C-H activation with elemental sulfur: Synthesis of cyclic thioureas from formaldehyde aminals and S8

Article abstract of DOI:10.1002/1521-3765(20011015)7:20<4477::AID-CHEM4477>3.0.CO;2-I

The C-H activation of cyclic formaldehyde aminals LCH₂ (L = RNCH₂CH₂CH₂-NR and RNCH₂CH₂-NR, R = Me, Et, iPr, tBu, or Ph) with S₈ proceeds at unusually low temperatures (T < 160°C) and results in the formation of the respective thioureas LC = S and H₂S. The reaction constitutes a new, solvent-free method for the synthesis of thioureas that eliminates the toxic and highly flammable CS₂. For R = tBu, the ionic carbenium thiocyanates [LCH]⁺ SCN^- dominate the product spectrum and the respective thioureas are obtained in low yield. The reactivity of the analogous sulfur and oxygen ring systems towards S₈ was investigated. 1,3-Dithiolane is cleanly converted into 1,3-dithiolane-2-thione (S₈, 14 d, 190°C) and resembles the cyclic formaldehyde aminals in this respect. 1,3-Dioxolane (L = OCH₂CH₂O) is completely inert towards sulfur even under forceful reaction conditions (190°C, 14 d). The formation of thioureas from aminals was investigated at the CBS-4 and B3LYP/6-31G(d) levels of theory.

Full text of DOI:10.1002/1521-3765(20011015)7:20<4477::AID-CHEM4477>3.0.CO;2-I

FULL PAPER
�
C H Activation with Elemental Sulfur: Synthesis of Cyclic Thioureas
from Formaldehyde Aminals and S
8
[a]
[a]
[a]
[a]
Michael K. Denk,* Shilpi Gupta, John Brownie, Sabiha Tajammul, and
Alan J. Lough[
b]
Abstract: The C�H activation of cyclic
the ionic carbenium thiocyanates
Dithiolane is cleanly converted into 1,3-
‡
�
formaldehyde aminals LCH (L ˆ RN-
[LCH] SCN dominate the product
spectrum and the respective thioureas
are obtained in low yield. The reactivity
of the analogous sulfur and oxygen ring
dithiolane-2-thione (S , 14 d, 1908C)
2
8
CH CH CH -NR and RNCH CH -
and resembles the cyclic formaldehyde
aminals in this respect. 1,3-Dioxolane
(L ˆ OCH CH O) is completely inert
2
2
2
2
2
NR, R ˆ Me, Et, iPr, tBu, or Ph) with S
8
proceeds at unusually low temperatures
T< 1608C) and results in the formation
2
2
(
systems towards S was investigated. 1,3-
towards sulfur even under forceful re-
action conditions (1908C, 14 d). The
formation of thioureas from aminals
was investigated at the CBS-4 and
B3LYP/6-31G(d) levels of theory.
8
of the respective thioureas LCˆS and
H S. The reaction constitutes a new,
2
Keywords: ab initio calculations ´
C�H activation ´ dehydrogenation
solvent-free method for the synthesis
of thioureas that eliminates the toxic
´
sulfur ´ thioureas
and highly flammable CS . For R ˆ tBu,
2
Introduction
leaching of gold and silver by thiourea from a variety of
mineral sources has accordingly been the subject of numerous
studies but, although technically feasible, has so far failed to
Thioureas[1, 2] are specialty chemicals with a wide range of
applications. They are used as vulcanization accelerators,
as bath additives in electroplating processes, and as ana-
[10]
[
1, 2b]
replace the environmentally notorious cyanide process that is
[
3]
[10a,b]
still the standard process for the extraction of gold.
[
4]
lytical reagents. Many thiourea derivatives show in vivo and
in vitro activity against bacteria, fungi, parasitic worms, and
Our interest in thioureas arose from our study of the stable
carbenes 4 (Scheme 1) which we obtained in good yields by
the reductive desulfurization of the respective thioureas 6
[
5]
viruses such as the HIV virus. An impressive number of
currently used drugs can be regarded as thiourea derivatives.[
Thioureas can show considerable toxicity towards higher
organisms as well, and some thiourea derivatives have been
6]
[16, 17]
with potassium.
use as insecticides[ or rodenticides.
7]
[8]
R
N
R
N
R
N
Thiourea and its derivatives find widespread use in the
mining industry where they are employed as flotation aids for
sulfidic ores and as complexing agents for the enrichment of
metals through solid ± liquid and liquid ± liquid extraction
processes. The high affinity of thioureas towards noble
metals is underlined by the fact that thioureas are capable of
dissolving gold or silver in the presence of oxygen. The
– H+
K
C
H
C
C
S
[
9]
– K2S
N
R
N
R
N
R
[
9]
1
3
5
R
N
R
N
R
N
[
a] Prof. Dr. M. K. Denk, S. Gupta, J. Brownie, Dr. S. Tajammul
Department of Chemistry, Erindale College
University of Toronto, Mississauga, 3359 Mississauga Road North
ON, L5L 1C6 (Canada)
– H+
K
C
H
C
C
S
– K2S
N
R
N
R
N
R
Fax : (‡1)905-828-5425
E-mail: mdenk@credit.erin.utoronto.ca
[
b] Dr. A. J. Lough
2
4
6
X-ray Laboratory, Department. of Chemistry
University of Toronto, Toronto, 80 St. George Street
ON, M5S 3H6 (Canada)
Scheme 1. Synthesis of diaminocarbenes 3 and 4 by deprotonation or
reductive desulfurization.
Chem. Eur. J. 2001, 7, No. 20
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4477

M. K. Denk et al.
FULL PAPER
The corresponding carbenes 3
are more readily obtained through
deprotonation of imidazolium salts
[
11]
1,
which are easily accessible
through the one-pot condensation
reaction of glyoxal, formaldehyde,
[
11, 12]
and primary amines.
Other
diamino carbenium salts such as 2
[
13]
are less readily accessible
and
also tend to give lower yields in the
deprotonation step.[
14, 15]
Due to
these shortcomings, the reduction
of thioureas is an important alter-
native for the synthesis of the
[
16, 17]
diaminocarbenes.
Thioureas are typically obtained
from the reaction of amines with
CS but the approach is not without
2
shortcomings. For example, the
synthesis of the cyclic thioureas 6
from the respective ethylenedi-
amines and CS gives yields that
2
decrease with increasing bulk of
the substituents on nitrogen
(Scheme 2). For N,N'-di-tert-butyl-
ethylenediamine, the yields are
inconsistent and often below 10%.
8
Scheme 3. Reaction of cyclic aminals (6a, 7, 10), 1,3-dithiolane and 1,3-dioxolane with S . For yields based on
amines, see Table 2.
R
R
Results and Discussion
R
Yield
NH
N
80 %
74 %
6
a
b
Me
Et
CS2
H2S
Synthesis and purification: The cyclic formaldehyde aminals 7
and 10 are readily obtained from the respective 1,w-di-
amines[ and are used without further purification. The onset
C
S
6
-
NH
R
N
R
6c
iPr 50 %
6d tBu 19 %
Ph 49 %
20]
6e
of the reaction with S (1508C) is indicated by the evolution of
8
6
H S. Sulfur and most of the aminals are noticeably volatile
2
Scheme 2. Synthesis of cyclic thioureas 6 from N,N'-disubstituted ethyl-
enediamines and CS
under these conditions and, to avoid the loss of sulfur or
aminal, the reactions are best carried out in closed systems.
Standard reflux procedures tend to give lower yields and
impure products. The best yields of thioureas are obtained by
2
.
Reasons for the often disappointing yields of the CS route
2
are not well documented in the literature but the issue of low
yields has led to the development of improved synthetic
procedures that use the addition of oxidizing agents, partic-
ularly iodine. For the synthesis of the thioureas investigated
in this study, the addition of iodine increases the crude yields
heating the aminal (0.1 mol) and S (stoichiometric amount)
8
to 1508C for 12 h in a 50 mL stainless steel cylinder (Swage-
lock). Much shorter reaction times are sufficient in most cases,
but a reaction time of 12 h leads to complete conversion even
for aminals with bulky substituents, and does not decrease the
yield for aminals that require shorter reaction times.
[
18]
(by a factor of 1.1 to 1.2) but tends to give products of lower
purity. The additional purification steps required more than
offset the increased crude yields.
The thioureas 6 and 9 are conveniently extracted from the
crude reaction mixtures with methanol. Evaporation of
A promising one-pot reaction, the synthesis of 1,3-diphe-
nylimidazoline-2-thione (6e) from N,N'-diphenylethylenedi-
amine, triethyl orthoformate, and elemental sulfur, was
the solvent gives products that are already pure enough
for the reduction to carbenes.[
16, 17]
Analytically pure samples
are obtained following a workup procedure outlined in
Scheme 4.
[
19]
reported by Wanzlick et al.
The method works well as
described, but we were unsuccessful in extending the ap-
proach to alkyl-substituted diamines.
The above-mentioned difficulties have encouraged us to
The procedure leads to only minimal losses, and can be
applied to large amounts of crude product (>200 g). Irre-
spective of the substituent R, the thioureas are very soluble in
methanol or dichloromethane. Methanol has a very low
[
20]
investigate the reaction of formaldehyde aminals
with
[
21]
elemental sulfur. We now report the facile conversion of
cyclic formaldehyde aminals, the imidazolidines 7 and the
hexahydropyrimidines 10, into the respective cyclic thioureas
solubility for S and is therefore the solvent of choice for the
8
[
22]
extraction of the crude reaction mixtures. The absence of S in
8
the crude methanol filtrates was verified by the GC/MS
analysis. Analytically pure samples are obtained by filtration
6
and 9 (see Scheme 3).
4478
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Chem. Eur. J. 2001, 7, No. 20

C ± H Activation with S8
4477±4486
s
i
Thioureas
Thioureas
Carbenium Salts
Impurities
s
i
Et2O
s
i
Carbenium Salts
Impurities
Crude
Product
MeOH
Carbenium Salts H O
2
Impurities
Sulfur
Scheme 4. Purification of the thioureas (6, 9) and carbenium salts (8, 11) from the crude product obtained from the oxidation of cyclic aminals with S
soluble, i ˆ insoluble.
8
:. s ˆ
�
1
Table 1. Solubilities (in gL of pure solvent) of selected thioureas (6, 9)
and carbenium salts (8, 11) at 258C.[
reaction temperatures (1808C) are required to achieve a
a)
[28]
complete conversion.
1,3-Dioxolane is completely inert,
Hexane
Et
2
O
CH
3
OH
Toluene
even under more forcing reaction conditions (1908C, 14 days).
6
6
6
6
6
8
9
1
a
b
c
d
e
5
5
40
11
18
insol.
6
17
240
300
86
84
insol.
44
90
500
450
58
119
432
520
194
138
0.2
Formation of side products: The lower yields of thioureas
obtained from the aminals 7d and 10b are caused by the
formation of the carbenium salts 8 and 11 which are the
unexpected main products in these cases. They are obtained in
spectroscopically pure form ( H NMR spectroscopy) from the
sublimation residues of the crude reaction mixtures and
characterized through their single-crystal X-ray structures
25
250
242
355
1
a
370
0.3
1
insol.
insol.
[
a] The values for the solvent used for recrystallization are given in
boldface.
(
see below).
Carbenium salts like 8/11 are not formed (IR, NMR) in the
other reactions. Their formation from 7d and 10b must be
attributed to the presence of the sterically demanding tBu
substituent.
of the diethyl ether solutions through a short (10 cm) column
of neutral Al O , and recrystallization of the evaporated
filtrates from hexanes or diethyl ether (Table 2).
The pure thiocyanate salts 8 and 11 are obtained by
dissolving the crude thiocyanate salt fraction in distilled water
2
3
Variation of the ring size of the aminals is without influence
on the yield or product distribution: the two tert-butyl
substituted aminals 10b (six-membered ring) and 7d (five-
membered ring) gave a mixture of the respective carbenium
salts and the thioureas in similar ratios, while the methyl-
substituted 7a (five-membered ring) and 10a (six-membered
ring) gave the respective thioureas in similar yields.
GC-MS analysis led to the identification of CS2 and
R�NˆCˆS which are present as minor (< 1%) side products
(5 mL per 1 g of crude material) which removes dark brown
impurities as an insoluble fraction. The orange-colored
aqueous solutions are extracted with toluene (5 mL portions)
until the organic layer remains colorless. Slow evaporation of
the aqueous solution gives the pure thiocyanate salts in the
form of large colorless prisms.
in all crude reaction mixtures. Due to their high volatility, they
are removed during the evaporation steps outlined in
Scheme 4. Substantial amounts of the diamine, N,N'-di-tert-
butyl-1,3-diaminopropane (12), were isolated from the dehy-
drosulfurization reaction of 10b, but only traces of the
corresponding diamines were detected (GC-MS) in the other
reactions.
Scope of reaction: To test the generality of the reaction, the
analogous oxygen and sulfur ring systems, 1,3-dioxolane and
1
,3-dithiolane, were allowed to react with sulfur (see
Scheme 3). 1,3-Dithiolane is cleanly transformed into the
,3-dithiolane-2-thione and thus reacts analogously to the
aminals, but longer reaction times (2 weeks) and higher
1
Extended reaction times or elevat-
Table 2. Synthesis of cyclic thioureas from diamines: melting points, yields and analytical data.
ed reaction temperatures do not
affect the yield or purity of the
products, except for 7d, for which
traces of the aromatic dehydrogen-
ation product 5a were detected after
o
Yield [%][a]
M. p. [ C]
Formula
Elemental analysis [%]
C
H
N
111 ± 112[b]
6
6
6
6
6
9
9
a
b
c
110 ± 111
66 ± 67
88
86 (80)
87 (74)
86 (50)
18 (19)
47 (49)
91 (80)
6 (0)
C
C
C
C
C
C
C
5
7
9
H
H
H
10
14
18
N
N
N
2
2
2
S
S
S
found:
calcd:
found:
calcd:
found:
calcd:
found:
calcd:
found:
calcd:
found:
calcd:
found:
calcd:
46.33
46.12
53.19
53.12
58.22
58.01
62.73
61.63
70.60
70.83
50.02
49.96
63.22
63.10
7.96
7.74
8.75
8.91
9.58
21.50
21.51
17.80
17.70
14.93
15.03
13.22
13.06
11.07
11.01
19.38
19.42
12.31
12.26
[b]
62 ± 63
72 h at 150 ± 1608C by GC-MS anal-
[
c]
62.2
ysis. The formation of 5a is due to the
dehydrogenation of 6d under the
reaction conditions and 5a could in
fact be obtained on a preparative
scale by heating mixtures of 6d and
S8 to 1908C for 100 h (yield >80%).
Increasing the amount of sulfur be-
yond the stoichiometrically required
[
c]
86.4
9.73
d
e
a
b
133
±
11
15
H
22
14
N
N
2
S
10.24
10.34
5.43
5.54
8.92
8.38
10.73
10.59
187 ± 188
78 ± 79
101
187 ± 188[d]
H
2
S
79[b]
-
N
S
6
H
12
2
12
H
24
N
2
S
0
.25 equivalents of S does not lead
8
to any significant changes in the
yields or the product distribution.
[
a] S
8
route, calculated on diamine; for yields based on aminals see Scheme 3. In parentheses: best yields
or CS /I route. [b] Ref. [18b]. [c] Ref. [18a]. [d] Ref. [19].
obtained with the CS
2
2
2
Chem. Eur. J. 2001, 7, No. 20
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4479

M. K. Denk et al.
FULL PAPER
The compounds 5a, 6d, 8, 11, and 12 were cha-
[
22±26]
racterized by single-crystal X-ray diffraction
structures are given in Figures 1 ± 5.
and their
NtBu)C�H]‡ [SCN] (8)
�
Figure 3. Molecular structure of [(tBuNCH
2
�CH
2
in the solid state (ORTEP view, thermal ellipsoids are at the 50%
probability level). Selected bond lengths [pm] and angles [8]: C(1)�N(1)
1
31.3(2), C(1)�N(2) 131.4(2), N(1)�C(2) 147.3(2), C(2)�C(3) 151.7(3),
Figure 1. Molecular structure of (tBuNCHˆCHNtBu)CˆS (5a) in the solid
N(2)�C(4) 149.2(2), N(3)�C(12) 157.8, N(3) ´´´ H(1A) 414.6, C(12)-N(3)-
H(1A) 141.43(05), N(1)-C(1)-N(2) 113.80(16), C(1)-N(1)-C(2) 108.83(15),
N(1)-C(2)-C(3) 102.47(16).
state (ORTEP view, thermal ellipsoids are at the 50% probability level).
Selected bond lengths [pm] and angles [8]: S(1)�C(3) 168.8(3), C(3)�N(1)
1
36.4(4), N(1)�C(4), 150.3(4), N(1)�C(1), 138.2(5), C(1)�C(2) 132.1(5),
C(2)�N(2) 137.6(4), N(2)�C(3) 136.4(4), N(2)�C(8) 151.3(4); S(1)-C(3)-
N(1) 127.0(2), S(1)-C(3)-N(2) 127.0(2), N(1)-C(3)-N(2) 105.9(3), C(3)-
N(2)-C(2) 109.3(2), N(2)-C(2)-C(1) 105.9(3), C(2)-C(1)-N(1) 108.6(3).
�CH
CH
NtBu)C�H]‡
Figure 4. Molecular structure of [(tBuNCH
2
2
2
�
[SCN] (11) in the solid state (ORTEP view, thermal ellipsoids are at the
5
0% probability level). Selected bond lengths [pm] and angles [8]:
Figure 2. Molecular structure of (tBuNCH
solid state (ORTEP view, thermal ellipsoids are at the 50% probability
2
�CH
2
NtBu)CˆS (6d) in the
�
�
�
C(1) N(1) 130.2(6), N(1) C(2) 149.9(6), N(1) C(4) 146.66(7); C(1)-
N(1)-C(4) 125.1(6), C(1)-N(1)-C(2) 116.0(5), N(1)-C(1)-N(1') 129.5(10),
C(4)-N(1)-C(2) 117.5(4).
o
level). Selected bond lengths [pm] and angles [ ]: C(1)�S(1) 167.4(4),
C(1)�N(2) 135.4(5),C(1)�N(5) 135.8(4), N(2)�C(6) 148.6(4), N(2)�C(3)
1
1
45.4(4), C(3)�C(4) 148.6(5); S(1)-C(1)-N(2) 125.3(3), S(1)-C(1)-N(5)
25.5(3), N(2)-C(1)-N(5) 109.2(3), C(1)-N(2)-C(6) 126.7(3), C(1)-N(2)-
carbenium salts are in planar or close to planar environments,
C(3) 109.5(3), C(3)-N(2)-C(6) 119.4(3).
except for 6d which has slightly pyramidal nitrogen atoms
(
sum of nitrogen bond angles ˆ 3538). An interpretation of the
The short C�N bond lengths observed for the thioureas
bond lengths in the context of aromatic delocalization in
2-(3H)-imidazole ± thiones (5a) and related systems has been
discussed recently.[
(
135 ± 138 pm) and carbenium salts (130 ± 131 pm) imply a
27]
substantial double-bond character. The closest contacts
between the thiocyanate anion and the carbenium cation
observed for 8 and 11 are in excess of 400 pm and rule out
covalent interactions. The disorder observed for 11 was
successfully modeled through a superposition of two envelope
geometries. The nitrogen atoms in the thioureas and the
Mechanism and thermochemistry: In principle, C�H activa-
tion reactions can occur through the insertion of sextet species
into the C�H bond or through multistep processes that are
initiated by the breaking of the C�H bond in homolytic
4480
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Chem. Eur. J. 2001, 7, No. 20

C ± H Activation with S8
4477±4486
R
N
R
N
– H•
a
CH2
C
H
Thioureas
N
R
N
R
H -
–
c
14
7
–e–
e–
f
–
b
d
–
H +
R
N
R
N
–H•
e
Carbenium
C
H
CH2
Thiocyanates
N
R
N
R
Figure 5. Molecular structure of tBuNHCH
2
�CH
2 2
CH NHtBu (12) in the
[7]+.
solid state (ORTEP view, thermal ellipsoids are at the 50% probability
level). Selected bond lengths [pm] and angles [8]: N(1)�C(1) 146.40(13),
C(1)�C(2) 152.34(14), C(2)�C(3) 152.23(15), N(1)�C(4) 147.88(13); N(1)-
8
Scheme 5. Elementary steps (a ± f) of the C�H activation of imidazolidines
by S
8
.
C(1)-C(2) 111.76(9), C(3)-C(2)-C(1) 114.54(9), H(1N)-N(1)-C(1) 111.3(12).
(
SET) oxidation step b as the rate-determining step of the
reaction.
The thermochemistry of the formation of the thioureas
from S8 and aminals was investigated by computational
.
fashion (formation of H ) or in heterolytic fashion (formation
of H or H ).
‡
�
The 1,1-elimination of hydrogen from animals to give stable
diaminocarbenes was examined by ab initio methods (see
methods[
and CBS-4
31, 32]
at the B3LYP/6-31G(d)//B3LYP/6-31G(d)
[31, 33]
�
1
[31, 34]
below) and is endothermic by ‡25 kcal mol (formation of
levels of theory (Table 3 and 4, respectively).
�
1
H ) or ‡14 kcalmol (formation of H S) and can be ruled out
Even more accurate thermochemical data can be obtained
from CBS-Q[ or G2
methods is typically restricted to systems with six heavy
atoms.[ The CBS-4 approach allows the inclusion S in the
calculations and was chosen as a good compromise between
high accuracy (mean absolute deviation better than 2 kcal
mol ) and speed. B3LYP/6-31G(d)//B3LYP/6-31G(d) ener-
gies have mean absolute deviations of about 8 kcalmol and
were included for comparison only.
The imidazolidine 7H (Scheme 6) was chosen as model
compound for the aminals 7a ± 7b. The pyramidal geometry
of the nitrogen atoms in 7H leads to two different isomers
2
2
34]
[31, 35]
as the primary step of the reaction. Future mechanistic studies
will focus on the reactions a ± c (Scheme 5) as the most likely
initial steps of the observed C�H activation reactions.
calculations but the use of these
31]
8
An important experimental result for future mechanistic
investigations is the fact that the thioureas 6, 9 and the
carbenium salts 8, 11 cannot be interconverted under the
reaction conditions that lead to their formation. This implies
that the direct hydride abstraction step c (see Scheme 5),
which would explain the formation of the carbenium salts,
cannot be the only operating pathway. Radical cations of
�
1
�
1
‡
.
imidazolidines such as [7] have been previously studied
by photoelectron spectroscopy.
Their intermediacy would pro-
vide a branching step leading to
carbenium salts (through hy-
8
Table 3. Oxidation of aminals with S . Selected energies (in Hartrees) at the B3LYP/6 ± 31G(d) level.
ZPE
E
o
E
298.15
H
298.15
G
298.15
drogen abstraction) or thiour-
eas (step d). The operation of
route a or route b is not mu-
tually exclusive and it is diffi-
cult to distinguish between the
two pathways if one relies on
arguments derived from prod-
uct distributions alone.
S8
0.011762
0.010145
0.015172
0.119250
0.119409
0.094104
0.098281
� 3185.538724
� 1.165337
� 3185.527535
� 1.162976
� 3185.526590
� 1.162032
� 3185.576877
� 1.1768
H
H
2
2
S
� 399.370264
� 228.489610
� 228.490046
� 227.277607
� 625.533207
� 399.367417
� 228.484819
� 228.485331
� 227.272870
� 625.527679
� 399.366473
� 228.483875
� 228.484387
� 227.271925
� 625.526735
� 399.389832
� 228.517424
� 228.517766
� 227.305075
� 625.562662
anti-7H
syn-7H
4
H
6H
The observed sequence of
reactivities for imidazolidines,
dioxolanes, and dithiolanes to-
wards S8 correlates well with
the lone pair energies of the
8
Table 4. Oxidation of aminals with S . Selected energies (in Hartrees) at the CBS-4 level.
ZPE
E
o
E
298.15
H
298.15
G
298.15
S
H
H
8
0.013977
0.010610
0.016379
0.126308
0.126496
0.101020
0.105082
� 3182.008354
� 1.172206
� 3181.997607
� 1.169845
� 3181.996663
� 1.168901
� 3182.046130
� 1.183673
2
2
S
� 398.936720
� 228.243185
� 228.243956
� 227.021839
� 624.828427
� 398.933875
� 228.238072
� 228.238951
� 227.017201
� 624.822610
� 398.932930
� 228.237128
� 228.238007
� 227.016257
� 624.821666
� 398.956239
� 228.271617
� 228.272219
� 227.049401
� 624.859111
respective
heteroelements
anti-7H
syn-7H
4
6
(
N > S ꢀ O), which is in good
H
H
agreement with the operation
of the single-electron transfter
Chem. Eur. J. 2001, 7, No. 20
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0720-4481 $ 17.50+.50/0
4481

M. K. Denk et al.
FULL PAPER
Carbenes are known to react with sulfur to give thioureas[36]
but, based on the CBS-4 data, their intermediacy in the aminal
oxidation seems unlikely. Even if the endothermic elimination
�
1
of hydrogen from the aminal (DG ˆ ‡24.6 kcalmol ) is
�
1
combined with the formation of H S (DG ˆ � 10.5 kcalmol )
2
the overall reaction still has a positive DG value of
14.1 kcalmol . The reaction of diaminocarbenes with S
8
has recently been the subject of thermochemical experi-
ments.[ The experimental value obtained for the reaction of
�
1
‡
36]
[36]
the analogous N,N'-dimesitylcarbene with S
2
(DH ˆ � 35 Æ
8
�
1
kcalmol ) is in very good agreement with the CBS-4 value
�
1
that we obtain for the reaction k (DH ˆ � 35.03 kcalmol ).
�
1
The B3LYP/6-31G(d) value (DH ˆ � 40.15 kcalmol ) sig-
nificantly deviates from this experimental value.
Conclusion
A novel method for the synthesis of tetrasubstituted thioureas
consists of heating cyclic formaldehyde aminals and with S to
8
1508C. The reaction is simple to perform, does not require
solvents, and gives thioureas in good to excellent yields and
purities. The transformation >CH !> CˆS amounts to a
2
C�H activation by S . The transformation can be carried out
8
in a similar fashion for the thia analogues of the investigated
aminals (1,3-dithiolanes), while the oxa analogues (1,3-
dioxolanes) were found to be inert towards S8.
8
Scheme 6. Oxidation of imidazolidines by S (reactions g ± k). Reaction
energies DG298.15 at the CBS-4 level and at the B3LYP/6 ± 31G(d) level (in
parentheses).
Experimental Section
General: Melting points were recorded in sealed capillaries and are
uncorrected. Mass spectra were determined at an ionizing voltage of 40 eV
or 70 eV as indicated. NMR spectra were recorded on Varian Gemini 200
with syn or anti orientation of the N�H bonds. The syn isomer
is slightly more stable and was the one used for the
determination of the thermodynamic parameters. The com-
putationally derived free energies indicate that there are in
fact two different reactions that can account for the formation
1
13
13
(
H), Bruker 500 MHz ( C), or Varian 400 MHz spectrometers ( C) at
normal spectrometer temperature. The spectra are referenced against
1
13
tetramethylsilane (TMS) ( H and C, internal). IR spectra were recorded
as nujol mulls on a Nicolet FT Spectrometer. All starting materials were
obtained from Aldrich and used as received. The synthesis of the aminals
of thioureas, reaction g, (by-product H S, DG ˆ
2
�
1
8
and their oxidation with S were conducted under an atmosphere of
�
�
19.82 kcalmol ) and reaction i, (by-product H , DG ˆ
2
[
30]
nitrogen or argon (purity 99.994 or better). Elemental analyses were
performed at Guelph Chemical Laboratories Ltd. (Canada).
�
1
9.28 kcalmol ).
Reaction i is characterized by a lower stoichiometry in
Reactions and procedures
sulfur and was ruled out experimentally: lowering the amount
of sulfur to the amount required by reaction i leads to 50%
conversion of the aminal. The abundance of easily accessible
starting materials makes reaction h, the 1,1-elimination of H2
from formaldehyde aminals to give carbenes, a worthwhile
Synthesis of N,N'-di-tert-butyl-1,3-propanediamine (12): 1,3-Dibromopro-
pane (100.00 g, 495.3 mmol), tert-butylamine (260 mL, 181.13 g, 2.47 mol),
and distilled water (20 mL) were added together in a 1 L two-necked
round-bottom flask with stirrer and reflux condenser. The clear two-phase
system slowly turned turbid and reached boiling temperature. The reaction
was completed by boiling under reflux overnight. Three portions (3 Â 20 g)
of NaOH were added to the cold mixture. The upper layer was separated
and the aqueous layer was extracted with diethyl ether (3 Â 100 mL). The
combined organic extracts were dried by stirring with NaOH (10 g)
overnight. Evaporation of the diethyl ether left shiny white flakes of pure
N,N'-di-tert-butyl-1,3-propylenediamine. Yield 78.3 g (85%).
�
1
target of synthetic studies. The DG value of ‡24.6 kcalmol
obtained at the CBS-4 level rules out a direct conversion but
the process could well become feasible by coupling reaction h
with a sufficiently exothermic hydrogenation reaction (Ta-
ble 5).
1,3-Diphenylimidazolidine (7e): Un-
like the other aminals obtained in this
Table 5. Reaction energies (in kcalmol� 1) at the CBS-4 level and at the B3LYP/6 ± 31G(d) level (in italics).
study, the formation of 7e required
acid catalysis. Following the procedure
DE
o
DE298.15
DH298.15
DG298.15
of Wanzlick et al.,
[19]
N,N'-diphenyl-
ethylenediamine (3.50 g, 16.5 mmol)
was dissolved in MeOH (100 mL). To
this solution was added paraformalde-
hyde (0.50 g, 16.6 mmol) and a solu-
tion of acetic acid (1.5 mL) in MeOH
g
h
i
j
k
� 11.99 � 18.04
‡ 31.32 ‡ 29.56
� 3.54 � 10.14
� 34.85 � 39.70
� 11.34 � 17.50
‡ 32.57 ‡ 30.74
� 10.93 � 17.05
‡ 33.16 ‡ 31.64
� 19.82 � 25.42
‡ 24.56 ‡ 22.50
� 9.28 � 15.44
� 33.84 � 37.95
� 2.39
� 9.03
� 1.87
� 8.51
� 34.95 � 40.08
� 8.99 � 8.47
� 35.03 � 40.15
� 9.07 � 8.55
� 8.45
� 7.90
� 10.54
� 9.97
(
10 mL). The reaction was stirred until
4482
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0720-4482 $ 17.50+.50/0 Chem. Eur. J. 2001, 7, No. 20

C ± H Activation with S8
4477±4486
the paraformaldehyde had dissolved. Methanol was removed in vacuo and
the resulting crude material was sublimed at 1258C/1 Torr (oil bath). Yield
1,3-Diethylimidazolidine-2-thione (6b): Long, colorless needles, m. p. 62 �
[
18b]
1
638C (lit.: 62 � 638C ); H NMR (200 MHz, C
6
D
6
, 258C): d ˆ 0.87 (t,
3
3.00 g (81%).
J(H,H) ˆ 7.2 Hz, 6H; NCH
2
CH
3
), 2.56 (s, 4H; CH
2
CH
2
), 3.51 (q,
, 258C):
CH ), 3.67
, 258C):
), 183.05 (CˆS);
), 41.98 (CH CH ),
3
); 1H NMR (200 MHz, CDCl
CH ), 3.54 (s, 4H; CH
); C NMR (400 MHz, C
), 49.05 (NCH CH
, 258C): d ˆ 12.00 (CH
J(H,H) ˆ 7.2 Hz, 4 H ; NCH
2
CH
3
3
Synthesis of imidazolidines 7 and hexahydropyrimidines 10: In a 100 mL
Schlenk flask, paraformaldehyde (5.00 g, 16.60 mmol) and diethyl ether
3
d ˆ 1.17 (t, J(H,H) ˆ 7.3 Hz, 6H; NCH
2
3
2
2
3
13
(
q, J(H,H) ˆ 7.3 Hz, 4H; NCH
2
CH
3
6 6
D
(
20 mL) were added to the diamine (16.90 mmol). The mixture was stirred
d ˆ 12.90 (CH
3
), 45.48 (CH
2
CH
2
2
3
until all of the paraformaldehyde was consumed. The upper layer was
separated and dried over NaOH (1.0 g) for 24 h. Yields 90 ± 100%.
13
C NMR (400 MHz, CDCl
5.36 (NCH CH
431 s, 1352 m, 1334 s, 1278 vs, 1253 m, 1202 w, 1194w, 1129 m, 1111 w, 1073
3
3
2
2
4
1
2
3
), 181.42 (CˆS); IR (NaCl, Nujol): nÄ ˆ 1502 vs, 1446 vs,
Synthesis of thioureas from 1,w-diamines and CS
2 2
: CS (11.7 mL, 14.8 g,
195 mmol) was added dropwise under external water cooling to a mixture
� 1
w, 1067 w, 994 vw, 893 vw, 783 m, 631 m cm
.
of the diamine (195 mmol) and pyridine (50 mL). After the strongly
exothermic reaction has ceased, the mixture was boiled to reflux for 24 h
1
,3-Diisopropylimidazolidine-2-thione (6c): Colorless needles, m. p. 86 �
[
18a]
1
8
(
78C (lit.: 86.48C ); H NMR (200 MHz, C
6
D
6
, CDCl
3
, 258C): d ˆ 0.91
), 5.17 (sept,
); H NMR (200 MHz, CDCl
, 258C): d ˆ
CH), 3.45 (s, 4H; NCH ), 4.93 (sept,
, 258C): d ˆ
), 182.28 (C ˆ S); MS
.
(
oil bath 1508C, gas evolution). Iodine (4.40 g, 17.3 mmol) was added to the
cold reaction mixture and the solution boiled to reflux for an additional
0 h. The pyridine was removed in vacuo, and the resulting brown solid was
d, 3J(H,H) ˆ 6.9 Hz, 12H; (CH
)
CH), 2.73 (s, 4H; NCH
3
2
1
2
3
J(H,H) ˆ 6.9 Hz, 2H; CH(CH
3
)
2
3
2
3
1
.17 (d, J(H,H) ˆ 6.6 Hz, 6H; (CH
3
13
)
2
2
extracted with dichloromethane. The dichloromethane solution was
washed with deionized water (3 Â 20 mL), the dichloromethane evaporated
in vacuo, and the residue sublimed at 1 Torr. Spectroscopic data see below.
Yields: 6a (80%), 6b (74%), 6c (50%), 6d (19%), 9a (80%), 9b (<1%).
3
J(H,H) ˆ 6.6 Hz, 2H; CH(CH
3
)
2
); C NMR (400 MHz, C
), 46.78 (CH(CH
6 6
D
1
9.12 ((CH CH) 40.38 (CH CH
3
)
2
2
2
3 2
)
‡
(
(
70 eV): m/z (%): 186 (100) [M] , 171 (40), 143 (30), 129 (68), 111 (13), 101
13), 83 (33), 70 (21); HR-MS: 186.118530, calcd: 186.1191; fit ˆ 2.9 ppm;
Reaction of imidazolidines and hexahydropyrimidines with S
8
: Sulfur
IR (KBr, Nujol): nÄ ˆ 1486 s, 1426 s, 1364 m, 1326 s, 1274 s, 1161 m, 1126 m,
(
1.22 g, 4.75 mmol) was added to the aminal (19.0 mmol) in a Swagelock
1
5
083 m, 1039 m, 985 w, 955 w, 920 w, 872 w, 803 w, 710 w, 674 w, 639 s, 605 m,
02 m, 456 m, 422 s cm
50 mL stainless steel cylinder. The vessel was sealed and placed in an oil
�
1
.
bath (1508C) for 12 h. The cold reaction mixture was extracted with
methanol (3 Â 10 mL). The combined methanol extracts were filtered and
the methanol was evaporated in vacuo. The thioureas were obtained by
extraction of the solid residue with toluene (2 Â 10 mL). The toluene
extract was filtered through a short column (length 10 cm , diameter 1 cm)
of neutral Al O . Analytically pure samples of the thioureas were obtained
2 3
by recrystallization from the solvent indicated in Table 1. The carbenium
salts were isolated by dissolving the toluene-insoluble fraction in water
1
,3-Di-tert-butylimidazolidine-2-thione (6d): Colorless octahedra, m. p.
1
1
30 � 1318C; H NMR (C
6
D
6
): d ˆ 1.55 (s, 18H; C(CH
, 258C): d ˆ 1.58 (s, 18H; C(CH
NMR (400 MHz,
258C): d ˆ 28.09
), 56.41 (C(CH
), 184.43 (CˆS); C NMR
258C): d ˆ 27.93 (C(CH ), 44.31 (NCH ), 56.42
), 183.13 (CˆS); MS (70 eV): m/z (%): 214 (76) [M] , 157 (35),
43 (56), 115 (10), 102 (100), 84 (12), 74 (16), 70 (12), 57 (49); IR (NaCl,
Nujol): nÄ ˆ 1655 w, 1630 m, 1365 m, 1315 s, 1264 m, 1199 w, 1119 w, 1033 m,
3
)
3
), 2.75 (s, 4H;
1
NCH
2
); H NMR (200 MHz, CDCl
3
3 3
)
),
1
3
3
.42 (s, 4H; NCH
C(CH ), 44.22 (NCH
400 MHz, CDCl
C(CH
2
);
C
6 6
C D ,
13
(
(
(
3
)
3
2
3 3
)
3
,
3
)
3
2
‡
.
3 3
)
1
(
5 mL). The resulting orange solution was decanted or filtered from the
brown, insoluble impurities, and extracted with toluene (5 mL portions)
until the organic phase remained colorless. The carbenium thiocyanates
were obtained by slow evaporation of the aqueous phase in the form or
large colorless crystals. Yields of thioureas (6, 9) and carbenium salts (8,
�
1
9
40 w, 885 vw, 841 vw, 745 w, 722 w, 651 m cm .
1,3-Diphenylimidazolidine-2-thione (6e): Thin plates, m.p. 124 ± 125;
1
H NMR (200 MHz, C D , 258C): d ˆ 3.05 (s, 4H; CH CH ), 7.00 (t,
6
6
2
2
1
1): 6a (90%), 6b (92%), 6c (90%), 6d (19%) ‡ 8 (80%), 6e (49%), 9a
3
J(H,H) ˆ 7.2 Hz, 2 H ; para-CH), 7.19 (t,
3
J(H,H) ˆ 7.2 Hz ; meta-CH), 7.59
(
91%), 9b (6%) ‡ 11 (86%). For the synthesis of 1,3-diphenylimidazo-
(d,
3
J(H,H) ˆ 7.8 Hz ; ortho-CH);
1
H NMR (200 MHz, CDCl , 258C): d ˆ
3
lidine-2-thione (6e), the crude reaction mixture was extracted with
chloroform (3 Â 10 mL) because 6e was practically insoluble in MeOH.
The solvent was removed in vacuo and the remaining brown-yellow solid
sublimed at 1058C/1 Torr. The sublimate consisted of pure N,N'-dipheny-
lethylenediamine (43%), the brown sublimation residue consisted of
spectroscopically pure 6e (49%).
4.14 (s; CH CH ), 7.26 (t,
7.6 Hz ; meta-CH), 7.56 (d,
3
J(H,H) ˆ 7.6 Hz ; para-CH), 7.42 (t, J(H,H) ˆ
3
2
2
3
J(H,H) ˆ 8.0 Hz; ortho-CH); 13
C NMR
(400 MHz, CDCl , 258C): d ˆ 42.29 (CH CH ), 125.36 (meta-CH), 126.52
3
2
2
(ortho-CH), 128.78 (para-CH), 140.76 (ipso-C), 181.17 (CˆS); IR (KCl,
Nujol): nÄ ˆ 1598 m, 1581 w, 1499 m, 1423 m, 1395 m, 1342 s, 1289 s, 1271 s,
1080 w, 761 s, 692 s, 562 s cm� 1
.
Attempted dehydrosulfurization of 1,3-dioxolane: Sulfur (0.68 g,
1
1
2
6 6
,3-Dimethylimidazolidine (7a): Colorless oil; H NMR (200 MHz, C D ,
2.65 mmol) and 1,3-dioxolane (0.79 g, 11.0 mmol) were added together in
58C): d ˆ 2.20 (s, 6H; NCH
3 2 2
), 2.56 (s, 4H; CH CH ), 3.18 (s, 2H;
a 50 mL Swagelock stainless steel cylinder. The cylinder was sealed and
1
NCH
2
N); H NMR (200 MHz, CDCl
3
, 258C): d ˆ 2.36 (s, 6H; NCH
3
), 2.76
1
placed in an oil bath (1508C) for 72 h. The H NMR spectrum of the crude
13
(
s, 4H; CH
2
CH
2
), 3.28 (s, 2H; NCH
2
N); C NMR (400 MHz, CDCl
3
,
reaction mixture showed only signals for the starting material (1,3-
dioxolane).
2
58C): d ˆ 41.60 (NCH
3 2 2 2
), 54.67 (CH CH ), 79.85 (NCH N); MS (70 eV):
‡ .
m/z (%): 100 (4) [M] , 99 (41), 85 (24), 57 (21), 42 (100), 28 (32), 18 (35);
IR (NaCl, neat): nÄ ˆ 1455 s, 1370 s, 1228 s, 1115 s, 1033 m, 967 w, 921 m, 872
Dehydrosulfurization of 1,3-dithiolane: Sulfur (0.87 g, 3.39 mmol) and 1,3-
dithiolane (1.44 g, 13.6 mmol) were added together in a 50 mL Swagelock
�
1
s, 810 s cm .
stainless steel cylinder. The cylinder was sealed and placed in an oil bath
,3-Diethylimidazolidine (7b): Colorless oil; 1H NMR (200 MHz, C
1
6
D
6
,
1
(
1508C). After 20 h, a H NMR spectrum of the crude reaction mixture
3
), 2.41 (q, 3J(H,H) ˆ
2
58C): d ˆ 1.01 (t, J(H,H) ˆ 7.4 Hz, 6 H ; CH
3 2
CH
showed only signals of the starting material (90%) and of 1,3-dithiolane-2-
7.4 Hz, 4H; CH
3
CH
2
), 2.61 (s, 4H; CH
2
CH
2
), 3.35 (s, 2H; NCH
2
N);
thione (10%). Complete conversion was achieved after 100 h at 1908C.
1
3
H NMR (200 MHz, CDCl
3
, 258C): d ˆ 1.10 (t, J(H,H) ˆ 7.2 Hz, 6H;
), 2.56 (q, J(H,H) ˆ 7.2 Hz, 4H; CH CH ), 2.80 (s, 4H; CH CH ),
N); C NMR (400 MHz, C
, 258C): d ˆ 14.47
), 49.60 (CH CH ), 52.55 (CH CH ), 76.78 (NCH N); IR (KCl,
1
H NMR (CDCl
3
): d ˆ 3.97 (s, 4H; SCH
2
).
3
CH
3.42 (s, 2H; NCH
CH CH
3
CH
2
3
2
2
2
13
Spectroscopic data
2
6 6
D
(
3
2
3
2
2
2
2
1
1
,3-Dimethylimidazolidine-2-thione (6a): Colorless hexagons, m. p. 110 ±
118C (lit.: 111 ± 1128C[ ); H NMR (200 MHz, C
18b]
1
neat): nÄ ˆ 3338 w, 2969 s, 2935 s, 2800 s, 1678 s, 1470 m, 1452 m, 1375 m, 1346
6
D
6
, 258C): d ˆ 2.35 (s;
1
m, 1315 w, 1289 m, 1197 m, 1147 m, 1105 m, 1049 w, 961 w, 866 w, 790
CH
CH
NCH
2
CH
CH
2
), 2.82 (s; NCH
3
); H NMR (CDCl
3
): d ˆ 3.13 (s; NCH
3
), 3.54 (s;
�
1
13
1
w cm .
2
2
); C NMR (400 MHz, C
), 46.78 ( J(C,H) ˆ 145 Hz; CH
6
D
6
, 258C): d ˆ 34.95 ( J(C,H) ˆ 138 Hz;
1
13
1,3-Diisopropylimidazolidine (7c): Colorless oil; 1H NMR (200 MHz,
), 184.52 (CˆS); C NMR
3
2
CH
2
1
3
(
(
(
400 MHz, CDCl
3
, 258C): d ˆ 35.11 ( J(C,H) ˆ 139 Hz; NCH
3
), 48.33
C
6
D
6
, 258C): d ˆ 0.98 (d, J(H,H) ˆ 6.3 Hz, 12H; CH(CH
3 2
) ), 2.37 (sept,
1
3
J(C,H) ˆ 145 Hz; CH
2
CH
2
), 184.0 (CˆS); MS (70 eV) m/z (%): 130
J(H,H) ˆ 6.3 Hz, 2H; CH(CH
3
)
2
), 2.64 (s, 4H; CH
2
CH
2
), 3.48 (s, 2H;
‡
.
1
3
100) [M] , 115 (7), 97 (7), 88 (10), 76 (57), 69 (25), 57 (33); HR-MS: m/z:
NCH
2
N); H NMR (200 MHz, CDCl
3
, 258C): d ˆ 1.08 (d, J(H,H) ˆ
1
1
30.0564, calcd: 130.0565; fit: 0.3 ppm; IR (NaCl, Nujol): nÄ ˆ 1619 w, 1507 s,
6.0 Hz, 12H; CH(CH
2.84 (s, 4H; CH CH
d ˆ 22.04 (CH(CH
(NCH N); MS (70 eV): m/z (%): 156 (3) [M] , 155 (14), 141 (11), 127
(85), 113 (56), 99 (30), 85 (44), 72 (100), 56 (48); IR (KBr, neat): nÄ ˆ 2969 vs,
3
)
2
), 2.51 (sept, 3J(H,H) ˆ 6.0 Hz, 2H; CH(CH
3 2
) ),
1
3
499 s, 1459 vs, 1451 vs, 1430 s, 1398 m, 1383 s, 1327 vs, 1286 vs, 1223 s, 1202
2
2
), 3.52 (s, NCH
2
N); C NMR (400 MHz, C
6
D
6
, 258C):
�
1
m, 1134 w, 1116 s, 1068 m, 1017 vw, 959 m, 641 m, 634 m, 626 m, 509 s cm
;
3 2 2 2 3 2
) ), 50.73 (CH CH ), 53.99 (CH(CH ) ), 73.36
‡
.
IR (CCl
4
, CaF
2
): nÄ ˆ 2931 w, 2868 w, 1504 s, 1469 w, 1441 w, 1398 m, 1342 vs,
2
�
1
1293 m, 1117 s cm
.
Chem. Eur. J. 2001, 7, No. 20
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0720-4483 $ 17.50+.50/0
4483

M. K. Denk et al.
FULL PAPER
2
1
927 s, 2874 m, 2799 s, 2607 m, 1471 m, 1458 m, 1381, s, 1371m, 1327 s, 1200 s,
18H; C(CH
3
)
3
), 2.15 (m, 2H; CH
2 2 2 2
CH CH ), 3.56 (m, 4H; NCH ), 8.07 (s,
�
1
‡
13
1
118 w, 1089 w, 1032 m, 779 w cm
,3-Di-tert-butylimidazolidine (7d): Colorless oil; 1H NMR (200 MHz,
, 258C): d ˆ 1.09 (s, 18H; C(CH ), 2.75 (s, 4H; NCH CH ), 3.67 (s,
); H NMR (200 MHz, CDCl
), 2.83 (s, 4H; CH CH ), 3.56 (s, 2H;
400 MHz, ), 46.0 (CH
258C): d ˆ 26.1 (C(CH
C(CH ), 63.3 (N CH
.
CH );
C
NMR (400 MHz, CDCl
3
,
258C): d ˆ 19.78 (t, J(C,H) ˆ
133.4 Hz, CH
2
CH
2
CH
2
), 27.49 (q, 1J(C,H) ˆ 127.6 Hz, C(CH
3 3
) ), 39.77 (t,
1
C
2
C(CH
(
(
1
2
1
J(C,H) ˆ 144.0 Hz; NCH
2 3 3
), 61.16 (s; C(CH ) ), 130.96 (s; SCN), 146.34 (d,
6
D
H; N
6
3
)
3
2
2
1
‡
1
J(C,H) ˆ 189.1 Hz; CH ); IR (NaCl, Nujol): nÄ ˆ 2360 m, 2057 s, 1672 s,
2
CH
2
3
, 258C): d ˆ 1.07 (s, 18H;
13
1461 s, 1411 m, 1395 m, 1369 s, 1331 s, 1236 s, 1192 s, 1092 m, 1009 m, 980 m,
3
)
3
2
2
N
2
CH
2
);
C
NMR
�
1
9
42 w cm .
C
6
D
6
,
3
)
3
2
‡
CH
2
), 52.0
.
)
3
2
2
); MS (70 eV): m/z (%): 184 (15) [M] , 183 (97),
N,N'-Di-tert-butyl-1,3-propanediamine (12): Colorless plates, m. p. 298C;
H NMR (200 MHz, C
3
1
27 (30), 113 (100), 98 (8), 84 (30), 71 (89), 57 (28); IR (NaCl, neat): nÄ ˆ
6
D
6
, 258C): d ˆ 0.59 (s, 2H; NH), 1.03 (s, 18H;
3
968 s, 2872 s, 2822 s, 1654 w, 1473 m, 1463 m, 1392 s, 1360 s, 1275 s, 1251 s,
C(CH
3
)
3
), 1.52 (quin, 2H; J(H,H) ˆ 6.4 Hz, CH
2 2 2
CH CH ), 2.58 (t,
3
); 1H NMR (200 MHz, CDCl
1
225 s, 1211 s, 1158 m, 1104 w, 1086 w, 1037 m, 922 w, 861w, 820 m, 743
J(H,H) ˆ 6.4 Hz, 4H; NCH
2
3
, 258C): d ˆ
CH CH ),
, 258C):
).
�
1
3
w cm
.
1.10 (s, 18H; C(CH
3
)
3
), 1.75 (quin, J(H,H) ˆ 6.4 Hz, 2H; CH
2
2
2
3
13
,3-Diphenylimidazolidine (7e): Colorless plates, m. p. 1278C; 1H NMR
2.71 (t, J(H,H) ˆ 6.4 Hz, 4H; NCH
2
); C NMR (400 MHz, C
6
D
6
1
d ˆ 29.42 (C(CH
3
)
3
), 32.87 (CH
2
CH
2
CH
2
), 41.52 (NCH
2
), 50.04 (C(CH
3
)
3
(
200 MHz, CDCl
3
, 258C): d ˆ 3.66 (s, 4H; CH
2
CH
2
), 4.67 (s, 2H; N
2
CH
2
),
.68 (d, 3J(H,H) ˆ 8.1 Hz, 4H; ortho-CH), 6.80 (t, J(H,H) ˆ 7.3 Hz, 2H;
3
6
3
13
para-CH), 7.30 (t, J(H,H) ˆ 7.7 Hz, 4H; meta-CH); C NMR (400 MHz,
C
1
6
D
6
, 258C): d ˆ 46.47 (CH
2 2 2 2
CH ), 65.85 (N CH ), 112.44 (ortho-CH),
17.64 (para-CH), 129.36 (meta-CH), 146.41 (ipso-C); MS (70 eV): m/z
Acknowledgements
‡
.
(
(
1
%): 224 (60) [M] , 223 (81), 119 (70), 106 (63), 91 (100), 77 (54), 65 (9), 51
21); IR (NaCl, Nujol): nÄ ˆ 1601 m, 1574 m, 1502 s, 1327 m, 1239 m, 1186 m,
We thank the Natural Sciences and Engineering Research Council of
Canada (NSERC) for support of this work through an operating grant. The
comments of Prof. Ian Still on parts of the manuscript are gratefully
acknowledged. We thank one of the referees for drawing our attention to
the work on aminal radical cations by Nelsen and Buschek (ref. [29]).
�
1
158 m, 995 m, 868 w, 745 s, 693 s cm .
1
,3-Di-tert-butylimidazolidinium thiocyanate (8): Colorless prisms;
1
H NMR (200 MHz, CDCl
3
, 258C): d ˆ 1.52 (s, 18H; C(CH
3
)
3
), 4.11 (s,
, 258C): d ˆ
), 130.81 (SCN), 152.33
‡
13
4
2
2 3
H; NCH ), 8.09 (s, 1H; CH ); C NMR (400 MHz, CDCl
7.92 (C(CH
3
)
3
), 45.37 (NCH
2
), 56.86 (C(CH
3
)
3
‡
(
CH ); IR (NaCl, Nujol): nÄ ˆ 2203 w, 2066 m, 1632 m, 1301 m, 1215 w, 1167
�
1
w, 1060 w, 907 s, 888 w, 761 m, 736 s cm
.
[
1] For a comprehensive review of the technological uses of thiourea and
its derivatives see: a) B. Mertschnek, F. Meck in Ullmannꢀs Encyclo-
pedia of Industrial Chemistry, Vol. A26, 1995, 803 ± 815; b) D. C.
Schröder, Chem. Rev. 1955, 55, 181 ± 221; c) E. E. Reid, Organic
Chemistry of Bivalent Sulfur, Chem. Publishing Co, New York, 1963,
p. 65.
[2] For synthetic methods see: Houben Weyl, Methoden der Organischen
Chemie, Band E3, Kohlensäure-Derivate, Thieme, Stuttgart, 1983,
484 ± 621.
[3] a) O. Azzaroni, P. L. Schilardi, R. C. Salvarezza, A. J. Arvia, Lang-
muir 1999, 15, 1508 ± 1514; b) P. Schilardi, S. M e ndez, R. C. Salvar-
ezza, A. J. Arvia, Langmuir 1998, 14, 4308 ± 4314; c) S. M e ndez, G.
Andreasen, P. Schilardi, M. Figueroa, L. V a zquez, R. C. Salvarezza,
A. J. Arvia, Langmuir 1998, 14, 2515 ± 2524; d) V. San Martín, S.
Sanllorente, S. Palmero, Electrochim. Acta 1998, 44, 579 ± 585; e) V. V.
Mozolis, S. P. Iokubaite, Russ. Chem. Rev. (Engl. transl.) 1973, 42,
587 ± 595; f) M. Alodan, W. Smyrl, Electrochim. Acta 1998, 44, 299 ±
309.
[4] a) G. Hennrich, H. Sonnenschein, U. Resch-Genger, J. Am. Chem.
Soc. 1999, 121, 5073 ± 5074; b) V. R. Pedireddi, S. Chatterjee, A.
Ranganathan, C. N. R. Rao, J. Am. Chem. Soc. 1997, 119, 10867 ±
10868; c) A. D. Burrows, S. Menzer, D. Michael, P. Mingos, A. J. P.
White, D. J. Williams, J. Chem. Soc. Dalton Trans. 1997, 4237 ± 4240;
d) J. Smith, J. L. Liras, S. E. Schneider, E. V. Anslyn, J. Org. Chem.
1,3-Dimethylhexahydropyrimidine-2-thione (9a): Colorless platelets, m.p.
[18b]
1
7
6 � 778C (lit.: 798C ); H NMR (200 MHz, C
6
3
D
6
, 258C): d ˆ 1.03 (q,
3
J ˆ 6.2 Hz, 4H; CH
2
CH
), 3.25 (s, 6H; NCH
CH
), 3.43 (s, 6H; NCH
CH CH ), 43.20 (NCH
CˆS); MS (40 eV): m/z (%): 144 [M] (100), 129 (2), 111 (8), 97 (6), 84
2
CH
2
), 2.43 (t,
J(H,H) ˆ 6.2 Hz, 4H;
CH
2
CH
2
CH
2
3
); 1H NMR (CDCl
3
): d ˆ 2.04 (quin,
3
3
J(H,H) ˆ 6.2 Hz, 2H; CH
2
2
CH
2
), 3.38 (t, J(H,H) ˆ 6.2 Hz, 4H;
CH
2
CH CH
2
2
3
); 13C NMR (400 MHz, C
6
D
6
, 258C):
d ˆ 21.21 (CH
2
2
2
3
), 48.41 (CH CH CH ), 180.59
2
2
2
‡
.
(
(
2
4), 70 (15), 55 (4), 44 (27), 42 (23), 32 (8), 28 (21); IR (KBr, pellet): nÄ ˆ
956 s, 2933 s, 2863 s, 1528 s, 1487 m, 1450 m, 1399 m, 1348 s, 1315 s, 1220 m,
1
099 m, 1037 m, 933 w, 900 vw, 864 w, 847 w, 638 w, 607 w, 572 w, 495 w, 429
�
1
w cm
.
1
,3-Di-tert-butylhexahydropyrimidine-2-thione (9b): Colorless prisms;
1
3
1
H NMR (200 MHz, CDCl
3
, 258C): d ˆ 1.64 (s, C(CH
3
)
3
), 2.07 (quin,
N);
3
J(H,H) ˆ 7.1 Hz, CH
2
CH
2
CH
2
), 3.16 (t, J(H,H) ˆ 7.1 Hz, CH
2
3
1
C NMR (400 MHz, CDCl
3
, 258C): d ˆ 28.10 (q, J(C,H) ˆ 124.2 Hz,
1
C(CH
3
)
3
), 29.36 (CH ), 42.39 (t, J(C,H) ˆ 137.6 Hz, NCH
), 185.32 (CˆS);
325.13; MS (40 eV): m/z (%): 228 (30), 227 (40), 197 (7), 171 (100), 157
2
CH
2
CH
2
2
), 52.09
1
5
(
C(CH
3
)
3
N
NMR (500 MHz, CDCl
3
,
258C): d ˆ
�
(
15), 125 (15), 116 (85), 98 (10), 72 (12), 57 (40), 41 (45); IR (NaCl, Nujol):
�
1
nÄ ˆ 1527 s, 1489 w, 1460 s, 1398 m, 1348 s, 1315 s, 1220 m, 1097 w, 864 w cm
.
1
1,3-Dimethylhexahydropyrimidine (10a): Colorless oil;
H
NMR
3
(
200 MHz,
C
6
D
6
,
258C): d ˆ 1.54 (quin, J(H,H) ˆ 4.8 Hz, 2H;
1
996, 61, 8811 ± 8818; e) S. Singh, S. P. Mathur, R. S. Thakur, M.
Katyal, Acta Cien. Indica Chem. 1987, 13, 40; f) P. S. Sidhu, G. H.
Penner, K. R. Jeffrey, B. Zhao, Z. L. Wang, I. Goh, J. Phys. Chem. B
3
CH
CH
2
CH
CH
2
CH
CH
2
2
), 2.11 (s, 6H; NCH
), 2.90 (s, 2H; NCH
3
), 2.25 (t, J(H,H) ˆ 4.8 Hz, 4H;
1
2
2
2
N); H NMR (200 MHz, CDCl
3
, 258C):
3
d ˆ 1.70 (quin, J(H,H) ˆ 5.6 Hz, 2H; CH
2
CH
2
CH
2
), 2.24 (s, 6H; NCH
3
),
1
997, 101, 9087 ± 9097.
3
13
2
.41 (t, J(H,H) ˆ 5.6 Hz, 4H; CH
2
CH
2
CH
CH
N); IR (NaCl, neat): nÄ ˆ 3396 br, 2939 s, 2851 s,
780 s, 2727 s, 2666 m, 2643 m, 2567 w, 2482 vw, 2463 vw, 1655 vw, 1466 s,
445 s, 1337 w, 1300 m, 1275 s, 1254 w, 1206 m, 1196 m, 1148 s, 1113 s, 1097
2
), 2.98 (s; NCH
2
N); C NMR
[
5] a) L. Y e pez-Mulia, R. Morales-Hurtado, N. Viveros-Guzm a n, R.
Cedillo-Rivera, F. Hern a ndez-Luis, R. Castillo, A. Hern a ndez-Cam-
pos, O. Mu nÄ oz, Arch. Med. Res. 1999, 30, 368 ± 374; b) H. Kogen, K.
Tago, M. Arai, E. Minami, K. Masuda, T. Akiyama, Bioorg. Med.
Chem. Lett. 1999, 9, 1347 ± 1350; c) S. Liu, C. Tang, B. Ho, M.
Ankersen, C. E. Stidsen, A. M. Crider, J. Med. Chem. 1998, 41, 4693 ±
(
(
400 MHz, C
CH CH CH
6
D
6
, 258C): d ˆ 23.43 (CH
2
2
CH
2 3
), 42.86 (NCH ), 54.22
2
2
2
), 79.61 (NCH
2
2
1
�
1
m, 1073 s, 1046 s, 987 m, 968 s, 945 m, 915 w, 906 vw, 894 w, 823 m, 783 m
.
1
,3-Di-tert-butylhexahydropyrimidine (10b): Colorless oil; 1H NMR
4
705; d) C. T. Supuran, A. Scozzafava, B. C. Jurca, M. A. Ilies, Eur. J.
(
200 MHz,
C
6
D
6
,
258C): d ˆ 1.04 (s, 18H; C(CH
3 3
) ), 1.61 (quin,
Med. Chem. 1998, 33, 83 ± 93; e) E. G. Chalina, L. Chakarova, Eur. J.
Med. Chem. 1998, 33, 975 ± 983; f) E. G. Chalina, L. Chakarova, D.
Staneva, Eur. J. Med. Chem. 1998, 33, 985 ± 990; g) L. F. Jalander, J.-E.
Lönnqvist, Heterocycles 1998, 48, 743 ± 747; h) K. Prabhakar, F.
Jadhav, J. Woerner, H.-W. Man, Bioorg. Med. Chem. Lett. 1997, 7,
145 ± 2148; i) O. Vajragupta, A. Pathomsakul, C. Matayatsuk, L.
Ruangreangyingyod, Y. Wonkrajang, W. O. Foye, J. Pharm. Sci. 1985,
5, 258 ± 260; j) S. N. Pandeya, P. Ram, V. Shankar, J. Sci. Ind. Res.
3
3
J(H,H) ˆ 5.4 Hz, 2H; CH
2
CH
2
CH
2
), 2.52 (t, J(H,H) ˆ 5.4 Hz, 4H;
1
3
CH
2
CH
2
CH
2
), 3.44 (s, 4H; NCH
2
N); C NMR (400 MHz, C
6
D
6
, 258C):
),
d ˆ 26.83 (C(CH
3
)
3
), 29.31 (CH CH
2
2
CH ), 45.99 (NCH ), 53.24 (C(CH )
2
2
3 3
6
2
1
9
5.31 (NCH
2
N); IR (NaCl, neat): nÄ ˆ 3396 w, 2939 s, 2851 s, 2780 s, 2727 s,
666 m, 2643 m, 2567 w, 2482 vw, 2463 vw, 1655 vw, 1466 s, 1445 s, 1337 w,
300 m, 1275 s, 1254 w, 1206 m, 1196 m, 1148 s, 1113 s, 1097 m, 1073 s, 1046 s,
87 m, 968 s, 945 m, 915 w, 906 vw, 894 w, 823 m, 783 m
2
�
1
.
8
1
,3-Di-tert-butylhexahydropyrimidinium thiocyanate (11): Colorless
1981, 40, 458; k) C. Mao, E. A. Sudbeck, T. K. Venkatachalam, F. M.
Uckun, Bioorg. Med. Chem. Lett. 1999, 9, 1393 ± 1398; l) F. M. Uckun,
1
prisms, m. p. 200 ± 2048C; H NMR (200 MHz, CDCl
3
, 258C): d ˆ 1.52 (s,
4484
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0720-4484 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 20

C ± H Activation with S8
4477±4486
C. Mao, S. Pendergrass, D. Maher, D. Zhu, L. Tuel-Ahlgren, T. K.
Venkatachalam, Bioorg. Med. Chem. Lett. 1999, 9, 2721 ± 2726.
Med. Chem. 1981, 24, 1089 ± 1092; c) J. Van Alphen, Rec. Trav. Chim.
1937, 36, 343 ± 350.
[
[
6] For example: carbimazole (thyreostatic), propylthiouracil (thyreo-
static), methylthiouracil (thyreostatic), and thiamylal (ultrashort
narcotic).
7] a) The Pesticide Manual, 9th ed. (Eds.: C. R. Worthing, R. J. Hance),
The British Crop Protection Council, Farnham, 1991; b) K. H. Büchel,
The Chemistry of Pesticides, Wiley, New York, 1983, p315; c) J.
Drabek, Spec. Publ. Royal Soc. Chem. 1990, 79, 170.
[19] H. W. Wanzlick, B. Lachmann, E. Schikora, Chem. Ber. 1965, 98,
3170 ± 3177.
[20] The reaction of formaldehyde with unsubstituted 1,2-diaminoethane
and 1,3-diaminopropane has recently been shown to lead to the
formation of complex aza-bicyclic and aza-macrocyclic systems:
a) M. R. Suissa, C. Rùmming, J. Dale, Chem. Commun. 1997, 113 ±
114; b) J. Dale, T. Sigvartsen, Acta Chem. Scand. 1991, 45, 1064 ± 1070;
c) J. Dale, C. Rùmming, T. Sigvartsen, Acta Chem. Scand. 1991, 45,
1071 ± 1075.
[21] For the recent use of sulfur in inorganic and organic synthetic
reactions see: a) S. Al-Ahmad, B. Boje, J. Magull, T. Rauchfuss. Y.
Zheng, J. Am. Chem. Soc. 1995, 117, 1145 ± 1146; b) D. Jungk, N.
Schmidt, J. Hahn, P. Versloot, J. G. Haasnoot, J. Reedijk, Tetrahedron
1994, 50, 11187; c) F. Bigoli, M. A. Pellinghelli, D. Atzei, P. Deplano,
[
[
8] R. Wegler, Chemie der Pflanzenschutz- und Schädlingsbekämpfungs-
mittel, Springer, Berlin, 1970, 605 ± 606.
9] a) L. Chai, M. Okido, W. Wei, Hydrometallurgy 1999, 53, 255 ± 266;
b) F. Z. El Aamrani, A. Kumar, J. L. Cortina, A. M. Sastre, Anal.
Chim. Acta 1999, 382, 205 ± 213; c) Y.-Z. Wei, M. Yamaguchi, M.
Kumagai, Y. Takashima, T. Hoshikawa, F. Kawamura, J. Alloys
Compd. 1998, 271 ± 273, 693 ± 696; d) G. Fairthorne, D. Fornasiero, J.
Ralston, Int. J. Miner. Process. 1997, 50, 227 ± 224; e) K. Ennassef, D.
Pareau, M. Z. Benabdallah, G. Durand, Bull. Soc. Chim. Fr. 1996, 133,
E. F. Trogu, Phosphorus
& Sulfur 1988, 37, 189 ± 194; d) T. S.
Cameron, A. Decken, M. Fang, S. Parsons, J. Passmore, D. J. Wood,
Chem. Commun. 1999, 1801 ± 1802.
151 ± 159; f) K. Ennassef, D. Pareau, M. Z. Benabdallah, G. Durand,
Bull. Soc. Chim. Fr. 1995,132, 985 ± 994; g) G. L. Yan, J. Alstad, J.
Radioanal. Nucl. Chem. Lett. 1995, 201, 191 ± 198; h) K. R. Koch, C.
Sacht, S. Bourne, Inorg. Chim. Acta 1995, 232, 109 ± 115; i) S.-G. Kim,
H. J. Lee, J.-K. Oh, E.-C. Lee, Hydrometallurgy 1995, 38, 7 ± 13;
j) P. A. Distin, G. D. Demopoulos, J. Met. 1985, 46; k) K.-H. König, M.
Schuster, G. Schneeweis, B. Steinbrech, Fresenius' Z. Anal. Chem.
[22] The use of noncyclic formaldehyde aminals gives lower yields and
leads to the formation of N-thioformyl derivatives which can become
the main products under certain reaction conditions. Details will be
published elsewhere.
[23] X-ray crystallographic data. 5a: C11
H
20
N
2
S, M
r
ˆ 212.35, crystal size ˆ
0.06 Â 0.13 Â 0.18 mm, orthorhombic, space group: Pca2
1
,
a ˆ
3
1985, 325, 621; l) A. S. Chernyak, M. Knothe, Hydrometallurgy 1983,
11.573(1), b ˆ 9.5648(8), c ˆ 11.169(1) Š, Vˆ 1236.4(1) Š , Z ˆ 4,
�
3
� 1
11, 265.
1
calcd ˆ 1.141 gcm
,
l(CuKa) ˆ 1.54178 Š, m(CuKa) ˆ 0.564mm
,
[
10] a) F. Korte, GIT Laborfachzeitschrift 1999, 1082 ± 1083; b) F. Korte,
Fresenius Environmental Bulletin 1998, 7, 128 ± 141; c) F. Korte, F.
Coulston, Ecotox. Environ. Safe. 1998, 41, 119 ± 129; d) S. Ubaldini, P.
Fornari, R. Massidda, C. Abruzzese, Hydrometallurgy 1998, 48, 113 ±
F(000) ˆ 464, scan type: 2q ± q, Tˆ 293(2) K, 4.62 < q < 57.18, 993
independent reflections (R
4s(F)) ˆ 1253, R ˆ 0.033, R
i
ˆ 0.0342), no. of observations [(F) >
ˆ 0.088, maximum peak in final Fourier
w
�
3
difference synthesis ˆ 0.28 eŠ . 6d: C11
H
22
N
2
S, M
r
ˆ 214.37, crystal
124; e) L. M. Abrantes, M. C. Costa, Hydrometallurgy 1996, 40, 99 ±
110; f) D. S. R. Murthy, P. M. Prasad, Hydrometallurgy 1996, 42, 27 ±
3
3; g) L. Tremblay, G. Desch eà nes, E. Ghali, J. McMullen, M.
size ˆ 0.34  0.42  0.28 mm, orthorhombic, space group: Pca2
1
, a ˆ
3
11.615(1), b ˆ 9.248(2), c ˆ 11.041(1) Š, Vˆ 1186.0(3) Š , Z ˆ 4,
�
3
� 1
1
calcd ˆ 1.201 gcm , l(MoKa) ˆ 0.71073 Š, m ˆ 0.564mm , F(000) ˆ
472, scan type: 2q ± q, Tˆ 173(2) K, 2.82 < q < 29.998, 2004 independ-
ent reflections (R
ˆ 0.0342), no. of observations [(F) > 4s(F)) ˆ 2343,
R ˆ 0.064, R ˆ 0.123, maximum peak in final Fourier difference
Lanouette, Int. J. Miner. Process. 1996, 48, 225 ± 244; h) G. Zuo, M.
Muhammed, Reactive Polymers 1995, 24, 165 ± 181; i) G. Zuo, M.
Muhammed, React. & Funct. Poly. 1995, 27, 187 ± 198; j) P. J. Conradie,
M. W. Johns, R. J. Fowles, Hydrometallurgy 1995, 37, 349 ± 366;
k) M. F. Almeida, M. A. Amarante, Minerals Engineering 1995, 8,
i
w
�
3
synthesis ˆ 0.93 eŠ . 8: C12
H
23
N
3
S, M
r
ˆ 241.39, crystal size ˆ 0.32 Â
0.30  0.15 mm, monoclinic, space group: P2(1)/n, a ˆ 6.9049(2), b ˆ
3
257 ± 271; l) D.-E. Akretche, S. K. Slimane, H. Kerdjoudj, Hydro-
14.7905(5), c ˆ 13.6393(5) Š, b ˆ 96.971(5)8, Vˆ 1382.64(8) Š , Z ˆ 4,
�
3
� 1
metallurgy 1995, 38, 189 ± 204; m) S. Singh, S. P. Mathur, R. S. Thakur,
L. Keemti, Orient. J. Chem. 1987, 3, 203; n) Yu. A. Zolotov, O. M.
Petrukhun, V. N. Shevchenko, V. V. Dunina, E. G. Rukhadze, Anal.
Chim. Acta 1978, 100, 613 ± 618.
1
calcd ˆ 1.160 gcm
,
l(MoKa) ˆ 0.7103 Š, m ˆ 0.215mm
,
F(000) ˆ
o
528, scan type 2q ± q, Tˆ 150.0(1) K, 4.08 < q < 26.38 , 2816 independ-
ent reflections (R
Fourier difference synthesis ‡0.487 eŠ and � 0.355 eŠ . 11:
S, M
ˆ 255.42, crystal size ˆ 0.25  0.18  0.12 mm, ortho-
i
ˆ 0.0483), R
w
ˆ 0.059, maximum peak in final
�
3
�
3
[
[
[
11] A. J. Arduengo, R. L. Harlow, M. Kline, J. Am. Chem. Soc. 1991, 113,
C
13
H
25
N
3
r
361.
rhombic, space group: Im2m, a ˆ 6.9330(12), b ˆ 10.1506(10), c ˆ
3
� 3
12] a) A. J. Arduengo, (Wilmington, Delaware), US Pat. 5077414, 1991;
b) B. L. Benac, E. M. Burgess, A. J. Arduengo, Org. Synth. 1986, 64, 92.
13] a) R. W. Alder, M. E. Blake, Chem. Commun. 1998, 441; b) R. W.
Alder, M. E. Blake, Chem. Commun. 1997, 1513 ± 1514; c) R. W.
Alder, P. R. Allen, G. Murray, A. G. Orpen, Angew. Chem. 1996, 108,
10.5640(17) Š,
Vˆ 743.43(19) Š ,
Z ˆ 2,
1
calcd ˆ 1.141 gcm
,
�
1
l(MoKa) ˆ 0.7103 Š, m ˆ 0.203mm , F(000) ˆ 280, scan type: 2q ± q,
Tˆ 100.0(1) K, 5.25 < q < 24.988, 716 independent reflections (R
i
ˆ
ˆ
0.082), R ˆ 0.071, R
w
ˆ 0.018, maximum peak in final Fourier differ-
�
3
� 3
ence synthesis ‡0.66 eŠ and � 0.26 eŠ . 12: C11
H
2
H
24
N
2
, M
r
3
1211 ± 1213; Angew. Chem. Int. Ed. Engl. 1996, 35, 1121 ± 1123;
186.34, crystal size 0.32 Â 0.25 Â 0.18 mm , monoclinic, space group
P2(1)/n, a ˆ 9.4791(3), b ˆ 8.6096(4), c ˆ 16.0961(3) Š, b ˆ
d) R. W. Alder, P. R. Allen, S. J. Williams, J. Chem. Soc. Chem.
Commun. 1995, 1267 ± 1268; e) H. Eilingsfeld, G. Neubauer, M.
Seefelder, H. Weidinger, Chem. Ber. 1964, 97, 1232.
3
� 3
103.054(3)8, Vˆ 1279.68(8) Š , Z ˆ 4, 1calcdˆ0.967 Mgm , l(MoKa) ˆ
�
1
0.71073 Š, m ˆ 0.057mm
150.0(1) K, 4.41 < q < 26.388, 2604 independent reflections (R
0.036), R ˆ 0.0372, R ˆ 0.0902, maximum peak in final Fourier
,
F(000) ˆ 424, scan type: 2q ± q, Tˆ
[
[
14] R. W. Alder, C. P. Butts, A. G. Orpen, J. Am. Chem. Soc. 1998, 120,
i
ˆ
11526 ± 11527.
w
�
3
15] This may be due in part to the formation of complexes between
diaminocarbenes and alkali halides a) R. W. Alder, M. E. Blake, C.
Bortolotti, S. Bufali, C. P. Butts, E. Linehan, J. M. Oliva, A. G. Orpen,
M. J. Quayle, Chem. Commun. 1999, 241 ± 242; b) R. W. Alder, M. E.
Blake, J. M. Oliva, J. Chem. Phys. A 1999, 103, 11200 ± 11211.
difference synthesis 0.173 and � 0.132 eŠ . Data were collected on
a Siemens P4 diffractometer. No absorption correction was applied.
Lorentz and polarization corrections were applied. Systematically
absent reflections were rejected and equivalent reflections were
merged. The heavy-atom positions were determined by direct
methods. Subsequent difference Fourier synthesis revealed the
positions of all other non-hydrogen atoms: hydrogen atoms were
placed in idealized position. The non-hydrogen atoms were refined by
the full-matrix least-squares method, with the hydrogen atoms riding
[
16] a) N. Kuhn, E. Niquet, M. Steimann, I. Walker, Z. Naturforsch. B
1999, 54, 1181 ± 1187; b) N. Kuhn, T. Kratz, Synthesis 1993, 561 ± 562.
[
17] a) M. K. Denk, A. Thadani, K. Hatano, A. J. Lough, Angew. Chem.
1997, 109, 2719 ± 2721; Angew. Chem. Int. Ed. Engl. 1997, 36, 2607 ±
2609; b) M. K. Denk, K. Hatano, M. J. Ma, Tetrahedron Lett. 1999, 40,
2057 ± 2060; c) M. K. Denk, J. Rodezno, S. Gupta, A. J. Lough, J.
�
1
2
on their supporting carbon atoms. A weighting Scheme (w ˆ s (F) ‡
2
0.001F ) was applied and the data were corrected for the effects of
Organomet. Chem. 2001, 617 ± 618, 737 ± 740; d) M. K. Denk, J.
Rodezno, J. Organomet. Chem. 2000, 608, 122 ± 125.
anomalous dispersion and secondary extinction. Crystallographic
[
24]
calculations were carried out using the SHELXTL/PC
program,
[
18] a) R. A. Donia, J. A. Shotton, L. A. Bentz, G. E. P. Smith, J. Org.
Chem. 1949, 14, 946 ± 951; b) C.-D. Li, S. L. Mella, A. C. Sartorelli, J.
version 5.1, on a Pentium 133 PC in the Chemical Crystallography
Laboratory, University of Toronto, Canada.
Chem. Eur. J. 2001, 7, No. 20
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0720-4485 $ 17.50+.50/0
4485

M. K. Denk et al.
FULL PAPER
[
24] a) G. M. Sheldrick, Acta Crystallogr. Sect. A 1990, 46, 467 ± 473;
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25] Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Center as supplementary publication nos.
CCDC-158166 (5a), CCDC-158167 (6d), CCDC-158168 (8), CCDC-
B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y.
Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R.
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Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, and J. A. Pople,
Gaussian, Inc., Pittsburgh PA, 1995. Molecular geometries were fully
optimized and vibrational frequencies were calculated as indicated.
The absence of virtual frequencies ensures that the calculated
[
158169 (11), CCDC-158170 (12). Copies of the data can be obtained
[
32]
free of charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
structures are minima rather than saddle points.
[32] a) J. B. Foresman, A. Frisch, Exploring Chemistry with Electronic
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[
[
26] C. K. Johnson, ORTEP, FORTRAN Thermal Ellipsoid Plot Program
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27] a) R. Cae-Olivares, O. Jim e nez-Sandoval, S. Hern a ndez-Ortega, M.
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28] M. K. Denk, J. Brownie, unpublished results.
29] J. M. Buschek, J. Am. Chem. Soc. 1974, 96, 7930 ± 7934.
30] The cyclic formaldehyde aminals investigated in this study are
[33] a) A. D. Becke, Phys. Rev. A 1988, 38, 3098; b) C. Lee, W. Yang, R. G.
Parr, Phys. Rev. B 1988, 37, 785; c) A. D. Becke, J. Chem. Phys. 1993,
98, 5648.
[
[
[
[
32a]
[34] The Gaussian keyword CBS-4m
was used to call up the modified
CBS-4 procedure. J. W. Ochterski, G. A. Peterson, J. A. Montgomery
Jr., J. Chem. Phys. 1996, 104, 2598.
[35] L. A. Curtiss, K. Raghavachari, G. W. Trucks, J. A. Pople, J. Chem.
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attacked by O
the complete consumption of the aminal. The main reaction product
40%) is the N,N'-di(formyl)-N,N'-di-tert-butylethylenediamine,
CH
2 2
. Reaction of neat 7d with O at 1208C resulted in
(
tBuN(CHˆO)CH
N(CHˆO)tBu, which was characterized by
[36] J. K. Huang, H. J. Schanz, E. D. Stevens, S. P. Nolan, Inorg. Chem.
2000, 39, 1042 ± 1045. The smaller reaction enthalpy of � 24.1 Æ
2
2
single-crystal X-ray crystallography. Details will be reported else-
where.
�
1
1.5 kcalmol reported for R ˆ 1-adamantyl is presumably due to
steric effects (repulsion between sulfur and the adamantyl substituent
in the respective thiourea).
[
31] The calculations were carried out with the Gaussian 94 suite of
programs: Gaussian 94, Revision D.4, M. J. Frisch, G. W. Trucks, H. B.
Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman,
T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A.
Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski,
Received: August 24, 2000
Revised: June 13, 2001 [F2692]
4486
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0720-4486 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 20