Periselectivity in the cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaines: Effect of substituent on the C-6 carbon

Article abstract of DOI:10.1055/s-2008-1067093

Periselectvity in cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaines is examined. The results of our studies show that depending on the substituent on the C-6 carbon, the reaction may proceed either through the [6+3] or the [3+2] pathw

Full text of DOI:10.1055/s-2008-1067093

PAPER
1955
Periselectivity in the Cycloaddition Reactions of Pentafulvenes with
3-Oxidopyrylium Betaines: Effect of Substituent on the C-6 Carbon
Cycloaddition of
P
.
entafulvenes
S
with 3-Oxido
y
pyrylium
B
e
a
taines m Krishnan, Rani Rajan, K. V. Radhakrishnan*
Organic Chemistry Section, Chemical Sciences & Technology Division, National Institute for Interdisciplinary Science and Technology
(CSIR), Trivandrum 695019, Kerala, India
Fax +91(471)491712; E-mail: radhupreethi@rediffmail.com
Received 28 November 2007; revised 10 March 2008
Investigations from our own laboratory have unraveled
Abstract: Periselectvity in cycloaddition reactions of pentaful-
the interesting reactivity profile of fulvenes in cycloaddi-
venes with 3-oxidopyrylium betaines is examined. The results of
our studies show that depending on the substituent on the C-6 car-
bon, the reaction may proceed either through the [6+3] or the [3+2]
tion reactions.5 Our recent investigations have shown that
pentafulvenes undergo facile [6+3] cycloaddition with 3-
pathway. The results of our investigations with various pentaful- oxidopyrylium betaines,6 leading to the formation of 5/8
fused cyclooctanoids (Scheme 1).7 The product is formed
venes are discussed.
by a [6+3] cycloaddition followed by a 1,5-H shift. In or-
der to study the generality of the [6+3] cycloaddition, we
utilized pentafulvenes with various alkyl, aryl, as well as
cycloalkyl substituents at the exocyclic position. The nor-
mal [6+3] cycloaddition followed by 1,5-H shift was ob-
served in all the examples studied.
Key words: pentafulvenes, oxidopyrylium betaines, cycloaddition,
periselectivity
The rich and fascinating chemistry presented through cy-
cloaddition reactions,1 where products are simple sum of
reactants is a corner stone in synthesis. The advent of ful-
venes as convincing frames expanded its credibility and
scope in cycloaddition reactions. Fulvenes belong to the
category of nonfunctionalized C=C bonds. They represent
an interesting class of organic compounds with a unique
p-electron system and are superior models of cyclic cross-
conjugated systems.2 Based on their dipole moments as
well as on their reactivity patterns, they would occupy an
intermediate position between the open chain olefinic and
aromatic targets in a number of synthetic studies.
The outcome of a cycloaddition reaction was generally
dictated by the specific nonbonded interactions in the
transition state. Introduction of a sterically encumbered
group as a controlling factor has lot more pronounced ef-
fect in this scenario, as its presence modifies the nonbond-
ing interactions and subsequently will influence the
preference for alternate cycloaddition pathways. Encour-
aged by this, we decided to take the benefit out from the
cycloaddition chemistry of 6,6-adamantylidenefulvene
(6) with 3-oxidopyrylium betaines. The selection of ful-
vene 6 was based on the excellent steric and rigid features
and also in view of its limited attention in cycloaddition
chemistry.
Pentafulvenes stand out among the various types of ful-
venes and are the most widely studied.3 They have been
identified as a well-known construction unit for many
fused ring systems through intra and intermolecular cy-
cloaddition reactions. They perform flexibly as a 2p-, 4p-
or 6p-moiety in cycloadditions depending on the compet-
ing partner.4 The periselectivity of these reactions is con-
trolled by the substituents on the fulvene and the other
substrate.
We then performed the reaction of adamantylideneful-
vene (6) with 3-oxdiopyrylium betaine under the same re-
ported conditions. The reaction afforded the [6+3] adduct
7a along with a novel [3+2] adduct 8a. Interestingly, com-
pared to fulvenes studied earlier,7 1,5-H shift was not ob-
served in the [6+3] adduct 7a. The reaction is shown in
Scheme 2.
3
O–
O
1,5-H shift
Et3N
O
O
CHCl3
AcO
O
O
5
O
O
1a
4
2
Scheme 1
SYNTHESIS 2008, No. 12, pp 1955–1959
x
x.
x
x
.
2
0
0
8
Advanced online publication: 16.05.2008
DOI: 10.1055/s-2008-1067093; Art ID: Z27607SS
© Georg Thieme Verlag Stuttgart · New York

1956
K. S. Krishnan
PAPER
9
O
11
4
1
Et3N
10
8
7
8
+
O
2
9
O
+
1
50 °C, CHCl3
7
6
AcO
O
3
6
O
5
2
3
2:1
O
4
5
6
1a
7a
8a
Scheme 2
The structures of the products were assigned by detailed
12
spectral analysis. IR spectrum of 7a showed the character-
4.8%
H
1
istic carbonyl absorption at 1694 cm–1. In the H NMR
11
10
H
NOE 5.3%
O
H
spectrum, the bridgehead proton H-5 appeared as a dou-
blet at d = 4.75 with a coupling constant of J = 8.3 Hz and
the solo ring junction hydrogen H-4 resonated as a doublet
with the same coupling constant. This finding was a
strong evidence for the proposed structure 7a. In the 13C
NMR spectrum, the carbonyl carbon resonated at d =
191.8 and the bridgehead carbons at C-5 and C-9 appeared
at d = 81.6 and 72.1, respectively. The spectral assignment
was well supported by proton–proton COSY analysis.
1
8
9
4
X
7
O
2
6
H 3
5
Figure 1 NOE enhancements in 8a
tion of the 1,5-H shift in the [6+3] cycloadduct is a notable
feature in these reactions.
Our next attempt was to study the reactivity profile of 6,6-
dithiodimethylenefulvene (10) with oxidopyrylium be-
taine. The fulvene 10 underwent smooth reaction with the
betaine at room temperature affording a mixture of [6+3]
and [3+2] adducts 11a and 11b, respectively, in 76% yield
(Scheme 4).
When the adduct 7a was heated in toluene under reflux
conditions, 1,5-H shift leading to the isomer 9a was ob-
served, but in low yields (Scheme 3). The product was
characterized by spectral analysis.
S
S
toluene
S
S
O
O
O
S
S
reflux, 24 h
Et3N
+
+
O
20% conversion
CHCl3, 76%
AcO
O
O
O
O
7a
9a
O
2.2:1
Scheme 3
O
10
1a
11a
11b
Scheme 4
In the [3+2] adduct 8a, the carbonyl absorption was de-
tected at 1704 cm–1. 1H NMR located the protons of the
7/5 ring junction as a triplet at d = 3.82 for H-9 and a com-
plex multiplet in the region d = 3.99–3.92 for H-3. In the
13C NMR spectrum, the carbonyl group was found to res-
onate at d = 194.2. The relative stereochemistry at the 7/5
ring junction was obtained from NOE studies. A trans ste-
reochemistry was assigned for the ring junction protons
H-3 and H-9, on the basis of the lack of enhancement in
the H-3 signal when the molecule was irradiated at the res-
onance frequency of H-9 (Figure 1). The observed magni-
fication in the signal intensities of H-8 and
adamantylidene proton H-12 provided positive evidence
for the structure of 8a.
The products were characterized by detailed spectral anal-
ysis (1H, 13C NMR and IR spectra). In both isomers H
1
NMR located methylene protons attached to the sulfur at-
oms as a multiplet in the region d = 3.60–3.20. The struc-
tures were further confirmed by mass spectra, which
showed molecular ion peaks with in the approved limits.
The formation of [3+2] adduct was reasoned to be due to
the decrease in the electron density of fulvene 10 caused
by the hyperconjugation of empty d orbital of sulfur and
olefin p-electrons.8
In conclusion, we have shown that the steric and electron-
ic features of substituents at the exocyclic position of ful-
venes strongly affect their cycloaddition reaction with 3-
oxidopyrylium betaines. The cycloaddition of alkyl, aryl
and cycloalkyl substituted fulvenes with 3-oxidopyrylium
betaines led to the regioselective formation of [6+3] ad-
duct followed by 1,5-H shift, while 6,6-adamantylidene-
fulvene (6) with a bulky substituent at the exocyclic
position afforded the product without 1, 5-H shift, along
Similar reactivity was observed with 6 and various 2-sub-
stituted 3-oxidopyrylium betaines affording a mixture of
[6+3] and [3+2] adducts and the results are summarized in
Table 1. The [6+3] adducts were found to be the major
products in all the examples studied. The results obtained
shows that the above cycloaddition reaction is sensitive to
the steric bulk of the adamantyl substituent. Steric inhibi-
Synthesis 2008, No. 12, 1955–1959 © Thieme Stuttgart · New York

PAPER
Cycloaddition of Pentafulvenes with 3-Oxidopyrylium Betaines
1957
Table 1 Cycloaddition of 6,6-Adamantylidenefulvene (6)a
Entry
Fulvene
Pyranulose acetate
Product
Yield (%)
O
1
74
73
O
O
AcO
O
1a
O
7a
8a
6
O
2:1
O
2
3
O
O
AcO
O
1b
O
7b
8b
O
3:1
O
n-Bu
65
64
O
O
AcO
O
O
O
n-Bu
O
1c
7c
8c
n-Bu
O
3.5:1
O
n-Oct
4
O
O
AcO
n-Oct
O
1d
7d
8d
O
n-Oct
4:1
O
Ph
3
5
O
52
AcO
O
3
Ph
O
8e
7e
1e
O
3
Ph
4:1
a Reactions conditions: 6 (1.0 equiv), pyranulose acetate 1 (1.2 equiv), Et3N (1.2 equiv), CHCl3, 50 °C, 6 h.
ter. Chemical shifts are reported in d (ppm) relative to TMS (1H) or
CDCl3 (13C) as internal standards. IR spectra were recorded on
Bomem MB series FT-IR spectrometer; absorptions are reported in
cm–1. Elemental analyses were performed on a Perkin Elmer 2400
Elemental analyzer.
with a novel [3+2] adduct. Another exciting reactivity was
shown by 6,6-dithiodimethylenefulvene (10) having less
electron density at the exocyclic position when compared
to a typical fulvene, as it produced a mixture of [6+3] ad-
duct followed by 1,5-H shift and the [3+2] adduct.
Compounds 7a and 8a; Typical Procedure
6,6-Adamantylidenefulvene (6; 100 mg, 0.50 mmol), pyranulose
acetate 1a (94 mg, 0.60 mmol) and anhyd Et3N (0.08 mL, 0.60
mmol) were taken in anhyd CHCl3 and stirred at 50 °C in a Schlenk
tube for 6 h under N2. The solvent was removed under reduced pres-
sure and the residue on chromatography on a silica gel (60–120
mesh) column using 10% EtOAc–hexane mixture as eluent
afforded the products 7a and 8a in 2:1 ratio as pale yellow viscous
liquids (74%, combined yield).
All reactions were conducted in oven-dried glassware. Solvents
used for the experiments were distilled and dried as specified. Pyr-
anulose acetates and fulvenes were prepared as per the literature
procedures. All other reagents were purchased from local supplier.
All reactions were monitored by TLC (Silica gel 60 F254, 0.25 mm,
Merck); visualization was effected with UV and/or by developing
in an I2 chamber or with basic KMnO4. Chromatography refers to
open column chromatography on silica gel (100–200 mesh). Melt-
ing points were recorded on a Büchi melting point apparatus and are
uncorrected. NMR spectra were recorded at 300 (1H) and 75 (13C)
MHz, respectively, on a Bruker Avance DPX-300 MHz spectrome-
7a
Yield: 49%; pale yellow viscous liquid; Rf = 0.52 (70:30 hexane–
EtOAc).
Synthesis 2008, No. 12, 1955–1959 © Thieme Stuttgart · New York

1958
K. S. Krishnan
PAPER
IR (KBr): 2917, 2857, 1694, 1455, 1380, 1263, 1152, 1073, 1020,
830 cm–1.
1H NMR: d = 6.86 (dd, J = 4.4, 10.4 Hz, 1 H), 6.46 (dd, J = 1.2, 3.7
Hz, 1 H), 6.26–6.22 (m, 2 H), 5.88 (d, J = 10.4 Hz, 1 H), 5.24 (d,
J = 4.3 Hz, 1 H), 4.75 (d, J = 8.3 Hz, 1 H), 3.48 (d, J = 8.3 Hz, 1
H), 2.54–2.50 (m, 1 H), 2.39–2.33 (m, 2 H), 2.13–1.61 (m, 11 H).
1H NMR: d = 6.83 (dd, J = 4.4, 10.3 Hz, 1 H), 6.46–6.44 (m, 1 H),
6.20–6.17 (m, 2 H), 5.84 (d, J = 10.3 Hz, 1 H), 5.27 (d, J = 4.4 Hz,
1 H), 3.12 (s, 1 H), 2.54–2.50 (m, 1 H), 2.20–2.16 (m, 2 H), 2.09–
1.54 (m, 11 H), 1.37–1.22 (m 6 H), 0.91 (t, J = 7.0 Hz, 3 H).
13C NMR: d = 193.2, 147.5, 147.2, 133.4, 131.1, 129.4, 128.6, 88.2,
72.7, 55.2, 51.6, 39.1, 36.9, 34.7, 33.7, 33.5, 32.9, 32.0, 28.2, 27.9,
27.6, 25.4, 23.2, 14.1.
13C NMR: d = 191.8, 147.8, 147.1, 133.5, 130.6, 129.8, 128.3, 81.6,
72.1, 52.3, 50.2, 38.9, 34.7, 34.6, 33.5, 32.8, 32.7, 32.0, 27.9, 27.6.
HRMS (EI): m/z calcd for C24H30O2 (M+): 350.2246; found:
350.2252.
HRMS (EI): m/z calcd for C20H22O2 (M+): 294.1620; found:
294.1624.
8c
Yield: 15%; pale yellow viscous liquid.
IR (KBr): 2916, 2856, 1699, 1463, 1411, 1268, 1090, 855 cm–1.
8a
Yield: 25%; pale yellow viscous liquid; Rf = 0.50 (70:30 hexane–
EtOAc).
1H NMR: d = 6.86 (dd, J = 4.7, 9.8 Hz, 1 H), 6.31 (dd, J = 1.25, 5.8
Hz, 1 H), 5.94 (d, J = 9.8 Hz, 1 H), 5.48 (dd, J = 2.4, 5.8 Hz, 1 H),
4.92 (dd, J = 4.7, 7.5 Hz, 1 H), 4.09–4.04 (m, 1 H), 3.52 (d, J = 8.3
Hz, 1 H), 2.75 (s, 1 H), 2.61–2.54 (m, 2 H), 2.07–1.60 (m, 11 H),
1.34–1.29 (m, 6 H), 0.90–0.88 (m, 3 H).
13C NMR: d = 195.6, 154.2, 151.9, 133.5, 131.6, 130.7, 128.3, 93.6,
74.7, 56.5, 49.4, 39.7, 37.6, 37.4, 36.7, 35.8, 35.3, 34.2, 29.9, 28.4,
27.0, 26.3, 23.4, 14.4.
IR (KBr): 2912, 2846, 1704, 1451, 1401, 1260, 1097, 845 cm–1.
1H NMR: d = 6.85 (dd, J = 4.6, 9.9 Hz, 1 H), 6.32 (dd, J = 1.2, 5.7
Hz, 1 H), 5.93 (dd, J = 1.0, 9.9 Hz, 1 H), 5.55 (dd, J = 2.4, 5.7 Hz,
1 H), 4.90 (dd, J = 4.6, 7.2 Hz, 1 H), 4.60 (d, J = 8.5 Hz, 1 H), 3.99–
3.92 (m, 1 H), 3.82 (t, J = 8.5 Hz, 1 H), 2.75 (s, 1 H), 2.52 (s, 1 H),
1.42–2.10 (m, 12 H).
13C NMR: d = 194.2, 151.6, 148.0, 144.7, 133.9, 130.3, 127.9, 84.9,
75.7, 55.3, 46.9, 40.1, 39.8, 38.7, 37.5, 37.4, 36.9, 35.1, 28.7, 28.2.
HRMS (EI): m/z calcd for C24H30O2 (M+): 350.2246; found:
350.2267.
HRMS (EI): m/z calcd for C20H22O2 (M+): 294.1620; found:
294.1623.
7d and 8d
7b and 8b
Total yield: 54%; ratio 7d/8d = 4:1.
Total yield: 73%; ratio 7b/8b = 3:1.
7d
Yield: 43%; pale yellow viscous liquid.
7b
Yield: 55%; pale yellow viscous liquid.
IR (KBr): 2917, 1692, 1457, 1372, 1259, 1094, 1021 cm–1.
IR (KBr): 2923, 2851, 1693, 1462, 1374, 1259, 1158, 1037, 793
cm–1.
1H NMR: d = 6.83 (dd, J = 4.4, 10.2 Hz, 1 H), 6.47–6.45 (m, 1 H),
6.20–6.16 (m, 2 H), 5.84 (d, J = 10.3 Hz, 1 H), 5.27 (d, J = 4.4 Hz,
1 H), 3.11 (s, 1 H), 2.54–2.33 (m, 3 H), 2.11–1.79 (m, 11 H), 1.33–
1.26 (m, 14 H), 0.88–0.85 (m, 3 H).
13C NMR: d = 193.3, 150.3, 147.5, 133.5, 131.1, 129.4, 128.6, 88.2,
72.7, 55.2, 51.6, 38.9, 37.3, 34.7, 33.5, 32.9, 32.0, 31.6, 30.1, 29.6,
29.5, 29.4, 28.2, 28.0, 27.6, 23.2, 22.7, 14.2.
1H NMR: d = 6.83 (dd, J = 4.3, 10.3 Hz, 1 H), 6.46–6.43 (m, 1 H),
6.21–6.16 (m, 2 H), 5.83 (d, J = 10.3 Hz, 1 H), 5.24 (d, J = 4.3 Hz,
1 H), 3.09 (s, 1 H), 2.54–2.37 (m, 4 H), 2.10–1.77 (m, 10 H), 1.58
(s, 3 H).
13C NMR: d = 193.6, 147.7, 133.5, 130.9, 129.4, 127.9, 124.0, 85.3,
72.9, 56.7, 46.9, 39.3, 38.9, 34.7, 34.6, 33.5, 32.8, 32.0, 27.9, 27.6,
23.8.
HRMS (EI): m/z calcd for C28H38O2 (M+): 406.2872; found:
406.2878.
HRMS (EI): m/z calcd for C21H24O2 (M+): 308.1776; found:
308.1773.
8d
8b
Yield: 11%; pale yellow viscous liquid.
IR (KBr): 2923, 1695, 1456, 1399, 1127, 754 cm–1.
Yield: 18%; pale yellow viscous liquid.
IR (KBr): 2923, 2846, 1693, 1454, 1377, 1259, 1097, 1037 cm–1.
1H NMR: d = 6.85 (dd, J = 4.7, 9.8 Hz, 1 H), 6.31 (dd, J = 1.3, 5.8
Hz, 1 H), 5.94 (d, J = 9.8 Hz, 1 H), 5.48 (dd, J = 2.4, 5.8 Hz, 1 H),
4.92 (dd, J = 4.7, 7.6 Hz, 1 H), 4.11–4.04 (m, 1 H), 3.52 (d, J = 8.2
Hz, 1 H), 2.74–2.70 (m, 2 H), 2.07–1.93 (m, 12 H), 1.31–1.25 (m,
14 H), 0.90–0.88 (m, 3 H).
13C NMR: d = 195.4, 152.6, 151.3, 135.7, 132.3, 131.9, 124.9, 89.5,
77.2, 54.9, 46.9, 39.3, 37.8, 36.7, 35.8, 35.4, 34.2, 31.9, 27.3, 26.9,
29.7, 29.4, 29.3, 29.2, 29.1, 27.5, 22.7, 14.1.
1H NMR: d = 6.76 (dd, J = 4.6, 9.8 Hz, 1 H), 6.25 (dd, J = 1.2, 5.8
Hz, 1 H), 5.85 (d, J = 9.8 Hz, 1 H), 5.43 (dd, J = 2.5, 5.8 Hz, 1 H),
4.81 (dd, J = 4.6, 7.5 Hz, 1 H), 4.05–4.00 (m, 1 H), 3.40 (d, J = 8.3
Hz, 1 H), 2.81–2.77 (m, 2 H), 2.28–1.95 (m, 12 H), 1.54 (s, 3 H).
13C NMR: d = 194.8, 150.6, 148.9, 145.2, 135.1, 131.3, 128.7, 87.9,
78.3, 57.1, 51.4, 44.9, 41.2, 40.6, 39.6, 37.7, 37.1, 36.8, 35.6, 29.9,
22.8.
HRMS (EI): m/z calcd for C21H24O2 (M+): 308.1776; found:
308.1779.
HRMS (EI): m/z calcd for C28H38O2 (M+): 406.2872; found:
406.2863.
7c and 8c
7e and 8e
Total yield: 65%; ratio 7c/8c = 3.5:1.
Total yield: 52%; ratio 7e/8e = 4:1.
7c
7e
Yield: 50%; pale yellow viscous liquid.
Yield: 42%; pale yellow viscous liquid.
IR (KBr): 2919, 2857, 1689, 1455, 1380, 1262, 1073, 746 cm–1.
IR (KBr): 2919, 2868, 1694, 1455, 1380, 1352, 1262, 1190, 1074,
758 cm–1.
Synthesis 2008, No. 12, 1955–1959 © Thieme Stuttgart · New York

PAPER
Cycloaddition of Pentafulvenes with 3-Oxidopyrylium Betaines
1959
1H NMR: d = 7.26–7.15 (m, 5 H), 6.82 (dd, J = 4.4, 10.2 Hz, 1 H),
6.46–6.44 (m, 1 H), 6.19–6.15 (m, 2 H), 5.83 (d, J = 10.2 Hz, 1 H),
5.26 (d, J = 4.3 Hz, 1 H), 3.11 (s, 1 H), 2.76–2.39 (m, 9 H), 2.05–
1.68 (m, 11 H).
HRMS (EI): m/z calcd for C13H12O2S2 (M+): 264.0279; found:
264.0271.
Isomerization of 7a to 9a
Compound 7a was heated in toluene under reflux for 36 h. After
column chromatography, product 9a was obtained in 20% yield.
1H NMR: d = 6.80 (dd, J = 4.4, 10.3 Hz, 1 H), 6.30–6.25 (m, 2 H),
5.87 (d, J = 10.3 Hz, 1 H), 5.17 (d, J = 4.4 Hz, 1 H), 4.63 (s, 1 H),
3.12–2.92 (m, 2 H), 2.40–1.64 (m, 14 H).
13C NMR: d = 193.1, 147.5, 147.1, 142.3, 133.5, 131.1, 129.5,
128.6, 128.5, 128.3, 125.8, 88.1, 72.7, 55.2, 51.6, 39.3, 38.9, 36.9,
36.4, 34.7, 33.5, 32.9, 32.0, 30.3, 28.0, 27.7, 25.3.
HRMS (EI): m/z calcd for C29H32O2 (M+): 412.2402; found:
412.2406.
8e
Acknowledgment
Yield: 10%; pale yellow viscous liquid.
The authors thank the Council of Scientific and Industrial Research
(CSIR), New Delhi for financial assistance (Task Force Project-
CMM-005 on Specialty Chemicals). K.S.K. thanks CSIR, New
Delhi for a Senior Research Fellowship. We thank Dr. R. Luxmi
Varma, Scientist, Chemical Sciences Division, Ms. S. Viji, and Ms.
Saumini Mathew for the NMR and high-resolution mass spectra.
IR (KBr): 2921, 2850, 1689, 1492, 1453, 1380, 1259, 1045 cm–1.
1H NMR: d = 7.30–7.13 (m, 5 H), 6.82 (dd, J = 4.7, 9.8 Hz, 1 H),
6.29 (dd, J = 1.2, 5.8 Hz, 1 H), 5.92 (d, J = 9.8 Hz, 1 H), 5.45 (dd,
J = 2.5, 5.8 Hz, 1 H), 4.89 (dd, J = 4.7, 7.5 Hz, 1 H), 4.07–4.01 (m,
1 H), 3.48 (d, J = 8.3 Hz, 1 H), 2.85–2.80 (m, 1 H), 2.72–2.68 (m,
1 H), 2.16–1.94 (m, 18 H).
13C NMR: d = 196.4, 151.6, 149.3, 142.3, 134.7, 133.9, 132.0,
130.1, 129.5, 128.6, 126.7, 89.0, 77.8, 55.5, 47.4, 39.9, 36.8, 36.1,
35.9, 35.0, 34.2, 33.4, 31.9, 29.7, 28.2, 27.5, 26.9.
References
(1) Comprehensive Organic Synthesis, Vol. 5; Trost, B. M.;
Fleming, I., Eds.; Pergamon: Oxford, 1991.
HRMS (EI): m/z calcd for C29H32O2 (M+): 412.2402; found:
(2) Krygowski, T. M.; Ciesielski, A. M. Chem. Pap. 1995, 49,
412.2438.
128.
11a and 11b
(3) Yates, P. Advances in Alicyclic Chemistry, Vol. 2;
Academic Press: New York, 1968.
Total yield: 76%; ratio 11a/11b = 4:1.
(4) (a) Hong, B.-C.; Chen, F.-L.; Chen, S.-H.; Liao, J.-H.; Lee,
G.-H. Org. Lett. 2005, 7, 557; and references cited therein.
(b) Zhang, X.; Khan, S. I.; Foote, C. S. J. Org. Chem. 1995,
60, 4102.
11a
Yield: 53%; pale yellow viscous liquid.
IR (KBr): 2929, 2855, 1693, 1450, 1389, 1292, 1053, 1003 cm–1.
(5) (a) Anas, S.; Sajisha, V. S.; Mohanlal, S.; Radhakrishnan, K.
V. Synlett 2006, 2399. (b) Nair, V.; Nair, A. G.;
Rahdakrishnan, K. V.; Nandakumar, M. V.; Rath, N. P.
Synlett 1997, 767. (c) Nair, V.; Anilkumar, G.;
Radhakrishnan, K. V.; Nandakumar, M. V.; Kumar, S.
Tetrahedron 1997, 53, 15903. (d) Nair, V.; Jayan, C. N.;
Radhakrishnan, K. V.; Anilkumar, G.; Rath, N. P.
Tetrahedron 2001, 57, 5807.
1H NMR: d = 7.14 (dd, J = 4.2, 10.4 Hz, 1 H), 6.58 (d, J = 5.2 Hz,
1 H), 6.43 (d, J = 5.2 Hz, 1 H), 5.95 (d, J = 10.4 Hz, 1 H), 4.80 (s, 1
H), 3.56–3.49 (m, 3 H), 3.39–3.27 (m, 2 H), 3.18–2.93 (m, 2 H).
13C NMR: d = 193.4, 145.9, 133.9, 133.4, 129.0, 131.1, 123.9, 77.3,
76.8, 63.7, 42.0, 40.9, 39.6.
HRMS (EI): m/z calcd for C13H12O2S2 (M+): 264.0279; found:
264.0254.
(6) (a) Hendrickson, J. B.; Farina, J. S. J. Org. Chem. 1980, 45,
3359. (b) Sammes, P. G.; Street, L. J. J. Chem. Soc., Perkin
Trans. 1 1983, 2729.
11b
Yield: 23%; pale yellow viscous liquid.
(7) (a) Radhakrishnan, K. V.; Krishnan, S. K.; Bhadbhade, M.
M.; Bhosekar, G. V. Tetrahedron Lett. 2005, 46, 4785.
(b) Krishnan, S. K.; Sajisha, S.; Anas, S.; Suresh, C. H.;
Bhadbhade, M. M.; Bhosekar, G. V.; Radhakrishnan, K. V.
Tetrahedron 2006, 62, 5952. (c) Krishnan, K. S.; Suresh, E.;
Mathew, S.; Radhakrishnan, K. V. Synthesis 2006, 1811.
(d) Krishnan, K. S.; Smitha, M.; Suresh, E.; Radhakrishnan,
K. V. Tetrahedron 2006, 62, 12345.
IR (KBr): 2934, 2851, 1699, 1456, 1379, 1285, 1053, 1009 cm–1.
1H NMR: d = 6.90 (dd, J = 4.6, 9.9 Hz, 1 H), 6.13 (d, J = 5.1 Hz, 1
H), 5.98 (d, J = 9.9 Hz, 1 H), 5.65–5.63 (m, 1 H), 4.93–4.89 (m, 1
H), 4.79 (d, J = 8.2 Hz, 1 H), 3.96–3.85 (m, 2 H), 3.47–3.36 (m, 4
H).
13C NMR: d = 192.3, 151.0, 142.4, 135.9, 132.4, 130.4, 128.3, 83.9,
76.0, 56.6, 50.9, 38.8, 38.5.
(8) Hong, B.-C.; Sun, S.-S.; Tsai, Y.-C. J. Org. Chem. 1997, 62,
7717.
Synthesis 2008, No. 12, 1955–1959 © Thieme Stuttgart · New York