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G. Della Sala et al.
PAPER
tained as trans/cis-mixture (2b–d,f) or as separated isomers (2a,e).
The E-isomer of 2f was obtained pure (white needles) by crystalli-
zation from MeOH.
ities achieved with both the Ti(IV) catalysts are similar in
most of the examples.
The employment of a compound in minimal amounts is
one of the main goals of green chemistry. In this respect
Cp2TiCl2 is preferable to Ti(i-PrO)4. The former is very
cheap and moisture stable compound,19 so it can be used
in catalytic amount of 1 mol%, whereas for the more sen-
sitive Ti(i-PrO)4, less than 5 mol% has never been report-
ed. Moreover, with Cp2TiCl2/MS only a simple filtration
is needed to remove the catalyst (Method B: see experi-
mental section).
trans-2-Phenyl-1 4,3-dithian-1-one (trans-2a)
1H NMR (400 MHz, CDCl3): = 7.45–7.36 (m, 5 H, ArH), 4.56 (s,
1 H, H-2), 3.58 (m, 1 H, H-6), 2.90 (ddd, 1 H, J = 14.1, 12.4, 2.6 Hz,
H-4), 2.77 (ddd, 1 H, J = 13.1, 13.1, 2.9 Hz, H -6), 2.70 (ddd, 1 H,
J = 14.1, 3.4, 1.4 Hz, H -4), 2.59–2.49 (m, 1 H, H-5), 2.45–2.31 (m,
1 H, H -5).
13C NMR (100.6 MHz, CDCl3): = 133.3, 129.4, 129.2, 128.8,
69.7, 54.8, 31.5, 29.6.
cis-2-Phenyl-1 4,3-dithian-1-one (cis-2a)
1H NMR (400 MHz, CDCl3): = 7.46–7.34 (m, 5 H, Ar-H), 4.77 (s,
1 H, H-2), 3.22 (m, 1 H), 3.05 (m, 1 H), 2.81–2.61 (m, 3 H), 1.87
(m, 1 H).
13C NMR (100.6 MHz, CDCl3): = 135.5, 129.1, 128.9, 128.4,
64.7, 47.4, 30.0, 13.9.
All reactions were carried out under dry N2. Glassware was flame-
dried (0.05 Torr) before use. The solvents employed were freshly
distilled and dried. Temperatures were measured externally; reac-
tions were monitored by TLC on Merck silica gel plates (0.25 mm)
and visualized by UV light and by exposition to I2 vapours.
Cp2TiCl2, Ti(i-PrO)4 and rac-(EBTHI)2TiCl2 (3), as well as TBHP
5-6 M in decane, were all purchased from Aldrich and used without
further purifications. Dithianes 1a,1b and 1g were purchased by Al-
drich. Dithiolane 1c13a and dithianes 1d15 and 1e13a were prepared as
described in literature; 1f20 was prepared by LiAlH4 reduction of 1g.
trans-2-Methyl-1 4,3-dithian-1-one (trans-2b)
1H NMR (400 MHz, CDCl3): = 3.62 (q, 1 H, J = 7.0 Hz, H-2),
3.41 (m, 1 H, H-6), 2.74 (ddd, 1 H, J = 14.0, 12.3, 2.5 Hz, H-4), 2.62
(ddd, 1 H, J = 13.3, 12.8, 2.8 Hz, H -6), 2.54 (m, 1 H, H -4) 2.51–
2.43 (m, 1 H, H-5), 2.35–2.22 (m, 1 H, H -5), 1.64 (d, 3 H, J = 7.0
Hz, CH3).
Diastereomeric ratios of products 2 were determined by integration
of characteristic 1H NMR peaks directly on the crude reaction mix-
tures. Yields refer to isolated pure compounds. trans- and cis-iso-
mers of products 2a,13c,15 2b,13c,15 2c,13a 2d15 and 2e13a,14 were
identified by comparison of their 1H NMR, 13C NMR and mp data
with those reported in the literature.
13C NMR (100.6 MHz, CDCl3): = 60.0, 53.4, 30.0, 29.5, 15.1.
trans-2-Phenyl-1 4,3-dithiolan-1-one (trans-2c)
1H NMR (400 MHz, CDCl3): = 7.49 (m, 2 H, ortho ArH), 7.42–
7.31 (m, 3 H, meta and para ArH), 5.41 (s, 1 H, H-2), 3.85 (ddd, 1
H, J = 11.5, 11.3, 5.5 Hz, H-5), 3.62 (ddd, 1 H, J = 11.5, 7.0, 2.2 Hz,
H -5), 3.36 (ddd, 1 H, J = 13.5, 5.4, 2.2 Hz, H-4), 2.91 (ddd, 1 H,
J = 13.5, 11.3, 7.0 Hz, H -4).
Flash chromatography was performed on Merck silica gel (60, par-
ticle size: 0.040–0.063 mm). NMR spectra were recorded on a
Bruker DRX 400 spectrometer (400 MHz) at r.t. EIMS spectra (EI,
30 eV) were performed on a Finnigan Polaris spectrometer. IR spec-
tra were recorded on a Bruker Vector 22 instrument. Mps were mea-
sured on a digital Electrothermal 9100 apparatus.
13C NMR (100.6 MHz, CDCl3): = 132.9, 128.8, 128.8, 128.3,
77.5, 52.9, 32.3.
2-Benzoyl-1 4,3-dithian-1-one (2d) (trans/cis-Mixture)
Titanium-Catalyzed Oxidation of 1a–f; General Procedure
To a stirred mixture of the appropriate Ti(IV) catalyst (see Tables 1
and 2 for the amount) and, if present, activated 4Å molecular sieves
(see Tables 1 and 2 for the amount) in anhyd CH2Cl2 (4 mL) was
added a 5–6 M solution of TBHP in decane (0.22 mL, 1.2 mmol) at
r.t. After 30 min the mixture was cooled at 0 °C and the substrate 1
(1 mmol) was introduced. After completion of the reaction, the mix-
ture was treated according to workup procedure using Method A, B
or, as is the case of 2f, Method C.
1H NMR (400 MHz, CDCl3): (trans-isomer, distinct signals)
= 8.02 (m, 2 H, ortho ArH), 7.64 (m, 1 H, para ArH), 7.51 (m, 2 H,
meta ArH), 5.25 (s, 1 H, H-2), 3.60 (ddd, 1 H, J = 13.6, 8.7, 3.1 Hz,
H-6), 2.96 (ddd, 1 H, J = 13.6, 9.4, 2.9 Hz, H -6), 2.84 (ddd, 1 H,
J = 14.3, 7.7, 2.9 Hz, H-4), 2.19-2.08 (m, 1 H, H-5). (cis-isomer,
distinct signals) = 7.96 (m, 2 H, ortho ArH), 7.61 (m, 1 H, para
ArH), 7.49 (m, 2 H, meta ArH), 5.56 (s, 1 H, H-2), 3.88 (ddd, 1 H,
J = 12.8, 12.8, 2.9 Hz, H-6), 3.27 (m, 1 H, H-4), 3.10 (m, 1 H, H -
6), 2.45–2.27 (m, 2 H, H-5, H -5). Overlapped signals: = 2.72–
2.53 [m, 2 H (trans), H -4, H -5, 1 H (cis), H -4].
Method A (Products 2a–e)
The mixture was poured into a beaker containing sat. aq Na2SO4.
After stirring for 10 min it was diluted with EtOAc and the acqueos
layer and the molecular sieves were separated by centrifugation and
again extracted twice with EtOAc. The combined organic extracts
were dried (MgSO4), filtered, and then the solvent was removed in
vacuo.
trans-2-Methyl-2-phenyl-1 4,3-dithian-1-one (trans-2e)
1H NMR (400 MHz, CDCl3): = 7.66 (m, 2 H, ortho ArH), 7.41 (m,
2 H, meta ArH), 7.33 (m, 1 H, para ArH), 2.88–2.60 (m, 4 H, H-4,
H -4, H-6, H -6), 2.53–2.43 (m, 1 H, H-5), 2.09–1.96 (m, 1 H, H -
5), 1.92 (s, 3 H, CH3).
Method B (Products 2a–e)
13C NMR (100.6 MHz, CDCl3): = 138.5, 129.0, 128.6, 127.3,
64.7, 45.2, 26.5, 22.5, 19.3.
The reaction mixture was filtered through a short silica gel column
to remove catalyst and molecular sieves. Then the solvent was re-
moved in vacuo.
cis-2-Methyl-2-phenyl-1 4,3-dithian-1-one (cis-2e)
1H NMR (400 MHz, CDCl3): = 8.00 (m, 2 H, ortho ArH), 7.43 (m,
2 H, meta ArH), 7.36 (m, 1 H, para ArH), 2.91 (m, 1 H), 2.79–2.65
(m, 2 H), 2.47–2.28 (m, 3 H), 1.93 (s, 3 H, CH3).
Method C (Product 2f)
The reaction mixture containg 2f was filtered through a pad of
Celite eluting with EtOH. Then, the solvent was removed in vacuo.
The residue was purified by flash chromatography on silica gel (elu-
ent: CHCl3 to CHCl3–MeOH, 98:2). The monosulfoxides were ob-
13C NMR (100.6 MHz, CDCl3): = 137.8, 128.7, 128.2, 128.1,
65.7, 47.1, 28.7, 28.0, 27.5.
Synthesis 2002, No. 4, 505–510 ISSN 0039-7881 © Thieme Stuttgart · New York