Application of [hydroxy(tosyloxy)iodo]benzene in the wittig-ring expansion sequence for the synthesis of β-benzocycloalkenones from α-benzocycloalkenones

Article abstract of DOI:10.3390/10010217

The conversion of α-benzocycloalkenones to homologous β-benzocycloalkenones containing six, seven and eight-membered rings is reported. This was accomplished via a Wittig olefination-oxidative rearrangement sequence using [hydroxy(tosyloxy)iodo]-benzene (HTIB) is the oxidant, that enables the synthesis of regioisomeric pairs of methyl-substituted β-benzocycloalkenones. The incorporation of carbon-13 at C-1 of the β-tetralone nucleus was also demonstrated. The Wittig-HTIB approach is a useful alternative to analogous sequences in which Tl(NO₃) ₃·3H₂O or the Prevost combination (AgNO ₃/I₂) are employed in the oxidation step.

Full text of DOI:10.3390/10010217

Molecules 2005, 10, 217-225
molecules
ISSN 1420-3049
http://www.mdpi.org
Application of [Hydroxy(tosyloxy)iodo]benzene in the Wittig-
Ring Expansion Sequence for the Synthesis of β-Benzocyclo-
alkenones from α-Benzocycloalkenones
Michael W. Justik and Gerald F. Koser*
Department of Chemistry, The University of Akron, Akron, Ohio, 44325. USA. Tel.: (+1) 330 972-
6066, Fax: (+1) 330 972-7370.
*
Author to whom correspondence should be addressed; e-mail koser@uakron.edu
Received: 5 July 2004 / Accepted: 14 July 2004 / Published: 31 January 2005
Abstract: The conversion of α-benzocycloalkenones to homologous β-benzocyclo-
alkenones containing six, seven and eight-membered rings is reported. This was
accomplished via a Wittig olefination-oxidative rearrangement sequence using
[
hydroxy(tosyloxy)iodo]-benzene (HTIB) is the oxidant, that enables the synthesis of
regioisomeric pairs of methyl-substituted β-benzocycloalkenones. The incorporation of
carbon-13 at C-1 of the β-tetralone nucleus was also demonstrated. The Wittig-HTIB
approach is a useful alternative to analogous sequences in which Tl(NO
Prevost combination (AgNO /I ) are employed in the oxidation step.
3
)
3
·3H O or the
2
3
2
Keywords: [Hydroxy(tosyloxy)iodo]benzene, benzocycloalkenones, ring expansion,
oxidative rearrangement
Introduction
Synthetic access to the β-benzocycloalkenones and their ring-substituted derivatives, 1, was
facilitated by the 1977 publication of a two-step protocol involving Wittig olefination of α-benzo-
cycloalkenones, 2, and oxidative ring expansion of the resulting alkenes with thallium(III) nitrate in
methanol [1]. This procedure, exemplified by equation 1, enables the regiospecific placement of alkyl
groups at the α-carbon atoms of the β-cycloalkenone ring, and affords dimethyl ketals when trimethyl
orthoformate is employed as a co-solvent. It was later demonstrated that thallium(III) nitrate can be
replaced with the Prevost combination, AgNO
3
and I , for two-step conversions of α-tetralones (n = 2)
2

Molecules 2005, 10
218
to β-benzosuberones [2], although the experimental procedure is a bit less convenient than the thallium
nitrate method.
R2
R2
O
Wittig
O
olefination
Tl(NO ) 3 H O
3 3 2
R1
R1
(1)
MeOH, RT
R1
n
n
R
R
R
n
2
1
1
2
n = 1, 2, 3; R = H or OMe; R = H or Me; R = H, Me or Et
We have recently reported that the treatment of arylalkenes with [hydroxy(tosyloxy)iodo]benzene
3, HTIB) in 95% methanol provides a general, regiospecific synthesis of α-aryl ketones (equation 2)
3]. This oxidative rearrangement is fundamentally equivalent to the ring-expansion step depicted in
(
[
eq. 1, and we now report that HTIB is an excellent alternative to Tl(NO
two-step synthesis of β-benzocycloalkenones from their lower α-benzocycloalkenone homologs. An
obvious advantage of HTIB is its relatively benign character in comparison to Tl(NO ·3H O and
AgNO [4].
3
)
3
·3H
2
O or AgNO
3
/I
2
for the
3
)
3
2
3
HO
I
OTs
I
O
Ar
R1
R2
R2
9
5% MeOH, RT
R1
+
+
+ TsOH (2)
Ar
3
Results and Discussion
Syntheses of the exocyclic alkenes and β-benzocycloalkenones shown in Table 1 were
accomplished as indicated in equation 3. The olefination procedure was adapted from the Fitjer-
Quabeck approach, wherein potassium tert-butoxide is utilized as the Wittig base in Et
2
O or benzene
[5]. More specifically, the α-benzocycloalkenones were added to a pre-stirred mixture of potassium
tert-butoxide and the appropriate alkyltriphenylphosphonium iodide in Et O at room temperature.
2
After approximately 4 h, the reaction mixtures were filtered through Celite® and concentrated.
Passage of the residual material through silica gel with hexanes gave the exocyclic alkenes
1
(
characterized by H-NMR) which were used without further purification.
The oxidative ring-expansions were effected by the addition of crystalline HTIB (10 mmol) to a
small excess of the alkene in 95% MeOH (mildly exothermic) at room temperature. After about 20
minutes and a preliminary aqueous workup, the resulting β-benzocycloalkenones were isolated by
column chromatography in yields (from the alkenes) of 80 to 99%.

Molecules 2005, 10
219
R2
R1
R2
O
O
+
2
-
Ph P CH R , I
PhI(OH)OTs
3
t
2
R1
(3)
KO Bu, Et O, RT
95% MeOH, RT
2
R1
n
n
n
Table 1.
Oxidative ring expansions of alkylidenebenzocycloalkenes to
β-benzocycloalkenones with HTIB in 95% MeOH
Entry
Alkene
Alkene Yield, %
Product
Isolated Yield, %
O
O
1
26
94
4
5
2
66
91
99
87
6
8
7
9
O
3
O
O
4
5
67
62
82
92
1
1
10
12
13
O
6
7
90
60
80
85
1
4
1
5
O
O
1
6
17
1
3
H
2
C
CH2
13
8
69
91
1
9
18

Molecules 2005, 10
220
As indicated in Table 1 (entries 1-3), conversions of unsubstituted α-benzocycloalkenones to
homologous β-benzocycloalkenones containing six, seven and eight-membered rings, via the Wittig-
HTIB sequence, were demonstrated. Furthermore, as with the Tl(III)-induced rearrangements, the
proper selection of substrates enables syntheses of regioisomeric pairs of methyl-substituted
β-benzocycloalkenones (cf. entries 4-7). For example, the treatment of 2-methyl-1-methylideneindan
with HTIB gave 3-methyl-2-tetralone (entry 4), while similar treatment of 1-ethylideneindan gave 1-
methyl-2-tetralone (entry 5).
1
3
The Wittig-HTIB sequence was also employed for incorporation of a C-label into the β-tetralone
1
3
13
nucleus (entry 8). To this end, C-methyltriphenylphosphonium iodide was prepared from C-labeled
1
3
iodomethane and utilized for the olefination of 1-indanone. Exposure of 1-( C-methylidene)indan (5.0
mmol) to HTIB (4.54 mmol) in 95% MeOH (25 mL) gave 1- C-2-tetralone in 91% isolated yield. The
1
3
location of the label at C-1 in the β-tetralone ring was clearly revealed by NMR analysis. Thus, the
1
singlet at δ 3.58 in the H-spectrum of unlabeled β-tetralone appears as a doublet at δ 3.62 (JCH
1
=
1
13
13
28.6 Hz) in the H spectrum of the C-isotopomer. A C-NMR spectrum of the labeled compound,
recorded after only 16 scans, exhibits a markedly enhanced singlet at δ 45.03, while the resonances of
the remaining carbons are either very weak in comparison or not perceptible.
A plausible mechanism for the HTIB-induced ring-expansions reported herein is presented in
Scheme 1. It is analogous to that proposed for the oxidative rearrangement of arylalkenes to α-aryl
ketones [3], and accounts for the regiochemistry of β-benzocycloalkenone formation. The similarity
between iodine(III) and thallium(III) reagents in the context of oxidative rearrangements has been
reviewed by Prakash [6] and almost certainly originates from their electrophilic character and capacity
for reduction to the respective iodine(I) and thallium(I) oxidation states.
Scheme 1.
OH
I
OH
I
Ph
Ph
R2
R1
R2
OTs
MeOH
R1
OTs
OTs
R2
OTs
Ph
I
R2
OMe
R1
OMe
MeOH
1
R
+ H O
+ PhI
2
R2
R2
OMe
OMe
R1
O
H O
2
+ TsOH
+ 2 MeOH
R1

Molecules 2005, 10
221
Conclusions
In summary, the Wittig-HTIB sequence is a useful method for regiospecific syntheses of β-
benzocycloalkenones from α-benzocycloalkenones, and is environmentally preferable to similar
protocols based on Tl(III) and Ag(I) reagents.
Experimental
General
NMR spectra were recorded on a Varian model Gemini-300 spectrometer at resonance frequencies
1
13
of 300 ( H-) and 75 ( C-) MHz. The NMR solvent in all cases was CDCl
3
; chemical shifts are
1
13
1
expressed relative to residual CHCl
3
( H spectra) or to CDCl
3
( C- spectra). Multiplets in H-NMR
spectra are sometimes specified with a range of chemical shifts corresponding to the highest and
lowest lines in the multiplet. IR spectra were recorded on a Bomem MB-100 FT-IR spectrophotometer.
IR samples were neat films or a Nujol® mull (Entry 4). The elemental analysis was performed by
Midwest Microlab, LTD (Indianapolis, IN). Melting points were recorded on a Thomas-Hoover
Unimelt melting point apparatus and are uncorrected. 2-Methyl-1-indanone and 2-methyl-1-tetralone
(
used for preparation of the alkenes in entries 4 and 6) were prepared by adaptation of literature
methods [7, 8]. All other solvents and chemical reagents were obtained from commercial sources and
used as received. Flash column chromatography was performed on a 42 mm internal diameter column
packed with Kieselgel (230-400 mesh) silica gel purchased from the Aldrich Chemical Company.
Thin layer chromatography (TLC) was done with glass backed 250 micron silica gel plates containing
a fluorescent indicator and purchased from Alltech. The 95% methanol used as the solvent for the
treatment of the substrate alkenes with [hydroxy(tosyloxy)iodo]benzene (HTIB), refers to a 95:5 (v/v)
mixture of methanol and water. Consumption of the oxidant was verified prior to work-up by adding a
drop of the reaction mixture to 10% KI (aq.) solution. Yields are based on the material used for the
spectroscopic data presented in this paper.
Preparation of Hypervalent Iodine Reagents
Typical Synthesis of (Diacetoxyiodo)benzene
A solution of 32% (w/v) peracetic acid (100 mL, 421 mmol) in acetic acid was added dropwise
o
with mechanical stirring to a cooled flask (15 C) containing iodobenzene (65.28 g, 320.0 mmol), over
a period of 1 hour. The rate of addition was adjusted to keep the temperature of the reaction mixture
o
between 25-30 C. Mechanical stirring was continued for 4 hours during which time a white
precipitate separated. Water (100 mL) was added to facilitate precipitation and to dilute any remaining
oxidant. The solid was isolated by vacuum filtration, washed with water (2 x 100 mL) and ether (150
mL), dried over P
2
5
O in a vacuum dessicator overnight and identified as (diacetoxyiodo)benzene; yield
9
4.86 g (92%); mp 160-161 °C (lit. [9] mp 159-161 °C).

Molecules 2005, 10
222
Typical Synthesis of [Hydroxy(tosyloxy)iodo]benzene (HTIB, 3)
A solution of (diacetoxyiodo)benzene (40.26 g 125.0 mmol) in boiling acetonitrile (120 mL) was
added at once to a solution of p-toluenesulfonic acid monohydrate (24.72 g, 130.0 mmol) in boiling
acetonitrile (80 mL), with magnetic stirring, to give a yellow-green solution. The solution was
allowed to cool to room temperature, and the crystalline [hydroxy(tosyloxy)iodo]benzene that
separated was isolated by vacuum filtration and washed with acetonitrile (100 mL) and ether (100
o
o
mL); yield, 45.39 g (93%); mp 136-7 C, dec. (lit.[10] mp 136-138.5 C).
Representative Procedure - Reaction of HTIB with 1-Methylideneindan (4) (Entry 1).
Crystalline HTIB (3.92 g, 10.0 mmol) was added to a stirred solution of 1-methylideneindan (1.43
g, 11.0 mmol) in 95% methanol (40 mL). The solid dissolved rapidly (~15 sec) with the evolution of
o
heat (41 C) to give a colorless solution. The solution was stirred at room temperature for 20 minutes
and the solvent was removed in vacuo to give an oily mixture. This mixture was partitioned between
CH
separated, washed with H
in vacuo to a bright yellow oil (1.51 g), which was subjected to flash column chromatography on silica
2
Cl
2
(40 mL) and H
2
O (25 mL) and transferred to a separatory funnel. The organic layer was
2
O (2 x 25 mL) and brine (1 x 30 mL), dried over MgSO , and concentrated
4
gel (hexanes; 5 % ethyl acetate/hexanes) to give β-tetralone (5) as a light yellow oil (R
f
= 0.29, 5 %
1
ethyl acetate/hexanes); yield, 1.38 g (94 %); H-NMR
(

δ

2.54 (t, J = 6.6, 2H), 3.06 (t, J = 6.6, 2H), 3.58
δ 28.13, 37.95, 44.91, 126.80, 126.87,
s, 2H), 7.11-7.15 (m, 1H), 7.20-7.24 (m, 3H); 13C-NMR

-1
127.58, 128.19, 133.28, 136.71, 210.71; IR (C=O) 1719 cm .
Summary of Purification, Yield and Spectral Data for β-benzocycloalkenones (Entries 2-7)
Conversion of Alkene 6 to Ketone 7 (Entry 2)
Flash column chromatography of the oil on silica gel (petroleum ether; 10% ethyl acetate/petroleum
1
ether) gave 2-benzosuberone (7) as a colorless oil; yield, 1.58 g (99%); H-NMR
(
5

δ
1.99 (m, 2H), 2.57
1
3
dd, J = 6.9, 6.9, 2H), 2.95 (m, 2H), 3.73 (s, 2H), 7.14-7.22 (m, 4H); C-NMR δ 26.11, 32.85, 43.56,
0.04, 127.14, 127.59, 129.24, 129.60, 133.61, 140.51, 208.90; IR (C=O) 1710 cm ; 2,4-dinitro-
-
1
phenylhydrazone, mp 174-176 °C (lit. [11] mp 169-170 °C).
Conversion of Alkene 8 to Ketone 9 (Entry 3)
Flash column chromatography of the oil on silica gel (hexanes; 5% ethyl acetate/hexanes) gave
7
,8,9,10-tetrahydro-5H-benzocyclooctan-6-one (9) as a colorless oil (R
f
= 0.32, 5% ethyl acetate/
2.84 (m, 2H), 3.82
δ 24.63, 31.14, 32.98, 40.87, 48.58, 126.73, 127.99, 129.98,
1
hexanes); yield, 1.51 g (87%); H-NMR



1
3
(
1
s, 2H), 7.14-7.30 (m, 3H) [12]; C-NMR
-1
30.27, 133.66, 141.13, 212.05; IR (C=O) 1700 cm ; oxime, mp 128-129 °C (lit.[13] mp 130-131 °C).

Molecules 2005, 10
223
Conversion of Alkene 10 to Ketone 11 (Entry 4)
Flash column chromatography on silica gel (5% ethyl acetate/hexanes; 10% ethyl acetate/hexanes)
gave a yellow oil (R
f
= 0.78, 10% ethyl acetate in hexanes). Kugelrohr distillation of this oil gave 3-
o
methyl-2-tetralone (11) as white rosettes; yield, 1.31 g (82%); mp 38-40 C (lit. [14] mp 37-40 °C);
1
H-NMR

δ
1.20 (d, J = 6.9, 3H), 2.54 (m, 1H), 2.84 (dd, J = 15.4, 11.0, 1H), 3.08 (dd, J = 15.4, 5.8,
1
3
1
H), 3.61 (s, 2H), 7.12-7.26 (m, 4H); C-NMR δ 14.89, δ 36.73, δ 42.31, δ 44.07, δ 126.76, δ 126.87,

-1
δ 127.80, δ 128.13, δ 133.51, δ 136.24, δ 212.28; IR (C=O) 1722 cm .
Conversion of Alkene 12 to Ketone 13 (Entry 5)
Flash column chromatography of the oil on silica gel (hexanes; 5% ethyl acetate/hexanes) gave
1
-methyl-2-tetralone (13) as a colorless oil (R
f
= 0.24, 5% ethyl acetate/hexanes); yield, 1.48 g (92%);
1.48 (d, J = 6.9, 3H), 2.43-2.69 (overlapping m’s, 2H), 3.08 (m, 2H), 3.54 (quartet, J = 6.9,
H), 7.21-7.29 (m, 4H); 13C-NMR
13.74, 27.70, 36.82, 47.12, 125.72, 126.36, 126.73, 127.18,
36.56, 137.63, 211.83; IR (C=O) 1714 cm ; Anal. Calcd. for C11
1
H- NMR
 δ
1
1
 δ 
-1
H12O: C: 82.46%, H: 7.55 %, Found:
C 82.35 %, H 7.60%.
Conversion of Alkene 14 to Ketone 15 (Entry 6)
Flash column chromatography of the oil on silica gel (hexanes; 5% ethyl acetate/hexanes) gave
3
(
(
-methyl-2-benzosuberone (15) as a colorless oil (R
f
= 0.27, 5% ethyl acetate/hexanes); yield, 1.40 g
2.80 (m, 1H), 2.92 (m, 2H), 3.72
δ 10.80, 27.94, 30.75, 41.69,
1
80%); H-NMR

δ


1
3
AB doublet pair, J = 54.9, 15.4, 2H), 7.14-7.26 (m, 4H); C-NMR

-
1
4
5.15, 122.57, 122.98, 124.46, 125.00, 129.39, 136.17, 206.11; IR (C=O) 1708 cm .
Conversion of Alkene 16 to Ketone 17 (Entry 7)
Flash column chromatography of the oil on silica gel (hexanes; 5% ethyl acetate/hexanes; 10%
ethyl acetate/hexanes) gave 1-methyl-2-benzosuberone (17) as a colorless oil (R
f
= 0.26, 5% ethyl
1
acetate/hexanes); yield, 1.47 g (85%); H-NMR

δ

2
.47 (m, 1H), 2.66 (m, 1H), 2.79 (m, 1H), 2.95 (m, 1H), 3.88 (quartet, 6.9, 1H), 7.12-7.26 (m, 4H);
1
3
C-NMR

δ 14.50, 27.07, 32.33, 42.21, 50.80, 127.12, 127.16, 127.21, 129.40, 138.61, 139.65, 211.89;
-
1
IR (C=O) 1709 cm ; 2,4-dinitrophenylhydrazone, mp 144-146 °C (lit. [15] mp 150-151 °C).
1
3
Preparation of C-Methyltriphenylphosphonium Iodide
1
3
A solution of C-labeled iodomethane [16] (5.00 g, 35.0 mmol) in benzene (20 mL) was added
dropwise to a cooled (-4 to 0 °C) solution of triphenylphosphine (8.39 g, 32.0 mmol) in benzene (50
mL) over one hour. A white solid began to separate after 40 minutes. This mixture was allowed to
warm to room temperature and stirred for a period of 4 hours. The white solid was collected by
vacuum filtration and identified by melting point as 1 C-methyltriphenylphosphonium iodide; yield,
3
1
2.60 (97%); melting point, 182-184 °C (lit. [17] mp 183-184 °C).

Molecules 2005, 10
224
1
3
Preparation of C-Methylideneindan (18)
Potassium tert-butoxide (1.35 g, 12.0 mmol) was added at once under argon to a mechanically
1
3
stirred mixture of C-methyltriphenylphosphonium iodide (4.86 g, 12.0 mmol) in dry ether (50 mL) to
give a canary yellow mixture. This mixture was vigorously stirred for 30 minutes. A solution of
1
-indanone (1.32 g, 10.0 mmol) in dry ether (20 mL) was added to the mixture over a period of 5
minutes. The color of the mixture gradually became a vivid blue as it was stirred overnight (14 hours).
The resulting mixture was filtered through Celite® (10 g), and the filtrate was concentrated in vacuo to
give a light yellow oil. The oil was eluted with hexanes through a pad of silica gel (30 g) on a sintered
glass funnel under aspirator vacuum. The eluant was concentrated in vacuo to give 1-( C-
methylidene)indan (18) as a colorless oil; yield, 0.91 g (69%); H-NMR δ 2.97 (m, 2H), 3.14 (m, 2H),
1
3
1
5
.16 (dt, JHH = 2.1, JHC = 127.20, 1H), 5.68 (dt, JHH = 2.1, JHC = 125.4, 1H), 7.34-7.44 (m, 3H), 7.66
1
3
(
d, J = 6.9, 1H); C-NMR δ 12.93, 30.01, 31.10, 102.73 (enhanced), 120.50, 120.53, 125.24, 126.31,
28.13, 128.15; IR ( C= C) 1715 cm .
1
2
13
-1
1
1
3
Reaction of C Labeled Methylideneindan with HTIB (Entry 8)
1
3
Crystalline HTIB (1.78 g, 4.54 mmol) was added to a stirred solution of 1-( C-methylidene)indan
18, 0.66 g, 5.0 mmol) in 95% methanol (25 mL). The solid dissolved rapidly with the evolution of
(
heat to give a colorless solution. The solution was stirred at room temperature for 20 minutes, and the
solvent was removed in vacuo to give an oily mixture. This mixture was partitioned between CH Cl
25 mL) and H O (25 mL). The organic layer was washed with H O (2 x 25 mL) and brine (1 x 20
mL), dried over MgSO , and concentrated in vacuo to give a bright yellow oil (0.79 g). Flash column
2
2
(
2
2
4
1
3
chromatography of the oil on silica gel (hexanes; 5 % ethyl acetate/ hexanes) gave 1- C-β-tetralone
19) as a light yellow oil (R
t, J = 6.6, 2H), δ 3.10 (t, J = 6.6, 2H), δ 3.62 (d, JHC = 128.6, 2H), δ 7.15-7.19 (m, 4H); C-NMR,
transients) δ 45.03; IR (C=O) 1718 cm .
1
(
(
f
= 0.30, 5 % ethyl acetate/hexanes); yield, 0.61 g (91 %); H-NMR


2.58
(16
1
3

-
1
References and Notes
1
2
.
.
Taylor, E. C.; Chiang C.-S.; McKillop, A. Tetrahedron Lett. 1977, 1827-1830.
El-Hossini, M. S.; McCullough, K. J.; McKay, R.; Proctor, G. R. Tetrahedron Lett. 1986, 27,
783-3786.
3
3
4
.
.
Justik, M. W.; Koser, G. F. Tetrahedron Lett., 2004, 45, 6159-6163.
According to current MSDS information (obtained online from Aldrich Chemical Company),
thallium(III) nitrate and thallium(I) nitrate are listed as “highly toxic” with a “danger of
cumulative effects”. Silver nitrate is described as “corrosive” and “dangerous for the
environment”. HTIB is listed as an “irritant”, and iodobenzene as “harmful”.
Fitjer, L.; Quabeck, U. Synth. Commun. 1985, 15, 855-864.
5
6
7
8
9
.
.
.
.
.
Prakash. O. Aldrichimica Acta 1995, 28, 63-71.
Bhattacharya, A.; Segmuller, B.; Ybarra, A. Synth. Commun. 1996, 26, 1775-84.
Kulagowski, J. J.; Moody, C. J.; Rees, C. W. J. Chem. Soc., Perkin Trans. 1 1985, 12, 2733-9.
Waddington, T.; Alcock, N. W. J. Chem. Soc. 1963, 4103-9.

Molecules 2005, 10
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1
1
1
1
1
1
1
1
0. Koser, G. F.; Wettach, R. H.; Troup, J. M.; Frenz, B. A. J. Org. Chem. 1976, 41, 3609-11.
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Sample Availability: Not available.
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