Iodoarene-Mediated α-Tosyloxylation of Ketones with MCPBA and p-Toluenesulfonic Acid

Abstract

Alkyl aryl ketones and dialkyl ketones could be converted into the corresponding α-tosyloxy ketones by the reaction with MCPBA and p-toluenesulfonic acid monohydrate (PTSA˙H₂O) in the presence of a catalytic amount of molecular iodine (I₂) in a mixture of acetonitrile and 2,2,2-trifluoroethanol, although the yields were dependent on the ketones (method A). The same conversion of alkyl aryl ketones and dialkyl ketones into the corresponding α-­tosyloxy ketones could be smoothly carried out by the reaction with MCPBA and PTSA˙H₂O in the presence of catalytic amounts of ­iodine and tert-butylbenzene in a mixture of acetonitrile and 2,2,2-trifluoroethanol (method B). In those reactions, p-iodotoluene and 4-tert-butyl-1-iodobenzene were formed at first in method A and method B, respectively, and then they were converted into p-[(hydroxy)(tosyloxy)]iodotoluene and 4-tert-butyl-1-[(hydroxy)(tosyloxy)iodo]benzene by the reaction with MCPBA and PTSA˙H₂O. p-[(Hydroxy)(tosyloxy)]iodotoluene and 4-tert-butyl-1-[(hydroxy)-(tosyloxy)iodo]benzene worked as an α-tosyloxylation reagent of ketones.

molecular iodine - tert-butylbenzene - MCPBA - α-tosyl­oxy ketone - ketone - p-toluenesulfonic acid - catalyst

References and Notes

Reviews:

1a Moriarty RM. Vaid RK. Koser GF. Synlett  1990,  365 

1b Koser GF. Aldrichimica Acta  2001,  34:  89 

1c Prakash O. Saini N. Sharma PK. Heterocycles  1994,  38:  409 

Papers:

1d Neilands O. Karele B. J. Org. Chem. USSR  1970,  6:  885 

1e Koser GF. Wettach RH. Troup JM. Frenz BA. J. Org. Chem.  1976,  41:  3609 

1f Koser GF. Wettach RH. J. Org. Chem.  1977,  42:  1476 

1g Koser GF. Wettach RH. Smith CS. J. Org. Chem.  1980,  45:  1543 

1h Koser GF. Relenyi AG. Kalos AN. Rebrovic L. Wettach RH. J. Org. Chem.  1982,  47:  2487 

1i Moriarty RM. Penmasta R. Awasthi AK. Epa WR. Prakash I. J. Org. Chem.  1989,  54:  1101 

1j Moriarty RM. Vaid RK. Hopkins TE. Vaid BK. Prakash O. Tetrahedron Lett.  1990,  31:  201 

1k Tuncay A. Dustman JA. Fisher G. Tuncay CI. Tetrahedron Lett.  1992,  33:  7647 

1l Moriarty RM. Vaid BK. Duncan MP. Levy SG. Prakash O. Goyal S. Synthesis  1992,  845 

1m Prakash O. Goyal S. Synthesis  1992,  629 

1n Prakash O. Rani N. Goyal S. J. Chem. Soc., Perkin Trans. 1  1992,  707 

1o Prakash O. Saini N. Sharma PK. Synlett  1994,  221 

1p Vrama RS. Kumar D. Liesen PJ. J. Chem. Soc., Perkin Trans. 1  1998,  4093 

1q Lee JC. Choi Ju.-H. Synlett  2001,  234 

1r Lai P. Taylor MS. Synthesis  2010,  1449 

Monomer reagents:

2a Muraki T. Togo H. Yokoyama M. J. Org. Chem.  1999,  64:  2883 

2b Nabana T. Togo H. J. Org. Chem.  2002,  67:  4362 

2c Misu Y. Togo H. Org. Biomol. Chem.  2003,  1:  1342 

2d Ueno M. Nabana T. Togo H. J. Org. Chem.  2003,  68:  6424 

Polymer reagents:

2e Abe S. Sakuratani K. Togo H. Synlett  2001,  22 

2f Abe S. Sakuratani K. Togo H. J. Org. Chem.  2001,  66:  6174 

2g Sakuratani K. Togo H. ARKIVOC  2003,  (vi):  11 

2h Ueno M. Togo H. Synthesis  2004,  2673 

Reviews:

3a Ochiai M. Miyamoto K. Eur. J. Org. Chem.  2008,  4229 

3b Dohi T. Kita Y. Chem. Commun.  2009,  2073 

3c Uyanik M. Ishihara K. Chem. Commun.  2009,  2086 

Papers:

3d Ochiai M. Takeuchi Y. Katayama T. Sueda T. Miyamoto K. J. Am. Chem. Soc.  2005,  127:  12244 

3e Dohi T. Maruyama A. Yoshimura M. Morimoto K. Tohma H. Kita Y. Angew. Chem. Int. Ed.  2005,  44:  6193 

3f Li J. Chan PWH. Che C. Org. Lett.  2005,  7:  5801 

3g Thottumkara AP. Bowsher MS. Vinod TK. Org. Lett.  2005,  7:  2933 

3h Dohi T. Maruyama A. Minamitsuji Y. Takenaga N. Kita Y. Chem. Commun.  2007,  1224 

3i Richardson RD. Page TK. Altermann S. Paradine SM. French AN. Wirth T. Synlett  2007,  538 

3j Yakura T. Konishi T. Synlett  2007,  765 

3k Sheng J. Li X. Tang M. Gao B. Huang G. Synthesis  2007,  1165 

3l Chen C. Feng X. Zhang G. Zhao Q. Huang G. Synthesis  2008,  3205 

3m Uyanik M. Akakura M. Ishihara K. J. Am. Chem. Soc.  2009,  131:  251 

3n Miyamoto K. Sei Y. Yamaguchi K. Ochiai M. J. Am. Chem. Soc.  2009,  131:  1382 

3o Ojha LR. Kudugunti S. Maddukuri PP. Kommareddy A. Gunna MR. Dokuparthi P. Gottam HB. Botha KK. Parapati DR. Vinod TK. Synlett  2009,  117 

3p Dohi T. Minamitsuji Y. Maruyama A. Hirose S. Kita Y. Org. Lett.  2008,  10:  3559 

3q Uyanik M. Fukatsu R. Ishihara K. Org. Lett.  2009,  11:  3470 

3r Uyanik M. Yasui T. Ishihara K. Bioorg. Med. Chem. Lett.  2009,  19:  3848 

3s Yakura T. Tian Y. Yamauchi Y. Omoto M. Konishi T. Chem. Pharm. Bull.  2009,  57:  252 

3t Dohi H. Takenaga N. Fukushima K. Uchiyama T. Kato D. Shiro M. Fujioka H. Kita Y. Chem. Commun.  2010,  46:  7697 

3u Zagulyaeva AA. Banek CT. Yusubov MS. Zhdankin VV. Org. Lett.  2010,  12:  4644 

3v Thottumkara PP. Vinod TK. Org. Lett.  2010,  12:  5640 

3w Miura T. Nakashima K. Tada N. Itoh A. Chem. Commun.  2011,  47:  1875 

3x Yu Z. Ju X. Wang J. Yu W. Synthesis  2011,  860 

4 Yamamoto Y. Togo H. Synlett  2005,  2486 

5a Yamamoto Y. Togo H. Synlett  2006,  798 

5b Yamamoto Y. Kawano Y. Toy PH. Togo H. Tetrahedron  2007,  63:  4680 

5c Akiike J. Yamamoto Y. Togo H. Synlett  2007,  2168 

5d Moroda A. Togo H. Synthesis  2008,  1257 

5e Ishiwata Y. Togo H. Tetrahedron Lett.  2009,  50:  5354 

5f Suzuki Y. Togo H. Synthesis  2010,  2355 

5g Kawano Y. Togo H. Tetrahedron  2009,  65:  6251 

5h Ishiwata Y. Togo H. Tetrahedron  2009,  65:  10720 

5i Tanaka A. Togo H. Synlett  2009,  3360 

Reviews:

6a Togo H. Iida S. Synlett  2006,  2159 

6b Togo H. J. Synth. Org. Chem.  2008,  66:  652 

Papers:

6c Mori N. Togo H. Synlett  2004,  880 

6d Mori N. Togo H. Synlett  2005,  1456 

6e Mori N. Togo H. Tetrahedron  2005,  61:  5915 

6f Ishihara M. Togo H. Synlett  2006,  227 

6g Iida S. Togo H. Synlett  2006,  2633 

6h Ishihara M. Togo H. Tetrahedron  2007,  63:  1474 

6i Iida S. Togo H. Tetrahedron  2007,  63:  8274 

6j Iida S. Togo H. Synlett  2007,  407 

6k Iida S. Togo H. Synlett  2008,  1639 

6l Iida S. Ohmura R. Togo H. Tetrahedron  2009,  65:  6257 

6m Suzuki Y. Moriyama K. Togo H. Tetrahedron Lett.  2010,  51:  5950 

6n Ushijima S. Togo H. Synlett  2010,  1562 

6o Ohmura R. Takahata M. Togo H. Tetrahedron Lett.  2010,  51:  4378 

6p Ushijima S. Togo H. Synlett  2010,  1067 

6q Ushijima S. Moriyama K. Togo H. Tetrahedron  2011,  67:  958 

7

Typical Procedure for Iodoarene-Mediated α-Tosyl-oxylation of Ketones with MCPBA and p -TsOH˙H ₂ O Method A I₂ (0.1 mmol), p-TsOH˙H₂O (2.1 mmol), and MCPBA (2.2 mmol) were dissolved in a mixture of MeCN (3 mL) and 2,2,2-trifluoroethanol (3 mL) under argon atmosphere. The resulting solution was stirred at r.t. until the color of I₂ faded completely (1-2 h). Then, a solution of acetophenone (1 mmol) in MeCN (2 mL) was added, and the mixture was stirred for 3 h at 60 ˚C under argon atmosphere. After the reaction, the reaction mixture was poured into a solution of sat. aq NaHCO₃ and Na₂SO₃, and the whole was extracted with CHCl₃ (3 × 20 mL). The organic layer was dried over Na₂SO₄. After removal of the solvent under reduced pressure, α-tosyloxyacetophenone was obtained in the crude state. Pure α-tosyloxyacetophenone was obtained in 71% yield (206 mg) by short flash column chromatography on silica gel (EtOAc-hexane = 1:3). Method B To a stirred solution of tert-butylbenzene (0.2 mmol) in a mixture of MeCN (3 mL) and 2,2,2-trifluoroethanol (3 mL) under argon atmosphere were added MCPBA (1.7 mmol),
I₂ (0.1 mmol), and p-TsOH˙H₂O (1.5 mmol). The resulting solution was stirred at r.t. until the color of I₂ faded completely (1-2 h). Then, a solution of acetophenone (1 mmol) in MeCN (2 mL) was added, and the mixture was stirred for 5 h at 60 ˚C under argon atmosphere. After the reaction, the reaction mixture was poured into a solution of sat. aq NaHCO₃ and Na₂SO₃, and the whole was extracted with CHCl₃ (3 × 20 mL). The organic layer was dried over Na₂SO₄. After removal of solvent under reduced pressure, α-tosyloxyacetophenone was obtained in the crude state. Pure α-tosyloxyacetophenone was obtained in 70% yield (204 mg) by short flash column chromatography on silica gel (EtOAc-hexane = 1:3).
α-Tosyloxyacetophenone Mp 90 ˚C (lit.^¹h mp 90-91 ˚C). IR (KBr): 1180, 1360, 1715 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.45 (s, 3 H), 5.27 (s, 2 H), 7.35 (d, J = 8.5 Hz, 2 H), 7.47 (t, J = 8.2 Hz, 2 H), 7.61 (t, J = 8.2 Hz, 1 H), 7.84 (d, J = 8.2 Hz, 2 H), 7.85 (d, J = 8.2 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.67, 69.90, 127.97, 128.13, 128.89, 129.89, 132.57, 133.71, 134.19, 145.28, 190.26.
α-Tosyloxy- p -methylacetophenone Mp 105 ˚C (lit.^¹¹ mp 82-83 ˚C). IR (KBr): 1170, 1350, 1700 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.41 (s, 3 H), 2.45 (s, 3 H), 5.24 (s, 2 H), 7.26 (d, J = 8.1 Hz, 2 H), 7.35 (d, J = 8.2 Hz, 2 H), 7.74 (d, J = 8.1 Hz, 2 H), 7.86 (d, J = 8.2 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.68, 21.77, 69.85, 128.07, 128.14, 129.57, 129.87, 131.24, 132.62, 145.23, 145.28, 189.80.
α-Tosyloxy- p -chloroacetophenone
Mp 123 ˚C (lit.^¹¹ mp 125 ˚C). IR (KBr): 1190, 1360, 1710 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.46 (s, 3 H), 5.21 (s, 2 H), 7.35 (d, J = 8.4 Hz, 2 H), 7.45 (d, J = 8.6 Hz, 2 H), 7.80 (d, J = 8.6 Hz, 2 H), 7.84 (d, J = 8.4 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.71, 69.79, 128.14, 129.28, 129.48, 129.94, 132.05, 132.44, 140.78, 145.43, 189.55.
α-Tosyloxy- p -nitroacetophenone Mp 137 ˚C (lit.^¹¹ mp 130-131 ˚C). IR (KBr): 1180, 1340, 1710 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.47 (s, 3 H), 5.25 (s, 2 H), 7.37 (d, J = 8.3 Hz, 2 H), 7.83 (d, J = 8.3 Hz, 2 H), 8.03 (d, J = 8.9 Hz, 2 H), 8.32 (d, J = 8.9 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.83, 70.04, 117.70, 124.17, 128.26, 129.45, 130.15, 132.32, 138.29, 145.81, 189.87.
α-Tosyloxy- m -nitroacetophenone Mp 129-130 ˚C. IR (KBr): 1615, 1375, 1348, 1188 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.46 (s, 3 H), 5.25 (s, 2 H), 7.37 (d, J = 8.0 Hz, 2 H), 7.72 (t, J = 8.0 Hz, 1 H), 7.84 (d, J = 8.0 Hz, 2 H), 8.21 (dt, J = 8.0, 1.2 Hz, 1 H), 8.46 (dt, J = 8.0, 1.2 Hz, 1 H), 8.63 (t, J = 1.2 Hz, 1 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 30.38, 69.87, 123.05, 128.15, 128.25, 130.03, 130.25, 132.35, 133.72, 135.29, 144.70, 145.88, 188.82. ESI-HRMS: m/z calcd for C₁₅H₁₃O₆NSNa [M + Na]: 358.0356; found: 358.0347.
α-Tosyloxypropiophenone Mp 68 ˚C (lit.^¹¹ mp 68-69 ˚C). IR (KBr): 1170, 1370, 1700 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 1.60 (d, J = 7.0 Hz, 3 H), 2.41 (s, 3 H), 5.79 (q, J = 7.0 Hz, 1 H), 7.29 (d, J = 8.1 Hz, 2 H), 7.46 (t, J = 7.2 Hz, 2 H), 7.75 (d, J = 7.2 Hz, 2 H), 7.88 (d, J = 8.1 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 18.84, 21.74, 128.04, 128.84, 129.85, 133.51, 133.77, 133.93, 143.48, 143.69, 145.10, 194.93.
α-(Tosyloxy)octyl Phenyl Ketone Mp 59-61 ˚C (lit.^²d mp 59-61 ˚C). IR (neat): 1180, 1340, 1700 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 0.86 (t, J = 6.9 Hz, 3 H), 1.20-1.43 (m, 10 H), 1.84-1.91 (m, 2 H), 2.40 (s, 3 H), 5.59 (dd, J = 8.2, 4.8 Hz, 1 H), 7.24 (d, J = 8.0 Hz, 2 H), 7.45 (t, J = 7.5 Hz, 2 H), 7.59 (t, J = 7.5 Hz, 1 H), 7.74 (d, J = 8.2 Hz, 2 H), 7.86 (d, J = 8.2 Hz, 2 H).
Tosyloxymethyl Naphthyl Ketone
Oil (lit.^¹²). IR (neat): 1176, 1365, 1700 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.40 (s, 3 H), 5.27 (s, 2 H), 7.29 (d, J = 8.4 Hz, 2 H), 7.50 (t, J = 8.3 Hz, 1 H), 7.53-7.60 (m, 2 H), 7.78 (dd, J = 1.2, 7.4 Hz, 1 H), 7.81 (d, J = 8.3 Hz, 2 H), 7.87 (d, J = 7.8 Hz, 1 H), 8.04 (d, J = 8.3 Hz, 1 H), 8.48 (dd, J = 0.9, 8.3 Hz, 1 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.65, 70.99, 124.13, 125.35, 126.82, 128.08, 128.34, 128.44, 128.50, 129.87, 130.16, 131.28, 132.60, 133.91, 134.05, 145.24, 193.91.
2,4,6-Trimethylphenyl (Tosyloxy)methyl Ketone Mp 58 ˚C. IR (neat): 1191, 1377, 1608 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.12 (s, 6 H), 2.27 (s, 3 H), 2.45 (s, 3 H), 4.84 (s, 2 H), 6.81 (s, 2 H), 7.33 (d, J = 8.0 Hz, 2 H), 7.87 (d, J = 8.0 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 18.96, 21.08, 21.65, 72.28, 128.05, 128.61, 129.81, 132.70, 133.83, 134.70, 139.82, 145.19, 201.17. ESI-HRMS: m/z calcd for C₁₈H₂₁O₄SNa [M + Na]: 355.0980; found: 355.0946.
2-Furyl (Tosyloxy)methyl Ketone Mp 63-64 ˚C (lit.^¹h mp 65-67 ˚C). IR (KBr): 1695, 1370, 1170, 810, 750 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.45 (s, 3 H), 5.09 (s, 2 H), 6.58 (dd, J = 3.7, 1.7 Hz, 1 H), 7.33 (dd, J = 3.7, 0.7 Hz, 1 H), 7.36 (d, J = 8.2 Hz, 2 H), 7.61 (dd, J = 1.7, 0.7 Hz, 1 H), 7.86 (d, J = 8.2 Hz, 2 H).
2-Thienyl (Tosyloxy)methyl Ketone Mp 92-93 ˚C (lit.^¹i mp 94-96 ˚C). IR (KBr): 1685, 1370, 1180, 730 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.45 (s,
3 H), 5.09 (s, 2 H), 7.16 (dd, J = 5.0, 3.9 Hz, 1 H), 7.35 (d, J = 8.1 Hz, 2 H), 7.73 (dd, J = 5.0, 1.0 Hz, 1 H), 7.79 (dd, J = 3.9, 1.0 Hz, 1 H), 7.85 (d, J = 8.1 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.66, 69.87, 128.17, 128.46, 129.94, 132.38, 133.13, 135.12, 140.12, 145.43, 183.64.
Ethyl α-Tosyloxybenzoylacetate Oil. IR (neat): 1440, 1590, 1690 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 1.18 (t, J = 7.0 Hz, 3 H), 2.85 (s, 3 H), 4.18 (m, 2 H), 5.59 (s, 1 H), 7.30 (d, J = 8.4 Hz, 2 H), 7.46 (t, J = 7.5 Hz, 2 H), 7.61 (t, J = 7.5 Hz, 1 H), 7.79 (d, J = 8.5 Hz, 2 H), 7.93 (d, J = 8.5 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 13.75, 21.63, 62.80, 78.03, 128.24, 128.71, 129.34, 129.82, 132.34, 133.28, 134.36, 145.68, 164.12, 188.19. HRMS-FAB: m/z calcd for C₁₈H₁₉O₆S [M + 1]: 363.0902; found: 363.0920.
Methyl α-Tosyloxyacetoacetate Oil. IR (neat): 1180, 1320, 1720 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 2.30 (s, 3 H), 2.48 (s, 3 H), 3.71 (s, 3 H), 5.20 (s, 1 H), 7.38 (d, J = 8.5 Hz, 2 H), 7.83 (d, J = 8.5 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.66, 26.53, 53.27, 80.34, 128.18, 129.98, 132.02, 145.90, 163.86, 196.98. HRMS-FAB: m/z calcd for C₁₂H₁₅O₆S [M + 1]: 287.0589; found: 287.0596.
2-Tosyloxy-3-pentanone Mp 45-46 ˚C (lit.^¹k mp 43-44 ˚C). IR (neat): 1190, 1360, 1720 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 1.03 (t, J = 7.3 Hz, 3 H), 1.35 (d, J = 7.0 Hz, 3 H), 2.47 (s, 3 H), 2.60 (m, 2 H), 4.80 (q, J = 7.0 Hz, 1 H), 7.37 (d, J = 8.0 Hz, 2 H), 7.81 (d, J = 8.0 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 6.96, 17.58, 21.65, 31.16, 80.68, 127.85, 129.99, 133.16, 145.29, 207.81.

5-Tosyloxy-6-undecanone Mp 72 ˚C (lit.^²d mp 72 ˚C). IR (neat): 1190, 1380, 1720 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 0.70-0.80 (m, 3 H), 0.86-1.75 (m, 15 H), 2.46 (s, 3 H), 2.51 (t, J = 7.5 Hz, 2 H), 4.64 (dd, J = 8.0, 4.6 Hz, 1 H), 7.36 (d, J = 8.0 Hz, 2 H), 7.80 (d, J = 8.0 Hz, 2 H). 1-Tosyloxy-2-octanone Oil. IR (neat): 1180, 1360, 1590, 1730 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 0.87 (t, J = 7.0 Hz, 3 H), 1.20-1.32 (m, 6 H), 1.48-1.62 (m, 2 H), 2.45 (s, 3 H), 2.49 (t, J = 7.2 Hz, 2 H), 4.49 (s, 2 H), 7.37 (d, J = 8.0 Hz, 2 H), 7.82 (d, J = 8.0 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 13.97, 21.68, 22.39, 22.76, 28.62, 31.43, 38.98, 71.78, 128.04, 130.00, 132.30, 145.44, 203.43. HRMS-FAB: m/z calcd for C₁₅H₂₃O₄S [M + 1]: 299.1317; found: 299.1295.
3-Tosyloxy-2-octanone Oil. IR (neat): 1180, 1360, 1600, 1740 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 0.80 (t, J = 7.3 Hz, 3 H), 1.00-1.30 (m,
6 H), 1.54-1.78 (m, 2 H), 2.23 (s, 3 H), 2.48 (s, 3 H), 4.58 (dd, J = 8.4, 4.6 Hz, 1 H), 7.36 (d, J = 8.7 Hz, 2 H), 7.81 (d, J = 8.7 Hz, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 13.91, 21.97, 22.35, 24.17, 26.01, 31.00, 31.52, 84.62, 128.13, 130.07, 132.98, 145.48, 205.78. HRMS-FAB: m/z calcd for C₁₅H₂₃O₄S [M + 1]: 299.1317; found: 299.1315.

8a Dohi T. Maruyama A. Minamitsuji Y. Takenaga N. Kita Y. Chem. Commun.  2007,  1224 

8b Dohi T. Ito M. Morimoto K. Minamitsuji Y. Takenaga N. Kita Y. Chem. Commun.  2007,  4152 

8c Dohi T. Ito M. Yamaoka N. Morimoto K. Fujioka H. Kita Y. Tetrahedron  2009,  65:  10797 

9 Merritt EA. Carneiro VMT. Silva LF. Olofsson B. J. Org. Chem.  2010,  75:  7416 

10 Suzuki Y. Moriyama K. Togo H. Tetrahedron Lett.  2010,  51:  5950 

11 Khanna MS. Grag CP. Kapoor RP. Tetrahedron Lett.  1992,  33:  1495 

12 Cho BT. Choi OK. Bull. Korean Chem. Soc.  2001,  22:  444