Mannich reactions of alkynes: Mechanistic insights and the role of sub-stoichiometric amounts of alkynylcopper(I) compounds in the catalytic cycle

Article abstract of DOI:10.1002/chem.201103987

Yellow polymeric alkynylcopper(I) compounds observed in the three-component Mannich reactions of alkynes, secondary amines and aldehydes are shown to be pre-catalysts that give rise to catalytic copper(I) alkyne complexes by interaction with secondary amines (see scheme). Interaction of these complexes with iminium ions (formed from aldehydes or their equivalents, including CH ₂Cl₂), results in the formation of Mannich bases in high yields. Copyright

Full text of DOI:10.1002/chem.201103987

COMMUNICATION
DOI: 10.1002/chem.201103987
Mannich Reactions of Alkynes: Mechanistic Insights and the Role of Sub-
Stoichiometric Amounts of Alkynylcopper(I) Compounds in the Catalytic
Cycle
Benjamin R. Buckley, Amna N. Khan, and Harry Heaney*[a]
The rapid development of organocopper chemistry, partic-
ularly since the middle of the last century, has been compre-
hensively documented.[1] Alkynylcopper(I) compounds have
been known for many years,[2] and various methods are
available for their preparation.[3] Reactions of arylethynyl-
copper(I) compounds were exploited by Castro and co-
workers in stoichiometric reactions,[4] notably in heterocyclic
synthesis.[5] Compared with the majority of copper(I) salts,
many polymeric alkynylcopper(I) derivatives are remarka-
bly stable. For example, phenylethynylcopper(I), which has
a polymeric ladderane structure,[6] may be stored for pro-
longed periods of time.[7] Early examples of ligand-associat-
ed catalytic reactions involving alkynylcopper(I) compounds
were reported by Miura and co-workers.[8] Although alky-
nylcopper(I) compounds are invoked in Sonogashira–Hagi-
hara reactions,[1f,9] the importance of nitrogen ligands in the
using arenecarboxaldehydes together with secondary amines
or imines have been widely studied recently,[19,20] including
enantioselective reactions using chiral ligands.[21]
Reactions of phenylacetylene with aqueous formaldehyde
and pyrrolidine have been reported a number of times,[22] in-
cluding reactions using DMSO as
a
co-solvent.[22b] In
a recent report, in which a molecular sieve-supported cop-
per(II) catalyst was used,[22c] it is interesting to note that 1,4-
diphenylbuta-1,3-diyne was formed in some reactions using
phenylacetylene. In an earlier study we showed that the re-
duction of copper(II) hydroxyacetate in the presence of phe-
nylacetylene results in the formation of the yellow polymer-
ic phenylethynylcopper(I) in addition to 1,4-diphenylbuta-
1,3-diyne:[3d] experiments using copper(II) chloride[22c,e] un-
doubtedly involve the reduction of copper(II) to a polymeric
copper(I) catalyst with the concomitant formation of the
Glaser coupling product.
catalytic cycle has been pointed out only recently.[10]
A
number of additional reactions have been depicted as in-
volving monomeric alkynylcopper(I) compounds.[11] Howev-
er, as far as we are aware, other than in copper-catalysed
alkyne–azide cycloaddition (CuAAC) reactions,[12,13,14] the
only example where an alkynylcopper(I) derivative has been
isolated from a catalytic system is that reported recently by
Zuidema and Bolm,[15] in which the polymeric phenylethy-
nylcopper(I) could be isolated in a catalytic version of the
Castro–Stephens coupling of aryl halides with phenylacety-
lene.
We were interested to establish whether polymeric alky-
nylcopper(I) compounds were involved in other catalytic
cycles and, as a result of our earlier interest in Mannich re-
actions involving both primary and secondary amines,[16] we
chose to study the Mannich reactions of alkynes. The early
studies of Mannich reactions almost always used secondary
amines and aqueous formaldehyde and involved the inter-
mediacy of unstable aminols;[17] various new protocols have
been devised, including the use of pre-formed iminium ions
in non-protic solvents.[18] Reactions of terminal alkynes
In connection with copper-catalysed Mannich reactions of
terminal alkynes, we were aware that Brandsma had pointed
to the possibility that the yellow solids, observed in some re-
actions, were copper acetylides.[23] However, the isolation of
a polymeric alkynylcopper(I) species from the Mannich re-
actions of alkynes, and their involvement in the catalytic
cycles, has not been reported previously.
We began our study by taking phenylacetylene (1) and
copper(I) iodide (15 mol%) in a 1:1 mixture of aqueous
formaldehyde (2) and DMSO: the addition of pyrrolidine
(3) resulted in the immediate formation of a yellow precipi-
tate. The latter mixture was then subjected to a microwave-
assisted reaction, which gave the anticipated Mannich base
4 in 86% yield, together with the polymeric phenylethynyl-
copper(I) 5, identified from its powder X-ray diffraction
(XRD) pattern, which was identical to the pattern obtained
previously.[3d] A microwave-assisted reaction of compounds
1 and 3 with aqueous formaldehyde 2 and DMSO, using 5 in
place of copper(I) iodide, also gave the Mannich base 4 in
97% yield, shown in Scheme 1. Similarly, a reaction using
para-methoxyphenylpropargyl ether 6 (in place of com-
pound 1) and the appropriate alkynylcopper(I) compound 7
gave product 8 in 88% yield, We conclude that pyrrolidine
is able to disaggregate alkynylcopper(I) polymers efficiently.
The recovered yellow polymeric pre-catalyst 5 was re-used
and gave the product 4 in a 95% yield.
[a] Dr. B. R. Buckley, A. N. Khan, Prof. Dr. H. Heaney
Department of Chemistry, Loughborough University
Loughborough, Leicestershire, LE11 3TU (UK)
Fax : (+44)1509-223925
E-mail: h.heaney@lboro.ac.uk
A similar microwave-assisted reaction, but using 1-ethy-
nylcyclohexene (9), pyrrolidine (3), aqueous formaldehyde
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201103987.
Chem. Eur. J. 2012, 18, 3855 – 3858
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3855

teraction of an alkynylgold
compound with CH2Cl2 has
been
suggested
recently,[27]
rather than with the iminium
ion that would be expected to
be formed under the reaction
conditions used. A similar inter-
pretation of copper(I)-catalysed
Mannich reactions of alkynes
was also adduced,[11k] rather
Scheme 1. The microwave-assisted alkynylcopper(I)-catalysed reactions of phenylacetylene and para-methoxy-
phenylpropargyl ether with formaldehyde and pyrrolidine.
(2)/DMSO and copper(I) iodide (15 mol%) as the catalyst,
gave product 10 in 78% yield; however, no yellow precipi-
tate was observed. We carried out a number of reactions to
gain information about the latter reaction. Although we
were unable to prepare a yellow polymer in a microwave-as-
sisted reaction, we were able to prepare a yellow alkynyl-
copper(I) polymer in low yield at ambient temperature by
the interaction of 9 with copper(II) acetate in degassed
methanol, and, in a reaction in which that material was sub-
stituted for copper(I) iodide, product 10 was obtained in
67% yield. We concluded that the alkynylcopper(I) pre-cat-
alyst involved in the reactions of compound 9 was relatively
unstable and the polymer was disaggregated so easily that it
was not observed in the presence of amine ligands. In a reac-
tion of 9, in which we used 5 mol% of the pre-catalyst 5, we
obtained a product that showed little contamination by the
product 4 and which, after chromatography, gave product 10
in 92% yield. However, by using 1 mol% of 5 as the pre-
catalyst in a similar reaction, product 10 was obtained in
82% yield, as shown in Scheme 2. The last two results sup-
than an interpretation that involves an initial rapid reaction
of CH2Cl2 with the secondary amine, despite the fact that
when a reaction in which benzaldehyde and CH2Cl2 were al-
lowed to compete for diethylamine and phenylacetylene,
little of the product formed from benzaldehyde was ob-
tained. We established the involvement of the phenylethy-
nylcopper(I) polymer in the reactions with CH2Cl2 by using
CH2Cl2 as the formaldehyde equivalent in the reactions of
phenylacetylene and pyrrolidine, together with copper(I)
chloride or the phenylethynylcopper(I) polymer 5 as the
pre-catalysts: in these reactions, the Mannich base 4 was ob-
tained in 82 and 84% yields, respectively. In the reaction
using copper(I) chloride as the pre-catalyst we noted the im-
mediate formation of a yellow precipitate, which is diagnos-
tic for the formation of phenylethynylcopper(I) 5, on the ad-
dition of 1,8-diazabicycloACHTNUTRGNE[UNG 5.4.0]undec-7-ene (DBU) to the
reaction mixture. The results of the various investigations
are consistent with the outline shown in Scheme 3.
Scheme 2. Phenylethynylcopper(I) as a pre-catalyst in the reaction of 1-
cyclohexenylethyne, formaldehyde and pyrrolidine.
Scheme 3. The use of dichloromethane as a formaldehyde equivalent in
reactions with phenylacetylene and pyrrolidine using copper(I) chloride
or the phenylethynylcopper(I) polymer as pre-catalysts.
port the conclusion that disaggregation of the 1-ethynylcy-
clohexene-derived copper(I) polymer occurs more easily
than when using alkynylcopper(I) polymers containing aryl
substituents, in reactions such as those shown in Scheme 1.
A number of other compound types can also act as alde-
hyde equivalents in Mannich reactions. Acetals can be used.
For example, Pictet and Spengler reported, in the seminal
example of their now venerable intramolecular Mannich re-
action, that heating 2-phenylethylamine and dimethoxyme-
thane with hydrochloric acid resulted in the formation of
1,2,3,4-tetrahydroisoquinoline.[24] Similarly, 1,1-dihaloalkanes
can function as aldehyde equivalents, and reactions of
amines with dichloromethane are well known.[25] Secondary
amines react rapidly with CH2Cl2 at room temperature and
form hydrogen chloride and aminals that can give rise to
products derived from iminium ions, which are in equilibri-
um with chloromethylamines and aminals.[26] The direct in-
We also carried out reactions of phenylacetylene (1) and
para-tolylethyne (11) with pyrrolidine (3) and benzaldehyde
(12) in water, by using the appropriate arylethynylcopper(I)
polymer (5 or 13) as the pre-catalyst and obtained com-
pounds 14 and 15 in 71 and 70% yields, respectively, as
shown in Scheme 4. Additional examples are shown in the
Supporting Information using a number of different secon-
dary amines. We were able to re-isolate the polymers quan-
titatively, within experimental error, and observed little re-
duction in the yield of compound 14 when using the re-iso-
lated polymer 5. A re-examination of the reaction of 1 with
compounds 3 and 12 in water with copper(I) iodide as the
pre-catalyst[11b] also resulted in the formation of the phenyle-
1
thynylcopper(I) polymer 5. Inspection of the H NMR spec-
3856
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 3855 – 3858

Mannich Reactions of Alkynes
COMMUNICATION
Conclusion
The results of a number of cop-
per(I)-catalysed Mannich reac-
tions of terminal alkynes, secon-
dary amines and aldehydes are
reported, which involve conver-
sion of the copper(I) salts into
Scheme 4. Microwave-assisted reactions of arylacetylenes with benzaldehyde and pyrrolidine using arylethy-
nylcopper(I) pre-catalysts.
yellow
arylethynylcopper(I)
trum of the organic soluble material indicated that the Man-
nich reaction product 14 had been formed in a good yield;
however, in our hands, the maximum isolated product yield
after chromatography was 74%.
pre-catalysts. The reactions proceeded most rapidly and effi-
ciently in microwave-assisted reactions,[32] in which the ary-
lethynylcopper(I) pre-catalysts involved in the catalytic
cycles was proved by their use in place of precursor cop-
per(I) salts, by their re-use and by cross-over experiments.
An alternative explanation of the mechanism of Mannich
reactions using dichloromethane as a formaldehyde equiva-
lent involves the known rapid conversion of dichlorome-
thane into iminium salts by the interaction with secondary
amines.
To establish conclusively that the ladderane copper poly-
mer was recycled, we carried out a crossover experiment in
which para-tolylethyne (11), benzaldehyde (12) and pyrroli-
dine (3) were allowed to interact in the presence of
15 mol% of phenylethynylcopper(I) 5: examination of the
reaction product by 1H NMR spectroscopy indicated that
a mixture of the phenyl- and p-tolyl products (14 and 15)
were present in a ratio of approximately 1:9. The result of
a similar crossover experiment involving the use of formal-
dehyde is shown in the Supporting Information.
Experimental Section
General procedure for the preparation of propargylamines in microwave-
assisted reactions: Amine (1.0 mmol), formaldehyde (aq. 37%, 0.4 mL),
alkyne (1.2 mmol), arylethynylcopper(I) polymer (15 mol%) and DMSO
(3.0 mL) were added to a microwave vial equipped with a magnetic stir-
ring bar. The sealed mixture was heated under microwave irradiation at
1008C for 10 min. The reaction mixture was cooled to ambient tempera-
ture and extracted with dichloromethane (3ꢁ10 mL). The combined or-
ganic extracts were washed with brine (3ꢁ10 mL) and dried over anhy-
drous magnesium sulfate, evaporated with silica gel in vacuo, placed on
a column of silica gel and eluted with light petroleum/ethyl acetate (9:1)
to give the products as light-yellow oils. The identities and purities of the
products were confirmed by TLC, 1H and 13C NMR spectroscopy and
high-resolution mass spectrometry (see the Supporting Information for
further details).
Our results prove that alkynylcopper(I) polymers are
formed and are involved in the Mannich reactions of al-
kynes. Dimeric species, similar to 16, are involved in the ac-
cepted Bohlmann mechanism of the Glaser reaction that
has received support from recent kinetic studies:[28] addition-
al similar examples have been proposed and include studies
of Kinugasa[29] and CuAAC reactions.[30] Calculations sup-
port the proposals in the case of CuAAC reactions, in which
intermediates having m,h-bonding (similar to compound 18)
are involved.[31] The involvement of iminium ions (e.g., ion
17), in Mannich reactions is well established.[17d,e] The pro-
posed catalytic cycle is illustrated in Scheme 5.
Acknowledgements
The authors are grateful to The Higher Education Commission of Paki-
stan and Loughborough University for research funding. B. R. B. also
thanks Research Councils UK for a RCUK fellowship.
Keywords: alkynes · Mannich bases · mechanistic studies ·
multicomponent reactions · propargylamines
[1] a) B. H. Lipshutz, S. Sengupta, Org. React. 1992, 41, 135–631; b) Or-
ganocopper Reagents, (Ed.: R. J. K. Taylor), Oxford University
Press, Oxford, 1994; c) B. H. Lipshutz, in Organometallics in Synthe-
sis A Manual, (Ed.: M. Schlosser.), Wiley, Chichester, 2002 pp. 665–
815; d) Modern Organocopper Chemistry, (Ed.: N. Krause), Wiley-
VCH: Weinheim, 2002; e) S. V. Ley, A. W. Thomas, Angew. Chem.
2003, 115, 5558–5607; Angew. Chem. Int. Ed. 2003, 42, 5400–5449;
f) H. Heaney, S. Christie, in Organometallic Complexes of Copper,
Science of Synthesis Vol
3 Organometallics (Ed.: I. A. OꢂNeil),
Thieme, Stuttgart, 2004 pp. 305–662.
Scheme 5. A proposed catalytic cycle for Mannich reactions of arylal-
kynes involving alkynylcopper(I) polymers.
[2] a) R. Nast, W. Pfab, Chem. Ber. 1956, 89, 415–421; b) D. Blake, G.
Calvin, G. E. Coates, Proc. Chem. Soc. 1959, 396–397.
Chem. Eur. J. 2012, 18, 3855 – 3858
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3857

H. Heaney et al.
[3] See, for example: a) V. A. Sazonova, N. Ya. Kronrod, Zh. Obshch.
Khim. 1956, 26, 1876–1881; Chem. Abs. 1957, 51, 4981c; b) R. E.
Atkinson, R. F. Curtis, J. A. Taylor, J. Chem. Soc. C 1967, 578–582;
c) H. Ito, K. Arimoto, H.-o. Sensui, A. Hosomi, Tetrahedron Lett.
1997, 38, 3977–3980; d) B. R. Buckley, S. E. Dann, D. P. Harris, H.
Heaney, E. C. Stubbs, Chem. Commun. 2010, 46, 2274–2276.
[4] a) C. E. Castro, R. D. Stephens, J. Org. Chem. 1963, 28, 2163;
b) R. D. Stephens, C. E. Castro, J. Org. Chem. 1963, 28, 3313–3315.
[5] a) C. E. Castro, E. J. Gaughan, D. C. Owsley, J. Org. Chem. 1966, 31,
4071–4078; b) A. M. Malte, C. E. Castro, J. Am. Chem. Soc. 1967,
89, 6770; c) K. Gump, S. W. Moje, C. E. Castro, J. Am. Chem. Soc.
1967, 89, 6770–6771; d) S. A. Mladenovic, C. E. Castro, J. Hetero-
cycl. Chem. 1968, 5, 227–230; e) C. E. Castro, R. Havlin, V. K.
Honwad, A. Malte, S. Moje, J. Am. Chem. Soc. 1969, 91, 6464–6470.
[6] S. S. Y. Chui, M. F. Y. Ng, C.-M. Che, Chem. Eur. J. 2005, 11, 1739–
1749.
[7] D. C. Owsley, C. E. Castro, Org. Synth. Coll. 1988, 6, 916–918.
[8] a) K. Okuro, M. Enna, M. Miura, M. Nomura, J. Chem. Soc. Chem.
Commun. 1993, 1107–1108; b) K. Okuro, M. Furuune, M. Enna, M.
Miura, M. Nomura, J. Org. Chem. 1993, 58, 4716–4721; c) M.
Miura, M. Enna, K. Okuro, M. Nomura, J. Org. Chem. 1995, 60,
4999–5004.
[9] a) K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 1975,
16, 4467–4470; b) K. Sonogashira, J. Organomet. Chem. 2002, 653,
46–49.
dron 1997, 53, 2941–2958; d) H. Heaney, G. Papageorgiou, R. F.
Wilkins, Tetrahedron 1995, 51, 10737–10750; e) P. C. B. Page, H.
Heaney, E. P. Sampler, J. Am. Chem. Soc. 1999, 121, 6751–6752;
f) B. R. Buckley, P. C. B. Page, H. Heaney, E. P. Sampler, S. Carley,
C. Brocke, M. A. Brimble, Tetrahedron 2005, 61, 5876–5888.
[17] a) B. Reichert, Die Mannich Reaktion, Springer, Berlin, 1959; b) H.
Hellmann, G. Opitz, Aminoalkylierung, Verlag Chemie, Weinheim,
1960; c) M. Tramontini, L. Angiolini, Tetrahedron 1990, 46, 1791–
1837; d) E. F. Kleinman in Comprehensive Organic Synthesis, (Eds.:
B. M. Trost, I. Fleming, C. H. Heathcock) Pergamon, Oxford, 1991,
vol. 2 Chapter 4.1, pp. 893–951; e) H. Heaney in Comprehensive Or-
ganic Synthesis, (Eds.: B. M. Trost, I. Fleming, C. H. Heathcock),
Pergamon, Oxford, 1991, Vol. 2, Ch. 4.2, pp. 953–973.
[18] a) G. Kinast, L.-F. Tietze, Angew. Chem. 1976, 88, 261–262; Angew.
Chem. Int. Ed. Engl. 1976, 15, 239–240; b) H. Heaney, G. Papageor-
giou, R. F. Wilkins, Tetrahedron Lett. 1988, 29, 2377–2380.
[19] a) C. Wei, Z. Li, C.-J. Li, Synlett 2004, 1472–1483; b) L. Chen, C.-J.
Li, Adv. Synth. Catal. 2006, 348, 1459–1484; C.-J. Li, Acc. Chem.
Res. 2010, 43, 581–590.
[20] a) J. J. McNally, M. A. Youngman, S. L. Dax, Tetrahedron Lett. 1998,
39, 967–970; b) A. B. Dyatkin, R. A. Rivero, Tetrahedron Lett. 1998,
39, 3647–3650; c) N. E. Leadbeater, H. M. Torenius, H. Tye, Mol.
Diversity 2003, 7, 135–144; d) Y. Ju, C.-J. Li, R. S. Varma, QSAR
Comb. Sci. 2004, 23, 891–894; e) J. B. Bariwal, D. S. Ermolatꢂev,
E. V. Van der Eycken, Chem. Eur. J. 2010, 16, 3281–3284.
[21] a) T. F. Knçpfel, P. Aschwanden, T. Ichikawa, T. Watanabe, E. M.
Carreira, Angew. Chem. 2004, 116, 6097–6099; Angew. Chem. Int.
Ed. 2004, 43, 5971–5973; b) N. Gommermann, P. Knochel, Chem.
Eur. J. 2006, 12, 4380–4392; c) T. Zeng, L. Yang, R. Hudson, G.
Song, A. R. Moores, C.-J. Li, Org. Lett. 2011, 13, 442–445, and cited
references.
[22] For recent examples see; a) A. Sharifi, H. Farhangian, F. Mohsen-
zaddeh, M. R. Naimi-Jamal, Monats. 2002, 133, 199–204; b) L. W.
Bieber, M. F. da Silva, Tetrahedron Lett. 2004, 45, 8281–8283; c) A.
Fodor, A. Kiss, N. Debreczeni, Z. Hell, I. Gresits, Org. Biomol.
Chem. 2010, 8, 4575–4581; d) T. Okamura, K. Asano, S. Matsubara,
Synlett 2010, 20, 3053–3056; e) M. G. Shaibakova, I. G. Titova, A. G.
Ibragimov, U. M. Dzhemilev, Russ. J. Org. Chem. 2011, 47, 161–167.
[23] a) L. Brandsma, Synthesis of Acetylenes, Allenes and Cumulenes:
Methods and Techniques, Elsevier, Oxford, 2004, pp 267; see also
b) G. R. Pettit, E. I. Saldana, J. Med. Chem. 1974, 17, 896–898.
[24] A. Pictet, T. Spengler, Ber. Dtsch. Chem. Ges. 1911, 44, 2030–2036.
[25] J. E. Mills, C. A. Maryanoff, R. M. Cosgrove, L. Scott, D. F. McCom-
sey, Org. Prep. Proc. Int. 1984, 16, 97–114.
[10] Z. Gonda, G. L. Tolnai, Z. Novꢃk, Chem. Eur. J. 2010, 16, 11822–
11826.
[11] See, for example: a) R. Shintani, G. C. Fu, J. Am. Chem. Soc. 2003,
125, 10778–10779; b) L. Shi, Y.-Q Tu, M. Wang, F.-M. Zhang, C.-A.
Fan, Org. Lett. 2004, 6, 1001–1003; c) I. Bae; H. Han; S. Chang, J.
Am. Chem. Soc. 2005, 127, 2038–2039; H. Han; S. Chang, J. Am.
Chem. Soc. 2005, 127, 2038–2039; d) F. Montel, R. Beaudegnies, J.
Kessabi, B. Martin, E. Muller, S. Wendeborn, P. M. J. Jung, Org.
Lett. 2006, 8, 1905–1908; e) W. Shi, Y. Luo, L. Chao, H. Zhang, J.
Wang; A. Lei, J. Am. Chem. Soc. 2008, 130, 14713–14720; A. Lei, J.
Am. Chem. Soc. 2008, 130, 14713–14720; f) C. Xie, L. Liu, Y.
Zhang, P. Xu, Org. Lett. 2008, 10, 2393–2396; g) H. Yoshida, T.
Morishita, H. Nakata, J. Ohshita, Org. Lett. 2009, 11, 373–376; h) R.
Yazaki; N. Kumagai; M. Shibasaki, J. Am. Chem. Soc. 2010, 132,
10275–10277; N. Kumagai; M. Shibasaki, J. Am. Chem. Soc. 2010,
132, 10275–10277; i) C. A. Correia; C.-J. Li, Adv. Synth. Catal.
2010, 352, 1446–1450; C.-J. Li, Adv. Synth. Catal. 2010, 352, 1446–
1450; j) O. P. Pereshivko, V. A. Peshkov, E. V. Van der Eycken, Org.
Lett. 2010, 12, 2638–2641; k) D. Yu, Y. Zhang, Adv. Synth. Catal.
2011, 353, 163–169.
[12] a) V. V. Rostovsev, V. V. Fokin, L. G. Green, K. B. Sharpless, Angew.
Chem. 2002, 114, 2708–2711; Angew Chem. Int. Ed. 2002, 41, 2596–
2599; b) M. Meldal, C. W. Tornøe, J. Org. Chem. 2002, 67, 3057–
3064.
[13] For reviews, see, for example: a) V. D. Bock, H. Hiemstra, J. H. van
Maarseveen, Eur. J. Org. Chem. 2006, 51–68; b) M. Meldal, C. W.
Tornøe, Chem. Rev. 2008, 108, 2952–3015; c) F. Amblard, J. H. Cho,
R. F. Schinazi, Chem. Rev. 2009, 109, 4207–4220; d) special issue:
Chem. Soc. Rev. 2010, 39, 1221–1408.
[26] a) J. E. Mills, C. A. Maryanoff, D. F. McComsey, R. C. Stanzione, L.
Scott, J. Org. Chem. 1987, 52, 1857–1859; b) H.-J. Federsel, E. Kçn-
berg, L. Lilljequist, B.-M. Swahn, J. Org. Chem. 1990, 55, 2254–
2256.
[27] D. Aguilar, M. Contel, E. P. Urriolabeitia, Chem. Eur. J. 2010, 16,
9287–9296.
[28] a) F. Bohlmann, H. Schçnowsky, E. Inhoffen, G. Grau, Chem. Ber.
1964, 97, 794–800; b) L. I. Fedenok, M. S. Shvartsberg, Tetrahedron
Lett. 2011, 52, 3776–3778.
[29] A. Mames, S. Stecko, P. Mikolajczyk, M. Soluch, B. Furman, M.
Chmielewski, J. Org. Chem. 2010, 75, 7580–7587.
[14] a) B. R. Buckley, S. E. Dann, H. Heaney, Chem. Eur. J. 2010, 16,
6278–6284; b) C. Shao, G. Cheng, D. Su, J. Xu, X. Wang, Y. Hu,
Adv. Synth. Catal. 2010, 352, 1587–1592; c) B. R. Buckley, S. E.
Dann, H. Heaney, E. C. Stubbs, Eur. J. Org. Chem. 2011, 770–776.
[15] E. Zuidema, C. Bolm, Chem. Eur. J. 2010, 16, 4181–4185.
[16] a) H. Heaney, G. Papageorgiou, R. F. Wilkins, J. Chem. Soc. Chem.
Commun. 1988, 1161–1163; b) M. J. Earle, R. A. Faithurst, H.
Heaney, G. Papageorgiou, R. F. Wilkins, Tetrahedron Lett. 1990, 31,
4229–4232; c) H. Heaney, G. Papageorgiou, R. F. Wilkins, Tetrahe-
[30] N. W. Smith, B. P. Polenz, S. B. Johnson, S. V. Dzyuba, Tetrahedron
Lett. 2010, 51, 550–553.
[31] a) M. Ahlquist, V. V. Fokin, Organometallics 2007, 26, 4389–4391;
b) B. F. Straub, Chem. Commun. 2007, 3868–3870.
[32] C. R. Strauss, D. W. Rooney, Green Chem. 2010, 12, 1340–1344.
Received: December 20, 2011
Published online: February 29, 2012
3858
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 3855 – 3858