Recoverable Dendritic Phase-Transfer Catalysts that Contain (+)-Cinchonine-Derived Ammonium Salts

Article abstract of DOI:10.1002/cctc.201600283

Four new phosphorus dendrimeric phase-transfer catalysts are prepared that contain 12 (+)-cinchoninium salts on the surface obtained by the quaternisation of the quinuclidinic N atom. The asymmetric alkylation of a glycinate Schiff base with benzyl bromide is used as a benchmark reaction, and the dendrimeric catalyst that contains an allyl group on the O-9 hydroxy group of the cinchonine units is the most active. The recovery and reuse of the catalyst are possible for five consecutive runs without loss of activity and with only a slight decrease in enantioselectivity. If other electrophiles are used, substituted benzyl bromides give better results than other activated alkyl bromides to afford the corresponding R amino acid derivatives. A comparison of these results with those reported previously for similar cinchoninium salts shows that dendrimers could be a better support than other polymers for this type of organocatalysis.

Full text of DOI:10.1002/cctc.201600283

DOI: 10.1002/cctc.201600283
Full Papers
Recoverable Dendritic Phase-Transfer Catalysts that
Contain (+)-Cinchonine-Derived Ammonium Salts
Jordi Rull,[a] JosØ Juan Jara,[a] Rosa M. Sebastiµn,*[a] Adelina Vallribera,*[a] Carmen Nµjera,[b]
Jean-Pierre Majoral,[c] and Anne-Marie Caminade[c]
Four new phosphorus dendrimeric phase-transfer catalysts are
prepared that contain 12 (+)-cinchoninium salts on the surface
obtained by the quaternisation of the quinuclidinic N atom.
The asymmetric alkylation of a glycinate Schiff base with
benzyl bromide is used as a benchmark reaction, and the den-
drimeric catalyst that contains an allyl group on the O-9 hy-
droxy group of the cinchonine units is the most active. The re-
covery and reuse of the catalyst are possible for five consecu-
tive runs without loss of activity and with only a slight de-
crease in enantioselectivity. If other electrophiles are used, sub-
stituted benzyl bromides give better results than other
activated alkyl bromides to afford the corresponding R amino
acid derivatives. A comparison of these results with those re-
ported previously for similar cinchoninium salts shows that
dendrimers could be a better support than other polymers for
this type of organocatalysis.
Introduction
Phase-transfer catalysis (PTC) was reported for the first time by
Starks in 1971.[1] This type of catalysis facilitates the migration
of a reactant from one phase into another in which the reac-
tion occurs, which avoids mass transfer limitations and increas-
es the efficiency of biphasic processes. If the reaction proceeds
between an organic and aqueous or solid phase, tetraalkylam-
monium or phosphonium salts are used commonly as cata-
lysts.[2] This type of catalysis is very versatile for organic synthe-
sis in both academia and industry because of its simple experi-
mental process, mild reaction conditions, inexpensive and sus-
tainable catalysts and solvents, and the possibility to be imple-
mented on a large scale.[3] The asymmetric version has been
developed over the last 20 years[4] and is applied in several
chemical transformations, such as alkylations,[5] Michael addi-
tions,[6] aldol and related reactions,[7] cyclopropanations,[8] ep-
oxidations[9] and aziridinations,[10] among others.[11]
they have an extraordinary ability to promote asymmetric
transformations in homogeneous or heterogeneous media as
organocatalysts or chiral ligands.[13] N-Alkylation on the quinu-
clidinic ring generates a variety of quaternary ammonium salts
that have been used extensively in asymmetric PTC.[3,13,14]
The phase-transfer alkylation of protected glycine derivatives
is a good method to afford optically active a-amino acid pre-
cursors and it is one of the most important reactions studied
with ammonium salts derived from Cinchona alkaloids. It is
used as a benchmark reaction to examine the performance of
new phase-transfer catalysts.[4,14] O’Donnell et al. reported the
first example of glycine imine ester alkylation with moderate
enantioselectivity levels (up to 66% ee).[15] Simple modifications
on Cinchona derivatives allowed Corey et al.[16] and Lygo
et al.[17] to obtain impressive degrees of enantioselectivity. Fur-
ther generations of Cinchona ammonium salts as catalysts
have been proposed by connecting two or three independent
cinchona alkaloid units attached to spacers or modifying the
electronic effects in the surroundings of the quinuclidine N
atom.[14] The recovery and reuse (up to the fourth cycle) of
these types of catalysts have been achieved mainly by their at-
tachment to polymers.[18] Although a variety of points are pres-
ent on the Cinchona alkaloid motif to anchor the catalyst on
a solid support, attachment at the O-9 hydroxy group or at the
N atom of the quinuclidine moiety of the alkaloid best pre-
serve the enantioselectivity of the catalyst.[19]
Cheap commercially available Cinchona alkaloids and their
derivatives have been used as chiral resolving agents[12] and
[a] Dr. J. Rull, J. J. Jara, Dr. R. M. Sebastiµn, Dr. A. Vallribera
Department of Chemistry and Centro de Innovación en Química
(ORFEO-CINQA)
Universitat Autònoma de Barcelona
Cerdanyola del Vall›s,08193 Barcelona (Spain)
E-mail: rosamaria.sebastian@uab.es
[b] Prof. C. Nµjera
Departamento de Química Orgµnica, Facultad de Ciencias and Centro de
Innovación en Química (ORFEO-CINQA)
Universidad de Alicante Apartado 99, 03080 Alicante (Spain)
Dendrimers are a new class of polymeric materials with
unique structural features such as a highly branched and well-
defined structure, globular shape and controlled surface func-
tionalities.[20] As a result of their robustness, size and potential
dendritic effect,[21] they have been used as supports for a large
number of organometallic and organocatalytic moieties (e.g.,
proline derivatives) for catalytic applications and can be recov-
ered and reused several times.[20,22] In most of the cases, den-
[c] Dr. J.-P. Majoral, Dr. A.-M. Caminade
CNRS; LCC (Laboratoire de Chimie de Coordination) and
UniversitØ de Toulouse, UPS, INPT; LCC
205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4 (France)
Supporting Information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
cctc.201600283.
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drimers are soluble in the organic medium used for the reac-
tions to perform homogeneous catalysis, and their easy recov-
ery is possible by precipitation from the reaction medium by
the addition of a non-polar solvent. However, Cinchona alka-
loids have been rarely anchored in these macromolecules.[23,24]
Recently, we reported the preparation of two dendrimers of
the first and fourth generation decorated at the surface with
12 and 96 (+)-cinchonine moieties, respectively, used as recov-
erable organocatalysts (in up to 10 cycles) for the a-amination
of several b-dicarbonyl compounds.[23] Nµjera and co-workers
used FrØchet dendrimers, up to the third generation, that con-
tained cinchonine-derived ammonium salts at the core for the
asymmetric PTC alkylation of N-(diphenylmethylene)glycine
isopropyl ester with different alkyl halides in good yields but
moderate enantioselectivities.[24a] The recovery process by
using dialysis membranes was only successful for the second-
generation dendrimeric salts that were used only for two con-
secutive catalytic runs.
The next step consisted of the nucleophilic substitution of
the Cl atoms of the outer shell of the dendrimers with com-
mercially available (+)-cinchonine (5a) and with three other
derivatives that resulted from its O-9-alkylation with allyl bro-
mide (5b), benzyl bromide (5c) and trimethylsilyl chloride
(5d)[28] to form the corresponding quaternary ammonium salts
(75–80% yield; Scheme 2). The first reaction was performed
between dendrimer 3-G1 and 5a heated in THF and THF/DMF
mixtures, however, no reaction was observed by NMR spectros-
copy (neither by the disappearance of CH2Cl signal at d=
4.68 ppm, nor by any change in the 31P NMR spectrum). There-
fore, we decided to modify the surface of the dendrimer by re-
placing the Cl atoms with I to make the substitution easier.
The treatment of 3-G1 with a slight excess of NaI in acetone
under reflux for 32 h allowed the formation of 4-G1, which con-
tains 12 I atoms on the surface, in a moderate yield of 77%
1
(Scheme 1). This reaction could be followed by H NMR spec-
troscopy ([D6]DMSO), in which the CH2Cl groups shifted from
d=4.67 to 4.54 ppm for CH2I. A shift in the 31P NMR spectrum
was also observed from d=63.4 to 62.3 ppm, which corre-
sponds to the external P atoms.
With these precedents, we planned to decorate, for the first
time, a first-generation phosphorus dendrimer with different
O-alkylated (+)-cinchonine ammonium salts and study their
catalytic activity and recyclability in the enantioselective PTC
alkylation of benzophenone glycine imine tert-butyl ester with
different electrophiles. This reaction is a powerful tool to pre-
pare useful amino acid derivatives and natural products.[25] The
catalytic moieties immobilised on the surface of the dendrim-
ers are in close proximity, which allows a positive or negative
effect on the kinetics of the catalysed reaction (dendritic
effect) compared to the free ammonium salts. This is analysed
in this work.
Dendritic quaternary ammonium salts 6-G1 a–d were ob-
tained by treatment of the first-generation dendrimer 4-G1
with 5a–d in THF at 708C over 24 h. The salts were isolated by
simple filtration and obtained in excellent 93–95% yields
(Scheme 2). These salts 6 were insoluble in THF at room tem-
perature, whereas the starting dendrimer 4-G1 was completely
1
soluble. H NMR spectra of the ammonium salts in DMSO or
CD2Cl2 at room temperature afforded complex, broad signals
(other solvents were tested that showed worse results); even
experiments at higher and lower temperatures were performed
without increased resolution. 31P NMR spectra in [D6]DMSO
showed in most cases a shift from d=62.3 (4-G1) to 61.1–
61.5 ppm in the salts; once again, this type of 31P NMR spec-
troscopy experiment was very useful to follow reactions on the
surface of dendrimers.
Results and Discussion
An enormous family of phosphorus dendrimers has been creat-
ed by Caminade et al.[26] Most of them have been built from
hexachlorocyclotriphosphazene as a core, using p-hydroxyben-
zaldehyde and dichlorothiophosphorus monomethylhydrazine
in an iterative way following a divergent method. Aldehyde
functions on the surface (1-G1) could be reduced with
BH3·SMe2 to the corresponding benzyl alcohols (2-G1) that
were transformed into the corresponding benzylic chlorides (3-
G1) after treatment with thionyl chloride in toluene under an-
hydrous conditions, as shown in Scheme 1 for a dendrimer of
the first generation.[27]
As noted in the introduction, many ammonium salts derived
from Cinchona alkaloids have been used as catalysts for the
asymmetric alkylation of active methylene compounds, espe-
cially glycine imino esters.[4,14] As a first stage, we decided also
to test the catalytic activity of our new dendrimers 6-G1 a–d in
the reaction of glycinate 7 with benzyl bromide 8 (Table 1)
under the conditions reported by Park and co-workers.[29] The
reaction was performed at room temperature, 08C and À208C,
using a 50% aqueous solution of KOH in a mixture of CHCl3/
Scheme 1. Synthesis of phosphorus dendrimers that contain benzyl chloride and iodide functions on the surface, 3-G1 and 4-G1, respectively.
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Scheme 2. Preparation of dendrimeric phase-transfer catalysts 6-G1 a–d.
toluene (Table 1). The amount of catalyst was reduced com-
pared to that in the study of Park et al.,[29] and we used
0.1 mol% of catalyst (1.2 mol% of cinchonine moieties) instead
of the 10% reported. The resulting imines were derivatised to
the corresponding trifluoroacetamides by their hydrolysis with
citric acid and the following protection of the primary amines
by reaction with trifluoroacetic anhydride (TFAA). This process
was performed to simplify the analysis of the ee by chiral GC
by avoiding the hydrolysis and the corresponding formation of
benzophenone, which masked the interesting peaks on the
chromatogram, as reported.[18,24a]
60%, respectively; Table 1, entries 2, 6 and 10). In addition, the
reaction time increased from 1 to 8 h if the temperature de-
creased. The other three catalysts were in general slightly less
enantioselective. However, at 08C benzyl-protected cinchonine
derivative 6-G1 c showed a similar activity to 6-G1 b (Table 1,
entries 6 and 7). No better results were obtained if a higher
amount of catalyst was used. Notably, if the reaction was per-
formed at À208C, the reaction medium was partially frozen,
which led to worse results (Table 1, entries 9–12). We used the
best reaction conditions, 08C with catalyst 6-G1 b, to test other
solvents such as toluene alone, CHCl3/toluene 1:7, dichlorome-
thane or THF, but in all cases the obtained ee values were
lower, and if DMF was used, racemic mixtures were isolated.
We explored other organic and inorganic bases such as 2-
tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-dia-
zaphosphorine (BEMP) and aqueous RbOH, LiOH and NaOH at
08C with 6-G1 c as the catalyst and similar yields (76–89%) but
lower enantioselectivities (12–76%) were obtained. No reaction
The best enantioselectivities were obtained in the reactions
catalysed by 6-G1 b; (R)-9 was obtained as the major isomer,
and its absolute configuration was determined by comparing
the chiral GC retention times of both isomers reported previ-
ously by some of us for the trifluoroacetamide derivative-
s.[4,18a,24] The ee was higher if the reaction was performed at
08C (89%) than at room temperature and at À208C (74 and
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Table 1. Catalyst screening at different temperatures.[a]
Table 2. Recycling of catalyst 6-G1 b in the reaction of 7 and 8 (Table 1).[a]
Catalyst 6-G1 b
Entry
Yield [%][b]
ee [%][c]
1
2
3
4
5
79
80
78
77
77
89
86
82
81
79
Entry
Catalyst[b]
T [8C]
Yield [%][c]
ee [%][d]
[a] Reactions were performed with 0.25 mmol of 7, 1.26 mmol of 8 and 6-
G1 b (0.1 mol%) in 1.5 mL (CHCl3/PhCH3, 3:7) and 50% KOH aqueous solu-
tion (141 mL) for 1 h at 08C. [b] Isolated yields after column chromatogra-
phy, acidic hydrolysis and formation of the trifluoroacetamide. [c] Deter-
mined by chiral CG of the isolated product 9.
1
2
3
4
5
6
7
8
6-G1 a
6-G1 b
6-G1 c
6-G1 d
6-G1 a
6-G1 b
6-G1 c
6-G1 d
6-G1 a
6-G1 b
6-G1 c
6-G1 d
25
25
25
25
0
0
0
0
À20
À20
À20
À20
75
80
81
78
73
79
75
70
62
60
66
58
68
74
70
70
80
89
86
78
48
60
48
36
and 31P NMR spectroscopy, which confirmed that it was
a robust macromolecule because its structure was maintained.
Our results for this bench reaction compared with those re-
ported in the literature for different modified Cinchona alkaloid
salts are quite good with regard to the yields and enantiose-
lectivities, and similar ranges were obtained.[14] However, to the
best of our knowledge, our dendrimers compared with sup-
ported cinchonine alkaloid in polymers (even in SynPhaseTM
lanterns) lead to a higher ee, and in addition, the reaction time
is reduced, from several hours to 1 h, in our case at 08C, using
only 0.1 mol% of our catalyst (1.2 mol% of cinchonine moiet-
ies).[18,19,31] The possibility of the existence of a collaborative
effect among the cinchonine moieties on the surface of the
dendrimer could be the explanation of this kinetic improve-
ment, which shows a positive dendritic effect. This effect does
not exist if Cinchona derivatives are incorporated at the core of
a dendrimer. As reported by some of us, in that case the activi-
ty and enantioselectivity of the dendritic catalysts were worse,
it was only possible to recycle them twice and low ee values
were obtained.[24a]
9
10
11
12
[a] Reactions were performed with 0.25 mmol of 7, 1.26 mmol of 8 and
catalyst 6 (0.1 mol%) in 1.5 mL (CHCl3/PhCH3, 3:7) and 50% KOH aqueous
solution (141 mL) for 1–8 h (followed by H NMR spectroscopy). [b] Higher
catalysts loadings did not give better results. [c] Isolated yields after
column chromatography, acidic hydrolysis and formation of the trifluor-
oacetamide. [d] Determined by chiral CG of the isolated product 9.
1
was observed if other bases such as 1,8-diazabicyclo[5.4.0]un-
dec-7-ene (DBU), aqueous Cs2CO3 and K2CO3 were used.
Under the tested conditions, suspensions of our catalysts
were observed in the reaction media, which shows that heter-
ogeneous phase-transfer catalysis was probably performed, al-
though catalysts 6-G1 b and 6-G1 c seemed to be partially solu-
ble. It is known for a family of phosphorus dendrimers that
contain charged moieties on the surface, such as those tested,
that if only water is used as solvent, generally they are mainly
insoluble in spite of the charged surface. However, if some
drops of an organic solvent (for example THF or DMF) are
added, some molecules of these solvents are incorporated in
the internal cavities of the dendrimer, which help to solubilise
this apolar part and promote its final solubility in aqueous
media.[30] If we take this behaviour into account, we could
think that some of all our dendrimers could be soluble in the
reaction media tested. On completion of the reactions (fol-
The scope of the catalytic enantioselective alkylation of the
N-(diphenylmethylene)glycine tert-butyl ester with various alky-
lating agents was evaluated (Figure 1). We took the preceding
results into account, and the reactions were performed with 6-
G1 b under the best conditions reported in Table 1. Different
benzyl bromides were used as electrophiles, some of which
contained activated and inactivated aromatic rings (products
9–17; Figure 1). Good yields (76–87%) and enantioselectivities
(76–89%) were obtained, which showed no significant influ-
ence of the electronic effects of the substituents. If two elec-
tron-donating groups were introduced in the electrophile,
compound 17 was obtained with lower ee values than com-
pound 14. However, some steric effects could be also responsi-
ble as observed in the preparation of products 15 and 16. Nev-
ertheless, alkylation with 1-(bromomethyl)naphthalene gave
good ee values (88%). The use of other electrophiles, such as
tert-butyl-2-bromoacetate, allyl, progargyl and methyl bro-
mides reduced the ee considerably (19–22; Figure 1). The R
configuration of 9–22 was assigned by the relative retention
times of the isomers described in the literature.[18,32] If we com-
pared these results with those obtained by some of us using
a polymer-supported cinchonine alkaloid, much better ee
1
lowed by H NMR spectroscopy), the catalysts could be recov-
ered by filtration, however, part of them were lost. If diethyl
ether was added to the final reaction crude mixtures, the com-
plete precipitation of the dendrimers was accomplished, and
practically the total amount of catalyst was recovered, which
supports the previous hypothesis.
The recycling of the most active prepared supported orga-
nocatalyst 6-G1 b was evaluated. The activity was maintained
over five cycles (yields 80–77%) but a slight decrease in enan-
tioselectivity (89–79%) was observed (Table 2). The recovery of
the catalyst by simple filtration after complete precipitation by
the addition of Et2O enhanced the role of the dendrimer as
1
a support. After the fifth cycle, the catalyst was analysed by H
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slightly and their structures were maintained as
probed by NMR spectroscopy. To the best of our
knowledge, these results are the best reported in
the literature for supported Cinchonine phase-trans-
fer catalysts. The anchoring of different N-alkylated
Cinchona alkaloids on the surface of dendrimers
through the vinyl group should be studied further.
Experimental Section
General information
Unless stated otherwise, reactions were performed in
oven-dried glassware sealed with rubber septa under
a N2 atmosphere and were stirred with Teflon-coated
magnetic stir bars. Liquid reagents and solvents were
transferred with a syringe using standard Schlenk tech-
niques. THF and pentane were dried by passage over
a column of activated alumina. Dichloromethane was
dried by passing through a column of activated molecu-
lar sieves by using an Innovative Technology PureSolv
apparatus. Chloroform was dried over calcium hydride.
All other solvents and reagents were used as received
unless otherwise noted.
Figure 1. Substrate scope for different alkylating agents using supported catalyst 6-G1 b.
Major isomer obtained represented, yield [%] (ee).
Silica gel was purchased from Scharlau (Silica Gel 60,
230–440 mesh). TLC was performed by using silica gel
60 F-254 precoated plates (0.25 mm) and visualised by
values in shorter reactions times were obtained using the
chiral dendritic catalyst.[18a]
UV irradiation and potassium permanganate stain. Sorbent silica
gel (particle size 40–63 mm) was used for flash chromatography.
NMR spectroscopy was performed at the Servei de Ressonància
Magn›tica Nuclear at the Universitat Autònoma de Barcelona. Rou-
tine 1H, 13C and 31P NMR spectra were recorded by using Bruker
Conclusions
1
AC250 (250 MHz for H), Avance360 (360 MHz for 1H) and AV400
We have prepared for the first time four dendrimers that con-
tain 12 quaternary ammonium salts on the surface derived
from (+)-cinchonine alkaloid (6-G1 a–d) by quaternisation of
the quinuclidinic N atom. The dendrimer that contained O-9-al-
lylated cinchonine moieties, 6-G1 b, was the most active if used
1
1
(400 MHz for H) instruments. H NMR chemical shifts are given rel-
ative to the residual protic solvent in CDCl3 (d=7.26 ppm).
13C NMR shifts are given relative to CDCl3 (d=77.23 ppm).
Abbreviations are as follows: s (singlet), d (doublet), t (triplet), q
(quartet), dd (doublet of doublet), dt (doublet of triplet), m (mul-
tiplet), br s (broad singlet), br m (broad multiplet).
as
a phase-transfer catalyst at only 0.1 mol% loading
(1.2 mol% referring to cinchonine moieties) for the alkylation
of glycine imine tert-butyl ester as a benchmark reaction at
08C. A better yield and enantioselectivity were obtained com-
pared with the use of the N-benzylcinchoninium salt for the al-
kylation with benzyl bromide.[15] Good yields and moderate
enantioselectivities were obtained if other electrophiles were
tested; differently substituted benzyl bromides gave better re-
sults. From these first experiments, compared with the use of
polymer-supported cinchonine alkaloid-derived ammonium
salts, this phosphorus dendrimer seems to have an improved
activity and enantioselectivity; the existence of a dendritic
effect should not be discarded by a collaborative effect of salts
on the surface, which was not observed if a similar salt was in-
corporated at the core in previous studies.[24a] Moreover, be-
cause of the advantages that supported phase-transfer cata-
lysts have for large-scale processes, from both practical and
economical aspects, the use of dendrimers seems to be
a good and more active alternative to polymers, as shown in
this work. The dendrimers were used in at least five cycles, and
their activity was maintained, the enantioselectivity decreased
IR spectra and specific rotation (ORD) were obtained at the Servei
d’Anàlisi Química of Universitat Autònoma de Barcelona. IR spectra
were recorded by using a Bruker Tensor27 with an ATR Golden.
Specific rotation values [a]D were obtained by using a JASCO J-175
polarimeter at 589.6 nm and they are given in 10À1 degcm2 gÀ1
.
Mass spectrometry chromatograms (HR-MS) were recorded by
using a Bruker AutoFlex-III (Bruker Daltoniks, Bremen, Germany) in-
strument at the Universidad de Zaragoza.
Elemental analyses were performed by the Serveis d’Anàlisi Química
of the Universitat de Autònoma de Barcelona. Elemental analyses of
C, N and H were performed by using an elemental analyser EA-
1108 CE Instrument from Thermo Fisher Scientific with 2,5-bis(5-
tert-butyl-2-benzo-oxazol-2-yl)thiophene (BBOT) as an internal stan-
dard.
Melting points were determined by using a Koffler-Reichert appara-
tus.
The ee of products 9–22 was determined by using chiral GC analy-
sis as described previously[18,32] (Crown-pack Chiralsil-l-Val column,
25 m ” 0.25 mm, P=85 kPa, 1 min 858C, 28CminÀ1 to 1808C) for
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the corresponding N-trifluoroacetamide esters. GC reference race-
mic samples were prepared from racemic 9–22, which were ob-
tained using N-tetrabutylammonium bromide as the PTC catalyst.
1H and 13C NMR spectroscopy and chiral GC chromatograms were
used to probe the purity.
The resulting solid was dissolved in dichloromethane and precipi-
tated with pentane (1:10) to isolate 6-G1 b (0.63 g, 93% yield) by fil-
tration as a pale orange solid. M.p. >2508C; [a]D20 =+51.7 (c=1,
DMSO); IR (ATR): n˜ =3416, 2947, 2881, 1603, 1504, 1460, 1422,
1262, 1197, 1162, 1064, 1017, 917, 835, 781, 757, 633 cmÀ1 31P NMR
;
([D2]CH2Cl2, 81.0 MHz, 373 K): d=61.5, 8.6 ppm; 1H NMR
([D2]CH2Cl2, 400 MHz, 373 K): d=1.09 (bs, 12H), 1.26 (m, 12H),
1.70–1.84 (complex absorption, 24H), 1.98 (m, 12H), 2.39 (m, 12H),
2.49–2.70 (complex absorption, 24H), 2.93 (m, 12H), 3.45–3.57
(complex absorption, 30H), 4.08–4.30 (complex absorption, 36H),
4.42 (m, 12H), 5.1 (m, 12H), 5.22–5.44 (complex absorption, 48H),
5.93–6.23 (complex absorption, 36H), 7.01 (d, J=8.4 Hz, 12H), 7.40
(m, 24H), 7.59 (d, J=8.4 Hz, 12H), 7.73–7.84 (complex absorption,
48H), 7.95 (m, 12H), 8.15 (m, 12H), 8.60 (br s, 6H), 8.71 (m, 12H),
8.97 ppm (d, J=12 Hz, 12H); 13C NMR ([D2]CH2Cl2, 100.6 MHz,
373 K): d=22.0, 23.2, 26.9, 33.6, 37.2, 54.9, 56.1, 61.2, 66.3, 70.3,
74.2, 117.7, 119.5, 121.2, 121.9, 124.1, 124.9, 126.7, 129.6, 129.6,
130.1, 130.3, 132.1, 132.7, 135.5, 135.72, 139.3, 140.8, 148.5, 149.7,
151.1, 152.1 ppm; elemental analysis calcd for C396H432I12N39O30P9S6
(8211.92): C 57.92, H 5.30, N 6.65; found: C 58.20, H 5.61, N 9.97.
Dendrimers 1-G1, 2-G1, 3-G1, alkylated cinchonine 5b–d and imine
7, were prepared following the procedures described previously
(see Supporting Information).[5f,27,28,33] All the electrophiles used
were commercially available.
Synthesis of new compounds
Synthesis of 4-G1
Compound 3-G1 (0.50 g, 0.16 mmol) was solubilised in acetone
(18 mL), and NaI (13 equiv., 0.23 g, 1.56 mmol) was added. The
temperature was brought up to reflux and the solution was left to
stir for 32 h. After cooling, the salts were removed by filtration,
and the product 4-G1 was recovered through evaporation of the
filtrate. The residue was washed with acetone (10 mL), and THF/
pentane 1:10. Compound 4-G1 was obtained as a pale orange solid
(0.52 g, 77% yield). M.p. >2508C; IR (ATR): n˜ =3450, 1603, 1501,
1215, 1193, 1179, 1100, 1017, 914, 839, 780, 753, 731, 698, 641,
Synthesis of 6-G1 c
622 cmÀ1
;
31P NMR (81 MHz, [D2]CH2Cl2): d=62.20, 8.51 and in
A mixture of 5c (0.39 g, 1.03 mmol) and 4-G1 (0.37 g, 0.087 mmol)
in anhydrous THF (20 mL) was stirred at 708C for 24 h. After the
mixture was cooled to RT, the suspension was filtered, and the
solid was washed with MeOH (3”20 mL) to isolate pure 6-G1 c
(0.72 g, 95% yield) as a white solid. M.p. >2508C; [a]D20 =+53.0
(c=1, DMSO); IR (ATR): n˜ =3423, 3063, 2883, 2837, 2789, 2651,
2586, 1656, 1609, 1502, 1451, 1392, 1355, 1305, 1204, 1167, 1107,
1
[D6]DMSO d=62.33, 9.48 ppm; H NMR (250 MHz, [D2]CH2Cl2), 3.30
3
3
(d, JHP =10.0 Hz, 18H), 4.42 (s, 24H), 7.05 (d, 12H), 7.12 (d, JHH
=
7.5 Hz, 24H), 7.32 (d, JHH =7.5 Hz, 24H), 7.66 (br m, 18H);13C{1H}
NMR (100.6 MHz, [D2]CH2Cl2), 4.8, 33.0 (d, 2JCP =13.8 Hz), 121.5,
3
3
121.7, 128.3, 130.1, 132.2, 136.9, 139.0 (d, JCP =13.8 Hz), 149.9 (d,
2JCP =7.9 Hz), 151.3 ppm (d, JCP =7.9 Hz); MALDI-TOF MS (ditranol
2
1052, 1025, 924, 840, 761, 700, 666, 636 cmÀ1 31P NMR ([D6]DMSO,
;
and NaTFA as matrix) m/z: found for [M+H]+ 4198 and [M + Na]+
4221; elemental analysis calcd for C132H120I12N15O18P9S6 (4198.46): C
37.76, H 2.88, N 5.00; found: C 37.93, H 3.20, N 5.32.
81.0 MHz, 373 K): d=61.3, 8.3 ppm; 1H NMR ([D6]DMSO, 400 MHz,
373 K): d=1.37 (m, 12H), 1.77 (m, 24H), 1.94 (s, 12H), 2.26 (m,
12H), 2.68 (m, 12H), 3.12 (m, 24H), 3.22 (m, 18H), 3.39 (m, 24H),
3.62 (m, 24H), 4.0 (complex absorption, 12H), 4.43 (d, J=12.0 Hz,
12H), 4.55 (d, J=12.0 Hz, 12H), 5.01 (complex absorption, 24H),
5.84 (m, 12H), 6.16 (br s, 12H), 7.00–7.55 (complex absorption,
132H), 7.62 (d, J=4 Hz, 12H), 7.69 (m, 12H), 7.80 (m, 12H), 7.95 (s,
6H), 8.08 (d, J=8 Hz, 12H), 8.39 (d, J=8 Hz, 12H), 8.92 ppm (d, J=
4.0 Hz, 12H); 13C NMR ([D6]DMSO, 100.6 MHz, 373 K): d=19.0, 23.5,
27.1, 32.0, 36.4, 49.0, 59.6, 60.1, 61.0, 71.2, 75.5 (m), 116.8, 119.5,
123.8, 124.0, 126.0, 127.6, 128.4, 128.6, 128.8, 129.1, 129.9, 137.3,
142.5, 148.6, 150.4, 150.6 ppm; elemental analysis calcd for
C444H456I12N39O30P9S6 (8812.62): C 60.51, H 5.22, N 6.20; found: C
60.83, H 5.56, N 6.44.
Synthesis of 6-G1 a
A mixture of 5a (0.78 g, 2.64 mmol) and 4-G1 (0.93 g, 0.22 mmol)
in anhydrous THF (20 mL) was stirred at 708C for 24 h. After the
mixture was cooled to RT, the suspension was filtered, and the
solid was washed with MeOH (3”20 mL) to isolate pure 6-G1 a
(1.62 g, 95% yield) as a white solid. M.p. >2508C; [a]D20 =+35.8
(c=1, DMSO); IR (ATR): n˜ =3227 (st OH), 2943, 2877, 1658, 1599,
1503, 1458, 1390, 1305, 1199, 1165, 1054, 926, 839, 771, 636 cmÀ1
;
31P NMR ([D6]DMSO, 81.0 MHz, 373 K): d=59.8, 6.0; 1H NMR
([D6]DMSO, 400 MHz, 373 K): d=0.85 (m, 12H), 1.22 (m, 12H), 1.38
(m, 12H), 1.56 (m, 24H), 1.77 (m, 24H), 2.04 (m, 12H), 2.35 (m,
12H), 2.40–2.94 (complex absorption, 24H), 3.22 (m, 18H), 3.25–
3.57 (complex absorption, 24H), 3.57 (m, 12H), 5.09 (br s, 24H),
5.57 (br s, 12H), 6.03 (m, 12H), 7-05-7.35 (m, 12H), 7.50–7.75 (com-
plex absorption, 96H), 7.99 (d, J=8.0 Hz, 18H), 8.25 (d, J=12.0 Hz,
12H), 8.81 ppm (s, 12H); 13C NMR ([D6]DMSO, 100.6 MHz, 373 K):
d=23.0, 25.7, 28.3, 39.1, 49.0, 49.6, 50.1, 61.1, 70.1, 70.2, 115.4,
119.4, 124.2, 124.3, 126.3, 126.6, 129.1, 130.1, 130.2, 140.1, 140.5,
140.6, 148.5, 149.5, 150.5, 151.0 ppm; elemental analysis calcd for
C360H384I12N39O30P9S6 (7731.15): C 55.93, H 5.01, N 7.07; found: C
56.15, H 5.27, N 7.32.
Synthesis of 6-G1 d
A mixture of 5d (0.77 g, 2.1 mmol) and 4-G1 (0.74 g, 0.18 mmol) in
anhydrous THF (20 mL) was stirred at 708C for 24 h. After the mix-
ture was cooled to RT, and the suspension was filtered. The solid
was washed with Et2O (3”20 mL) to isolate pure 6-G1 d (1.44 g,
93% yield) as a white solid. M.p. >2508C; [a]D20 =+17.7 (c=1,
DMSO); IR (ATR): n˜ =3427, 2949, 2890, 2334, 1608, 1503, 1458,
1411, 1302, 1250, 1199, 1165, 1058, 1012, 936, 842, 769, 636 cmÀ1
;
31P NMR ([D6]DMSO, 81.0 MHz, 373 K): d=61.1, 8.1 ppm; 1H NMR
([D6]DMSO, 400 MHz, 373 K): d=À0.04, À0.02, 0.01 (s, 108H), 0.87
(m, 12H), 1.41 (m, 12H), 1.55 (m, 24H), 1.76 (m, 12H), 2.02 (m,
12H), 2.50 (br s, 12H), 2.62–2.90 (complex absorption, 24H), 3.19
(s, 18H), 3.00–4.00 (complex absorption 48H), 5.11 (complex ab-
sorption, 24H), 5.52 (br s, 12H), 6.05 (m, 12H), 7.10–7.95 (complex
absorption, 108H), 8.00 (d, J=8.0 Hz, 12H), 8.25 (d, J=8.0 Hz,
12H), 8.82 ppm (s, 12H); 13C NMR ([D6]DMSO, 100.6 MHz, 373 K):
Synthesis of 6-G1 b
A mixture of 5b (0.34 g, 1.00 mmol) and 4-G1 (0.35 g, 0.08 mmol)
in anhydrous THF (20 mL) was stirred at 708C for 24 h. After the
mixture was cooled, the solvent was evaporated under vacuum.
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uoka, Angew. Chem. Int. Ed. 2013, 52, 4312–4348; Angew. Chemie, 2013,
125, 4408–4445; d) M. J. O’Donnell, Acc. Chem. Res. 2004, 37, 506–517.
[5] a) A. Bhattacharya, U.-H. Dolling, E. J. J. Grabowski, S. Karady, K. M. Ryan,
L. M. Weinstock, Angew. Chem. Int. Ed. Engl. 1986, 25, 476–477; b) J. Lv,
L. Zhang, L. Liu, Y. Wang, Chem. Lett. 2007, 36, 1354–1355; c) S. E. Den-
mark, N. D. Gould, L. M. Wolf, J. Org. Chem. 2011, 76, 4260–4336; d) Y.-
G. Wang, M. Ueda, X. Wang, Z. Han, K. Maruoka, Tetrahedron 2007, 63,
6042–6050; e) Y. Arakawa, N. Haraguchi, S. Itsuno, Angew. Chem. Int. Ed.
2008, 47, 8232–8235; Angew Chemie 2008, 120, 8356–8359; f) P. Nun,
V. PØrez, M. CalmØs, J. Martinez, F. Lamaty, Chem. Eur. J. 2012, 18, 3773–
3779.
[6] a) T. Perrard, J.-C. Plaquevent, J.-R. Desmurs, D. HØbrault, Org. Lett. 2000,
2, 2959–2962; b) T. Ooi, S. Fujioka, K. Maruoka, J. Am. Chem. Soc. 2004,
126, 11790–11791; c) T. Ooi, D. Ohara, K. Fukumoto, K. Maruoka, Org.
Lett. 2005, 7, 3195–3197; d) X. Wang, M. Kitamura, K. Maruoka, J. Am.
Chem. Soc. 2007, 129, 1038–1039; e) H. Kawai, Y. Sugita, E. Tokunaga, H.
Sato, M. Shiro, N. Shibata, Chem. Commun. 2012, 48, 3632–3634.
[7] a) T. Ooi, M. Taniguch, M. Kameda, K. Maruoka, Angew. Chem. Int. Ed.
2002, 41, 4542–4544; b) T. Ooi, M. Kameda, M. Taniguchi, K. Maruoka, J.
Am. Chem. Soc. 2004, 126, 9685–9694; c) S. Shirakawa, K. Ota, S. J.
Terao, K. Maruoka, Org. Biomol. Chem. 2012, 10, 5753–5755.
d=2.1, 22.7, 25.8, 28.0, 39.1, 48.8, 49.6, 61.1, 70.3, 115.2, 119.3,
124.4, 126.3, 126.5, 129.0, 130.1, 140.7, 148.5, 149.7, 150.3 ppm; ele-
mental analysis calcd for C396H480I12N39O30P9S6Si12 (8627.39): C 55.32,
H 5.63, N 6.35; found: C 55.67, H 5.99, N 6. 54.
General procedure for the alkylation of N-(diphenylmethyle-
ne)glycine tert-butyl ester (7)
To a stirred suspension of 7 (0.25 mmol), the catalysts 6-G1 a–d
(0.1 mol%) and the corresponding base (141 mL) in the appropri-
ate solvent (1.5 mL) at the selected temperature was added the
corresponding alkylating agent (1.26 mmol). When the reaction
was finished (1H NMR spectroscopy), Et2O (5 mL) was added to pre-
cipitate the catalyst completely, the mixture was filtered and the
solid was washed with Et2O (2”10 mL) to recover the catalyst for
further use. The recovered catalysts were analysed by 31P NMR
spectroscopy. The filtrate was washed with water (2”5 mL), and
the organic phase was dried over Mg2SO4, filtered and evaporated
under reduced pressure to give the corresponding alkylated gly-
cine.
[8] C. D. Fiandra, L. Piras, F. Fini, P. Disetti, M. Moccia, M. F. A. Adamo, Chem.
Commun. 2012, 48, 3863–3865.
[9] a) R. Helder, J. C. Hummelen, R. W. P. M. Laane, J. S. Wiering, H. Wynberg,
Tetrahedron Lett. 1976, 17, 1831–1834; b) J. Ye, Y. Wang, R. Liu, G.
Zhang, Q. Zhang, J. Chen, X. Liang, Chem. Commun. 2003, 2714–2715;
c) M.-S. Yoo, D.-G. Kim, M. W. Ha, S.-S. Jew, H.-G. Park, B.-S. Jeong, Tetra-
hedron Lett. 2010, 51, 5601–5603.
General procedure for preparation of the corresponding N-
trifluoroacetamide amido esters (9–22)
[10] a) E. Murugan, A. Siva, Synthesis 2005, 2022–2028; b) Y. Murakami, Y.
Takeda, S. Minakata, J. Org. Chem. 2011, 76, 6277–6285.
To a stirred mixture of alkylated glycine derivatives in THF (3 mL)
was added an aqueous solution of citric acid 25% (2 mL). After 4 h
the mixture was extracted with Et2O (3”10 mL), and the resulting
aqueous phase was basified with an aqueous saturated solution of
K2CO3 (10 mL) and extracted with EtOAc (3”15 mL). The organic
phase was dried over Mg2SO4, filtered and evaporated to give com-
pounds the intermediate amino acids. These amino acids were dis-
solved in CH2Cl2 (5 mL), and TFAA (1 mL) was added slowly at 08C.
The mixture was heated to reflux for 30 min and evaporated to
give the corresponding N-trifluoroacetamide amido esters.
[11] a) R. A. Bhunnoo, Y. Hu, D. I. LainØ, R. C. D. Brown, Angew. Chem. Int. Ed.
2002, 41, 3479–3480; b) J. Qi, A. B. Beeler, Q. Zhang, J. A. Porco, Jr., J.
Am. Chem. Soc. 2010, 132, 13642–13644; c) P. Maity, S. D. Lepore,
Angew. Chem. Int. Ed. 2011, 50, 8338–8341; Angew. Chemie, 2011, 123,
8488–8491; d) E. Yamamoto, A. Nagai, A. Hamasaki, M. Tokunaga, Chem.
Eur. J. 2011, 17, 7178–7182; e) L. Bernardi, E. Indrigo, S. Pollicino, A.
Ricci, Chem. Commun. 2012, 48, 1428–1430.
[12] a) J. Jacques, A. Collet, S. H. Wilen in Enantiomers, Racemates and Reso-
lutions, John Wiley & Sons, Inc., New York, 1981; b) D. Kozma in CRC
Handbook of Optical Resolutions via Diastereomeric Salts, CRC Press,
Boca Raton, 2002.
[13] a) C. E. Song in Cinchona Alkaloids in Synthesis and Catalysis: Ligands,
Immobilization and Organocatalysis, Wiley-VCH, Weinheim, 2009; b) T.
Marcelli, H. Hiemstra, Synthesis 2010, 1229–1279; c) E. M. O. Yeboah,
S. O. Yeboah, G. S. Singh, Tetrahedron 2011, 67, 1725–1762; d) D. Ager,
E. M. Carreira, Y. Hisashi in Comprehensive Chirality, Elsevier, Oxford,
2012, pp. 223–247; e) H. Li, Y. L. Chen Deng, A. L. Zhou in Privileged
Chiral Ligands and Catalysts, Wiley-VCH, Weinheim, 2012, pp. 361–408.
[14] S. S. Jew, H. Park, Chem. Commun 2009, 7090–7103.
[15] a) M. J. O’Donnell, W. D. Bennett, S. Wu, J. Am. Chem. Soc. 1989, 111,
2353–2355; b) M. J. O’Donnell, S. Wu, J. C. Huffman, Tetrahedron 1994,
50, 4507–4518.
[16] a) E. J. Corey, F. Xu, M. C. Noe, J. Am. Chem. Soc. 1997, 119, 12414–
12415; b) E. J. Corey, Y. Bo, J. Busch-Petersen, J. Am. Chem. Soc. 1998,
120, 13000–13001.
Acknowledgements
This research was supported by the Ministerio de Ciencia e Inno-
vación (CTQ2011-2264 and Consolider Ingenio 2010 CSD2007-
00006), Ministerio de Economía y Competitividad (CTQ 2014–
53662-P and CTQ2014-51912-REDC) FEDER and the DURSI-Gener-
alitat de Catalunya (2014SGR-1105). We thank the Consolider In-
genio Program for the contract of J.R. and UAB for the grant of
J.J.J.
[17] a) B. Lygo, P. G. Wainwright, Tetrahedron Lett. 1997, 38, 8595–8598; b) B.
Lygo, B. I. Andrews, Acc. Chem. Res. 2004, 37, 518–525.
[18] a) R. Chinchilla, P. Mazón, C. Nµjera, Tetrahedron: Asymmetry 2000, 11,
3277–3281; b) R. Chinchilla, P. Mazón, C. Nµjera, Molecules 2004, 9,
349–364; c) R. Chinchilla, P. Mazón, C. Nµjera, Adv. Synth. Catal. 2004,
346, 1186–1194.
[19] B. Thierry, J. C. Plaquevent, D. Cahard, Molec. Divers. 2005, 9, 277–290.
[20] a) A. M. Caminade, C. O. Turrin, R. Laurent, A. Ouali, B. Delavaux-Nicot in
Dendrimers: Towards Catalytic, Material and Biomedical Uses, Wiley-VCH,
Chistester, 2011; b) E. Badetti, A. M. Caminade, J. P. Majoral; M. Moreno-
MaÇas, R. M. Sebastiµn, Langmuir 2008, 24, 2090–2101; M. Moreno-
MaÇas, R. M. Sebastiµn, Langmuir 2008, 24, 2090–2101; c) M. Koprow-
ski, R. M. Sebastiµn, V. Maraval, M. Zablocka, V. Cadierno, B. Donnadieu,
A. Igau, A. M. Caminade, J. P. Majoral, Organometallics 2002, 21, 4680–
4687; d) G. Franc, E. Badetti, C. Dahayon, Y. Coppel, C. O. Turrin, J. P. Ma-
joral, R. M. Sebastiµn, A. M. Caminade, New. J. Chem. 2010, 24, 547–
Keywords: alkylation
organocatalysis · phase-transfer catalysis
· dendrimers · enantioselectivity ·
[1] C. M. Starks, J. Am. Chem. Soc. 1971, 93, 195–199.
[2] Y. Sasson, R. Neumann in Handbook in Phase Transfer Catalysis, Blackie
Academic & Professional, London, 1997.
[3] For reviews on phase-transfer catalysis, see a) E. V. Dehmlow, S. S.
Dehmlow in Phase Transfer Catalysis, 3rd ed., Wiley-VCH, Weinheim,
1993; b) C. M. Starks, C. L. Liotta, M. Halpern in Phase-Transfer Catalysis,
Chapman & Hall, New York, 1994; c) Y. Sasson, R. Neumann in Hand-
book of Phase-Transfer Catalysis, Blackie Academic
London, 1997.
[4] a) T. Ooi, K. Maruoka, Angew. Chem. Int. Ed. 2007, 46, 4222–4266;
Angew. Chemie 2007, 119, 4300–4345; b) S. E. Denmark, N. D. Gould,
L. M. Wolf, J. Org. Chem. 2011, 76, 4260–4336; c) S. Shirakawa, K. Mar-
& Professional,
ChemCatChem 2016, 8, 2049 – 2056
www.chemcatchem.org
2055
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
555; e) G. Franc, E. Badetti, V. Colli›re, J. P. Majoral, R. M. Sebastiµn, A. M.
Caminade, Nanoscale 2009, 1, 233–237; f) M. Keller, V. Colli›re, O.
Reiser, A. M. Caminade, J. P. Majoral, A. Ouali, Angew. Chem. Int. Ed.
2013, 52, 3626–3629; Angew. Chemie 2013, 125, 3714–3717; g) P. Neu-
mann, H. Dib, A. M. Caminade, E. Hey-Hawkins, Angew. Chem. Int. Ed.
2015, 54, 311 –314; Angew. Chemie 2015, 127, 316–319.
C. O. Turrin, J. P. Majoral, Chem. Soc. Rev. 2015, 44, 3890–3899; c) A. M.
Caminade, R. Laurent, A. Ouali, J. P. Majoral, Inorg. Chim. Acta. 2014,
409, 68–88; d) A. M. Caminade, J. P. Majoral, New J. Chem. 2013, 37,
3358–3373.
[27] P. Servin, R. Laurent, L. Gonsalvi, M. Tristany, M. Peruzzini, J. P. Majoral,
A. M. Caminade, Dalton Trans. 2009, 4432–4434.
[21] A. M. Caminade, A. Ouali, R. Laurent, C. O. Turrin, J. P. Majoral, Chem.
Soc. Rev. 2015, 44, 3890–3899.
[22] a) A. M. Caminade, A. Ouali, M. Keller, J. P. Majoral, Chem. Soc. Rev. 2012,
41, 4113–4125; b) M. Keller, A. Perrier, R. Linhardt, L. Travers, S. Witt-
mann, A. M. Caminade, J. M. Majoral, O. Reiser, A. Ouali, Adv. Synth.
Catal. 2013, 355, 1748–1754.
[23] J. Rull, M. Casals, R. M. Sebastiµn, A. Vallribera, J. P. Majoral, A. M. Cami-
nade, ChemCatChem 2015, 7, 2698–2704.
[24] a) G. Guillena, R. Kreiter, R. Van de Coevering, R. J. M. Klein Gebbink, G.
Van Koten, P. Mazon, R. Chinchilla, C. Nµjera, Tetrahedron: Asymmetry
2003, 14, 3705–3712; b) X. D. Liu, X. L. Bai, X. P. Qiu, L. X. Gao, Chin.
Chem. Lett. 2005, 16, 975–978.
[28] S. E. Denmark, R. C. Weintraub, Heterocycles 2011, 82, 1527–1540.
[29] H. G. Park, B. S. Jeong, M. S. Yoo, J. H. Lee, M. K. Park, Y. J. Lee, M. J. Kim,
S. S. Jew, Angew. Chem. Int. Ed. 2002, 41, 3036–3038.
[30] R. M. Sebastiµn, G. Magro, A. M. Caminade, J. P. Majoral, Tetrahedron
2000, 56, 6269–6277.
[31] J. H. Lee, M. S. Yoo, J. H. Jung, S. S. Jew, H. G. Park, B. S. Jeong, Tetrahe-
dron 2007, 63, 7906–7915.
[32] W. Oppolzer, R. Moretti, C. Zhou, Helv. Chim. Acta 1994, 77, 2363–2380.
[33] a) S. Jayaraman, D. Kumaraguru, J. B. Arockiam, S. Paulpandian, B. Rajen-
diran, S. Ayyanar, Synlett 2014, 25, 1685–1691; b) I. Busygin, V. Niemi-
nen, A. Taskinen, J. Sinkkonen, E. Toukoniitty, R. Sillanpaa, D. Y. Murzin,
R. Leino, J. Org. Chem. 2008, 73, 6559–6569.
[25] a) B. Imperiali, S. L. Fisher, J. Org. Chem. 1992, 57, 757–759; b) B. Imperi-
ali, T. J. Prins, S. L. Fisher, J. Org. Chem. 1993, 58, 1613–1616; c) B. Lygo,
B. I. Andrews, Tetrahedron Lett. 2003, 44, 4499–4502; d) B. Lygo, B. I. An-
drews, D. Slack, Tetrahedron Lett. 2003, 44, 9039–9041.
Received: March 9, 2016
[26] a) A. M. Caminade, A. Ouali, R. Laurent, C. O. Turrin, J. P. Majoral, Coord.
Chem. Rev. 2016, 308, 478–497;b) A. M. Caminade, A. Ouali, R. Laurent,
Published online on June 8, 2016
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