Nucleophilic substitution at an sp2 carbon of vinyl halides with an intramolecular thiolate moiety: synthesis of 2-alkylidenethietanes

Article abstract of DOI:10.1016/j.tetlet.2008.04.127

Various 2-alkylidenethietanes were synthesized by intramolecular nucleophilic substitution reactions at an sp² carbon of vinyl halides with thiolate moieties. The reaction pathway of the substitution reactions was confirmed as a very rare S

Full text of DOI:10.1016/j.tetlet.2008.04.127

Tetrahedron Letters 49 (2008) 4125–4129
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: http://www.elsevier.com/locate/tetlet
Nucleophilic substitution at an sp2 carbon of vinyl halides with an
intramolecular thiolate moiety: synthesis of 2-alkylidenethietanes
Mao-Yi Lei a, Koji Fukamizu b, Yong-Jun Xiao a, Wei-Min Liu a, Scott Twiddy a, Shunsuke Chiba a,
Kaori Ando c, Koichi Narasaka a,
*
a Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
b Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
c Department of Chemistry, Faculty of Engineering, Gifu University, 1-1 Yanagido Gifu 501-1193, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Various 2-alkylidenethietanes were synthesized by intramolecular nucleophilic substitution reactions at
an sp2 carbon of vinyl halides with thiolate moieties. The reaction pathway of the substitution reactions
was confirmed as a very rare SNVp mechanism by theoretical and experimental studies.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 25 February 2008
Revised 12 April 2008
Accepted 23 April 2008
Available online 27 April 2008
This Letter is dedicated to Professor E. J.
Corey on the occasion of his 80th birthday
Keywords:
Nucleophilic vinylic substitution
2-Alkylidenethietane
SNVp mechanism
Density functional theory (DFT)
Concerted nucleophilic substitution at an sp3 carbon, typically
an SN2 reaction, is one of the most fundamental reactions in organ-
ic chemistry, giving a substitution product with inversion of the
configuration.1 On the other hand, two mechanisms are proposed
for concerted SN2 reaction at a vinylic sp2 carbon,2 namely, the
SNVp and SNVr pathways. In the SNVp mechanism, a nucleophile
interacts with the p* orbital of the vinylic carbon and gives a sub-
stitution product with retention of the configuration (Scheme 1a).
In the SNVr mechanism, a nucleophile attacks at the r* orbital of
the C–X bond and substitution occurs with inversion of the config-
uration (Scheme 1b). However, both SNVr and SNVp mechanisms
were so far considered as unfavorable processes at unactivated
vinylic carbons.3
δ –
Nu
R2
R3
R1
R2
R3
R1
X
R2
R3
R1
δ –
(a)
(b)
–X–
–X–
Nu
X
–
+
δ
Nu
R2
R3
R2
R3
Nu
R1
Nu–
R1
δ –
X
(Nu– = nucleophile; X = leaving group)
Scheme 1.
favored, whereas the SNVr pathway is preferred by Clꢀ and Brꢀ.4c
However, estimated activation energies of both reaction pathways
in those theoretical studies were so high that the substitution reac-
tions hardly proceed under the mild reaction conditions. There are
a few reports on substitution reactions at an sp2 carbon atom,
which suggested that the reaction proceeded in an SNVr manner.5
The substitution reaction of alkenyliodonium salts was found to
give the products with inversion of the stereochemistry via an
intermolecular SNVr mechanism.6 2-Bromoallylamines were
cyclized to aziridines by basic treatment and the stereochemistry
of the products suggests that the amino group approaches from
behind the bromine atom.7
Recent theoretical studies have indicated the possibilities of the
SNVr and SNVp mechanisms on unactivated vinylic carbons.4 For
example, theoretical calculations performed by Glukhovtsev show
that the activation energy of in-plane nucleophilic attack (SNVr) of
a
chlorine ion to chloroethene (32.6 kcal molꢀ1
) is about
10 kcal molꢀ1 lower compared to the out-of-plane attack (SNVp)
(42.7 kcal molꢀ1).4a Lee reported that in the gas-phase vinylic sub-
stitution of chloroethene by OHꢀ and SHꢀ, the SNVp mechanism is
* Corresponding author. Tel.: +65 6316 8900; fax: +65 6791 1961.
E-mail address: narasaka@ntu.edu.sg (K. Narasaka).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.04.127

4126
M.-Y. Lei et al. / Tetrahedron Letters 49 (2008) 4125–4129
We recently showed that haloalkenes bearing intramolecular
Sn powder
aq. HBr
OH
R1
O
hydroxy, sulfonamide, active methine, and thiol counterparts at
suitable positions gave the corresponding 5-membered cyclized
products via an intramolecular vinylic substitution reaction.8 Con-
cerning the cyclizations with O, N, C-nucleophiles, the reactions
proceeded only with E-isomers to afford the corresponding cycli-
zed products. The Z-isomers gave no cyclization products with
recovery of the starting haloalkenes (Scheme 2), being consistent
with our theoretical studies by DFT calculations.
+
(a)
Br
H
R1
Br
Et2O–H2O
rt
Br
3
4
5b: R1 = (CH2)2Ph, 91%
5c: R1 = CH2Ph, 33%
5d: R1 = (CH2)4CO2Et, 50%
5e: R1
5f: R1
= cyclo-C6H11, 92%
= p-MeO-C6H4, 50%
5h: R1 = (CH2)2CHBr(=CH2), 78%
In contrast, it was found that the cyclization reaction with thiols
proceeded with both E- and Z-isomers in spite of the low product
yield (Scheme 3a). The activation energies for the SNVp reactions
of thiols were relatively small, which would suggest the SNVp path-
way as a possible mechanism. It was also found that a unique
4-membered compound, 2-alkylidenethietane 1a,9 was formed in
78% yield by the cyclization of thiol 2a (Scheme 3b). In this case,
only the SNVp type transition structure (activation energy:
20.0 kcal molꢀ1 in DMF) was formed, probably due to steric repul-
sion between the thiolate and the isopropylidene group.
SiMe3
Br
OH
O
TiCl4
+
(b)
Ph
Ph
Br
CH2Cl2
–78 °C
H
Ph
4g
6
Ph
5g 76%
syn : anti = 5 : 1)
(
Scheme 4.
In this Letter, we present a study on the scope of this thietane
formation by the cyclization of 3-bromo-3-alkenethiolates and
experimental studies to confirm the reaction mechanism.
The synthetic routes to the starting materials are summarized
in Schemes 4 and 5. 3-Bromo homoallyl alcohols 5 were synthe-
sized by the reaction of 2,3-dibromopropene (3) with aldehydes
4 in the presence of tin powder (Scheme 4a).10 The reaction of
(Z)-b-bromoallylsilane 6 with 3-phenylpropionaldehyde (4g) gave
5g with syn selectivity (Scheme 4b).11 These homoallyl alcohols 5
were converted into the corresponding thioacetates 7 by substitu-
tion of the intermediate tosylates with potassium thioacetate or by
Mitsunobu reaction with thioacetic acid12 (Scheme 5).
Although the cyclization of tetrasubstituted vinyl bromide 2a
proceeded smoothly (Scheme 3), the cyclization of thiol 2b with
a terminal methylene moiety gave only a trace amount of the
desired thietane 1b in a complex mixture including disulfide 8
(Scheme 6).13
O
OH
S
Me
1) TsCl, pyridine
R1
Br
R1
2) MeCOS–K+, DMF
Br
R2
R2
7b-e, g,h
43–64% (2 steps)
R2 = H or (CH2)2Ph
5b-e, g,h
OH
O
S
Me
EtO2CN=NCO2Et
PPh3, MeCOSH
Br
Br
THF
OMe
OMe
5f
7f 10%
Scheme 5.
We envisioned that generation of the thiolate anion in situ
could prevent the formation of disulfide 8. As expected, when thio-
acetate 7b was treated with 1.5 mol equiv of K2CO3 and 10 mol
equiv of MeOH at 120 °C in degassed DMI, thietane 1b was ob-
tained in 93% yield (Scheme 7).14
Various 2-alkylidenethietanes 1 were synthesized starting from
thioacetates 7 by the nucleophilic vinylic substitution reaction
δ–
X
δ–
X
SH
Nu =
X =
Nu
O
NTs
C(CN)SO2Ph
Nu
Nu
1.5 mol equiv. K2CO3
–X–
R
R
Br
Ph
R
DMI, 80 °C, 2 h
2b
Cl
Br
SNVσ
Ph
Br
S
Scheme 2.
S
+
S
Ph
Br
Ph
1b trace
8 17%
Br
Ph(CH2)2
S
SH
Scheme 6.
1.5 mol equiv. NaH
(a)
DMI, 120 °C
Ph(CH2)2
O
from
from
E
-isomer: 34%
1.5 mol equiv. K2CO3
10 mol equiv. MeOH
Z-isomer: 12%
S
Me
Ph
S
Me
Br
DMI (degassed)
120 °C, 1.5 h
Br
Ph
Me
Br
Me
SH
Me
7b
1.5 mol equiv. K2CO3
S
(b)
DMI, 120 °C, 1.5 h
Ph
S
Ph
2a
1a 78%
Ph
(DMI =
N
,
N
-dimethylimidazolidinone)
1b 93%
Scheme 3.
Scheme 7.

M.-Y. Lei et al. / Tetrahedron Letters 49 (2008) 4125–4129
4127
Table 1
Synthesis of 2-alkylidenethietanes 1a
S
S
Ph
10
1.5 mol equiv. K2CO3
10 mol equiv. MeOH
Entry
Thioacetate 7
Conditions
Thietane 1 (yield/%)b
Ph
Me
Br
(a)
+
Me
S
DMI (degassed)
120 °C, 1.5 h
O
Me
Me
Br
Me
Me
S
O
S
Me
Ph
9
1
120 °C, 3 h
Ph
10'
Ph
7a
83% (10 : 10' = 3 : 1)
1a (94)
O
O
S
S
Me
Ph
1.5 mol equiv. K2CO3
10 mol equiv. MeOH
S
2
120 °C, 3 h
S
Me
Ph
(b)
Br
Br
Br
1c (92)
Br
Br
DMI (degassed)
120 °C, 1.5 h
7c
O
7h
1h 87%
S
S
S
Me
3c
100 °C, 10 h
Scheme 8.
(CH2)4CO2Et
(CH2)4CO2Et
1d (67)
with intramolecular thiolate moieties, and the results are summa-
rized in Table 1. The yield of thietane 1a was improved to 94% by
the use of thioacetate 7a (Table 1, entry 1). 2-Methylenethietanes
1 possessing primary and secondary alkyl groups at the C(4)-posi-
tion could be synthesized in good yield (entries 2–4). Benzylic thio-
acetate 7f was cyclized to thietane 1f in moderate yield due to the
concurrent elimination of thioacetic acid, forming a conjugated
diene as a side product (entry 5). 3,4-Dialkylsubstituted 2-methy-
lenethietane 1g15 was formed smoothly in 92% yield (entry 6).
Formation of a 5-membered ring proceeded from thioacetate
916 to give a mixture of 2-methylenetetrahydrothiophene 10 and
2,3-dihydrothiophene 100 in 83% yield (Scheme 8a). This result
prompted us to try a competition reaction among 4- versus
5-membered ring formation. It was noted that the reaction of
thioacetate 7h gave only 4-membered ring product 1h without
any 5-membered ring compound (Scheme 8b).
7d
O
S
Me
4
5
120 °C, 3 h
Br
Br
1e (<65)d
7e
O
S
S
Me
120 °C, 2 h
OMe
OMe
1f (30)
7f
O
S
S
Me
Next, we explored theoretical calculations17 using the GAUSSIAN
program.18 All calculations were performed at the B3LYP19/6-
31+G(d) level and the solvent effect was included by using the
Onsager continuum model20 for DMF (e = 37.06) as a solvent.21
Interestingly, the cyclization of thiolate anion 11 from 7a gave
the SNVr and SNVp transition states (Fig. 1), both of which have
low enough activation energies (22.4 kcal molꢀ1 for SNVr,
18.2 kcal molꢀ1 for SNVp) to undergo substitution reactions under
the presented reaction conditions.
6
120 °C, 1.5 h
Br
Ph
Ph
Ph
Ph
1g (92)
7g
a
Reactions were carried out in degassed DMI with 1.5 mol equiv of K2CO3 and 10
mol equiv of MeOH.
b
Isolated yield.
c
10 mol equiv of EtOH was used instead of MeOH.
1H NMR yield.
d
Figure 1. Transition structures for the nucleophilic cyclization of thiolate anion 11 [B3LYP/6-31+G(d), SCRF (dipole, solv = DMF)]. Selected bond lengths are shown in Å. The
italicized numbers are the values in the gas phase.

4128
M.-Y. Lei et al. / Tetrahedron Letters 49 (2008) 4125–4129
1968; pp 185–332; (c) Kelsey, D. R.; Bergman, R. G. J. Am. Chem. Soc. 1971, 93,
1953.
O
O
O
Et3N
R3
R3
•
+
Ph3P
CH2Cl2
rt
4. (a) Glukhovtsev, M. N.; Pross, A.; Radom, L. J. Am. Chem. Soc. 1994, 116, 5961;
(b) Lucchini, V.; Modena, G.; Pasquato, L. J. Am. Chem. Soc. 1995, 117, 2297; (c)
Kim, C. K.; Hyun, K. H.; Kim, C. K.; Lee, I. J. Am. Chem. Soc. 2000, 122, 2294; (d)
Bach, R. D.; Baboul, A. G.; Schlegel, H. B. J. Am. Chem. Soc. 2001, 123, 5787.
5. It was reported that intermolecular substitution reactions of b-halostyrenes
with thiolate and selenide anions occur with retention of the configuration, but
the reaction mechanisms were not revealed, see: (a) Marchese, G.; Naso, F.;
Modena, G. J. Chem. Soc. B 1968, 958; (b) Marchese, G.; Naso, F.; Modena, G. J.
Chem. Soc. B 1969, 290; (c) Tiecco, M.; Testaferri, L.; Tingoli, M.; Chianelli, D.;
Montanucci, M. Tetrahedron Lett. 1984, 25, 4975.
6. (a) Ochiai, M.; Oshima, K.; Masaki, Y. J. Am. Chem. Soc. 1991, 113, 7059; (b)
Okuyama, T.; Takino, T.; Sato, K.; Ochiai, M. J. Am. Chem. Soc. 1998, 120, 2275;
(c) Ochiai, M.; Nishi, Y.; Hirobe, M. Tetrahedron Lett. 2005, 46, 1863.
7. Shiers, J. J.; Shipman, M.; Hayes, J. F.; Slawin, A. M. Z. J. Am. Chem. Soc. 2004, 126,
6868.
8. (a) Ando, K.; Kitamura, M.; Miura, K.; Narasaka, K. Org. Lett. 2004, 6, 2461; (b)
Miyauchi, H.; Chiba, S.; Fukamizu, K.; Ando, K.; Narasaka, K. Tetrahedron 2007,
63, 5940.
9. For reports on the synthesis of 2-alkylidenethietane derivatives, see: (a)
Bolster, J.; Kellogg, R. M. J. Org. Chem. 1980, 45, 4804; (b) Bonini, B. F.; Franchini,
M. C.; Fochi, M.; Mangini, S.; Mazzanti, G.; Alfredo Ricci, A. Eur. J. Org. Chem.
2000, 2391; (c) Ozaki, S.; Matsui, E.; Saiki, T.; Yoshinaga, H.; Ohmori, H.
Tetrahedron Lett. 1998, 39, 8121.
Cl
Ph
Ph
12
13
14 33%
R3
Br
1) LiBr, AcOH, 80 °C
2) NaBH4, MeOH, 0 °C
R3
OH
OH
+
Ph
Br
Ph
Z
-3i 21%
R3
E-3i 8%
O
1) TsCl, pyridine
S
Me
Z
-3i
-3i
2) MeCOS–K+, DMF
Br
Ph
Z
-7i 55%
(R3 =
n
-C9H19
)
O
R3
1) TsCl, pyridine
S
Me
E
2) MeCOS–K+, DMF
Br
Ph
E-7i 49%
Scheme 9.
10. Mandai, T.; Nokami, J.; Yano, T.; Yoshinaga, Y.; Otera, J. J. Org. Chem. 1984, 49,
172.
11. Uenishi, J.; Ohmi, M. Heterocycles 2003, 61, 365.
12. Moree, W. J.; van der Marel, G. A.; Liskamp, R. J. J. Org. Chem. 1995, 60, 5157.
13. Treatment of thiol 2b with K2CO3 even at room temperature gave a complex
mixture including disulfide 8.
O
R3
1.5 mol equiv. K2CO3
10 mol equiv. MeOH
R3
14. Experimental procedure for nucleophilic substitution of thioacetate 7b to 2-
alkylidenethietane 1b: To a solution of thioacetate 7b (103 mg, 0.329 mmol)
and MeOH (103 mg, 3.21 mmol) in DMI (16.5 mL) was added K2CO3 (68 mg,
0.492 mmol), and the mixture was stirred at 120 °C for 1.5 h. The reaction was
quenched by adding pH 9 ammonium buffer solution at 0 °C, and extracted
three times with diethyl ether. The combined extracts were washed with H2O
and brine, and dried over MgSO4. The solvent was removed in vacuo, and the
resulting crude products were purified by flash column chromatography (silica
gel; hexane/acetone/triethylamine = 95:5:2) to give 2-alkylidenethietane 1b
(56 mg, 0.293 mmol) in 93% yield. Pale yellow oil; 1H NMR (500 MHz, CDCl3) d
7.28 (2H, dd, J = 7.3, 7.5), 7.20 (1H, t, J = 7.3), 7.14–7.16 (2H, m), 4.94 (1H, ddd,
J = 2.0, 2.1, 2.2), 4.71 (1H, ddd, J = 2.2, 2.4, 2.5), 3.60–3.65 (1H, m), 3.58 (1H,
dddd, J = 2.1, 2.2, 7.1, 7.6), 3.14 (1H, dddd, J = 2.0, 2.4, 7.1, 14.8), 2.62–2.68 (1H,
m), 2.53–2.59 (1H, m), 2.07–2.20 (2H, m); 13C NMR (125 MHz, CDCl3) d 141.0,
141.0, 128.4 (overlapped), 126.0, 103.5, 43.5, 40.3, 37.9, 33.5; IR (ZnSe) 3026,
S
Me
Ph
S
DMI (degassed)
120 °C, 1.5 h
Br
Ph
Z
-7i
Z
-1i 70%
O
1.5 mol equiv. K2CO3
10 mol equiv. MeOH
R3
R3
S
Me
Ph
S
DMI (degassed)
120 °C, 1.5 h
Br
Ph
E-7i
E
-1i 62%
(R3=
n-C9H19)
2917, 2852, 1631, 1496, 1454, 1120, 1076, 1030, 831, 748, 698, 650 cmꢀ1
HRMS (FAB+) calcd for C12H15S (M+H+): 191.0894, found: 191.0867.
;
Scheme 10.
15. The stereochemistry of 1g was confirmed by the vicinal coupling constant
(J = 10.4 Hz) of the corresponding sulfone 15, which was prepared by oxidation
of 1g with m-chloroperbenzoic acid (m-CPBA) as shown below.
We envisaged that the reaction mechanism could be confirmed
by examination of the stereochemical outcomes of two reaction
pathways, that is, the inversion of the configuration for SNVr and
the retention for SNVp. Thus, the Z- and E-isomers of thioacetates
7i were used for the substitution reactions to clarify the reaction
mechanism. The syntheses of Z-7i and E-7i are shown in Scheme
9. Allene 14, synthesized from undecanoyl chloride (12) and phos-
phorous ylide 13,22 was treated with LiBr in acetic acid,23 and then
NaBH4 to afford both the Z- and E- isomers of homoallyl alcohol 3i,
which were transformed to thioacetates 7i following Scheme 5.24
The cyclization of Z-7i and E-7i yielded thietanes Z-1i and E-1i,
respectively, with complete stereospecificity (Scheme 10).25 These
results suggest that the present cyclization proceeds with reten-
tion of the configuration, namely by the SNVp mechanism.
O
m
-CPBA
S
H
J
= 10.4 Hz
NaHCO3
1g
H
CH2Cl2, rt
Ph
Ph
15 70%
16. Thioacetate 9 was prepared by the same procedure as Scheme 5 from the
corresponding alcohol, which can be synthesized by the reaction of 4-bromo-
4-pentenal with phenethylmagnesium bromide.
17. The presented calculation is the same as that in our previous articles, see Ref. 8.
18. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.;
Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.;
Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi,
R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;
Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe,
M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
GAUSSIAN 03, Revision C.02, Gaussian, Wallingford, CT, 2004.
Acknowledgment
We acknowledge the Nanyang Technological University for
funding of this research.
References and notes
19. (a) Becke, A. D. J. Chem. Phys. 1992, 96, 2155; (b) Lee, C.; Yang, W.; Parr, R. G.
Phys. Rev. B 1988, 37, 785.
20. (a) Onsager, L. J. Am. Chem. Soc. 1936, 58, 1486; (b) Wong, M. W.; Frisch, M. J.;
Wiberg, K. B. J. Am. Chem. Soc. 1991, 113, 4776.
21. DMI has almost the same dielectric constant (37.60) as DMF. Since DMF and
DMI are able to dissolve many salts and tend to surround metal cations rather
than nucleophilic anions, the use of free anions as model systems may be
suitable.
1. Hughes, E. D.; Juliusburger, F.; Masterman, S.; Topley, B.; Weiss, J. J. Chem. Soc.
1935, 1525.
2. For reviews, see: (a) Rapport, Z. Acc. Chem. Res. 1992, 25, 474; (b) Okuyama, T.;
Lodder, G. In Advances in Physical Organic Chemistry; Tidwell, T. T., Richard, J. P.,
Eds.; Academic Press: New York, 2002; Vol. 37, pp 1–56; (c) Okuyama, T. J.
Synth. Org. Chem. Jpn. 2006, 64, 348.
3. (a) Miller, S. I.; Yonan, P. K. J. Am. Chem. Soc. 1957, 79, 5931; (b) Miller, S. I. In
Advances in Physical Organic Chemistry; Gold, V., Ed.; Academic Press: New York,

M.-Y. Lei et al. / Tetrahedron Letters 49 (2008) 4125–4129
4129
22. Fu, C.; Ma, S. Eur. J. Org. Chem. 2005, 3942.
n
-C8H17
23. Ma, S.; Xie, H.; Wang, G.; Zhang, J.; Shi, Z. Synthesis 2001, 5, 713.
24. The stereochemistries of the alkenes 7i were determined by NOE
measurements as shown below.
O
S
m
-CPBA
H
NaHCO3
O
Z-1i
CH2Cl2, rt
H
n
-C8H17
n
-C8H17
H
Ph
H
H
H
H
Z
-16 81%
H
H
Br
AcS
Br
AcS
H
n
-C8H17
O
S
m
-CPBA
Ph
Ph
O
NaHCO3
H
H
H
E-1i
Z
-7i
E-7i
CH2Cl2, rt
H
Ph
25. The stereochemistries of the alkenes 1i were determined by NOE
measurements of the corresponding sulfones 16, which were prepared by
oxidation of 1i with m-chloroperbenzoic acid (m-CPBA).
E
-16 85%