The effects of C-S and C-Se bonds on torquoselectivity: stereoselective olefination of α-thio and α-selenoketones with ynolates

Article abstract of DOI:10.1016/j.tet.2009.08.060

Highly Z-selective olefination of acyclic α-thio and α-selenoketones with ynolates has been achieved, and the theoretical calculations of the transition states in the ring-opening of the intermediates, the β-lactone enolates, revealed that the torquoselectivity was controlled by the secondary orbital interactions between the σ orbital of the C-S bond or a lone pair orbital on the S and σ^* orbitals of the breaking C-O bond, and the σ orbital of the breaking C-O bond or a lone pair orbital on the O on the ring and the σ^* orbitals of the C-S bond. The synthetic applications of the resulting olefins are also shown.

Full text of DOI:10.1016/j.tet.2009.08.060

Tetrahedron 65 (2009) 8832–8838
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
The effects of C–S and C–Se bonds on torquoselectivity: stereoselective olefination
of
a-thio and
a-selenoketones with ynolates
,
Takashi Yoshikawa a, Seiji Mori b, Mitsuru Shindo c
*
a Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-koen, Kasuga 816-8580, Japan
b Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan
c Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga-koen, Kasuga 816-8580, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 July 2009
Received in revised form 24 August 2009
Accepted 25 August 2009
Available online 29 August 2009
Highly Z-selective olefination of acyclic
the theoretical calculations of the transition states in the ring-opening of the intermediates, the
a
-thio and
a
-selenoketones with ynolates has been achieved, and
-lactone
enolates, revealed that the torquoselectivity was controlled by the secondary orbital interactions be-
tween the orbital of the C–S bond or a lone pair orbital on the S and orbitals of the breaking C–O
bond, and the orbital of the breaking C–O bond or a lone pair orbital on the O on the ring and the
orbitals of the C–S bond. The synthetic applications of the resulting olefins are also shown.
b
s
s
*
s
s
*
Keywords:
Torquoselectivity
Olefination
Ó 2009 Elsevier Ltd. All rights reserved.
Ynolates
Orbital interactions
Theoretical calculation
1. Introduction
propose the geminal bond participation.3 However, experimental
studies on the effects of the substituents as well as their synthetic
applications have not been as thoroughly reported, probably due to
difficulties in the preparation of the corresponding four-membered
rings.2
Recently, we developed a novel olefination methodology for
carbonyl compounds with ynolates providing tetrasubstituted ole-
fins with high stereoselectivities in which the b-lactone enolate
Torquoselectivity is a fundamental concept for the control of
stereoselectivity in the thermal electrocyclic ring-opening reaction
of unsaturated four-membered rings such as cyclobutenes and
oxetenes.1 According to Houk, the geometry of the alkenyl products
is controlled by the torquoselectivity wherein the electron donating
groups rotate outward and the electron withdrawing groups inward,
via the orbital interactions between the breaking C–C
s
or
s
*
orbitals
intermediates (oxetenes) are ring-opened with high torquose-
lectivity (Scheme 1).4 Olefinations of acylsilanes,5 acylgermanes,6
esters,7 and alkynyl ketones8 are based on the effect of controlling
groups directly attached to the carbonyl group. In the course of this
and the appropriate bonding and/or antibonding orbitals of the
substituents on the ring (Fig. 1).1,2 On the other hand, Inagaki et al.
study, we have achieved a highly Z-selective olefination of
a-alkoxy
and -aminoketones providing tetrasubstituted olefins where one
a
carbon was inserted between the carbonyl group and the directing
group, like the alkoxy group (Scheme 2).9 In other words, the
alkoxymethyl and aminomethyl groups rotate inward exclusively in
Figure 1. Torquoselectivity.
* Corresponding author. Fax: þ81 92 583 7875.
Scheme 1. Torquoselective olefination with ynolates.
E-mail address: shindo@cm.kyushu-u.ac.jp (M. Shindo).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.08.060

T. Yoshikawa et al. / Tetrahedron 65 (2009) 8832–8838
8833
Table 1
Olefination of
a
-thioketones with ynolates
Scheme 2. Torquoselective olefination of a-oxyketones.
the ring-opening of the oxetenes, while an alkoxy group rotates
outward exclusively in the olefination of esters.6 Initially we had
considered the chelation control by the ethereal alkoxy and the
amino groups as hard Lewis bases; however, the secondary orbital
interactions turned out to be critical for the torquoselectivity rather
than chelation. Theoretical calculations and experimental evidence
revealed that, in the transition states of the conrotatory ring-
opening, the secondary orbital interactions between the breaking
Entry
2
R1
R2
R3
3
Yield (%)
Z:E
1
2
3
4
5
6
2a
2b
2c
2d
2e
2f
Ph
Ph
Pr
Ph
t-Bu
Pr
Me
H
Et
Me
H
Et
C12H25
C12H25
C12H25
Ph
Ph
Ph
3a
3b
3c
3d
3e
3f
77
>99:1
>99:1
>99:1
95:5
83:17
97:3
32a
76
82
19b
81
C–O
the breaking C–O
termined the torquoselectivity (Fig. 2). These results demonstrate
the importance of the orbital as an electron donating group and
the
orbital as an electron accepting group rather than chelation.10
s
*
orbital and the C–H
s
orbital (TSZ1), and partially between
a
A methylated ketone was generated
s
orbital and the C–O
s
*
orbital (TSZ2), de-
s
s
*
Based on this information, we decided to examine the olefination of
thiomethyl and selenomethyl ketones since these substituents
would work as electron accepting groups to give Z-olefins, even
though sulfur and selenium atoms are softer Lewis bases than
oxygen atoms. Theory indicates that the antibonding orbitals of C–S
and C–Se bonds have potent electron accepting ability11 but there
has been no experimental evidence to support this indication. In
this paper, we describe the effects of C–S and C–Se bonds on the
b
The methylated ketones were generated
torquoselectivity and the Z-selective olefination of
-selenoketones.
a-thio and
a
Scheme 3. Olefination of cyclic a-thioketones.
Figure 2. Torquoselectivity controlled by chelation or the secondary orbital interaction.
2. Results and discussion
2.1. Olefination of
a-thioketones
We began our study on the olefination of
a-dodecylthioketones
(2a–2c) with ynolates. The lithium ynolate, prepared from ethyl
2,2-dibromopropionate with t-BuLi,12 reacted with the ketones
in THF at room temperature to afford the desired tetrasubstituted
alkenes (3a–3c) with excellent Z-selectivity in good to moderate
yields (Table 1, entries 1–3). The olefination of a-phenylthioketones
(2d–2f) furnished the tetrasubstituted alkenes (3d–3f) with accept-
able high Z-selectivity (Table 1, entries 4–6). When the substrates
Figure 3. Possible conformation of the intermediates.
of 2b and 2e were used, the yields were low, and the a-methylated
ketones were isolated, due to the partial enolization of the ketones.
In contrast to the acyclic ketones, 2-phenylthiocycloalkanones
The fact that the A-value of CH3S– (4.35 kJ/mol) is much larger than
that of CH3O– (2.30–3.14 kJ/mol) would support this hypothesis.13
induced no torquoselectivity (Scheme 3), although
a-siloxy-
cyclohexanone was olefinated to give an alkene in a Z/E ratio of
83:17.9 If this reaction was controlled by the secondary orbital in-
2.2. Olefination of a-selenoketones
teractions, as was seen in the case of a-siloxycyclohexanone, the
conformation of the directing group (RS–) might be more strongly
fixed in the equatorial position (Fig. 3). Our previous work dem-
onstrated that high torquoselectivity required the alkoxy-directing
group to be in the axial orientation in the lactone enolate in-
termediate, but in the equatorial position it induced no selectivity.
The olefination of the
alkenes with high Z-selectivity after methyl esterification
(Scheme 4). From this result, acyclic -seleno functionalities as well
as -oxy and -amino groups were found to be good directing
groups in the torquoselective olefination with ynolates.
a-phenylselenoketone 6 provided the
8
a
a
a

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T. Yoshikawa et al. / Tetrahedron 65 (2009) 8832–8838
desulfurization, the trisubstituted olefins are therefore preferable
to the tetrasubstituted olefins, probably due to the steric strain in
the transition states of the protonation of the allylic radical or anion
species. This represents a stereoselective synthesis of multi-
substituted b,g-unsaturated esters.
The seleno product 8 was converted into the E-allylic alcohol 11
via oxidation of the selenide followed by a [2,3]-sigmatropic rear-
rangement (Scheme 6).15
Scheme 4. Olefination of a-selenoketone.
2.3. Synthetic utility
In order to show the synthetic utility of the olefination, several
reactions of the sulfur and selenium functionalities were examined.
Attempts at desulfurization of the olefins with activated Zn–
NiCl2–NH4Cl aq14 provided the unconjugated
b,g-unsaturated
esters in only the Z-form (Scheme 5). Since, even in the absence of
a conjugated phenyl group (Scheme 5b) or a conjugated carbonyl
group (Scheme 5c), the double bond was isomerized by the
Scheme 6. [2,3]-Sigmatropic rearrangement.
2.4. Theoretical studies
B3LYP hybrid density functional calculations16 were carried out
for the olefination of a-methylthioacetone as a model compound.
Since the C–S
than the C–O
s
s
*
orbital is expected to be more electron accepting
orbital (Table 2), this torquoselectivity should also
*
be controlled by the secondary orbital interactions. We obtained
ten transition states leading to the Z-alkene (TSZ1-TSZ10), and eight
transition states (TSE1-TSE8) leading to the E-alkene in the ring-
opening of the b-lactone enolates. The chelated transition structure
Table 2
NBO energies of C–X
s
- and
s
*
-orbitals in Hartrees at the B3LYP/6–31G
*
level
C–H
C–C
C–O
C–S
Es (au)
Es (au)
*
ꢀ0.51
ꢀ0.58
ꢀ0.79
ꢀ0.58
0.17
0.43
0.40
0.32
Scheme 5. Stereoselective synthesis of b,g-unsaturated esters by desulfurization.
Figure 4. Structures of the transition states leading to the E- and Z-forms.

T. Yoshikawa et al. / Tetrahedron 65 (2009) 8832–8838
8835
for the methylthio case (see Fig. 2) could not be located as for the
C5–S6 bond (C), the
s
orbital of C5–S6 bond and the
s
s
*
orbital of
s orbital
*
methoxy analogue.9 Representative structures are shown in Fig-
ure 4, with their relative energies listed in Table 3. Since the
structure of TSZ2 was quite similar to that of TSZ1, and those of
TSE2 and TSE3 likewise similar to that of TSE1, except for the ar-
rangements of the coordinating ether, TSZ2, TSE2, and TSE3 are not
shown in this table (see Supplementary data). TSZ1 and TSE1 were
the most stable in energy, leading to the Z- and E-alkenes, re-
spectively, and TSZ1 was more stable in enthalpy by 12.4 kJ/mol
and in Gibbs energy by 12.3 kJ/mol, which is fairly consistent with
the experimental results. In the most stable transition state for the
methylthio case, TSZ1, the C5–S6 bond was nearly anti-periplanar to
the breaking C4/O1 bond (the dihedral angle of O1–C4–C5–S6 is
ꢀ164ꢁ). In TSZ3, which was higher in enthalpy by 4.7 kJ/mol and in
Gibbs energy by 4.3 kJ/mol, the S–Me bond in the methylthio group
was almost perpendicular to the breaking C4/O1 bond (the
dihedral angle of O1–C4–C5–S6 is ꢀ79ꢁ), and the C5–Ha bond was
anti-periplanar to the breaking C4/O1 bond (the dihedral angle of
O1–C4–C5–Ha is ꢀ165ꢁ) (Table 4). The other TSZs were much higher
in energy than TSZ1 and TSZ3.
C4–O1 bond (D), and the
orbital of C8–Hc bond and the
of the anti-periplanar C4–O1 bond (F). These results show that 1)
the thiomethyl substituent works both as an electron-donor and an
electron-acceptor since the energy of the C–S
than that of the oxymethyl substituent while the energy of the C–S
bond was lower (see Table 2), and that 2) the orbital overlaps
were larger in TSZ than in TSE. Although the interactions between
the orbitals of the anti-peri-
orbital of C4–O1 bond and the
s bond was higher
s
*
s
*
s
planar C5–Ha and C5–Hb bonds (E) exclusively stabilized TSZ3 and
TSE4, no definitive differences were observed. On the other hand,
only small differences among TSs were observed in the geminal
bond participation3 (see Table in Supplementary data). Conse-
quently, these orbital interactions dominate the torquoselectivity.
3. Conclusion
We have found a highly Z-selective olefination of a-thio and a-
selenoketones with ynolates. Theoretical calculations revealed that
the torquoselectivity was controlled by the secondary orbital in-
teractions between the
s orbital of the C–S bond or a lone pair orbital
Table 3
on the S and
between the
s
*
orbital of the breaking C–O bond and the interactions
orbital of the breaking C–O bond or a lone pair orbital
Relative activation energies (DDEz), activation enthalpies (DDHz), and Gibbs free
energies of activation (DDGz) at 298.15 K of TSs relative to TSZ1 in kJ/mol
s
on the O and the
s orbital of the C–S bond. These are the first
*
DDE
DD
H
DDG
experimental examples of the effects of sulfur and selenium on the
torquoselectivity. This work not only contributes to a practical
application of olefination but also provides new insights into
torquoselectivity.
TSZ1
TSZ3
TSE1
TSE4
0.0
5.6
12.8
16.8
0.0
4.7
12.4
16.0
0.0
4.3
12.3
16.8
4. Experimental
Table 4
Representative bond angles in degrees
4.1. General procedures
(O1–C4–C8) (O1–C4–C5) (O1–C4–C8–Hc) (O1–C4–C5–S6) (O1–C4–C5–Ha)
1H and 13C NMR spectra were measured in CDCl3 solution and
referenced to TMS (0.00 ppm) and CDCl3 (77.0 ppm), respectively.
All reactions were performed in oven-dried glassware under posi-
tive pressure of argon, unless otherwise noted. HPLC was per-
formed using a Mightysil Si 60 column (10 mmꢂ25 cm). The
stereochemistry was determined by NOE experiments, unless
otherwise indicated.
TSZ1 117
TSZ3 119
TSE1 94
TSE4 93
93
95
115
121
ꢀ179
ꢀ179
170
ꢀ164
ꢀ79
151
ꢀ46
78
ꢀ165
ꢀ82
172
ꢀ165
NBO (natural bond orbital) analyses17 were carried out to ex-
amine the differences in the stability with respect to the secondary
orbital interactions (Table 5). The largest energy preference of TSZ1
4.2. General procedure for the preparation of a-thioketones
over TSE1 was the interaction between a lone pair on S6 and the
s
*
orbital of the breaking C4–O1 bond (A) by ꢀ11.9 kJ/mol. In TSZ1,
there were other important interactions between the lone pair on
O1 and the
s s
orbital of the anti-periplanar C5–S6 bond (B), the
*
orbital of the C4–O1 bond and the
s orbital of the anti-periplanar
*
Table 5
Second-order interaction energies between NBOs of the transition states in kJ/mol
S6
C5
To a solution of diisopropylamine (1.28 mL, 9.10 mmol) in THF
(14 mL), cooled to ꢀ78 ꢁC under argon, was added dropwise a so-
lution of n-butyllithium (3.44 mL, 8.75 mmol, 2.54 M in hexane).
The solution was stirred for 20 min at ꢀ78 ꢁC and then trime-
thylsilyl chloride (freshly distilled from calcium hydride, 4.44 mL,
35 mmol) and a solution of the ketone (7.0 mmol) in THF (3 mL)
were added. After 1 h, to the resulting reaction mixture was added
triethylamine (4.88 mL, 35 mmol) and a saturated NaHCO3 solution
(14 mL), and the mixture was allowed to warm to room tempera-
ture. The resulting mixture was filtered with aspirator and sepa-
rated. The water phase was extracted with hexane. The organic
phase was washed with water, a saturated NaHCO3 solution, and
brine. The combined organic phase was dried over Na2SO4, filtered,
and concentrated to afford the silyl enol ether.
O
O
O
SMe
SMe
SMe
Li
Li
Li
lone
O
O
O
pair
O1
lone
Me
O(2)
Me
H
Me
S(2)
C4
pair
A
B
C
H
O
O
O
SMe
SMe
SMe
H
Li
Li
Li
O
O
O
Me
Me
D
E
F
TSs
A
B
C
D
E
F
TSZ1
TSZ3
TSE1
TSE4
ꢀ16.0
ꢀ0.4
ꢀ6.8
ꢀ16.3
ꢀ0.8
ꢀ8.1
ꢀ0.7
ꢀ22.6
ꢀ3.5
ꢀ3.8
ꢀ35.5
ꢀ39.0
ꢀ27.4
ꢀ25.9
>ꢀ0.4
ꢀ0.5
ꢀ30.2
>ꢀ0.4
ꢀ36.4
ꢀ4.1
ꢀ14.4
ꢀ3.9
To a solution of silyl enol ether in THF (105 mL) was added N-
bromosuccinimide (1.87 g, 10.5 mmol) at 0 ꢁC. After being stirred at
>ꢀ0.4
>ꢀ0.4

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T. Yoshikawa et al. / Tetrahedron 65 (2009) 8832–8838
0 ꢁC for 30 min, the reaction mixture was poured into a saturated
NaHCO3 solution and extracted with Et2O. The organic phase was
dried over MgSO4, filtered, and concentrated to afford a residue.
Hexane was added to the residue, which then was filtered. The
41.3 (t), 58.5 (d), 127.5 (d), 128.8 (d), 132.2 (d), 133.0 (s), 207.0 (s); IR
(Neat): 1707 cmꢀ1; MS (EI) m/z 222 (Mþ), 151 (100%); HRMS (EI)
calcd for C13H18OS: 222.1078, found: 222.1059.
filtrate was concentrated to give the
a
-bromoketone.
4.2.7. 2-(Phenylthio)cyclohexanone (4a). Yield 86% . Pale yellow oil:
To a solution of sodium hydride (NaH, 252 mg, 6.6 mmol, 62.7%
in oil) in THF (24 mL) was added the thiol (6.6 mmol) at 0 ꢁC. After
30 min, to the resulting mixture was added dropwise a solution of
1H NMR (400 MHz, CDCl3)
d: 1.65–2.33 (m, 7H), 2.88–2.96 (m, 1H),
3.83 (ddd, J¼1.6, 5.2, 6.0 Hz, 1H), 7.24 (tt, J¼1.6, 7.2 Hz, 1H), 7.29 (tt,
J¼1.6, 6.8 Hz, 2H), 7.40 (dd, J¼1.6, 8.0 Hz, 2H); 13C NMR (100 MHz,
a
-bromoketone (6.0 mmol) in THF (6 mL) at 0 ꢁC. After being stirred
CDCl3) d: 22.6 (t), 27.2 (t), 33.9 (t), 39.0 (t), 56.3 (d), 127.2 (d), 128.8
at room temperature for 1.5 h, the reaction mixture was quenched
with a saturated NH4Cl solution at 0 ꢁC and extracted with Et2O.
The organic phase was washed with water, brine, dried over MgSO4,
filtered, and concentrated to give a residue, which was purified by
(d), 131.6 (d), 133.6 (s), 207.2 (s); IR (Neat): 1713 cmꢀ1; MS (EI) m/z
206 (Mþ, 100%).
4.2.8. 2-(Phenylthio)cycloheptanone (4b). Yield 87% over 3 steps.
column chromatography to afford the
a
-thio ketone.
Pale yellow oil: 1H NMR (400 MHz, CDCl3)
d: 1.28–2.28 (m, 8H), 2.39
(ddd, J¼2.8, 7.2,13.2 Hz,1H), 2.78 (ddd, J¼3.6,11.6,13.2 Hz,1H), 3.78
4.2.1. 2-(Dodecylthio)-1-phenylpropan-1-one (2a). Yield 91%. Pale
yellow solid: 1H NMR (400 MHz, CDCl3)
(dd, J¼5.6, 10.4 Hz, 1H), 7.21–7.31 (m, 3H), 7.40 (dd, J¼1.2, 8.0 Hz,
d
: 0.88 (t, J¼6.8 Hz, 3H),
2H); 13C NMR (100 MHz, CDCl3)
d: 25.3 (t), 27.0 (t), 29.8 (t), 30.3 (t),
1.21–1.32 (m, 18H), 1.43–1.52 (m, 2H), 1.56 (d, J¼6.8 Hz, 3H), 2.37 (dt,
J¼7.2, 12.0 Hz, 1H), 2.53 (dt, J¼7.6, 12.0 Hz, 1H), 4.32 (q, J¼7.2 Hz, 1H),
7.46 (tt, J¼1.6, 7.6 Hz, 2H), 7.56 (tt, J¼1.6, 7.2 Hz, 1H), 8.01 (dd, J¼1.2,
39.8 (t), 57.2 (d), 127.2 (d), 128.7 (d), 131.6 (d), 133.6 (s), 208.5 (s); IR
(Neat): 1699 cmꢀ1; MS (EI) m/z 220 (Mþ), 110 (100%).
8.0 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d: 14.2 (q), 16.4 (q), 22.7(t),
4.3. General procedure for the olefination of a-thio ketone
28.7 (t), 28.9 (t), 29.1 (t), 29.3 (t), 29.4 (t), 29.5 (t), 29.6 (t), 29.6 (tꢂ2),
31.9 (t), 41.5 (d), 128.4 (d), 128.4 (d), 132.8 (d), 135.6 (s), 195.8 (s); IR
(CHCl3): 1676 cmꢀ1; MS (EI) m/z 334 (Mþ), 229 (100%). Anal. Calcd
for C21H34OS: C, 75.39; H, 10.24. Found: C, 75.48; H, 10.17.
To a solution of ethyl 2,2-dibromopropionate (312 mg,1.2 mmol)
in THF (6 mL), cooled to ꢀ78 ꢁC under argon, was added dropwise
a solution of tert-butyllithium (3.58 mL, 4.8 mmol, 1.34 M in pen-
tane). The yellow solution was stirred for 3 h at ꢀ78 ꢁC and allowed
to warm to 0 ꢁC. After 30 min, the resulting pale yellow reaction
mixture was warmed to room temperature, and a solution of thio-
ketone 2 (1.0 mmol) in THF (2 mL) was added. After 0.5 h, methyl
iodide (0.62 mL, 10 mmol) and HMPA (1.7 mL, 10 mmol) were
added. After 18 h, a saturated NH4Cl solution (10 mL) was added and
the resulting mixture was extracted with ethyl acetate. The organic
phase was washed with water, a saturated NaHCO3 solution, brine,
dried over MgSO4, filtered, and concentrated to give a residue,
which was purified by column chromatography followed by pre-
parative HPLC to afford the ester 3.
4.2.2. 2-(Dodecylthio)-1-phenylethanone (2b). Yield 93%. Yellow
solid: 1H NMR (400 MHz, CDCl3)
d
: 0.88 (t, J¼6.8 Hz, 3H), 1.24–1.37
(m, 18H), 1.54–1.62 (m, 2H), 2.56 (dd, J¼7.2, 7.2 Hz, 2H), 3.78 (s, 2H),
7.47 (t, J¼8.0 Hz, 2H), 7.58 (tt, J¼1.6, 7.2 Hz, 1H), 7.98 (dd, J¼2.0,
7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d: 14.2 (q), 22.7 (t), 28.8 (t),
29.0 (t), 29.2 (t), 29.4 (t), 29.5 (t), 29.6 (t), 29.7 (t), 29.7 (t), 31.9 (t),
32.4 (t), 37.1 (t), 128.5 (d), 128.7 (d), 133.2 (d), 135.2 (s), 194.4 (s); IR
(CHCl3): 1674 cmꢀ1; MS (EI) m/z 320 (Mþ), 105 (100%). Anal. Calcd
for C20H32OS: C, 74.94; H, 10.06. Found: C, 74.84; H, 10.00.
4.2.3. 3-(Dodecylthio)heptan-4-one (2c). Yield 95% over 3 steps.
Yellow solid: 1H NMR (400 MHz, CDCl3)
d
: 0.88 (t, J¼6.8 Hz, 3H),
4.3.1. (Z)-Methyl 4-dodecylthio-2-methyl-3-phenyl-2-pentenoate
0.94 (t, J¼7.2 Hz, 3H), 0.97 (J¼7.2 Hz, 3H), 1.25–1.35 (m, 18H), 1.47–
(3a). Colorless oil: 1H NMR (400 MHz, CDCl3)
d: 0.88 (t, J¼7.2 Hz,
1.91 (m, 6H), 2.31–2.45 (m, 2H), 2.58 (dd, J¼6.8, 7.6 Hz, 2H), 3.10
3H), 1.16 (d, J¼6.8 Hz, 3H), 1.20–1.41 (m, 18H), 1.55–1.62 (m, 1H),
1.63 (s, 3H), 2.45–2.59 (m, 2H), 3.80 (s, 3H), 4.62 (q, J¼6.8 Hz, 1H),
7.15 (d, J¼6.4 Hz, 2H), 7.29–7.38 (m, 3H); 13C NMR (100 MHz, CDCl3)
(dd, J¼7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3)
d: 12.1 (q), 13.8 (q),
14.1 (q), 17.6 (t), 22.7 (t), 23.2 (t), 28.9 (t), 29.2 (t), 29.4 (tꢂ2), 29.5
(t), 29.6 (t), 29.6 (t), 29.6 (t), 29.8 (t), 31.9 (t), 40.6 (t), 55.0 (d), 206.8
(s); IR (Neat): 1704 cmꢀ1; MS (EI) m/z 314 (Mþ), 243 (100%); HRMS
(EI) calcd for C19H38OS: 314.2643, found: 314.2667.
d: 14.2 (q), 17.9 (q), 19.8 (q), 22.7 (t), 29.2 (t), 29.4 (t), 29.4 (t), 29.6
(t), 29.7 (tꢂ2), 29.7 (t), 29.7 (t), 31.6(t), 31.9 (t), 41.2 (d), 51.7 (q),
126.7 (s), 127.1 (d), 127.5 (d), 129.2 (d), 137.0 (s), 148.1 (s), 169.9 (s);
IR (Neat): 1716 cmꢀ1; MS (EI) m/z 404 (Mþ), 203 (100%); HRMS (EI)
calcd for C25H40O2S: 404.2749, found: 404.2761.
4.2.4. 1-Phenyl-2-(phenylthio)propan-1-one (2d). Yield 89%. Pale
yellow oil: 1H NMR (400 MHz, CDCl3)
d
: 1.54 (d, J¼6.8 Hz, 3H), 4.63 (q,
J¼6.8 Hz, 1H), 7.26–7.36 (m, 5H), 7.45 (t, J¼8.0 Hz, 2H), 7.56 (tt, J¼1.2,
4.3.2. (Z)-Methyl 4-dodecylthio-2-methyl-3-phenyl-2-butenoate
7.6 Hz, 1H), 7.95 (dd, J¼1.2, 8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d:
(3b). Colorless oil: 1H NMR (400 MHz, CDCl3)
d
: 0.88 (t, J¼7.2 Hz,
17.0 (q), 46.1 (d), 128.4 (dꢂ2), 128.7 (d), 131.6 (s), 132.8 (d), 134.3 (d),
135.5 (s), 195.9 (s); IR (Neat): 1682 cmꢀ1; MS (EI) m/z 242 (Mþ), 137
(100%); HRMS (EI) calcd for C15H14OS: 242.0765, found: 242.0771.
3H), 1.20–1.32 (m, 18H), 1.43–1.50 (m, 2H), 1.76 (s, 3H), 2.39 (dd,
J¼7.2, 7.6 Hz, 2H), 3.78 (s, 2H), 3.81 (s, 3H), 7.19 (dd, J¼1.2, 8.4 Hz,
2H), 7.30 (tt, J¼1.2, 7.6 Hz, 1H), 7.37 (tt, J¼1.2, 6.8 Hz, 2H); 13C NMR
(100 MHz, CDCl3) d: 14.2 (q), 17.7 (q), 22.7 (t), 28.9 (t), 29.3 (t), 29.4
4.2.5. 3,3-Dimethyl-1-(phenylthio)butan-2-one (2e). Yield 84%. Col-
(t), 29.6 (t), 29.6 (t), 29.6 (t), 29.7 (t), 29.7 (t), 31.9 (t), 32.2 (t), 36.2
(t), 51.7 (q), 126.6 (s), 127.4 (d), 128.0 (d), 128.1 (d), 140.6 (s), 146.1
(s), 169.5 (s); IR (Neat): 1717 cmꢀ1; MS (EI) m/z 390 (Mþ), 190
(100%); HRMS (EI) calcd for C24H38O2S: 390.2593, found: 390.2556.
orless oil: 1H NMR (400 MHz, CDCl3)
d: 1.19 (s, 9H), 3.96 (s, 2H), 7.21
(tt, J¼1.6, 7.2 Hz,1H), 7.29 (tt, J¼1.6, 7.2 Hz, 2H), 7.38 (dd, J¼1.6, 8.0 Hz,
2H); 13C NMR (100 MHz, CDCl3)
d
: 26.5 (qꢂ3), 40.5 (t), 44.2 (s), 126.5
(d), 128.7 (d), 129.9 (d), 135.3 (s), 209.1 (s); IR (Neat): 1707 cmꢀ1; MS
(EI) m/z 208 (Mþ), 57 (100%).
4.3.3. (Z)-Methyl 4-dodecylthio-2-methyl-3-propyl-2-hexenoate
(3c). Colorless oil: 1H NMR (400 MHz, CDCl3)
d
: 0.88 (t, J¼6.4 Hz,
4.2.6. 3-(Phenylthio)heptan-4-one (2f). Yield 70% over 3 steps. Pale
3H), 0.93 (t, J¼7.2 Hz, 3H), 1.20–1.35 (m, 18H), 1.40–1.61 (m, 6H),
yellow oil: 1H NMR (400 MHz, CDCl3)
d
: 0.89 (t, J¼7.2 Hz, 3H), 1.02
1.92 (s, 3H), 2.02 (dt, J¼4.4, 12.4 Hz, 1H), 2.20–2.40 (m, 3H), 3.71 (s,
(t, J¼7.2 Hz, 3H), 1.54–1.63 (m, 4H), 1.70 (dd, J¼7.2, 7.2 Hz, 2H), 3.55
3H), 4.16 (dd, J¼6.8, 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3)
d: 12.4
(dd, J¼7.2, 7.2 Hz, 1H), 7.25–7.31 (m, 3H), 7.36 (dd, J¼1.6, 8.0 Hz,
(q), 14.1 (q), 14.9 (q), 16.3 (q), 22.7 (t), 23.0 (t), 26.4 (t), 29.1 (t), 29.3
(t), 29.4 (t), 29.6 (t), 29.6 (t), 29.7 (t), 29.9 (t), 31.4 (t), 31.4 (t), 31.9 (t),
2H); 13C NMR (100 MHz, CDCl3)
d: 11.9 (q), 13.7 (q), 17.2 (t), 23.7 (t),

T. Yoshikawa et al. / Tetrahedron 65 (2009) 8832–8838
8837
49.9 (q), 51.4 (d), 126.3 (s), 147.1 (s), 170.3 (s); IR (Neat): 1717 cmꢀ1
;
MS (EI) m/z 384 (Mþ), 55 (100%); HRMS (EI) calcd for C23H44O2S:
384.3062, found: 384.3077.
a yellow oil: 1H NMR (270 MHz, CDCl3)
d
: 1.65 (d, J¼6.8 Hz, 3H),
4.69 (q, J¼6.8 Hz,1H), 7.23–7.57 (m, 8H), 7.89 (dd, J¼1.6, 7.0 Hz, 2H);
13C NMR (100 MHz, CDCl3)
d: 17.2 (q), 39.7 (d), 126.9 (s), 128.3 (d),
128.4 (d), 128.9 (d), 129.0 (d), 132.8 (d), 135.8 (s), 136.6 (d), 196.3 (s);
IR (Neat): 1672 cmꢀ1; MS (EI) m/z 242 (Mþ), 137 (100%); HRMS (EI)
calcd for C15H14OS: 242.0765, found: 242.0771.
4.3.4. (Z)-Methyl 2-methyl-3-phenyl-4-phenylthio-2-pentenoate (3d).
Colorless oil: 1H NMR (400 MHz, CDCl3)
d
: 1.28 (d, J¼7.2 Hz, 3H),1.56
(s, 3H), 3.65 (s, 3H), 5.23 (q, J¼6.8 Hz,1H), 7.16 (dd, J¼1.6, 8.0 Hz, 2H),
7.22–7.39 (m, 6H), 7.44 (dd, J¼1.6, 8.0 Hz, 2H); 13C NMR (100 MHz,
4.5. (Z)-Methyl 2-methyl-3-phenyl-4-(phenylseleno)pent-2-
enoate (8)
CDCl3)
d: 17.9 (q), 19.9 (q), 45.4 (d), 51.7 (q), 127.0 (d), 127.1 (s), 127.2
(d), 127.8 (d), 128.7 (d), 128.9 (d), 132.4 (d), 135.3 (s), 137.4 (s), 148.5
(s), 169.4 (s); IR (Neat): 1714 cmꢀ1; MS (EI) m/z 312 (Mþ), 203
(100%); HRMS (EI) calcd for C19H20O2S: 312.1184, found: 312.1185.
To a solution of ethyl 2,2-dibromopropionate (468 mg,1.8 mmol)
in THF (9 ml), cooled to ꢀ78 ꢁC under argon, was added dropwise
a solution of tert-butyllithium (4.59 mL, 7.2 mmol, 1.57 M in pen-
tane). The yellow solution was stirred for 10 min at ꢀ78 ꢁC and
4.3.5. (Z)-Methyl 2,4,4-trimethyl-3-phenylthiomethyl-2-pentenoate
(3e). Pale yellow oil: 1H NMR (400 MHz, CDCl3)
d
: 1.32 (s, 9H), 2.05
(s, 3H), 3.61 (s, 3H), 3.80 (s, 2H), 7.18 (tt, J¼1.2, 7.6 Hz, 1H), 7.25–7.36
(m, 4H); 13C NMR (100 MHz, CDCl3)
allowed to warm to 0 ꢁC. After 30 min, a solution of
a-phenyl-
selenylpropiophenone (434 mg,1.5 mmol) in THF (3 mL) was added
at room temperature. After 1 h, the mixture was concentrated in
vacuo, and then diluted with hexane. The resulting solution was
washed with water. The combined water phase was acidified with
1 M HCl solution and extracted with CH2Cl2. The organic phase was
washed with brine, dried over MgSO4, filtered, and concentrated to
give the carboxylic acid. To a solution of the carboxylic acid (150 mg,
0.434 mmol) and MeOH (0.035 ml, 0.868 mmol) in CH2Cl2 was
added EDC$HCl (91.6 mg, 0.478 mmol) and DMAP (2.4 mg,
0.0199 mmol) at room temperature. After 4 h, a saturated NH4Cl
solution was added and the mixture was extracted with CH2Cl2. The
organic phase was washed with brine, dried over MgSO4, filtered,
and concentrated to give a residue, which was purified by column
chromatography followed by HPLC to afford the methyl ester
(117.5 mg, 64% over 2 steps) as a pale yellow oil: 1H NMR (400 MHz,
d: 18.8 (q), 30.3 (qꢂ3), 35.9 (s),
37.0 (t), 51.7 (q), 126.1 (d), 128.7 (d), 129.9 (d), 130.1 (s), 137.2 (s),
144.3 (s), 171.8 (s); IR (Neat): 1716 cmꢀ1; MS (EI) m/z 278 (Mþ), 57
(100%); HRMS (EI) calcd for C16H22O2S: 278.1341, found: 278.1324.
4.3.6. (Z)-Methyl 2-methyl-4-phenylthio-3-propyl-2-hexenoate (3f).
Pale yellow oil: 1H NMR (400 MHz, CDCl3)
d
: 0.97 (t, J¼7.2 Hz, 3H),
1.01 (t, J¼7.2 Hz, 3H), 1.13–1.57 (m, 2H), 1.67–1.81 (m, 2H), 1.79 (s,
3H), 2.07 (dt, J¼4.8, 13.2 Hz, 1H), 3.56 (s, 3H), 4.80 (dd, J¼7.2, 8.0 Hz,
1H), 7.16–7.25 (m, 3H), 7.32 (dd, J¼1.2, 8.0 Hz, 2H); 13C NMR
(100 MHz, CDCl3) d: 12.4 (q), 14.9 (q), 16.2 (q), 22.7 (t), 26.5 (t), 32.1
(t), 51.2 (q), 54.0 (d), 126.3 (s), 126.7 (d), 128.4 (d), 132.2 (d), 135.5
(s), 147.8 (s), 169.6 (s); IR (Neat): 1713 cmꢀ1; MS (EI) m/z 292 (Mþ),
183 (100%); HRMS (EI) calcd for C17H24O2S: 292.1497, found:
292.1488.
CDCl3)
d
: 1.33 (d, J¼7.2 Hz, 3H), 1.56 (s, 3H), 3.61 (s, 3H), 5.40 (q,
J¼7.2 Hz, 1H), 7.22–7.41 (m, 8H), 7.58 (dd, J¼1.6, 7.6 Hz, 2H); 13C
4.3.7. (Z)-Methyl2-(2-phenylthiocyclohexylidene)propionate(5aZ). Pale
NMR (100 MHz, CDCl3) d: 17.9 (q), 20.5 (q), 41.1 (d), 51.6 (q),126.0 (s),
yellow oil: 1H NMR (400 MHz, CDCl3)
d
: 1.28–1.42 (m, 1H), 1.55–
127.3 (d), 127.7 (d), 127.8 (d), 127.9 (d), 128.9 (d), 130.0 (s), 135.5 (d),
138.0 (s), 149.8 (s), 169.4 (s); IR (Neat): 1709 cmꢀ1; MS (EI) m/z 360
(Mþ), 203 (100%); HRMS (EI) calcd for C19H20O2Se: 360.0629, found:
360.0633.
1.63 (m,1H),1.78–1.96 (m, 3H),1.81 (s, 3H), 2.02–2.08 (m,1H), 2.48–
2.52 (m, 2H), 3.51 (s, 3H), 5.04 (t, J¼3.2 Hz, 1H), 7.23–7.29 (m, 3H),
7.39 (dd, J¼1.6, 6.8 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d: 15.6 (q),
21.3 (t), 26.6 (t), 27.4 (t), 32.6 (t), 49.6 (d), 51.4 (q),121.9 (s),127.3 (d),
128.5 (d), 133.4 (d), 135.0 (s), 146.8 (s), 169.4 (s); IR (Neat):
1713 cmꢀ1; MS (EI) m/z 276 (Mþ), 167 (100%); HRMS (EI) calcd for
C16H20O2S: 276.1184, found: 276.1159.
4.6. Representative procedure for desulfurization
To a solution of (Z)-methyl 2-methyl-3-phenyl-4-phenythio-2-
pentenoate (3d, 10 mg, 0.032 mmol) in THF (2.5 ml) was added ac-
tivated zinc (250 mg), a saturated NH4Cl solution (0.5 ml) and NiCl2
(50 mg, anhydrous), and the mixture was vigorously stirred at room
temperature for 11 h. The mixture then was filtered and washed
with a saturated NaHCO3 solution, brine, dried over MgSO4, filtered,
and concentrated to give a residue, which was purified by pre-
parative TLC (silica gel, hexane/AcOEt¼75:25) to afford (Z)-methyl
2-methyl-3-phenyl-3-pentenoate (9, 6.7 mg, quant.) as a pale yel-
low oil.
4.3.8. (Z)-Methyl 2-(2-phenylthiocycloheptylidene)propionate (5bZ).
Pale yellow oil: 1H NMR (400 MHz, CDCl3)
d: 1.14–1.55 (m, 4H),
1.70–1.82 (m, 2H), 1.81 (s, 3H), 1.84–1.92 (m, 1H), 2.24–2.32 (m, 2H),
2.46 (dd, J¼6.0, 13.6 Hz, 1H), 3.44 (s, 3H), 5.09 (dd, J¼7.6, 10.0 Hz,
1H), 7.23–7.27 (m, 3H), 7.35–7.39 (m, 2H); 13C NMR (100 MHz,
CDCl3) d: 15.7 (q), 25.7 (t), 27.6 (t), 28.0 (t), 30.7 (t), 33.0 (t), 49.9 (d),
51.2 (q), 125.3 (s), 127.6 (d), 128.4 (d), 134.1 (s), 134.7 (d), 149.5 (s),
169.4 (s); IR (Neat): 1712 cmꢀ1; MS (EI) m/z 290 (Mþ), 181 (100%);
HRMS (EI) calcd for C17H22O2S: 290.1341, found: 290.1326.
4.6.1. (Z)-Methyl 2-methyl-3-phenyl-3-pentenoate (9). 1H NMR
4.4. 2-(Phenylseleno)-1-phenylpropan-1-one (6)
(400 MHz, CDCl3)
d
: 1.26 (d, J¼7.2 Hz, 3H), 1.53 (d, J¼6.8 Hz, 3H),
3.43 (q, J¼7.2 Hz, 1H), 3.64 (s, 3H), 5.69 (q, J¼6.8 Hz, 1H), 7.11 (dd,
To a solution of diisopropylamine (0.547 mL, 3.9 mmol) in THF
(12 mL), cooled to ꢀ78 ꢁC under argon, was added dropwise a so-
lution of n-butyllithium (2.62 mL, 3.75 mmol, 1.43 M in hexane).
The solution was stirred for 20 min at ꢀ78 ꢁC. A solution of pro-
piophenone (403 mg, 3.0 mmol) in THF (3 mL) was then added.
After 1 h, phenylselenyl chloride (1.15 mg, 6.0 mmol) was added to
the reaction mixture at ꢀ78 ꢁC. After 1.5 h, a saturated NaHCO3
solution was added and the mixture was allowed to warm to room
temperature. The water phase was extracted with ethyl acetate. The
organic phase was washed with brine, dried over MgSO4, filtered,
and concentrated to give a residue, which was purified by column
J¼1.6, 8.8 Hz, 2H), 7.25 (t, J¼7.2 Hz, 1H), 7.33 (t, J¼7.2 Hz, 2H); 13C
NMR (100 MHz, CDCl3) d: 14.9 (q), 16.7 (q), 47.6 (d), 51.8 (q), 123.4
(d), 126.7 (d), 127.9 (d), 128.7 (d), 139.4 (s), 140.4 (s), 174.8 (s); IR
(Neat): 1739 cmꢀ1; MS (EI) m/z 204 (Mþ), 189 (100%, Mþ-Me);
HRMS (EI) calcd for C13H16O2: 204.1150, found: 204.1142.
4.6.2. (E)-Methyl 2-methyl-3-propyl-3-hexenoate (10). Colorless
oil: 1H NMR (400 MHz, CDCl3)
d
: 0.89 (t, J¼7.2 Hz, 3H), 0.95 (t,
J¼7.2 Hz, 3H), 1.24 (d, J¼7.2 Hz, 3H), 1.32–1.42 (m, 2H), 3.07 (q,
J¼6.8 Hz, 1H), 3.66 (s, 3H), 5.29 (t, J¼7.2 Hz, 1H); 13C NMR
(100 MHz, CDCl3) d: 14.3 (q), 14.5 (q), 16.9 (q), 21.3 (t), 22.2 (t), 32.1
chromatography to afford the
a
-selenoketone (782 mg, 90%) as
(t), 45.8 (d), 51.7 (q), 128.9 (d), 137.4 (s), 175.5 (s); IR (Neat):

8838
T. Yoshikawa et al. / Tetrahedron 65 (2009) 8832–8838
1739 cmꢀ1; MS (EI) m/z 184 (Mþ), 55 (100%); HRMS (EI) calcd for
The f/f and F refer to the filled/vacant NBO and Fock matrices,
*
C11H20O2: 184.1463, found: 184.1461.
respectively. The 3f and 3f refer to the NBO energies of the bond-
*
ing/lone pair and those of antibonding/Rydberg, respectively. NBOs
are mutually orthogonal. Boys and the natural localized MO anal-
ysis18 gave essentially the same conclusion.
4.6.3. (E)-Methyl 2-hydroxy-2-methyl-3-phenylpent-3-enoate (11). To
a solution of the
g-seleno ester (10 mg, 0.0278 mmol) in CH2Cl2
(0.3 ml) was added H2O2 (0.1 ml) slowly at 0 ꢁC. The reaction
mixture was stirred for 20 min at room temperature before a satu-
rated Na2SO3 solution was added. The resulting mixture was
extracted with CH2Cl2, dried over MgSO4, filtered, and concentrated
to give the residue, which was purified by preparative TLC to afford
the trisubstituted olefin (5.3 mg, 87%) as a colorless oil: 1H NMR
Acknowledgements
This research was partially supported by a Grant-in-Aid for
Scientific Research on Priority Areas (19020052 and 20038005) and
(B) (19390007). One of the authors (TK) also acknowledges the
support of the JSPS. The generous allotment of computational time
from the Research Center for Computational Science, the National
Institutes of Natural Sciences, Japan, is also gratefully acknow-
ledged.
(270 MHz, CDCl3)
3.69 (s, 3H), 6.00 (q, J¼6.8 Hz, 1H), 7.06 (dd, J¼1.6, 7.6 Hz, 2H), 7.24–
7.36 (m, 3H); 13C NMR (100 MHz, CDCl3)
: 14.7 (s), 23.9 (q), 52.7
d
: 1.45 (d, J¼6.8 Hz, 3H), 1.57 (s, 3H), 3.25 (s, 1H),
d
(q), 123.9 (d), 127.2 (d), 128.0 (d), 129.6 (d), 137.4 (s), 143.1 (s), 176.2
(s); IR (Neat): 3539 cmꢀ1, 1732 cmꢀ1; MS (EI) m/z 220 (Mþ), 161
(100%); HRMS (EI) calcd for C13H16O3: 220.1099, found: 220.1097.
Supplementary data
4.7. Computational details
NOE experiments and Cartesian coordinates of transition states
can be found in the online version, at doi:10.1016/j.tet.2009.08.060.
All calculations in the present study were performed with the
Gaussian 03 program (Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.;
Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.;
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.;
Bakken, V.; 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.; and Pople, J. A. Gaussian 03, revision E.01; Gaussian
Inc.: Wallingford, CT, 2004.). We employed the B3LYP hybrid
functional with the 6-31G(d) basis sets for the transition states of
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the ring-opening process of a b-lactone enolate intermediate, the
lithium 4-methylthiomethyl-3,4-dimethyloxet-2-enoxide, in which
two Me2O molecules are solvated to the lithium atom. The normal
coordination analyses were performed for stationary points. One
imaginary frequency was confirmed at each optimized TS structure.
The origin of the stereoelectronic effects of the ring-opening of the
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17. NBO Version 5.G implemented by Glendening, E. D.; Reed, A. E.; Carpenter, J. E.;
Weinhold, F.
b-lactone enolate derivative was examined with the aid of NBO
analysis. The transition states of the ring-opening are reactant-like
rather than product-like by optimal Lewis structure search. Second-
order perturbation analysis of bonding NBOs and antibonding NBOs
was carried out for these transition states. The second-order in-
teraction energy is expressed as follows.
Fi2j
C
f
jFj
f
ꢃD2
3f
ð2Þ
E
¼ ꢀ2
¼ ꢀ2
(1)
ffꢃ
ꢃ
3f
ꢀ
D3
18. Reed, A. E.; Weinhold, F. J. Chem. Phys. 1985, 83, 1736–1740.