Lignin-type, α,β-unsaturated aldehydes of lignin-type in organic solvents

Article abstract of DOI:10.1134/S1070363212050064

A 1:1 reaction of [HO(CH₂)₃]₃P with 4-hydroxy-3-methoxy-cinnamaldehyde (coniferaldehyde) or 3,5-dimethoxy-4- hydroxycinnamaldehyde (sinapaldehyde) in acetone at room temperature affords phosphonium zwitterions of the type R₃P⁺CH(4-O ^--Ar)CH₂CHO; other phosphines [R = Et, n-Bu, (CH ₂)₂CN, and p-Tol] do not react under the same conditions. In alcohols R'OH(D) [R' = CD₃, Et, (CD₃)₂CD, s-Bu, HOCH₂CH₂], the above phosphines (except the cyano-derivative) and those where R = i-Pr, Cy, Me₂Ph, MePh ₂ do react within an equilibrium established between the reactants and the zwitterion-hemiacetal products R₃P⁺CH(4-O ^--Ar)CH₂CH(OH)(OR') that are formed as a mixture of two diastereomers. The nature of the phosphine and the alcohol affects the equilibrium and the diastereomeric ratio.

Full text of DOI:10.1134/S1070363212050064

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 5, pp. 840–847. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © D.V. Moiseev, B.R. James, A.V. Gushchin, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 5, pp. 732–740.
Lignin-Type, α,β-Unsaturated Aldehydes
of Lignin-Type in Organic Solvents
D. V. Moiseeva,b, B. R. Jamesa, and A. V. Gushchinb
a Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
e-mail: moisdv@hotmail.com; brj@chem.ubc.ca
b Department of Organic Chemistry, Lobachevskii Nizhny Novgorod State University,
pr. Gagarina 23, Nizhny Novgorod, 603950 Russia
Received March 22, 2011
Abstract—A 1:1 reaction of [HO(CH2)3]3P with 4-hydroxy-3-methoxy-cinnamaldehyde (coniferaldehyde) or
3,5-dimethoxy-4-hydroxycinnamaldehyde (sinapaldehyde) in acetone at room temperature affords
phosphonium zwitterions of the type R3P+CH(4-O–-Ar)CH2CHO; other phosphines [R = Et, n-Bu, (CH2)2CN,
and p-Tol] do not react under the same conditions. In alcohols R'OH(D) [R' = CD3, Et, (CD3)2CD, s-Bu,
HOCH2CH2], the above phosphines (except the cyano-derivative) and those where R = i-Pr, Cy, Me2Ph, MePh2
do react within an equilibrium established between the reactants and the zwitterion-hemiacetal products
R3P+CH(4-O–-Ar)CH2CH(OH)(OR') that are formed as a mixture of two diastereomers. The nature of the
phosphine and the alcohol affects the equilibrium and the diastereomeric ratio.
DOI: 10.1134/S1070363212050064
Our group has been involved in investigating
interactions of phosphines with unsaturated com-
pounds in aqueous media, the interest evolving from
discovery of the use of the water-soluble phosphine
(HOCH2)3P for the bleaching of pulps [1–4]. The topic
is also of interest within homogeneous catalysis in
aqueous media involving unsaturated organic sub-
strates using transition metal-phosphine systems [5, 6].
A review covering both these aspects of the chemistry
of this specific phosphine has appeared recently [7].
We have reported previously studies on the reactions
of tertiary phosphines with substituted benzaldehydes
[8], benzyl and cinnamyl alcohols [9], and quinones [10].
with aromatic α,β-unsaturated aldehydes depend on
substituents present in the aromatic ring. Thus,
cinnamaldehyde, in the presence of tris(hydroxy-
propyl)phosphine, [HO(CH2)3]3P (THPP), undergoes
self-condensation into the two isomeric products
shown in Scheme 1, the reaction being initiated by
nucleophilic attack of the phosphine at the C-atom
adjacent to the Ph group [11]; however, lignin-type
aldehydes, which contain a p-OH-group, react with
tertiary phosphines to afford bisphosphonium zwitter-
ion products via the same nucleophilic phosphine
attack (Scheme 2) [12].
Reactions of α,β-unsaturated aldehydes such as
ArCH=CHCHO (Ar = aryl) with tertiary phosphines in
organic media have been investigated recently, but
only with (α-hydroxy)phosphines [e.g. Ph2PCH(OH)R,
where R = H, alkyl or aryl], which readily decompose
reversibly to RCHO and Ph2PH. The secondary phos-
Prior to our detailed studies on the interaction of
α,β-unsaturated aldehydes with tertiary phosphines in
aqueous media [11, 12], these systems were not well
understood, the relevant literature being summarized in
our reports. The studies revealed that the reactions
Scheme 1.
O
THPP (1 equiv)
+
Ph
Ph
O
Ph
H2O
O
Ph
Ph
840

LIGNIN-TYPE, α,β-UNSATURATED ALDEHYDES
841
Scheme 2.
R3P+
O
O
O
+ R3P
_O
_O
R3P
R3P
+
HO
+
O_
phine product adds across the olefinic bond to
generate, in this exemplified case, PPh2C*H(Ar)·
CH2CHO, where C* represents a chiral carbon center
[13, 14]. Examples of enantioselective syntheses of
this new type of tertiary phosphine have appeared, the
products being more readily obtained by reactions of
the unsaturated aldehydes with the secondary
phosphines [14–16].
and in several alcohols.
A 1:1 reaction of THPP with coniferaldehyde (Ia)
or sinapaldehyde (Ib) in acetone at room temperature
under Ar gives immediate precipitation, respectively,
of a yellow or yellow-brownish phosphonium zwitter-
ion (IIa or IIb) as a mixture of (R)- and (S)-
stereoisomers (Scheme 3) that are the products of γ-
nucleophilic attack by the phosphine. The products IIa
and IIb, which are formed in high yield, are insoluble
in acetone, CH2Cl2, CHCl3, and CH3CN, but are
readily soluble in water, MeOH, and DMSO.
This current report describes results on the
interaction of tertiary phosphines R3P (R = Ar or alkyl)
with lignin-type α,β-unsaturated aldehydes in acetone
Scheme 3.
+
(HOCH2CH2CH )
2 3P
MeO
MeO
γ
*
α
O
O
β
+ (HOCH2CH2CH2)3P
(CH3)2CO
_O
HO
X
X
X = H (Ia), MeO (Ib)
X = H (IIa), MeO (IIb).
Dissolution of IIa or IIb in CD3OD gives a red
solution in which there is ~70% conversion to the
corresponding hemiacetal of the phosphonium salts
(IIIa or IIIb, respectively) while the remaining 30%
1H NMR signals of THPP are seen; as well as the
corresponding 1H signals of Ia or Ib, implying reversible
equilibria as shown in the top half of Scheme 4, the
aldehydes Ia and Ib in CH3OH/CD3OD do not form
hemiacetals as evidenced by 1H NMR spectroscopy.
31
reconverts to THPP and Ia (or Ib). The P–{1H} and
Scheme 4.
R3P+
R3 P+
*
OCD3
3
R2 P+
O
R3 P+
OH
OH
MeO
_O
MeO
HO
MeO
_O
MeO
O_
OH
*
OD
_O
X
X
X
X
Va, Vb
IV
VI
X = H (IIIa), MeO (IIIb), R = (CH2)3OH.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

842
MOISEEV et al.
P+
R3
P+
*
OCD3
R3
*
*
MeO
DO
MeO
_O
MeO
_O
+CD3OD
_CD3OD
OD
O
O
+ R3P
H D
H D
X
X
X
P+
OCD3
R3
*
*
MeO
_O
MeO
DO
OD
O
+ R3P +
D D
D
X
X
Species IIIa and IIIb are each present as a mixture
of two diastereomers, and the NMR data for both
systems are essentially the same; data for just the IIa
system are presented here. The 31P–{1H} spectrum
reveals the IIIa diastereomers as two, slightly different
in intensity singlets in the phosphonium region [12] at
δP 37.8 and 37.4 ppm (cf. Table 1, entry 3). The
reversibility (see Scheme 4) is confirmed by observed
~3.84 for both diastereomers) overlaps with the OMe
resonances, and the J values cannot be determined.
After 24 h, the β-proton signals have disappeared, and
the corresponding α-proton triplets of doublets have
simplified to doublets (4JPH 0.8 Hz) implying
replacement of both β-protons by deuterons;
simultaneously, the β-proton signal of Ia (δH 6.53 ppm,
d.d) disappears and the α- and γ-protons resonances
collapse into singlets at δH 9.44 and 7.53 ppm,
respectively. That two β-protons were initially detected
for IIIa is consistent with IIa being the synthesized,
solid product in acetone. If the product resulted from
nucleophilic phosphine attack at the α-carbon
(exemplified by IV), then its dissolution in CD3OD,
following typical rapid decomposition of the α-(hyd-
roxy)phosphonium zwitterion to give free phosphine
1
slow H/D-exchange processes, monitored by H NMR
spectroscopy. Fifteen minutes after dissolution of IIa,
the α-proton of each IIIa diastereomer appears as a
triplet of doublets (at δH 4.47 and 4.44 ppm,
respectively) due to coupling to the two β-protons
(3JHH 4.0 Hz) and to the P-atom (4JPH 0.8 Hz); the β-
protons appear, respectively, as broad multiplets at δH
2.44 and 2.04 ppm, while the γ-proton signal (at δH
Table 1. 31P–{1H} and selected 1H NMR data, and equilibrium data for a phosphine and its phosphonium hemiacetal product
formed in a 1:1 reaction with sinapaldehyde (Ib) in CD3OD at room temperature under Ar
(RS)/(SR)а
(RR)/(SS)а
Entry
Phosphine
R3P, δP
R'R3P+/R3P
drb
δP
α-H, δH
4.37
4.38
4.36
4.32
4.37
4.28
4.29
–
γ-H, δH
δP
α-H, δH
4.33
4.33
4.32
4.28
4.31
4.20
4.21
–
γ-H, δH
1
2
3
4
5
6
7
8
Et3P
–17.5
–30.5
–29.5
–45.5
–26.7
20.8
40.1
35.4
37.8
27.9
26.4
41.6
32.9
–
3.74
39.7
35.0
37.4
27.6
26.1
41.2
32.5
–
3.73
5.2
4.0
2.5
2.5
0.4
1.1
1.1
1.1
1.1
1.2
1.2
1.2
–
n-Bu3P
3.74
3.72
c
c
THPP
Me2PPh
MePPh2
i-Pr3P
3.92
4.66
3.90
4.65
4.04
4.01
0.7
c
c
d
Cy3P
12.3
[NC(CH2)2]3Pe
–22.5
–
–
–
a
The assignments of the diastereomers are tentative (see text). b dr = diastereomeric ratio. c Overlap with OMe resonances. d See text. e No
reaction with this phosphine.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

LIGNIN-TYPE, α,β-UNSATURATED ALDEHYDES
843
and unsaturated aldehyde (see Scheme 3 in [11]),
would generate a monodeuterated hemiacetal via
THPP attack at the γ-C atom (Scheme 4, top half), and
the two β-protons would not be observed. When a 10-
fold excess of Ia was added under Ar to the NMR tube
temperature, Ar) does not form a type-II phosphonium
zwitterion, confirming an already well-established,
obvious point [8, 12] that the presence of a p-OH-
group is critical for generation of the O–···P+
zwitterions. Of note, when coniferaldehyde Ia was
reacted with Et3P, n-Bu3P, [NC(CH2)2]3P or p-Tol3P at
a 1:1 ratio in acetone under Ar, no precipitation was
observed and the 31P–{1H} spectra revealed just the
signal of the free phosphine; however, when the Et3P
system was monitored in acetone-d6 containing trace
water, slow H/D exchange of the aldehyde β-proton
was observed, implying the presence of a reversible
reaction that lies on the side of the reactants. It seems
that the insolubility of IIa and IIb in acetone allows
for their complete formation, the corresponding
equilibria being forced to the right-hand side. Not
completely ruled out is the possibility that a hydroxyl-
propyl group of THPP forms a hemiacetal such as VI
via an intramolecular interaction within IIa, IIb. The
solution NMR and MS data could be consistent with
the hemiacetal formulation, and spectroscopic evidence
has been presented for such a 6-membered ring species
formed from reaction of coniferaldehyde and (CH2OH)3P
in aqueous dioxane [4], but the formation of an 8-mem-
bered ring species such as VI seems highly unlikely.
31
1
containing IIa in CD3OD, the P–{1H} and H NMR
resonances of THPP disappeared as the equilibria are
pushed to the right (Scheme 4) and only IIIa and Ia
were detected, the β-proton of the latter again being
slowly replaced by deuteron.
Dissolution of IIa and IIb in D2O revealed
chemistry that we have reported previously [12]. The
initial 31P–{1H} solution spectrum of IIb revealed
singlets at δP 37.9 and 37.1 ppm in a 1:12 ratio
corresponding, respectively, to IIb and its diol Vb,
both previously characterized (species 3e and 4e in
[12]). The 31P–{1H} spectrum of IIa correspondingly
shows 1:9 intensity singlets at δP 38.0 and 37.2 ppm
for IIa and Va, respectively. The 1H spectra also prove
the formation of the phosphonium salts (IIa, IIb, and
their respective diols Va and Vb); the data for IIb and
Vb are as reported earlier [12], while the data for the
α-, β-, γ-proton moieties of IIa and Va are essentially
1
the same. Parallel H NMR data have been discussed
for the corresponding reactions of sinapaldehyde (Ib)
with Et3P and i-Pr3P [12]. The IIa and IIb systems
subsequently undergo slow self-condensation to
generate bisphosphonium zwitterionic species,
chemistry that again has been well substantiated [12].
The low-resolution ESI-MS of IIa (or IIb) freshly
dissolved in H2O shows peaks at m/z 387.3 and 405.3
(or m/z 417.3, 435.3) that correspond to the protonated
forms of IIa, Va and IIb, Vb, respectively.
Dissolution of IIa or IIb in DMSO-d6 solution
generated green solutions whose NMR spectra showed
decomposition back to the precursor aldehyde and
THPP. The origin of the green color is unknown, but
must result from a species formed by a weak, non-
NMR detectable interaction (presumably acid-base or
H-bond) between THPP (likely an OH group [7]) and
the carbonyl- or phenol-oxygen of the aldehyde.
A difference between Ia and Ic is also seen with the
use of a catalytic amount of THPP (6–10%). In an
acetone-d6/D2O mixture (1:1 by volume, room
temperature, Ar), a slow H/D-exchange of the β-proton
of Ia takes place. After 3 days, the intensity of the β-
proton NMR signal (d.d, δH 6.57 ppm) has decreased
by 75%; a 31P–{1H} singlet at δP 38.2 ppm attributable
1
to Va was detected, and a set of low intensity H
resonances due to the THPP moiety of Va was also
observed (see [12]). When Ic was used with the
catalytic amount of THPP at room temperature in
acetone–H2O (1:1 by volume, room temperature, Ar),
the cross-condensation product 6-(3,4-dimethoxy-
phenyl)-3,5-hexadien-2-one was isolated (Scheme 5).
The corresponding reaction with cinnamaldehyde was
described in our previous paper, where this THPP-
promoted classic base-catalyzed aldol-type condensa-
tion was discussed in detail [11].
Treatment of 3,4-dimethoxy-cinnamaldehyde (Ic)
with THPP under the same conditions (acetone, room
Scheme 5.
O
MeO
MeO
MeO
MeO
O
THPP (10 mol %)
(CH3)2CO_H2O
O
+
Ic
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

844
MOISEEV et al.
As discussed above, in CD3OD solution an
respectively (2JPH ≈ 15.5 Hz), although in the THPP
system the δH shift for the γ-H cannot be determined
due to overlap with the OMe resonances. The data
suggest that the R'R3P+/R3P product ratio, where R'
represents the phenolate form of the sinapaldehyde
moiety, depends on both steric and electronic factors
of the phosphine. The highest value of 5.2 (Entry 1 and
Fig. 1b) is seen with Et3P, which has a cone angle θ of
132° [17], while n-Bu3P and [NC(CH2)2]3P with the
same θ value have ratio values of 4.0 and zero,
respectively (entries 2 and 8); the trend of Et3P > n-
Bu3P > the non-reactive [NC(CH2)2]3P likely cor-
responds to decreasing nucleophilicity of the phos-
phine, although the nuclophilicities of Et3P and n-Bu3P
are essentially the same [18]. The THPP data (entry 3)
with a ratio value of 2.5 fit this trend if the reasonable
assumptions are made that θ for THPP is also 132°,
and that its nucleophilicity lies between that of
[NC(CH2)2]3P and n-Bu3P. Me2PPh, with the lowest θ
(122°) gives a ratio of 2.5, while the low ratio value of
0.4 for MePPh2 (θ = 136°) must be due to the negative
effect of Ph groups on the nucleophilicity (Entries 4
and 5). The bulkier phosphine i-Pr3P (θ = 160°) gives a
product ratio of 0.7 (Entry 6), while the ratio for the
most bulky tricyclohexylphosphine, Cy3P (θ = 170°),
was immeasurable because of the low solubility of
Cy3P in CD3OD. The product diastereotopic ratio is
equilibrium exists between the free phosphine and
unsaturated aldehyde reactants and the phosphonium
hemiacetal products (Scheme 4). The effect of the
nature of the phosphine in reaction with sinapaldehyde
Ib (at room temperature, under Ar) was studied, and
the data, measured after 24 h when the H/D exchange
processes are complete, are summarized in Table 1.
The 31P–{1H} and 1H NMR data are closely analogous
to those discussed above in detail for the THPP/
coniferaldehyde (Ia) system. The specific diastereomer
31
assignments of the P–{1H} signals are tentative, and
are based on our earlier studies on reactions of
cinnamaldehyde with tertiary phosphines in aqueous
media [11], and on neat reagent reactions of cinnamal-
dehyde with Ph2PH [14]: such reactions are stereo-
specific and in the diastereomeric products the (RR)/
(SS) product was favoured over the (RS)/(SR) product.
Thus, for the diastereomeric mixture of phosphonium-
hemiacetals, the most intense 31P–{1H} signal (see
Fig. 1) is assigned to the (RR)/(SS) product. In all the
systems, the α-H of the (RS)/(SR) and (RR)/(SS)
isomers appears in the 1H spectrum as a doublet in the
range δH 4.28–4.38 and 4.20-4.33 ppm, respectively
(Table 1), due to weak coupling to the P-atom (4JPH
≈
1 Hz); the corresponding γ-H appears as a doublet in
the range δH 3.74–4.66 and 3.72–4.65 ppm,
(a)
(b)
(c)
(d)
(e)
δ, ppm
Fig. 1. 31P–{1H} spectrum of a solution of Et3P and Ib (1:1, Ar) in: (a) (CH2OH)2, (b) CD3OD, (c) EtOH, (d) i-PrOD-d8, and
(e) s-BuOH.
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LIGNIN-TYPE, α,β-UNSATURATED ALDEHYDES
845
Table 2. 31P–{1H} NMR data and equilibrium data for Et3P and its phosphonium hemiacetal product formed from Ib in
different alcohols (1:1 reaction, room temperature, Ar)
Entry
Solvent
ε
R3P, δP
(RS)/(SR), δP
(RR)/(SS), δP
R'R3P+/R3P
dr
1
2
3
4
5
6
(CH2OH)2
CD3OD
EtOH
37.7
32.7
24.6
18.3
15.8
12.5
–
40.4
40.1
41.1
40.0
39.7
40.7
∞
5.2
1.7
0.5
0.4
0
1.2
1.1
1.1
–17.5
–17.5
–18.8
–18.7
–18.9
i-PrOD-d8
s-BuOH
t-BuOHb
40.4
40.0
1.3
а
а
а
–
–
–
a See the text. b No reaction.
close to unity and varies little within the systems, with
the bulkier MePPh2, i-Pr3P and Cy3P affording the
highest diastereotopic ratio value of 1.2.
ginally greater variation in the diastereotopic ratio
values is seen when the alcohols are varied, the i-
PrOD-d8 system having the highest value of 1.3 (but
see below).
The effect of using different alcohols for the 1:1
Et3P/Ib reaction was also studied under the room
temperature/Ar conditions, and Table 2 shows the
equilibria data measured after 24 h (see Scheme 6,
where within the CD3OD and i-PrOD-d8 systems the
OH and β-H atoms will be present as D-atoms). The
data strongly suggest that the R'R3P+/R3P product ratio
depends on the dielectric constant (ε) of the alcohol. In
glycol, with the highest ε value (37.7), quantitative
yield of the phosphonium hemiacetal is seen (entry 1
and Fig. 1a). Within other alcohols, the intensity of the
31P–{1H} signal of Et3P gradually increases (i.e. the
equilibria shift to the left) in the order: CD3OD (ε =
32.7) > EtOH (24.6) > (CD3)2CDOD (18.3) > s-BuOH
(15.8), as shown in Fig. 1. The zwitterionic product is
clearly stabilized in a higher dielectric medium. Mar-
In the case of t-BuOH (ε = 12.5), which has a
melting point of 25°C, the solubility of Ib is low, and
so the reaction mixture (initially of a green color) was
warmed until the aldehyde had dissolved to give a
brown solution; however, no phosphonium 31P–{1H}
signal was seen, and after 2 h at room temperature,
when the solution again became green, still no
phosphonium resonances were detected. Of note, the
reaction mixture in s-BuOH (see below) is deep red,
while in glycol the color is orange. The reasons for the
observed varying colors are unclear: interaction of the
alcohols with the reactant aldehyde (see the DMSO
system above where no zwitterionic product is seen),
or with the phenolate-oxygen of the phosphonium
hemiacetal, might be involved.
Scheme 6.
Et3P+
Et3P+
*
OR
*
MeO
HO
MeO
_O
MeO
_O
+ROH
_ROH
*
O
OH
O
+ Et3P
OMe
OMe
VII
OMe
31
A 1:1 reaction of Et3P with 4-methoxy-cinnamal-
dehyde in CD3OD after 25 min reveals a broad singlet
new P–{1H} resonances are generated over one day.
The system shows similarities to the reaction of
cinnamaldehyde with THPP in water (or D2O), which
finally generates two isomeric self-condensation
aldehyde products with co-production of the phosphine
31
in the phosphonium region at δP 40.5 in the P–{1H}
spectrum, and this is attributed to a cationic phos-
phonium species; however, the system is unstable, and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

846
MOISEEV et al.
oxide (Scheme 1) [11]. Kinetic and mechanistic details
have recently been published by Galkin’s group on the
related but simpler reactions of α,β-unsaturated
carboxylic acids with Ph3P where, for example, acrylic
acid in acetic acid media gives just the phosphonium
acetate [Ph3P+CH2CH2CO2H]OAc– [19], while in
alcohol media the Ph3P+CH2CH2CO2– zwitterion is
formed [20].
corresponding phosphonium hemiacetals, R3P+C*H(4-
O––Ar)CH2C*H(OH)(OMe), in a diastereomeric ratio
of 1.1–1.2. Stronger donor phosphines shift the
equilibrium to the product side, while the bulkier
phosphines give the diastereotopic ratio value of 1.2.
Alcohols with higher dielectric constant favor
significantly the formation of the zwitterionic hemi-
acetals, while a bulky alcohol increased the product
diastereotopic ratio. In DMSO, the equilibrium
reaction with THPP lies completely to the left.
In the case of the chiral alcohol s-BuOH, the
stereochemistry is necessarily more complicated. Four
31P–{1H} phosphonium resonances were anticipated
due to the four possible diastereomers, (SSS)/(RRR),
(SSR)/(SRR), (SRS)/(RSR), and (RSS)/(RRS) (see VIII),
but only three singlets at δP 40.4, 40.1 and 40.0 ppm
with relative intensity 1.0:0.5:0.6 were detected
(Fig. 1e). One rational is that the chirality at the γ-C
atom of VII (see Scheme 6) determines the chirality of
an attacking molecule of s-BuOH. For example, if the
γ-C atom has (S)-chirality perhaps only (S)-butanol can
lead to the hemiacetal and vice versa; in this case only
two diastereomers are possible [(SSS)/(RRR) and
(SRS)/(RSR)]. Further, if the hemiacetal formation is
not complete in this solvent, one of the three resonan-
ces could be that of VII. Of note in this regard, the
minor resonance in the 31P–{1H} spectrum of the reac-
tion mixture in i-PrOD-d8 (Fig. 1d) does show a shoulder
that could be due to free VII and, in which case, the
actual diastereotopic ratio would be higher than 1.3.
EXPERIMENTAL
Sinapaldehyde,
coniferaldehyde,
and
other
aldehydes were used as received from Aldrich. 4-
Methoxy-cinnamaldehyde and 3,4-dimethoxy-cinnamal-
dehyde were prepared by condensing acetaldehyde
with 4-methoxybenzaldehyde and 3,4-dimethoxy-
benzaldehyde, respectively [21]. THPP (an oil,
> 80%), n-Bu3P, Et3P, Me2PPh, MePPh2, Cy3P, i-Pr3P
(all Strem products) and p-Tol3P (Aldrich) were used
without purification, while [NC(CH2)2]3P was prepared
by a literature method [22]. D2O, CD3OD, DMSO-d6,
acetone-d6, and i-PrOD-d8 (Cambridge Isotope Labs.)
were used as received. Acetone was dried over CaCl2,
distilled under N2, degassed by a freeze-pump-thaw
technique, and then saturated with Ar. Ethylene glycol
was stirred for 2 days under Ar at 50°C and then
distilled under vacuum; s-BuOH was refluxed under
Ar for 4 h and then distilled; EtOH was dried over
CaH2 and then distilled under Ar. NMR spectra were
recorded on a Bruker AV300 spectrometer at 300 K
Et3P+
OH Me
MeO
_O
*
*
*
O
Et
1
(300 MHz for H; 121 MHz for 31P–{1H}), with a
residual deuterated solvent proton (relative to external
SiMe4) and 85% aq. H3PO4 being used as references;
s = singlet, d = doublet, t = triplet, m = multiplet;
J values are given in Hz. Elemental analyses were
performed on a Carlo Erba 1108 analyzer. Low
resolution mass spectrometry was performed on a
Bruker Esquire electrospray (ESI) ion-trap spectro-
meter with samples dissolved in H2O; the positive ion
polarity scanned the range 60-1000 m/z.
OMe
VIII
CONCLUSIONS
The interactions of tertiary phosphines with lignin-
type α,β-unsaturated aldehydes in organic media
(Schemes 3 and 4) are different from those studied
previously in aqueous solution. The solvent, the
phosphine, and the aldehyde all affect the nature of the
products. In acetone, only [HO(CH2)3]3P of the
phosphines studied reacts with coniferaldehyde (Ia) or
sinapaldehyde (Ib) to precipitate the phosphonium
zwitterions [HO(CH2)3]3P+CH(4-O--Ar)CH2CHO; Et3P,
n-Bu3P, (NCCH2CH2)3P, and p-Tol3P were unreactive.
Aldehydes without a p-OH group do not react with
[HO(CH2)3]3P. Ia and Ib react with tertiary phosphines
in MeOH via an equilibrium process to give the
Synthesis of IIa from THPP and coniferaldehyde
(Ia). A solution of THPP (100 mg, 0.48 mmol, assum-
ing 100% purity) in acetone (1.5 ml) was added to a
solution of Ia (86 mg, 0.48 mmol) in acetone (1.5 ml),
and the mixture was stirred for 3 h at r.t. (~20°C)
under Ar. The yellow solid product was filtered off,
and dried under vacuum overnight (yield 145 mg,
78%). C19H31O6P. Calculated, %: C 59.06, H 8.09.
Found, %: C 59.3, H 8.4. Low-resolution ESI-MS: m/z
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

LIGNIN-TYPE, α,β-UNSATURATED ALDEHYDES
847
387.3 (80%) [M + H]+, 405.3 (100%) [M + H2O + H]+;
ACKNOWLEDGMENTS
1
Mcalc 386.4. H and 31P–{1H} NMR data (and for IIb
We thank the Natural Sciences and Engineering
Research Council of Canada for funding via a
Discovery Grant.
see below) are discussed in the Results and Discussion
section.
Synthesis of IIb from THPP and sinapaldehyde
(Ib). Use of the procedure given above, but with Ib
(100 mg, 0.48 mmol), produced a yellow-brown solid
(yield 140 mg, 70%). C20H33O7P. Calculated, %: C
57.68, H 7.99. Found, %: C 57.3, H 8.1. Low-
resolution ESI-MS: m/z 417.3 (40%) [M + H]+, 435.3
(100%) [M + H2O + H]+; Mcalc 416.4.
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NMR study of coniferaldehyde/THPP (16:1) reac-
tion in acetone-d6/D2O. A solution of THPP (2.1 mg,
0.01 mmol) in D2O (1 ml) was added to a solution of
coniferaldehyde (28.5 mg, 0.16 mmol) in acetone-d6
(1 ml) under Ar at r.t. The mixture was stirred for
5 min, when 0.7 ml of the solution was transferred into
a J-Young NMR tube under Ar; the NMR spectra were
then recorded periodically (see Results and Discussion).
Aldol condensation of 3,4-dimethoxy-cinnamal-
dehyde and acetone in the presence of THPP. A 2 ml,
air-free aqueous solution of THPP (21 mg, 0.1 mmol)
was added to a 2 ml air-free acetone solution of the
aldehyde (192 mg, 1.0 mmol), and the mixture was
stirred under Ar for 20 h at r.t. Removal of the solvents
left a brown solid that was extracted with Et2O (2×5 ml);
the ether layers were dried with Na2SO4 overnight, and
the product was separated by column chromatography
on silica gel (230–400 mesh) using Et2O as eluent.
Removal of Et2O in vacuo gave 6-(3,4-dimethoxy-
phenyl)-3,5-hexadien-2-one as a yellow solid (yield
1
153 mg, 66%). H NMR spectrum (CDCl3), δH, ppm:
3
3
7.28 d.d (1H, CH=CHCO, JHH 15.5, JHH 15.5 Hz),
7.06–6.99 m (2H, m- and o-H), 6.93–6.70 m (3H,
3
ArCH=CH and o-H), 6.23 d (1H, CH=CHCO, JHH
15.4 Hz), 3.93 s (3H, OCH3), 3.91 s (3H, OCH3), 2.31
s (3H, CH3).
NMR study of the 1:1 reaction of sinapaldehyde
(Ib) with phosphines in alcohols. A phosphine (0.15 mmol;
22 μl Et3P, 37 μl n-Bu3P, 29 μl i-Pr3P, 21 μl Me2PPh,
28 μl MePPh2, 31.0 mg THPP) was added to a solution
of Ib (31.0 mg, 0.15 mmol) in an alcohol (1 g) under
Ar; 0.7 ml of the solution was transferred into a J-
Young NMR tube under Ar, and the 31P–{1H} NMR
spectra were recorded periodically (see Results and
Discussion). Different concentrations of Cy3P and
[NC(CH2)2]3P were used because of their low
solubility: 13.5 mg (0.05 mmol) Cy3P and 10.0 mg
(0.05 mmol) aldehyde; [NC(CH2)2]3P 13.9 mg (0.07
mmol) and 15.0 mg (0.07 mmol) aldehyde.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012