Stereoselective Synthesis of P-Stereogenic N-Phosphinyl Compounds

Article abstract of DOI:10.1002/ejoc.201501260

A number of P-stereogenic N-phosphinyl compounds were stereoselectively prepared in good yields by a straightforward approach, thanks to the diversified and, up until now, unexplored reactivity of (R)- and (S)-dicyclohexylidene-D-glucose methyl phenyl pho

Full text of DOI:10.1002/ejoc.201501260

DOI: 10.1002/ejoc.201501260
Communication
P-Stereogenic N-Phosphinyl Compounds
Stereoselective Synthesis of P-Stereogenic N-Phosphinyl
Compounds
Ahmed Chelouan,[a] Rocío Recio,[a] Eleuterio Álvarez,[b] Noureddine Khiar,*[b] and
Inmaculada Fernández*[a]
Abstract: A number of P-stereogenic N-phosphinyl com- glucose methyl phenyl phosphinates toward metal amides.
pounds were stereoselectively prepared in good yields by a
straightforward approach, thanks to the diversified and, up until
Under adequate conditions, structurally different phosphin-
amides with one or two P-chiral centers were obtained.
now, unexplored reactivity of (R)- and (S)-dicyclohexylidene-D-
Introduction
chiral separation.[8] However, in the course of this work, Han
et al. reported the first stereoselective synthesis of P-chirogenic
phosphinamides by using cyclic 1,3,2-benzoxazaphosphinine 2-
oxides as chiral starting substrates.[9] Herein, we report our re-
sults in the synthesis of structurally relevant enantiopure phos-
phinamides, N-(phosphinyl)imines, a β-(phosphinyl)phosphin-
ate, and a β-(phosphinyl)phosphinamide by using dicyclohexyl-
Since the Horner[1] and Knowles[2] groups reported the first
asymmetric hydrogenation of olefins by using a P-chiral phos-
phine, a large number of structurally diverse organophosphorus
derivatives have been used as chiral ligands in asymmetric ca-
talysis.[3] The interest in P-stereogenic ligands has declined sig-
nificantly over the past three decades, mainly because of the
success of ligands for which the chirality resides in the “back-
bone” and not in the phosphorus atom, associated with the
difficulty of stereoselectively synthesizing P-chirogenic deriva-
tives. However, the outstanding performance of these ligands in
asymmetric homogeneous transition-metal catalysis[4] and their
excellent results as chiral Lewis bases in asymmetric organo-
catalysis[5] have triggered a resurgence in the appeal of the
stereoselective synthesis of P-chirogenic compounds in general
and of phosphinamides in particular.[6]
idene-D-glucose methyl phenyl phosphinates as chiral N-phos-
phinylating agents.
Within a research program directed toward the synthesis of
chiral sulfoxides and phosphine oxides from renewable biomass
and their application in organic and organometallic catalysis,
we reported an enantiodivergent approach for the synthesis
of different phosphine oxides.[10] For this purpose, we applied
modified Mislow methodology[11] by using
carbinol derived from -glucose as the chiral alcohol instead of
a secondary
D
(–)-menthol. This method facilitates the stereodivergent synthe-
The synthesis of compounds with two stereogenic phos-
phorus atoms is more challenging and has generally been
achieved by the dimerization of enantiopure lithiomethyl-phos-
phine oxide or by the enantioselective deprotonation of phos-
phine–boranes and phosphine–sulfides.[7] However, as far as we
know, there is no method for the synthesis of 1,3-bis(P-chiro-
genic) compounds. Moreover within the family of P-stereogenic
compounds, the synthesis of phosphinamides, which hold great
promise as Brønsted acid and Lewis base organocatalysts, has
scarcely been addressed, and until quite recently, the few P-
stereogenic phosphinamides that are known were prepared by
sis of both diastereomeric methyl phenyl phosphinates, 1RP and
1SP, by treatment of dicyclohexylidene-D-glucose (DCG-OH)
with phosphinyl chloride 2 in the presence of triethylamine or
pyridine as the base (Scheme 1). These phosphinates proved to
be good C-phosphinylating agents and yielded the correspond-
[a] Departamento de Química Orgánica y Farmacéutica, Facultad de
Farmacia, Universidad de Sevilla,
c/Profesor García González, 12, 41012 Seville, Spain
E-mail: inmaff@us.es
[b] Asymmetric Synthesis and Functional Nanosystems Group,
Instituto de Investigaciones Químicas (IIQ),
CSIC – Universidad de Sevilla,,
C/ Américo Vespucio 49, 41092 Seville, Spain
E-mail: khiar@iiq.csic.es
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201501260.
Scheme 1. Diastereodivergent synthesis of (S)- and (R)-dicyclohexylidene-
glucose methyl phenylphosphinates 1SP and 1RP.
D-
Eur. J. Org. Chem. 2016, 255–259
255
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
ing phosphine oxides by reaction with organometallic reagents ber of equivalents of the amide used, and the nature of the
with inversion of configuration at the stereogenic phosphorus counterion (Na or Li) determine the enantiomeric excess of the
atom.[10]
final product and its structure, as shown in Table 1. For the
reaction to take place, the amide was generated by adding
metal (sodium or lithium) to liquid ammonia at –78 °C, which
was then added to a solution of phosphinate 1SP in THF at
–40 °C. The reaction of 1SP with sodium amide yielded desired
phosphinamide 12SP, and the reaction took place instantane-
ously. An excess amount of sodium amide (3 equiv.) and an
increased reaction time (up to 10 min) favored epimerization of
the final product, and aqueous workup of the reaction reduced
the yield of the isolated product (Table 1, entry 1). Reducing
the reaction time to 1 min led to higher enantioselectivities
(Table 1, entries 2 and 3). Lowering the number of equivalents
of sodium amide (up to 1.2 equiv.) caused a significant increase
in the enantiomeric excess (ee) of the product but significantly
reduced the chemical yield (Table 1, entry 4). The best result
was obtained with 2.1 equiv. of sodium amide, subsequent
workup with solid ammonium chloride, and purification with
neutral silica gel (Table 1, entry 6); this resulted in phosphin-
amide 12SP in 69 % yield with 96 % ee. Simple crystallization
from toluene/dichloromethane (3:1) yielded the enantiopure
(S)-methyl-phenyl-phosphinamide in 50 % yield. Interestingly,
by using lithium amide instead of sodium amide as the nucleo-
phile under the same reaction conditions yielded quantitatively
bis-phosphinamide 13(SP,SP) as the unique product.
Results and Discussion
To study their capacity as N-phosphinylating agents, in the
present study we used diastereomer 1SP, easily prepared on
multigram scale, as the reference phosphinate (Scheme 1).
Treatment of phosphinate 1SP with lithium alkyl or arylamides,
prepared by treatment of the corresponding amine with nBuLi
at –78 °C, yielded the N-phosphinylated products, the enantio-
meric purities of which were determined by HPLC on a chiral
stationary phase (Scheme 2). The reactions proceeded stereo-
selectively in all cases, as shown by HPLC, and enantiopure
phosphinamides 3SP–11SP were obtained in moderate to high
yields. The reaction occurred with inversion of configuration at
phosphorus, as demonstrated by X-ray study of N-(o-methoxy-
phenyl) derivative 11SP, and a similar behavior was assumed
for the rest of the phosphinamides.[12] In this way, differently
substituted N-alkyl-phosphinamides (see compounds 3SP–7SP,
Scheme 2) and N-aryl-phosphinamides (see compounds 8SP–
11SP, Scheme 2), with large structural diversity, were stereo-
selectively prepared.
Table 1. Reactivity of phosphinate 1SP with amides.
Entry
M
(equiv.)
Time Workup
[min]
Product Yield[a]
[%]
ee[b]
[%]
1
2
3
4
5
6
7
Na (3.0)
Na (3.0)
Na (3.0)
Na (1.2)
Na (2.1)
Na (2.1)
Li (2.1)
10 H2O
12SP
12SP
12SP
12SP
12SP
12SP
16
29
30
10
51
69
76
81
80
99
92
1
1
1
1
1
1
NH4Cl[c]/CC[d]
NH4Cl/THF aq.
NH4Cl
acid resin/CC[d]
NH4Cl/CC[d]
NH4Cl/CC[d]
Scheme 2. Asymmetric synthesis of N-alkyl- and N-aryl-phosphinamides from
phosphinate 1SP.
96[e]
≥98[f]
13(SP,SP) quant.
Taking into account the synthetic interest in methyl-phenyl-
phosphamides and the limited number of methods described
for their stereoselective synthesis in good yields,[8,9] we decided
to address their preparation by breaking the P–ODCG bond
with different “NH2” equivalents used as nucleophiles. Our ini-
tial studies were conducted by applying a standard method
consisting of the condensation of metal amides MNH2 (M = Na,
[a] Yield of isolated product. [b] Determined by HPLC on a chiral stationary
phase: AD (2-propanol/hexane, 22:78, 0.5 mL min–1). [c] Solid ammonium
chloride was added. [d] The crude reaction product was directly purified by
short column chromatography (CC) on silica gel. [e] 100 % ee after crystalliza-
tion from CH2Cl2/toluene (1:3); 50 % yield. [f] Only one product was observed
by analysis of the crude mixture by NMR spectroscopy.
Having delineated a suitable method for the enantioselective
Li) as nucleophiles. This required, first, fine-tuning the reaction synthesis of phosphinamide 12SP, we decided to investigate its
conditions, as factors such as temperature, reaction time, num- transformation into some other derivatives of interest in asym-
Eur. J. Org. Chem. 2016, 255–259
www.eurjoc.org
256
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
metric synthesis. Given the excellent results provided by chiral
Next, and in clear analogy to the methodology developed
N-(sulfinyl)imines as electrophilic substrates in the synthesis of by Davis' group for the synthesis of N-(p-tolylsulfinyl)imines,[18]
chiral amines, which have resulted in many applications,[13,14] we envisaged the one-pot synthesis of N-(phosphinyl)imines by
in addition to our own interest in this field,[15] the analogous condensation with lithium hexamethyldisilazane (LHMDS), fol-
N-(phosphinyl)imines caught our attention as chiral substrates. lowed by in situ imination of N-bis(trimethylsilyl)-(S)-methyl-
Clearly, the phosphinyl group, like the sulfinyl group, can act as phenyl-phosphinamide intermediate 17 (Scheme 3). However,
an electron-withdrawing group to activate the C=N bond for in this case intermediate 17 was not formed; instead, a single
the addition of nucleophiles. Moreover, unlike the sulfinyl product was obtained in high yield. This new compound has
group, the possibility of oxidation or racemization of phos- still the sugar moiety, as shown by 1H NMR spectroscopy,
phorus in N-(phosphinyl)imines is excluded, which facilitates re- whereas 31P NMR spectroscopy shows the presence of two
covery of the chiral auxiliary once the process has finished. In phosphorus(V) atoms that appear as doublets (JPP = 9 Hz) at
this sense, N-(P,P-diaryl-phosphinoyl)imines behave as good δ = 37.2 and 29.6 ppm (Scheme 3).
electrophiles in reactions with different nucleophiles.[16] How-
ever, there are only a few examples that describe N-(phosphin-
yl)imines that are chiral at phosphorus. Royer et al. recently
published their work on the stereoselective dimetalaluminum
alkynylation of N-(phosphinyl)imines that were prepared from
menthyl methyl phenyl phosphinate as a chiral starting sub-
strate.[17] Colobert et al. described the addition of Grignard rea-
gents to various chiral N-(tert-butyl-phenyl-phosphinyl)imines,
obtained by a process based on racemate resolution of tert-
butyl-phenyl-phosphine oxide as the precursor.[8a,8b] More re-
cently, Riera et al. described the role of borane as a directing
group in the stereoselective addition of organometallic rea-
gents to borane P-stereogenic N-phosphanylimines.[8f] In our
Scheme 3. Nucleophilic versus basic behavior of LHMDS in the reaction with
case, we addressed the stereoselective synthesis of different N-
(methyl-phenyl-phosphinyl)aldimines by using enantiopure (S)-
methyl-phenyl-phosphinamide 12SP as the starting chiral mate-
rial by condensation with various aldehydes, and the results are
shown in Table 2.
DCG methyl phosphinate 1SP.
Taken all together, these data indicate that the product
formed is the β-(phosphinyl)phosphinate. This result can be ra-
tionalized by recognizing that bulky LHMDS acts as a base lead-
ing to the intermediate formation of methyl carbanion [1SP]– by
abstraction of a proton from the methyl group. Subsequently,
coupling of anion [1SP]– with phosphinic ester precursor 1SP
affords β-(phosphinyl)phosphinate derivative 18(SP,RP) almost
quantitatively (91 % yield) as a single diastereomer (Scheme 3).
Upon subjecting diastereomeric phosphinate 1RP to identical
conditions, corresponding diastereomer 18(RP,SP) was obtained
in high yield (73 %). It should be recalled that taking into ac-
count that in both cases one chiral fragment of DCG remains in
the final products, the obtained compounds are diastereomers,
which greatly simplifies analysis of the stereochemical outcome
of the process. The reaction was also conducted with an equi-
molar mixture of diastereomeric phosphinates 1SP and 1RP and
no chiral discrimination was observed in the nucleophilic sub-
stitution process.
Table 2. Synthesis of N-(methyl-phenyl-phosphinyl)imines 14SP–16SP from
phosphinamide 12SP.
Entry
R
T
[°C]
Additive
(equiv.)
Product Yield[a]
[%]
1
2
3
4
5
6
2-naphthyl
2-naphthyl
2-naphthyl
Ph
r.t.
r.t.
0
r.t.
r.t.
r.t.
CuSO4 (2.0)
14SP
14SP
14SP
15SP
15SP
16SP
16
29
30
10
51
69
Cs2CO3 (2.2)
TiCl4/Et3N (1.5:3.0)
CuSO4 (2.2)
Cs2CO3 (2.2)
Cs2CO3 (2.2)
Ph
pMeOC6H4
[a] Yield of isolated product after chromatographic purification.
The described procedure is not limited to the preparation of
β-(phosphinyl)phosphinates but can lead to other interesting P-
stereogenic compounds by trapping the intermediate anion
with other electrophiles. In this sense, addition of anion [1SP]–,
generated at –40 °C in 2 h, over a solution of diastereopure
(R)-DAG tert-butanesulfinate 19RS afforded corresponding β-
(sulfinyl)phosphinate 20(RP,RS), which is a precursor of mixed
S,P ligands, in good yield with good diastereoselectivity
(Scheme 4).
As can be seen from Table 2, in the case of arylaldimines
14SP–16SP the best results were obtained by using dichloro-
methane as the solvent in the presence of cesium carbonate
(2.2 equiv.) at room temperature; the products were obtained
in low to moderate yields (up to 69 % in the case of p-methoxy-
phenyl derivative 16SP; Table 2, entry 6) in enantiopure form.
Currently, these chiral N-(phosphinyl)imines are being evaluated
as chiral electrophilic substrates in different processes. As in the
case of the N-(sulfinyl)imine analogues, this is very rich and
Moreover, obtained β-(phosphinyl)phosphinates 18, with an
diversified chemistry, and the results will be published in due electrophilic phosphorus atom, can be used as intermediates
course.
for the synthesis of other compounds with two P-stereogenic
Eur. J. Org. Chem. 2016, 255–259
www.eurjoc.org
257
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Keywords: Asymmetric synthesis · Nucleophilic substitution ·
Phosphorus · Chirality
[1] L. Horner, H. Siegel, H. Büthe, Angew. Chem. Int. Ed. Engl. 1968, 7, 942–
943; Angew. Chem. 1968, 80, 1034–1035.
Scheme 4. Asymmetric synthesis of β-(sulfinyl)phosphinate 20(RP,RS).
[2] W. S. Knowles, M. J. Sabacky, Chem. Commun. (London) 1968, 1445–1446.
[3] a) W. Tang, X. Zhang, Chem. Rev. 2003, 103, 3029–3069; b) S. Lühr, J.
Holz, A. Börner, ChemCatChem 2011, 3, 1708–1730.
centers. The reaction of sodium amide with β-(phosphinyl)phos-
phinate derivative 18(SP,RP) afforded almost quantitatively β-
(phosphinyl)phosphinamide 21(SP,RP), the configuration of
which was assigned by assuming that the reaction proceeded
by displacement of the sugar moiety with inversion of configu-
ration at the phosphorus center, as in 1SP (Scheme 5).
[4] a) D. Parmar, E. Sugiono, S. Raja, M. Rueping, Chem. Rev. 2014, 114, 9047–
9153; b) S. E. Denmark, J. Fu, Chem. Rev. 2003, 103, 2763–2793; c) S.
Kotani, M. Sugiura, M. Nakajima, Chem. Rec. 2013, 13, 362–370.
[5] a) J. H. Kim, I. Corié, S. Vellalath, B. List, Angew. Chem. Int. Ed. 2013, 52,
4474–4477; Angew. Chem. 2013, 125, 4570–4573; b) X.-W. Liu, T. N. Le, Y.
Lu, Y. Xiao, J. Ma, X. Li, Org. Biomol. Chem. 2008, 6, 3997–4003; c) T.
Akiyama, J. Itoh, K. Fuchibe, Adv. Synth. Catal. 2006, 348, 999–1010; d)
S. E. Denmark, S. K. Ghosh, Angew. Chem. Int. Ed. 2001, 40, 4759–4762;
Angew. Chem. 2001, 113, 4895–4898 ; e) M. Rueping, B. J. Nachtsheim,
S. A. Moreth, M. Bolte, Angew. Chem. Int. Ed. 2008, 47, 593–596; Angew.
Chem. 2008, 120, 603–606; f) S. Vellalath, I. Corié, B. List, Angew. Chem.
Int. Ed. 2010, 49, 9749–9752; Angew. Chem. 2010, 122, 9943–9946.
[6] a) S. Juge, M. Stephan, J. A. Laffite, J. P. Genet, Tetrahedron Lett. 1990,
31, 6357–6360; b) H. Adams, R. C. Collins, S. Jones, C. J. A. Warner, Org.
Lett. 2011, 13, 6576–6579; c) T. León, A. Riera, X. Verdaguer, J. Am. Chem.
Soc. 2011, 133, 5740–5743; d) H. Zijlstra, T. León, A. de Cózar, C. Fon-
seca Guerra, D. Byrom, A. Riera, X. Verdaguer, F. M. Bickelhaupt, J. Am.
Chem. Soc. 2013, 135, 4483–4491; e) Z. S. Han, N. Goyal, M. A. Herbage,
J. D. Sieber, B. Qu, Y. Xu, Z. Li, J. T. Reeves, J.-N. Desrosiers, S. Ma, N.
Grinberg, H. Lee, H. P. R. Mangunuru, Y. Zhang, D. Krishnamurthy, B. Z.
Lu, J. J. Song, G. Wang, C. H. Senanayake, J. Am. Chem. Soc. 2013, 135,
2474–2477; f) M. Casimiro, L. Roces, S. García-Granda, M. J. Iglesias, F.
López Ortiz, Org. Lett. 2013, 15, 2378–2381; g) M. A. del Águila-Sánchez,
N. M. Santos-Bastos, M. C. Ramalho-Freitas, J. García López, M.
Costa de Souza, J. A. L. Camargos-Resende, M. Casimiro, G. Alves-Rome-
iro, M. J. Iglesias, F. López Ortiz, Dalton Trans. 2014, 43, 14079–14091.
[7] a) B. D. Vineyard, W. S. Knowles, M. J. Sabacky, G. L. Bachman, D. J. Weink-
auff, J. Am. Chem. Soc. 1977, 99, 5946–5952; b) T. Imamoto, T. Oshiki, T.
Onozawa, T. Kusumoto, K. Sato, J. Am. Chem. Soc. 1990, 112, 5244–5252;
c) A. R. Muci, K. R. Campos, D. A. Evans, J. Am. Chem. Soc. 1995, 117,
9075–9076; d) A. Ohashi, S. Kikushi, M. Yasukata, T. Imamoto, Eur. J. Org.
Chem. 2002, 2535–2546; e) T. Imamoto, K. Sugita, K. Yoshida, J. Am.
Chem. Soc. 2005, 127, 11934–11935.
Scheme 5. Asymmetric synthesis of β-(phosphinyl)phosphinamide 21(SP,RP).
Conclusions
We reported an efficient approach for the preparation of struc-
turally diverse P-chirogenic compounds with one or two P-chiral
phosphorus atoms. The method is based on the interesting re-
activity of dicyclohexylidene-D-glucose methyl phenyl phos-
phinates, 1RP and 1SP, easily accessible on multigram scale from
a sugar carbinol, toward metal amides. Using nonhindered
amides, such as NaNH2, LiNH2, and RNHLi, nucleophilic substitu-
tion at the phosphorus atom takes place to give the corre-
sponding phosphinamides with inversion of configuration. By
contrast, bulky lithium hexamethyldisilazane acts as base in-
stead of a nucleophile, which results in the formation of the
methyl-phosphinyl carbanion intermediate. This carbanion can
then act as a nucleophile towards the same phosphinate to
yield a β-(phosphinyl)phosphinate or can be trapped by other
nucleophiles to afford other P-chirogenic compounds of inter-
est. The obtained compounds, with an electrophilic phosphinic
ester moiety, can further be used as starting materials for the
synthesis of different P-chirogenic compounds of interest,
which widens the scope of this approach. The application of
this approach for the synthesis of highly efficient organocata-
lysts will be reported in due course.
[8] a) I. N. Francesco, A. Wagner, F. Colobert, Chem. Commun. 2010, 46,
2139–2141; b) I. N. Francesco, C. Egloff, A. Wagner, F. Colobert, Eur. J. Org.
Chem. 2011, 4037–4045; c) T. A. Hamor, W. B. Jennings, C. J. Lovely, K. A.
Reeves, J. Chem. Soc. Perkin Trans. 2 1992, 843–849; d) M. J. P. Harger, J.
Chem. Soc. Perkin Trans. 1 1977, 2057–2063; e) M. Benamer, S. Turcaud,
J. Royer, Tetrahedron Lett. 2010, 51, 645–648; f) A. Flores-Gaspar, S. Or-
gué, A. Grabulosa, A. Riera, X. Verdaguer, Chem. Commun. 2015, 51,
1941–1944.
[9] Z. S. Han, L. Zhang, Y. Xu, J. D. Sieber, M. A. Marsini, Z. Li, J. T. Reeves,
K. R. Fandrick, N. D. Patel, J.-N. Desrosiers, B. Qu, A. Chen, A. M. Rudzinski,
L. P. Samankumara, S. Ma, N. Grinberg, F. Roschangar, N. K. Yee, G. Wang,
J. J. Song, C. H. Senanayake, Angew. Chem. Int. Ed. 2015, 54, 5474–5477;
Angew. Chem. 2015, 127, 5564–5567.
Supporting Information (see footnote on the first page of this
[10] a) A. Benabra, A. Alcudia, N. Khiar, I. Fernández, F. Alcudia, Tetrahedron:
Asymmetry 1996, 7, 3353–3356; b) I. Fernández, N. Khiar, A. Roca, A.
Benabra, A. Alcudia, J. L. Espartero, F. Alcudia, Tetrahedron Lett. 1999, 40,
2029–2032.
[11] O. Korpiun, R. A. Lewis, J. Chickos, K. Mislow, J. Am. Chem. Soc. 1968, 90,
4842–4846.
article): Experimental details, characterization data, and copies of
1
the H NMR and 13C NMR spectra of all key intermediates and final
products.
[12] CCDC-1414786 (for 11SP) contains the supplementary crystallo-
graphic data for this compound. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
http//www.ccdc.cam.ac.uk/data_request/cif.
[13] J. Ellman, M. T. Robak, M. A. Herbage, Chem. Rev. 2010, 110, 3600–3740.
[14] a) Z. Han, D. Krishnamurthy, D. Pflun, P. Grover, S. A. Wald, C. H. Senanay-
ake, Org. Lett. 2002, 4, 4025–4028; b) Y. Li, J. Hu, Angew. Chem. Int. Ed.
2005, 44, 5882–5886; Angew. Chem. 2005, 117, 6032–6036; c) J. L. Gar-
Acknowledgments
We are grateful to the Spanish Ministerio de Economía y Com-
petitividad (MEC) (grant number CTQ2013-49066-C2-2-R) and
the Junta de Andalucía (grant number P11-FQM-08046) for fi-
nancial support. We gratefully thank CITIUS for NMR facilities.
Eur. J. Org. Chem. 2016, 255–259
www.eurjoc.org
258
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
cía Ruano, J. Alemán, M. Prado, I. Fernandez, J. Org. Chem. 2004, 69,
4454–4463; d) J. L. García-Ruano, A. Alcudia, M. del Prado, D. Barros,
M. C. Maestro, I. Fernandez, J. Org. Chem. 2000, 65, 2856–2862; e) J. L.
García Ruano, I. Fernández, M. del Prado Catalina, J. A. Hermoso, J. Sanz-
Aparicio, M. Martínez-Ripoll, J. Org. Chem. 1998, 63, 7157–7161; f) J. L.
García Ruano, I. Fernandez, M. del Prado, A. Alcudia, Tetrahedron: Asym-
metry 1996, 7, 3407–3414; g) J. L. García-Ruano, I. Fernandez, Ch. Ham-
douchi, Tetrahedron Lett. 1995, 36, 295–298.
Fernández, V. Valdivia, B. Gori, F. Alcudia, E. Álvarez, N. Khiar, Org. Lett.
2005, 7, 1307–1310.
[16] a) S. M. Weinreb, R. K. Orr, Synthesis 2005, 1205–1227; b) K. Soai, T.
Hatanaka, T. Miyazawa, J. Chem. Soc., Chem. Commun. 1992, 1097–1098;
c) A. E. Mattson, K. A. Scheidt, Org. Lett. 2004, 6, 4363–4366; d) Y. Suto,
M. Kanai, M. Shibasaki, J. Am. Chem. Soc. 2007, 129, 500–501.
[17] M. Benamer, S. Turcaud, J. Royer, Tetrahedron Lett. 2010, 51, 645–648.
[18] F. A. Davis, P. Zhou, C. H. Liang, R. E. Reddy, Tetrahedron: Asymmetry 1995,
6, 1511–1514.
[15] a) I. Fernández, A. Alcudia, B. Gori, V. Valdivia, R. Recio, M. V. García, N.
Khiar, Org. Biomol. Chem. 2010, 8, 4388–4393; b) I. Fernández, V. Valdivia,
A. Alcudia, A. Chelouan, N. Khiar, Eur. J. Org. Chem. 2010, 1502–1509; c)
I. Fernández, V. Valdivia, N. Khiar, J. Org. Chem. 2008, 73, 745–748; d) I.
Received: October 2, 2015
Published Online: November 23, 2015
Eur. J. Org. Chem. 2016, 255–259
www.eurjoc.org
259
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim