, 1H, CHaAr), 4.48 (d, J = 14.6 Hz, 1H, CHbAr),
3.81 (s, 3H, OMe), 3.81 (s, 3H, OMe), 3.45 (t, J = 7.8 Hz,
Data for (E)-N-(2,4-dimethoxybenzyl)-N-((E)-prop-1-enyl)but-
2-enamide, (8). 1H NMR (300 MHz, DMSO-d6, 80 °C) δ 6.96
(d, J = 13.6 Hz, 1H, NCHvCHCH3), 6.83–6.75 (m, 1H,
CHvCHCH3), 6.77 (d, J = 10.9 Hz, 1H, CHvCHCH3), 6.57
(d, J = 2.4 Hz, 1H, Ar), 6.47 (d, J = 8.4 Hz, 1H, Ar), 6.49 (dd,
J1 = 8.4 Hz, J2 = 2.5 Hz, 1H, Ar), 5.01–4.90 (m, 1H,
NCHvCHCH3), 4.68 (s, 2H, ArCH2N), 3.82 (s, 3H, OMe),
3.75 (s, 3H, OMe), 1.85 (dd, J1 = 6.8 Hz, J2 = 1.6 Hz, 3H,
CH3), 1.62 (dd, J1 = 6.6 Hz, J2 = 1.6 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3) 2 conformers δ 169.8, 157.7, 157.3, 143.3,
129.3, 127.2, 126.8, 122.2, 117.7, 116.8, 110.6, 107.1, 104.1,
98.4, 55.4, 55.3, 44.2, 18.3, 15.5.
1H, NCHaCvCH2), 2.92–2.80 (m, 2H, NCHbCvCH2
&
NCH2CH), 1.18 (d, J = 6.4 Hz, 3H, CHCH3); IR (neat) 2921,
2858, 1645, 1589, 1507 cm−1; Anal. Calcd for C15H19NO3: C,
68.94; H, 7.33; N, 5.36. Found: C, 68.79; H, 7.40; N, 5.25.
(1E)-1-(prop-2-en-1-ylsulfonyl)prop-1-ene (5h).32 Following
general procedure for cycloisomerization, starting with 1h
(100 mg, 0.68 mmol) after 3 h was obtained after silica gel
chromatography (Hex–AcOEt 4 : 1, Rf = 0.43 in Hex–AcOEt
2 : 1) 5h (90 mg, 0.61 mmol, 90%) was obtained as colorless oil.
1H NMR (300 MHz, CDCl3) δ 6.96–6.82 (m, 1H, CHCH3),
Diethyl 3,4-dimethylenecyclopentane-1,1-dicarboxylate (11a)33.
Following general procedure for cycloisomerization, starting
with 10a (100 mg, 0.42 mmol) after 20 min 11a (80 mg,
0.34 mmol, 80%) was obtained after silica gel chromatography
(Hex–AcOEt 20 : 1, Rf = 0.42 in Hex–AcOEt 6 : 1) as pale
yellow oil. 1H NMR (300 MHz, CDCl3) δ 5.38 (s, 2H, 2 ×
CvCHa), 4.95 (s, 2H, 2 × CvCHb), 4.19 (q, J = 7.2 Hz, 4H, 2
× OCH2CH3), 3.03 (s, 4H, 2 × CCH2C), 1.24 (t, J = 7.0 Hz, 6H,
2 × OCH2CH3); Anal. Calcd for C13H18NO4: C, 65.53; H, 7.61.
Found: C, 65.42; H, 7.53.
6.30 (apparent dd, J1
= 15.1 Hz, J2 = 1.6 Hz, 1H,
SO2CHvCH), 5.94–5.88 (m, 1H, CH2CHvCH2), 5.51 (d, J =
10.2 Hz, 1H, CH2CHvCH2), 5.44 (d, J = 17.0 Hz, 1H,
CH2CHvCH2), 3.71 (AB system, 2H, CH2CHvCH2), 1.97 (dd,
J1 = 6.7 Hz, J2 = 1.6 Hz, 3H, CHvCHCH3); 13C NMR
(75 MHz, CDCl3) δ 145.7, 128.6, 124.9, 124.4, 59.4, 17.4. IR
(neat) 2975, 2922, 1640 cm−1; Anal. Calcd for C6H10O2S: C,
49.29; H, 6.89. Found: C, 49.38; H, 6.80.
(3,4-Dimethylenecyclopentane-1,1-diyl)bis(methylene)bis(oxy)-
bis(tert-butyldimethylsilane) (11b). Following general procedure
for cycloisomerization, starting with 10b (100 mg, 0.26 mmol)
after 20 min 11b (63 mg, 0.16 mmol, 63%) was obtained after
silica gel chromatography (hexane, Rf = 0.62 in hexane) as color-
1-(2,4-Dimethoxybenzyl)-3-ethyl-4-methylenepyrrolidin-2-one
(9). Following general procedure for cycloisomerization, starting
with 6 (100 mg, 0.68 mmol) after 16 h 9 was obtained after
silica gel chromatography (Hex–AcOEt 6 : 1 to 2 : 1, Rf = 0.23 in
Hex–AcOEt 2 : 1) (38 mg, 0.25 mmol, 38%) as a brown oil and
55 mg of a mixture of 7 + 8 which was separated by column
chromatography (Hex–AcOEt 6 : 1) to give 15 mg of 7 (15%)
1
less oil. H NMR (300 MHz, CDCl3) δ 5.34 (s, 2H, CvCH2),
4.83 (s, 2H, CvCH2), 3.39 (s, 4H, 2 × CH2O), 2.26 (s, 4H,
2 × CH2), 0.87 (s, 18H, 2 × C(CH3)3), 0.00 (s, 12H, 2 ×
(CH3)2Si)); 13C NMR (75 MHz, CDCl3) δ 147.8, 104.6, 64.7,
47.0, 38.6, 25.9, 18.3, −5.5; IR (neat) 2955, 2930, 2857,
1676 cm−1; Anal. Calcd for C21H42O2Si2: C, 65.90; H, 11.06.
Found: C, 65.73; H, 11.19.
1
and 35 mg of 8 (35%) as colorless oils. Data for 9: H NMR
(300 MHz, CDCl3) δ 7.12 (d, J = 9.1 Hz, 1H, Ar), 6.46–6.42
(m, 2H, Ar), 5.05–5.01 (m, 2H, CvCH2), 4.57 (d, J = 14.5 Hz,
1H, CHaAr), 4.39 (d, J = 14.6 Hz, 1H, CHbAr), 3.82–3.67 (m,
This journal is © The Royal Society of Chemistry 2012
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2 For reviews on olefin metathesis, see: (a) S. P. Nolan and H. Clavier,
Chem. Soc. Rev., 2010, 39, 3305–3316; (b) S. Monfette and D. E. Fogg,
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S.-I. Murahashi, Wiley-VCH, Weinheim, 2004, Ch. 6.
3 A. Mallagaray, G. Domínguez, A. Gradillas and J. Pérez-Castells, Org.
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4 S. Hanessian, S. Giroux and A. Larsson, Org. Lett., 2006, 8, 5481–5484.
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General procedure for cyclotrimerization reaction
Catalyst [Ru]-II (7.2 mg, 0.008 mmol) was placed in a flame-
dried two-necked flask equipped with a condenser, and two
cycles of vacuum-argon were performed. Anhydrous DMF
(0.2 mL) was added and the suspension was heated at 120 °C for
12 min. The dark solution was cooled to r.t., anhydrous toluene
(0.9 mL) was added followed by the addition of a mixture of
diyne (0.42 mmol) and monoyne (1.27 mmol) in anhydrous
toluene (1.5 mL). The reaction was gently refluxed until no more
starting material was detected (TLC), cooled to r.t., filtered
through Celite and solvents were removed under reduced
pressure. The resulting dark-brown oil was purified by flash
chromatography.
6 C. Menozzi, P. I. Dalko and J. Cossy, Synlett, 2005, 2449.
7 J. Gavenonis, R. V. Arroyo and M. L. Snapper, Chem. Commun., 2010,
46, 5692–5694, and references cited therein.
8 M. Arisawa, Y. Terada, K. Takahashi, M. Nakagawa and A. Nishida,
J. Org. Chem., 2006, 71, 4255–4261.
Diethyl 5-phenyl-1,3-dihydro-2H-indene-2,2-dicarboxylate (13a)34.
Following general procedure for cyclotrimerization, starting with
12a (100 mg, 0.42 mmol) after 24 h 13a (124.5 mg, 0.37 mmol,
87%) was obtained after silica gel chromatography (Hex–AcOEt
49 : 1 to 20 : 1, Rf = 0.37 in Hex–AcOEt 9 : 1) as a brown oil.
1H NMR (300 MHz, CDCl3) δ 7.56–7.53 (m, 2H, Ar),
7.42–7.37 (m, 4H, Ar), 7.33–7.23 (m, 2H, Ar), 4.21 (q, J =
7.1 Hz, 4H, 2 × OCH2CH3), 3.64 (s, 2H, H-3), 3.63 (s, 2H,
H-1), 1.26 (t, J = 7.1 Hz, 6H, 2 × OCH2CH3); Anal. Calcd for
C21H22O4: C, 74.54; H, 6.55. Found: C, 74.37; H, 6.63.
9 (a) B. M. Trost, A. C. Gutierrez and E. M. Ferreira, J. Am. Chem. Soc.,
2010, 132, 9206–9218; (b) B. M. Trost, A. C. Gutierrez and
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(c) B. M. Trost and D. F. Toste, J. Am. Chem. Soc., 1999, 121, 9728–9729.
10 B. Çetinkaya, S. Demir, I. Özdemir, L. Toupet, D. Sémeril, C. Bruneau
and P. H. Dixneuf, New J. Chem., 2001, 25, 519–521.
11 Y. Yamamoto, Y. Nakagai and K. Itoh, Chem.–Eur. J., 2004, 10, 231–236.
12 For cycloisomerization of enynes see: S. Kezuka, T. Okado, E. Niou and
R. Takeuchi, Org. Lett., 2005, 7, 1711–1714, and ref. 6–11 cited therein.
13 Catalyst [Ru]-II (20 mg, 0.023 mmol) was loaded in an NMR tube and
anhydrous DMF-d7 (99.5 atom% D) (0.7 mL) and one drop of anhydrous
DMF was added. The tube was filled with argon, closed and the temperature
was progressively increased (30 °C min−1) and 1H was acquired every min.
14 For NMR study on [Ru]-II under variable temperatures, see:
M. M. Gallagher, A. D. Rooney and J. J. Rooney, J. Organomet. Chem.,
2008, 693, 1252–1260.
15 P. Serp, M. Hernandez, B. Richard and P. Kalck, Eur. J. Inorg. Chem.,
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16 A. J. Arduengo, R. Krafczyk and R. Schmutzler, Tetrahedron, 1999, 55,
14523–14534.
17 (a) S. Hyeok Hong, A. G. Wenzel, T. T. Salguero, M. W. Day and
R. H. Grubbs, J. Am. Chem. Soc., 2007, 129, 7961–7968;
(b) M. B. Herbert, Y. Lan, B. K. Keitz, P. Liu, K. Endo, M. W. Day,
K. N. Houk and R. H. Grubbs, J. Am. Chem. Soc., 2012, 134, 7861–
7866.
Dibenzyl
4,7-dimethyl-5-phenyl-1,3-dihydro-2H-indene-2,2-
dicarboxylate (13b). Following general procedure for cyclotri-
merization, starting with 12b (100 mg, 0.259 mmol) after 24 h
13b was obtained after silica gel chromatography (Hex–AcOEt
20 : 1, Rf = 0.38 in Hex–AcOEt 9 : 1) (105.4 mg, 0.21 mmol,
1
83%) as a brown oil. H NMR (300 MHz, CDCl3) δ 7.40–7.22
(m, 16H, Ar), 5.15 (s, 4H, 2 × ArCH2O), 3.61 (s, 4H, H-1 &
H-3), 2.22 (s, 3H, CH3–C4), 2.10 (s, 3H, CH3–C7); 13C NMR
(75 MHz, CDCl3) δ 171.6, 142.0, 141.1, 139.3, 137.5, 135.5,
130.6, 130.0, 129.4, 128.6, 128.3, 128.0, 126.6, 67.4, 59.9,
40.3, 39.7, 18.6, 16.7; IR (neat) 3033, 2950, 2920, 1733,
1600 cm−1; Anal. Calcd for C33H30O4: C, 80.79; H, 6.16.
Found: C, 80.6 3; H, 6.39.
18 A. Mallagaray, S. Medina, G. Domínguez and J. Pérez-Castells, Synlett,
2010, 14, 2114–2118, and references cited therein.
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23 B. L. Pagenkopf and T. Livinghouse, J. Am. Chem. Soc., 1996, 118,
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24 R. K. Singh, Synthesis, 1985, 54–55.
25 W. A. Nugent, J. Feldman and J. C. Calabrese, J. Am. Chem. Soc., 1995,
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26 T. S. Abram, R. Baker, C. M. Exon and V. B. Rao, J. Chem. Soc., Perkin
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27 A. Fürstner, M. Liebl, C. W. Lehmann, M. Picquet, R. Kunz, C. Bruneau,
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29 D. Crich, T. Hwang, S. Gastaldi, F. Recupero and D. J. Wink, J. Org.
Chem., 1999, 64, 2877–2882.
Dibenzyl 4,5,7-trimethyl-6-phenyl-1,3-dihydro-2H-indene-2,2-
dicarboxylate (13c). Following general procedure for cyclotri-
merization, starting with 12b (100 mg, 0.259 mmol) after 24 h
13c was obtained after silica gel chromatography (Hex–AcOEt
20 : 1, Rf = 0.44 in Hex–AcOEt 9 : 1) (92.3 mg, 0.18 mmol,
71%) as a pale yellow oil. 1H NMR (300 MHz, CDCl3) δ
7.42–7.37 (m, 2H, Ar), 7.33–7.22 (m, 11H, Ar), 7.10–7.07 (m,
2H, Ar), 5.14 (s, 4H, 4H, 2 × ArCH2O), 3.66 (s, 2H, H-3),
3.60 (s, 3H, H-1), 2.17 (s, 3H, CH3), 1.90 (s, 3H, CH3), 1.85 (s,
3H, CH3); 13C NMR (75 MHz, CDCl3) δ 171.7, 142.0, 141.2,
137.4, 135.8, 135.5, 133.5, 129.5, 129.4, 128.9, 128.5, 128.3,
128.3, 128.0, 126.4, 67.4, 59.6, 40.4, 40.2, 17.4, 17.3, 16.4;
IR (neat) 3063, 3033, 2924, 1733, 1601 cm−1; Anal. Calcd for
C34H32O4: C, 80.93; H, 6.39. Found: C, 80.78; H, 6.37.
30 D. Sémeril, C. Bruneau and P. H. Dixneuf, Helv. Chim. Acta, 2001, 84,
3335–3341.
31 M. E. Krafft, L. V. R. Boñaga, J. A. C. Wright and C. Hirosawa, J. Org.
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32 R. C. Fuson, C. C. Price and D. M. Burness, J. Org. Chem., 1946, 11,
475–481.
Notes and references
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13214–13216.
34 N. Saino, F. Amemiya, E. Tanabe, K. Kase and S. Okamoto, Org. Lett.,
2006, 8, 1439–1442.
1 Reviews on non-metathetic behaviour of Ru catalysts: (a) B. Alcaide,
P. Almendros and A. Luna, Chem. Rev., 2009, 109, 3819–3858;
(b) B. Schmidt, Eur. J. Org. Chem., 2004, 1865–1880; (c) B. Alcaide and
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6672 | Org. Biomol. Chem., 2012, 10, 6665–6672
This journal is © The Royal Society of Chemistry 2012