1,2-Reduction of α,β-unsaturated hydrazones using dimethylamine-borane/p-toluenesulfonic acid: An easy route to allyl hydrazines

Article abstract of DOI:10.1016/S0040-4020(02)00914-6

α,β-Unsaturated hydrazones can be easily converted into N-allyl hydrazines by reaction with dimethylamine-borane/p-toluenesulfonic acid under mild reaction conditions. The reduction works well for N′-allylhydrazides but N′-allyl-N,N-dimethylhydrazines are

Full text of DOI:10.1016/S0040-4020(02)00914-6

Tetrahedron 58 (2002) 7925–7932
1,2-Reduction of a,b-unsaturated hydrazones
using dimethylamine–borane/p-toluenesulfonic acid:
an easy route to allyl hydrazines
a
a
Maria E. Casarini,a Franco Ghelfi,a Emanuela Libertini, Ugo M. Pagnoni
,
*
and Andrew F. Parsonsb
a
`
Dipartimento di Chimica, Universita degli Studi di Modena e Reggio Emilia, via Campi 183, 41100 Modena, Italy
bDepartment of Chemistry, University of York, Heslington, York YO10 5DD, UK
Received 13 May 2002; revised 9 July 2002; accepted 23 July 2002
Abstract—a,b-Unsaturated hydrazones can be easily converted into N-allyl hydrazines by reaction 0 with dimethylamine–borane/
p-toluenesulfonic acid under mild reaction conditions. The reduction works well for N0-allylhydrazides but N -allyl-N,N-dimethylhydrazines
are rapidly reoxidised by air and so need to be manipulated under an inert atmosphere prior to N0-acylation. Competitive conjugate reduction
can also be observed and the regioselectivity of the dimethylamine–borane attack is determined by steric and/or electronic factors. The
procedure is also effective for the CvN reduction of unconjugated hydrazones. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
auxiliaries of the type R¼NR1R2, which exploited the well-
known weakness of the heteroatom–heteroatom connection
to encourage facile ‘deprotection’.7 This strategy proved
successful and N–N bond cleavage of lactams B with
R¼dimethylamino or R¼benzoylamino, was smoothly
achieved with Raney-Ni† in ethanol/water at 100–1108C.7,8
(Pyrrolidin-2-ones g-lactams) are a class of heterocyclic
compounds frequently found in molecules, of natural or
anthropic origin, endowed with interesting biological
properties.1 Owing to their great value in medicinal
chemistry, the synthesis of these substances have received
considerable attention by researchers, an interest that still
continues to bloom.2
While the parent amides A are easily formed by acylation of
N-allyl hydrazines C, the preparation of C is not a routine
operation owing to the lack of suitable synthetic procedures.
The commonly used methods of allylation of hydrazines D,
as described by Konig9 and Tiecco,10 (Scheme 2) are
tedious and somewhat inefficient, affording often frus-
tratingly low yields. Another major drawback of this
approach rests in the limited number of allylating reagents,
which restricts the number of accessible hydrazines. To
widen our research on the deprotection of N-amino-
pyrrolidin-2-ones, we have investigated a more versatile
Among the many approaches developed for their prepa-
ration, the halogen atom transfer radical cyclization of
N-allyl a-perchloroamides A (HATRC), promoted e.g. by
the redox couple Cuþ/Cu2þ, stands out for versatility,
efficiency and convenience (Scheme 1).3 To be effective, the
transformation of dichloroamide A into the g-lactam B
requires a ‘cyclization adjuvant’, typically a benzyl group
(R¼Bzl), bound to the amide nitrogen atom.4 Several
bioactive pyrrolidin-2-ones, however, are devoid of any
substituent at the N-1 position5 and, unfortunately, N-benzyl
groups can be difficult to remove from amides.6 To
overcome this problem, we recently pioneered cyclization
Scheme 1.
Scheme 2.
Keywords: reduction; hydrazones; hydrazines; boron and compounds.
*
†
Corresponding author. Tel.: þ39-59-2055043; fax: þ39-59-373543;
The dimethylamino protection can be also cleaved by magnesium
monoperoxy phtalate.27
e-mail: ghelfi.franco@unimo.it
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00914-6

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M. E. Casarini et al. / Tetrahedron 58 (2002) 7925–7932
Scheme 3.
Table 1. Reduction of cinnamaldehyde acetylhydrazone 1
Entry Reductant t (h) T (8C) Conversion (%)a
most convenient approach in terms of safety and
practicality.
Products
1a (%)a 1c (%)a
Amino-borane complexes have attracted the interest of
many synthetic organic chemists. Their stability, tolerance
to acids, solubility in many solvents and reducing power
have resulted in numerous laboratory and industrial
applications.37–39 One of the most valuable and promising
being the reduction of the CvN double bond to form
C–N.37,40–42 A large variety of amines have been used to
prepare amino-boranes and a number of these reagents are
now commercially available. PB is, however, somewhat
expensive and, moreover, commercial solutions contain an
excess of pyridine which reduces the appeal of the reagent.
Two particularly more attractive substitutes are the
dimethylamine–borane complex (DMAB) and the triethyl-
amine–borane complex (TEAB). These solid complexes are
economical, safe, soluble in both protic and aprotic solvents
and hence suitable for large-scale preparations.
1b
2b
3b
4c
5c
PB
0.2
0.2
0.2
20
0
0
0
0
60
100
100
86
0
83
93
54
–
15
3
6
DMAB
TMAB
NaBH4
NaBH4
–
20
0
–
–
Substrate (1 mmol); THF (2.5 ml) and MeOH (2.5 ml).
a
GC values.
Borane–amine complex (1.6 mmol), HClMeOH 3.6N (5 ml).
NaBH4 (1.6 mmol).
b
c
and easier route to N-allylhydrazines of type C. This work
has shown that C can be efficiently prepared by
1,2-reduction of a,b-unsaturated hydrazones E using
dimethylamine–borane under acid conditions (Scheme 2).
As discussed below, the procedure is both simple and
efficient and also works satisfactorily in large-scale
preparations.
To evaluate the effectiveness of DMAB, TEAB and the
standard hydride donor NaBH4, versus PB, we initially
chose cinnamaldehyde acetylhydrazone 1 as a reference
substrate (Scheme 3). The reducing agents were tested
under the optimum conditions reported by Kikugawa for the
reduction of tosylhydrazones with PB and alcoholic HCl.36
2. Results and discussion
The starting a,b-unsaturated hydrazones, which are
commonly used as building blocks for the assembly of
pyrazoles,11 – 13 are widespread and easily prepared.
Recently, these compounds have also been profitably
employed as heterodienic components in Diels–Alder
cycloadditions.14–17 The synthetic value of enhydrazones
stimulated the development of many procedures for their
preparation.18–23 Among these, certainly the most direct
route involves the hydrazono-de-oxo-bisubstitution reaction
which occurs between hydrazine derivatives and conjugated
carbonyl compounds.12,24–26 The Michael-type addition, a
side reaction which afflicts the condensation reaction
between amines and enketones,28,29 is not such a prevalent
side-reaction with hydrazines and so several conjugated
hydrazones of this type can be prepared.30–32
The use of DMAB showed the most promise, delivering the
1,2-reduction product 1a (Scheme 3, Table 1) with the
highest yield and the best selectivity. The side-product 1c,
which resulted from conjugate attack, was only formed in
3% yield.43 Interestingly, NaBH4 did not react with 1,
even under forcing conditions (Table 1, entries 4 and 5).
This may be explained by the fact that hydrazones, among
the CvN-containing functional groups, exhibit the highest
electron density on the iminic carbon44 and should,
therefore, be less prone to attack by hydride donors. Indeed
N,N-dialkylhydrazones have been exploited as nucleophilic
reagents.45 In contrast, reduction using amino-borane
complexes work well although this requires the presence
of a strong acid. Under these conditions, the CvN double
bond is protonated, which enhances the susceptibility
towards attack by nucleophiles.40,46
Whilst the deoxygenation of unsaturated carbonyl com-
pounds through reduction of the intermediate tosylhydra-
zones has been thoroughly investigated,33,34 the conversion
of enhydrazones into the respective allyl hydrazines has, to
our knowledge, never been comprehensively investigated.
As far we are aware, this transformation has only surfaced
According to the role played by Hþ, two mechanisms can be
proposed for the reduction of imines with amino-boranes in
acidic media.47 In one case (Scheme 4, path i) protonation
could promote the release of borane from DMAB, which
could lead to coordination of BH3 with the imine nitrogen.
Intramolecular hydride transfer would complete the reac-
tion. Alternatively, the Schiff base could be protonated,
in rare examples using LiAlH4,35 DuPhos-Rh/H2 or
24
pyridine–borane/Hþ (PB)36 as reducing agents. The
procedure using PB/Hþ, which avoids the use of a
dangerous gas and anhydrous solvents, is certainly the

M. E. Casarini et al. / Tetrahedron 58 (2002) 7925–7932
7927
Scheme 4.
Scheme 5.
making the iminium carbon atom more susceptible to
hydride transfer from DMAB (Scheme 4, path ii). The
second route was the one favoured by Billman and
McDowell in the reduction of imines,47 and the related
reduction of hydrazones could follow the same mechanism.
It must be stressed, however, that borane can reduce
hydrazones in the presence of a proton carrier,48–50 but
considering the different behaviour exhibited by PB, TEAB
and DMAB in the reduction of 1 (Table 1), it is unlikely that
these reagents behave as simple BH3 carriers and so simple
hydride transfer from borane can be well ruled out. A recent
article by Mayr did support path ii reporting that amino-
boranes behave indeed as true hydride donors, with strength
comparable to NaBH3CN, towards positively charged
electrophiles.51
looked for a more effective method for achieving the
requisite acidity and our attention turned to the use of acetic
acid or 37% aqueous HCl. Although DMAB/acetic acid
gave excellent results in the reduction of Schiff bases46
the same combination, in our hands,‡ was disappointing
affording unsatisfactory conversions and yields. Aqueous
hydrochloric acid appeared to be more promising: in fact,
reduction of 1 (1 mmol) with DMAB (1.6 mmol) and 37%
aqueous HCl (2.3 ml) in CH2Cl2 (2 ml) gave the same result
as when using methanolic HCl; both protocols affording 1a
in excellent yield (95%). The procedure, however, turned
out to be unsuitable for reactions on a larger scale. While
1 mmol of 2 (Scheme 5) provided 2a in good yield (72%)
and acceptable selectivity (2a/2c, 4.80:1), the outcome
when using 15 mmol of 2 was definitely worse (2a, 60% and
2a/2c, 2.85:1). The reason for the deterioration is likely to
be due to the presence of two immiscible liquid phases in the
reaction mixture, which prevents homogenisation and this
Unfortunately, reduction with DMAB required the prepa-
ration of titrated solutions of hydrochloric acid in methanol.
The reactions also required high dilution (i.e. 10 ml of
solvent per mmol of substrate) and this made the procedure
unattractive for large-scale preparations. Therefore, we
‡
Using various amounts of acetic acid.

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M. E. Casarini et al. / Tetrahedron 58 (2002) 7925–7932
Table 2. Reduction of a,b-unsaturated hydrazones by DMAB/PTS
often suffered from some competitive conjugate reduction
(type c products), the regiochemical outcome of which
being governed, as expected for Michael-type acceptors,52
by steric and/or electronic factors. For example, as the size
of the g substituents(s) (R or R2) increased (Scheme 5, Table
2) so more attack at the imine carbon atom resulted to the
point that with 3-methyl-crotonaldehyde N-benzoyl hydra-
zone (5), the 1,2-addition product became exclusive (Table
2, entries 3–5).
Entry Hydarazone DMAB t
(mmol) (h)
Conversion
(%)a
aþc
a/cc
(%)b
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9
1.6
1.6
1.6
1.6
1.6
1.6
2
2
2
1.6
1.6
1.6
1.6
0.5
0.5
1
0.7
0.7
0.7
0.75
0.7
1
3
3
3
3
100
100
100
100
100
100
96
100
75
80
97
96
97(89)d 5.93(5.85)d
1
95
93
98
92
90
85
70
55
77
61
10.88
5.20
1
1
1
0
On the other hand, bulky substituents linked to the imine
a-carbon atom diverted the attack towards the conjugated
g-position. This was indeed the case with hydrazone 8, and
even with 9, where substitution at the g-position could not
prevent conjugate addition by DMAB (Table 2, entries 8
and 9). However, when a phenyl group was introduced at the
g-position, 1,2-reduction practically became the sole
reaction with unsaturated hydrazones prepared from either
ketones (Table 2, entries 6 and 7) or aldehydes (Table 2,
entry 1). This may be explained by the conjugation between
the aromatic ring and the 1-azadienic system, which is
expected to increase the activation energy for the unwanted
CvC reduction.
9
10e
11e,f 10
12e,f 11
13e,f 12
0.43
12.75
8.63
1
10
93
100
66(70)g 8.43(7.75)g
Substrate (1 mmol); PTS (6 mmol); CH2Cl2 (3.5 ml) and MeOH (0.5 ml).
a
GC values.
Determined on isolated material.
b
c
d
e
1
Ratios calculated by H NMR spectroscopy.
The results in parentheses are obtained when using 15 mmol of 2.
Reaction performed under argon, and products isolated after
trichloroacetylation.
Diethyl ether (4 ml) and anhydrous PTS were used.
The results in parentheses are obtained when using 25 mmol of 12.
f
g
Since it was reported that the nature of the amino groups
linked to the imine nitrogen could affect the regioselectivity
of the nucleophilic addition to 1-azadienic arrangements,53
we also studied the reduction of the unsaturated dimethyl-
hydrazones 10–12 (Scheme 5) with DMAB/PTS. Unfortu-
nately, attempted reduction of each of these substrates was
unsuccessful and only unreacted starting material was
isolated in each case. The failure, originally thought to be
due to no reaction, was actually due to the astonishing
propensity of N0,N0-dimethyl-allylhydrazines 10a, 11a and
12a (Scheme 5) to be reoxidised by air; a shortcoming that
even precluded their isolation from the reaction mixture.
Reduction was thus performed under argon and the crude
products were immediately N-acylated under an inert
atmosphere.
may be particularly acute when using large volumes of
solvents.
In an attempt to develop a practical method suitable for
multigram preparations, we thought that p-toluenesulfonic
acid (PTS) could be an expedient proton donor to couple
with DMAB. This strong organic acid is solid, cheap and
soluble in many solvents. The commercial PTS, however, is
supplied in the monohydrated form, and its complete
solubilization in the reaction mixture required dilution of
the reaction solvent (CH2Cl2) with a small amount of
methanol (CH2Cl2/CH3OH, 7:1).
A number of reactions were tried using this solvent system
to investigate the reduction of 2 using DMAB/PTS. The best
selectivity for 2a over 2c (5.93:1) and the highest yields of
the allyl hydrazine 2a (83%) were obtained, under
satisfactory dilution conditions (i.e. 4 ml of solvent per
mmol of substrate) when using 6 equiv. of PTS and
1.6 equiv. of amino-borane (Table 2, entry 2). We were
also pleased to observe that the use of DMAB/PTS was
equally effective on large-scale runs (e.g. 2a, 76% and 2a/
2c, 5.85:1; Table 2, entry 2).
Using this new protocol (Table 2, entry 10), the conversions,
albeit high, were only partial. Moreover, in the presence of
hydrated PTS, the dimethylhydrazones proved to be
susceptible to hydrolysis and significant amounts (8–13%)
of allyl esters were formed which hindered product
isolation. To overcome these drawbacks, we resorted to
using anhydrous p-toluenesulfonic acid.
With satisfaction we noted that DMAB/anhydrous PTS in
diethyl ether worked well, minimizing the side reactions and
affording the acylated allyl hydrazines 10a, 11a and 12a in
good yields (Table 2, entries 11–13). The regioselectivities
were similar to those observed for the corresponding
conjugated acylhydrazones (Table 2, entries 2, 3 and 13).
Therefore, the electronic effects of the nitrogen substituents
R4 and R5 have little effect on the regioselectivity
presumably because, in all cases, the DMAB reacts with
similar iminium ions.
It is evident from the stoichiometry of the reaction that
DMAB provides only one equivalent of hydride for the
reduction and that an excess of the reducing agent was
required to compensate for its decomposition because of the
strong acidity of reaction medium. Efforts to activate the
DMAB under neutral conditions through Pd/C, according to
Couturier’s method,39 were attempted but unfortunately
failed since the saturated hydrazone was the main product
observed in all the attempted trials (i.e. this resulted in 3,4-
rather than 1,2-reduction).
Finally, for the unequivocal characterization of the side
products 2–4c, 10c and 12c, formed by over-reduction of
the parent a,b-unsaturated hydrazones, we investigated
their preparation by reaction of hydrazones 2b-4b, 10b and
The scope and generality of the 1,2-reduction (type a
products) of various unsaturated acylhydrazones using
DMAB/PTS was then examined (Table 2). The reaction

M. E. Casarini et al. / Tetrahedron 58 (2002) 7925–7932
7929
Table 3. Reduction of hydrazones b by DMAB/PTS
azeotropic distillation of a solution of monohydrated
p-toluenesulfonic acid in toluene with a Dean–Stark
apparatus.55
Entry Hydrazone DMAB (mmol) t (h) Conversion (%)a c (%)b
1
2
3
2b
3b
4b
10b
12b
1.6
1.6
1.6
1.6
1.6
0.7
0.7
0.7
1
100
100
100
100
100
86
91
95
85
83
4.1.1. Preparation of cinnamaldehyde acetylhydrazone
(1). In a single-necked round-bottom flask (100 ml)
acetohydrazide (3.70 g, 50 mmol) and cinnamaldehyde
(6.61 g, 50 mmol) were successively added to CH2Cl2
(80 ml). The stirred solution, after 1 h at room temperature,
was cooled to precipitate the cinnamaldehyde acetylhydra-
zone. The crude product was filtered off and purified by
recrystallization from CH2Cl2. White solid, mp 164–1658C.
1H NMR (CDCl3): d 2.35 (s, 3H), 6.86–6.95 (m, 2H), 7.10–
7.74 (m, 6H). IR (KBr) 1673 (CvO) cm21. MS (EI, m/z):
188 (15, Mþ), 145 (63), 129 (100), 115 (22), 43 (26). Anal.
calcd for C11H12N2O: C, 70.19; H, 6.43; N, 14.88. Found: C,
70.1; H, 6.5; N, 14.7. The hexanal N-acetyl hydrazone (2b),
hexanal N-benzoyl hydrazone (3b) and butanal N-benzoyl
hydrazone (4b) were secured following the same procedure.
4c,d,e
5c,d,e
1
Substrate (1 mmol); PTS (6 mmol); CH2Cl2 (3.5 ml) and MeOH (0.5 ml).
a
GC values.
Determined on isolated material.
Reaction performed under argon (trichloroacetylated products).
Anhydrous PTS was used.
Using diethyl ether (4 ml) as the solvent.
b
c
d
e
12b with DMAB/PTS.54 As expected, and without any
modification of the reaction protocol, the targeted hydra-
zines c were smoothly obtained (Table 3). The N,N-di-
methyl hydrazines 10c and 12c were more stable to
oxidation (by air) than the corresponding hydrazines 10a
and 12a, although the reduction of 10b and 12b was
performed under an inert atmosphere and the reaction
products were promptly acylated.
4.1.2. Preparation of cinnamaldehyde dimethylhydra-
zone (11). In a single-necked round-bottom flask (100 ml)
N,N-dimethylhydrazine (3.61 g, 60 mmol) and cinnamalde-
hyde (6.61 g, 50 mmol) were successively added, at room
temperature, to a suspension of MgSO4 (5 g) in CH2Cl2
(80 ml). After stirring overnight, the mixture was filtered.
The crude product, obtained after evaporation of solvent and
unreacted hydrazine did not require any further purification.
Liquid, bp 143–1458C/7 mm Hg. 1H NMR (CDCl3): d 2.97
(s, 6H), 6.64 (d, J¼15.7 Hz, 1H), 6.98 (dd, J¼8.8, 15.7 Hz,
1H), 7.18 (d, J¼8.8 Hz, 1H), 7.21–7.49 (m, 5H). IR (film)
1553 (CvN) cm21. MS (EI, m/z): 174 (100, Mþ), 159 (9),
130 (35), 115 (23), 104 (17). Anal. calcd for C11H14N2: C,
75.82; H, 8.10; N, 16.08. Found: C, 75.9; H, 7.9; N, 16.2.
The dimethylhydrazones of 1-cyclohexen-1-carboxalde-
hyde (10), trans-2-hexenal (12), 1-cyclohexanecarboxalde-
hyde (10b) and hexanal (12b), were prepared following the
same procedure.
3. Conclusion
In connection with our studies aimed at developing easy
removable cyclization auxiliaries for preparation of unpro-
tected pyrrolidin-2-ones through the rearrangement of
N-allyl a-perchloroamides, we required a versatile, efficient
and practical route to N-allylhydrazines. This work has
demonstrated a proficient approach to these compounds by
1,2-reduction of enhydrazones using DMAB/PTS. In some
cases, competitive conjugate reduction was observed. The
regioselectivity of the attack rests on the substitution pattern
of the a-(C-2) and g-(C-4) carbon atoms, but is unaffected
by the nature of the amino group bound to the imine
nitrogen. This versatile process, using readily available
starting materials, offers an effective route to substituted
hydrazines on both at small and large scale. The procedure
is also effective for the reduction of unconjugated
hydrazones.
4.2. General procedure for the 1,2-reduction of
a,b-unsaturated acylhydrazones with DMAB/PTS
In a double-necked round-bottom flask (25 ml), fitted with a
reflux condenser were added DMAB (0.094 g, 1.6 mmol)
and cinnamaldehyde acetohydrazone 1 (0.188 g, 1 mmol)
and the apparatus was thermostatted at 08C. Then, CH2Cl2
(2 ml) and a solution of PTS monohydrate (1.141 g,
6 mmol) in CH2Cl2/CH3OH, 3:1 (2 ml), previously cooled
to 08C, were introduced (gas evolves) while stirring. After
0.5 h, Na2CO3 (10% w/v, 6 ml) and CH3OH (2 ml) were
added and the mixture refluxed for a further 0.5 h to cleave
any residual boron–nitrogen bond. The organic phase was
then separated and the aqueous phase extracted with
CH2Cl2. The combined organic layers were dried over
MgSO4 and concentrated. Column chromatography of the
crude product on silica gel, using a petroleum ether (bp
40–608C)/diethyl ether gradient, gave 0.183 g of 1a (96%).
4. Experimental
4.1. General
1H NMR, IR and MS spectra were recorded respectively on
Bruker DPX200, Philips PU 9716 and HP 5890 GC–HP
5989A MS Engine. HRMS for compounds 2a, 3a, 4a and
12a were recorded on a Fisons Instruments VG Analytical
Autospec Spectrometer. Reagents were standard grade
commercial products, purchased from Aldrich or Fluka,
and used without further purification. N-Benzoyl hydra-
zones of chalcone (7), 3-methylcyclohexenone (9) and
N-acetyl hydrazones of trans-2-hexenal (2), benzylidenace-
tone (6) and 2-cyclohexenone (8) were prepared according
to the procedure reported by Feid-Allah,12 whereas
N-benzoyl hydrazones of crotonaldehyde (4) and
3-methyl-crotonaldehyde (5) were obtained following the
protocol described by Burk.24 Dried PTS was obtained by
4.2.1. N0-Cinnamyl-acetohydrazide (1a). Solid, mp 90–
918C. 1H NMR (CDCl3): d 1.90 (s, 3H), 3.57 (d, J¼6.5 Hz,
2H), 4.70 (s, 1H), 6.20 (dt, J¼6.5, 15.9 Hz, 1H), 6.52 (d,
J¼15.9 Hz, 1H), 7.12–7.38 (m, 5H), 8.1 (s, 1H). IR (KBr)
1641 (CvO) cm21. MS (EI, m/z): 190 (1, Mþ), 132 (24),

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M. E. Casarini et al. / Tetrahedron 58 (2002) 7925–7932
130 (55), 117 (100), 115 (50), 91 (17), 43 (10). Anal. calcd
for C11H14N2O: C, 69.45; H, 7.42; N, 14.72. Found: C, 69.5;
H, 7.3; N, 14.7.
2 mmol of DMAB, the chalcone benzoylhydrazone 7
(0.326 g, 1 mmol) was converted to 7a (0.295 g, 90%).
1
Solid, mp 109–1118C. H NMR (CDCl3): d 4.90 (d, J¼
7.9 Hz, 1H), 6.42 (dd, J¼7.9, 15.8 Hz, 1H), 6.74 (d, J¼
15.8 Hz, 1H), 7.13–7.71 (m, 15H). IR (KBr) 1642 (CvO)
cm21. MS (EI, m/z): 328 (1, Mþ), 194 (14), 193 (100), 178
(9), 115 (44), 105 (12), 91 (11), 77 (13). Anal. calcd for
C22H20N2O: C, 80.46; H, 6.14; N, 8.53. Found: C, 80.7; H,
6.0; N, 8.3.
4.2.2. N0-(trans-2-Hexenyl)-acetohydrazide (2a). Accord-
ing to the general procedure the trans-2-hexenal aceto-
hydrazone 2 (0.154 g, 1 mmol) was converted to an
inseparable mixture of 2a (0.130 g, 83%) and 2c (0.022 g,
14%). When this reaction was scaled up and carried out
using 2.31 g of 2 (15 mmol), 2.087 g of a 85/15 mixture of
2a (76%) and 2c (13%) were secured. Solid. 1H NMR
(CDCl3): d 0.80 (t, J¼7.3 Hz, 3H), 1.28 (m, 2H), 1.72–2.08
(m, 2H), 1.85 (s, 3H), 3.28 (d, J¼6.2 Hz, 2H), 4.36 (bs, 1H),
5.22–5.68 (m, 2H), 8.72 (bs, 1H). IR (KBr) 1649 (CvO)
cm21. MS (EI, m/z): 156 (4, Mþ), 113 (11), 98 (100), 83
(21), 60 (39), 55 (74), 43 (38). HRMS. Calcd for C8H17N2O
(MþHþ): 157.1341. Found: 157.1342.
4.2.8. N0-Cyclohexyl-acetohydrazide (8c). According to
the general procedure, the 2-cyclohexenone acetohydrazone
8 (0.152 g, 1 mmol) was converted to 8c (0.132 g, 85%).
1
Solid, mp 62–648C. H NMR (CDCl3): d 0.90–1.90 (m,
10H), 1.94 (s, 3H), 2.77 (m, 1H). IR (KBr) 1641 (CvO)
cm21. MS (EI, m/z): 156 (8, Mþ), 113 (60), 98 (75), 83 (34),
71 (49), 60 (100), 55 (67), 43 (38). Anal. calcd for
C8H16N2O: C, 61.51; H, 10.32; N, 17.93. Found: C, 61.4; H,
10.5; N, 17.7.
4.2.3.
N0-(trans-2-Hexenyl)-benzoylhydrazide
(3a).
According to the general procedure the trans-2-hexenal
benzoylhydrazone 3 (0.216 g, 1 mmol) was converted to an
inseparable mixture of 3a (0.189 g, 87%) and 3c (0.018 g,
4.2.9. N0-(3-Methyl-2-cyclohexenyl)-benzoylhydrazide
(9a). According to the general procedure, the 3-methyl-2-
cyclohexenone benzoylhydrazone 9 (0.228 g, 1 mmol) was
converted to 9a (0.049 g, 21%). Solid, mp 127–1298C.
1H NMR (CDCl3): d 1.30–2.10 (m, 6H), 1.71 (s, 3H),
3.57 (m, 1H), 5.47 (m, 1H), 7.36–7.85 (m, 5H). IR (KBr)
1638 (CvO) cm21. MS (EI, m/z): 230 (2, Mþ), 137 (16),
122 (14), 110 (16), 105 (30), 95 (100), 77 (18). Anal. calcd
for C14H18N2O: C, 73.01; H, 7.88; N, 12.16. Found: C,
73.2; H, 8.0; N, 12.1. From the crude product, 0.114 g of
N0-(3-methyl-cyclohexyl)-benzoylhydrazide 9c (49%)
was also recovered. Solid, mp 133–1358C. 1H NMR
(CDCl3): d 0.94 (d, J¼6.5 Hz, 3H), 1.00–2.02 (m,
8H), 2.92 (m, 1H), 7.39–7.81 (m, 5H). IR (KBr) 1641
(CvO) cm21. MS (EI, m/z): 232 (5, Mþ), 189 (11), 122
(100), 112 (63), 105 (94), 77 (27). Anal. calcd for
C14H20N2O: C, 72.38; H, 8.68; N, 12.06. Found: C, 73.5;
H, 8.8; N, 12.0.
1
8%). Solid. H NMR (CDCl3): d 0.92 (t, J¼7.3 Hz, 3H),
1.36–1.55 (m, 2H), 2.05 (q, J¼6.9 Hz, 2H), 3.53 (d, J¼
6.2 Hz, 2H), 5.47–5.85 (m, 2H), 7.39–7.85 (5H, m). IR
(KBr) 1627 (CvO) cm21. MS (EI, m/z): 218 (2, Mþ), 175
(2), 122 (21), 105 (100), 98 (40), 77 (52). HRMS. Calcd for
C13H19N2O (MþHþ): 219.1497. Found: 219.1497.
4.2.4. N0-(2-Butenyl)-benzoylhydrazide (4a). According
to the general procedure, the crotonaldehyde benzoyl-
hydrazone 4 (0.188 g, 1 mmol) was converted to an
inseparable mixture of 4a (0.148 g, 78%) and 4c (0.029 g,
15%). Solid. 1H NMR (CDCl3): d 1.69 (dd, J¼1.1, 6.0 Hz,
3H), 3.49 (d, J¼6.4 Hz, 2H), 5.41–5.84 (m, 2H), 7.38–7.82
(m, 5H). IR (KBr) 1633 (CvO) cm21. MS (EI, m/z): 190 (2,
Mþ), 149 (4), 122 (27), 105 (100), 77 (37), 70 (41). HRMS.
Calcd for C11H15N2O (MþHþ): 191.1184. Found: 191.1186.
4.2.5. N0-(3-Methyl-2-butenyl)-benzoylhydrazide (5a).
According to the general procedure, the 3-methyl-2-butenal
benzoylhydrazone 5 (0.202 g, 1 mmol) was converted to 5a
4.3. General procedure for the 1,2-reduction of
a,b-unsaturated N,N-dimethylhydrazones with
DMAB/PTS
1
(0.200 g, 98%). Solid, mp 47–488C. H NMR (CDCl3): d
1.67 (s, 3H), 1.73 (s, 3H), 3.55 (d, J¼7.2 Hz, 2H), 5.30 (t,
J¼7.2 Hz, 1H), 7.41–7.83 (m, 5H). IR (KBr) 1628 (CvO)
cm21. MS (EI, m/z): 204 (2, Mþ), 189 (2), 136 (14), 122
(27), 105 (100), 84 (49), 77 (33), 69 (30). Anal. calcd for
C12H16N2O: C, 70.56; H, 7.89; N, 13.71. Found: C, 70.8; H,
7.7; N, 13.5.
DMAB (0.094 g, 1.6 mmol) and 1-cyclohexen-1-carbox-
aldehyde N,N-dimethylhydrazone 10 (0.152 g, 1 mmol)
were weighed in a screw capped Schlenk tube equipped
with a perforable septum; then, under argon and at 08C,
diethyl ether (2 ml) and a solution of PTS anhydrous
(1.033 g, 6 mmol) in diethyl ether (2 ml), both cooled to
08C, were added. After 3 h, the reaction mixture was
quenched with Na2CO3 (10% w/v, 6 ml), always keeping
the inert atmosphere. The organic phase (ether) was
cannulated into another Schlenk tube, evaporated and
restored as CH2Cl2 (2 ml). After cooling at 08C, triethyl-
amine (1.2 mmol) and trichloroacetyl chloride (1.1 mmol)
were introduced. The mixture, after overnight stirring, was
diluted with NaOH (5% w/v, 6 ml), and extracted with
CH2Cl2. The combined organic layers were dried over
MgSO4 and concentrated. Column chromatography of
the crude product on silica gel, using a petroleum ether
(bp 40–608C)/diethyl ether gradient, gave 0.230 g of a
89/11 mixture of trichloroacetylated 10a (69%) and 10c
(8%).
4.2.6. N0-(3-Phenyl-1-methyl-propenyl)-acetohydrazide
(6a). According to the general procedure the benzyliden-
acetone acetohydrazone 6 (0.202 g, 1 mmol) was converted
to 6a (0.188 g, 92%). Solid, mp 75–768C. 1H NMR
(CDCl3): d 1.28 (d, J¼6.5 Hz, 3H), 1.92 (s, 3H), 3.71 (m,
1H), 6.09 (dd, J¼8.0, 15.9 Hz, 1H), 6.53 (d, J¼15.9 Hz,
1H), 7.18–7.43 (m, 5H). IR (KBr) 1648 (CvO) cm21. MS
(EI, m/z): 204 (1, Mþ), 144 (11), 131 (100), 116 (9), 115 (9),
91 (28). Anal. calcd for C12H16N2O: C, 70.56; H, 7.89; N,
13.71. Found: C, 70.7; H, 8.0; N, 13.9.
4.2.7. N0-(1,3-Diphenyl-propenyl)-benzoylhydrazide
(7a). According to the general procedure, but using

M. E. Casarini et al. / Tetrahedron 58 (2002) 7925–7932
7931
4.3.1. N-[(1-Cyclohexenyl)-methyl]-N0,N0-dimethylhydra-
zine (10a), trichloroacetylated. Oil. H NMR (CDCl3): d
1.50–1.77 (m, 4H), 1.92–2.14 (m, 4H), 2.64 (s, 6H), 4.00
(s, 2H), 5.61 (m, 1H). IR (film) 1687 (CvO) cm21. MS (EI,
m/z): 298 (1, Mþ), 204 (50), 169 (53), 153 (10), 133 (10),
41 (100). HRMS. Calcd for C11H18Cl3N2O (MþHþ):
299.0485. Found: 299.0485.
Solid, mp 57–608C. 1H NMR (CDCl3): d 0.90 (t, J¼6.4 Hz,
3H), 1.16–1.68 (m, 8H), 2.95 (t, J¼7.2 Hz, 2H), 7.38–7.81
(5H, m). IR (KBr) 1627 (CvO) cm21. MS (EI, m/z): 220 (4,
Mþ), 149 (40), 122 (35), 105 (100), 100 (53), 77 (30). Anal.
calcd for C13H20N2O: C, 72.19; H, 7.46; N, 12.95. Found: C,
72.3; H, 7.7; N, 13.1.
1
4.4.3. N0-Butyl-benzoylhydrazide (4c). According to the
general procedure, the butanal benzoylhydrazone 4b
(0.190 g, 1 mmol) was converted to 4c (0.182 g, 95%).
Oil. 1H NMR (CDCl3): d 0.96 (t, J¼6.7 Hz, 3H), 1.30–1.68
(m, 4H), 2.96 (t, J¼7.0 Hz, 2H), 7.34–7.78 (m, 5H). IR
(film) 1627 (CvO) cm21. MS (EI, m/z): 192 (3, Mþ), 149
(22), 122 (27), 105 (100), 77 (35), 72 (32). Anal. calcd for
C11H16N2O: C, 67.31; H, 10.27; N, 14.27. Found: C, 67.1;
H, 10.1; N, 14.1.
4.3.2. N-Cinnamyl-N0,N0-dimethylhydrazine (11a), tri-
chloroacetylated. Following the general procedure, the
cinnamaldehyde dimethylhydrazone (11) (0.174 g, 1 mmol)
was converted to 0.196 g of trichloroacetylated 11a (61%).
Solid, mp 72–748C. 1H NMR (CDCl3): d 2.69 (s, 6H), 4.23
(dd, J¼1.2, 6.4 Hz, 2H), 6.34 (dt, J¼6.4, 15.9 Hz, 1H), 6.67
(dt, J¼1.2, 15.9 Hz, 1H), 7.21–7.47 (m, 5H). IR (KBr) 1682
(CvO) cm21. MS (EI, m/z): 320 (Mþ, 1), 276 (2), 117
(100), 91 (8). Anal. calcd for C13H15Cl3N2O: C, 48.55; H,
4.70; N, 8.71. Found: C, 48.7; H, 4.8; N, 8.5.
4.5. General procedure for the reduction of
unconjugated N,N-dimethylhydrazones with
DMAB/PTS
4.3.3. N-(trans-2-Hexenyl)-N0,N0-dimethylhydrazine
(12a), trichloroacetylated. Following the general pro-
cedure, the trans-2-hexenal dimethylhydrazone (12)
(0.140 g, 1 mmol) was converted to 0.191 g of a 89/11
mixture of trichloroacetylated 12a (59%) and 12c (7%).
When this reaction was scaled-up and carried out using
3.50 g of 12 (25 mmol), 5.035 g of a 88/12 mixture of 12a
(62%) and 12c (8%) were secured. Oil. 1H NMR (CDCl3): d
0.92 (t, J¼7.5 Hz, 3H), 1.26–1.54 (m, 2H), 2.05 (q, J¼
7.1 Hz, 2H), 2.64 (s, 6H), 4.01 (d, J¼5.9 Hz, 2H), 5.59–
5.85 (m, 2H). IR (film) 1688 (CvO) cm21. MS (EI, m/z):
286 (Mþ, 2), 204 (100), 96 (100), 141 (35), 86 (30), 55 (77).
HRMS. Calcd for C10H18Cl3N2O (MþHþ): 287.0485.
Found: 287.0480.
DMAB (0.094 g, 1.6 mmol) and cyclohexanecarboxalde-
hyde N,N-dimethylhydrazone 10b (0.154 g, 1 mmol) were
weighed in a screw capped Schlenk tube equipped with a
perforable septum; then, under argon and at 08C, diethyl
ether (2 ml) and a solution of PTS anhydrous (1.033,
6 mmol) in diethyl ether (2 ml), both cooled to 08C, were
added. After 3 h, the reaction mixture was quenched with
Na2CO3 (10% w/v, 6 ml), always keeping the inert
atmosphere. The organic phase (ether) was cannulated
into another Schlenk tube, evaporated and restored as
CH2Cl2 (2 ml). After cooling at 08C, triethylamine
(1.2 mmol) and trichloroacetyl chloride (1.1 mmol) were
introduced. The mixture, after overnight stirring, was
diluted with NaOH (5% w/v, 6 ml), and extracted with
CH2Cl2. The combined organic layers were dried over
MgSO4 and concentrated. Column chromatography of
the crude product on silica gel, using a petroleum ether
(bp 40–608C)/diethyl ether gradient, gave 0.255 g of
trichloroacetylated 10c (85%).
4.4. General procedure for the reduction of
unconjugated acylhydrazones with DMAB/PTS
In a double-necked round-bottom flask (25 ml), fitted with a
reflux condenser were added DMAB (0.094 g, 1.6 mmol)
and hexanal acetohydrazone 2b (0.156 g, 1 mmol) and the
apparatus was thermostatted at 08C. Then CH2Cl2 (2 ml)
and a solution of PTS monohydrate (1.141, 6 mmol) in
CH2Cl2/CH3OH, 3:1 (2 ml), previously cooled to 08C, were
introduced (gas evolves) while stirring. After 0.5 h, Na2CO3
(10% w/v, 6 ml) and CH3OH (2 ml) were added and the
mixture refluxed for a further 0.5 h to cleave any residual
boron–nitrogen bond. The organic phase was then separated
and the aqueous phase extracted with CH2Cl2. The com-
bined organic layers were dried over MgSO4 and concen-
trated. Column chromatography of the crude product on
silica gel, using a petroleum ether (bp 40–608C)/diethyl
ether gradient, gave 0.136 g of 2c (86%).
4.5.1. N-[(Cyclohexyl)-methyl]-N0,N0-dimethylhydrazine
(10c), trichloroacetylated. Oil. 1H NMR (CDCl3): d 0.80–
1.98 (m, 11H), 2.55 (s, 6H), 3.57 (d, J¼7.4 Hz, 2H). IR
(film) 1687 (CvO) cm21. MS (EI, m/z): 300 (3, Mþ), 265
(1), 169 (3), 155 (100), 83 (6), 73 (39), 55 (13). Anal. calcd
for C11H19Cl3N2O: C, 43.80; H, 6.35; N, 9.29. Found: C,
43.9; H, 6.5; N, 9.1.
4.5.2. N-Hexyl-N0,N0-dimethylhydrazine (12c), trichloro-
acetylated. According to the previous procedure, hexanal
N,N-dimethylhydrazone 12b (0.142 g, 1 mmol) was con-
verted to 12c (0.240 g, 83%). Oil. 1H NMR (CDCl3): d 0.88
(t, J¼7.3 Hz, 3H), 1.18–1.40 (m, 6H), 1.66 (m, 2H), 2.58 (s,
6H), 3.31 (m, 2H). IR (film) 1686 (CvO) cm21. MS (EI,
m/z): 288 (Mþ, 7), 253 (4), 144 (27), 143 (100), 98 (37).
Anal. calcd for C10H19Cl3N2O: C, 41.47; H, 6.61; N, 9.67.
Found: C, 41.4; H, 6.5; N, 9.5.
4.4.1. N0-Hexyl-acetohydrazide (2c). Oil. 1H NMR
(CDCl3): d 0.82 (t, J¼7.3 Hz, 3H), 1.02–1.64 (m, 8H),
1.88 (s, 3H), 2.75 (t, J¼6.2 Hz, 2H). IR (film) 1648 (CvO)
cm21. MS (EI, m/z): 158 (4, Mþ), 116 (18), 100 (55), 87
(71), 60 (33), 45 (100). Anal. calcd for C8H18N2O: C, 59.96;
H, 12.58; N, 17.48. Found: C, 59.9; H, 12.6; N, 17.6.
4.4.2. N0-Hexyl-benzoylhydrazide (3c). According to the
general procedure, the hexanal benzoylhydrazone 3b
(0.218 g, 1 mmol) was converted to 3c (0.200 g, 91%).
Acknowledgements
`
We thank the Ministero della Universita e della

7932
M. E. Casarini et al. / Tetrahedron 58 (2002) 7925–7932
´
27. Lassaletta, J. M. Private communication. See also: Fernandez,
R.; Ferrete, A.; Lassaletta, J. M.; Llera, J. M.; Martin-Zamora,
E. Angew. Chem. Int. Ed. 2002, 41, 831–833.
Ricerca Scientifica e Tecnologica (MURST) for financial
assistance.
28. Eisch, J. J.; Sanchez, R. J. Org. Chem. 1986, 51, 1848–1852.
¨
29. Moller, F. Houben-Weil; Georg Thieme: Stuttgart, 1957; Vol.
References
11/1. pp 285–289.
30. Tamura, Y.; Tsugoshi, T.; Nakajima, Y.; Kita, Y. Synthesis
1984, 930–933.
1. Giambastiani, G.; Pacini, B.; Porcelloni, M.; Poli, G. J. Org.
Chem. 1998, 63, 804–807.
31. Hudrlik, P. F.; Hudrlik, A. M.; Yimenu, T.; Waugh, M. A.;
Nagendrappa, G. Tetrahedron 1988, 44, 4399–4428.
2. Galeazzi, R.; Mobbili, G.; Orena, M. Targets in Heterocycles
Systems, Chemistry and Properties; Attanasi, O., Spinelli, D.,
Eds.;, 1997; Vol. 1, pp 355–400 SCI.
´
ˇ
ˇ
´
32. Dumic, M.; Koruncev, D.; Kovacevic, K.; Polak, L.; Kolbah,
D. Houben-Weil; George Thieme: Stuttgart, 1990; Vol. E14b.
pp 487–506.
3. Ghelfi, F.; Bellesia, F.; Forti, L.; Ghirardini, G.; Grandi, R.;
Libertini, E.; Montemaggi, M. C.; Pagnoni, U. M.; Pinetti, A.;
De Buyck, L.; Parsons, A. F. Tetrahedron 1999, 55,
5839–5852.
33. Hutchings, R. O.; Natale, N. R. J. Org. Chem. 1978, 43,
2299–2301.
4. Curran, D. P.; Tamine, J. J. Org. Chem. 1991, 56, 2746–2750.
5. Naito, T.; Honda, Y.; Bhavakul, V.; Yamaguchi, S.; Fujiwara,
A.; Miyata, O.; Ninomiya, I. Chem. Pharm. Bull. 1997, 45,
1932–1939.
34. Hutchings, R. O.; Milewski, C. A.; Maryanoff, B. E. J. Am.
Chem. Soc. 1972, 95, 3662–3668.
35. Smith, R. F.; Blondell, R. D.; Abgott, R. A.; Lipkowitz, K. B.;
Richmond, J. A.; Fountain, K. A. J. Org. Chem. 1974, 39,
2036–2040.
6. Webster, F. X.; Millar, J. G.; Silverstein, R. M. Tetrahedron
Lett. 1986, 27, 4941–4944.
36. Kikugawa, Y.; Kawase, M. Synth. Commun. 1979, 49–52.
37. Lane, C. F. Aldrichim. Acta 1973, 6, 51–58.
38. Brown, H. C.; Kanth, J. V. B.; Dalvi, P. V.; Zaidlewicz, M.
J. Org. Chem. 1999, 64, 6263–6274.
7. Ghelfi, F.; Parsons, A. F. J. Org. Chem. 2000, 65, 6249–6253.
8. Gatti, L. N-ammino-2-pirrolidinoni: rottura del legame N–N.
Thesis, University of Modena e Reggio, 2001.
9. Konig, K. H.; Zeeh, B. Chem. Ber. 1970, 103, 2052–2061.
10. Tiecco, M.; Testaferri, L.; Marini, F. Tetrahedron 1996, 52,
11841–11848.
`
39. Couturier, M.; Andresen, B. M.; Tucker, J. L.; Dube, P.;
Brenek, S. J.; Negri, J. T. Tetrahedron Lett. 2001, 42,
2763–2766.
11. Hart, T. W.; Vacher, B. Tetrahedron Lett. 1992, 33,
7215–7218.
40. Pelter, A.; Rosser, R. M.; Mills, S. J. Chem. Soc., Perkin
Trans. 1 1984, 717–720.
12. Feid-Allah, H. M. Pharmazie 1981, 36, 754–756.
13. Barluenga, J.; Tomas, M. Adv. Heterocycl. Chem. 1993, 57,
1–80.
41. Salunkhe, A. M.; Burkhardt, E. R. Tetrahedron Lett. 1997, 38,
1519–1522.
42. Alexandre, F.-R.; Pantaleone, D. P.; Taylor, P. P.;
Fotheringham, I. G.; Ager, D. J.; Turner, N. J. Tetrahedron
Lett. 2002, 43, 707–710.
14. Buonora, P.; Olsen, J.-P.; Oh, T. Tetrahedron 2001, 57,
6099–6138.
15. Behforouz, M.; Ahmadian, M. Tetrahedron 2000, 56,
5259–5288.
43. Schmitt, J.; Panouse, J. J.; Hallot, A.; Pluchet, H.; Comoy, P.;
Cornu, P.-J. Bull. Soc. Chim. Fr. 1963, 816–824.
44. Friestad, G. K. Tetrahedron 2001, 57, 5461–5496.
16. Boger, D. L. In Heterodiene Additions. Comprehensive
Organic Synthesis; Paquette, L. A., Ed.; Pergamon: New
York, 1991; Vol. 5, pp 451–512.
`
45. Fernandez, R.; Lassaletta, J. M. Synlett 2000, 1228–1240.
46. Tennant, G. In Imines, Nitrones, Nitriles and Isocyanides.
Comprehensive Organic Chemistry; Barton, D., Ollis, D.,
Eds.; Pergamon: New York, 1979; Vol. 2, pp 407–418.
47. Billman, J. H.; McDowell, J. W. J. Org. Chem. 1961, 26,
1437–1440.
17. Jayakumar, S.; Ishar, M. P. S.; Mahajan, M. P. Tetrahedron
2002, 58, 379–471.
18. Palacios, F.; Aparicio, D.; de los Santos, J. M. Tetrahedron
1994, 50, 12727–12742.
19. Cristau, H.-J.; Gasc, M.-B. Tetrahedron Lett. 1990, 31,
341–344.
48. Nulu, J.; Nematollahi, J. Tetrahedron Lett. 1969, 10,
1321–1324.
20. Attanasi, O. A.; De Crescentini, L.; Filippone, P.; Gatti, G.;
Mantellini, F.; Santeusanio, S. Tetrahedron 1998, 54,
7581–7594.
49. Blair, J. A.; Gardner, R. J. J. Chem. Soc. (C) 1970,
1714–1717.
50. McMurray, J. E. J. Am. Chem. Soc. 1968, 90, 6821–6825.
51. Funke, M.-A.; Mayr, H. Chem. Eur. J. 1997, 3, 1214–1222.
52. Oare, D. A.; Heathcock, C. H. Top. Stereochem. 1974, 19,
232–236.
21. Tamion, R.; Mineur, C.; Ghosez, L. Tetrahedron Lett. 1995,
36, 8977–8980.
22. Koldobskii, A. B.; Vakhmistrov, V. E.; Kalinin, V. N. Dokl.
Akad. Nauk. 1996, 346, 771–773, Chem. Abstr. 1996, 125,
166916c.
53. Tomioka, K.; Shioya, Y.; Nagaoka, Y.; Yamada, K. J. Org.
Chem. 2001, 66, 7051–7054.
54. For a comprehensive collection of hydrazone CvN reducing
23. Jolivet, S.; Toupet, L.; Texier-Boullet, F.; Hamelin, J.
Tetrahedron 1996, 52, 5819–5832.
´
ˇ
ˇ
´
procedures, see: Dumic, M.; Koruncev, D.; Kovacevic, K.;
Polak, L.; Kolbah, D. Houben-Weil, George Thieme: Stuttgart,
1990; Vol. E14b. pp 544–547.
24. Burk, M. J.; Martinez, J. P.; Feaster, J. E.; Cosford, N.
Tetrahedron 1994, 50, 4399–4428.
´ ´
25. Perez, J. M.; Avendan˜o, C.; Menendez, J. C. Tetrahedron
55. Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell,
A. R. Vogel’s Textbook of Practical Organic Chemistry;
Longman: Harlow, UK, 1989; p 876.
1995, 51, 6573–6586.
26. Beaudegnies, R.; Ghosez, L. Tetrahedron: Asymmetry 1994, 5,
557–560.