Influence of geminal disubstitution on samarium diiodide induced reductive cyclizations of γ-aryl ketones

Article abstract of DOI:10.1055/s-0030-1259526

Geminal disubstitution at the alkyl chain of γ-aryl ketones significantly influences the efficacy of samarium diiodide induced cyclizations providing significantly higher yields. β,β-Disubstituted aryl ketones 11a-e and γ,γ-disubstituted aryl ketone 14 could be converted into the corresponding hexahydronaphthalene derivatives in good yields. On the other hand, α,α-disubstituted ketone 9 only gave the secondary alcohol 10 along with recovered starting material. Aryl ketones containing substituents with hetero-atoms could also be cyclized in high yields and substrates such as 11d with sterically demanding cyclic substituents efficiently afforded spiro compounds. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0030-1259526

LETTER
525
Influence of Geminal Disubstitution on Samarium Diiodide Induced Reductive
Cyclizations of g-Aryl Ketones
Geminal
D
isubstituntions in 2
S
mI
d
-Induced
K
r
etyl-Ary
é
l
C
ouplings Niermann, Hans-Ulrich Reissig*
Freie Universität Berlin, Institut für Chemie und Biochemie, Takustr. 3, 14195 Berlin, Germany
Fax +49(30)83855367; E-mail: hans.reissig@chemie.fu-berlin.de
Received 23 November 2010
the desired cyclization product under standard conditions,
Abstract: Geminal disubstitution at the alkyl chain of g-aryl ke-
tones significantly influences the efficacy of samarium diiodide
induced cyclizations providing significantly higher yields. b,b-Di-
substituted aryl ketones 11a–e and g,g-disubstituted aryl ketone 14
but fragmentation product 8 which is probably the result
of a reductive elimination of the acetone subunit.9 Our re-
sults with precursors that cannot undergo this undesired
could be converted into the corresponding hexahydronaphthalene fragmentation process are disclosed here.
derivatives in good yields. On the other hand, a,a-disubstituted ke-
tone 9 only gave the secondary alcohol 10 along with recovered
starting material. Aryl ketones containing substituents with hetero-
atoms could also be cyclized in high yields and substrates such as
11d with sterically demanding cyclic substituents efficiently afford-
ed spiro compounds.
a
+
45%
(2/3 = 91:9)
O
H
H
OH
OH
1
2
3
Key words: samarium diiodide, cyclization, geminal disubstitu-
tion, g-aryl ketone, hexahydronaphthalene
MeOOC
H
OH
Samarium diiodide has become one of the most efficient
reagents in organic syntheses for the formation of new
carbon–carbon bonds.1 In our group it was used to pro-
mote intramolecular reductive ketyl–aryl couplings fur-
nishing functionalized dearomatized products with often
very high diastereoselectivity.1h In this manner, ketones
with (substituted) phenyl,2,3 naphthyl,4 aniline,5 indole,
pyrrole,6 and quinoline7 moieties in g-position were suc-
cessfully employed as precursors in this reductive cycliza-
tion reaction. Recently, we reported the shortest formal
total synthesis of strychnine applying a samarium diiodide
cascade reaction as crucial step.6f
a
5 (24%)
O
MeO
+
O
O
4
O
H
6 (36%)
R
a
R
R
O
R
7
8 (66%)
R = COOMe
Simple g-aryl ketones as substrates react with samarium
diiodide to afford hexahydronaphthalene derivatives in a
6-trig-cyclization with excellent diastereoselectivity.
Thus, treatment of g-phenyl ketone 1 with two equivalents
of samarium diiodide in the presence of HMPA and tert-
butanol in THF furnished 1,3-diene 2 and its isomer 1,4-
diene 3 in 45% yield (Scheme 1).2g Ketone 4, bearing a
methoxycarbonyl group as b-substituent of the spacer
unit, gave the corresponding hexahydronaphthalene de-
rivative 5 along with g-lactone 6 in a slightly higher cy-
clization yield of 60%.2a Since it is well established that
geminal dialkyl substituents have a favorable influence on
numerous cyclization reactions,8 we investigated the ef-
fect of such substitution patterns on the samarium diiodide
induced reductive cyclization. Unfortunately, the easily
accessible ketone 7 with two methoxycarbonyl substitu-
ents was not a suitable model substrate. It did not provide
Scheme 1 Samarium diiodide induced conversion of g-aryl ketones
with different substitution patterns. Reagents and conditions: (a) SmI2
(2.2–2.4 equiv), HMPA (18 equiv), t-BuOH (2 equiv), THF, r.t.
We started our investigation with dimethyl substituted
aryl ketones 9,10 11a,11 and 14,12 bearing the groups in
a-, b-, or g-position, respectively (Scheme 2). Attempts to
cyclize ketone 9 failed. Instead of the expected bicyclic
product most of the substrate was recovered along with a
small amount of secondary alcohol 10 as simple reduction
product. The conversion of this ketone was probably un-
successful due to the high steric hindrance at the reacting
carbonyl group.1h,9 Apparently, the generated samarium
ketyl is strongly hampered to approach the phenyl ring
and hence cyclization does not occur.13
Gratifyingly, ketones 11a and 14 led to the desired cy-
clization products in good yields under standard condi-
tions,14 although mixtures of the conjugated 1,3-dienes
12a/15 and their 1,4-diene isomers 13a/16 were isolated
(Scheme 2).15 In the case of 14, tetralin derivative 17 was
SYNLETT 2011, No. 4, pp 0525–0528
x
x.
x
x.
2
0
1
1
Advanced online publication: 02.02.2011
DOI: 10.1055/s-0030-1259526; Art ID: G36010ST
© Georg Thieme Verlag Stuttgart · New York

526
A. Niermann, H.-U. Reissig
LETTER
also obtained in small amount. It is assumed that this com- In summary, we could demonstrate that geminal disubsti-
pound is generated by oxidative rearomatization of 15 or tution at the alkyl chain of g-aryl ketones significantly in-
16 during workup or purification. Compared to the cy- creases the yields of samarium diiodide induced
clization of parent system 1, conversion of the dimethyl cyclizations, given that substitution is not positioned to
substituted ketones 11a and 14 proceeded with a signifi- close to the carbonyl function as in the case of a,a-disub-
cantly increased cyclization yield.16
stituted derivative 9. These successful cyclizations allow
a fast entry to highly substituted hexahydronaphthalene
derivatives including new spiro compounds. Our model
studies should allow an improved design of samarium di-
iodide induced cyclizations and hence increase the syn-
thetic value of this approach to polycyclic compounds.
We then explored the influence of other b-positioned sub-
stituents in precursors 11. All substrates 11b–e furnished
the expected products 12 and 13 in satisfying to very good
yields under standard conditions of the samarium diiodide
induced cyclization reaction. Oxygen-containing substitu-
ents in 11b,c were fully compatible with the method em-
ployed. In fact, bis(methoxymethyl)-substituted ketone
11b provided the highest cyclization yield of all exam-
ples. Sterically demanding cyclic systems such as 11d
also underwent smooth conversion into the spiro com-
pounds 12d and 13d. Furthermore, 1,3-dithiane derivative
11e could be converted into the corresponding cyclization
products 12e and 13e in moderate yield.
Acknowledgment
The authors thank the Deutsche Forschungsgemeinschaft and the
Bayer Schering Pharma AG for support. We gratefully acknowl-
edge the help of Dr. R. Zimmer during preparation of this manus-
cript.
References and Notes
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a
O
OH
35%a
9
10
Tetrahedron 2003, 59, 10351. (g) Edmonds, D. J.; Johnston,
D.; Procter, D. J. Chem. Rev. 2004, 104, 3371. (h) Berndt,
M.; Gross, S.; Hölemann, A.; Reissig, H.-U. Synlett 2004,
422. (i) Gopalaiah, K.; Kagan, H. B. New J. Chem. 2008, 32,
607. (j) Rudkin, I. M.; Miller, L. C.; Procter, D. J.
R
R
R
R
+
a
R
R
O
H
H
OH
OH
Organomet. Chem. 2008, 34, 19. (k) Nicolaou, K. C.;
Ellery, S. P.; Chen, J. S. Angew. Chem. Int. Ed. 2009, 48,
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Flowers, R. A. II; Skrydstrup, T. Organic Synthesis Using
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2011, 40, in press; DOI: 10.1039/C0CS00116C.
11
12
13
R,R
Me (11a)
yield
75%
83%
70%
81%
56%
products
12a/13a
12b/13b
12c/13c
12d/13d
12e/13e
ratio 12/13
83:17
CH2OMe (11b)
CH2OBn (11c)
-(CH2)5- (11d)
-S(CH2)3S- (11e)
88:12
(2) (a) Dinesh, C. U.; Reissig, H.-U. Angew. Chem. Int. Ed.
1999, 38, 789; Angew. Chem. 1999, 111, 874.
78:22
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2000, 56, 4267. (c) Berndt, M.; Reissig, H.-U. Synlett 2001,
1290. (d) Ohno, H.; Maeda, S.-i.; Okumura, M.; Wakayama,
R.; Tanaka, T. Chem. Commun. 2002, 316. (e) Ohno, H.;
Wakayama, R.; Maeda, S.-i.; Iwasaki, H.; Okumura, M.;
Iwata, C.; Mikamiyama, H.; Tanaka, T. J. Org. Chem. 2003,
68, 5909. (f) Ohno, H.; Okumura, M.; Maeda, S.-i.; Iwasaki,
H.; Wakayama, R.; Tanaka, T. J. Org. Chem. 2003, 68,
7722. (g) Wefelscheid, U. K.; Berndt, M.; Reissig, H.-U.
Eur. J. Org. Chem. 2008, 3635.
76:24
43:57
a
+
O
70%
(15/16/17 = 74:19:7)
H
H
OH
OH
14
(3) For related ketyl–aryl couplings, see: (a) Kise, N.;
Suzumoto, T.; Shono, T. J. Org. Chem. 1994, 59, 1407.
(b) Schmalz, H.-G.; Siegel, S.; Bats, J. W. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2383; Angew. Chem. 1995, 107,
2597. (c) Shiue, J.-S.; Lin, M.-H.; Fang, J.-M. J. Org. Chem.
1997, 62, 4643. (d) Heimann, J.; Schäfer, H. J.; Fröhlich, R.;
Wibbeling, B. Eur. J. Org. Chem. 2003, 2919.
15
16
+
OH
17
(4) (a) Berndt, M.; Hlobilova, I.; Reissig, H.-U. Org. Lett. 2004,
6, 957. (b) Aulenta, F.; Berndt, M.; Brüdgam, I.; Hartl, H.;
Sörgel, S.; Reissig, H.-U. Chem. Eur. J. 2007, 13, 6047.
(c) Wefelscheid, U. K.; Reissig, H.-U. Adv. Synth. Catal.
2008, 350, 65. (d) Wefelscheid, U. K.; Reissig, H.-U.
Tetrahedron: Asymmetry 2010, 21, 1601.
Scheme 2 Conversion of geminal disubstituted g-aryl ketones with
a
samarium diiodide. Yield based on recovered starting material.
Reagents and conditions: (a) SmI2 (3 equiv), HMPA (18 equiv),
t-BuOH (2 equiv), THF, r.t.
Synlett 2011, No. 4, 525–528 © Thieme Stuttgart · New York

LETTER
Geminal Disubstitutions in SmI2-Induced Ketyl–Aryl Couplings
527
(5) (a) Gross, S.; Reissig, H.-U. Synlett 2002, 2027.
(b) Kumaran, R. S.; Brüdgam, I.; Reissig, H.-U. Synlett
2008, 991.
(6) (a) Gross, S.; Reissig, H.-U. Org. Lett. 2003, 5, 4305.
(b) Blot, V.; Reissig, H.-U. Synlett 2006, 2763. (c) Blot, V.;
Reissig, H.-U. Eur. J. Org. Chem. 2006, 4989.
12.6 Hz, 1 H, 4-H), 2.03 (d, J = 12.6 Hz, 1 H, 4-H), 2.23 (dd,
J = 3.5, 13.0 Hz, 1 H, 8a-H), 2.49 (tdd, J = 3.1, 13.0, 19.5
Hz, 1 H, 8-H), 2.57 (m, 1 H, 8-H), 5.54 (tddd, J = 0.9, 3.1,
8.6, 9.5 Hz, 1 H, 7-H), 5.58–5.60 (m, 1 H, 5-H), 5.67 (dddd,
J = 1.3, 3.1, 5.4, 9.5 Hz, 1 H, 6-H) ppm; * overlapping
signals. 13C NMR (176 MHz, CDCl3): d = 22.4 (t, C-8), 23.2,
26.6 (2 q, CH3), 32.8 (s, C-3) 33.9 (q, CH3), 46.9 (d, C-8a),
48.7 (t, C-4), 55.9 (t, C-2), 74.9 (s, C-1), 118.9, 122.2, 123.5
(3 d, C-5, C-6, C-7), 136.5 (s, C-4a) ppm.
(d) Beemelmanns, C.; Reissig, H.-U. Org. Biomol. Chem.
2009, 7, 4475. (e) Beemelmanns, C.; Blot, V.; Gross, S.;
Lentz, D.; Reissig, H.-U. Eur. J. Org. Chem. 2010, 2716.
(f) Beemelmanns, C.; Reissig, H.-U. Angew. Chem. Int. Ed.
2010, 49, 8021; Angew. Chem. 2010, 122, 8195. (g) For a
related electrochemical cyclization, see: Kise, N.; Mano, T.;
Sakurai, T. Org. Lett. 2008, 10, 4617.
Spectroscopic Data for (1S*,8aS*)-1,3,3-Trimethyl-
1,2,3,4,6,8a-hexahydronaphthalen-1-ol (13a)
1H NMR (700 MHz, CDCl3): d = 0.90, 0.98, 1.12 (3 s, 3 H
each, CH3), 1.52 (br s, 1 H, OH), 1.59 (d, J = 13.2 Hz, 1 H,
2-H), 1.68 (dd, J = 2.2, 13.2 Hz, 1 H, 2-H), 1.87, 1.92 (AB
part of an ABX system, JAB = 13.0 Hz, JBX = 2.2 Hz, 1 H
each, 4-H), 2.62 (mc, 1 H, 8a-H), 2.67–2.71 (m, 2 H, 6-H),
5.47 (X part, mc, 1 H, 5-H), 5.85 (mc, 2 H, 7-H, 8-H) ppm.
13C NMR (176 MHz, CDCl3): d = 24.9, 26.2 (2 q, CH3), 27.0
(t, C-6), 32.2 (s, C-3), 33.9 (q, CH3), 48.7 (t, C-4), 49.0 (d,
C-8a), 55.3 (t, C-2), 74.5 (s, C-1), 120.1 (d, C-5), 124.3,
125.6 (2 d, C-7, C-8), 141.6 (s, C-4a) ppm. Data from
mixture: IR (film): n = 3365 (OH), 2950–2830 (CH), 1630
(C=C) cm–1. HRMS (EI, 80 eV, 60 °C): m/z calcd for
C13H20O [M]+: 192.1514; found: 192.1513. Anal. Calcd for
C13H20O (192.1): C, 81.20; H, 10.48; found: C, 80.93; H,
10.31.
(7) Aulenta, F.; Wefelscheid, U. K.; Brüdgam, I.; Reissig, H.-U.
Eur. J. Org. Chem. 2008, 2325.
(8) (a) For a recent review, see: Jung, M. E.; Piizzi, G. Chem.
Rev. 2005, 105, 1735. (b) Mitchell, L.; Parkinson, J. A.;
Percy, J. M.; Singh, K. J. Org. Chem. 2008, 73, 2389.
(c) Karaman, R. Tetrahedron Lett. 2009, 50, 6083. (d) Kim,
H.; Park, Y.; Hong, J. Angew. Chem. Int. Ed. 2009, 48, 7577;
Angew. Chem. 2009, 121, 7713.
(9) Berndt, M. Dissertation; Freie Universität Berlin: Germany,
2003.
(10) Compound 9 was synthesized in a two-step procedure: 1.
ethyl isobutyrate, phenethyl iodide, LDA, HMPA, THF,
–78 °C; 2. TMSCH2Li, pentane, 0 °C then MeOH, 55% (2
steps). For the second step, see: Demuth, M. Helv. Chim.
Acta 1978, 61, 3136.
(11) Conjugate addition of a benzyl cuprate to mesityl oxide
furnished compound 11a in low yield: BnMgCl, CuCN,
BF3·OEt2, mesityl oxide, Et2O, –78 °C, 15%.
(12) Mahmud, S. A.; Ansell, M. F. J. Chem. Soc., Perkin Trans.
1 1973, 2789.
(13) The samarium ketyl is very likely in equilibrium with ketone
9 which was re-isolated. Reduction of the ketyl and
subsequent protonation furnishes 10.
Cyclization of 14
According to the general procedure, the SmI2 solution in
THF (15.8 mL, 1.58 mmol), HMPA (1.66 mL, 9.47 mmol),
14 (0.100 g, 0.53 mmol), and t-BuOH (0.078 g, 1.05 mmol)
afforded after purification by flash chromatography
(hexane–EtOAc, 9:1) compounds 15, 16, and 17 as a 74:19:7
mixture in 70% yield (71 mg). Separation by HPLC yielded
pure samples.
Analytical Data for (1S*,8aS*)-1,4,4-Trimethyl-
1,2,3,4,8,8a-hexahydronaphthalen-1-ol (15)
(14) General Procedure for Samarium Diiodide Induced
Colorless solid; mp 50–52 °C. 1H NMR (700 MHz, CDCl3):
d = 1.09, 1.14, 1.17 (3 s, 3 H each, CH3), 1.35 (dt, J = 4.5,
13.6 Hz, 1 H, 3-H), 1.46* (br s, 1 H, OH), 1.47* (ddd,
J = 2.9, 4.4, 13.6 Hz, 1 H, 3-H), 1.60 (ddd, J = 2.9, 4.4, 13.6
Hz, 1 H, 2-H), 1.77 (dt, J = 4.5, 13.6 Hz, 1 H, 2-H), 2.47 (tdd,
J = 3.1, 13.8, 20.0 Hz, 1 H, 8-H), 2.61–2.67 (m, 2 H, 8-H, 8a-
H), 5.52 (dddd, J = 0.8, 3.3, 5.0, 9.0 Hz, 1 H, 7-H), 5.64 (br
d, J = 5.7 Hz, 1 H, 5-H), 5.69 (dddd, J = 1.4, 3.0, 5.7, 9.0 Hz,
1 H, 6-H) ppm; * overlapping signals. 13C NMR (176 MHz,
CDCl3): d = 20.4 (q, CH3), 22.7 (t, C-8), 26.2, 28.5 (2 q,
CH3), 35.9 (s, C-4), 38.5, 38.8 (2 t, C-3, C-2), 42.4 (d, C-8a),
75.6 (s, C-1), 115.2 (d, C-5), 122.2 (d, C-6), 123.1 (d, C-7),
145.0 (s, C-4a) ppm. IR (film): n = 3375 (OH), 2970-2865
(=CH, CH), 1665 (C=C) cm–1.
Cyclizations of Aryl Ketones
HMPA (18 equiv) was added to a previously prepared stock
solution of SmI2 in THF (0.1 M, 3 equiv) under argon, and
the solution was stirred for 20 min. During this time the
solution turned from dark blue to dark violet. In a separate
flask, the substrate (1 equiv) and t-BuOH (2 equiv) were
dissolved in THF (10 mL) under argon. Argon was bubbled
through the solution for 20 min. The substrate solution was
then transferred with a syringe to the samarium diiodide
solution. The mixture was stirred at r.t. until the color
changed from violet to grey. Saturated aq NaHCO3 solution
was added, the organic layer was separated, and the aqueous
layer was extracted with Et2O (3×). The combined organic
layers were washed with H2O and brine, dried with MgSO4,
and the solvent was removed under reduced pressure to give
the crude product, which still contained small amounts of
HMPA. Flash chromatography on Al2O3 (activity grade 3)
yielded the cyclization products.
Analytical Data for (1S*,8aS*)-1,4,4-Trimethyl-
1,2,3,4,6,8a-hexahydronaphthalen-1-ol (16)
1H NMR (700 MHz, CDCl3): d = 1.03, 1.08. 1.09 (3 s, 3 H
each, CH3), 1.32 (dt, J = 4.2, 13.8 Hz, 1 H, 3-H), 1.43 (ddd,
J = 2.9, 4.4, 13.8 Hz, 1 H, 3-H), 1.55 (br s, 1 H, OH), 1.63
(ddd, J = 2.9, 4.2, 12.9 Hz, 1 H, 2-H), 1.86 (ddd, J = 2.9, 4.2,
12.9 Hz, 1 H, 2-H), 2.66–2.70 (m, 2 H, 6-H), 2.97–3.01 (m,
1 H, 8a-H), 5.47–5.51 (m, 1 H, 5-H), 5.81–5.85 (m, 1 H, 7-
H), 5.87 (tdd, J = 1.8, 3.3, 10.2 Hz, 1 H, 8-H) ppm. 13C NMR
(176 MHz, CDCl3): d = 21.5, 25.7 (2 q, CH3), 27.1 (t, C-6),
28.7 (q, CH3), 34.4 (s, C-4), 37.8, 38.0 (2 t, C-2, C-3), 44.7
(d, C-8a), 71.0 (s, C-1), 116.2 (d, C-5), 124.5, 125.4 (2 d,
C-8, C-7), 142.2 (s, C-4a) ppm. IR (film): n = 3410 (OH),
2960–2810 (=CH, CH), 1650 (C=C) cm–1. HRMS (ESI-
TOF-MS): m/z calcd for C13H20ONa [M + Na]+: 215.1406;
found: 215.1405.
(15) Cyclization of 11a
According to the general procedure, the SmI2 solution in
THF (15.8 mL, 1.58 mmol), HMPA (1.66 mL, 9.47 mmol),
11a (0.100 g, 0.53 mmol), and t-BuOH (0.078 g, 1.05 mmol)
afforded after purification by flash chromatography
(hexane–EtOAc, 9:1) compounds 12a and 13a as a 83:17
mixture in 75% yield (76 mg).
Spectroscopic Data for (1S*,8aS*)-1,3,3-Trimethyl-
1,2,3,4,8,8a-hexahydronaphthalen-1-ol (12a)
1H NMR (700 MHz, CDCl3): d = 0.93, 0.96. 1.26* (3 s, 3 H
each, CH3), 1.28* (br s, 1 H, OH), 1.50 (d, J = 13.4 Hz, 1 H,
2-H), 1.62 (dd, J = 2.2, 13.4 Hz, 1 H, 2-H), 1.88 (dd, J = 2.2,
Synlett 2011, No. 4, 525–528 © Thieme Stuttgart · New York

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A. Niermann, H.-U. Reissig
LETTER
Analytical Data for 1,4,4-Trimethyl-1,2,3,4-
tetrahydronaphthalen-1-ol (17)
ppm. IR (film): n = 3385 (OH), 2960–2860 (=CH, CH),
1660 (C=C) cm–1. HRMS (ESI-TOF-MS): m/z calcd for
C13H18ONa [M + Na]+: 213.1250; found: 213.1250.
(16) At the moment it is more likely that the isolation of isomeric
mixtures is the result of an unselective kinetically controlled
protonation. Since equilibration experiments with the
products isolated are so far not fully conclusive, further
investigation of this problem is required.
Colorless solid; mp 68–70 °C. 1H NMR (700 MHz, CDCl3):
d = 1.30, 1.31, 1.55 (3 s, 3 H each, CH3), 1.68 (br s, 1 H,
OH), 1.71–1.83, 1.96–1.99 (2 m, 4 H, 2-H, 3-H), 7.18–7.24
(m, 2 H, Ar), 7.29–7.31 (m, 1 H, Ar), 7.58–7.59 (m, 1 H, Ar)
ppm. 13C NMR (176 MHz, CDCl3): d = 30.8, 31.5, 31.7 (3 q,
CH3), 34.06 (s, C-4), 35.9, 36.1 (2 t, CH2), 71.0 (s, C-1),
126.0, 126.1, 126.4, 127.4 (4 d, Ar), 142.0, 144.7 (2 s, Ar)
Synlett 2011, No. 4, 525–528 © Thieme Stuttgart · New York

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