First synthesis of N-(3-carboxylpropyl)-5-amino-2-hydroxy-3-tridecyl-1,4- benzoquinone, an unusual quinone isolated from Embelia ribes

Article abstract of DOI:10.1021/jo702101w

(Chemical Equation Presented) The first synthesis of the unusual nitrogen-containing 3-alkyl-1,4-benzoquinone, N-(3-carboxylpropyl)-5-amino-2- hydroxy-3-tridecyl-1,4-benzoquinone, isolated from Embelia ribes, is reported. The key steps are a microwave-ass

Full text of DOI:10.1021/jo702101w

First Synthesis of
N-(3-Carboxylpropyl)-5-amino-2-hydroxy-3-
tridecyl-1,4-benzoquinone, an Unusual Quinone
Isolated from Embelia ribes
Christopher S. P. McErlean and Christopher J. Moody*
School of Chemistry, UniVersity of Nottingham, UniVersity Park,
Nottingham, NG7 2RD, United Kingdom
c.j.moody@nottingham.ac.uk
ReceiVed September 26, 2007
The first synthesis of the unusual nitrogen-containing 3-alkyl-
1,4-benzoquinone, N-(3-carboxylpropyl)-5-amino-2-hydroxy-
3-tridecyl-1,4-benzoquinone, isolated from Embelia ribes, is
reported. The key steps are a microwave-assisted combined
Mitsunobu reaction-Claisen rearrangement to introduce the
alkyl side chain into 2,5-dimethoxyphenol, followed by
alkene reduction, oxidation to the quinone, and sequential
displacement of the methoxy groups with hydroxide and
GABA tert-butyl ester. Two other naturally occurring
benzoquinones, O-methylrapanone and rapanone, were also
prepared en route.
FIGURE 1. Some naturally occurring 3-alkyl-2-hydroxy-1,4-benzo-
quinones.
metachromins 69 also incorporate amino acid derived side chains
at C-5 (Figure 1).
Extracts of various parts of the shrub Embelia ribes, known
commonly as vidanga, are widely used in traditional Chinese
medicine to treat a range of ailments. The extracts contain a
diverse array of chemotypes, including coumarins, flavonoids,
terpenes, and 1,4-benzoquinones. One of the major chemical
constituents is embelin (2,5-dihydroxy-3-undecyl-1,4-benzo-
quinone) 1, first isolated several years ago, and reported to elicit
a wide range of biological effects including anthelmintic,
analgesic, antifertility, antitumor, and antioxidant properties.1
Recently a new benzoquinone derivative was isolated from the
roots of Embelia ribes and assigned the N-(3-carboxylpropyl)-
5-amino-2-hydroxy-3-tridecyl-1,4-benzoquinone structure 2.2 It
shares the long unbranched 3-alkyl side chain of embelin 1,
although it has two extra carbons (C-13 as opposed to C-11),
and has the unusual incorporation of γ-aminobutyric acid
(GABA) linked to the quinone through nitrogen. Although other
quinones with 13-carbon side chains are known, e.g., rapanone
3 previously isolated from a variety of sources, better known
are the sesquiterpene benzoquinones,3-5 some of which such
as the nakijiquinones 4,6,7 the smenospongines 5,8 and the
Naturally occurring quinones exhibit wide-ranging properties.3-5
Not only do they constitute a large group of natural pigments,
although surprisingly their contribution to natural coloring is
relatively small, but they also participate in a range of important
biological redox processes. Consequently, they have attracted
the attention of synthetic chemists and there have been a number
of approaches to some of the 3-alkyl-2-hydroxy-1,4-benzo-
quinone natural products shown in Figure 1.10-14 Our own
(3) Thomson, R. H. Naturally Occurring Quinones, 2nd ed.; Academic
Press: London, UK, 1971.
(4) Thomson, R. H. Naturally Occurring Quinones III. Recent adVances,
3rd ed.; Chapman and Hall: London, UK, 1987.
(5) Thomson, R. H. Naturally Occurring Quinones IV. Recent adVances,
4th ed.; Blackie: London, UK, 1997.
(6) Shigemori, H.; Madono, T.; Sasaki, T.; Mikami, Y.; Kobayashi, J.
Tetrahedron 1994, 50, 8347.
(7) Kobayashi, J.; Madono, T.; Shigemori, H. Tetrahedron 1995, 51,
10867.
(8) Aoki, S.; Kong, D.; Matsui, K.; Rachmat, R.; Kobayashi, M. Chem.
Pharm. Bull. 2004, 52, 935.
(9) Takahashi, Y.; Kubota, T. J. F.; Kobayashi, J. Tetrahedron 2007,
63, 8770.
(10) Kubo, I.; Kim, M.; Ganjian, I.; Kamikawa, T.; Yamagiwa, Y.
Tetrahedron 1987, 43, 2653.
(11) Poigny, S.; Guyot, M.; Samadi, M. Tetrahedron 1998, 54, 14791.
(12) Yadav, J. S.; Upender, V.; Rao, A. V. R. J. Org. Chem. 1992, 57,
3242.
(1) Joshi, R.; Kamat, J. P.; Mukherjee, T. Chem.-Biol. Interact. 2007,
167, 125.
(2) Lin, P. C.; Li, S. A.; Wang, S. J.; Yang, Y.; Shi, J. G. J. Nat. Prod.
2006, 69, 1629.
10.1021/jo702101w CCC: $37.00 © 2007 American Chemical Society
Published on Web 11/14/2007
10298
J. Org. Chem. 2007, 72, 10298-10301

SCHEME 1
interest in quinone natural products dates back to an early
synthesis of coenzyme PQQ,15 and more recently the alkyl
benzoquinones primin, pallasone-B, verapliquinones-A and -B,
and panicein-A.16 These syntheses employed the Claisen rear-
rangement to introduce the alkyl chain, and were rendered more
concise by the use of a microwave-assisted combined Mit-
sunobu-Claisen rearrangement sequence. Hence primin (2-
methoxy-6-pentyl-1,4-benzoquinone) was obtained from 2-meth-
oxyphenol in four reaction steps with a total reaction time of
60 min in an overall yield of 43%.17 We now report the use of
similar methodology in the first synthesis of N-(3-carboxyl-
propyl)-5-amino-2-hydroxy-3-tridecyl-1,4-benzoquinone 2.
The synthesis started with 2,5-dimethoxyphenol that was
reacted with 1-tridecen-3-ol with triphenylphosphine and di-
isopropyl azodicarboxylate (DIAD) in toluene at 220 °C under
microwave irradiation for 20 min to give the alkylated phenol
7 as an inconsequential mixture of E/Z-isomers in moderate
yield. Although both steps of this processsthe Mitsunobu
reaction18,19 and Claisen rearrangement20-23sare known to be
microwave accelerated, they had never been combined in a
single pot until our original work.17 In the present case, carrying
out the conversion as two separate operations resulted in lower
yield. The alkene mixture was reduced by using microwave-
assisted catalytic transfer hydrogenation24,25 to give the required
tridecylphenol 8 in essentially quantitative yield. Oxidation with
oxygen in the presence of salcomine26,27 gave the 3-alkyl-2,5-
dimethoxy-1,4-benzoquinone 9 (72%) (Scheme 1). Selective
hydrolysis of the 2-methoxy group gave the corresponding
2-hydroxyquinone 10, the regiochemistry in the hydrolysis of
such dimethoxyquinones (vinylogous methyl esters) being
rationalized by the relative stability of the enolate intermediate.28
Quinone 10 (O-methylrapanone) also occurs naturally, and as
an aside, was converted into rapanone 3 itself by hydrolysis of
the remaining methoxy group under more forcing conditions.
In both cases, the spectroscopic data matched those of the natural
products. Finally, quinone 10 was converted into the new
naturally occurring quinone 2. Direct reaction with GABA gave
a complex mixture, and therefore the tert-butyl ester of GABA
was used in the addition-elimination sequence to give the
desired quinone 11, deprotection of which under basic
conditionssthe more normal acid mediated cleavage of the tert-
butyl ester giving less satisfactory resultssgave the natural
product N-(3-carboxylpropyl)-5-amino-2-hydroxy-3-tridecyl-1,4-
benzoquinone structure 2 (Scheme 1). This short synthesis
illustrates the versatility of the Mitsunobu-Claisen rearrange-
ment protocol in routes to naturally occurring benzoquinones.
(13) Danheiser, R. L.; Cha, D. D. Tetrahedron Lett. 1990, 31, 1527.
(14) Stahl, P.; Waldmann, H. Angew. Chem., Int. Ed. 1999, 38, 3710.
(15) MacKenzie, A. R.; Moody, C. J.; Rees, C. W. J. Chem. Soc., Chem.
Commun. 1983, 1372.
(16) Davis, C. J.; Hurst, T. E.; Jacob, A. M.; Moody, C. J. J. Org. Chem.
2005, 70, 4414.
(17) Jacob, A. M.; Moody, C. J. Tetrahedron Lett. 2005, 46, 8823.
(18) Steinreiber, A.; Stadler, A.; Mayer, S. F.; Faber, K.; Kappe, C. O.
Tetrahedron Lett. 2001, 42, 6283.
(19) Lampariello, L. R.; Piras, D.; Rodriquez, M.; Taddei, M. J. Org.
Chem. 2003, 68, 7893.
Experimental Section
Commercially available reagents and solvents were used through-
out without further purification, except for tetrahydrofuran, dichlo-
romethane, and diethyl ether, which were freshly distilled. Light
petroleum refers to the fraction with bp 40-60 °C. Thin layer
chromatography was carried out on aluminum foil backed plates.
The plates were visualized under UV light or by vanillin stain. Flash
chromatography was carried out on silica gel, with the eluent
specified. IR spectra were recorded as solutions with chloroform
as solvent. 1H and 13C NMR spectra were recorded at 400 and 500
MHz (13C frequencies 100 and 125 MHz, respectively); chemical
shifts are quoted in ppm. In the 13C spectra, signals corresponding
to C, CH, CH2, or CH3 groups, as assigned from DEPT, are noted.
3,6-Dimethoxy-2-(tridec-2-enyl)phenol 7. A 35 mL sealable
microwave reactor vessel was charged with a solution of tridec-
1-en-3-ol (400 mg, 2.02 mmol) in toluene (10 mL). To that
(20) Giguere, R. J.; Bray, T. L.; Duncan, S. M.; Majetich, G. Tetrahedron
Lett. 1986, 27, 4945.
(21) Bagnell, L.; Cablewski, T.; Strauss, C. R.; Trainor, R. W. J. Org.
Chem. 1996, 61, 7355.
(22) Baxendale, I. R.; Lee, A. L.; Ley, S. V. J. Chem. Soc., Perkin Trans.
2002, 1, 1850.
(23) Kotha, S.; Mandal, K.; Deb, A. C.; Banerjee, S. Tetrahedron Lett.
2004, 45, 9603.
(24) Banik, B. K.; Barakat, K. J.; Wagle, D. R.; Manhas, M. S.; Bose,
A. K. J. Org. Chem. 1999, 64, 5746.
(25) Berthold, H.; Schotten, T.; Honig, H. Synthesis 2002, 1607.
(26) DeJong, C. R. H. I.; Hageman, H. J.; Hoentjen, G.; Mus, W. J.
Organic Syntheses; Wiley: New York, 1988; Collect. Vol. VI, p 412.
(27) Parker, K. A.; Taveras, D. In Encyclopedia of Reagents for Organic
Synthesis; John Wiley & Sons Ltd: Chichester, UK, 1995; Vol. 6, p 4423.
(28) Ling, T.; Poupon, E.; Rueden, E. J.; Theodorakis, E. A. Org. Lett.
2002, 4, 819.
J. Org. Chem, Vol. 72, No. 26, 2007 10299

solution was added 2,5-dimethoxyphenol (560 mg, 3.63 mmol),
triphenylphosphine (952 mg, 3.63 mmol) and DIAD (715 µL, 3.63
mmol). The reaction mixture was irradiated in a CEM Discover
microwave reactor to 220 °C for 20 min. After cooling to room
temperature the solvent was removed and the residue was subjected
to flash chromatography, eluting with 10% ether in light petroleum,
to give the title compound (300 mg, 44%) as a mixture of geometric
isomers and as a clear oil; Rf 0.69 (25% ether in light petroleum);
The mixture was extracted with dichloromethane (3 × 10 mL).
The combined organic phases were dried over MgSO4, the solvent
was evaporated, and the residue was subjected to flash chroma-
tography, eluting with 25% ether in light petroleum, to give the
title compound (28.3 mg, 74%) as a yellow/orange solid; mp 74-
76 °C (lit.11 mp 87-88 °C); Rf 0.33 (50% ether in light petroleum);
UV (EtOH) λmax/nm 207 (log ꢀ 3.78), 286 (4.00), 416 (2.58); IR
(CHCl3) νmax/cm-1 3352, 2926, 2854, 1644, 1609, 1390, 1355,
1
1
IR (CHCl3) νmax/cm-1 3536, 2920, 2854, 1462, 1097, 1080; H
1319; H NMR (500 MHz; CDCl3) δ 7.22 (1 H, s), 5.84 (1 H, s),
3.86 (3 H, s), 2.44 (2 H, dd, J ) 7.5, 7.5 Hz), 1.47-1.25 (22 H),
0.88 (3 H, app t, J ) 7.0 Hz); 13C NMR (125 MHz; CDCl3) δ
182.9 (C), 181.8 (C), 161.2 (C), 151.6 (C), 119.3 (C), 102.2 (CH),
56.8 (CH3), 32.0 (CH2), 29.7-28.1 (9 × CH2), 22.78 (CH2), 22.72
(CH2), 14.2 (CH3); HRMS (ESI+) found (MH+) 337.2361, C20H33O4
requires 337.2379.
NMR (400 MHz; CDCl3) δ Major isomer 6.66 (1 H, d, J ) 8.8
Hz), 6.35 (1 H, d, J ) 8.8 Hz), 5.71 (1 H, s), 5.60-5.44 (2 H, m),
3.85 (3 H, s), 3.77 (3 H, s), 3.37 (2 H, d, J ) 6.0 Hz), 1.96 (2 H,
q, J ) 6.8 Hz), 1.39-1.25 (16 H, m), 0.89 (3 H, app t, J ) 6.8
Hz); Minor isomer 6.79 (1 H, d, J ) 8.8 Hz), 6.54 (1 H, s), 6.14
(1 H, d, J ) 8.8 Hz), 5.86-5.73 (2 H, m), 4.53 (2 H, d, J ) 6.0
Hz), 3.84 (3 H, s), 3.76 (3 H, s), 2.07 (2 H, ddd, J ) 7.2, 7.2, 6.8
Hz), 1.39-1.25 (16 H, m), 0.89 (3 H, app t, J ) 6.8 Hz); 13C NMR
(100 MHz; CDCl3) δ Major isomer 152.5 (C), 144.2 (C), 141.2
(C), 130.8 (CH), 127.3 (CH), 116.1 (C), 107.9 (CH), 101.1 (CH),
69.7 (CH2), 56.3 (CH3), 56.0 (CH3), 31.9 (CH2), 29.6 (CH2), 29.54
(CH2), 29.51 (CH2), 29.3 (CH2), 29.2 (CH2), 28.9 (CH2), 26.5 (CH2)
22.7 (CH2), 14.1 (CH3); the following signals were observed for
the Minor isomer 136.0 (CH), 124.6 (CH), 112.2 (CH), 103.3 (CH),
56.5 (CH3), 55.6 (CH3), 32.6 (CH2); HRMS (ESI+) found (MH+)
335.2581, C21H35O3 requires 335.2586.
3,6-Dimethoxy-2-tridecylphenol 8. To a solution of 3,6-
dimethoxy-2-(tridec-2-enyl)phenol 7 (20.0 mg, 0.06 mmol) in
methanol (3 mL) was added ammonium formate (20.0 mg, 0.30
mmol) and Pd/C (10 mg). The mixture was irradiated in a CEM
Discover microwave reactor with a reflux condenser attached at
15 W and 65 °C for 15 min. The reaction mixture was filtered
through a plug of Celite and the solvent was removed. The residue
was subjected to flash chromatography, eluting with 10% ether in
light petroleum, to give the title compound (20 mg, 99%) as a clear
oil; Rf 0.69 (25% ether in light petroleum); IR (CHCl3) νmax/cm-1
3539, 2926, 2854, 1489, 1123, 1092; 1H NMR (500 MHz; CDCl3)
δ 6.64 (1 H, d, J ) 8.7 Hz), 6.34 (1 H, d, J ) 8.7 Hz), 5.70 (1 H,
s), 3.85 (3 H, s), 3.78 (3 H, s), 2.66 (2 H, dd, J ) 8.0, 7.5 Hz),
1.58-1.22 (22 H, m), 0.90 (3 H, app t, J ) 7.0 Hz); 13C NMR
(125 MHz; CDCl3) δ 152.8 (C), 144.3 (C), 141.1 (C), 118.2 (C),
107.5 (CH), 100.9 (CH), 56.4 (CH3), 55.9 (CH3), 32.0 (CH2), 29.97
(CH2), 29.92 (CH2), 29.82 (CH2), 29.81 (CH2), 29.78 (CH2), 29.76
(CH2), 29.70 (CH2), 29.4 (CH2), 29.2 (CH2), 23.4 (CH2), 22.8 (CH2),
14.2 (CH3); HRMS (ESI+) found (MH+) 337.2718, C21H37O3
requires 337.2742.
2,5-Dihydroxy-3-tridecyl-1,4-benzoquinone (rapanone) 3. Aque-
ous sodium hydroxide (2 M; 1 mL) was added to a solution of
5-O-methylrapanone 10 (15.0 mg, 0.045 mmol) in ethanol (2 mL).
The mixture was heated to 70 °C for a period of 2 h and allowed
to cool to room temperature. The reaction mixture was diluted with
hydrochloric acid (2 M; 5 mL) then extracted with ethyl acetate (3
× 5 mL). The combined organic phases were dried over MgSO4
and the solvent was evaporated to give the title compound (12.8
mg, 89%) as an orange solid; mp 139-140 °C (methanol) (lit.29
mp 141-142 °C); Rf 0.0 (50% ether in light petroleum); UV (EtOH)
λ
max/nm 206 (log ꢀ 4.09), 290 (4.11); IR (CHCl3) νmax/cm-1 3357,
2926, 2854, 1640, 1364; 1H NMR (500 MHz; CDCl3) δ 7.68 (2 H,
br s), 6.01 (1H, s), 2.45 (2 H, dd, J ) 8.0, 7.5 Hz), 1.49-1.26 (22
H, m), 0.89 (3 H, app t, J ) 7.0 Hz); HRMS (ESI-) found (M -
H+•) 321.2071, C19H29O4 requires 321.2066.
N-(3-tert-Butoxycarbonylpropyl)-5-amino-2-hydroxy-3-tri-
decyl-1,4-benzoquinone 11. To a solution of 5-O-methylrapanone
10 (7.0 mg, 0.0208 mmol) in ethanol (1 mL) was added a solution
of tert-butyl 4-aminobutyrate hydrochloride (12.2 mg, 0.063 mmol)
and potassium tert-butoxide (7.0 mg, 0.063 mmol) in ethanol (1
mL). The mixture was stirred at room temperature for 20 h, diluted
with hydrochloric acid (2 M; 10 mL), and extracted with dichlo-
romehane (4 × 10 mL). The combined organic phases were dried
over MgSO4, the solvent was evaporated, and the residue was
subjected to flash chromatography, eluting with 25% ether in
light petroleum, to give the title compound (7.9 mg, 82%) as a
purple solid; mp 82-85 °C; Rf 0.62 (50% ether in light petrol-
eum); UV (EtOH) λmax/nm 210 (log ꢀ 4.39), 317 (4.35), 499
(3.33); IR (CHCl3) νmax/cm-1 3696, 3358, 2927, 2854, 1721, 1649,
1597, 1394; 1H NMR (500 MHz; CDCl3) δ 8.05 (1 H, br s),
6.55 (1 H, br s), 5.37 (1 H, s), 3.21 (2 H, dd, J ) 13.0, 7.0 Hz),
2.39 (2 H, dd, J ) 7.0, 7.0 Hz), 2.33 (2 H, t, J ) 7.0 Hz), 1.95 (2
H, pent, J ) 7.0 Hz), 1.46 (9 H, s), 1.30-1.25 (22 H, m), 0.88 (3
H, app t, J ) 7.0 Hz); 13C NMR (125 MHz; CDCl3) δ 182.5 (C),
178.9 (C), 172.0 (C), 155.0 (C), 149.8 (C), 115.8 (C), 91.8 (CH),
81.1 (C), 42.3 (CH2), 32.7 (CH2), 32.0 (CH2), 29.77-29.45 (9 ×
CH2), 28.2 (CH3), 23.4 (CH2), 22.78 (CH2), 22.73 (CH2), 14.2
(CH3); HRMS (ESI+) found (MH+) 464.3394, C27H46NO5 requires
464.3376.
N-(3-Carboxypropyl)-5-amino-2-hydroxy-3-tridecyl-1,4-ben-
zoquinone 2. To a solution of N-(3-tert-butoxycarbonylpropyl)-5-
amino-2-hydroxy-3-tridecyl-1,4-benzoquinone 11 (9.0 mg, 0.019
mmol) in ethanol (3 mL) was added aqueous sodium hydroxide (2
M; 1 mL). The mixture was stirred at 80 °C for 2 h, cooled to
room temperature, and acidified with hydrochloric acid (2 M; 2
mL). The ethanol was evaporated and the aqueous residue was
extracted with ethyl acetate (4 × 5 mL). The combined organic
phases were dried over MgSO4, and the solvent was evaporated.
Preparative TLC, eluting with 10% MeOH in dichloromethane, gave
the title compound (6.0 mg, 76%) as a red solid; mp 177-180 °C
(lit.2 mp not given); UV (MeOH) λmax/nm 326 (log ꢀ 3.92), 500
2,5-Dimethoxy-3-tridecyl-1,4-benzoquinone 9. To a solution
of 3,6-dimethoxy-2-tridecylphenol 8 (20.0 mg, 0.06 mmol) in
acetonitrile (2 mL) was added salcomine (5.8 mg, 0.018 mmol)
and the mixture was stirred overnight open to the air. The solvent
was evaporated and the residue was subjected to flash chromatog-
raphy, eluting with 25% ether in light petroleum, to give the title
compound (14.9 mg, 72%) as a yellow solid; mp 56-57 °C (lit.11
mp 54-55 °C); Rf 0.25 (25% ether in light petroleum); UV (MeOH)
λ
max/nm 209 (log ꢀ 3.86), 286 (3.92), 369 (2.72); IR (CHCl3) νmax/
cm-1 2927, 2854, 1652, 1596, 1458, 1325, 1048; H NMR (500
MHz; CDCl3) δ 5.73 (1 H, s), 4.05 (3 H, s), 3.80 (3 H, s), 2.43 (2
H, dd, J ) 7.5, 7.5 Hz), 1.43-1.17 (22 H, m), 0.88 (3 H, app t, J
) 7.0 Hz); 13C NMR (125 MHz; CDCl3) δ 183.6 (C), 182.4 (C),
158.8 (C), 155.9 (C), 130.8 (C), 105.4 (CH), 61.3 (CH3), 56.4 (CH3),
31.9 (CH2), 29.7-28.7 (9 × CH2), 23.1 (CH2), 22.7 (CH2), 14.1
(CH3); HRMS (ESI+) found (MH+) 351.2524, C21H35O4 requires
351.2535.
1
2-Hydroxy-5-methoxy-3-tridecyl-1,4-benzoquinone (5-O-meth-
ylrapanone) 10. To a solution of 2,5-dimethoxy-3-tridecyl-1,4-
benzoquinone 9 (40.0 mg, 0.114 mmol) in a mixture of methanol:
THF (1:1; 2 mL) was added water (1 mL) and potassium hydroxide
(19 mg, 0.34 mmol). The mixture was stirred at room temperature
for 1 h and was then diluted with hydrochloric acid (2 M; 10 mL).
(29) Shah, V.; Sunder, R.; Desouza, N. J. J. Nat. Prod. 1987, 50, 730.
10300 J. Org. Chem., Vol. 72, No. 26, 2007

(2.74); IR (CHCl3) νmax/cm-1 3620, 3409, 2926, 2854, 1682, 1573,
(CH2), 22.0 (CH2), 14.0 (CH3); HRMS (ESI+) found (MH+)
408.2737, C23H38NO5 requires 408.2750.
1
1455, 1370, 1139; H NMR (500 MHz; DMSO-d) δ 7.80 (1 H,
br s), 5.31 (1 H, s), 3.24-3.17 (2 H, m), 2.31-2.21 (4 H, m),
1.79-1.75 (2 H, m), 1.37-1.26 (22 H, m), 0.88 (3 H, app t, J )
7.0 Hz); 13C NMR (125 MHz; DMSO-d) δ 182.5 (C), 178.4 (C),
174.1 (C), 156.7 (C), 149.3 (C), 115.7 (C), 91.7 (CH), 31.3 (CH2),
30.9 (CH2), 29.0-28.7 (9 × CH2), 27.6 (CH2), 22.7 (CH2), 22.1
Supporting Information Available: Copies of 1H and 13C NMR
spectra of compounds 7-11, 3, and 2. This material is available
free of charge via the Internet at http://pubs.acs.org.
JO702101W
J. Org. Chem, Vol. 72, No. 26, 2007 10301