Synthesis and stereochemistry of some new 1,3-dioxane derivatives of 1,4-diacetylbenzene

Article abstract of DOI:10.1007/s007060200035

The synthesis and stereochemistry of new 1,3-dioxane derivatives of 1,4-diacetylbenzene are reported. The anancomeric structure of these compounds, the axial orientation of the aryl group for both 1,3-dioxane rings, and the cis and trans isomerism of some

Full text of DOI:10.1007/s007060200035

Monatshefte fuÈr Chemie 133, 631±641 ꢀ2002)
Synthesis and Stereochemistry
of Some New 1,3-Dioxane Derivatives
of 1,4-Diacetylbenzene
1
2
ꢀ3
Ion Grosu1;Ã, Luminita Muntean , L oÈcõ Toupet , Gerard Ple ,
Monica Pop1, Mirela Balog1, Sorin Mager1, and Elena Bogdan1
1
Babes-Bolyai University, Organic Chemistry Department and CSOFSTM,
RO-3400 Cluj-Napoca, Romania
ꢀ
2
Universite de Rennes I, UMR C 6626, F-35042 Rennes, France
3
ꢀ
Universite de Rouen, IRCOF, UMR 6014, Faculte des Sciences de Rouen,
F-76821 Mont Saint Aignan, France
ꢀ
Summary. The synthesis and stereochemistry of new 1,3-dioxane derivatives of 1,4-diacetylbenzene
are reported. The anancomeric structure of these compounds, the axial orientation of the aryl group
for both 1,3-dioxane rings, and the cis and trans isomerism of some of these compounds is dis-
cussed considering data of conformational analysis, NMR investigations, and single crystal X-ray
diffractometry.
Keywords. 1,3-Dioxanes; Conformation analysis; NMR; cis-trans-Isomers; X-Ray.
Introduction
Investigations of the stereochemistry of 1,3-dioxane derivatives bearing aryl groups
at position 2 of the heterocycle revealed interesting structural aspects. The A values
ꢀfree conformational enthalpy [1]) of aryl groups located in the acetal part of the 1,3-
dioxane ring are high ꢀe.g. APh ˆ 13.04 kJ=mol [2, 3]). The 2-aryl-1,3-dioxanes
are anancomeric compounds with the characteristic conformational equilibrium
between I and II shifted toward I with the aryl group in the equatorial position
ꢀScheme 1 [4±8]). The conformational equilibrium of 2,2-disubstituted-1,3-
dioxanes ꢀIII, IV; e.g. 2-phenyl-2-methyl-1,3-dioxanes, Scheme 1) is shifted toward
the conformer exhibiting the aryl group in the axial position [2, 9, 10]. The axial
preference of the phenyl group is predicted from the higher A value of the methyl
group at position 2 ꢀAMe ˆ 16.63 kJ=mol [2]) with respect to the Avalue of the phenyl
group ꢀAPh ˆ 13.04 kJ=mol [2]) at the same position. Thermodynamic measurements
of 2-methyl-2-phenyl-1,3-dioxanes showed a considerably higher preference of
the methyl group for the equatorial position ꢀÁG0IIIÀIV ˆ 10:11 kJ=mol [2]) than
that calculated from the A-values of methyl and phenyl groups ꢀÁA ˆ AMeÀAPh ˆ
3.63 kJ=mol).
Ã
Corresponding author. E-mail: igrosu@chem.ubbcluj.ro

632
I. Grosu et al.
Scheme 1
Scheme 2
Studies on the rotameric behaviour of the aryl groups revealed a weak prefer-
ence of the equatorial phenyl group for the bisectional orientation ꢀIa) [11±13]
and a high preference of the axial phenyl group for the orthogonal orienta
tion ꢀIVb, Scheme 2 [9, 10, 14±18]). This is consistent with the H NMR shifts
[9].
1
For some 2-aryl-2,5,5-trimethyl-1,3-dioxanes, the chemical shifts for the
signals belonging to the equatorial methyl groups at C5 are close to 0 ppm or even
exhibit negative values [10]. The axial protons at positions 4 and 6 are located in
the deshielding area of the orthogonal aryl groups, whereas the equatorial protons
at these positions are in the shielding area. The differences between the chemical
shifts of the equatorial and axial protons of these positions are considerably lower

Synthesis and Stereochemistry of 1,3-Dioxane Derivatives
633
Scheme 3
than in the compounds bearing the same aromatic substituent in equatorial
orientation, and unusually in some of the cases the axial protons are more de-
shielded than the equatorial ones [6, 10]. The values of the shielding or deshielding
in¯uence of the orthogonal axial aromatic substituents are in agreement with the
estimated values using the model of Haigh and Mallion [19]. Data on the barrier
for the rotation of the aryl groups at C2 were obtained from NMR investigations
[5, 20].
Interesting results were obtained in the NMR investigations of compounds
bearing nonsymmetric axial aryl groups ꢀꢀ-naphtyl, ꢁ-naphtyl, o-nitrophenyl, m-
nitrophenyl). In these compounds, the bond between the aromatic substituent and
the 1,3-dioxane ring is an axis of chirality ꢀScheme 3 [10]). The chirality of the
molecule determines the diastereotopicity of the positions 4 and 6 of the 1,3-
dioxane ring, which is consistent with the NMR data [10].
Investigations on the stereochemistry of compounds bearing two 1,3-dioxane
rings on the same aromatic system obtained from benzenedicarboxaldehydes have
revealed the equatorial orientation of the aromatic ring for both heterocycles [5±7].
The derivatives bearing different substituents in positions 5 and 50 of the 1,3-
dioxane rings show three diastereoisomers ꢀcis,cis, cis,trans, and trans,trans) in
agreement with the disposition of the groups with higher precedence in position
5 ꢀ50) on the same side ꢀcis) or on different sides ꢀtrans) with the aromatic group
at position 2.
It was considered of interest to investigate the stereochemistry of 1,3-dioxane
derivatives of 1,4-diacetylbenzene and to determine the conformational be-
haviour of the heterocycles, the orientation of the aromatic substituent in both
heterocycles, and to identify and to characterize the possible cis and trans
isomers.
Results and Discussion
Compounds 1±7 exhibiting two 1,3-dioxane rings located on the same aromatic
system were obtained by the condensation of 1,4-diacetylbenzene with several
propanediols ꢀScheme 4).
In some cases ꢀsynthesis of 2 and 3), the mono-1,3-dioxane derivatives were
observed in the raw products; in the case of 3 it could be isolated by crystallization
ꢀ8, Scheme 5).

634
I. Grosu et al.
Scheme 4
Scheme 5
Compounds 1±3 are single con®gurational isomers, whereas 4±7 exhibit three
isomers with the cis or trans disposition of the aryl group at position 2 and 20 and of
the substituents with highest precedence at positions 5 and 50 ꢀcis,cis ꢀV), cis,trans
ꢀVI), and trans,trans ꢀVII) Scheme 6). All investigated compounds exhibit
anancomeric structures, and the axial orientation of the aromatic ring in both 1,3-
dioxane rings is assumed.
The preference of the methyl groups at positions 2 and 20 for the equatorial
orientation and of the aromatic substituent for the axial one, as predicted by
thermodynamic data for similar compounds [2], was con®rmed by NMR investiga-
tions and by the molecular structure in the solid state as established for 2 by
X-ray diffractometry.

Synthesis and Stereochemistry of 1,3-Dioxane Derivatives
635
Scheme 6
Fig. 1. ORTEP drawing of compound 2
The ORTEP diagram ꢀFig. 1) of 2 shows a centrosymmetric structure with chair
conformations for the heterocycles and the axial orientation of the aromatic
substituent. The bond lengths, bond angles, and torsion angles in the heterocycles
exhibit normal values. The aromatic substituent is orthogonal, the value of the

636
I. Grosu et al.
angle between the plane of the aromatic ring ꢀC1±C2±C3) and the best plane of the
1,3-dioxane ring ꢀC9±C6±C10) is close to 90ꢀ ꢀ93.3ꢀ).
NOE experiments performed on 2 in C6D6 solution con®rmed the same
arrangement of the substituents as in the solid state. Thus, irradiation of the singlet
originating from the methyl groups at position 2 ꢀꢂ ˆ 1.69 ppm) showed a small
effect on the protons of the heterocycles ꢀsomewhat stronger on the equatorial
ones; doublet, ꢂ ˆ 3.28 ppm), whereas the irradiation of the signal of the aromatic
protons ꢀsinglet, ꢂ ˆ 7.65 ppm) caused a strong enhancement of the signals of the
protons of the heterocycles, observed especially on the doublet pertaining to the
axial ones ꢀꢂ ˆ 3.42 ppm).
The NMR spectra of compounds 1±3 exhibited different signals for the axial
and equatorial protons at positions 4 ꢀ40) and 6 ꢀ60) as well as for those of the axial
and equatorial groups located at position 5 ꢀ50) of the 1,3-dioxane rings. At the
same time, the spectra display a unique set of signals for the protons and carbons of
the heterocycles and only one singlet for the protons of the aromatic ring, showing
1
that the two heterocycles are equivalent. For example, the H NMR spectrum of 2
exhibits two doublets, one for the equatorial ꢀꢂeq ˆ 3.28 ppm) and another one for
the axial ꢀꢂax ˆ 3.42 ppm) protons at positions 4 ꢀ40) and 6 ꢀ60) and two singlets for
the protons of the axial ꢀꢂax ˆ 1.21 ppm) and equatorial ꢀꢂeq ˆ 0.14 ppm) methyl
groups at position 5 ꢀ50).
The strong shielding of the protons of the equatorial methyl groups
ꢀꢂ5-ꢀMe)eq ˆ 0.14 ppm; usually ꢂ5-ꢀMe)eq > 0.4±0.5 ppm) and of the equatorial pro-
tons at positions 4 ꢀ40) and 6 ꢀ60) ꢀꢂ4eq,6eq ˆ 3.28 ppm; in compounds obtained
from aromatic aldehydes, ꢂ4eq,6eq > 4.4±4.5 ppm) are due to the magnetic aniso-
tropy of the aromatic ring that prefers the axial orthogonal orientation. Unusually,
the signal of the equatorial protons at positions 4 ꢀ40) and 6 ꢀ60) is more shielded
than the signal pertaining to the axial ones. A careful inspection of the NMR
spectra reveals further splittings of the peaks of the signals of the protons at
positions 4 ꢀ40) and 6 ꢀ60) due to long-range couplings between the axial and the
equatorial protons of these positions. The values of the coupling constants were
calculated from simulated spectra ꢀJ4ax,6eq ˆ À10.5; J4ꢀeq)ax,6ꢀax)eq ˆ À0.5 and
J4eq,6eq ˆ À1.9 Hz).
The main isomers ꢀcis,cis, V; Scheme 6) of compounds 4 and 5 were isolated as
single compounds. This isomer exhibits the aromatic ring in the axial orientation
and the groups at positions 5 and 50 in equatorial positions. The NMR spectra of
these compounds exhibit a unique set of signals for the protons of the 1,3-dioxane
rings and a singlet for the aromatic protons showing the equivalence of the two
heterocycles. The equatorial orientation of the substituents at positions 5 and 50
was deduced from the values of the coupling constants involving the protons at
positions 5 and 50. Thus, the 1H NMR spectrum of the cis,cis isomer of 5 exhibits a
triplet for the axial protons at positions 4 ꢀ40) and 6 ꢀ60) of the heterocycles
ꢀoverlapped doublet of doublets with two close and large coupling constants;
J4ꢀ6)ax,5ax ˆ J4ꢀ6)eq,4ꢀ6)ax ˆ 11.6 Hz; ꢂ ˆ 3.86 ppm) and a doublet of doublets with a
large coupling constant ꢀJ4ꢀ6)eq,4ꢀ6)ax ˆ 11.6 Hz) and a smaller one J4ꢀ6)eq,4ꢀ6)ax
ˆ
5.7 Hz; ꢂ ˆ 3.99 ppm) pertaining to the equatorial protons at the same positions.
The protons at positions 5 ꢀ50) showed an overlapped triplet of triplets ꢀꢂ ˆ
3.31 ppm).

Synthesis and Stereochemistry of 1,3-Dioxane Derivatives
637
The A-values of methyl and ethyl groups at position 5 of the 1,3-dioxane ring
are very close ꢀAMe ˆ 3.30±3.70 kJ=mol; AEt ˆ 2.80±3.40 kJ=mol [2]). Compound
6 was obtained as a mixture of the three possible isomers in a ratio close to
V:VI:VII ˆ 1:2:1 as it can be estimated from statistic rules. This result is supported
1
by the H NMR spectrum for the protons of the methyl groups at positions 2
and 20 containing four signals with close intensities ꢀꢂ ˆ 1.72, 1.725, 1.75, and
1.755 ppm). One signal belongs to isomer V, another one to isomer VII, and
remaining two signals pertain to the ring with an axial methyl group ꢀat position 5)
and to the ring with an axial ethyl group ꢀat position 5) of isomer VI. The dif-
ferences of magnetic environments for the majority of similar protons in the three
isomers are small and, the majority of the signals belonging to the three isomers are
overlapped. However, two sets of signals with similar intensities were observed.
One of these sets belongs to the protons of the rings ꢀdenoted with A, experimental
part) exhibiting axial ethyl groups and the other one to the rings showing equatorial
ethyl groups ꢀdenoted with B).
The A values of methyl ꢀAMe ˆ 3.30±3.70 kJ=mol [2]) and hydroxymethyl
groups ꢀACH OH ˆ À0.70 to ‡ 0.50 kJ=mol [2]) at the position 5 of the 1,3-dioxane
2
ring are somewhat different, showing a preference of the hydroxymethyl group
for the axial orientation. Thermodynamic measurements on 5-hydroxymethyl-5-
methyl-1,3-dioxanes con®rmed the preference of the hydroxymethyl group for
the axial orientation ꢀÁG0 ˆ À2.30 to À4.30 kJ=mol [2]). The crude product of 7
contained isomers VII ꢀtrans,trans) and VI ꢀcis,trans) in a ratio of VII:VI ˆ 1:1
and small amounts of isomer V ꢀScheme 6). A mixture of VII and VI in
equimolar ratio was isolated from the crude product by crystallization. As in the
1
case of 6, the H NMR spectrum of the mixture did not exhibit different signals
for the two isomers but showed two sets of signals ꢀratio of intensities: 3:1)
belonging to the rings ꢀof the two isomers) with axial hydroxymethyl ꢀmajor
one, rings A) and to the rings bearing the hydroxymethyl group in equatorial
orientation ꢀrings B).
Experimental
1H and 13C NMR spectra were recorded at room temperature using C6D6, CDCl3, or CD3OD as
solvents in 5 mm tubes on a Bruker AM 400 NMR spectrometer equipped with a dual 13C±1H
probe operating at 400 MHz for protons and 100 MHz for carbon atoms. Melting points were
measured with a Kleinfeld melting point apparatus and are uncorrected. The experimental
conditions for the X-ray structure determination of compound 2 and details of the re®nements are
given in Table 1.
The structural data were deposited at the Cambridge Crystallographic Data Center, deposition
number CCDC 177903.
Compounds 1±8 ꢀgeneral procedure)
Stoichiometric amounts of 1,3-diol ꢀ0.2 mol), diketone ꢀ0.1 mol), and catalytic amounts ꢀ0.1 g) of
p-toluenesulfonic acid were dissolved in 200 cm3 benzene. The mixture was re¯uxed, and H2O was
removed by a Dean-Stark trap. When 80% of the H2O was separated the mixture was cooled to room
temperature, and the catalyst was neutralized ꢀstirring, 0.5 h) with 0.2 g sodium acetate. The reaction
mixture was washed twice with 100 cm3 H2O. After drying with Na2SO4 the benzene was removed,

638
I. Grosu et al.
Table 1. Parameters of the crystallographic determinationsa for compound 2
Chemical formula
C10H15O2
Formula weight
167.22
Crystal system=space group
Crystal size=mm
Unit cell dimensions
monoclinic, P21=c
0.33 Â 0.30 Â 0.25
Ê
a=A
Ê
b=A
10.181ꢀ2)
6.502ꢀ2)
14.854ꢀ4)
90
Ê
c=A
ꢀ=ꢀ
ꢁ=ꢀ
108.55ꢀ2)
90
ꢃ=ꢀ
V=A3
932.2ꢀ4)
4
Z
Dcalc=Mg Á mÀ3
1.191
ꢄ=mmÀꢀ 1
0.081
2ꢅmax=
Scan mode
54
$=2ꢅ ˆ 1
60
tmax=s
Re¯ns collected=unique
Final R indices
R indices
2139=2027
R1 ˆ 0.0396, wR2 ˆ 0.0996
R1 ˆ 0.0758, wR2 ˆ 0.1132
a
Collected on an automatic diffractometer CAD4 NONIUS with graphite monochromatized MoKꢀ
radiation; the cell parameters were obtained by ®tting a set of 25 high-ꢅ re¯ections; after Lorentz and
polarization corrections [21] the structure was solved with SIR-97 [22] which reveals the non
hydrogen atoms of the structure; after anisotropic re®nement, all hydrogene atoms were found with a
Fourier difference synthesis; w ˆ 1=ꢀꢆ2ꢀF2) ‡ ꢀ0.0951P)2 ‡ 0.1000P) where P ˆ ꢁF02 ‡ 2Fc2†=3 with
resulting R ˆ 0.039, Rw ˆ 0.099, and Sw ˆ 1.026 ꢀresidual Áꢇ40.21 eAÀ3
)
and the compounds were puri®ed by crystallization from EtOH or MeOH. Elemental analyses agreed
favourably with the calculated values.
1,4-Bis-ꢀ2-methyl-1,3-dioxan-2-yl)-benzene ꢀ1; C16H22O4)
1
Yield: 48%; white crystals; m.p.: 156±158ꢀC; H NMR ꢀC6D6, ꢂ, 400 MHz): 0.64 ꢀm, 2H, 5-Heq,
50-Heq), 1.73 ꢀs, 6H, 2-CH3-eq, 20-CH3-eq), 1.88 ꢀm, overlapped peaks, 2H, 5-Hax, 50-Hax), 3.60±3.66
ꢀoverlapped peaks, 8H, 4-Heq, 40-Heq, 6-Heq, 60-Heq, 4-Hax, 40-Hax, 6-Hax, 60-Hax), 7.63 ꢀs, 4H,
13
50
aromatic protons) ppm; C 0NMR ꢀC6D6, ꢂ, 100 MHz): 20.31 ꢀC5, C ), 27.46 ꢀ2-CH3-eq, 20-CH3-
0
0
eq), 55.62 ꢀC4, C4 , C6, C6 ), 95.23 ꢀC2, C2 ), 122.20 ꢀtertiary aromatic carbon atoms), 136.22
ꢀquaternary aromatic carbon atoms) ppm.
1,4-Bis-ꢀ2,5,5-trimethyl-1,3-dioxan-2-yl)-benzene ꢀ2; C20H30O4)
Yield: 53%; white crystals; m.p.: 204±205ꢀC; 1H NMR ꢀC6D6, ꢂ, 400 MHz): 0.14 ꢀs, 6H, 5-CH3-eq,
50-CH3-eq), 1.21 ꢀs, 6H, 5-CH3-ax, 50-CH3-ax), 1.69 ꢀs, 6H, 2-CH3-eq, 20-CH3-eq), 3.28 ꢀd, 4H,
J ˆ 10.5 Hz, 4-Heq, 40-Heq, 6-Heq, 60-Heq), 3.42 ꢀd, 4H, J ˆ 10.5 Hz, 4-Hax, 40-Hax, 6-Hax, 60-Hax),
13
7.65 ꢀs, 4H, aromatic protons) ppm; C NMR ꢀC6D6, ꢂ, 100 MHz): 21.17 ꢀ5-CH3-eq, 50-CH3-eq),
50
40
60
22.71 ꢀ5-CH3-ax, 50-CH3-ax), 29.58 ꢀC5, C ) 32.21 ꢀ2-CH3-eq, 20-CH3-eq), 71.38 ꢀC4, C , C6, C ),
0
100.17 ꢀC2, C2 ), 127.26 ꢀtertiary aromatic carbon atoms), 141.33 ꢀquaternary aromatic carbon
atoms) ppm.

Synthesis and Stereochemistry of 1,3-Dioxane Derivatives
639
1,4-Bis-ꢀ2-methyl-5,5-diethyloxycarbonyl-1,3-dioxan-2-yl)-benzene ꢀ3; C28H38O12)
Yield: 44%; white crystals; m.p.: 155±156ꢀC; 1H NMR ꢀC6D6, ꢂ, 400 MHz): 0.69 ꢀt, 6H, J ˆ 7.1 Hz,
5-COO±CH2±CH3-eq, 50-COO±CH2±CH3-eq), 1.02 ꢀt, 6H, J ˆ 7.1 Hz, 5-COO±CH2±CH3-ax, 50-
COO±CH2±CH3-ax), 1.60 ꢀs, 6H, 2-CH3-eq, 20-CH3-eq), 3.62 ꢀq, 4H, J ˆ 7.1 Hz, 5-COO±CH2±CH3-
eq, 50-COO±CH2±CH3-eq), 4.12 ꢀq, 4H, J ˆ 7.1 Hz, 5-COO±CH2±CH3-ax, 50-COO±CH2±CH3-ax),
4.20 ꢀd, 4H, J ˆ 11.5 Hz, 4-Hax, 40-Hax, 6-Hax, 60-Hax), 4.84 ꢀd, 4H, J ˆ 11.5 Hz, 4-Heq, 40-Heq, 6-Heq,
60-Heq), 7.51 ꢀs, 4H, aromatic protons) ppm; 13C NMR ꢀC6D6, ꢂ, 100 MHz): 8.14 ꢀ5-COO±CH2±CH3-
eq, 50-COO±CH2±CH3-eq), 8.55 ꢀ5-COO±CH2±CH3-ax, 50-COO±CH2±CH3-ax), 26.14 ꢀ2-CH3-eq,
50
20-CH3-eq), 48.26 ꢀC5, C ), 56.03 ꢀ5-COO±CH2±CH3-eq, 50-COO±CH2±CH3-eq), 56.35 ꢀ5-COO±
40
60
20
CH2±CH3-ax, 50-COO±CH2±CH3-ax), 58.60 ꢀC4, C , C6, C ), 95.61 ꢀC2, C ), 121.45 ꢀtertiary
aromatic carbon atoms), 135.02 ꢀquaternary aromatic carbon atoms), 161.49 ꢀ5-COO±CH2±CH3-eq,
50-COO±CH2±CH3-eq), 162.52 ꢀ5-COO±CH2±CH3-ax, 50-COO±CH2±CH3-ax) ppm.
1,4-Bis-ꢀ2,5-dimethyl-1,3-dioxan-2-yl)-benzene ꢀ4; C18H26O4)
Yield: 48%; white crystals; m.p.: 200±201ꢀC; 1H NMR ꢀC6D6, ꢂ, 400 MHz): 0.01 ꢀd, 6H, J ˆ 6.8 Hz,
5-CH3-eq, 50-CH3-eq), 1.71 ꢀs, 6H, 2-CH3-eq, 20-CH3-eq), 1.98 ꢀm, overlapped ttq, 2H, J ˆ 6.8,
J0 ˆ 4.6 Hz, 5-Hax, 50-Hax), 3.27 ꢀt, overlapped dd, 4H, J ˆ J0 ˆ 11.4 Hz, 4-Hax, 40-Hax, 6-Hax, 60-Hax),
3.63 ꢀdd, 4H, J ˆ 11.4, J00 ˆ 4.6 Hz, 4-Heq, 40-Heq, 6-Heq, 60-Heq), 7.65 ꢀs, 4H, aromatic protons) ppm;
50
13C NMR ꢀC6D6, ꢂ, 100 MHz):011.63 ꢀ5-CH3-eq, 50-CH3-eq), 29.23 ꢀC5, C ), 32.73 ꢀ2-CH3-eq, 20-
0
0
CH3-eq), 67.40 ꢀC4, C4 , C6, C6 ), 100.11 ꢀC2, C2 ), 127.58 ꢀtertiary aromatic carbon atoms), 141.41
ꢀquaternary aromatic carbon atoms) ppm.
1,4-Bis-ꢀ2-methyl-5-phenyl-1,3-dioxan-2-yl)-benzene ꢀ5; C28H30O4)
Yield: 51%; white crystals; m.p.: 223±224ꢀC; 1H NMR ꢀCDCl3, ꢂ, 400 MHz): 1.61 ꢀs, 6H, 2-CH3-eq,
20-CH3-eq), 3.31 ꢀheptet, overlapped tt, 2H, J ˆ 11.6, J0 ˆ 5.7 Hz, 5-Hax, 50-Hax), 3.86 ꢀt, overlapped
dd, 4H, J ˆ J0 ˆ 11.6 Hz, 4-Hax, 40-Hax, 6-Hax, 60-Hax), 3.99 ꢀdd, 4H, J ˆ 11.6, J00 ˆ 5.7 Hz, 4-Heq,
40-Heq, 6-Heq, 60-Heq), 6.99 ꢀm, 4H, 5-C6H5, 50-C6H5), 7.20 ꢀm, 6H, 5-C6H5, 50-C6H5), 7.52 ꢀs,
4H,±C6H4±, aromatic protons) ppm; 13C NMR ꢀCDCl3, ꢂ, 100 MHz): 32.32, ꢀ2-CH3-eq, 20-CH3-eq),
0
50
40
60
40.80 ꢀC5, C ) 66.33 ꢀC4, C , C6, C ), 100.37 ꢀC2, C2 ), 127.20, 127.34, 127.41 ꢀ5-C6H5, 50-C6H5,
tertiary aromatic carbon atoms), 128.57 ꢀ±C6H4±, tertiary aromatic carbon atoms), 138.06 ꢀ5-C6H5,
quaternary aromatic carbon atoms), 140.20, ꢀ±C6H4±, quaternary aromatic carbon atoms) ppm.
1,4-Bis-ꢀ5-ethyl-2,5-dimethyl-1,3-dioxan-2-yl)-benzene ꢀ6; C22H34O4)
Yield: 57%; white crystals; m.p.: 183±186ꢀC; 1H NMR ꢀC6D6, ꢂ, 400 MHz), ꢀmixture of three
diastereoisomers): 0.09, 0.10 ꢀs, 6H, 5-CH3-eq, 50-CH3-eq; rings A), 0.42 ꢀt, 6H, J ˆ 6.6 Hz, 5-CH2±
CH3-eq, 50-CH2±CH3-eq; rings B), 0.50 ꢀq, 4H, J ˆ 6.6 Hz, 5-CH2±CH3-eq, 50-CH2±CH3-eq; rings
B), 0.83 ꢀt, 6H, J ˆ 7.5 Hz, 5-CH2±CH3-ax, 50-CH2±CH3-ax; rings A), 1.25 ꢀs, 6H, 5-CH3-ax, 50-
CH3-ax; rings B), 1.72, 1.725, 1.75, 1.755 ꢀs, 6H, 2-CH3-eq, 20-CH3-eq; rings A and B), 1.81 ꢀq, 4H,
J ˆ 7.5 Hz, 5-CH2±CH3-ax, 50-CH2±CH3-ax; rings A), 3.39, 3.46 ꢀd, 4H, J ˆ 11.0 Hz, 4-Hax, 40-Hax,
6-Hax, 60-Hax; rings A and B), 3.42, 3.47 ꢀd, 4H, J ˆ 11.0 Hz, 4-Heq, 40-Heq, 6-Heq, 60-Heq; rings A
and B), 7.71 ꢀs, 4H, aromatic protons) ppm; 13C NMR ꢀC6D6, ꢂ, 100 MHz): 1.28 ꢀ5-CH2±CH3-eq, 50-
CH2±CH3-eq; rings B), 2.63 ꢀ5-CH2±CH3-ax, 50-CH2±CH3-ax; rings A), 12.36 ꢀ5-CH3-eq, 50-CH3-
eq; rings A), 13.90 ꢀ5-CH3-ax, 50-CH3-ax; rings B), 21.03 ꢀ5-CH2±CH3-eq, 50-CH2±CH3-eq; rings
B), 22.89 ꢀ5-CH2±CH3-ax, 50-CH2±CH3-ax; rings A), 27.03 ꢀ2-CH3-eq, 20-CH3-eq; rings A), 64.28,
0
0
0
65.52 ꢀC4, C4 , C6, C6 ; rings A and B), 95.07 ꢀC2, C2 ; rings A and B), 122.13 ꢀtertiary aromatic
carbon atoms), 136.28 ꢀquaternary aromatic carbon atoms) ppm.

640
I. Grosu et al.
1,4-Bis-ꢀ5-hydroxymethyl-2,5-dimethyl-1,3-dioxan-2-yl)-benzene ꢀ7; C20H30O6)
1
Yield: 60%; white crystals; m.p.: 213±218ꢀC; H NMR ꢀCD3OD, ꢂ, 400 MHz), ꢀmixture of two
diastereoisomers): 0.60 ꢀs, 6H, 5-CH3-eq, 50-CH3-eq; rings A), 1.24 ꢀs, 6H, 5-CH3-ax, 50-CH3-ax;
rings B), 1.51, 1.60 ꢀs, 6H, 2-CH3-eq, 20-CH3-eq; rings B), 3.34 ꢀd, 4H, J ˆ 5.7 Hz, 5-CH2±OH-eq,
50-CH2±OH-eq; rings B), 3.48 ꢀd, 4H, J ˆ 11.2 Hz, 4-Hax, 40-Hax, 6-Hax, 60-Hax; rings A), 3.59 ꢀd,
4H, J ˆ 11.0 Hz, 4-Hax, 40-Hax, 6-Hax, 60-Hax; rings B), 3.69 ꢀd, 4H, J ˆ 11.2 Hz, 4-Heq, 40-Heq, 6-Heq,
60-Heq; rings A), 3.70 ꢀd, 4H, J ˆ 11.0 Hz, 4-Heq, 40-Heq, 6-Heq, 60-Heq; rings B), 3.91 ꢀd, 4H,
J ˆ 5.7 Hz, 5-CH2±OH-ax, 50-CH2±OH-ax; rings A), 7.35 ꢀs, 4H, aromatic protons) ppm; 13C NMR
ꢀCD3OD, ꢂ, 100 MHz): 17.05 ꢀ5-CH3-eq, 50-CH3-eq; rings A), 32.19 ꢀ2-CH3-eq, 20-CH3-eq; rings A
and B), 65.76 ꢀ5-CH2±OH-eq, 50-CH2±OH-eq; rings B), 67.040 ꢀ5-CH2±OH-ax, 50-CH2±OH-ax;
0
0
rings A), 67.43 ꢀC4, C4 , C6, C6 ; rings A and B), 95.07 ꢀC2, C2 ; rings A and B), 126.76, 126.98
ꢀtertiary aromatic carbon atoms) ppm.
2-Methyl-2-ꢀp-acetylphenyl)-5,5-diethyloxycarbonyl-1,3-dioxane ꢀ8; C19H24O7)
1
Yield: 11%; white crystals; m.p.: 73±74ꢀC; H NMR ꢀC6D6, ꢂ, 400 MHz): 0.69 ꢀt, 3H, J ˆ 7.1 Hz,
5-COO±CH2±CH3-eq), 0.99 ꢀt, 3H, J ˆ 7.1 Hz, 5-COO±CH2±CH3-ax), 1.55 ꢀs, 3H, 2-CH3-eq), 2.10
ꢀs, 3H, 2-C6H4±CO±CH3), 3.67 ꢀq, 2H, J ˆ 7.1 Hz, 5-COO±CH2±CH3-eq), 4.08 ꢀd, 2H, J ˆ 10.9 Hz,
4-Hax, 6-Hax), 4.11 ꢀq, 2H, J ˆ 7.1 Hz, 5-COO±CH2±CH3-ax), 4.80 ꢀd, 2H, J ˆ 10.9 Hz, 4-Heq, 6-
Heq), 7.72 ꢀd, 2H, J ˆ 6.6 Hz, 30-H, 50-H, aromatic protons), 7.34 ꢀd, 2H, J ˆ 6.6 Hz, 20-H, 60-H,
aromatic protons) ppm; 13C NMR ꢀC6D6, ꢂ, 100 MHz): 13.36 ꢀ5-COO±CH2±CH3-eq), 13.70
ꢀ5-COO±CH2±CH3-ax), 25.86 ꢀ2-CH3-eq), 31.06 ꢀ2-C6H4±CO±CH3), 53.35 ꢀC5), 61.380 ꢀ5-COO±
0
CH2±CH3-eq), 61.57 ꢀ5-COO±CH2±CH3-ax), 63.91 ꢀC4, C6), 100.63 ꢀC2), 126.58 ꢀC2 , C6 , aromatic
0
0
0
carbon atoms), 128.89 ꢀC3 , C5 , aromatic carbon atoms), 137.00 ꢀC1 , aromatic carbon atom), 144.78
0
ꢀC4 , aromatic carbon atom), 166.77 ꢀ5-COO±CH2±CH3-eq), 167.57 ꢀ5-COO±CH2±CH3-ax), 195.67
ꢀ2-C6H4±CO±CH3) ppm.
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Received September 12,2001. Accepted ꢀrevised) November 5,2001