Spontaneous dehydrogenation of 2-hydrazinoethyl- and 4-hydrazinobut-2- enylphosphonium salts

Article abstract of DOI:10.1007/s11172-012-0328-7

2-Hydrazinoethyl- and 4-hydrazinobut-2-enylphosphonium salts undergo spontaneous dehydrogenation leading to the corresponding hydrazones or diazenes, depending on the structure of the starting compounds or the reaction conditions. A possible mechanism of the trans-formations is discussed.

Full text of DOI:10.1007/s11172-012-0328-7

Russian Chemical Bulletin, International Edition, Vol. 61, No. 12, pp. 2338—2343, December, 2012
2338
Spontaneous dehydrogenation of 2ꢀhydrazinoethylꢀ
and 4ꢀhydrazinobutꢀ2ꢀenylphosphonium salts
M. Zh. Ovakimyan, G. Ts. Gasparyan, M. L. Movsisyan, and M. R. Grigoryan
Scientific and Technological Center of Organic and Pharmaceutical Chemistry,
National Academy of Sciences of the Republic of Armenia,
26 prosp. Azatutyan, 0014 Yerevan, Republic of Armenia.
Eꢀmail: mickael.movsisyan@gmail.com
2ꢀHydrazinoethylꢀ and 4ꢀhydrazinobutꢀ2ꢀenylphosphonium salts undergo spontaneous deꢀ
hydrogenation leading to the corresponding hydrazones or diazenes, depending on the strucꢀ
ture of the starting compounds or the reaction conditions. A possible mechanism of the transꢀ
formations is discussed.
Key words: hydrazines, phosphonium salts, hydrazones, diazenes, spontaneous dehydroꢀ
genation, dehydrogenation—hydrogenation, hydride ion.
Scheme 1
Ketone and aldehyde hydrazones find wide practical
use.1 They are structural parts of novel azapeptides, antiꢀ
biotics, and many other compounds with valuable properꢀ
ties.2—5 In addition, they are employed as building blocks
in organic synthesis (specifically, as intermediates in the
synthesis of heterocycles,6 chiral amines,7a,b ꢀamino
alcohols,7c ligands for asymmetric homogeneous catalꢀ
ysis,7d and pharmaceuticals of high enantiomeric purity7e).
Carbanions generated by hydrazones can form carꢀ
bon—carbon bonds.8
Later,11,12 it has been found that heating of (2ꢀhydrꢀ
azinoethyl)(triphenyl)(or tributyl)ꢀ and (3ꢀchloroꢀ4ꢀhydrꢀ
azinobutꢀ2ꢀenyl)(triphenyl)(or tributyl)phosphonium salts
in ethanol or DMF in the absence of a base cause these
salts themselves to undergo dehydrogenation leading to
the corresponding hydrazone derivatives. In some cases,
this process occurs even during the roomꢀtemperature synꢀ
thesis of these phosphonium salts (Scheme 2).
Phosphorusꢀcontaining substituents are known9 to regꢀ
ulate essential biological functions. For this reason, hydrꢀ
azones containing such substituents are of interest as useful
substrates for the preparation of biologically active comꢀ
pounds.
In the last few years, we have discovered the tendency
of hydrazinoethylꢀ and hydrazinobutꢀ2ꢀenylphosphonium
salts and structurally related phosphine oxides to undergo
spontaneous dehydrogenation under moderate heating,
giving the corresponding hydrazone derivative or their
prototropic azo isomers.
Scheme 2
Earlier,10 we have found that hydrolysis of (triphenyl)ꢀ
(2ꢀphenylhydrazinoethyl)phosphonium bromide in the
presence of aqueous alkali yields a mixture of the cisꢀ and
transꢀisomers of diphenylphosphorylacetaldehyde phenylꢀ
hydrazones as major products. Since basic hydrolysis of
phosphonium salts usually yields a reduction product of
the more anionꢀsensitive substituent of the quaternary
phosphonium salt and the corresponding tertiary phosꢀ
phine oxide, a possible reaction pathway to the above comꢀ
pounds should involve initial dephenylation of the starting
quaternary phosphonium salt, the formation of 1ꢀ(2ꢀdiꢀ
phenylphosphorylethyl)ꢀ2ꢀphenylhydrazine, and its in situ
dehydrogenation (Scheme 1).
R = Bu, Ph
It has been also found13 that hydrazine derivatives conꢀ
taining no phosphonium or phosphoryl group in the ꢀpoꢀ
sition undergo spontaneous dehydrogenation only at high
temperatures, no matter whether strong oxidants are
used or not.
Recently,14 we have obtained structurally similar hydrꢀ
azones 1 and 2 (except that they contain no Cl atom in the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2316—2321, December, 2012.
1066ꢀ5285/12/6112ꢀ2338 © 2012 Springer Science+Business Media, Inc.

Dehydrogenation of phosphonioalk(en)ylhydrazines Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2339
Scheme 5
unsaturated substituent) by dehydrogenation of (4ꢀhydrꢀ
azinobutꢀ2ꢀenyl)phosphonium intermediates formed by
reactions of 1,4ꢀbis(triphenylphosphonio)butꢀ2ꢀene diꢀ
chloride with phenylhydrazine and N,Nꢀdimethylhydrꢀ
azine (Scheme 3).
Scheme 3
The hydrideꢀmediated mechanism is supported by our
recent data14 obtained in the study of a reaction of 1,4ꢀbisꢀ
(triphenylphosphonio)butaꢀ1,3ꢀdiene dichloride with pheꢀ
nylhydrazine. The reaction gives 2ꢀphenylhydrazonoꢀ1,4ꢀ
bis(triphenylphosphonio)butane dichloride in high yield,
conceivably proceeding through the formation of interꢀ
mediate A followed by its NH—CH dehydrogenation and
C=C hydrogenation (Scheme 6).
Scheme 6
R1 = H, R2 = Ph (1); R1 = R2 = Me (2)
When continuing these investigations, we found that
(triphenyl)[2ꢀ(2ꢀphenylhydrazino)propyl]phosphonium
bromide (3) prepared from (allyl)(triphenyl)phosphonium
bromide and phenylhydrazine also undergoes dehydrogeꢀ
nation in boiling chloroform for 6 h to give (triphenyl)ꢀ
[2ꢀ(phenylhydrazono)propyl]phosphonium bromide (4) in
90% yield (Scheme 4).
The conjecture of a possible hydride shift in phosphoꢀ
nium compounds was first made by McEwen et al.,17 who
demonstrated that phosphobetaine prepared from (ethyl)ꢀ
(methyl)(phenyl)phosphine and ꢀdeuterated styrene
oxide undergoes intramolecular nucleophilic substitution
accompanied by 1,3ꢀhydride shift (Scheme 7).
Scheme 4
Scheme 7
Based on the results obtained, we advanced a hypotheꢀ
sis of the cyclic character of this reaction involving the
shift of the lone electron pair of the N atom toward the
onium P atom and abstraction of the hydride ion from the
adjacent methylene group at the N atom, with allowance
for the tendency of the ꢀH atoms in alkylamines15 and
alkylhydrazines16 to be detached as hydride ions (Scheme 5).
Therefore, the presence of basic reagents that can genꢀ
erate a negative charge on the N atom of the hydrazine

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
Ovakimyan et al.
Scheme 9
group in hydrazineꢀcontaining phosphonium salts could
be expected to facilitate dehydrogenation noticeably.
For instance, we found that moderate heating of
a suspension of salt 3 in benzene in the presence of Et3N
even in 3 h gives dehydrogenation product 4 in a nearly
equal ratio with the starting compound 3 (1H NMR data).
However, further heating upon the addition of more Et3N
does not increase the yield of salt 4; moreover, the fraction
of salt 4 in the reaction mixture drops (1H NMR data). At
the same time, the 31P NMR spectrum exhibits a signal
characteristic of triphenylphosphine oxide and the
1H NMR spectrum shows characteristic signals of triethylꢀ
amine hydrobromide.
By carrying out a special experiment, we ascertained
that Et3N•HBr and Ph3PO are produced by an attack of
triethylamine on the P atom of salt 4 followed by anionꢀ
ization of the azaallyl group, which is consistent with the
literature data18 (see Scheme 4).
Similar results were obtained in a roomꢀtemperature
reaction of salt 3 with a slight excess of dry Na2CO3 in
chloroform (Scheme 8). Salt 3 was halfꢀconverted into
salt 4 in 2 h and this conversion of salt 3 remained the
same upon the 5ꢀh stirring of the reaction mixture, while
phosphonium salt 4 underwent (conceivably baseꢀcataꢀ
lyzed) isomerization into azo compound 5.
nation of salt 3, simultaneously favoring an attack of the
OH– ions on the P atom. The resulting anionization of the
phenyl group leads to tertiary phosphine oxide 6 and its
dehydrogenation product 7.
Moderate heating of (triphenyl)(propꢀ1ꢀenyl)phosꢀ
phonium bromide (prepared by prototropic isomerization
of (allyl)(triphenyl)phosphonium bromide in the presence
of Na2CO3) with ethylhydrazine in acetonitrile exclusiveꢀ
ly afforded azo compound 8 via dehydrogenation of an
ethylhydrazine intermediate (Scheme 10).
Scheme 8
Scheme 10
An attempt to increase the yield of salt 4 by a roomꢀ
temperature reaction of salt 3 with an equimolar amount
of MeONa, a stronger base, in methanol for 2 h resulted
only in a 14% yield of salt 4, the other reaction products
being Ph3PO (65%) and acetone phenylhydrazone (60%)
as a result of basic reduction of salt 4.
It should be noted that we failed to obtain a dehydroꢀ
genation product from [2ꢀ(2ꢀN,Nꢀdimethylhydrazino)ꢀ
propyl](triphenyl)phosphonium bromide13 synthesized
from (allyl)(triphenyl)phosphonium bromide and N,Nꢀdiꢀ
methylhydrazine. A reaction of the dimethylhydrazino
phosphonium salt with Na2CO3 mainly involves 1,2ꢀcleavꢀ
age leading to (triphenyl)(propꢀ1ꢀenyl)phosphonium
bromide (Scheme 11).
When generalizing our experimental data on spontaꢀ
neous dehydrogenation of 2ꢀhydrazinoethylꢀ and 4ꢀhyꢀ
drazinobutꢀ2ꢀenylphosphonium salts, as well as data on
the behavior of salt 3 in basic media, we can conclude that
the abstraction of the NH proton is decisive for the reacꢀ
tion. This provides additional evidence for the reaction
mechanism we have proposed earlier.
As expected, the same reaction at 60 C gave only
basic hydrolysis products.
A roomꢀtemperature reaction of salt 3 with an equimoꢀ
lar amount of 25% aqueous NaOH afforded the same prodꢀ
ucts: salt 4 (15%) and Ph3PO (36%). In the same reaction
involving a double molar amount of NaOH at 68—70 C,
the dehydrogenation of salt 3 was suppressed. As a result,
we obtained (diphenyl)[2ꢀ(2ꢀphenylhydrazino)propyl]ꢀ
phosphine oxide (6) and its dehydrogenation product
(diphenyl)[2ꢀ(2ꢀphenyldiazenyl)propyl]phosphine oxide
(7) (Scheme 9).
Therefore, an increase in both the reaction temperaꢀ
ture and the molar amount of alkali prevents dehydrogeꢀ

Dehydrogenation of phosphonioalk(en)ylhydrazines Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
2341
yield of salt 4 was 0.9 g (92%), yellow crystals, m.p. 217—218 C.
Found (%): C, 66.10; H, 5.54; Br, 16.00; N, 5.82; P, 6.21.
C27H26BrN2P. Calculated (%): C, 66.26; H, 5.32; Br, 16.36;
It should be emphasized that hydrazineꢀcontaining
unsaturated phosphonium salts have been obtained earliꢀ
er19 from (triphenyl)(propargyl)phosphonium bromide and
various hydrazines, including phenylhydrazine. The corꢀ
responding phosphonium salt is thus a prototropic isomer
of salt 4. However, we detected no traces of this isomer
among the reaction products.
1
N, 5.73; P, 6.34. H NMR, : 2.00 (s, 3 H, Me); 5.15 (d, 2 H,
2
P+CH2, JP,H = 13.56 Hz); 6.25 (d, 2 H, H(2)Ph, H(6)Ph
,
,
3JH,H = 11.11 Hz); 6.60 (t, 1 H, H(4)Ph); 6.90 (t, 2 H, H(3)Ph
H(5)Ph); 7.55—8.00 (m, 15 H, P+Ph3); 8.95 (s, 1 H, NHPh).
31P NMR, : 27.3 (s).
Reaction of salt 3 with triethylamine. A. A mixture of salt 3
(1 g, 2 mmol) and triethylamine (0.2 g, 2 mmol) in anhydrous
benzene (15 mL) was heated at 70—75 C for 3 h. The solvent
was removed and the products were extracted with water and
chloroform. The organic extract was dried with MgSO4, filtered,
and concentrated. The residue was washed with anhydrous diꢀ
ethyl ether and dried in vacuo. The yield of a mixture of salts 3
and 4 was 0.9 g (3 : 4 = ~53 : 47, 1H NMR data).
B. A 53 : 47 mixture of salts 3 and 4 (0.9 g, see above) and
triethylamine (0.2 g, 2 mmol) were suspended in anhydrous benꢀ
zene (15 mL). The resulting suspension was heated at 70—75 C
for 9 h. The precipitate that formed was filtered off and the
products were extracted with water and chloroform. Triethylꢀ
amine hydrobromide was isolated from the aqueous extract. Yield
0.07 g, m.p. 246—248 C (decomp.). The organic extract was
dried with MgSO4, filtered, and concentrated. The residue was
washed with anhydrous diethyl ether and dried in vacuo. The
yield of a mixture of salts 3 and 4 was 0.65 g (3 : 4 = ~77 : 23,
1H NMR data). The benzene filtrate was concentrated and fracꢀ
tional recrystallization of the residue from AcOEt—PriOH gave
triphenylphosphine oxide (0.1 g; m.p. 156 C) and acetone
phenylhydrazone (0.07 g; m.p. 42 C).
Reaction of salt 4 with triethylamine. A mixture of salt 4 (0.5 g,
1 mmol) and triethylamine (0.2 g, 2 mmol) in anhydrous benzꢀ
ene (10 mL) was heated at 70 C for 6 h. The precipitate that
formed was filtered off and the products were extracted with
water and chloroform. Triethylamine hydrobromide was isolatꢀ
ed from the aqueous extract. Yield 0.1 g, m.p. 246—248 C (deꢀ
comp.). The organic extract was dried with MgSO4, filtered, and
concentrated. The residue was washed with anhydrous diethyl
ether and dried in vacuo. Salt 4 (0.2 g, 40%) was recovered, m.p.
217—218 C; the 1H and 31P NMR spectra are identical with
those of an authentic sample. The benzene filtrate was conꢀ
centrated and fractional recrystallization of the residue from
AcOEt—PriOH gave triphenylphosphine oxide (0.1 g; m.p.
156 C) and acetone phenylhydrazone (0.05 g; m.p. 42 C).
Reaction of salt 3 with sodium carbonate. A. A mixture of
salt 3 (1 g, 2 mmol) and anhydrous Na2CO3 (0.25 g, 2.35 mmol)
in chloroform (15 mL) was stirred at room temperature for 2 h.
The reaction mixture was filtered and concentrated. The residue
was washed with anhydrous diethyl ether. The yield of a mixture
of salts 3 and 4 was 0.95 g (3 : 4 = ~50 : 50, 1H NMR data).
B. The synthesis was performed as described under entry A
with the exception that the mixture was stirred for 5 h. The
reaction gave a mixture of salts 3 and 5 (0.98 g, 3 : 5 = ~44 : 56,
1H NMR data).
Experimental
(Allyl)(triphenyl)phosphonium bromide and 1,4ꢀbis(triꢀ
phenylphosphonio)butꢀ2ꢀene dichloride were prepared accordꢀ
ing to known procedures.20,21 All reactions were carried out unꢀ
der dry nitrogen in a 50ꢀmL threeꢀnecked flask equipped with
a magnetic stirring bar, a reflux condenser, and a gas inlet tube.
1H and 31P NMR spectra were recorded on a Mercuryꢀ300 Variꢀ
an spectrometer (300.077 (1H) and 121.47 MHz (31P)) at 303 K
in DMSOꢀd6. Chemical shifts are referenced to Me4Si (1H) and
85% H3PO4 (31P) as the internal standards.
[4ꢀ(N,NꢀDimethylhydrazono)butꢀ2ꢀenyl](triphenyl)phosꢀ
phonium chloride (2). A solution of N,Nꢀdimethylhydrazine
(0.4 g, 7 mmol) in anhydrous acetonitrile (5 mL) was added to
a suspension of 1,4ꢀbis(triphenylphosphonio)butꢀ2ꢀene dichloꢀ
ride (1.6 g, 2.5 mmol) in anhydrous acetonitrile (20 mL). The
reaction mixture was heated at 50—51 C for 5 h and concentratꢀ
ed. The products were extracted with water and chloroform. The
organic extract was dried with MgSO4, filtered, and concentratꢀ
ed in vacuo. The residue was washed with benzene and anhydrous
diethyl ether and dried in vacuo. The yield of salt 2 was 0.42 g
(40%). Found (%): C, 69.24; H, 8.44; Cl, 9.13; N, 6.33; P, 7.01.
C24H36ClN2P. Calculated (%): C, 68.82; H, 8.60; Cl, 8.48;
N, 6.69; P, 7.41. 1H NMR, : 1.80 (s, 6 H, NMe2); 4.80
(dd, 2 H, P+CH2, 2JP,H = 16.8 Hz, 3JH,H = 7.5 Hz); 5.45 (dtd, 1 H,
CH2CH, 3JH,H = 15.4 Hz, 3JH,H = 7.5 Hz, 3JP,H = 6.6 Hz); 6.39
3
3
(ddd, 1 H, CH2CH=CH, JH,H = 15.4 Hz, JH,H = 9.1 Hz,
4JP,H = 5.2 Hz); 6.82 (d, 1 H, N=CH, JH,H = 9.1 Hz);
3
7.55—7.90 (m, 15 H, P+Ph3). 31P NMR, : 26.18 (s).
Triphenylphosphine oxide (0.35 g, 50%), m.p. 156 C, was
isolated from the benzene extract.
(Triphenyl)[2ꢀ(2ꢀphenylhydrazino)propyl]phosphonium broꢀ
mide (3). A solution of phenylhydrazine (1.4 g, 13 mmol) in
anhydrous acetonitrile (5 mL) was added to a suspension of
(allyl)(triphenyl)phosphonium bromide (5 g, 13 mmol) in anhyꢀ
drous acetonitrile (15 mL). The reaction mixture was heated at
77—78 C for 8 h. The precipitate that formed was filtered off,
washed with anhydrous diethyl ether, and dried in vacuo. The
yield of salt 3 was 4.9 g (77%), light yellow crystals, m.p.
232—234 C. Found (%): C, 66.02; H, 5.52; Br, 16.04; N, 5.41;
P, 6.49. C27H28BrN2P. Calculated (%): C, 65.99; H, 5.70; Br,
1
16.29; N, 5.70; P, 6.31. H NMR, : 1.21 (d, 3 H, Me, 3JH,H
=
3
= 6.3 Hz); 3.25 (dqt, 1 H, CH(Me)N, JH,H = 6.3 Hz,
3JH,H = 6.2 Hz, JP,H = 9.5 Hz); 3.46 (ddd, 1 H, P+C(Ha)Hb,
3
2
3
2JH,H = 15.6 Hz, JP,H = 11.6 Hz, JH,H = 6.2 Hz); 4.20 (ddd,
2
2
3
1 H, P+CHa(Hb), JH,H = 15.6 Hz, JP,H = 13.5 Hz, JH,H
=
(Triphenyl)[2ꢀ(2ꢀphenyldiazenyl)propyl]phosphonium bromide
(5). 1H NMR, : 1.50 (dd, 3 H, Me, 3JH,H = 6.4 Hz, 4JP,H = 2.3 Hz);
4.20—4.35 (m, 1 H, CH(Me)N=NPh); 4.40—4.65 (m, 2 H,
P+CH2); 7.20—7.40 (m, 5 H, NPh); 7.60—7.80 (m, 15 H,
P+Ph3). 31P NMR, : 28.3 (s).
= 6.2 Hz); 4.40 (d, 1 H, NHNHPh, 2JH,H = 7.2 Hz); 6.60—7.10
(m, 5 H, NPh); 7.55—7.90 (m, 15 H, P+Ph3). 31P NMR, : 27.8 (s).
(Triphenyl)[2ꢀ(phenylhydrazono)propyl]phosphonium bromide
(4). A solution of salt 3 (1 g, 2 mmol) in chloroform (15 mL) was
heated at 60 C for 6 h. The solvent was removed and the residue
was washed with anhydrous diethyl ether and dried in vacuo. The
Reaction of salt 3 with sodium methoxide. A. A solution of
salt 3 (1 g, 2 mmol) in methanol (10 mL) was added to a solution

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 12, December, 2012
Ovakimyan et al.
of MeONa (0.1 g, 1.85 mmol) in methanol (10 mL). The reacꢀ
tion mixture was stirred at room temperature for 2 h. The solvent
was removed, the products were extracted with water and chloroꢀ
form, and the chloroform extract was concentrated. Fractional
recrystallization of the residue from AcOEt—PriOH gave salt 3
(0.14 g, 14%), triphenylphosphine oxide (0.36 g, 65%; m.p.
156 C), and acetone phenylhydrazone (0.18 g, 60%; m.p. 42 C).
CH(Me)N=NEt); 4.20—4.45 (m, 2 H, P+CH2); 7.60—7.80 (m,
15 H, P+Ph3). 31P NMR, : 28.32 (s).
Reaction of [2ꢀ(2ꢀN,Nꢀdimethylhydrazino)propyl](triphenyl)ꢀ
phosphonium bromide with Na2CO3. A mixture of [2ꢀ(2ꢀN,Nꢀ
dimethylhydrazino)propyl](triphenyl)phosphonium bromide
(1.2 g, 2.7 mmol) and dry Na2CO3 (0.3 g, 2.8 mmol) in chloroꢀ
form (15 mL) was stirred at room temperature for 5 h. The
reaction mixture was filtered and concentrated. The residue was
washed with anhydrous diethyl ether and dried in vacuo to give
(triphenyl)(propꢀ1ꢀenyl)phosphonium bromide20 (1 g, 97%),
m.p. 213—214 C. The 1H and 31P NMR spectra are identical
with those of an authentic sample.
1
The H and 31P NMR spectra of salt 3 are identical with those
of the sample obtained from (allyl)(triphenyl)phosphonium
bromide and phenylhydrazine.
B. A reaction of salt 3 (1 g, 2 mmol) with MeONa (0.1 g,
1.85 mmol) at 58—60 C followed by the workup described above
yielded triphenylphosphine oxide (0.5 g, 90%; m.p. 156 C) and
acetone phenylhydrazone (0.25 g, 84%; m.p. 42 C).
References
Reaction of salt 3 with aqueous NaOH. A. A mixture of salt 3
(1 g, 2 mmol) and 25% aqueous NaOH (0.32 g) in benzene
(15 mL) was stirred at room temperature for 4 h. The organic
layer was separated and the residue was diluted with water and
chloroform. Triphenylphosphine oxide was isolated from the
organic (benzene) layer. Yield 0.2 g (36%), m.p. 156 C. The
chloroform extract was dried with MgSO4, filtered, and concenꢀ
trated. The residue was washed with anhydrous diethyl ether and
dried in vacuo. Fractional recrystallization of the residue from
AcOEt—PriOH gave salt 4 (0.15 g, 15%), acetone phenylhydrꢀ
azone (0.09 g, 30%; m.p. 42 C), and the starting salt 3 (0.35 g).
B. A mixture of salt 3 (1 g, 2 mmol) and 25% aqueous NaOH
(0.6 g) in benzene (15 mL) was stirred at 68—70 C for 4 h. The
organic layer was separated, dried with MgSO4, filtered, and
concentrated. The residue was dissolved in anhydrous diethyl
ether. The undissolved substance was dried in vacuo to give phosꢀ
phine oxide 6 (0.1 g, 14%). 1H NMR, : 1.21 (dd, 3 H, Me,
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4
3JH,H = 6.4 Hz, JH,H = 1.0 Hz); 2.29 (ddd, 1 H, P+C(Ha)Hb,
2
3
2JH,H = 15.2 Hz, JP,H = 9.1 Hz, JH,H = 5.0 Hz); 2.67 (ddd,
2
2
3
1 H, P+CHa(Hb), JH,H = 15.2 Hz, JP,H = 12.2 Hz, JH,H
=
= 7.7 Hz); 3.36 (m, 1 H, CH); 5.51 (br, 1 H, NH); 6.68 (tt, 1 H,
H(4)Ph); 6.79 (m, 2 H, H(2)Ph, H(6)Ph); 7.10 (m, 2 H, H(3)Ph
H(5)Ph); 7.69—7.80 (m, 10 H, PPh2). 31P NMR, : 36.02 (s).
,
The ethereal extract was concentrated and dried in vacuo to
1
give phosphine oxide 7 (0.3 g, 43%). H NMR, : 1.48 (d, 3 H,
Me, 3JH,H = 6.6 Hz); 2.65 (ddd, 1 H, P+C(Ha)Hb, 2JH,H = 15.0 Hz,
3
2JP,H = 13.3 Hz, JH,H = 7.3 Hz); 3.01 (ddd, 1 H, P+CHa(Hb),
2JH,H = 15.0 Hz, 2JP,H = 9.0 Hz, 3JH,H = 5.6 Hz); 4.40 (m, 1 H,
CH); 7.34—7.52 (m, 5 H, NPh); 7.34—7.52 (m, 10 H, PPh2).
31P NMR, : 34.02 (s).
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The product from the aqueous layer was extracted with
chloroform. The organic extract was dried with MgSO4, filtered,
and concentrated. The residue was washed with anhydrous diꢀ
ethyl ether and dried in vacuo to give the starting salt 3 (0.4 g).
[2ꢀ(2ꢀEthyldiazenyl)propyl](triphenyl)phosphonium bromide
(8). A mixture of (allyl)(triphenyl)phosphonium bromide (1 g,
2.6 mmol) and dry Na2CO3 (0.55 g, 5.2 mmol) in anhydrous
acetonitrile (15 mL) was stirred at room temperature for 2 h.
The reaction mixture was filtered and ethylhydrazine (0.16 g,
2.7 mmol) was added. The resulting mixture was heated at
45—50 C for 4 h. The solvent was removed in vacuo. The resiꢀ
due was recrystallized from AcOEt—PriOH. The yield of salt 8
was 0.9 g (78%). Found (%): C, 62.24; H, 5.53; Br, 18.52; N, 6.21;
P, 7.42. C23H26BrN2P. Calculated (%): C, 62.59; H, 5.89;
Br, 18.14; N, 6.35; P, 7.03. 1H NMR, : 1.19 (t, 3 H, CH2CH3,
3JH,H = 7.1 Hz); 1.40 (dd, 3 H, Me, 3JH,H = 6.4 Hz, 4JP,H = 2.3 Hz);
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3
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Received February 21, 2012;
in revised form July 26, 2012