Efficient tandem process for the catalytic deprotection of N-allyl amides and lactams in aqueous media: A novel application of the bis(allyl)- ruthenium(IV) catalysts [Ru(η3:η2: η3-C12H18)Cl2] and [Ru(η3:η3-C10H16)-(μ-Cl) Cl}2]

Article abstract of DOI:10.1002/chem.200700477

An operationally simple and highly efficient methodology for the removal of the allyl protecting group in amides and lactams has been developed by using the commercially available bis(allyl)-ruthenium(IV) catalysts [Ru(η³:η²:η³-C₁₂H ₁₈)Cl₂] (C₁₂H₁₈ = dodeca-2,6,10-triene-1,12-diyl) and [(Ru(η³:η³- C₁₀H₁₆)(μ-Cl)Cl}₂] (C₁₀H ₁₆ = 2,7-dimethylocta-2,6-diene-1,8-diyl). The tandem process, which takes place in aqueous media and proceeds in a one-pot manner, involves the initial isomerization of the C=C bond of the allyl unit and subsequent oxidative cleavage of the resulting enamide.

Full text of DOI:10.1002/chem.200700477

DOI: 10.1002/chem.200700477
Efficient Tandem Process for the Catalytic Deprotection of N-Allyl Amides
and Lactams in Aqueous Media: A Novel Application of the BisCAHTRE(UNG allyl)–
Ruthenium(IV) Catalysts [Ru(h3:h2:h3-C12H18)Cl2] and [{Ru(h3:h3-C10H16)-
(m-Cl)Cl}2]**
ACHTREUNG
Victorio Cadierno,* JosØ Gimeno,* and Noel Nebra[a]
Abstract: An operationally simple and highly efficient methodology for the remov-
al of the allyl protecting group in amides and lactams has been developed by using
the commercially available bis
G
Keywords: allylic compounds
amides · aqueous-phase catalysis ·
lactams protecting groups
ruthenium
·
C12H18)Cl2] (C12H18 =dodeca-2,6,10-triene-1,12-diyl) and [{Ru(h3:h3-C10H16)
Cl)Cl}2] (C10H16 =2,7-dimethylocta-2,6-diene-1,8-diyl). The tandem process, which
takes place in aqueous media and proceeds in a one-pot manner, involves the ini-
tial isomerization of the C=C bond of the allyl unit and subsequent oxidative
cleavage of the resulting enamide.
·
·
Introduction
cleavage step can be easily achieved in the presence of tran-
sition-metals via appropriate coordination.[1,2] Thus, except
for a few miscellaneous methods, transition-metal-catalyzed
reactions are currently the most efficient and selective strat-
egies for the deprotection of N-allylamines.[1,2] These metal-
mediated methodologies can be roughly classified into two
groups according to their mechanistic features: 1) those
based on a nucleophilic substitution reaction, in which the
amine unit becomes a leaving group (Scheme 1; path a) and
Neither the continuous improvements in selectivity nor the
invention of new reactions have abated the dependence of
synthetic organic chemists on protecting groups.[1] So, the
proper selection of efficient protecting groups, as well as the
search of selective deprotection methodologies, still remain
crucial issues in modern organic chemistry. In particular,
among the plethora of alternatives, the use of allyl moieties
for the protection of amines is becoming more and more
popular as, in contrast to classical protecting groups (for ex-
ample, BOC (tert-butoxycarbonyl), FMOC (9-fluorenyl-
methyl carbamate), tosylamide, etc.), they remain inert
under both acidic and basic conditions.[1] Moreover, due to
À
the presence of an orthogonal p bond, the final N C bond
[a] Dr. V. Cadierno, Prof. J. Gimeno, Dipl.-Chem. N. Nebra
Departamento de Química Orgµnica e Inorgµnica
Instituto Universitario de Química Organometµlica
“Enrique Moles” (Unidad Asociada al CSIC)
Universidad de Oviedo, Juliµn Clavería 8
E-33006 Oviedo (Spain)
Scheme 1. Strategies used for the catalytic deprotection of N-allylamines.
2) those based on the isomerization of the allylamine into
an enamine which is subsequently cleaved upon acidic hy-
drolysis (Scheme 1; path b). While the former involves the
intermediate formation of a p-allyl complex (Pd catalysts),
the catalytically active species in the latter are usually hy-
dride complexes able to promote the isomerization of the al-
lylic C=C double bond (Ru and Rh catalysts).[1,2]
Fax : (+34)98-510-3446
E-mail: vcm@uniovi.es
jgh@uniovi.es
[**] C12H18 =dodeca-2,6,10-triene-1,12-diyl and C10H16 =2,7-dimethylocta-
2,6-diene-1,8-diyl.
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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Chem. Eur. J. 2007, 13, 6590 – 6594

FULL PAPER
An important drawback of the p-allyl–palladium method-
ology (path a) is the requirement of stoichiometric amounts
of a nucleophilic compound, which acts as the allyl group
scavenger.[2,3] Therefore, although they involve two steps,
the isomerization-based methodologies (path b) are un-
doubtedly more convenient.[2,4] In this context, we have re-
cently described a catalytic one-pot procedure for the re-
moval of the allyl protecting group in amines (Scheme 2),[5]
Results and Discussion
Despite its great synthetic interest,[15] the deprotection of al-
lylic amides and lactams has been scarcely documented,[8–13]
only one general procedure being presently available.[8] It
consists of a two-step process involving: 1) the initial catalyt-
ic isomerization of the allyl unit, promoted by the Grubbs
(PCy3)2] in refluxing toluene,[16] to
carbene [RuACTHER(UNG =CHPh)Cl2ACHTREUGN
give enamides and 2) the subsequent scission of the internal
C=C bond of the isolated enamides by the system RuCl3/
NaIO4 in a 1,2-dichloroethane/water mixture (Scheme 3). In
the latter step, RuCl3 catalyzes the oxidative cleavage of the
C=C bond to generate a N-formyl amide or lactam which
decarboxylates in aqueous media.
Inspired by these results, we decided to explore the ability
of the bis
(allyl)–ruthenium(IV) complexes [Ru(h3:h2:h3-
ACHTREUNG
C12H18)Cl2] (1) and [{Ru(h3:h3-C10H16)
AHCTREU(NG m-Cl)Cl}2] (2) to pro-
mote the removal of the allyl unit of amides under oxidative
conditions through a tandem allyl group isomerization/en-
amide C=C cleavage process. The deprotection of N-allyl
benzamide (3a) was used as a model reaction. Thus, we
Scheme 2. Deprotection of N-allylamines catalyzed by the RuIV com-
plexes 1 and 2.
which is based on the ability of
the commercially available bis-
A
com-
plexes [Ru(h3:h2:h3-C12H18)Cl2]
(C12H18 =dodeca-2,6,10-triene-
1,12-diyl) (1) and [{Ru(h3:h3-
Scheme 3. General procedure for the (CO)N–allyl cleavage. Conditions: a) 5 mol% [RuACHTREUG(N =CHPh)Cl2ACHTREUNG(PCy3)2],
toluene, reflux; b) 3.5 mol% RuCl3, NaIO4 (2 equiv), 1,2-dichloroethane/water (1:1 v/v), RT, aqueous workup
under basic conditions, see reference [8].
C10H16)
A
(C10H16 =
2,7-dimethylocta-2,6-diene-1,8-
diyl) (2) to promote C=C mi-
grations in water,[6,7] allowing
the direct hydrolysis of the initially formed enamines. Re-
markably, this is the first synthetic procedure for the remov-
al of the allyl protecting group in amines which can be per-
formed in pure aqueous media, organic solvents being up
till now required for the initial isomerization step (path b).
Although a wide range of N-allylamines could be efficiently
and selectively deprotected by using this methodology,[5] one
important limitation was encountered when N-allylic amides
and lactams were used as substrates. In these cases, only the
isomerization of the C=C bond was observed as the higher
stability of enamides compared with enamines prevented
the hydrolytic (CO)N–allyl cleavage.
In this paper, we would like to report that such a limita-
tion can be easily overcome by introducing a stoichiometric
amount of KIO4 in the reaction media. Under these condi-
tions, oxidative cleavage of the initially formed enamide
readily takes place leading to the clean formation of the de-
sired NH amide or lactam. Herein, we present a novel cata-
lytic procedure which represents a simple, general, and
more convenient alternative to previously known methods
for the deprotection of (CO)N–allyl units[8–13] as: 1) it is per-
formed in a one-pot manner, 2) it takes place for the first
time in an environmental benign and inexpensive solvent
(water),[14] and 3) it is applicable to the deprotection of N,N-
diallylamides for which no catalytic methodologies are
known.
have found that, under optimized conditions (3 mol% of
Ru; 0.1m solution of the substrate in water, 1008C), both
complexes are efficient catalysts for this transformation if
one equivalent of KIO4 is present in the reaction media, af-
fording deallylated benzamide in >97% yield after approxi-
mately 3 h (entry 1 in Table 1).[17] The use of lower tempera-
tures and/or catalyst loadings slows down the reaction con-
siderably. For example, by using a catalyst loading of
0.1 mol% of Ru (complex 2) 12 h are required to deprotect
3a in 96% GC yield.
Under these optimal reaction conditions, catalysts 1 and 2
are also active in the deprotection of a large number of sec-
ondary N-allyl amides (Table 1). Thus, as observed for N-
allyl benzamide (3a), its ortho, meta, and para-substituted
derivatives undergo a fast (3 h) and quantitative removal of
the allyl unit regardless of the presence of electron-with-
drawing (3b–d, entries 2–4) or electron-donating groups
(3e–g, entries 5–7). As shown in entries 8–11, this transfor-
mation is not restricted to aromatic amides, the deprotection
of alkylic substrates 3h–k being readily (<5 h) and efficient-
ly (>98% GC yields) achieved under the standard reaction
conditions. Close examination of the reaction mixtures
shows that they are emulsions rather than homogeneous sol-
utions, the catalytic transformation taking place probably at
the interface. As previously observed in the aqueous depro-
tection of allylic amines,[5] no remarkable differences in ac-
Chem. Eur. J. 2007, 13, 6590 – 6594
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www.chemeurj.org
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V. Cadierno, J. Gimeno and N. Nebra
Table 1. Ruthenium-catalyzed deprotection of secondary N-allyl amides
in water.[a]
Table 2. Ruthenium-catalyzed deprotection of tertiary N-allyl amides in
water.[a]
Entry
1
Substrate
Cat.
t [h]
Yield [%][b]
Entry Substrate
Cat. t [h] Yield [%][b]
R=Ph (3a)
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
3
3
3
3
3
3
3
3
2
2
3
3
3
3
2
2
5
5
3
3
5
5
97
99
99
99
99
99
99
99
99
98
98
99
99
99
98
99
99
99
99
99
99
99
1
2
3
4
5
6
7
8
R1 =Me; R2 =Me (4a)
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
3
3
3
3
2
2
7
6
7
95
93
80
83
89
92
84
82
83
85
97
97
85
80
87
93
2
R=2-C6H4F (3b)
R=3-C6H4F (3c)
R=4-C6H4F (3d)
R=2-C6H4OMe (3e)
R=3-C6H4OMe (3 f)
R=4-C6H4OMe (3g)
R=n-pent (3h)
R1 =Me; R2 =n-pent (4b)
3
R1 =Me; R2 =CH2CH2C5H9 (4c)
R1 =Me; R2 =4-C6H4F (4d)
R1 =Me; R2 =2-C6H4OMe (4e)
R1 =Bn; R2 =Ph (4 f)
4
5
7
6
20
17
2
2
7
7
R1 =3-C6H4COMe; R2 =Me (4g)
R1 =2-C6H4CO2Et; R2 =2-C6H4F (4h)
8
7
9
R=n-hept (3i)
[a] Reactions were performed under a N2 atmosphere at 1008C by using
1.0 mmol of the corresponding N-allyl amide, 1.0 mmol of KIO4, and
10 mL of H2O. [b] Yields were determined by GC analysis.
10
11
R=CH2Bn (3j)
R=CH2CH2C5H9 (3k)
[a] Reactions were performed under a N2 atmosphere at 1008C by using
1.0 mmol of the corresponding N-allyl amide, 1.0 mmol of KIO4, and
10 mL of H2O. [b] Yields were determined by GC analysis.
Table 3. Ruthenium-catalyzed deprotection of N,N-diallyl amides in
water.[a]
tivity between the mononuclear derivative 1 and the dimeric
compound 2 have been noted.
Our catalytic protocol can be extrapolated to the depro-
tection of tertiary N-allyl amides. Table 2 illustrates several
examples in which both aliphatic (4a–f, entries 1–6) or aro-
matic (4g–h, entries 7–8) substituents are attached to the N-
atom. As expected, the corresponding unprotected amides
are generated in high yields (>80%) within 2–7 h.[18] Never-
theless, it should be noted that no completely clean transfor-
mations were observed in all cases (entries 2, 4, 5, 7 and 8),
the formation of minor amounts of the corresponding car-
boxylic acid R2CO2H, as the result of the enamide group hy-
drolysis, being detected by GCMS analysis.
Remarkably, complexes 1 and 2 can also be applied to the
selective deprotection of N,N-diallyl amides in marked con-
trast to the Grubbs carbene-based methodology
(Scheme 3).[8,19] Thus, as shown in Table 3, amides 5a–l can
be completely deallylated in excellent yields (>87%) after
only 1–8 h without detection by GCMS analysis of ring-clos-
ing metathesis (RCM) products in the crude reaction mix-
tures. It is interesting to note that, in order to achieve the
complete removal of both allylic units, two equivalents of
KIO4 are required, the use of only one equivalent leading to
incomplete transformations. As far as we know this is the
first synthetic procedure able to perform the chemoselective
deprotection of N,N-diallylic amides, allowing us to extend
the use of allyl groups for the protection of (CO)NH2
units.[1]
Entry
1
Substrate
Cat.
t [h]
Yield [%][b]
R=Ph (5a)
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
5
5
4
4
5
5
4
4
2
3
5
5
3
3
8
8
3
3
5
5
3
3
1
1
99
99
99
99
99
96
99
99
99
99
99
99
96
98
87
92
96
97
89
92
99
99
95
96
2
R=2-C6H4F (5b)
R=3-C6H4F (5c)
R=4-C6H4F (5d)
R=2-C6H4OMe (5e)
R=3-C6H4OMe (5 f)
R=4-C6H4OMe (5g)
R=nPr (5h)
3
4
5
6
7
8
9
R=n-pent (5i)
10
11
12
R=n-hept (5j)
R=CHCl2 (5k)
R=CF3 (5l)
[a] Reactions were performed under a N2 atmosphere at 1008C by using
1.0 mmol of the corresponding N,N-diallyl amide, 2.0 mmol of KIO4, and
10 mL of H2O. [b] Yields were determined by GC analysis.
6592
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Deprotection of N-Allyl Amides and Lactams
FULL PAPER
Concerning the tolerance of functional groups, as clearly
shown in Tables 1, 2, and 3, this methodology is compatible
with the presence in the substrates of halide (3b–d, 4d,h,
and 5b–d,k,l), alkoxy (3e–g, 4e, and 5e–g), ketone (4g),
and ester (4h) substituents. In addition, as stated in the Ex-
perimental Section, the reactions can be performed on a
preparative scale, the isolation of the final unprotected
amides being easily achieved by simple extraction from the
aqueous phase and subsequent flash chromatography. All
these facts confer to catalysts 1 and 2 genuine potential for
practical application in synthetic organic chemistry.
Once we had confirmed the generality of this catalytic
transformation with acyclic N-allyl and N,N-diallyl amides,
we decided to check the ability of complexes 1 and 2 to cat-
alyze the allyl-group removal in lactams. The catalytic per-
formances shown in Table 4 clearly demonstrate that our ex-
perimental protocol using complexes 1 and 2 is also efficient
for the N-allyl deprotection of lactams. Thus, regardless of
Conclusion
An operationally simple and highly efficient procedure for
the catalytic removal of the allyl protecting group in amides
and lactams has been developed by using the commercially
available bis
C12H18)Cl2] (C12H18 =dodeca-2,6,10-triene-1,12-diyl) (1) and
[{Ru(h3:h3-C10H16)
(m-Cl)Cl}2] (C10H16 =2,7-dimethylocta-2,6-
(allyl)–ruthenium(IV) complexes [Ru(h3:h2:h3-
ACHTREUNG
AHCTREUNG
diene-1,8-diyl) (2). The process, which takes place in the
presence of KIO4, consists of a Ru-catalyzed tandem process
involving the initial isomerization of the allyl unit and subse-
quent oxidative C=C bond cleavage of the resulting en-
AHCTREUNG
amide.[20] The (CO)N–allyl cleavage protocol presented
herein represents an appealing and competitive alternative
to previously known catalytic procedures as: 1) in contrast
to the Grubbs carbene/RuCl3 two-step methodology, it is
performed in a one-pot manner by using a single ruthenium
source, 2) it takes place for the first time in an environmen-
tal benign and inexpensive solvent (water), and 3) it can be
applied to the deprotection of N,N-diallylamides for which
no precedents have been till now reported. In addition, as
lactams usually present pharmacologic activity, serving also
as crucial intermediates for the preparation of a large varie-
ty of natural products, the development of efficient proce-
Table 4. Ruthenium-catalyzed deprotection of N-allyl lactams in water.[a]
Entry
Substrate
n=1 (6a)
n=2 (6b)
Cat.
t [h]
Yield [%][b]
À
dures for the protection/deprotection of their N H unit
presents a particular synthetic interest. We are confident
that the simplicity, selectivity, and efficiency of the catalytic
method reported in this paper will be of interest to a wide
range of synthetic organic chemists, who may include its use
in their future research programs.
1
2
1
2
1
2
1
2
1
2
1
2
4.5
5.3
0.3
0.5
0.3
0.3
0.5
0.5
0.5
0.5
4.0
4.0
99
95
98
97
99
99
97
99
99
99
96
95
1
2
3
4
5
6
n=3 (6c)
n=4 (6d)
n=5 (6e)
n=9 (6 f)
Experimental Section
General procedure for the catalytic deallylation reactions: Under a nitro-
gen atmosphere, the corresponding N-allylic substrate (1 mmol), the
[a] Reactions were performed under a N2 atmosphere at 1008C by using
1.0 mmol of the corresponding N-allyl lactam, 1.0 mmol of KIO4, and
10 mL of H2O. [b] Yields were determined by GC analysis.
ruthenium catalyst precursor
1 or 2 (3 mol% of Ru), KIO4 (1 or
2 mmol), and water (10 mL) were introduced into a sealed tube and the
reaction mixture was stirred at 1008C for the indicated time. The course
of the reaction was monitored by regular sampling and analysis by gas
chromatography. The identity of the resulting deallylated products was
assessed by comparison with commercially available (Aldrich Chemical
or Acros Organics), or independently synthesized (following reported
procedures), pure samples and by their fragmentation in GCMS analysis.
We note that all these reactions can be performed in a preparative scale.
the ring size, clean and selective transformations (>98%
GC yields) were observed in all cases within 0.3–5.3 h under
the standard reaction conditions.
Finally, it is also interesting to note that systems contain-
ing an extra carbonyl unit attached to the nitrogen atom can
also be deprotected by using 1 and 2. As a representative
example, treatment of an aqueous suspension of N-allyl glu-
tarimide (7) with a catalytic amount of complex 1 or 2
(3 mol% of Ru) in the presence of KIO4, quantitatively lib-
erates glutarimide in approximately 30 min (Scheme 4).
Representative example: Under a nitrogen atmosphere, N-allyl benzamide
(3a) (2.1 g, 13 mmol), complex
1 (0.130 g, 0.39 mmol), KIO4 (3.0 g,
13 mmol), and water (80 mL) were introduced into a sealed tube and the
reaction mixture was stirred at 1008C for 3.5 h (96% GC yield). The
aqueous phase was then saturated with NaCl and extracted with dichloro-
methane (4”25 mL). The combined organic extracts were then dried
over MgSO4, concentrated, and purified by column chromatography over
silica gel by using a 10% ethyl acetate/hexanes mixture as eluent to give
1.369 g (11.3 mmol) of analytically pure benzamide (87% yield).
Acknowledgements
We are indebted to the Ministerio de Educación y Ciencia (MEC) of
Spain (project CTQ2006–08485/BQU) and the Gobierno del Principado
Scheme 4. Deprotection of N-allyl glutarimide by using catalysts 1 and 2.
Chem. Eur. J. 2007, 13, 6590 – 6594
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6593

V. Cadierno, J. Gimeno and N. Nebra
de Asturias (FICYT project IB05–035) for financial support. N.N. and
V.C. thank the MEC and the European Social Fund for the award of a
PhD grant and a “Ramón y Cajal” contract, respectively.
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[15] There are relatively few methods presently available for the depro-
tection of an amide moiety (see reference [1]), the most general in-
volving the oxidative cleavage of an activated aryl group attached to
the nitrogen atom by CeIV ammonium nitrate. See for example:
D. R. Kronenthal, C. Y. Han, M. K. Taylor, J. Org. Chem. 1982, 47,
2765–2768 and references therein.
[16] The authors suggest that a ruthenium-hydride, resulting from the de-
composition of the Grubbs catalyst, is the real active species in the
C=C isomerization process, see references [4e,8].
[17] a) Deprotection of 3a also takes place in the presence of other oxi-
dizing agents (for example, NaIO4, KMnO4). At least one equivalent
of oxidant is required, otherwise incomplete reactions are observed.
b) As expected, in the absence of oxidant, a mixture of (E)-and
[5] V. Cadierno, S. E. García-Garrido, J. Gimeno, N. Nebra, Chem.
Commun. 2005, 4086–4088.
[6] Complexes 1 and 2 are efficient catalysts for the redox isomerization
of allylic alcohols into carbonyl compounds in both organic and
aqueous media: a) V. Cadierno, S. E. García-Garrido, J. Gimeno,
Chem. Commun. 2004, 232–233; b) V. Cadierno, S. E. García-Garri-
do, J. Gimeno, A. Varela-lvarez, J. A. Sordo, J. Am. Chem. Soc.
2006, 128, 1360–1370.
[7] For a general review on the stoichiometric reactivity and catalytic
applications of complexes 1 and 2 see: V. Cadierno, P. Crochet, S. E.
García-Garrido, J. Gimeno, Curr. Org. Chem. 2006, 10, 165–183.
[8] a) B. Alcaide, P. Almendros, J. M. Alonso, Tetrahedron Lett. 2003,
44, 8693–8695; b) B. Alcaide, P. Almendros, J. M. Alonso, Chem.
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(Z)-N-(1-propenyl)benzamide is formed (approximately
a 1.2:1
ratio). c) The use of classical organic solvents (for example, toluene,
THF, CH2Cl2) or water/organic solvent mixtures drastically reduces
the efficiency of this deprotection protocol, the maximum yield at-
tained in these cases being 30% (always in the presence of KIO4).
[18] The presence of a benzyl substituent on the nitrogen atom leads to
slower transformations, the deprotection of amide 4 f requiring at
least 17 h to attain a 97% yield (Table 2, entry 6). A similar effect
of the benzyl group has been previously observed by us in the de-
protection of N-allylic amines promoted by complexes 1 and 2. See
reference [5].
[9] Deprotection of tertiary N-allyl amides by AlMe3 in the presence of
[19] Treatment of N,N-diallyl amides with [RuACTHERNGU(=CHPh)Cl2ACHTRE(UGN PCy3)2] leads
catalytic amounts of [NiCl2ACHTRE(UNG dppp)] (dppp=1,3-bis(diphenylphospha-
to the expected formation of pyrrolinyl amides through a RCM pro-
cess, see for example: C. Bressy, C. Menant, O. Piva, Synlett 2005,
577–582.
nyl)propane) has been described: T. Taniguchi, K. Ogasawara, Tetra-
hedron Lett. 1998, 39, 4679–4682.
[10] The N-allyl cleavage of a 3-amino-b-lactam and a 2-hydroxy-g-
lactam, induced by RhCl3 followed by KMnO4 or acidic treatments,
has been also reported: a) G. Cainelli, M. DaCol, P. Gelletti, D. Gia-
comini, Synlett 1997, 923–924; b) O. Kanno, M. Miyauchi, I. Kawa-
moto, Heterocycles 2000, 53, 173–181.
[20] For a review on ruthenium-catalyzed tandem processes see: C. Bru-
neau, S. DØrien, P. H. Dixneuf, Top. Organomet. Chem. 2006, 19,
295–326.
[11] The N-allyl bond of AcN(R)CH2CH=CH2 (R=Bn, CH2Bn) has
Received: March 27, 2007
been cleaved in the presence of a catalytic amount of Pd
A
Published online: May 22, 2007
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