Cyclizations producing hydrindanones with two methyl groups at the juncture positions mediated by samarium diiodide and electrolysis

Article abstract of DOI:10.3390/molecules170911079

One-electron reductive intramolecular cyclization of enones with ketones or aldehydes mediated by samarium diiodide and electrolysis to afford cis-trimethylhydrindanolones. The reactions gave selectivities ranging from 1:1 to 100:0 depending on the condit

Full text of DOI:10.3390/molecules170911079

Molecules 2012, 17, 11079-11088; doi:10.3390/molecules170911079
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Cyclizations Producing Hydrindanones with Two Methyl
Groups at the Juncture Positions Mediated by Samarium
Diiodide and Electrolysis
Masakazu Sono *, Natsuko Ise, Tsutomu Shoji and Motoo Tori *
Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho,
Tokushima 770-8514, Japan
* Authors to whom correspondence should be addressed; E-Mails: sono@ph.bunri-u.ac.jp (M.S.);
tori@ph.bunri-u.ac.jp (M.T.); Tel.: +81-88-602-8462 (M.T.); Fax: +81-88-654-3051 (M.T.).
Received: 29 June 2012; in revised form: 8 August 2012 / Accepted: 3 September 2012 /
Published: 13 September 2012
Abstract: One-electron reductive intramolecular cyclization of enones with ketones or
aldehydes mediated by samarium diiodide and electrolysis to afford cis-trimethyl-
hydrindanolones. The reactions gave selectivities ranging from 1:1 to 100:0 depending on
the conditions.
Keywords: samarium diiodide; electrolysis; cyclization; hydrindanone
1. Introduction
Samarium diiodide has been used for many synthetic reactions [1–4] and the mechanism of its
reactions has also been studied [5,6]. We are interested in preparing bicyclic compounds such as
perhydroindenes [7,8], perhydronaphthalenes [9], and guaianes [10] and have published some results
in this area. Compounds bearing methyl groups at the juncture positions are interesting from
the synthetic point of view. For example deoxopinguisone (1) [11,12] and -pinguisene (2) [13,14]
(Figure 1) have four methyl groups in the bicyclo[4.3.0]nonane framework, all in a -orientation; two
of them are at the ring juncture positions, and have been synthetic targets [15,16]. We now planned to
construct hydrindanone systems by 5-exo mode cyclization, although such a case involving a cascade
cyclization giving one substituent at the ring-juncture position was described by Procter and his
group [17,18]. Electrolysis is easy to carry out using water as a solvent, which is environmentally

Molecules 2012, 17
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benign [19,20]. We now describe the carbon-carbon bond formation reactions leading from B to A
mediated by SmI2 as well as electrolysis for the synthesis of hydrindanones (Figure 1).
Figure 1. Target molecules and retrosynthesis.
2. Results and Discussion
For the synthetic work we chose compounds 9 and 10 (Scheme 1), which were prepared starting
from ketone 3. Several routine reactions afforded aldehyde 9 and ketone 10. This route can also be
used in chiral form, because compound 3 is now commercially available and easy to prepare [21].
Scheme 1. Preparation of compounds 9 and 10.
Aldehyde 9 was subjected to reaction with SmI2 (3 equiv.) in THF with or without additives.
The results are shown in Table 1. The products were isomeric keto-alcohols 11 and 12, whose
stereochemistries were established from the NOESY spectra. Without an additive, the reactions
proceeded smoothly and both compounds were obtained in a ratio of 87:13 in favor of compound 11 at
0 °C (entry 1). When the reaction temperature was raised to rt (entry 2), the ratio of compound 12
increased to 31%. The yields were always good. When MeOH was added as a proton source, the ratio
was about 7:3 in favor of compound 11 (entries 3 and 4). The yield varied from 47% to 58%. The
reason why the yields were not so high is presumably due to the simple reduction of the double bond
to give the corresponding dihydro derivatives, which were not isolated but detected in GC-MS. The
ratio of 11 and 12 did not change very much when using HMPA (entries 7 and 8), however, when NiI2
was added (entries 9 and 10) the ratio of 12 was slightly increased [22].

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Table 1. The reaction of aldehyde 9 with SmI2.
Ratio
Entry
Additives
Temp (°C) Yield (%)
11
87
69
72
69
82
84
75
56
12
13
31
28
31
18
16
25
44
1
2
3
4
5
6
7
8
none
none
0
rt
0
quant.
quant.
58
MeOH 2 equiv.
MeOH 2 equiv.
HMPA 12 equiv.
HMPA 12 equiv.
NiI2
rt
0
47
50
rt
0
44
quant.
quant.
NiI2
rt
We next studied the reaction of ketone 10 under various conditions (Table 2). The products were
isomeric keto-alcohols 13 and 14, and a mixture of bicyclic compounds 15, whose structures were
determined by spectroscopic analyses. When ketone 10 was subjected to reaction with SmI2 without
additive at 0 °C (entry 1), the products were 13 and 14 in a ratio of 84:16. In this case the major
product had the hydroxy group in a -orientation as determined by the NOESY spectrum (Table 2).
Table 2. The reaction of compound 10 with SmI2.
Ratio
14
Temp.
Entry
Additives
Yield (%)
(°C)
0
13
84
67
84
55
61
31
53
86
15
-
1
2
3
4
5
6
7
8
none
none
quant.
84
16
rt
33
-
MeOH 2 equiv.
MeOH 2 equiv.
HMPA 12 equiv.
HMPA 12 equiv.
NiI2
0
quant.
quant.
78
16
-
rt
45
-
0
17
22
40
-
rt
71
29
0
quant.
85
47
NiI2
rt
14
-
When the temperature was raised to rt (entry 2), the ratio of compound 14 increased. This tendency
was the same as that of the aldehyde mentioned above. However, when HMPA was added, a third

Molecules 2012, 17
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product 15 was also obtained (entries 5 and 6). The ratio of 15 was 40% of the products at rt from a
total yield of 71% (entry 6). This product was formed by an aldol type condensation of the samarium
enolate of the α,β-unsaturated enone. When NiI2 was added, the yield was high and the ratio of
compound 12 was slightly increased (entries 7 and 8) [22].
Electrolysis does not use organic solvents and expensive reagents, but rather water and electric
power. In order to compare the selectivity, compounds 9 and 10 were subjected to electrolysis
conditions as shown in Table 3. The yields were moderate and the ratio was 11:12 = 62:38 in the case
of aldehyde 9. The results were not very different from those of samarium iodide reduction. However,
in the case of ketone 10, only -alcohol 13 was formed selectively (entry 2).
Table 3. The electrolysis of 9 and 10.
Entry
Solvent
Additive
Et4NTsO
Et4NTsO
Time (h)
SM
9
Yield (%)
Ratio
1
2
tBuOH-H2O (4:6)
tBuOH-H2O (4:6)
2
2
53
76
11:12 = 62:38
13:14 = 100:0
10
Comparison of the half-wave potentials of α,β-unsaturated carbonyls with those of corresponding
saturated carbonyl compounds has been extensively studied in electrochemistry [23]. The first waves
of carbonyl groups, referred to as SCE., are −2.45 V (cyclohexanone), −2.25 V (methyl ethyl ketone),
−1.8 V (propionaldehyde), −1.55 V (cyclohex-2-en-1-one), −1.50 V (acrolein), and −1.42 V (methyl
vinyl ketone), respectively [23]. Therefore, the reduction of ,-unsaturated carbonyl moiety seems
easier than that of the isolated ketone carbonyl group with electrochemistry, but the selectivity of the
one-electron reduction of the carbonyl moiety using SmI2 depends on the stereoelectronic properties of
the substrate [6]. Samarium transfers one-electron to the carbonyl group of the enone moiety to form a
radical anion (C to D) (Figure 2). Then one more samarium atom reduces the ketone carbonyl group
and the carbon-carbon bond is formed as shown by arrow a to afford E (alkene first mechanism [2]).
The hydroxy group is outside the bicyclic ring formed, because the samarium ion radical is large and
the outside position is more energetically favored than inside of the ring. Thus, this configuration is
more or less predominant. However, with HMPA as the additive, the reducing power must be higher
than that with samarium alone [24], and the enone moiety is susceptible to reduction to afford a
samarium enolate D. Then the aldol-type cyclization occurs to afford bicyclic anion radical F from D
(shown by arrow b in Figure 2). Further reduction of this anion radical F and protonation afford
product 15. Electrolysis also creates a similar transition state leading to similar results. The reason why
compound 10 produces 13 much more selectively is not clear at this stage. However, it is assumed that
solvent molecules surround the methyl ketone carbonyl group resulting in the bulkier CO (solvent)
moiety with consequent protrusion outside of the ring leading to the -alcohol 13 [24].

Molecules 2012, 17
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Figure 2. Mechanisms of reductive cyclization (R = H, Me).
3. Experimental
3.1. General
1
IR spectra were measured on a JASCO FT/IR-5300 spectrophotometer. The H and 13C-NMR
spectra were taken using a Varian Unity 600 (at 600 MHz and 150 MHz, respectively) and a Varian
Unity 200 (200 MHz and 50 MHz, respectively) spectrometer. Mass spectra including high-resolution
mass spectra were recorded on a JEOL JMS-700 MStation. A Chemcopak Nucleosil 50-5 column
(4.8 × 250 mm) was used for HPLC (JASCO pump system). For GC-MS an Agilent GC 6890 system
equipped with a MS detector 5973 was used and the product ratios were determined by the area %.
Silica gel 60 (70–230 mesh, Fuji Silysia) was used for column chromatography and silica gel 60 F254
plates (Merck) were used for TLC.
3.1.1. General Procedure for Smi2 Reduction
A solution of substrate in dry THF was introduced into a solution of SmI2 at a certain temperature.
Saturated solution of sodium potassium tartrate was added and the solvent was evaporated. The
mixture was extracted with ether and worked up as usual. The residue was purified by silica-gel
column chromatography.
3.1.2. General Procedure for Electrolysis
Zn and Pt were used for the cathode and anode, respectively, with Et4NOTs in tBuOH-H2O (2:3)
(20 mL), CCE at 100 mA (from −1.5 to −2.0 V vs. SCE) at rt. Work-up: benzene was added and most
of the water was removed under reduced pressure. The residue was extracted with EtOAc and the
organic layer was washed with Sat. NaCl solution. The organic layer was dried (MgSO4), and the
filtrate was evaporated to give a residue, which was purified by silica-gel column chromatography
or HPLC.

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3.2. Preparation of Methyl 3-(1-Methyl-2-oxocyclohex-3-enyl)propanoate (4)
Ketone (3, 1 g, 0.5 mmol) was treated with phenyltrimethylammonium tribromide (1.9 g,
0.88 mmol) in THF (5 mL) at 0 °C for 10 min. After the usual work-up, the residue (925 mg) was
successively treated with LiBr (585 mg, 5.6 mmol) and Li2CO3 (148 mg, 3.3 mmol) in DMF (4 mL) at
150 °C for 18 h. Usual work-up and purification afforded enone 4 (684 mg, 69%). Oil; IR (FT): 1730,
1660, 1630 cm−1; 1H-NMR (200 MHz, CDCl3): δ 1.09 (3H, s), 1.73–1.99 (4H, m), 2.03–2.47 (4H, m),
3.65 (3H, s), 5.91 (1H, dt, J = 10.2, 1.8 Hz), 6.89 (1H, dt, J = 10.2, 4.0 Hz); 13C-NMR (50 MHz,
CDCl3): δ 21.4 (CH3), 22.9 (CH2), 28.9 (CH2), 31.1 (CH2), 33.4 (CH2), 43.7 (C), 51.4 (CH3), 128.2
(CH), 148.6 (CH), 173.9 (C), 203.1 (C); MS m/z 196 (M)+, 181, 165, 136, 110, 68 (base), 55, HRMS
Found m/z 196.1078. Calcd for C11H16O3 196.1100.
3.3. Preparation of 6-(3-Hydroxypropyl)-6-methylcyclohex-2-en-1-ol (5)
A solution of enone 4 (172 mg, 0.88 mmol) in ether (20 mL) was treated with LiAlH4 (101 mg,
2.64 mmol) at 0 °C for 2 h. Usual work-up afforded the diol 5 (109 mg, 73%) after purification as a
1
mixture of diatereomers. Oil; IR (FT): 3330, 3020, 1660 cm−1; H-NMR (200 MHz, CDCl3): δ 0.87
(3H, s), 0.88 (3H, s), 1.2–1.7 (12H, m), 1.92–2.08 (2H, m), 3.03 (2H, br s), 3.5–4.0 (6H, m), 5.5–6.0
(4H, m); 13C-NMR (50 MHz, CDCl3): δ 18.3 (CH3), 21.3 (CH3), 22.7 (CH2), 22.8 (CH2), 26.2 (CH2),
26.6 (CH2), 29.6 (CH2), 30.3 (CH2), 32.1 (CH2), 35.1 (CH2), 35.6 (C), 35.8 (C), 63.3 (CH2), 71.7 (CH),
72.2 (CH), 128.1 (CH), 128.6 (CH), 129.7 (CH), 129.8 (CH); MS (CI) m/z 169 [M-2+H]+, 153, 135
(base), 109; HRMS (CI) Found m/z 169.1223 [M-2+H]+. Calcd for C10H17O2 169.1229.
3.4. Preparation of 6-(3-t-Butyldimethylsilyloxypropyl)-6-methylcyclohex-2-en-1-ol (6)
A solution of diol (5, 480 mg, 2.6 mmol) in CH2Cl2 (6 mL) was treated with Et3N (0.5 mL,
3.4 mmol) and TBDMSCl (473 mg, 3.1 mmol) at rt for 18 h. Usual work-up and purification afforded
1
silyl ether 6 (658 mg, 82%). Oil; IR (FT): 3400, 1660 cm−1; H-NMR (200 MHz, CDCl3): δ 0.04
(6H, s), 0.88 (9H, s), 0.89 (3H, s), 1.16–1.75 (6H, m), 1.92–2.04 (2H, m), 3.58 (1H, d, J = 6.6 Hz),
13
3.60 (2H, t, J = 7.0 Hz), 3.74 (1H, br s), 5.62–5.74 (1H, m), 5.79 (1H, dt, J = 9.2, 2.6 Hz); C-NMR
(50 MHz, CDCl3): δ −5.3 (CH3), 18.4 (C), 21.4 (CH3), 22.9 (CH2), 26.0 (CH3), 26.5 (CH2), 29.7 (CH2),
31.5 (CH2), 35.7 (C), 64.0 (CH2), 72.0 (CH), 128.3 (CH), 130.0 (CH); MS (CI) m/z 284 (M)+, 267,
227, 135 (base), 93, 83, 75; HRMS (CI) Found m/z 284.2155 (M)+. Calcd for C16H32O2Si 284.2172.
3.5. Preparation of 6-(3-t-Butyldimethylsilyloxypropyl)-6-methylcyclohex-2-en-1-one (7)
A solution of alcohol 6 (68 mg, 0.24 mmol) was oxidized with PDC (270 mg, 0.72 mmol) in
CH2Cl2 in the presence of molecular sieves 3A (201 mg) at rt for 18 h. Usual work-up afforded enone
1
7 (59 mg, 87%) after purification. Oil; IR (FT): 1680 cm−1; H-NMR (200 MHz, CDCl3): δ 0.03
(6H, s), 0.87 (9H, s), 1.07 (3H, s), 1.32–1.63 (4H, m), 1.69–1.97 (2H, m), 2.19–2.50 (2H, m), 3.56
(2H, t, J = 7.0 Hz), 5.88 (1H, dt, J = 10.2, 2.0 Hz), 6.83 (1H, dt, J = 10.2, 4.0 Hz); 13C-NMR (50 MHz,
CDCl3): δ −5.4 (CH3X2), 18.2 (C), 21.7 (CH3), 23.1 (CH2), 25.9 (CH3X3), 27.4 (CH2), 32.3 (CH2),
33.5 (CH2), 44.2 (C), 63.5 (CH2), 128.6 (CH), 148.5 (CH), 204.4 (C); MS (CI) m/z 283 [M+H]+, 267,
225, 151 (base); CI-HRMS Found m/z 283.2097 [M+H]+. Calcd for C16H31O2Si 283.2093.

Molecules 2012, 17
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3.6. Preparation of 4-(3-t-Butyldimethylsilyloxypropyl)-3,4-dimethylcyclohex-2-en-1-one (8)
MeLi (0.88 mL, 1 mmol) was added to a stirred solution of enone 7 (39 mg, 0.22 mmol) and the
mixture was stirred at 0°C for 22 h. Usual work-up afforded a residue 36 mg), which was successively
treated with PDC (140 mg, 0.36 mmol) in CH2Cl2 (4 mL) at rt for 4 h. Usual work-up and purification
1
afforded enone 8 (33 mg, 80%). Oil; IR (FT): 1680, 1620 cm−1; H-NMR (200 MHz, CDCl3): δ 0.04
(6H, s), 0.89 (9H, s), 1.14 (3H, s), 1.18–1.76 (6H, m), 1.90 (3H, d, J = 1.2 Hz), 2.39 (1H, J = 6.4 Hz),
2.43 (1H, dd, J = 6.4, 2.1 Hz), 3.5–3.7 (2H, m), 5.80 (1H, d, J = 1.2 Hz); 13C-NMR (50 MHz, CDCl3):
δ −5.3 (CH3X2), 18.3 (C), 20.0 (CH3), 24.2 (CH3), 25.9 (CH3X3), 27.7 (CH2), 33.4 (CH2), 34.1 (CH2),
34.8 (CH2), 38.2 (C), 63.2 (CH2), 127.2 (CH), 168.9 (C), 199.3 (C); MS (CI) m/z 297 [M+H]+, 281,
239 (base), 57, CI-HRMS Found m/z 297.2226. Calcd for C17H33O2Si 297.2250.
3.7. Preparation of 3-(1,2-Dimethyl-4-oxocyclohex-2-enyl)propanal (9)
Enone 8 (67 mg, 0.23 mmol) was treated with AcOH:H2O:THF (3:1:1) (6 mL) at rt overnight.
Usual work-up afforded a residue (25 mg), which was subjected to PDC (978 mg, 2.6 mmol) oxidation
in CH2Cl2 (30 mL in the presence of molecular sieves 3A (903 mg) at rt for 2 h. Usual work-up
1
afforded enone 9 (33 mg, 80%) after purification. Oil; IR (FT): 1720, 1670, 1620 cm−1; H-NMR
(200 MHz, CDCl3): δ 1.16 (3H, s), 1.65–1.97 (4H, m), 1.88 (3H, d, J = 1.3 Hz), 2.19–2.60 (2H, m),
2.40 (2H, t, J = 5.8 Hz), 5.82 (1H, d, J = 1.3 Hz), 9.80 (1H, t, J = 1.3 Hz); 13C-NMR (50 MHz,
CDCl3): δ 19.9 (CH3), 23.8 (CH3), 29.8 (CH2), 33.3 (CH2), 33.9 (CH2), 37.7 (C), 39.1 (CH2), 127.9
(CH), 167.3 (C), 198.9 (C), 201.3 (CH); MS m/z 180 (M+), 162, 152, 124, 109, 95 (base), 81, 67, 55;
HRMS Found m/z 180.1151 (M)+. Calcd for C11H16O2 180.1151.
3.8. Preparation of 4-(3-Oxobutyl)-3,4-dimethylcyclohex-2-en-1-one (10)
Diol 5 (509 mg, 3 mmol) was oxidized with PDC (3.4 g, 9 mmol) in CH2Cl2 at rt overnight. Usual
work-up afforded a residue (97 mg), which was treated with MeLi (9.3 mL, 10 mmol) in THF (30 mL)
at rt for 16 h. The residue after usual work-up was further treated with PDC (2.6 g, 7 mmol) in CH2Cl2
at rt overnight. Usual work-up afforded enone 5 (349 mg, 60%) after purification. Oil; IR (FT): 1710,
1
1670, 1610 cm−1; H-NMR (200 MHz, CDCl3): δ 1.16 (3H, s), 1.64–1.97 (4H, m), 1.89 (3H, d,
J = 1.1 Hz), 2.17 (3H, s), 2.23–2.58 (4H, m), 5 .83 (1H, d, J = 1.1 Hz); 13C-NMR (50 MHz, CDCl3): δ
19.9 (CH3), 24.0 (CH3), 30.1 (CH3), 31.6 (CH2), 33.3 (CH2), 34.0 (CH2), 37.8 (C), 38.5 (CH2), 127.7
(CH), 167.7 (C), 198.9 (C), 207.9 (C); MS m/z 194 (M+), 176, 124 (base), 109, 95, 79, 67, 55; HRMS
Found m/z 194.1295 (M)+. Calcd for C12H18O2 194.1307.
3.9. (3R*,3aR*,7aS*)-3-Hydroxy-3a,7a-dimethylhexahydro-1H-inden-5(6H)-one (11)
1
Oil; IR (FT): 3440, 1710 cm−1; H-NMR (600 MHz, CDCl3): δ 0.90 (3H, s, 3a-CH3), 1.16 (3H, s,
7a-CH3), 1.55-1.74 (4H, m, H-1,1,2,7), 1.84 (1H, ddd, J = 15.5, 11.8, 4.9 Hz, H-7), 2.12 (1H, dd,
J = 14.4, 1.9 Hz, H-4), 2.13-2.19 (1H, m, H-2), 2.25 (1H, dtd, J = 14.4, 4.9, 1.9 Hz, H-6), 2.29
(1H, dd, J = 14.4, 1.9 Hz, H-4), 2.39 (1H, dddd, J = 14.4, 11.8, 6.0, 1.1 Hz, H-6), 3.96 (1H, dd,
J = 8.5, 6.6 Hz, H-3); 13C-NMR (150 MHz, CDCl3): δ 16.9 (3a-CH3), 22.3 (7a-CH3), 29.4 (C-2), 34.8
(C-1), 36.8 (C-7), 37.8 (C-6), 41.5 (C-7a), 47.5 (C-4), 50.7 (C-3a), 78.0 (C-3) , 212.5 (C-5); MS m/z

Molecules 2012, 17
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182 (M+), 164, 139, 124, 111 (base), 96, 84, 79, 69, 55; HRMS Found m/z 182.1298 (M)+. Calcd for
C11H18O2 182.1307.
3.10. (3S*,3aR*,7aS*)-3-Hydroxy-3a,7a-dimethylhexahydro-1H-inden-5(6H)-one (12)
1
Oil; IR (FT): 3320, 1710 cm−1; H-NMR (600 MHz, CDCl3): δ 0.89 (3H, s, 3a-CH3), 1.04 (3H, s,
7a-CH3), 1.53 (1H, ddd, J = 12.9, 10.2, 6.5 Hz, H-1), 1.60–1.71 (2H, m, H-2,7), 1.91–1.95 (1H,
m, H-1), 2.07 (1H, br d, J = 14.3 Hz, H-4), 2.07–2.14 (1H, m, H-7), 2.16–2.23 (1H, m, H-2),
2.25–2.30 (1H, m, H-6), 2.38 (1H, br d, J = 14.3 Hz, H-4), 2.37–2.42 (1H, m, H-6), 3.96 (1H, dd,
J = 7.7, 4.5 Hz, H-3); 13C-NMR (150 MHz, CDCl3): δ 21.6 (3a-CH3), 23.4 (7a-CH3), 30.3 (C-2), 34.9
(C-1), 35.8 (C-7), 37.6 (C-6), 41.6 (C-7a), 45.5 (C-4), 51.3 (C-3a), 81.9 (C-3), 213.0 (C-5); MS (EI)
m/z 182 (M+), 164, 139, 124, 111, 95, 84 (base), 69, 55; HRMS Found m/z 182.1308 (M)+. Calcd for
C11H18O2 182.1307.
3.11. (3R*,3aR*,7aS*)-3-Hydroxy-3,3a,7a-trimethylhexahydro-1H-inden-5(6H)-one (13)
1
Oil; IR (FT): 3480, 1710 cm−1; H-NMR (600 MHz, CDCl3): δ 0.89 (3H, s, 3a-CH3), 1.15 (3H, s,
7a-CH3), 1.16 (3H, s, 3-CH3), 1.69 (1H, ddd, J = 14.2, 7.4, 4.9 Hz, H-7), 1.77–1.81 (3H, m, H-1,2,2),
1.84 (1H, m, H-7), 1.85–1.89 (1H, m, H-1), 1.96 (1H, dd J = 14.0, 1.1 Hz, H-4), 2.20 (1H, dddd,
J = 17.3, 9.3, 4.9, 1.1 Hz, H-6), 2.28 (1H, d, J = 14.0 Hz, H-4), 2.34 (1H, ddd, J = 17.3, 7.4, 4.9 Hz,
13
H-6); C-NMR (150 MHz, CDCl3): δ 16.7 (3a-CH3), 23.5 (3-CH3), 26.6 (7a-CH3), 36.1 (C-6), 36.3
(C-7), 37.1 (C-2), 37.6 (C-1), 42.7 (C-7a), 49.7 (C-4), 50.9 (C-3a), 84.1 (C-3), 213.7 (C-5); MS m/z
196 (M)+, 178, 150, 139, 123, 111, 84 (base), 69, 55; HRMS Found m/z 196.1452 (M)+. Calcd for
C12H20O2 196.1464.
3.12. (3S*,3aR*,7aS*)-3-Hydroxy-3,3a,7a-trimethylhexahydro-1H-inden-5(6H)-one (14)
1
Oil; IR (FT): 3400, 1700 cm−1; H-NMR (200 MHz, CDCl3): δ 0.86 (3H, s), 0.98 (3H, s), 1.18
(3H, s), 1.40–1.50 (3H, m), 1.54-1.61 (2H, m), 1.71–1.79 (2H, m), 1.81–1.85 (1H, m), 1.88 (1H, d,
J = 11.8 Hz), 1.88–1.94 (1H, m); 13C-NMR (50 MHz, CDCl3): δ 17.2 (CH3), 22.9 (CH3), 26.8 (CH3),
35.1 (CH2), 35.4 (CH2), 35.7 (CH2), 36.6 (CH2), 42.6 (CH2), 44.2 (C), 53.4 (C), 92.3 (C), 213.5 (C);
MS m/z 196 (M+), 178, 151, 139, 125, 109, 95, 84 (base), 69, 55; HRMS Found m/z 196.1460 (M)+.
Calcd for C12H20O2 196.1463.
3.13. 8-Hydroxy-5,8,9-trimethylbicyclo[3.3.1]nonan-2-one (Mixture of Diatereoisomers) (15)
1
Oil; IR (FT): 3420, 1700 cm−1; H-NMR (200 MHz, CDCl3): δ 0.90 (0.25H, s), 0.93 (0.75H, d,
13
J = 7.1 Hz), 0.96 (0.75H, s), 1.08 (0.25H, s), 1.40 (0.75H, s), 1.42 (0.25H, s); C-NMR (150 MHz,
CDCl3): δ 28.0, 28.7, 31.4, 35.8, 38.2, 39.5, 40.5, 65.5, 66.6, 69.9, 71.8, 214.1 (CO); HRMS Found
m/z 196.1465 (M)+. Calcd for C12H20O2 196.1463.

Molecules 2012, 17
11087
4. Conclusions
We have developed methods to create cis-fused trimethylated hydrindanones in excellent- to
high-yields by intra-molecular 5-exo cyclization mediated by SmI2 and electrolysis.
Acknowledgments
We thank Masami Tanaka and Yasuko Okamoto, Tokushima Bunri University, for measurement of
600 MHz NMR and mass spectra, respectively.
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