Synthesis of 3,4-dihydro-2h-thiopyrans by the reaction of 4,5-dihydrothiophenium-1-bis[ethoxy(and methoxy)carbonyl]methylides with sodium iodide

Article abstract of DOI:10.1002/jhet.5570390131

Sulfonium ylides 1a-h reacted with sodium iodide to afford the corresponding thiopyrans 2a-h. On the other hand, compounds 1a-d were treated with thionyl chloride to give the ring opening products 3a-d. The reaction of compounds 3a-d with sodium iodide and triethylamine provided the corresponding thiopyrans 2a-d.

Full text of DOI:10.1002/jhet.5570390131

Jan-Feb 2002
Synthesis of 3,4-Dihydro-2H-thiopyrans by the Reaction of 4,5-
Dihydrothiophenium-1-bis[ethoxy(and methoxy)carbonyl]methylides
with Sodium Iodide
217
Hiroshi Maruoka, Kenji Yamagata and Motoyoshi Yamazaki*
Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan
Received December 29, 2000
Sulfonium ylides 1a-h reacted with sodium iodide to afford the corresponding thiopyrans 2a-h. On the
other hand, compounds 1a-d were treated with thionyl chloride to give the ring opening products 3a-d. The
reaction of compounds 3a-d with sodium iodide and triethylamine provided the corresponding thiopyrans
2a-d.
J. Heterocyclic Chem., 39, 217 (2002).
Thiopyrans are attractive compounds for chemical syn-
examined the reaction of the sulfonium ylides with
sodium iodide to see whether or not cleavage at the sul-
fur—C-5 bond takes place. The starting compounds dihy-
drothiophenium-1-bis(ethoxycarbonyl)methylides
1a,c,e,g were prepared by previously reported method
[8]. Dihydrothiophenium-1-bis(methoxycarbonyl)-
methylides 1b,d,f,h were synthesized by the reaction of
the corresponding 2-amino-4,5-dihydro-3-thiophenecar-
bonitriles [8] with dimethyl diazomalonate [9] in the
presence of rhodium(II) acetate dimer.
When a mixture of sulfonium ylides 1a,c-h and sodium
iodide (2 equivalents) in acetone was refluxed for 7 hours,
the corresponding 3,4-dihydro-2H-thiopyrans 2a,c-h were
obtained, and the expected ring opening products could not
be isolated. In a similar manner, no reaction occurred in
the case of 1b, and 1b was recovered unchanged. When
N,N-dimethylformamide was used in place of acetone,
compound 1b reacted with sodium iodide at 100° to pro-
vide 2b. Although ring expansion of thiophenes to thiopy-
rans via a process involving sulfonium ylide intermediates
has been reported [3,4], to our knowledge, ring expansion
of sulfonium ylides by use of sodium iodide has not been
thesis because their similarity with pyrans hints at useful
biological properties that should be relatively easy to dis-
cover due to their simple framework [1,2]. Rearrangement
of sulfonium ylides is known to produce thiopyrans [3,4].
This paper presents a new synthesis of thiopyrans from
sulfonium ylides. In the course of our studies on hetero-
cyclic enaminonitriles, we have shown that the reactions
of 2-amino-4,5-dihydro-3-furancarbonitriles with sodium
iodide [5,6] or titanium(IV) chloride [7] proceed through
an initial ring opening between the oxygen and the 5-
position of the furan ring by the attack of a halide ion on
the 5-position of the furan ring. Under the same condi-
tions, in the case of the corresponding 4,5-dihydro-3-
thiophene carbonitriles, ring opening reactions did not
take place. In contrast with 4,5-dihydro-3-thiophenecar-
bonitriles, the sulfonium ylides 1 of 4,5-dihydro-3-thio-
phenecarbonitriles undergo cleavage at the sulfur—C-5
bond and subsequent recyclization in the presence of a
base [8]. These findings suggest that the sulfur—C-5
bond of the sulfonium ylides is more easily cleaved than
that of 4,5-dihydro-3-thiophenecarbonitriles. Hence, we

218
H. Maruoka, K. Yamagata and M. Yamazaki
Vol. 39
δ 1.80-2.03 [m, 4H, 2xCH (pyrrolidine)], 3.44-3.72 [m, 8H,
reported. A reasonable pathway for the formation of 2 is
shown in Scheme. An iodide ion attacks at the 5-position
of 1 to form the intermediate carbanion A, which then
undergoes fast intramolecular cyclization to give 2.
Subsequently, the reaction of 1a-d with thionyl chloride
resulted in the formation of the expected ring opening
products 3a-d in moderate yields. Finally, we synthesized
2a-d from 3a-d. Compounds 3a-d were allowed to react
with sodium iodide and triethylamine in refluxing acetone
to afford the desired 2a-d together with the corresponding
2-amino-4,5-dihydro-3-thiophenecarbonitriles. The struc-
tural assignments of 2 and 3 were made on the basis of ele-
mental analyses and the spectral data.
2
4-H, 5-H, 2xCH (pyrrolidine)], 3.76 ppm (s, 6H, 2xCO CH ).
2
2
3
Anal. Calcd. for C H N O S: C, 54.18; H, 5.85; N, 9.03.
14 18
2 4
Found: C, 54.12; H, 5.77; N, 9.06.
3-Cyano-4,5-dihydro-4-phenyl-2-pyrrolidinothiophenium-1-
bis(methoxycarbonyl)methylide (1h).
This compound was obtained as colorless needles (4.49 g,
58%), mp 194-196° (chloroform-petroleum ether); ir (potassium
-1 1
bromide): ν 2180 (C≡N), 1625 (C=O) cm ; H nmr: δ 1.76-2.06
[m, 4H, 2xCH (pyrrolidine)], 3.46-4.15 [m, 7H, 4-H, 5-H,
2
2xCH (pyrrolidine)], 3.76 (s, 6H, 2xCO CH ), 7.30-7.52 ppm
2
2
3
(m, 5H, aromatic H).
Anal. Calcd. for C H N O S: C, 62.16; H, 5.74; N, 7.25.
20 22
2 4
Found: C, 61.89; H, 5.71; N, 7.24.
General Procedure for the Preparation of 2a-h from 1a-h.
Procedure A.
EXPERIMENTAL
A mixture of 1a,c-h (10 mmoles) and NaI (3.00 g, 20 mmoles)
in acetone (20 ml) was refluxed for 7 hours. After removal of the
solvent in vacuo, cold water was added to the residue. The result-
ing mixture was extracted with chloroform. The extract was dried
over anhydrous sodium sulfate and concentrated in vacuo. The
residue was purified by column chromatography on silica gel
with chloroform as the eluent to give 2a,c-h. Further the elution
with chloroform-acetone (4:1) gave the starting material 1e (0.89
g, 26%), 1f (0.63 g, 20%) and 1h (0.43 g, 11%), respectively.
All melting points are uncorrected. The ir spectra were
recorded on a JASCO A-302 spectrometer. The H nmr spectra
1
were measured in deuteriochloroform on a HITACHI R-90 H
spectrometer (90 MHz). Chemical shifts (δ) are reported in parts
per million (ppm) relative to tetramethylsilane as internal stan-
dard. Elemental analyses were performed on a HERAUS CHNO-
RAPID analyzer.
General Procedure for the Preparation of 4,5-Dihydrothio-
phenium-1-bis(methoxycarbonyl)methylides 1b,d,f,h.
Procedure B.
A mixture of 4,5-dihydro-2-morpholino(or -2-pyrrolidino)-3-
thiophenecarbonitriles [8] (20 mmoles), dimethyl diazomalonate
[9] (4.74 g, 30 mmoles) and rhodium(II) acetate dimer (80 mg,
0.18 mmole) in toluene (40 ml) was refluxed for 2 hours. After
removal of the solvent in vacuo, the residue was purified by col-
umn chromatography on alumina with methylene chloride-ace-
tone (4:1) as the eluent to give 1b,d,f,h.
A mixture of 1b (3.26 g, 10 mmoles) and NaI (1.50 g, 10
mmoles) in N,N-dimethylformamide (20 ml) was heated at 100°
with stirring for 5 hours. After work-up as described for the
preparation of 2a,c-h from 1a,c-h. The residue was purified by
column chromatography on silica gel with chloroform as the elu-
ent to give 2b.
Diethyl 5-Cyano-3,4-dihydro-6-morpholino-2H-thiopyran-2,2-
dicarboxylate (2a).
3-Cyano-4,5-dihydro-2-morpholinothiophenium-1-bis(methoxy-
carbonyl)methylide (1b).
This compound was obtained as pale yellow oil (3.15 g, 89%);
ir (neat): ν 2190 (C≡N), 1740 (C=O) cm ; H nmr: δ 1.28 (t, J =
This compound was obtained as colorless prisms (2.94 g,
45%), mp 110-112° (methylene chloride-petroleum ether); ir
(potassium bromide): ν 2210 (C≡N), 1630 (C=O) cm ; H nmr:
-1 1
-1
1
7 Hz, 6H, 2xCO CH CH ), 2.46 (s, 4H, 3-H, 4-H), 3.29-3.40 [m,
2
2
3
4H, 2xCH (morpholine)], 3.63-3.79 [m, 4H, 2xCH (morpho-
δ 3.42-3.73 [m, 12H, 4-H, 5-H, 4xCH (morpholine)], 3.73 ppm
2
2
2
line)], 4.26 ppm (q, J = 7 Hz, 4H, 2xCO CH CH ).
(s, 6H, 2xCO CH ).
2
2
3
2
3
Anal. Calcd. for C H N O S: C, 54.22; H, 6.26; N, 7.90.
Anal. Calcd. for C H N O S: C, 51.52; H, 5.56; N, 8.58.
16 22
2 5
14 18
2 5
Found: C, 53.98; H, 6.17; N, 8.12.
Found: C, 51.46; H, 5.51; N, 8.61.
Dimethyl 5-Cyano-3,4-dihydro-6-morpholino-2H-thiopyran-2,2-
dicarboxylate (2b).
3-Cyano-4,5-dihydro-2-morpholino-4-phenylthiophenium-1-
bis(methoxycarbonyl)methylide (1d).
This compound was obtained as colorless prisms (2.93 g,
90%), mp 50-52° (diethyl ether-petroleum ether); ir (potassium
bromide): ν 2190 (C≡N), 1740 (C=O) cm ; H nmr: δ 2.46 (s,
This compound was obtained as colorless needles (5.09 g,
63%), mp 133-135° (acetone-petroleum ether); ir (potassium bro-
mide): ν 2195 (C≡N), 1620 (C=O) cm ; H nmr: δ 3.28-4.19 [m,
-1
1
-1 1
4H, 3-H, 4-H), 3.30-3.40 [m, 4H, 2xCH (morpholine)], 3.69-
11H, 4-H, 5-H, 4xCH (morpholine)], 3.76 (s, 6H, 2xCO CH ),
2
2
2
3
3.81 [m, 4H, 2xCH (morpholine)], 3.81 ppm (s, 6H,
7.35-7.50 ppm (m, 5H, aromatic H).
2
2xCO CH ).
Anal. Calcd. for C H N O S: C, 59.69; H, 5.51; N, 6.96.
2
3
20 22
2 5
Anal. Calcd. for C H N O S: C, 51.52; H, 5.56; N, 8.58.
Found: C, 59.41; H, 5.49; N, 7.04.
14 18
2 5
Found: C, 51.78; H, 5.76; N, 8.82.
3-Cyano-4,5-dihydro-2-pyrrolidinothiophenium-1-bis(methoxy-
Diethyl 5-Cyano-3,4-dihydro-6-morpholino-4-phenyl-2H-
thiopyran-2,2-dicarboxylate (2c).
carbonyl)methylide (1f).
This compound was obtained as colorless prisms (2.79 g,
45%), mp 132-133° (methylene chloride-petroleum ether); ir
(potassium bromide): ν 2198 (C≡N), 1630 (C=O) cm ; H nmr:
This compound was obtained as pale yellow oil (4.14 g, 96%); ir
-1
1
-1
1
(neat): ν 2200 (C≡N), 1740, 1730 (C=O) cm ; H nmr: δ 1.05 (t,

Jan-Feb 2002
Synthesis of 3,4-Dihydro-2H-thiopyrans
219
J = 7 Hz, 3H, CO CH CH ), 1.24 (t, J = 7 Hz, 3H, CO CH CH ),
4H, 2xCH (pyrrolidine)], 3.79 (s, 3H, CO CH ), 4.21 (t, J = 7
2 2 3
2
2
3
2
2
3
2.77 (dd, J = 5.5, 16 Hz, 1H, 3-H), 3.13 (dd, J = 7, 16 Hz, 1H, 3-H),
3.31-3.57 [m, 4H, 2xCH (morpholine)], 3.67-3.81 [m, 4H, 2xCH
Hz, 1H, 4-H), 7.28 ppm (s, 5H, aromatic H).
Anal. Calcd. for C H N O S: C, 62.16; H, 5.74; N, 7.25.
2
2
20 22 2 4
(morpholine)], 3.92 (dd, J = 5.5, 7 Hz, 1H, 4-H), 4.23 (q, J = 7 Hz,
4H, 2xCO CH CH ), 7.27 ppm (s, 5H, aromatic H).
Found: C, 62.03; H, 5.75; N, 7.24.
2
2
3
General Procedure for the Preparation of 3a-d from 1a-d.
Anal. Calcd. for C H N O S: C, 61.38; H, 6.09; N, 6.51.
22 26
2 5
A solution of 1a-d (10 mmoles) and thionyl chloride (1.79 g,
15 mmoles) in chloroform (10 ml) was refluxed for 5 hours. After
removal of the solvent in vacuo, the residue was basified with a
saturated aqueous sodium hydrogen carbonate, and extracted
with chloroform. The extract was dried over anhydrous sodium
sulfate and concentrated in vacuo. The residue was purified by
column chromatography on alumina with chloroform as the elu-
ent to give 3a-d.
Found: C, 61.11; H, 5.97; N, 6.56.
Dimethyl 5-Cyano-3,4-dihydro-6-morpholino-4-phenyl-2H-
thiopyran-2,2-dicarboxylate (2d).
This compound was obtained as colorless prisms (3.82 g,
95%), mp 68-70° (diethyl ether-petroleum ether); ir (potassium
bromide): ν 2180 (C≡N), 1735 (C=O) cm ; H nmr: δ 2.75 (dd,
-1
1
J = 5.5, 16 Hz, 1H, 3-H), 3.15 (dd, J = 7, 16 Hz, 1H, 3-H), 3.20-
3.78 [m, 8H, 4xCH (morpholine)], 3.45 (s, 3H, CO CH ), 3.78
2
2
3
Diethyl [(4-Chloro-2-cyano-1-morpholino-1-buten-1-
yl)thio]propanedioate (3a).
(s, 3H, CO CH ), 4.20 (dd, J = 5.5, 7 Hz, 1H, 4-H), 7.27 ppm (s,
2
3
5H, aromatic H).
This compound was obtained as pale yellow oil (2.17 g, 56%);
Anal. Calcd. for C H N O S: C, 59.69; H, 5.51; N, 6.96.
20 22
2 5
-1 1
ir (neat): ν 2200 (C≡N), 1735 (C=O) cm ; H nmr: δ 1.30 (t, J =
Found: C, 59.96; H, 5.64; N, 7.15.
7 Hz, 6H, 2xCO CH CH ), 2.54-2.73 (m, 2H, 3-H), 2.85-3.01
2
2
3
Diethyl 5-Cyano-3,4-dihydro-6-pyrrolidino-2H-thiopyran-2,2-
dicarboxylate (2e).
(m, 2H, 4-H), 3.24-3.36 [m, 4H, 2xCH (morpholine)], 3.70-3.80
2
[m, 4H, 2xCH (morpholine)], 4.18 [s, 1H, CH(CO CH CH ) ],
2
2
2
3 2
4.26 ppm (q, J = 7 Hz, 4H, 2xCO CH CH ).
2
2
3
This compound was obtained as colorless prisms (1.69 g,
50%), mp 37-38° (diethyl ether-petroleum ether); ir (potassium
bromide): ν 2170 (C≡N), 1735 (C=O) cm ; H nmr: δ 1.28 (t, J =
Anal. Calcd. for C H ClN O S: C, 49.16; H, 5.93; N, 7.17.
16 23
2 5
Found: C, 49.19; H, 5.67; N, 7.39.
-1 1
7 Hz, 6H, 2xCO CH CH ), 1.83-1.98 [m, 4H, 2xCH (pyrroli-
Dimethyl [(4-Chloro-2-cyano-1-morpholino-1-buten-1-yl)thio]-
propanedioate (3b).
2
2
3
2
dine)], 2.43 (s, 4H, 3-H, 4-H), 3.56-3.71 [m, 4H, 2xCH (pyrroli-
2
dine)], 4.26 ppm (q, J = 7 Hz, 4H, 2xCO CH CH ).
2
2
3
This compound was obtained as pale yellow oil (2.61 g, 72%);
Anal. Calcd. for C H N O S: C, 56.79; H, 6.55; N, 8.28.
16 22
2 4
-1
1
ir (neat): ν 2200 (C≡N), 1735 (C=O) cm ; H nmr: δ 2.55-2.71
(m, 2H, 3-H), 2.85-3.02 (m, 2H, 4-H), 3.25-3.37 [m, 4H, 2xCH
Found: C, 57.00; H, 6.61; N, 8.37.
2
(morpholine)], 3.72-3.89 [m, 4H, 2xCH (morpholine)], 3.80 (s,
Dimethyl 5-Cyano-3,4-dihydro-6-pyrrolidino-2H-thiopyran-2,2-
dicarboxylate (2f).
2
6H, 2xCO CH ), 4.23 ppm [s, 1H, CH(CO CH ) ].
2
3
2
3 2
Anal. Calcd. for C H ClN O S: C, 46.35; H, 5.28; N, 7.72.
Found: C, 46.29; H, 5.23; N, 7.97.
14 19
2 5
This compound was obtained as colorless needles (1.74 g,
56%), mp 126-128° (acetone-petroleum ether); ir (potassium bro-
mide): ν 2170 (C≡N), 1742 (C=O) cm ; H nmr: δ 1.84-1.98 [m,
-1 1
Diethyl [(4-Chloro-2-cyano-1-morpholino-3-phenyl-1-buten-1-
yl)thio]propanedioate (3c).
4H, 2xCH (pyrrolidine)], 2.43 (s, 4H, 3-H, 4-H), 3.57-3.72 [m,
2
4H, 2xCH (pyrrolidine)], 3.81 ppm (s, 6H, 2xCO CH ).
2
2
3
This compound was obtained as pale yellow oil (3.72 g, 80%);
ir (neat): ν 2190 (C≡N), 1730 (C=O) cm ; H nmr: δ 1.29 (t, J =
Anal. Calcd. for C H N O S: C, 54.18; H, 5.85; N, 9.03.
-1 1
14 18
2 4
Found: C, 54.24; H, 5.93; N, 8.97.
7 Hz, 6H, 2xCO CH CH ), 2.82 (dd, J = 5.5, 11 Hz, 1H, 4-H),
2
2
3
3.19-3.35 [m, 5H, 4-H, 2xCH (morpholine)], 3.69-3.83 [m, 4H,
Diethyl 5-Cyano-3,4-dihydro-4-phenyl-6-pyrrolidino-2H-
thiopyran-2,2-dicarboxylate (2g).
2
2xCH (morpholine)], 4.04-4.37 (m, 1H, 3-H), 4.19 [s, 1H,
2
CH(CO CH CH ) ], 4.25 (q, J = 7 Hz, 4H, 2xCO CH CH ),
2
2
3 2
2
2
3
This compound was obtained as colorless prisms (3.85 g,
93%), mp 92-93° (diethyl ether-petroleum ether); ir (potassium
7.32 ppm (s, 5H, aromatic H).
Anal. Calcd. for C H ClN O S: C, 56.59; H, 5.83; N, 6.00.
22 27
2 5
-1 1
bromide): ν 2190 (C≡N), 1735 (C=O) cm ; H nmr: δ 0.93 (t, J =
Found: C, 56.78; H, 5.80; N, 6.25.
7 Hz, 3H, CO CH CH ), 1.24 (t, J = 7 Hz, 3H, CO CH CH ),
2
2
3
2
2
3
Dimethyl [(4-Chloro-2-cyano-1-morpholino-3-phenyl-1-buten-
1-yl)thio]propanedioate (3d).
1.86-2.04 [m, 4H, 2xCH (pyrrolidine)], 2.72 (dd, J = 7, 16 Hz,
2
1H, 3-H), 3.03 (dd, J = 7, 16 Hz, 1H, 3-H), 3.56-4.03 [m, 4H,
2xCH (pyrrolidine)], 4.23 (t, J = 7 Hz, 1H, 4-H), 4.24 (q, J = 7
This compound was obtained as pale yellow oil (3.33 g, 76%);
ir (neat): ν 2200 (C≡N), 1740 (C=O) cm ; H nmr: δ 2.80-2.91
2
-1
1
Hz, 4H, 2xCO CH CH ), 7.27 ppm (s, 5H, aromatic H).
2
2
3
Anal. Calcd. for C H N O S: C, 63.75; H, 6.32; N, 6.76.
(m, 1H, 4-H), 3.21-3.39 [m, 5H, 4-H, 2xCH (morpholine)], 3.70-
22 26
2 4
2
Found: C, 63.50; H, 6.30; N, 6.73.
3.82 [m, 4H, 2xCH (morpholine)], 3.80 (s, 6H, 2xCO CH ),
2
2
3
4.00-4.22 (m, 1H, 3-H), 4.22 [s, 1H, CH(CO CH ) ], 7.32 ppm (s,
2
3 2
Dimethyl 5-Cyano-3,4-dihydro-4-phenyl-6-pyrrolidino-2H-
thiopyran-2,2-dicarboxylate (2h).
5H, aromatic H).
Anal. Calcd. for C H ClN O S: C, 54.73; H, 5.28; N, 6.38.
20 23
2 5
This compound was obtained as colorless prisms (2.46 g,
64%), mp 125-127° (acetone-petroleum ether); ir (potassium bro-
Found: C, 54.60; H, 5.56; N, 6.29.
General Procedure for the Preparation of 2a-d from 3a-d.
-1 1
mide): ν 2180 (C≡N), 1740 (C=O) cm ; H nmr: δ 1.85-2.10 [m,
4H, 2xCH (pyrrolidine)], 2.76 (dd, J = 7, 16 Hz, 1H, 3-H), 3.06
A mixture of 3a-d (10 mmoles), NaI (3.00 g, 20 mmoles) and
2
(dd, J = 7, 16 Hz, 1H, 3-H), 3.40 (s, 3H, CO CH ), 3.61-3.86 [m,
triethylamine (2.02 g, 20 mmoles) in acetone (20 ml) was
2
3

220
H. Maruoka, K. Yamagata and M. Yamazaki
Vol. 39
Koho, JP 03 07,279 (1991) ; Chem. Abstr., 114, 207031d (1991); R. J.
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refluxed for 7 hours. After removal of the solvent in vacuo, cold
water was added to the residue. The resulting mixture was
extracted with chloroform. The extract was dried over anhydrous
sodium sulfate and concentrated in vacuo. The residue was puri-
fied by column chromatography on silica gel with chloroform as
the eluent. The first fraction provided 4,5-dihydro-2-morpholino-
3-thiophenecarbonitrile [8] [from 3a (0.82 g): yield 42%, from
3b (0.67 g): yield 34%] and 4,5-dihydro-2-morpholino-4-phenyl-
3-thiophenecarbonitrile [8] [from 3c (1.08 g): yield 40%, from 3d
(0.95 g): yield 35%]. The second fraction gave the corresponding
thiopyrans 2a (1.66 g, 47%), 2b (1.71 g, 52%), 2c (2.32 g, 54%)
and 2d (1.89 g, 47%), respectively. Compounds 2a-d were iden-
tical with samples prepared from 1a-d and sodium iodide on the
basis of a comparison of the ir spectra.
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