Synthesis and characterization of aliphatic α-dithiones, di(1-adamantyl)- and di-tert-butylethanedithiones

Article abstract of DOI:10.1021/ja0371496

2,3-Di(1-adamantyl)thiirene 1-oxide quickly reacted with Lawesson's reagent in CH₂Cl₂ at room temperature to provide di(1-adamantyl)ethanedithione (1) as thermally labile, violet crystals in 20% isolated yield. The use of CS₂ as the solvent gave 1 in 46% isolated yield. The reaction in the presence of dimethyl acetylenedicarboxylate furnished dimethyl 4,5-di(1-adamantyl)-2,3-thiophenedicarboxylate in 51% yield. A tentative mechanism for the formation of 1 is proposed on the basis of the experimental observations. The structure of 1 was characterized on the basis of spectroscopic data (NMR, mass, IR, Raman, and UV/vis) and DFT calculations. 1 rearranged to 3,4-di(1-adamantyl)-1,2-dithiete quantitatively with kinetic parameters of ΔH_? = 17.6 ± 0.2 kcal mol^-1, ΔS_? = -23.0 ± 0.7 cal K^-1 mol^-1, and ΔG_? = 24.4 ± 0.4 kcal mol^-1. Peracid oxidation and Pt-complex formation of 1 are also reported. Copyright

Full text of DOI:10.1021/ja0371496

Published on Web 09/13/2003
Synthesis and Characterization of Aliphatic r-Dithiones, Di(1-adamantyl)- and
Di-tert-butylethanedithiones
Yutaka Ono, Yoshiaki Sugihara, Akihiko Ishii, and Juzo Nakayama*
Department of Chemistry, Faculty of Science, Saitama UniVersity, Sakura-ku, Saitama, Saitama 338-8570, Japan
Received July 9, 2003; E-mail: nakaj@post.chem.saitama-u.ac.jp
In 1973, Ku¨sters and de Mayo succeeded in the first synthesis
of a stable R-dithione, 4,4′-bis(p-dimethylamino)dithiobenzil (1).1,2
The dark red crystalline 1 has the s-trans structure 2 in the solid,
but exists in solution as an equilibrium mixture of R-dithione 2
and its valence tautomer 1,2-dithiete 3. The position of the
dithione-dithiete equilibrium depends on the substituent attached
to the sp2 carbon atom.3,4 Thus, electron-donating substituents
stabilize dithiones as is true for 1, while electron-withdrawing
substituents favor dithietes as is evidenced by successful preparation
of dithietes 45 and 5.6 On the other hand, several 1,2-dithietes, which
during the reaction. Reportedly 14a (or 14b) is trapped by
are stabilized by bulky alkyl substituents, are also known.7,8 Typical
examples are highly stable 6 and 7, whose convenient synthesis
was developed by us.7 Here, we report the synthesis, isolation, and
characterization of the first aliphatic R-dithiones, di(1-adamantyl)-
ethanedithione (8) and di-tert-butylethanedithione (9), the valence
tautomers of 6 and 7, respectively.2
cycloaddition with CS2 to give dithiole-2-thione 15.16 The reaction
was therefore carried out in CS2 as the solvent. Unexpectedly,
however, the reaction gave 8 in a better yield (46% isolated yield),
and not the expected 15. On the other hand, the reaction in the
presence of dimethyl acetylenedicarboxylate (DMAD), a trapping
agent of R-keto carbenes,17 in CS2 gave congested thiophene 16 in
51% yield. A separate experiment revealed that DMAD does not
react with 8 to give 16.
Thus, a tentative mechanism that involves the formation of
sulfonium ion 17 and then sulfur ylide 18 is proposed. 18 would
produce 8 with a highly twisted structure by extrusion of 20, while
reaction of 17 with DMAD would produce 19, which finally leads
to the formation of 16.
Recently, we developed a convenient synthesis of thiirene 1-oxide
10 and related derivatives.9 With the expectation of obtaining
thiirene 1-sulfide 11 or its desulfurizaton product 12, 10 was treated
with Lawesson’s Reagent (LR) in CH2Cl2 at room temperature.10
The reaction took place with quick development of violet coloration.
The reaction mixture was treated after 15 min to provide thermally
labile violet crystals of 811 in 20% yield (65% yield based on the
UV/vis spectral data). The 13C NMR spectrum of 8 showed the
single CdS carbon peak at δ 269.7, while the UV/vis spectrum
exhibited a weak absorption at 520 nm (ꢀ 124) characteristic of
the CdS group.11 The FAB mass spectrum gave the molecular ion
peak at m/z 358.11,12 DFT calculations (B3LYP/6-31G* level)
predicted that the IR spectrum of 8, based on the optimized
geometry, would show the intense absorption at 1118 cm-1 that
originates from the asymmetrical vibration associated with the two
CdS bonds, while the observed spectrum showed an intense
absorption at 1149 cm-1 13,14
.
Meanwhile, the same calculations
The violet crystals of 8 turn faint-yellow at 151-153 °C and
melt at 194-196 °C due to isomerization to dithiete 6, mp 197-
198 °C. It also isomerizes to 6 in solution quantitatively. The
predicted that the Raman spectrum would show an intense band at
1116 cm-1 that originates from the symmetrical vibration of the
two CdS bonds, while the observed spectrum showed an intense
1
progress of the isomerization was thus monitored by H NMR in
band at 1148 cm-1 13,14
.
dilute CDCl3 solution (0.014 M) to determine the kinetic parameters.
The reaction is first order in 8 and gave the rate constants of (6.13
( 0.08) × 10-6, (2.33 ( 0.10) × 10-5, and (1.34 ( 0.03) × 10-4
s-1 at 295, 308, and 328 K, respectively, thus providing kinetic
parameters of ∆Hq ) 17.6 ( 0.2 kcal mol-1, ∆Sq ) -23.0 ( 0.7
cal K-1 mol-1, and ∆Gq298 ) 24.4 ( 0.4 kcal mol-1. The ∆Sq value
of the isomerization is comparable to that of the cyclization of 22
Dithione 9 was also formed in about 20% yield by treatment of
thiirene 1-oxide 13 with LR, although it was not isolated in pure
form.15
We thought initially that the unexpected formation of 8 would
be explained by reaction of carbene 14a (ring-opening product of
12) or isomeric biradical 14b with activated sulfur species generated
9
12114
J. AM. CHEM. SOC. 2003, 125, 12114-12115
10.1021/ja0371496 CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
Supporting Information Available: Experimental procedures for
the preparation and reactions of 8 and kinetic parameter determination
of the isomerization of 8 to 6. Calculated and observed IR and Raman
spectra of 8 (PDF). This material is available free of charge via the
Internet at http://pubs.acs.org.
References
Figure 1. Optimized structure of 8.
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Because, despite numerous attempts, we could not obtain good
single crystals of 8 suitable for X-ray crystallographic analysis, the
optimized structure was determined by DFT calculations (Figure
1). The two adamantyl groups are twisted with a large dihedral
angle of 106.2°. Reportedly the two adamantyl groups in 6 are
twisted only by about 6.0° in the crystalline state.20,21 Thus, the
isomerization of 8 to 6 would require that the two adamantyl groups
become nearly coplanar with s-cis conformation at the transition
state against increasing steric repulsion; the s-trans coplanar
conformation of 8 is less stable by 34.7 kcal mol-1 than the
optimized twisted conformation. This would be the very reason
that 8 is isolated in pure form. The calculations also predicted that
8 is less stable than the optimized structure of 6 by 2.69 kcal
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(11) 8: Violet fine needles (from pentane); 1H NMR (CDCl3, 400 MHz) δ
1.67-1.74 (12H, br m), 2.07-2.13 (18H, br m); 13C NMR (CDCl3, 100.6
MHz) δ 28.77, 36.19, 43.78, 53.96, 269.70; IR (KBr) ν 2908, 2848, 1451,
1342, 1149, 1060, 1010, 965, 884, 881, 710, 655, 636, 573 cm-1; Raman
ν 2914, 2891, 2849, 1433, 1351, 1313, 1265, 1252, 1206, 1180, 1148,
mol-1 22
.
The oxidation of 6 with m-chloroperbenzoic acid (MCPBA, 3
equiv), where the final products are furnished by ring-opening of
bis-sulfoxide intermediate 25, produces a mixture of bis-sulfines,
24EE, 24EZ, and 24ZZ, in a ratio of ca. 30:10:1.23 On the other
hand, the oxidation of 8 with MCPBA (3 equiv) in CH2Cl2, which
proceeds through stepwise oxidation of the CdS groups, furnished
24EE, 24EZ, and 24ZZ in 31%, 27%, and 41% yields (thus in the
ratio 31:27:41), respectively.
1098, 1058, 1008, 973, 933, 881, 823, 812, 766, 673, 646, 623 cm-1
;
UV/vis (CH2Cl2) λmax (ꢀ) 347 (3780) 520 (124) nm; HRMS (FAB) calcd
for C22H30S2 (M+), 358.1789; found, 358.1780.
(12) In the EI mode, the fragmentation pattern of 8 resembles that of 6 closely
because of probable isomerization of 8 to 6 prior to the ionization.
(13) (a) The calculations have been performed by using the Gaussian 98
(revision A.7) program on personal computers running RedHat Linux 7.2.
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(14) Vibration modes were visualized by GaussView 2.1 program. Gaussian,
Inc.: Pittsburgh, PA, 2000.
(15) 9: 1H NMR (CDCl3, 400 MHz) δ 1.46 (18H, s); 13C NMR (CDCl3, 100.6
MHz) δ 30.1, 32.3, 270.8 (CdS); UV/vis (CH2Cl2) λmax 518 nm.
(16) Nakayama, J.; Masui, N.; Sugihara, Y.; Ishii, A. Bull. Chem. Soc. Jpn.
1998, 71, 1181-1186 and references therein.
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(19) The small ∆Sq value in conversion of 2 to 3 would be attributed to the
restricted rotation of the aryl group by conjugation with the CdS group.1b
Such conjugation is not expected for the aliphatic dithione 8, thus
conversion of 8 to 6 giving a larger ∆Sq value than that of 2 to 3.
(20) Yokomori, Y.; Nakayama, J. 1994, unpublished results.
(21) Donahue, J. P.; Holm, R. H. Acta Crystallogr. 1998, C54, 1175-1178.
(22) The actual energy difference would be much greater because 6 is thermally
stable and does not show any tendency to isomerize to 8. The relative
stabilities of the parent ethanedithione and 1,2-dithiete are a matter of
controversy in calculation studies.3
Treatment of 8 with two molar amounts of ethylenebis-
(triphenylphosphine)platinum(0) (26) gave a 1:1 dithiolene complex
27 in 45% yield; no expected bis-platinum complex 28 was formed.
The same complex 27 was also produced in 48% yield by treatment
of 6 with 26.
Acknowledgment. This work was supported by a Grant-in-Aid
for Scientific Research in Priority Areas (No. 13029016) from the
Ministry of Education, Science, Culture, and Technology, Japan.
(23) Nakayama, J.; Mizumura, A.; Yokomori, Y.; Krebs, A.; Shu¨tz, K.
Tetrahedron Lett. 1995, 36, 8583-8586.
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