HETEROCYCLES

Paper | Regular issue | Vol. 85, No. 2, 2012, pp. 333-343
Received, 26th October, 2011, Accepted, 8th December, 2011, Published online, 12th December, 2011.
DOI: 10.3987/COM-11-12378

■ One-Pot Synthesis of Macrocyclic Di- and Tetralactones Using [2+2] Photocycloaddition Reactions of Di-2-pyrones with α,ω-Diolefins

Hui Min Zhang, Kazuya Kawabata, Hideki Miyauchi, and Tetsuro Shimo*

Department of Applied Chemistry and Chemical Engineering, Faculty of Engineering, Kagoshima University, Korimoto, Kagoshima 890, Japan

Abstract

Sensitized photocycloaddition reactions of 6,6’-dimethyl-4,4’-[1,4-bis(methylenoxy)phenylene]-di-pyrone (1) with poly(ethyleneglycol)divinyl ethers (2a, b) or 2,2’-dimethyltrimethylene dimethacrylate (4), together with the reactions of 6,6’-dimethyl-4,4’-polymethylenedioxy-2-pyrones (6a, b) with 4 were described. The reactions of 1 with 2a, b gave crown ether type macrocyclic compounds (3a and 3a’ (isomer of 3a), 3b and 3b’ (isomer of 3b)) possessing 19- and 22-membered rings across the C3−C4 and C3’−C4’ double bonds in 1, respectively. Similar reactions of 1 with 4 and 6a, b with 4 afforded different types of macrocycles (5 and 5’, 7a, b and 7a’, b’) having 19- to 21-membered rings across the C5−C6 and C5’−C6’ double bonds in 2-pyrone ring. The stereochemical features of 3a’ and 5 were determined by X-ray crystal analysis. The reaction mechanism was inferred by MO methods.

INTRODUCTION
The synthesis of macrocyclic ring systems is an important area in organic chemistry. There are several strategies to prepare macrocyclic compounds, including cyclization, capping and condensation using thermal reactions.1 Photochemical reactions are also an effective approach.2 Although the [2+2] cycloaddition reaction is a useful method in the synthesis of a variety of macrocycles with one or two cyclobutane rings,3 little attention has been paid to the synthesis of macrocyclic compounds from the sequential inter- and intramolecular [2+2] photocycloaddition reactions between substrates possessing two enones and α, ω-diolefins, because of the predicted complications with several reactions. We have recently succeeded in accomplishing a one-pot synthesis of macrocyclic compounds from the sequential inter- and intramolecular [2+2] photocycloadditions of di-2-pyrones with α,ω-diolefins,4 together with an MO analysis that the origin of a remarkable change in regioselectivities of the inter- and intramolecular photocycloadditions.5 We planned to extend the one-pot synthesis of macrocyclic compounds to di-2-pyrone tethered by the p- position of the benzene ring (1) and polymethylenedioxy-di-2-pyrones (6a, b) to investigate the generality of the sequential inter- and intramolecular photoreactions with electron-rich and electron-poor α,ω-diolefins (2a, b and 4) .

RESULTS AND DISCUSSION
p-Di-2-pyrone (1) was prepared from dehydrochlorination of 4-hydroxy-6-methyl-2-pyrone with 1,4-bis(chloromethyl)benzene using 1,8-diazabicyclo[5.4.0]-7-undecene in 30% yield. Polymethylene-dioxy-di-2-pyrones (6a, b) were prepared according to the method previously described in the literature.6　A solution of 1 (20 mM) with two equivalents of di(ethyleneglycol)divinyl ether (2a) in acetonitrile was irradiated in the presence of benzophenone as a sensitizer with a 300 W high-pressure mercury lamp using a UV cutoff filter under 320 nm and under a nitrogen atmosphere. The reaction was followed by TLC and 24 h irradiation was required to fully convert the entire starting compound 1. An amount of two equivalents of 2a was required because of the polymerization of 2a by irradiation. After removal of the solvent, the oily residue was chromotographed by silica gel (eluent: ethyl acetate/hexane = 2:1, v/v) to afford a mixture of 3a and 3a’ (1:1) (3,4-3,4-[2+2] cycloadducts) in 20% yield, which were the major products from 1H NMR spectra of the reaction mixture, together with a complex mixture that we were unable to isolate (Scheme 1).

The isomers of 3a and 3a’, having C2 symmetry and Cs symmetry, respectively, were separated by recrystallization from acetonitrile/chloroform (2:1, v/v). The structure of 3a’ was confirmed as the regioselective [2+2] cycloadduct, 4,17-dimethyl-3,7,14,18,23,26,29-heptaoxahexacyclo- [29.29,12.0.01,6.06,30.015,20.015,22]tritriaconta-4,9,11,16,32-pentaen-2,19-dione (22-exo, 30-exo adduct), across the C3-C4 and C3’-C4’ double bonds in 1 with two olefin parts in 2a by X-ray crystallographic analysis (Figure 1). The ORTEP drawing of 3a’ shows a 19-membered ring structure with two cyclobutane rings. Another product 3a was estimated as the facial selective isomer at the C3−C4 and C3’-C4’ double bonds in 1 with 2a because this compound gave similar 1H NMR spectral data as acquired for 3a’. The stereochemistry of 3a’ in each cyclobutane ring was the exo conformation between 3,4-dihydropyrone ring and the alkoxy group, as determined from the X-ray structural analysis. The result of the similar photoreaction of 1 with 2b is summarized in Table 1. The stereochemistry of each product (3b, 3b’) was estimated to be C2 symmetry and Cs symmetry, respectively, from the comparison of the 1H NMR data with those of 3a and 3a’.

Photoreaction of 1 with 2, 2’-dimethyltrimethylene dimethacrylate (4) was also carried out in the same reaction conditions mentioned above. After removal of the solvent, the oily residue was chromatographed by silica gel (eluent: ethyl acetate/hexane = 2:1, v/v) to afford a 1:1 mixture of 5 and 5’ (exo-exo 5,6-5,6-[2+2] cycloadducts) in 30% yield. Compounds 5 and 5’ were separated by fractional recrystallization from acetonitrile. The structure of 5 was confirmed as the regioselective [2+2] cycloadduct, 2,19,21,25,25,29-hexamethyl-3,7,14,18,23,27-hexaoxahexacyclo-[27.230,31.12,29.119,21.0.01,6. 015,20]nonacosa-5,9,11,15,30-pentaen-4,17,22,28-tetraone (21-exo, 29-exo adduct, C2 symmetry), across the C5−C6 and C5’−C6’-double bonds in 1 with two olefin parts in 4 by X-ray crystallographic analysis (Figure 2).

The ORTEP drawing of 5 shows the 21-membered ring structure. Another product 5’ was estimated as the facial selective isomer (Cs symmetry) at the C5−C6 and C5’−C6’ double bonds in 1 with 4 because these compounds showed similar spectral properties to the NMR data of 5. The chemical shifts of the methyl groups at the 25-position of 5 and 5’ showed δ 0.44 (5), δ 0.26 and 0.52 (5’), respectively, owing to the shielding effect of the benzene ring in 5 and 5’. Photoreaction of 6a (n=5) with 4 was also carried out in the same reaction conditions mentioned above. After removal of the solvent, the oily residue was chromatographed by silica gel (eluent: ethyl acetate/hexane = 3:1, v/v) to afford a 1:1 mixture of 7a and 7a’ (exo-exo 5,6-5,6-[2+2] cycloadducts) in 23% yield (Scheme 2). Product 7a was isolated by recrystallization from acetonitrile, but unfortunately it was hard to obtain as a single crystal. The structure of 7a was estimated as the regioselective [2+2] cycloadduct, 2,18,20,24,24,28-hexamethyl-3,7,13,17,22, 26-hexaoxapentacyclo-[26.12,28.118,20.0.01,6.014,19]octacosa-5,14-dien-4,16,21,27-tetraone (20-exo, 27-exo adduct, C2 symmetry) from the comparison of the 1H-NMR spectral data with 5 and 5’. Another product 7a’ was estimated as the facial selective isomer (Cs symmetry). The result of the similar photoreaction of 6b (n=6) with 4 is summarized in Table 1. Unfortunately a mixture of [2+2] cycloadducts 7b and 7b’ were difficult to isolate despite many crystallization trials. Since the yields of the macrocyclic compounds 3, 5, 7 were relatively low (20−30%), we considered the formation of the other stereoisomers of the macrocycles possessing two cyclobutane rings, oxetanes between di-2-pyrones and benzophenone (sensitizer),7 and inter- or intramolecular [2+2] photocycloadducts of di-2-pyrones6 in this system.

We next describe the photocycloaddition mechanism using the PM5 level.8 Figure 3 shows energies and coefficients of the higher singly occupied molecular orbital (HSOMO) and lower ones (LSOMO) of the triplet states by means of the PM5 level, and those of the LUMO and HOMO of the ground states of two α,ω-diolefins, 2 and 4, by means of the PM5 level. Since these photoadditions were sensitized by a triplet sensitizer (benzophenone), they were inferred to proceed via a two-step radical path, and that the first steps were mainly influenced by the energies and coefficients of the two frontier orbitals, respectively. The reasonable processes via radical intermediates (I and II in Figure 4) are inferred from the narrow gap (Δε) of the energies and the large coefficients (Ci and Cr) between two substrates are quantitatively confirmed by the large two-center frontier orbital interactions in Table 2.

Interactions, (CiCr)2/Δε (in γ2/eV), have a tendency to be larger between C3 (2-pyrone) and Cβ (olefin 2), or C6 (2-pyrone) and Cβ (olefin 4) than others. In the concrete, with 2 having an electron-donating group, the C3-Cβ interactions between the LSOMO and HOMO are larger than others, and with 4 having an electron-withdrawing group, the C6-Cβ interactions between the HSOMO and LUMO are relatively large. The photoreactions of 1 with 2, and 1 or 6 with 4 are strongly supported to go through the respective intermediates (I and II) in Figure 4. In summary, sensitized photocycloaddition reactions of p-di-2-pyrone (1) with electron-rich α,ω-diolefins (2a, b) gave crown ether-type macrocyclic compounds (3a, b) across the C3-C4 and C3’-C4’ double bonds in 1 with two olefin parts in 2a, b, having 19- and 22-memered rings. On the other hand, similar photoreactions of 1 or polymethylene dioxy-di-2-pyrones (6a, b) with electron-poor α,ω-diolefin (4) afforded macrocyclic dioxatetralactones (5 and 7) across the C5-C6 and C5’-C6’ double bonds in 1 or 6 with two olefin parts in 4 having 19- to 21-membered rings. A sequential inter- and intramolecular [2+2] photocycloaddition mechanism in this system was reasonably interpreted by an MO analysis.

EXPERIMENTAL
All melting points were measured on Yanagimoto Melt-tem apparatus and uncorrected. NMR spectra were measured at 400MHz on the JNM GSX-400 (TMS as an internal standard). IR spectra were recorded with a JASCO IR Report-100spectrometer. Mass spectra were recorded with a JEOL JMS-HX110A (FABMS) using m-nitrobenzyl alcohol as matrix. Elemental analysis was made using a Yanaco MT-5. Single crystal X-ray diffraction analyses of 3a’, 5, and 7a were performed on a Rigaku RAXIS-RAPID imaging plate diffractometer with graphite monochromated Mo Kα radiation. Lorentz and polarization corrections were applied to the intensity data. The structures were solved by direct methods using SHELX-979 or SIR 9210 and refined by a full-matrix least-squares method. The non-hydrogen atoms were refined anisotopically. All calculations were performed using the teXsan11 crystallographic soft ware package. Photoirradiations were carried out in the Pyrex tube using 300 W high-pressure mercury lamp. Wakogel C200 was used for preparative column chromatography.
6,6’-Dimethyl-4,4’-[1,4-bis(methylenoxy)phenylene]-di-2-pyrone (1) ….. To a refluxing MeCN (200 mL) solution of 4-hydroxy-6-methyl-2-pyrone (20.0 g, 160 mmol) and DBU (26.2 g, 170 mmol) was slowly added 1,4-bis(chloromethyl)benzene 14.0 g, 80 mmol) and refluxing was continued for 72 h. After cooling to room temperature, the reaction mixture was evaporated in vacuo and the resulting oily residue was dissolved in CHCl3 (200 mL). To the concentrate was added acetic acid and water, and the mixture was stirred for 1 h at room temperature. The mixture was washed with brine, dried with anhydrous magnesium sulfate, and filtered. The filtrate was concentrated to dryness under reduced pressure, and the residue was recrystallized from MeCN to give 1 (8.21 g, 30%).
1: mp 210−212 ºC. 1H NMR (CDCl3) δ 2.22 (6H, s, Me), 5.03 (4H, s, CH2), 5.48, 5.85 (each 2H, d, J = 1.6 Hz, CH), 7.41 (4H, s, Ar-H). IR (KBr) 1710, 1640 cm-1. LR MS m/z 355 (MH+). Anal. Calcd for C20H18O6: C, 67.79, H, 5.12. Found: C, 67.66, H, 5.16).
4,17-Dimethyl-3,7,14,18,23,26,29-heptaoxahexacyclo-[29.29,12.0.01,6.06,30.015,20.015,22]tritriaconta-4,9,11,16,32-pentaen-2,19-dione (22-exo, 30-exo adduct) (3a) (C2 symmetry) and (3a’) (Cs symmetry) ….. To a solution of 1 (1.42 g, 4.00 mmol) with di(ethyleneglycol)divinyl ether (2a) (1.22 g, 8.02 mmol) in MeCN (200 mL) was irradiated in the presence of benzophenone (0.327 g, 1.80 mmol) for 24 h. After removal of the solvent, the oily residue was chromatographed by silica gel (eluent: EtOAc/hexane = 2:1, v/v) to give a mixture of 3a and 3a’ (1:1) (369 mg, 20% yield). Compound 3a’ was separated by recrystallization from a mixture of MeCN and CHCl3 (2:1).
3a: oil. 1H NMR (CDCl3) δ 2.04 (2H, m, CH2), 2.05 (6H, s, Me), 2.16 (2H, t, J =12.8 Hz, CH2), 3.28-3.40 (2H, m, CH2), 3.48 (2H, t, J = 9.6Hz, CH), 3.59-3.73 (2H, m, CH2), 3.70 (2H, d, J = 5.2 Hz, CH), 4.19 (2H, d, J = 10.8 Hz, CH2), 4.47 (2H, d, J = 10.8 Hz, CH2), 5.06 (2H, s, CH), 7.32 (4H, Ar-H). IR (neat) 1760, 1685 cm-1. LR MS m/z 513 (MH+). HR MS (MH+) calcd for C28H33O9 513.2125. found: 513.2094.
3a’: mp 231−233 ºC. 1H NMR (CDCl3) δ 2.04 (6H, s, Me), 2.09 (2H, ddd, J = 12.4, 9.6, 5.6 Hz, CH2), 2.19 (2H, dd, J = 12.4, 9.6 Hz, CH2), 3.17 (2H, ddd, J = 13.2, 7.6, 5.2 Hz, CH2), 3.28 (2H, ddd, J = 13.2, 7.6, 6.0 Hz, CH2), 3.39 (2H, dt, J = 7.6, 5.2 Hz, CH2), 3.45 (2H, dt, J = 7.6, 6.0 Hz, CH2), 3.59 (2H, t, J = 9.6 Hz, CH), 3.77 (2H, d, J = 5.6 Hz, CH), 4.15 (2H, d, J = 10.0 Hz, CH2), 4.36 (2H, d, J = 10.0 Hz, CH2), 4.95 (2H, s, CH), 7.33 (4H,s, Ar-H). IR (KBr) 1760, 1695 cm-1. LR MS m/z 513 (MH+). Anal. Calcd for C28H32O9: C, 65.61, H, 6.29. Found: C, 65.59, H, 6.15.
X-Ray crystal data for 3a’ (C28H32O9): M = 512.54, crystal dimensions 0.54x0.42x0.38 mm3, orthorhombic, space group Pnma, a = 8.32670(10) Å, b = 31.8091(4) Å, c = 10.0349(2) Å, α = 90 º, β = 90 º, γ = 90 º, V = 2657.89(7) Å3, Z = 4, ρcalc = 1.281 mg/m3, 2θmax = 55.0 º, T = 113(2) K, R = 0.0417, Rw = 0.1190, GOF = 1.162.

4,17-Dimethyl-3,7,14,18,23,26,29,32-octaoxahexacyclo-[32.29,12.0.01,6.06,33.015,20.015,22]hexatriaconta-4,9,11,16,35-pentaen-2,19-dione (22-exo, 33-exo adduct) (3b) (C2 symmetry) and (3b’) (Cs symmetry) ….. To a solution of 1 (0.708 g, 2.00 mmol) with tri(ethyleneglycol)divinyl ether (2b) (0.724 g, 3.58 mmol) in MeCN (200 mL) was irradiated in the presence of benzophenone (0.364 g, 2.00 mmol) for 7 h. After removal of the solvent, the oily residue was chromatographed by silica gel (eluent: EtOAc/hexane = 2:1, v/v) to give a mixture of 3b and 3b’ (1:1) (308 mg, 28% yield). Compounds 3b and 3b’ were separated by recrystallized from a mixture of MeCN and CHCl3 (2:1).
3b: mp 196−199 ºC. 1H NMR (CDCl3) δ 2.04 (6H, s, Me), 2.16 (2H, ddd, J = 12.8, 10.4, 5.6 Hz, CH2), 2.31 (2H, t, J = 12.8 Hz, CH2), 3.40-3.62 (8H, m, CH2), 3.56 (2H, dd, J = 12.8, 10.4 Hz, CH), 3.74 (2H, m, CH2), 3.88 (2H, d, J = 5.6 Hz, CH), 3.99 (2H, m, CH2), 4.12 (2H, d, J = 11.2 Hz, CH2), 4.42 (2H, d, J = 11.2 Hz, CH2), 4.98 (2H, s, CH), 7.33 (4H,s, Ar-H). IR (KBr) 1763, 1689 cm-1. LR MS m/z 557 (MH+). HR MS (MH+) calcd for C30H37O10 557.2387. found: 557.2354. Anal. Calcd for C30H36O10: C, 64.74, H, 6.52. Found: C, 64.56, H, 6.57.
3b’: mp 222−226 º. 1H NMR (CDCl3) δ 2.04 (6H, s, Me), 2.17 (2H, ddd, J = 12.8, 10.4, 5.6 Hz, CH2), 2.31 (2H, t, J = 12.8 Hz, CH2), 3.40-3.63 (8H, m, CH2), 3.59 (2H, dd, J = 12.8, 10.4 Hz, CH), 3.74 (2H, m, CH2), 3.89 (2H, d, J = 5.6 Hz, CH), 3.99 (2H, m, CH2), 4.19 (2H, d, J = 11.2 Hz, CH2), 4.37 (2H, d, J = 11.2 Hz, CH2), 4.94 (2H, s, CH), 7.35 (4H,s, Ar-H). IR (KBr) 1757, 1684 cm-1. LR MS m/z 557 (MH+). HR MS (MH+) calcd for C30H37O10 557.2387. found: 557.2390. Anal. Calcd for C30H36O10: C, 64.74, H, 6.52. Found: C, 64.24, H, 6.62.
2,19,21,25,25,29-Hexamethyl-3,7,14,18,23,27-hexaoxahexacyclo-[27.230,31.12,29.119,21.0.01,6.015,20]nona-cosa-5,9,11,15,30-pentaen-4,17,22,28-tetraone (21-exo, 29-exo adduct) (5) C2 symmetry) and (5’) (Cs symmetry) ….. To a solution of 1 (0.893 g, 2.52 mmol) with 2,2’-dimethyltrimethylene dimethacrylate (4) (1.01 g, 4.21 mmol) in MeCN (200 mL) was irradiated in the presence of benzophenone (0.204 g, 1.12 mmol) for 18 h. After removal of the solvent, the oily residue was chromatographed by silica gel (eluent: EtOAc/hexane = 2:1, v/v) to give a mixture of 5 and 5’ (1:1) (449 mg, 30% yield). A mixture of compounds 5 and 5’ was separated by recrystallized from a mixture of MeCN and CHCl3 (1:1).
5: mp 251−254 ºC. 1H NMR (CDCl3) δ 0.44, 1.37, 1.53 (each 6H, s, Me), 2.25 (2H, d, J = 13.2 Hz, CH2), 2.83 (2H, d, J = 13.2 Hz, CH2), 3.18 (2H, s, CH), 3.57, 3.75 (each 2H, d, J = 10.8 Hz), 4.84, 4.93 (each 2H, d, J = 10.4 Hz), 5.49 (2H, s, CH). IR (KBr) 1730, 1703, 1628 cm-1. LR MS m/z 595 (MH+), Anal. Calcd for C33H38O10·CH3CN: C, 65.79, H, 6.53, N, 1.99. Found: C, 66.10, H, 6.51, N, 2.20.
X-Ray crystal data for 5 (C33H38O10·CH3CN) : M = 635.70, crystal dimensions 0.20 x 0.10 x 0.10 mm3, monoclinic, space group C2/c (#15), a = 33.161(10) Å, b = 9.219(3) Å, c = 11.998(4) Å, β = 108.6990 (19) º, V = 3474.5(18) Å3, Z = 5, ρcalc = 1.454 g/cm3, 2θmax = 55.0 º, T = 123 K, R = 0.0817, Rw = 0.2257, GOF = 1.057.
5’: oil. 1H NMR (CDCl3) δ 0.26 , 0.52 (each 3H, s, Me), 1.41, 1.53 (each 6H, s, Me), 2.26, 2.83 (each 2H, d, J = 13.6 Hz, CH2), 3.16 (2H, s, CH), 3.54, 3.76 (each 2H, d, J = 10.8 Hz, CH2), 4.84, 4.89 (each 2H, d, J = 9.6 Hz, CH2), 5.50 (2H, s, CH), 7.42 (4H, s, Ar-H). IR (KBr) 1720, 1703, 1622 cm-1. LR MS m/z 595 (MH+). HR MS (MH+) calcd for C33H39O10 595.2543. found: 595.2520.

2,18,20,24,24,28-Hexamethyl-3,7,13,17,22,26-hexaoxapentacyclo-[26.12,28.118,20.0.01,6.014,19]octacosa-5,14-dien-4,16,21,27-tetraone (20-exo, 27-exo adduct) (7a) (C2 symmetry) and (7a’) (Cs symmetry) ….. To a solution of 6a (0.640 g, 2.00 mmol) with 4 (0.724 g, 3.00 mmol) in MeCN (100 mL) was irradiated in the presence of benzophenone (0.182 g, 1.00 mmol) for 10 h. After removal of the solvent, the oily residue was chromatographed by silica gel (eluent: EtOAc/hexane = 1:1, v/v) to give a mixture of 7a and 7a’ (1:1) (198 mg, 23% yield). Compound 7a was separated by fractional recrystallization from MeCN.
7a: mp 272−274 ºC. 1H NMR (CDCl3) δ 1.01 (2H, m, CH2), 1.04, 1.33, 1.52 (each 6H, s, Me), 1.76 (4H, m, CH2), 2.32 (2H, d, J = 13.2 Hz, CH2), 2.64 (2H, dd, J = 13.2, 1.2 Hz, CH2), 3.45 (2H, s, CH), 3.80 (2H, d, J = 11.2 Hz, CH2), 3.92 (4H, m, CH2), 4.14 (2H, d, J = 11.2 Hz, CH2), 5.28 (2H, s, CH). IR (KBr) 1731, 1705, 1627 cm-1. LR MS m/z 561 (MH+). HR MS (MH+) calcd for C30H41O10 561.2700. found: 561.2690. Anal. Calcd for C30H40O10: C, 64.23, H, 7.14. Found: C, 64.51, H, 6.95.
7a’: mixture with 7a. 1H NMR (CDCl3) δ 1.01 (2H, m, CH2), 1.04, 1.32, 1.54 (each 6H, s, Me), 1.76 (4H, m, CH2), 2.29 (2H, d, J = 13.2 Hz, CH2), 2.74 (2H, dd, J = 13.2, 1.2 Hz, CH2), 3.37 (2H, s, CH), 3.90 (2H, d, J = 10.8 Hz, CH2), 3.95 (4H, m, CH2), 4.06 (2H, d, J = 10.8 Hz, CH2), 5.28 (2H, s, CH).
2,19,21,25,25,29-Hexamethyl-3,7,14,18,23,27-hexaoxapentacyclo-[27.12,29.119,21.0.01,6.015,20]nonacosa-5,15-dien-4,17,22,28-tetraone (21-exo, 28-exo adduct) (7b) (C2 symmetry) and (7b’) (Cs symmetry) ….. To a solution of 6b (0.670 g, 2.00 mmol) with 4 (0.723 g, 3.00 mmol) in MeCN (100 mL) was irradiated in the presence of benzophenone (0.180 g, 1.00 mmol) for 24 h. After removal of the solvent, the oily residue was chromatographed by silica gel (eluent: EtOAc/hexane = 1:1, v/v) to give a mixture of 7b and 7b’ (1:1) (215 mg, 25% yield), whose compounds were difficult to separate each other by recrystallization.
7b and 7b’ (1:1 mixture): 1H NMR (CDCl3) δ 1.00 (4H, m, CH2), 1.04, 1.36, 1.53 (each 6H, s, Me), 1.73 (4H, m, CH2), 2.27 (2H, d, J = 13.2 Hz, CH2), 2.78 (2H, d, J = 13.2 Hz, CH2), 2.80 (2H, d, J = 13.2 Hz, CH2), 3.30 (2H, s, CH), 3.90 (4H, m, CH2), 4.05, 4.07 (4H, d, J = 11.2 Hz, CH2), 5.29 (2H, s, CH). IR (KBr) 1713, 1631 cm-1. LR MS m/z 575 (MH+). HR MS (MH+) calcd for C31H43O10 575.2856. found: 575.2845.

ACKNOWLEDGEMENT
The authors are grateful to Professor Shinmyozu (Institute for Materials Chemistry and Engineering, Kyushu University) for the measurements of the single crystal X-ray diffraction.

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