Novel preparation of (2-azidomethyl)benzoic acid and an application as a protective group

Article abstract of DOI:10.1081/SCC-120014042

A novel preparation method of 2-(azidomethyl)benzoic acid, a precursor of (2-azidomethyl)benzoyl (AZMB) protective group, was developed which can provide pure sample in gram scale without chromatographic purifications. Reductive cleavage using triphenylphosphine was found to be effective in the case of sterically hindered ester that resists under basic hydrolysis.

Full text of DOI:10.1081/SCC-120014042

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NOVEL PREPARATION OF (2-AZIDOMETHYL)BENZOIC
ACID AND AN APPLICATION AS A PROTECTIVE GROUP
Hiroko Matsuda a , Masaru Hashimoto b & Toshikatsu Okuno b
a The United Graduate School of Agricultural Sciences , Iwate University , 3 Bunkyo-cho
Hirosaki, 036-8561, Japan
b Faculty of Agriculture and Life Science , Hirosaki University , 3 Bunkyo-cho Hirosaki,
036-8561, Japan
Published online: 16 Aug 2006.
To cite this article: Hiroko Matsuda , Masaru Hashimoto & Toshikatsu Okuno (2002) NOVEL PREPARATION OF (2-
AZIDOMETHYL)BENZOIC ACID AND AN APPLICATION AS A PROTECTIVE GROUP, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 32:21, 3347-3355, DOI: 10.1081/SCC-120014042
To link to this article: http://dx.doi.org/10.1081/SCC-120014042
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 21, pp. 3347–3355, 2002
NOVEL PREPARATION OF
(2-AZIDOMETHYL)BENZOIC ACID
AND AN APPLICATION AS A
PROTECTIVE GROUP
Hiroko Matsuda,1 Masaru Hashimoto,1,2,
*
and Toshikatsu Okuno1,2
1The United Graduate School of Agricultural Sciences,
Iwate University, 3 Bunkyo-cho Hirosaki,
036-8561, Japan
2Faculty of Agriculture and Life Science, Hirosaki
University, 3 Bunkyo-cho Hirosaki, 036-8561, Japan
ABSTRACT
A novel preparation method of 2-(azidomethyl)benzoic acid,
a precursor of (2-azidomethyl)benzoyl (AZMB) protective
group, was developed which can provide pure sample in
gram scale without chromatographic purifications. Reductive
cleavage using triphenylphosphine was found to be effective in
the case of sterically hindered ester that resists under basic
hydrolysis.
Key Words: (2-Azidomethyl)benzoate; Hydroxyl protective
group; Selective cleavage
*Corresponding author. E-mail: hmasaru@cc.hirosaki-u.ac.jp
3347
DOI: 10.1081/SCC-120014042
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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3348
MATSUDA, HASHIMOTO, AND OKUNO
In the syntheses of polyhydroxylated molecules, protective groups of
alcohol functions play key roles and variety of those which can be intro-
duced and removed under mild conditions distinguishing with other ones
have been developed.[1] Recentry, Sekine and his co-workers have developed
a novel benzoyl derivative (2-azidomethyl)benzoyl (AZMB) ester 4, cleav-
able by a reduction (MePPh2, NaBH3CN, Pd/C-H2) of the azido group
which results a formation of phtalamide, and they have also demonstrated
the effectiveness of 4 in synthesis of nucleosides.[2] Now, we would like to
report an alternative preparation of (2-azidomethyl)benzoic acid (2), a
precursor of 4, as well as our findings in its applications.
Heating phthalide with dichlorotriphenylphosphorane at 180ꢀC with-
out solvent[3] and following treatment of the crude product with methanol
in the presence of pyridine gave methyl ester 1 (Sch. 1). Without purifica-
tion, 1 was treated with sodium azide in aqueous ethanol to take place a
replacement of the chlorine with azido group. Then, methyl ester was
hydrolyzed by aqueous sodium hydroxide and the crude product was
recrystallized from hot hexane to provide pure
2
as needles
(m.p. ¼ 78.0–79.0ꢀC, lit 73–75ꢀC[2]) in 74% yield overall. It was found
that 2 is stable enough to store for several months in refrigerator.
Sekine et al. disclosed an efficient procedure of AZMB group,[2] however,
this method also provide it readily in gram scale. For protection of alco-
hols, 2 was converted into the corresponding acid chloride 3, before use,
by excess thionyl chloride at 60ꢀC and catalytic amount of N,N-dimethyl-
formamide. The crude 3 was subjected to alcohol protection after removal
of the volatile materials under reduced pressure.
We applied AZMB group to a preparation of 3-free thioglucopyranose
derivative 10 (Sch. 2). The crude 3 was treated with alcohol 5[4] in the pres-
ence of N,N-dimethyl-4-aminopyridine to produce AZMB ester 6 in 93%
yield. The reaction was very slow when pyridine was employed instead of
DMAP. Acetolysis of 6 was performed by heating at 140ꢀC in a mixture
Scheme 1.

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(2-AZIDOMETHYL)BENZOIC ACID
3349
Scheme 2.
Scheme 3.
of potassium acetate, acetic acid, and acetic anhydride to give 7 in 86%
yield. The azido group was not affected under those harsh conditions.
AZMB group was also found to be quite stable under acidic conditions
that treatment of 7 with 60% aqueous trifluoroacetic acid solution for
2 days took place removals of the acetonide, S-acetyl, O-acetyl groups,
and succeeding rearrangement from the furanose to a thiopyranose ring
to afford 8 in 73% yield. Migration or cleavage of AZMB group was not
observed during the reaction. After transformation into bisacetonide 9,
deprotection of AZMB group was attempted. It was found that AZMB
group did not react at all when hydrolysis was performed with sodium
hydroxide in aqueous tetrahydrofuran (THF) at 70ꢀC. However, when it
was performed with triphenylphosphine in aqueous THF the cleavage
of the AZMB proceeded smoothly to afford 10 in quantitative yield.
Interestingly, benzoate analogue 11, which could be prepared in the similar
manner to that of 9, was hydrolyzed by aqueous NaOHeven it took 10 h.
Thus, it can be concluded that AZMB group can be more stable than
benzoate derivative under aqueous basic conditions.
Availability of AZMB group could also be demonstrated employing 7.
Treatment of 7 with triphenylphosphine in the presence of sodium dihydro-
genphosphate in aqueous THF at 70ꢀC for 1 h resulted a selective cleavage

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3350
MATSUDA, HASHIMOTO, AND OKUNO
of AZMB group smoothly to afford alcohol 12 in 78% yield (Sch. 3).[5]
When the reaction was performed without phosphate, the yield of 12 was
decreased (<50%) due to undesired by-products. Interestingly, basic metha-
nolysis of 7 employing two equivalents of sodium methoxide gave thiirane 5
in 98% yield.[6]
Utilizing this protective group, synthesis of oligo-thiosaccharide which
may prevent using benzyl group due to sulfide function is now under
progress in our laboratory.
EXPERIMENTAL
2-Azidomethylbenzoic Acid (2)
A mixture of phthalide (5.30 g, 39.0 mmol) and Ph3PCl2 (15 g,
45 mmol) was heated at 180ꢀC for 2 h under Ar atmosphere. Upon heat-
ing, the solid reaction mixture changed to an orange solution. After cool-
ing to 0ꢀC, methanol (10 mL) and pyridine (10 mL) were added
successively into the mixture and the whole mixture was stirred for 1 h.
Hexane (200 mL) and H2O (100 mL) were added to the mixture. The pre-
cipitate was removed by filtration and the aqueous layer was removed. The
organic layer was washed with brine (100 mL), dried over anhydrous
MgSO4, and concentrated in vacuo to provide methyl 2-chloromethyl-
1
benzoate (1) in an almost pure state. HNMR (400 MHz, CDCl , ppm)
3
ꢀ 3.93 (3H, s), 5.05 (2H, s), 7.39 (1H, ddd, J ¼ 1.6, 6.8, 8.5 Hz), 7.54 (2H,
m), 7.97 (1H, dd, J ¼ 1.6, 8.8 Hz). 13C NMR (100 MHz, CDCl3, ppm) ꢀ
44.4, 52.2, 128.4, 129.0, 130.8, 131.1, 132.5, 138.7, 167.0. The crude 1 was
dissolved in ethanol (50 mL) and H2O (25 mL) and it was stirred with
sodium azide (6.0 g, 92.3 mmol) at 60ꢀC for 2 h. After the mixture was
concentrated under reduced pressure until the whole volume became a
third, the resulting mixture was extracted with hexane (50 mL Â 3), com-
bined, and concentrated in vacuo to give a residue which was diluted with
methanol (50 mL) and aqueous sodium hydroxide solution (3.0 g in 20 mL
of H2O). After stirring vigorously for 3 h, the mixture was concentrated
until the whole volume became a third. The residual mixture was washed
with ether (20 mL) and then aqueous solution was acidified by addition of
12 M aqueous HCl solution (5.0 mL) to give an emersion. After extraction
with AcOEt (50 mL Â 3), the combined organic solutions were washed with
brine (50 mL), dried over anhydrous MgSO4, and concentrated in vacuo to
give white solid. Recrystallization from hexane afforded pure 2 as white
needles. M.p. ¼ 78.0–79.0ꢀC (lit. 73–75ꢀC[2]). The IR and NMR data were
identical with these of reported by Sekine et al.[2]

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(2-AZIDOMETHYL)BENZOIC ACID
2-Azidomethylbenzoyl Chloride (3)
3351
A mixture of 2 and catalytic amount of N,N-dimethylformamide in
thionly chloride (excess) was heated at 60ꢀC for 2 h. After cooling to room
temperature, toluene was added, and substances volatile were removed
azeotropically by rotary evaporator and then those were removed
thoroughly using vacuum pump for 30 min to give a crude acid chloride 3
[1HNMR (400 MHz, CDCl , ppm) ꢀ 4.75 (2H, s), 7.53 (1H, t, J ¼ 7.2 Hz),
3
7.60 (1H, d, J ¼ 7.2 Hz), 7.67 (1H, t, J ¼ 7.46 Hz), 8.32 (1H, d, J ¼ 7.2 Hz)]
which was directly used for the esterification.
AZMB Ester 6
The acid chloride 3, prepared by the above procedure employing 85 mg
of 2 (480 mmol), thionyl chloride (1.0 mL), and N,N-dimethylformamide
(3.0 mL), was stirred with alcohol 5 (134 mg, 615 mmol) and 4-(N,N-dimethyl-
amino)pyridine (117 mg, 959 mmol) in CH2Cl2 (2.0 mL) at 0ꢀC for 2 h. The
mixture was poured into water and extracted with ether (30 mL Â 3). The
combined organic layer was washed with brine, dried over MgSO4 and
concentrated in vacuo. Silica gel column chromatography eluted with
26
AcOEt : hexane (15 : 85) gave 6 (215 mg, 570 mmol, 93%) as an oil ½ꢁŠ
D
À 52.4ꢀ (c 11.4, CHCl3). HNMR (400 MHz, CDCl , ppm) ꢀ 1.34, 1.52
1
3
(each, 3H, s), 2.44 (1H, dd, J ¼ 1.4, 4.9 Hz), 2.62 (1H, dd, J ¼ 1.4, 6.3 Hz),
3.07 (1H, ddd, J ¼ 4.9, 6.3, 8.8 Hz), 3.82 (1H, dd, J ¼ 2.9, 8.8 Hz), 4.70
(1H, d, J ¼ 3.9 Hz), 4.80, 4.88 (each 1H, d, J ¼ 14.6 Hz), 5.49 (1H, d,
J ¼ 2.9 Hz), 6.02 (1H, d, J ¼ 3.9 Hz), 7.43 (1H, dt, J ¼ 1.0, 7.5 Hz), 7.53
(1H, brd, J ¼ 7.5 Hz), 7.59 (1h, dt, J ¼ 1.0, 7.5 Hz), 8.03 (1H, dd, J ¼ 1.0,
7.5 Hz). 13C NMR (100 MHz, CDCl3, ppm) ꢀ 24.8, 26.2, 26.7, 29.0, 53.0,
78.2, 83.2, 85.0, 105.5, 112.5, 127.8, 128.3, 130.0, 131.1, 133.4, 137.9, 165.2.
IR (film, cmÀ1) 2100, 1720, 1250, 1080, 1020. EI-MS (%, rel int.) 362
((M À CH3)þ, 7), 291 (4), 132 (100), HIMS Calcd. for C16H16N3O5S
[(M À CH3)þ]: 362.0811. Found: m/z ¼ 362.0830.
Thioacetate 7
A suspension of 6 (316 mg, 838 mmol) and potassium acetate (400 mg,
4.12 mmol) in a mixture of acetic acid (1.0 mL) and acetic anhydride (10 mL)
was stirred at 140ꢀC for 14 h. After cooling to room temperature, the solvent
was removed by rotary evaporator. The residue was suspended with H2O
(50 mL) and it was extracted with AcOEt (30 mL Â 3). The combined

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3352
MATSUDA, HASHIMOTO, AND OKUNO
organic layer was washed with brine anhydrous MgSO4, and concentrated
in vacuo. Silica gel column chromatography of the residue with
AcOEt : hexane (20 : 80) gave 7 (345 mg, 720 mmol, 86%) as fine needles
(from AcOEt–hexane). M.p. ¼ 108–109ꢀC. ½ꢁŠ À 50.8ꢀ (c 7.4, CHCl3).
26
D
1HNMR (400 MHz, CDCl , ppm) ꢀ 1.33, 1.55, 2.06, 2.20 (each 3H, s),
3
4.17 (1H, ddd, J ¼ 2.9, 4.9, 10.7 Hz), 4.39 (1H, dd, J ¼ 4.9, 11.7 Hz), 4.47
(1H, dd, J ¼ 2.9, 11.7 Hz), 4.54 (1H, dd, J ¼ 2.9, 10.7 Hz), 4.60 (1H, d,
J ¼ 3.4 Hz), 4.79 (2H, s), 5.49 (1H, d, J ¼ 2.9 Hz), 5.98 (1H, d, J ¼ 3.4 Hz),
7.43 (1H, dt, J ¼ 1.0, 7.5 Hz), 7.50 (1H, brd, J ¼ 7.5 Hz), 7.59 (1H, dt,
J ¼ 1.4, 7.5 Hz), 8.03 (1H, dd, J ¼ 1.4, 7.5 Hz). 13C NMR (100 MHz,
CDCl3, ppm) ꢀ 20.7, 26.3, 26.7, 30.5, 76.4, 77.3, 83.0, 105.1, 112.5, 127.5,
128.3, 128.4, 130.0, 131.5, 133.4, 137.7, 165.1, 170.5, 192.6. IR (KBr, cmÀ1
)
2110, 1740, 1715, 1700, 1250, 1240, 1080. EI-MS (%, rel int.) 464
((M À CH3)þ, 5), 408 (8), 132 (86), 43 (100), HIMS Calcd. for
C20H22N3O8S [(M À CH3)þ]: 464.1128. Found: m/z ¼ 464.1118.
a-3-O-AZMB-5-Thioglucopyranose (8)
A solution of 7 (230 mg, 480 mmol) in aqueous 60% trifluoroacetic
acid (25 mL) was stirred at room temperature for 2 days. The solvent
was evaporate in vacuo and the residue was purified by silica gel column
chromatography eluted with acetone : CH2Cl2 (30 : 70) gave 8 (124 mg,
26
D
349 mmol, 73%) as an oil. ½ꢁŠ þ 96.0ꢀ (c 12.3, CHCl3). 1HNMR
(400 MHz, CD3OD, ppm) ꢀ 3.51 (1H, ddd, J ¼ 4.0, 4.8, 9.2 Hz). 3.83 (1H,
dd, J ¼ 9.2, 10.8 Hz), 3.90 (3H, m), 4.79 (2H, s), 4.93 (1H, d, J ¼ 3.6 Hz),
7.44 (1H, d, J ¼ 1.5, 8.0 Hz), 7.52 (1H, brd, J ¼ 8.0 Hz), 7.58 (1H, dt, J ¼ 1.5,
8.0 Hz), 8.04 (1H, dd, J ¼ 1.5, 8.0 Hz). 13C NMR (100 MHz, CD3OD, ppm)
ꢀ 45.0, 53.7, 62.0, 74.3, 75.1, 76.2, 78.5, 129.1, 130.8, 131.6, 131.9, 133.4,
138.1, 168.4. IR (film, cmÀ1) 3375, 2100, 1710, 1265, 1140, 1090, 1050. FAB-
MS (%, rel int.) 354 ((M À H)À, 9), 101 (100), 42 (41), HIMS Calcd. for
C14H16N3O6S [(M À H)À]: 354.0760. Found: m/z ¼ 354.0778.
a-3-O-AZMB-1,2-4,5-Diisopropylidene-5-thioglucopyranose (9)
A solution of 8 (32.0 mg, 94.3 mmol) in a mixture of 2,2-dimethoxy-
propane (1.0 mL) and acetone (1.0 mL) was stirred with p-toluenesulfonic
acid monohydrate (1.9 mg, 10 mmol) at room temperature for 3 h. After
neutralization by the addition of triethylamine (5 mL), the solvent was
removed under reduced pressure. Silica gel column chromatography of

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(2-AZIDOMETHYL)BENZOIC ACID
3353
the residue with acetone : CH2Cl2 (10 : 90) gave 9 (38.3 mg, 91.4 mmol, 97%)
26
D
as an oil. ½ꢁŠ þ 74.0ꢀ (c 11.0, CHCl3). 1HNMR (400 MHz, CDCl , ppm) ꢀ
3
1.36, 1.41, 1.47, 1.67 (each 3H, s), 3.38 (1H, dt, J ¼ 5.2, 11.2 Hz), 3.74 (1H, t,
J ¼ 11.2 Hz), 3.89 (1H, dd, J ¼ 5.2, 11.2 Hz), 3.99 (1H, t, J ¼ 10.0 Hz), 4.34
(1H, dd, J ¼ 5.2, 8.4 Hz), 4.71, 4.79 (each 1H, d, J ¼ 14.4 Hz), 5.16 (1H, d,
J ¼ 5.2 Hz), 5.35 (1H, dd, J ¼ 8.4, 10.0 Hz), 7.41 (1H, dt, J ¼ 1.6, 8.0 Hz),
7.50 (1H, brd, J ¼ 8.0 Hz), 7.56 (1H, dt, J ¼ 1.6, 8.0 Hz), 7.95 (1H, dd,
J ¼ 1.6, 8.0 Hz). 13C NMR (100 MHz, CDCl3, ppm) ꢀ 18.8, 26.7, 27.8,
29.2, 36.4, 52.6, 61.4, 72.7, 74.7, 76.4, 78.4, 99.4, 110.4, 128.0, 129.6,
129.7, 130.7, 132.4, 136.7, 166.0. IR (film, cmÀ1) 2100, 1725, 1255, 1215,
1190, 1080, 1050, 1030. EI-MS (%, rel int.) 420 ((M À CH3)þ, 9), 318 (12),
258 (10), 200 (12), 132 (100), HIMS Calcd. for C19H22N3O6S [(M À CH3)þ]:
420.1229. Found: m/z ¼ 420.1212.
a-1,2-4,5-Diisopropylidene-5-thioglucopyranose (10)
A solution of 9 (48.0 mg, 110 mmol) in a mixture of THF (1.0 mL) and
H2O (0.5 mL) was heated at 70ꢀC with triphenylphosphine (34.6 mg
132 mmol) for 2 h. The reaction completed within 1 h by monitored with
silica gel TLC. The mixture was concentrated in vacuo to give a residue.
Silica gel column chromatography of the residue with AcOEt : hexane
(25 : 75) gave 10 (29.3 mg, 106 mmol, 97%) as a prism. M.p. ¼ 99–100ꢀC
26
D
1
(from hexane). ½ꢁŠ þ 174.2ꢀ (c 8.3, CHCl3). HNMR (400 MHz, CDCl ,
3
ppm) ꢀ 1.41, 1.44, 1.51, 1.58 (each 3H, s), 2.79 (1H, br), 3.17 (1H, dt, J ¼ 5.4,
10.8 Hz), 3.65 (1H, dd, J ¼ 7.8, 9.7 Hz), 3.62 (2H, m), 3.84 (1H, dd,
J ¼ 11.7 Hz), 4.15 (1H, dd, J ¼ 4.8, 7.3 Hz), 5.10 (1H, d, J ¼ 4.8 Hz).
13C NMR (100 MHz, CDCl3, ppm) ꢀ 19.1, 26.6, 28.3, 29.4, 61.4, 74.1,
74.3, 75.9, 80.1, 99.7, 109.9. IR (KBr, cmÀ1) 3475, 1380, 1220, 1160, 1050,
1015, 865. EI-MS (%, rel int.) 276 (Mþ, 4), 261 ((M À CH3)þ, 16), 218 (34),
59 (100), 43 (72), HIMS Calcd. for C12H20O5S [(M À CH3)þ]: 276.1031.
Found: m/z ¼ 276.1017.
Treatment of 7 with NaOMe
A solution of 7 (14.0 mg, 29.2 mmol) and sodium methoxide (3.0 mg,
55.5 mmol) in a mixture of methanol (1.0 mL) and THF (0.4 mL) was stirred
at room temperature. After stirring for 10 h, the mixture was poured into
brine (50 mL) and it was extracted with Et2O (30 mL Â 3). The combined
organic layer was dried with anhydrous MgSO4, and concentrated in vacuo.
Silica gel column chromatography of the residue with AcOEt : hexane

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3354
MATSUDA, HASHIMOTO, AND OKUNO
(20 : 80) gave 6 (10.8 mg, 28.6 mmol, 98%), 1HNMR data of the sample was
identical with that of AZMB ester thiirane 6.
Treatment of 7 with PPh3
A mixture of 7 (10.1 mg, 21.1 mmol), sodium dihydrogenphosphate
dihydrate (8.6 mg, 55.1 mmol), and triphenylphosphine (8.0 mg, 30.5 mmol)
in a mixture of THF (1.0 mL) and H2O (0.3 mL) was heated at 70ꢀC for 1 h.
The mixture was poured into water (20 mL) and extracted with ethyl acetate
(20 mL Â 3). The combined organic solution was washed with saturated
sodium chloride solution (20 mL), dried over anhydrous magnesium sulfate,
and concentrated in vacuo. Silicagel column chromatography of the residue
with AcOEt : hexane (35 : 65) gave 12 as amolphous powder (5.3 mg,
16.6 mmol, 78%).[8] 1HNMR (400 MHz, CDCl , ppm) ꢀ 1.25, 1.50, 2.07,
3
2.41 (each 3H, s), 3.96 (1H, ddd, J ¼ 3.9, 4.9, 10.7 Hz), 4.10 (1H, d,
J ¼ 1.9 Hz), 4.18 (1H, dd, J ¼ 1.9, 10.7 Hz), 4.45 (1H, dd, J ¼ 4.9, 11.7 Hz),
4.47 (1H, dd, J ¼ 3.9, 11.7 Hz), 4.53 (1H, d, J ¼ 3.4 Hz), 5.92 (1H, d,
J ¼ 3.4 Hz). The structure of 12 was confirmed by converting the sample
into reported acetate[7] as follows. A solution of 12 (3.0 mg, 9.38 mmol) in
a mixture of acetic anhydride (100 mL) and pyridine (1.0 mL) at room
temperature for 12 h. After concentration in vacuo, the residue was
purified employing silica gel column chromatography. Elution with
AcOEt : hexane (15 : 85) gave the corresponding acetate (3.1 mg, 8.56 mmol,
91%). M.p. ¼ 151ꢀC (from hexane, lit. 152–154ꢀC[7]). The 1HNMR
spectrum of this sample was identical with that of reported, prepared by
following their procedure.
ACKNOWLEDGMENT
This work was supported by Grant-Aid Scientific Research
(No. 12780434) from Ministry of Education, Science, Sports and Culture
of Japan.
REFERENCES
1. Green, W.T.; Wuts, P.G.M. Protective Groups in Organic Synthesis,
3rd Ed.; John Wiley and Sons: New York, 1991; 17–245.
2. Wada, T.; Ohkubo, A.; Mochizuki, A.; Sekine, M. Tetrahedron Lett.
2001, 42, 1069–1072. They prepared AZMB acid 2 from methyl

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(2-AZIDOMETHYL)BENZOIC ACID
3355
2-methylbenzoate by sequential reactions of (1) NBS, (2) TMGN3, and
(3) NaOHin 76% yield.
3. Burton, D.J.; Koppes, W.M. Chem. Commun. 1973, 425.
4. Driguez, Z.; Henrissat, B. Tetrahedron Lett. 1981, 22, 5061–5062.
5. The structure of 12 was confirmed after converting into known acetate
as described in experimental section.
6. During the reaction, only starting 7 and thiirane 5 were observed by
TLC. No intermediate material was detected.
7. Yuasa, H.; Tamura, J.; Hashimoto, H. J. Chem. Perkin Trans. I 1990,
2763.
8. Sekine’s conditions (MePPh2, dioxane–H2O, r.t., 1 h)[2] also gave alcohol
12 in slightly lower yield (59%) along with unknown by-product.
Received in Japan August 31, 2001

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