Weak attractive interactions between methylthio groups and electron-deficient alkenes in peri-naphthalenes: A competition with conjugative effects

Article abstract of DOI:10.1002/chem.200600068

The solid-state conformations of five peri-disubstituted naphthalenes bearing a methylthio group and an electron-deficient alkene indicate a weak attractive interaction between the functional groups in four cases in which out-of-plane displacements lead to a common orientation of the MeS...sp²-C vector to the alkene bond. In some cases the interaction is not strong enough to outweigh the tenden cy of the alkene to conjugate with the aromatic ring, and in one case this optimisation of conjugation alone controls the molecular conformation. The methylthio group lies close to the aromatic plane in all but one example for which the plane of the sulfide group is presented to the alkene.

Full text of DOI:10.1002/chem.200600068

DOI: 10.1002/chem.200600068
Weak Attractive Interactions between Methylthio Groups and Electron-
Deficient Alkenes in peri-Naphthalenes: A Competition with Conjugative
Effects
Jane OꢀLeary and John D. Wallis*[a]
Abstract: The solid-state conforma-
tions of five peri-disubstituted naphtha-
lenes bearing a methylthio group and
an electron-deficient alkene indicate a
weak attractive interaction between
the functional groups in four cases in
which out-of-plane displacements lead
MeS···sp2-C vector to the alkene bond.
In some cases the interaction is not
strong enough to outweigh the tenden-
cy of the alkene to conjugate with the
aromatic ring, and in one case this opti-
misation of conjugation alone controls
the molecular conformation. The meth-
ylthio group lies close to the aromatic
plane in all but one example for which
the plane of the sulfide group is pre-
sented to the alkene.
Keywords: conjugation
· sulfur ·
through-space interactions · X-ray
diffraction
to
a
common orientation of the
Introduction
bonds.[8–11] For the 1,5 interaction with an electron-deficient
alkene there is substantial variation in the inter-group sepa-
ration when the nucleophilic group is dimethylamino de-
pending on the particular alkene, varying from 2.749(5) Š in
8 for a -CH=CHBr group,[6] to 2.6417(16) Š in 9 for a -CH=
Bürgi, Dunitz and Schefter interpreted the short intramolec-
ular interactions between amino groups and carbonyl groups
in the solid-state structures of a group of alkaloids as repre-
senting partially completed chemical reactions,[1] which was
consistent with the unexpected chemical properties observed
for these compounds.[2] Kirby and co-workers have recently
shown that in some of these cases the interaction observed
in the crystalline state may be promoted by intermolecular
hydrogen bonding to the carbonyl oxygen atom.[3] Subse-
quently the peri-naphthalene molecular skeleton (1) has
provided a very useful system for investigating such electro-
phile/nucleophile interactions, since the peri-carbon atoms
of the naphthalene framework are just 2.5 Š apart, well
within the sum of van der Waals radii for most pairs of
atoms. Dunitz and co-workers first used this system for in-
vestigating the interactions of dimethylamino or methoxy
groups with various carbonyl functionalities[4] for example,
in 2 and 6, and with nitriles[5] for example, in 7, and others
have extended this to interactions with an aldehyde[6] as in 3
and with various carboxamides as in 4 and 5.[7,8]
CHNO2 group,[8] to 2.531(2) Š in 10 for
a -CH=
C(CN)CO2Et group[11] to 2.413(2) Š in 11 for a -CH=
C(CN)2 group[9] and culminating in the near complete for-
mation of
a
single bond in zwitterions 12[9] (C N
À
[8]
À
1.651(3) Š) and 13 (C N 1.6397(17) Š). In contrast, for in-
teractions where the methoxy group is the electron-rich
centre there is very little variation in the separation between
groups (2.53–2.67 Š) and even for interaction with a carbo-
cation in 14 the MeO···C+ separations are 2.43(1) and
2.45(1) Š long.[12] It is noteworthy that in most cases in the
dimethylamino and methoxy series, the “attacked” sp2-C
atom does show a small pyramidality with the carbon atom
displaced towards the other peri-located group. Charge den-
sity studies provide more insight into these interactions. For
both 4 and 11, containing the interactions of dimethylamino
groups with a carboxamide[13] or an alkene dinitrile,[14]
a
(3,À1) critical point has been observed between the groups
with electron densities at this point of 0.11(1) and
0.19(2) eŠÀ3, respectively. No such studies on the methoxy
series have yet been made. Recently we prepared a series of
sixbiphenyls containing 1,6 interactions between a dimethy-
lamino group and an aldehyde or an electron-deficient
alkene.[15] These all show short contacts between groups, but
either at about 2.9–3.0 Š, as in 15–17, or by bond formation
to give a zwitterion such as 18. In the uncyclised materials
We have broadened these studies to the interactions of di-
methylamino or methoxy groups with C=C double
[a] Dr. J. OꢀLeary, Prof. J. D. Wallis
School of Biomedical and Natural Sciences
Nottingham Trent University
Clifton Lane, Nottingham NG11 8NS (UK)
Fax: ( +44)115-848-6636
E-mail: john.wallis@ntu.ac.uk
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FULL PAPER
there is no pattern of pyramidalisation of the sp2-C atoms,
suggesting that these represent intermolecular interactions,
while the peri-naphthalene series is indeed probing covalent
bond formation. Peri-naphthalenes have also been utilised
in studying interactions of dimethylamino groups with sele-
nium or silicon centred groups,[16,17] probing the effect on re-
activity of hydrogen bonding to the nitrogen atom of an
amide,[18] and charge density analyses of the salts of proton
sponges to understand these particularly interesting hydro-
gen-bonded systems.[19]
We decided to extend these studies by using the methyl-
thio group as the nucleophilic group. The sulfur atom is
more nucleophilic than the oxygen atom, but it is a larger
atom. Furthermore, there is the issue of which lone pair on
sulfur is involved in the interaction and the asymmetric ef-
fective shape of the bonded sulfur atom.[20] Here we report
the structures of the five molecules 19–23 in which a methyl-
thio group lies peri to an electron-deficient alkene. Molecule
22, with just a trans-disubstituted alkene, differs from the
others since the alkene substituent cis to the naphthalene
ring is just a hydrogen atom, whereas the other molecules
have the larger carbon atom at that position (as carbonyl,
nitrile or methyl) which may have a role to play in control-
ling the orientation of the alkene by repulsion with the
ortho-hydrogen atom of the naphthalene system.
Discussion
The preparative route for the desired peri methylthio-naph-
thyl-alkenes (Scheme 1) depends on the peri-methylthioal-
dehyde 27, which was prepared in sixsteps from naphthalic
anhydride. Conversion of the latter to thiolactone 24 by
known procedures,[21,22] followed by ring opening and esteri-
fication gave the methyl ester 25. Reduction with diisobuty-
laluminium hydride (DIBAL) at low temperature gave only
the alcohol 26 which was converted to aldehyde 27 by
Swern oxidation. The target alkenes 19–23 were made from
the aldehyde by Knoevenagel condensations. Crystals were
grown by slow evaporation of solutions and most structures
were measured at 120 K (150 K for 20) using MoKa radia-
tion. The structures of 19–23 show MeS···sp2-C separations
in the range 2.787(2)–2.9226(14) Š, a range of orientations
for the alkene group lying at 36.4(3)–57.2(3)o to the neigh-
À
bouring aromatic bond C7 C8, and displacements of the
peri substituents to opposite sides of the naphthalene ring
which vary from small (<0.1 Š) to quite substantial (>
0.4 Š). The methylthio group lies close to the aromatic
plane in all cases apart from 21 where it lies nearer to per-
pendicular to the aromatic plane. The molecular structures
are illustrated in Figures 1–3 showing views perpendicular
and edge-on to the aromatic planes. Selected molecular ge-
ometry for 19–23 is given in Table 1 along with data for the
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J. D. Wallis and J. OꢀLeary
Scheme 1.
naphthalene-1-diazonium cation with
a peri-methylthio
group (34) and the atomic-labelling scheme.
Structures of compounds 19–23: Compound 19 has the
À
alkene group lying at 57.2(3)8 to the aromatic C7 C8 bond
so that it presents a face to the methylthio group, and the
MeS···sp2-C separation is 2.787(2) Š, the shortest in the
Figure 2. Views of molecules 19–20 and 22–23 edge-on to the aromatic
ring in order of decreasing angular rotation of the alkene out of the naph-
thalene plane and increasing displacements of the functional groups from
this plane.
Figure 1. Views of molecules 19–23 perpendicular to the aromatic ring.
Figure 3. View of molecule 21 edge-on to the aromatic ring.
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Interactions between Methylthio Groups and Electron-Deficient Alkenes
FULL PAPER
Table 1. Selected molecular geometry for compounds 19–23 and 34.[a]
S···C11 [Š][b]
a[8]
b [8]
g [8]
d [8]
e [8]
DC’ [Š]
19
20
21
22
23
2.787(2)
2.850(3)
2.9226(14)
2.8948(19)
2.8296(19)
121.37(19)
120.9(2)
117.04(11)
119.55(15)
120.10(15)
119.36(16)
119.73(19)
122.88(10)
120.51(13)
120.19(14)
124.8(2)
125.8(2)
124.78(12)
125.83(16)
125.29(17)
123.87(19)
123.5(2)
121.71(11)
122.98(16)
123.38(16)
115.93(19)
115.9(2)
117.94(12)
116.70(16)
117.24(18)
0.049(9)
0.037(11)
0.036(6)
0.014(8)
0.030(8)
34[32]
2.938(6)
118.9(3)
122.5(3)
127.7(3)
121.7(3)
112.4(3)
–
DC [Š][c]
T1 [8]
T2 [8]
q [8]
S···H11 [Š]
À
C11 C12 [Š]
DS [Š]
19
20
21
22
23
1.339(3)
1.338(4)
1.3489(18)
1.326(3)
1.332(3)
0.018(2)
0.120(3)
0.3397(14)
0.361(2)
0.1308(18)
À0.069(3)
À0.257(4)
À0.4532(18)
À0.297(3)
À0.1172(3)
5.6(2)
1.7(3)
109.15(12)
5.26(19)
7.94(18)
57.2(3)
48.5(4)
46.70(19)
36.4(3)
53.55(26)
114.61(14)
118.2(2)
115.85(8)
125.94(13)
115.59(13)
2.63(2)
2.58(2)
2.715(14)
2.49(2)
2.61(2)
34[32]
–
0.232(6)
À0.196(6)
65.4(3)
–
99.8(3)
–
[a] DC’: deviation of C11 from plane [C8, C12, H11]; DS and DC: deviation of S and C11 from the plane defined by the ten ring carbon atoms; T1: tor-
À
sion C2-C1-S-C(H3); T2: torsion C7-C8-C11-C12; q: angle S···C11 C12. [b] S···N for 32. [c] DN for 32.
series. The methylthio group lies very close to the aromatic
plane, and is displaced slightly towards the alkene (by 1.08)
due to the steric interaction between the S-methyl group
and the ortho-hydrogen atom H2 of the naphthalene group
the ortho-hydrogen atom H7 (2.71(2) Š), which prevents
the alkene lying at an even lower angle to the aromatic
system. In contrast, in 19 which contains the bislactone ring,
the orientation of the alkene is not controlled by the corre-
sponding contact between a carbonyl carbon atom and the
ortho-hydrogen atom, which lie 3.07(3) Š apart—well out-
side of van der Waals contact.
The structure of compound 21 is distinctly different from
the other four structures. The methylthio group lies com-
pletely out of the aromatic plane; the torsion angle of the
(H2···C(H3): 2.48(3) Š; H2···H(CH2S-): 2.22(4) and
G
2.30(4) Š). The alkene group is displaced significantly away
from the methylthio group (by 4.08). The out of plane dis-
placements of the sulfur and carbon atoms attached to the
peri positions are the smallest in the series (DS: 0.018(3),
DC: À0.069(3) Š). The sp2-C atom is pyramidalised towards
the sulfur atom and shows the largest value in the series
(0.049(9) Š). The angle of approach of the sulfur atom to
the alkene bond is 114.61(14)o.
À
À
CH3 S bond with the aromatic C1 C2 bond is 109.15(12)8.
À
The alkenyl group lies at 46.70(19)8 to the aromatic C7 C8
bond (similar to 20), and the MeS···sp2-C separation is the
largest in the series at 2.9226(14) Š. Without a steric inter-
action with ortho-hydrogen atom H2, the methylthio group
is now displaced away from the alkene group by 2.98, and
the alkene is only displaced away from the methylthio group
by 1.98 compared to double that amount in 19 and 20. The
displacements of the peri-sulfur and -carbon atoms from the
aromatic plane have increased to 0.3397(14) and
À0.453(2) Š. This produces an angle of approach of the
sulfur atom to the alkene of 115.85(8)8, similar to that in 19
and 20. Thus, the increase in the MeS···sp2-C separation is a
consequence of increases in both the in-plane and out-of-
plane displacements of peri substituents. Nevertheless, the
Compared to 19, in molecule 20 the dicyanoethenyl group
À
is oriented at just 48.5(4)8 to the aromatic C7 C8 bond, that
is, about 98 less than for the substituted alkene in 19, and
the peri-sulfur and -carbon atoms are displaced further out
of the aromatic plane in opposite directions (DS: 0.120(3),
DC: À0.257(4) Š). The in-plane displacements of the peri
substituents are very similar to those in 19, but the exocyclic
angle between the two rings of the naphthalene system (g)
is widened by 1.08. The increase in the MeS···sp2-C distance
by 0.064 Š to 2.850(3) Š is mainly due to the larger out of
plane displacements. These act to produce an angle of ap-
proach of the sulfur atom to the alkene of 118.2(2)8. The de-
crease in the tilt of the alkenyl group relative to the aromat-
ic plane increases the conjugation with the aromatic system,
but there is a 1,6 contact between a cyano-carbon atom and
À
S CH3 bond lies alongside the alkene and is not directed to
the other side of the naphthalene plane, but there is only
one near van der Waals contact between them: C11···H-
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J. D. Wallis and J. OꢀLeary
A
peri-S and -C11 atoms in 21. However, the observed separa-
tion is only about 0.07 Š larger than that in 20 for which the
alkene adopts a similar orientation. This may be due to the
greater susceptibility of the lone pair perpendicular to the
sulfide plane to attack by electrophiles,[29] but ideally further
structures with out-of-plane methylthio groups are needed
for comparison. The adoption of this structure, rather than
one with the methylthio group lying in the aromatic plane,
may be a result of preferable packing effects. A search for
polymorphs, or structural measurements on different esters
would be instructive.
the S C bond to the aromatic ring with the change in tor-
sion about this bond.
The bonded sulfur atom is known to be asymmetric in
shape. For thiocarbonyl sulfur atoms Nybergꢀs estimation
from intermolecular S···S contacts suggest values of 1.6 and
2.0 Š for the minimum and maximum radii[23] corresponding
to the effective sizes in the thiocarbonyl plane and perpen-
dicular to it. From the CSD[24] the shortest S···S contacts be-
tween sulfur atoms in sp3-C–S–sp3-C sulfide groups are
about 3.25 Š
Compound 22 is different from the other four molecules
in that it has a terminal hydrogen atom on the alkene cis to
the naphthalene ring. Thus, whereas in compounds 20 and
21 the minimum angular orientation between the aromatic
system and the alkene is controlled by a sp-C···H steric in-
teraction, in the nitroethenyl compound 22 it is controlled
by a H···H interaction. In the structures of 20 and 21 the al-
kenyl group lies at 48.5(4) and 46.70(19)8 to the aromatic
Figure 4. Orientations of sulfide groups for a) minimum S···S van der
Waals contact, b) maximum S···S van der Waals contact.
plane, and the corresponding H7···C
A
while for face-to-face contacts (Figure 4b) the shortest con-
tacts are about 3.75 Š corresponding to effective radii of
about 1.62 and 1.87 Š. For our intramolecular case we can
refer to the peri-dithionaphthalene derivatives 28–30. Com-
2.71(2) and 2.648(15) Š, which are close to the van der
Waals separations for a hydrogen atom and a carbon atom,
thus strongly suggesting that these structures are exhibiting
the minimum possible angular orientation of the alkene to
the aromatic ring. In contrast, in the nitroethenyl derivative
22 the alkenyl group lies at the lowest angle to the aromatic
plane in this series, 36.4(3)o, (Figure 2) with a H7···H12 sepa-
ration between the alkene and the aromatic ring of just
2.34(3) Š. In this structure the methylthio group lies close
to the aromatic plane, and the peri groups are strongly dis-
placed to opposite sides of the naphthalene ring to increase
the separation between the sulfur atom and the alkenyl hy-
drogen atom H11 to 2.49(2) Š—the shortest such separation
observed in this series. Indeed, both this S···H11 contact and
the H7···H12 contact are controlling the angular position of
the alkenyl group. The out-of-plane displacements of the
peri substituents (DS: 0.361(2), DC11: À0.297(3) Š) are only
exceeded by those of the cyano ester 21 in this series. The
MeS···sp2-C separation of 2.8948(19) Š is also one of the
[26]
À
pound 28, with face-to-face disulfide contacts, shows a S S
separation of 3.182(1) Š.[27] The two molecules of compound
30, in which the sulfide groups are not too far from both
being in the aromatic plane and thus edge on to each other,
[28]
À
show S S separations of 2.918(2) and 2.934(2) Š,
and
other intramolecular contacts between the shorter radii for
sulfide and thiocarbonyl sulfur atoms have been observed at
about 2.9 Š.[20] peri-Naphthalene 29 with an edge-to-face
contact between the sulfide groups has an intermediate S···S
separation (3.005(1) Š).[27] This suggests that in the strained
situation of the peri-naphthalenes the effective radius of the
bonded sulfide sulfur atom is about 0.13 Š larger perpendic-
ular to the sulfide plane than in this plane, though our esti-
mates are based, of course, only on a small amount of data.
This factor will contribute to the larger separation of the
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Interactions between Methylthio Groups and Electron-Deficient Alkenes
FULL PAPER
longest in the series. The in-plane displacements of the peri
groups are similar to those in 19 and 20, but the methylthio
group is displaced slightly away from the alkene (by 0.58, cf.
0.6–1.08 towards the alkene in 19 and 20), and the alkene is
displaced slightly less away from the methylthio group (by
3.28, cf. 3.6–4.08 in 19 and 20). Thus, the molecule has prefer-
red to optimise the conjugation of the alkene with the aro-
matic ring at the expense of an interaction between the peri
groups. It is also notable that the barely significant pyramid-
alisation of C11 (0.014(8) Š) and the angle of approach of
the sulfur to the alkene bond (125.94(13)8) are totally out of
step with the values for the other four compounds
(0.030(8)–0.049(9) Š, 114.61(14)–118.2(2)8). The orientation
of the alkene mitigates strongly against an interaction be-
tween the peri groups.
actions involving dimethylamino groups, the bislactone
group is the most reactive, leading to bond formation be-
tween the groups in zwitterion 12. Furthermore, the alkene
À
holds an orientation of 50—608 to the aromatic C7 C8 bond
for the shorter interactions involving dimethylamino groups
(2.413–2.642 Š in 9–11) and only defers to optimisation of
conjugation with the aromatic ring for Me2N···sp2-C separa-
tions greater than about. 2.7 Š for example, in the (E)-2-
bromoethenyl derivative 8. For comparison, in the dimethyl-
amino derivative 9, the nitroethenyl group lies at 51.38(6)8
to the aromatic system, whereas in the methylthio analogue
22 it lies at 30.33(8)8. Thus, the interactions of electron-defi-
cient alkenes with methylthio groups are clearly weaker
than those with dimethylamino groups, and only for the bis-
lactone 19 does the interaction appear to control the con-
formation of the molecule. For the methoxynaphthalenes 31
and 32, the analogues of 19 and 20 containing the bis-
Compound 23 differs from compound 22 in that geminal
to the nitro group it carries a methyl group whose steric in-
teraction with ortho-hydrogen atom H7 forces the alkene
group to lie much further out of the aromatic plane making
A
an alkene orientation comparable to its dimethylamino and
À
À
an angle of 53.55(26)8 with the C7 C8 bond. The contact
methylthio analogues (55.98 to the C7 C8 bond), whereas
between the methyl group and hydrogen atom (C14···H7
2.855(18), H14C···H7 2.44(3) Š) is close to van der Waals
separation, but longer than in 20 and 21 where the corre-
sponding contact is with a cyano-carbon atom rather than a
methyl group. The molecular conformation adopted is inter-
mediate between those of structures 19 and 20. Thus, there
is an in-plane methylthio group, the MeS···C11 distance is
2.8296(19) Š and the sum of the out-of-plane displacements
of the peri-substituent atoms (0.248 Š) is intermediate be-
tween those for 19 (0.087 Š) and 20 (0.377 Š). The degree
of pyramidalisation of carbon C11 is similar to that of 19
and 20 as is the angle of approach of sulfur to the alkene
(115.59(13)8). The methylthio group is displaced one degree
less towards the alkene which is itself displaced by one
degree less away from the methylthio group compared to 19
and 20.
the latter adopts a smaller torsional rotation of the alkene
(46.28), which is limited by a (Nꢀ)C···H11 steric interaction
with the ortho-hydrogen atom (2.625(16) Š). The out-of-
plane displacements in dinitrile 32: (O À0.024(1), C11
0.154(1) Š) are also distinctly larger than for bis(lactone) 31
A
(O À0.018(2), C11 0.078(2) Š). Thus, these two structures
mirror the results from the methylthio series.
The effective radii of the sulfur and carbon atoms in a
peri-naphthalene containing an in-plane methylthio group
may be estimated from the separation between like groups
in the symmetrical peri-naphthalenes 30 (2.918(2) Š) and 33
(2.799(2) Š).[30] Thus, a purely steric MeS···sp2-C interaction
could be estimated to be about 2.86 Š. Only the separation
in compound 19 is significantly shorter than this. When the
face of the sulfide group is presented to the alkene, the
MeS···sp2-C steric interaction would be estimated at 2.99 Š
from symmetrical structures 28 and 33. Only compound 21
shows such an orientation and the MeS···sp2-C separation is
notably shorter at 2.9226(14) Š. In ortho-unsubstituted
methylthiobenzenes the methylthio group usually lies close
to the benzene plane,[24] but there are a few examples with
torsional displacements of up to 428.[31] The only other peri-
naphthalene containing a methylthio group is the diazonium
salt 34[32] (Table 1), in which the methylthio group is rotated
65.48 out of the naphthalene plane and the sulfur atom lies
at 2.938(5 Š from the a-nitrogen atom, just slightly longer
than the MeS···sp2-C separation in compound 21 for which
the methylthio group lies well out of the aromatic plane.
Glaser and co-workers have demonstrated that the electron
density in an aryldiazonium group is concentrated at the a-
nitrogen atom which may account for the long MeS···a-N
separation.[33]
The three compounds 20–22 adopt conformations in
which the alkene substituent has optimized its conjugation
with the naphthalene ring, the limiting factor being a steric
interaction with the ortho-hydrogen atom H7 (for 20 and
21) and also with the peri-sulfur atom for 22. However, in
compounds 19 and 23 the alkene lies at larger angles (54–
À
578) to the aromatic C7 C8 bond. The bislactone 19, which
shows the shortest MeS···sp2-C separation (2.787(2) Š) in
the series, whose conformation is not determined by a steric
interaction, and which shows the largest pyramidality at the
carbon, provides the strongest evidence for an attractive in-
teraction between the methylthio group and the electron-de-
ficient alkene group. Compound 23, in which the alkene is
forced by a steric interaction to adopt a similar conforma-
tion to that of 19, shows a slightly longer MeS···sp2-C inter-
action (by 0.043 Š). Most notable, however, are the out-of-
plane distortions which maintain a common angle of ap-
proach of the sulfur atom to the alkene in all compounds
but 22, indicative of an interaction. All molecules but 22
show a significant pyramidalisation of the sp2-C atom to-
wards the sulfur atom. In the corresponding series of inter-
The optimisation of crystal packing can also influence the
precise conformation adopted by a particular molecule, and
can affect the separation between adjacent groups. Hence,
we should not read too much into the precise separations
between the functional groups, since in the cases studied
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J. D. Wallis and J. OꢀLeary
the reaction was complete after 40 min. The mixture was poured on to
water (20 mL) and extracted with CH2Cl2. The organic extracts were
washed with water and brine, dried (MgSO4) and evaporated to yield a
yellow oil, which was purified by flash chromatography on silica gel (cy-
clohexane/diethyl ether, 3:1) to yield the product 25 as a colourless oil
(0.13 g, 74%); 1H NMR (CDCl3): d=7.88 (dd, J=8.2, 1.2 Hz, 1H; Ar-
H1), 7.77–7.73 (m, 2H; Ar-H2), 7.60 (d, J=6.9 Hz, 1H; Ar-H1), 7.48–7.41
(m, 2H; Ar-H2), 3.96 (s, 3H; OCH3), 2.41 ppm (s, 3H; SCH3); 13C NMR
(CDCl3): d=171.8 (C=O), 134.6, 134.6, 132.7, 131.6, 131.3, 130.5, 128.3,
127.7, 126.3, 124.9 (Ar-C10), 52.7 (OCH3), 21.5 ppm (SCH3); FTIR (liquid
film): n˜ =2922, 2848, 1724, 1498, 1431, 1276, 1200, 1147, 1064, 1019, 963,
826, 769 cmÀ1; HRMS (ES): m/z: calcd for C13H12O2S + NH4; found:
250.0909 [M+NH4]+.
here the interaction between them is not generally strong
enough to dominate the effects of crystal packing, unlike in
the corresponding dimethylamino series. However, it is the
patterns in the conformations which provide the lead to our
conclusions, most notably the constant orientation of sulfur
relative to the alkene bond, and comparisons with the corre-
sponding dimethylamino series. In addition, the consistent
observation of small pyramidalisations of the sp2-C atom
suggests a weak interaction between methylthio and alkene
groups. Nevertheless, one should not forget that the calcula-
tion of these pyramidalities needs some caution since they
depend on the refined position of a hydrogen atom, which
are not as securely located as the heavier atoms. However,
the observation of significant pyramidalities in those com-
pounds with a constant orientation of the sulfur atom to the
alkene is consistent with a weak interaction at work be-
tween the methylthio and alkene groups.
1-Hydroxymethyl-8-methylthionaphthalene (26): Diisobutylaluminium
hydride (1.5m solution in toluene, 62 mL, 92 mmol) was added at À788C
to
a stirred solution of methyl 8-methylthionaphthoate (25; 9.75 g,
42 mmol) in dry toluene (100 mL), under nitrogen. The mixture was stir-
red at this temperature for 1 h, allowed to warm to room temperature
and stirred for 30 min. The mixture was quenched at À788C with 1m HCl
(62 mL) and warmed to room temperature. The mixture was transferred
to a separating funnel and washed with 1m HCl. The organic solution
was dried (MgSO4) and evaporated. The crude oil was purified by flash
chromatography on silica gel (cyclohexane/diethyl ether, 3:1) to yield a
yellow solid, which was recrystallised from hexane to yield the product
26 as a white solid (6.6 g, 77%), m.p. 52–558C; 1H NMR (CDCl3): d=
7.73 (d, J=7.9 Hz, 1H; Ar-H1), 7.65 (dd, J=7.9, 1.5 Hz, 1H; Ar-H1), 7.50
(dd, J=6.9, 1.5 Hz, 1H; Ar-H1), 7.44 (dd, J=7.5, 1.5 Hz, 1H; Ar-H1),
7.38–7.31 (m, 2H; Ar-H2), 5.21 (br. s, 2H; CH2OH), 3.45 (br. s, 1H;
OH), 2.51 ppm (s, 3H; SCH3); 13C NMR (CDCl3): d=137.2, 135.7, 133.9,
131.1, 130.3, 130.1, 128.1, 127.7, 125.7, 125.1 (Ar-C10), 65.9 (CH2OH),
19.4 ppm (SCH3); FTIR (KBr): n˜ =3330, 2918, 1654, 1566, 1498, 1425,
1358, 1318, 1206, 1169, 1092, 1056, 995, 803, 760 cmÀ1; HRMS (ES): calcd
for C12H12OS + NH4: 222.0953; found: 222.0945 [M+NH4]+.
Conclusions
A MeS···sp2-C attractive interaction controls the solid-state
structure of compound 19, whereas in compounds 20, 21 and
23 the conformation is determined both by this interaction,
and optimisation of conjugation between the alkene and the
aromatic system subject to steric interactions. In all four
cases the orientation of the MeS···C vector lies at 114—1188
to the alkene and the attacked carbon atom is slightly pyra-
midalised. The conformation of compound 22 is determined
solely by optimisation of conjugation in direct contrast to
the dimethylamino analogue, indicating the weaker nature
of the MeS···sp2-C interaction. These molecules, in which
conjugation, steric effects and attractive interactions be-
tween functional groups are competing, will be of particular
interest for charge density studies which are now being used
to characterise weaker bonding interactions. Since sulfides
prefer to attack electrophiles perpendicular to the plane of
the sulfide group, it will be interesting to study compounds
where the face of the sulfide is forced to be disposed to the
alkene as in 21.
Preparation of 8-methylthio-1-naphthaldehyde (27): A solution of dry
DMSO (2.75 g, 35.5 mmol) in CH2Cl2 (10 mL) was added at À788C to a
stirred solution of oxalyl chloride (1.55 mL, 17.8 mmol) in CH2Cl2
(100 mL) under nitrogen. After 2 min a solution of the alcohol 26 (3.3 g,
16 mmol) in CH2Cl2 (15 mL) was added. After 20 min Et3N (11.5 mL)
was added and the mixture stirred for a further 5 min. The mixture was
transferred to a separating funnel and the aqueous phase extracted with
CH2Cl2. The combined organic extracts were sequentially washed with
2m HCl, saturated NaHCO3 and brine, dried (MgSO4) and evaporated to
yield the product 27 as a brown oil (2.94 g, 90%), which solidified on
standing, m.p. 40–438C (lit. [21] 43–448C); 1H NMR (CDCl3): d=11.10
(s, 1H; CHO), 7.86 (dd, J=8.2, 1.2 Hz, 1H; Ar-H1), 7.72–7.64 (m, 3H;
Ar-H3), 7.45–7.33 (m, 2H; Ar-H2), 2.34 ppm (s, 3H; SCH3); 13C NMR
(CDCl3): d=191.9 (C=O), 136.8, 134.2, 133.3, 132.8, 131.6, 131.1, 128.1,
128.0, 126.0, 125.1 (Ar-C10), 20.3 ppm (SCH3); FTIR (KBr): n˜ =1677,
1498, 829, 798, 761 cmÀ1
.
2,2-Dimethyl-5-(8’-methylthionaphthyl-1’-methylidene)-1,3-dioxane-4,6-
dione (19): Meldrumꢀs acid (0.54 g, 3.75 mmol) and ethylenediammonium
diacetate (0.05 g, 0.3 mmol) were added to a stirred solution of the alde-
hyde 27 (0.5 g, 2.5 mmol) in dry methanol (7 mL) under nitrogen. After
stirring for 1 h at room temperature a precipitate was obtained, which
was collected by vacuum filtration and washed with methanol to yield
the product 19 as a yellow solid (0.34 g). The filtrate was evaporated and
the residue purified by flash chromatography on silica gel (cyclohexane/
diethyl ether, 1:1) to yield further product 19 as a yellow solid (0.16 g),
total yield (0.50 g, 61%), m.p. 136–1388C; 1H NMR (CDCl3): d=9.58 (s,
1H; =CH), 7.90 (d, J=8.2 Hz, 1H; Ar-H1), 7.87–7.81 (m, 2H; Ar-H2),
7.49–7.37 (m, 3H; Ar-H3), 2.36 (s, 3H; SCH3), 1.85 ppm (s, 6H; C-
Experimental Section
General comments: NMR spectra were measured at 258C on a JEOL
JNM-EX270 spectrometer at 270 MHz for 1H and at 67.8 MHz for 13C
using CDCl3 as solvent, and measured in ppm downfield from TMS,
unless otherwise stated. IR spectra were recorded on a PerkinElmer
Spectrum RX 1 FT-IR spectrometer and are reported in cmÀ1. UV/Vis
spectra were recorded on a Perkin–Elmer Lambda 25 instrument and are
reported in nm. Mass spectra were recorded at the EPSRC Mass Spec-
trometry Centre at Swansea University. X-ray diffraction datasets were
measured by the EPSRC National Crystallography Service at Southamp-
ton University. Flash chromatography was performed on 40–63 silica gel
(Merck).
AHCTREUNG
A
ACHTREUNG
Methyl 8-methylthionaphth-1-oate (25): Powdered KOH (0.5 g, 9 mmol)
was stirred in DMSO (2 mL) and after 5 min the thiolactone 24[20,21]
(0.14 g. 0.75 mmol) was added followed by MeI (0.2 mL, 3 mmol). The
resulting dark green mixture gradually lightened to a yellow colour and
(KBr): n˜ =1734, 1605, 1559, 1396, 1352, 1280, 1193, 1020, 926, 823,
762 cmÀ1; UV/Vis (methanol): lmax =225, 306, 324 nm; HRMS (EI): calcd
for C18H16O4S: 328.0769; found: 328.0777 [M]+.
7730
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7724 – 7732

Interactions between Methylthio Groups and Electron-Deficient Alkenes
FULL PAPER
1,1-Dicyano-2-(8’-methylthionaphth-1’-yl)ethene
(20):
Malononitrile
dine (2 drops) was added and the mixture stirred overnight. The metha-
nol was evaporated and the residue purified by flash chromatography on
silica gel (cyclohexane/diethyl ether, 5:1) to yield the product 22 as an
orange solid (0.032 g, 13%), m.p. 73–788C; 1H NMR (CDCl3): d=9.38
(d, J=13.1 Hz, 1H; 1-H), 7.92 (dd, J=7.4, 2.2 Hz, 1H; Ar-H1), 7.76 (dd,
J=8.2, 1.2 Hz, 1H; Ar-H1), 7.64 (dd, J=7.4, 1.2 Hz, 1H; Ar-H1), 7.50–
7.42 (m, 3H; Ar-H3), 7.30 (d, J=13.1 Hz, 1H; 2-H), 2.46 ppm (s, 3H;
SCH3); 13C NMR (CDCl3): d=143.1 (1-C), 135.2, 135.1 (Ar-C2), 132.3 (2-
(0.25 g, 3.75 mmol) and ethylenediammonium diacetate (0.05 g,
0.3 mmol) were added to a stirred solution of the aldehyde 27 (0.50 g,
2.5 mmol) in dry methanol (7 mL) under nitrogen. The mixture was stir-
red at room temperature overnight. The resulting precipitate was collect-
ed by vacuum filtration and washed with methanol to yield the product
as a yellow solid (0.06 g). The filtrate was evaporated and the residue pu-
rified by flash chromatography on silica gel (cyclohexane/diethyl ether,
5:1) to yield the product 20 as a yellow solid (0.40 g), total yield (0.46 g,
75%), m.p. 114–1168C; 1H NMR (CDCl3): d=9.27 (s, 1H; 2-H), 8.02 (d,
J=7.9 Hz, 1H; Ar-H1), 7.88–7.80 (m, 2H; Ar-H2), 7.67–7.49 (m, 3H; Ar-
H3), 2.43 ppm (s, 3H; SCH3); 13C NMR (CDCl3): d=164.9 (2-C), 135.2,
133.9, 133.7, 133.6, 132.2, 130.2, 129.8, 129.5, 127.1, 125.8 (Ar-C10), 113.8
(CN), 112.5 (CN), 80.9 (1-C), 21.5 ppm (SCH3); FTIR (KBr): n˜ =3027,
2228, 1578, 1493, 1431, 1348, 1206, 914, 833, 798, 764 cmÀ1; UV/Vis
(methanol): lmax =2212, 298; HRMS (EI): calcd for C15H10N2S: 250.0565;
found: 250.0564 [M]+.
,
C), 131.7, 130.2, 129.3, 129.0, 128.1, 126.5, 125.5 (Ar-C8 one peak is
doubly degenerate), 20.3 ppm (SCH3); FTIR (KBr): n˜ =1627, 1489, 1345,
962, 823, 763, 737 cmÀ1; UV/Vis (methanol): lmax =223, 296; HRMS (ES):
calcd for C13H11NO2S + H: 246.0589; found: 246.0591 [M+H]+.
(E)-1-(8’-Methylthionaphth-1’-yl)-2-nitroprop-1-ene (23): Nitroethane
(0.15 mL, 2.0 mmol), ethylenediammonium diacetate (0.018 g, 0.09 mmol)
and piperidine (3 drops) were added to a stirred solution of the aldehyde
27 (0.20 g, 1.09 mmol) in dry methanol (3 mL) under nitrogen. After the
mixture had been stirred for two days, the methanol was evaporated and
the residue purified by flash chromatography on silica gel (cyclohexane/
diethyl ether, 5:1) to yield the product 23 as an orange solid (0.094 g,
36%), m.p. 76–778C; 1H NMR (CDCl3): d=8.93 (s, 1H; 1-H), 7.80 (dd,
J=8.9, 0.8 Hz, 1H; Ar-H1), 7.64 (dd, J=7.5, 1.8 Hz, 1H; Ar-H1), 7.40 (m,
3H; Ar-H3), 7.17 (dd, J=7.3, 1.6 Hz, 1H; Ar-H1), 2.39 (s, 3H; SCH3),
2.19 ppm (s, 3H; 3-H3); 13C NMR (CDCl3): d=145.3 (2-C), 138.0 (1-C),
135.9, 135.1, 131.1, 130.8, 130.7, 128.4, 127.8, 127.3, 126.2, 125.3 (Ar-C10),
19.4 (SCH3); 13.7 ppm (3-C); FTIR (KBr): n˜ =1646, 1509, 1424, 1385,
1325, 1308, 977, 824, 796, 762 cmÀ1; UV/Vis (methanol): lmax =220, 297;
HRMS (CI): calcd for C14H13NO2S + H: 260.07453; found: 260.07336
[M+H]+.
Methyl (E)-2-cyano-3-(8’-methylthionaphth-1’-yl)-1-propenoate (21):
Methyl cyanoacetate (0.15 g, 1.5 mmol) and ethylenediammonium diace-
tate (0.018 g, 0.09 mmol) were added to a stirred solution of the aldehyde
27 (0.2 g, 1.0 mmol) in dry methanol (3 mL) under nitrogen. After stir-
ring for 1 h. at room temperature a precipitate was obtained, which was
collected by vacuum filtration and washed with methanol to yield the
product 21 as a yellow solid (0.14 g, 51%), m.p. 106–1088C; 1H NMR
(CDCl3): d=9.55 (s, 1H; 3-H), 7.96 (d, J=8.2 Hz, 1H; Ar-H1), 7.81 (dd,
J=8.2, 1.0 Hz, H; Ar-H1), 7.75–7.69 (m, 2H; Ar-H2), 7.56–7.45 (m, 2H;
Ar-H2), 3.97 (s, 3H; OCH3), 2.41 ppm (s, 3H; SCH3); 13C NMR (CDCl3):
d=163.1 (C=O), 160.5 (3-C), 135.1, 134.3, 132.8, 132.4, 132.2, 130.8,
129.7, 128.9, 126.5, 125.6 (Ar-C10), 115.4 (CN), 101.2 (2-C), 53.2 (OCH3),
21.2 ppm (SCH3); FTIR (KBr): n˜ =2944, 2222, 1728, 1590, 1429, 1274,
1239, 1088, 830, 757 cmÀ1; UV/Vis (methanol): lmax =223, 295; HRMS
(ES): calcd for C16H12NO2S + H: 284.0745; found: 284.0743 [M+H]+.
X-ray analyses: Diffraction data (MoKa radiation) was collected at low
temperature (120–150 K) on a Bruker-Nonius KappaCCD diffractometer
using phi and omega scans to fill Ewald sphere at low temperature
Table 2. Data reduction included a correction for Lorentzian polarisation
and an absorption correction was applied from multiple scan measure-
ments. Structures were solved with SHELXS[34] and refined against F2
with SHELXL[35]. Hydrogen atoms were located in difference maps and
refined in almost all cases. CCDC-295225—CCDC-295229 contain the
supplementary crystallographic data for this paper. These data can be ob-
(E)-1-(8’-Methylthionaphth-1’-yl)-2-nitroethene
(22):
Nitromethane
(0.08 mL, 1.5 mmol) and ethylenediammonium diacetate (0.018 g,
0.09 mmol) were added to a stirred solution of the aldehyde 27 (0.18 g,
1.0 mmol) in dry methanol (3 mL) under nitrogen. After the mixture had
been stirred for several hours at room temperature, TLC (cyclohexane/
diethyl ether, 5:1) showed just starting materials were present so piperi-
Table 2. Details of crystallographic measurements and refinements.
19
20
21
22
23
crystallisation solvent
formula
Mr
ethyl acetate
C18H16O4S
328.38
acetone
C15H10N2S
250.3
ethyl acetate
C16H13NO2S
283.35
diethyl ether
C13H11NO2S
245.30
diethyl ether
C14H13NO2S
259.31
T [K]
120
150
120
120
120
crystal system
space group
a [Š]
b [Š]
c [Š]
monoclinic
Cc
monoclinic
P21/c
monoclinic
C2/c
orthorhombic
P212121
4.7575(2),
14.4311(7),
16.5082(10)
-
1133.39
4
1.44
monoclinic
P21/c
10.6181(5)
11.5922(5)
13.0123(6)
105.599(2)8
1542.65
4
7.5941(4)
13.6436(9)
12.2968(8)
107.972(3)8
1211.92
4
16.2151(2)
7.9116(1)
22.0688(4)
105.0853(7)8
2733.58
8
7.8992(3)
19.0699(6)
8.0840(4)
93.216(2)
1215.83
4
b[8]
V[Š3]
Z
1calcd [gcmÀ3
]
1.41
1.37
1.38
1.42
m
A
]
0.23
0.25
0.24
0.27
0.26
F
A
688
520
1184
512
544
crystal size [mm]
V range [8]
no. reflections collected
no. independent reflections
no reflections with [F2 >4s(F2)]
Rint
0.20”0.20”0.10
2.66-27.46
4997
2679
2468
0.15”0.15”0.02
0.21-30.51
8654
2916
1583
0.15”0.15”0.15
2.93-27.45
19361
3040
2456
0.20”0.15”0.02
2.91-27.48
8789
2540
2201
0.35”0.20”0.10
3.35-27.50
15149
2794
1880
0.042
0.099
0.055
0.050
0.066
parameters
261
1.16
0.039/0.082
0.420/À0.268
203
0.92
0.061/0.151
0.564/À0.643
233
1.06
0.037/0.102
0.241/À0.389
198
1.04
0.038/0.087
0.221/À0.314
215
0.99
0.045/0.112
0.258/À0.322
GOF on F2
R1 [F2 >4s(F2)]/wR2
residual electron density, max./min. [e Š3]
Chem. Eur. J. 2006, 12, 7724 – 7732
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7731

J. D. Wallis and J. OꢀLeary
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Received: January 17, 2006
Published online: July 20, 2006
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