A new simple synthesis of cis- and
trans-3,5-di-tert-butyl-3,5-diaryl-1,2,4-trithiolanes from ketones and
tetraphosphorus decasulfide
Kentaro Okuma,*a Shinji Shibata,a Kosei Shiojia and Yoshinobu Yokomorib
a Department of Chemistry, Faculty of Science, Fukuoka University, Jonan-ku, Fukuoka 814-0180, Japan.
E-mail: kokuma@fukuoka-u.ac.jp
b Department of Applied Chemistry, National Defense Academy, Hashirimizu, Yokosuka 239-8686, Japan
Received (in Cambridge, UK) 18th May 2000, Accepted 30th June 2000
The reaction of pivalophenones with tetraphosphorus dec-
asulfide afforded cis- and trans-3,5-di-tert-butyl-3,5-diaryl-
1,2,4-trithiolanes, which equilibrated to give other isomers in
refluxing toluene via thiopivalophenones and thiopivalophe-
none S-sulfides.
cis-1a was on the other aromatic plane whereas the tert-butyl
group of trans-1a was on the aromatic plane.
Both structures were confirmed by single crystal X-ray
crystallographic analysis (Fig. 1)9: no unusual bond lengths or
angles are observed in the 1,2,4-trithiolane rings. The trithiolane
rings of both products have similar conformations to other
trithiolanes. The C–S bond lengths of the trithiolane rings are
between 1.796 and 1.875 Å—longer than normal (1.763–1.767
Å)6 because the trithiolane rings are compressed by bulky tert-
butyl groups. However, the S–S bond lengths (2.027 Å for cis-
1a and 2.016 Å for trans-1a) are shorter than the one reported
by Senning et al. (2.0345 Å).7 As suggested by their NMR
spectra, the aromatic groups of cis-1a were out of plane whereas
the tert-butyl group of trans-1a was on the aromatic plane.
Other reactions were similarly carried out. The results are
shown in Table 2.
More than three decades ago, Elam and Davis reported the
synthesis of dimethylthioketene dimer by the reaction of
tetramethylcyclobutane-1,3-dione with tetraphosphorus deca-
sulfide. They isolated the corresponding trithiolane as a side
product (2.8%).8 However, they did not apply the general
synthesis of 1 from ketones. The reaction of pivalophenone with
P4S10 generally afforded thiopivalophenone in good yield.10
The present reaction is the first practical method on the
synthesis of 1 from ketones by using P4S10.
1,2,4-Trithiolanes (1), some of which have been obtained from
natural products, are well-known.1 Methods for their synthesis
include: reaction of thiobenzophenone with o-chloranil,2 reac-
tion of thiobenzophenones with 1,1-diphenylethylene sulfide,3
reaction of thiones with Lowesson reagents,4 reaction of dialkyl
ketones with hydrogen sulfide elemental sulfur, and amines,5
and fragmentation of 1,2,3-thiadiazoles.6 Recently, Senning and
co-workers reported that reaction of a-chlorosulfenyl disulfides
with morpholine afforded the corresponding dispirotrithio-
lanes.7 However, there are only a few reports on the synthesis of
trithiolanes from ketones using thiation reagents although it is
well known that the reaction of ketones with tetraphosphorus
decasulfide (P4S10) affords the corresponding thioketones.8 We
have investigated the synthesis of trithiolanes from ketones
using P4S10 as a thiation reagent and report herein the isolation
and X-ray crystallographic analysis of cis- and trans-1 from
P4S10 and their thermal isomerization.
Treatment of 4-methylpivalophenone with P4S10 in refluxing
pyridine for 48 h resulted in the formation of trans-3,5-di-tert-
butyl-3,5-di-p-tolyl-1,2,4-trithiolane (trans-1a), cis-3,5-di-tert-
butyl-3,5-di-p-tolyl-1,2,4-trithiolane (cis-1a), and 4-methyl-
thiopivalophenone (2a) in 13, 35, and 23% yields, respectively.
Refluxing for 72 h resulted in the formation of cis-1a in 35 %
yield along with trans-1a (24%) and 2a (16%) (Scheme 1).
The structures cis-1a and trans-1a were confirmed by NMR
and elemental analysis. Table 1 lists the 1H NMR and 13C NMR
data for cis- and trans-1a. The chemical shift of the tert-butyl
group of trans-1a is higher than that of cis-1a, whereas chemical
shifts of the aromatic groups of trans-1a are lower than those of
cis-1a. This observation suggests that each aromatic group of
Thiocarbonyl S-sulfides (thiosulfines) are well-known to
exhibit high reactivity such as dienophile-like behavior, for
example, and can add to a variety of thiones to give 1.
3,3,5,5-Tetraaryl-1,2,4-trithiolanes are thermally unstable and
dissociate into thiocarbonyl S-sulfides and thiobenzophenone in
refluxing chloroform.3 Since cis- and trans-1 were isolated, the
thermal behavior of these isomers was investigated. A solution
of cis-1a in deuterated toluene was heated at 110 °C for 72 h.
1
The H NMR spectroscopic analysis of the solution revealed
that cis-1a gradually converted to trans-1a (26%), along with 2a
(44%), whereas cis-1 a was recovered in 25% yield. While
trans-1a also converted to cis-1a, the rate of conversion was
low. After being heated at 110 °C for 72 h, 66% of trans-1a still
remained, suggesting that trans-1a is more stable than the
corresponding cis-isomer. The most straightforward explana-
tion for the conversion of cis-1a to trans-1a involves the
isomerization of cis-1a to the thiocarbonyl S-sulfide (3a) and 2a
followed by recombination via 1,3-dipolar cycloaddition be-
tween 3a and 2a (Scheme 2).
Table 1 Spectral data of cis- and trans-1a
1H NMR
13C NMR
trans-1a 1.04 (s, 18H, t-Bu), 2.35 (s, 6H,
ArMe), 7.10 (d, 4H, J = 8.0 Hz,
Ar), 7.81 (d, 4H, J = 8.0 Hz, Ar)
20.93, 29.78, 40.71,
100.65, 127.11,
130.84, 136.15, 140.11
cis-1a
1.21 (s, 18H, t-Bu), 2.20 (s, 6H,
ArMe), 6.81 (d, 4H, J = 8.2 Hz,
7.40 (d, 4H, J = 8.2 Hz, Ar)
20.75, 28.81, 41.96,
97.76, 126.52, 130.39,
135.74, 137.96
Scheme 1
DOI: 10.1039/b004013o
Chem. Commun., 2000, 1535–1536
This journal is © The Royal Society of Chemistry 2000
1535
Okuma
