Flash Vacuum Thermolysis of Unstabilized Cycloalkenethiones
FULL PAPER
hPa. Tetraethylenepentamine (35.3 g, 0.19 mol) was added drop- 2.86 (m, 2 H4), 2.98 (m, 2 H5), 6.74 (dt, J ϭ 5.2 and 2.0 Hz, 1 H2),
wise and the obtained thiols, collected in the DeanϪStark appa-
ratus (yields ca. 60%), were dried over magnesium sulfate. These
thiols (6.17 mmol) were directly transformed into the correspond-
ing propargyl sulfides by reaction of propargyl bromide and cesium
carbonate (1 equiv.) following the experimental procedure de-
scribed in the general method [B].
7.94 (dt, J ϭ 5.2 and 2.9 Hz, 1 H3).
Cyclohex-2-enethione (3): HRMS; m/z: 112.0373 (Mϩ·, calcd.
C6H8S 112.03468). Ϫ MS (B/E linked scan, daughter ions of Mϩ·);
m/z (%): 84 (92), 79 (88), 78 (30), 77 (65), 71 (100), 70 (39), 69 (71),
67 (32), 66 (63), 65 (36), 58 (39), 51 (26), 45 (65), 39 (56). Ϫ UV/
Vis (Ϫ196°C): λ ϭ 236, 287, 531 (sh), 554, 583 nm (sh). Ϫ IR
(Ϫ196°C): ν˜ ϭ 1586, 1400, 1252, 1151, 1126, 973 cmϪ1. Ϫ 1H
NMR (Ϫ80°C, CD2Cl2/CFCl3): δ ϭ 1.97 (m, 2 H5), 2.32 (m, 2 H4),
2.96 (dd ഠ t, J ഠ 6.4 Hz, 2 H6), 6.72 (dt, J ϭ 9.6 and 1.9 Hz, 1
H2), 6.89 (dt, J ϭ 9.6 and 4.2 Hz, 1 H3).
Sulfide 12: Obtained from 3-bromocyclohexene. Yield 0.80 g (85%).
1
Ϫ H NMR (CDCl3): δ ϭ 1.5Ϫ1.9 (4 H), 1.96 (m, 2 H), 2.17 (t,
J ϭ 2.7 Hz, 1 H), 3.21 (m, 2 H), 3.55, 5.66 and 5.76 (3 m, 3 H). Ϫ
13C NMR (CDCl3): δ ϭ 18.6, 19.9, 25.0, 28.8, 40.7, 70.9, 80.6,
126.9, 130.6. Ϫ IR (liquid film): ν˜ ϭ 2115 and 3295 cmϪ1
(ϪCϵCH). Ϫ C9H12S (152): calcd. S 21.06, found S 21.18.
Cyclohept-2-enethione (5): HRMS; m/z: 126.0506 (Mϩ·, calcd.
C7H10S 126.05030). Ϫ UV/Vis (Ϫ196°C): λ ϭ 244, 302, 523 (sh),
553, 580 nm (sh). Ϫ IR (Ϫ196°C): ν˜ ϭ 1582, 1447, 1398, 1218,
1170, 1105, 1037, 840 cmϪ1. Ϫ 1H NMR (Ϫ80°C, CD2Cl2/CFCl3):
δ ϭ 1.89 (m, 2 H6), 2.31 (m, 2 H5), 2.42 (m, 2 H4), 3.27 (dd ഠ t,
J ഠ 6.0 Hz, 2 H7), 6.71 (dt, J ϭ 11.2 and 6.1 Hz, 1 H3), 6.80 (dm,
J ϭ 11.2 Hz, 1 H2).
Sulfide 13: Obtained from 3-bromocycloheptene. Yield 55%. Spec-
tra identical with those previously described[23]
.
Sulfide 14: The reaction of 3-bromocyclododecene [prepared from
80% (E)-cyclododecene and N-bromosuccinimide] with thiourea
was performed, due to the low volatility of products, with ethanol
and aq. sodium hydroxide as described for the preparation of n-
dodecane-1-thiol[10b], and the resulting thiol (62% yield) treated as
above by propargyl bromide and cesium carbonate. Sulfide 14 was
purified by flash chromatography on silica (eluent: n-pentane).
Yield 0.60 g (41%). Ϫ 1H NMR (CDCl3): δ ϭ 1.0Ϫ1.8 (16 H), 2.03
(m, 1 H), 2.21 (t, J ϭ 5.0 Hz, 1 H), 2.26 (m, 1 H), 3.09 and 3.19
(dd AB, J ϭ 16.8 and 5.0 Hz, 2 H), 3.47 (m, 1 H), 5.17 (dd, J ϭ
15.1 and 1.4 Hz, 1 H), 5.46 (dt, J ϭ 15.1 and 4.3 Hz, 1 H). Ϫ 13C
NMR (CDCl3): δ ϭ 20.1, 25.8, 26.4, 27.2, 27.3, 28.1, 28.3, 33.8,
33.9, 40.9, 49.2, 72.3, 82.7, 132.5, 135.9. Ϫ IR (liquid film): ν˜ ϭ
2108 and 3300 cmϪ1 (ϪCϵCH). Ϫ C15H24S (236): calcd. S 13.56,
found S 13.38.
FVT of Sulfides 10 and 11: Generation of Compounds 2, 4, 16, and
17
Sulfides 10 and 11 were thermolyzed at 700°C and the FVT prod-
ucts analyzed as above.
Cyclopent-3-enethione (2) ؉ Cyclopenta-1,3-dienethiol (16): HRMS;
m/z: 98.0186 (Mϩ·, calcd. C5H6S 98.01892). Ϫ MS (B/E linked
scan, daughter ions of Mϩ·); m/z (%): 71 (46), 70 (42), 69 (53), 65
(45), 63 (45), 62 (25), 58 (32), 57 (23), 53 (71), 45 (100), 39 (61), 27
(27). Ϫ UV/Vis (Ϫ196°C): λ ϭ 216, 491 nm. Ϫ IR (Ϫ196°C): ν˜ ϭ
2460, 1640, 1510, 1445, 1426, 1357, 1234, 1039, 990 cmϪ1. Ϫ 1H
NMR (Ϫ40°C, CD2Cl2ϪCFCl3, 16): δ ϭ 2.89 (s, 1 H, SH), 3.10
(m, 2 H5), 6.31 (m, 1 H2), 6.37 (m, 1 H4), 6.44 (m, 1 H3).
Preparation of gem-Dithiol 15
Cyclohex-3-enethione (4) ؉ Cyclohexa-1,3-dienethiol (17): HRMS;
m/z: 112.0343 (Mϩ·, calcd. C6H8S 112.03468). Ϫ MS (B/E linked
scan, daughter ions of Mϩ·); m/z (%): 84 (28), 79 (100), 78 (17), 77
(43), 71 (8), 69 (11), 67 (12), 66 (29), 65 (14), 58 (15), 51 (8), 45 (6),
39 (5). Ϫ UV/Vis (Ϫ196°C): λ ϭ 230, 475 nm. Ϫ IR (Ϫ196°C):
ν˜ ϭ 2500, 1640, 1580, 1447, 1426, 1366, 1350, 1325, 1250, 1125,
exo-Tricyclo[4.2.1.02,5]non-7-en-3-one (0.25 g, 1.86 mmol, prepared
following the literature[11]) and morpholine (75 mg, 0.86 mmol)
were dissolved in DMF (5 mL) and cooled to Ϫ10°C. Hydrogen
sulfide was bubbled through the solution for 6 h. The mixture was
kept 40 h at 0°C, then poured on ice. After addition of dilute HCl,
the solution was extracted with pentane, washed with water, and
dried with magnesium sulfate. Compound 15 (0.31 g, 91%) was
thus obtained in a practically pure state. Ϫ 1H NMR (CDCl3): δ ϭ
1.40 (m, 2 H), 1.95 (m, 2 H), 2.32 (br. s, 1 H), 2.56 (m, 1 H), 2.62
(s, 1 H, SH), 2.69 (br. s, 1 H), 2.94 (br. s, 1 H), 3.09 (s, 1 H, SH),
6.02 (m, 2 H). Ϫ 13C NMR (CDCl3): δ ϭ 33.0, 41.6, 42.9, 43.9,
44.1, 44.5, 56.5, 135.4, 137.0. Ϫ IR (liquid film): ν˜ ϭ 2530 cmϪ1
(SH). Ϫ C9H12S2 (184): calcd. S 34.79, found S 32.19.
980, 915 cmϪ1
.
FVT of Sulfide 14
30 mg of sulfide 14 was introduced, using a sliding spatula, into
the FVT oven preheated at 700°C. The products were analyzed by
MS [m/z (%): 196 (13), 166 (15), 123 (20), 111 (30), 97 (54), 91 (60),
81 (80), 79 (72), 67 (100), 56 (83)]; by IR at Ϫ196°C showing transi-
ent absorptions, disappearing between Ϫ120 and Ϫ80°C, at 2540,
2070, 1950, 1510 and 1250 cmϪ1; and by NMR at room tempera-
ture indicating the presence of cyclododecene and allene in a
80:20 ratio.
FVT of Sulfides 8, 9, 12, and 13: Generation of Cycloalkenethiones
1, 3, and 5
Thioketones 1, 3, and 5 were typically prepared by thermolysis at
600°C (from sulfides 8 and 9) or 550°C (from 12 and 13) and their
spectra recorded as indicated in the general conditions. The given
yields and ratios were determined by NMR, using when appropri-
ate a quantitative standard of benzene or p-dioxane. Thioacrolein,
obtained in the FVT of 9 at 800°C, was characterized at Ϫ196°C
FVT of gem-Dithiol 15: Vinylthioketene (18) and Cyclo-
butanethione 19
The products of FVT (800°C) of gem-dithiol 15, introduced as
above with a sliding spatula, were analyzed by MS [m/z (%): 150
(72, Mϩ· of 19), 136 (43), 135 (86), 134 (100), 117 (41), 116 (58),
115 (76), 91 (100), 84 (41), 79 (44), 77 (48), 71 (49), 69 (43), 66 (82),
65 (48), 63 (47)], and by IR at Ϫ196°C pointing out the presence
by comparison with its previously described IR spectrum[24]
Cyclopent-2-enethione (1): HRMS; m/z: 98.0163 (Mϩ·, calcd. C5H6S
.
98.01892). Ϫ MS (B/E linked scan, daughter ions of Mϩ·); m/z (%): of the transient bands of 18 at 1740 and 1600 cmϪ1. These two
71 (54), 70 (47), 69 (100), 65 (43), 63 (37), 58 (56), 57 (32), 53 (65),
absorptions vanished together below Ϫ130°C while another set of
45 (96), 39 (63), 27 (31). Ϫ UV/Vis (Ϫ196°C): λ ϭ 297, 502 (sh),
bands, belonging possibly to 19, remained present until Ϫ80°C
524, 552 nm (sh). Ϫ IR (Ϫ196°C): ν˜ ϭ 1553, 1427, 1372, 1264, [1610, 1585, 1435, 1405, 1355, 1285, 1235, 1170, 1080, 1025, 990,
1
1183, 1082, 921 cmϪ1. Ϫ H NMR (Ϫ80°C, CD2Cl2/CFCl3): δ ϭ 960, 915, 885, 830, 805, 770, 720 cmϪ1]. The NMR spectrum
Eur. J. Org. Chem. 1999, 869Ϫ874
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