Stereoselective 1,4-Phenyl Migration from Silicon to Carbon in α-Siloxy Cyclic Acetal Systems: A Concise Synthesis of 1,2-cis-Phenyl C-Glycoside and Enantioenriched Silanol

Abstract

The treatment of O-glycoside with alcohol in the presence of montmorillonite K10 clay and 4-Å MS yields the 1,4-aryl migration product with a 1,2-cis-phenyl C-glycoside scaffold and a chiral silyl moiety with high stereoselectivity.

Key words

asymmetric synthesis - aryl C-glycosides - chiral silanol - montmorillonite K10 - aryl migration

References and Notes

• For reviews, see:
• 1a Hacksell U. Daves GD. Progress Med. Chem.  1985,  22:  1 
• 1b Rohr J. Thiericke R. Nat. Prod. Rep.  1992,  9:  103 
• 1c Nicotra F. Top. Curr. Chem.  1997,  187:  55 
• For reviews of stereoselective synthesis of aryl C-glycosides, see:
• 2a Suzuki K. Matsumoto T. In Recent Progress in the Chemical Synthesis of Antibiotics and Related Microbial Products   Vol. 2:  Lukacs G. Springer; Berlin: 1993.  p.352 
• 2b Jaramillo C. Knapp S. Synthesis  1994,  1 
• For the pioneering works of 1,2-cis-C-glycoside using silicon tether, see:
• 3a Martin OR. Rao SP. Kurz KG. El-Shenawy HA. J. Am. Chem. Soc.  1988,  110:  8698 
• 3b Stork G. Suh HS. Kim G. J. Am. Chem. Soc.  1991,  113:  7054 
• 3c Rousseau C. Martin OR. Org. Lett.  2003,  5:  3763 
• For examples of the organometal-mediated aryl C-glycosylation in a 1,2-cis fashion, see:
• 3d Rainier JD. Cox JM. Org. Lett.  2000,  2:  2707 
• 3e Singh I. Seitz O. Org. Lett.  2006,  8:  4319 
• 4 Tomooka K. Nakazaki A. Nakai T. J. Am. Chem. Soc.  2000,  122:  408 
• 5 Huang and co-workers have reported the related BF₃˙OEt₂-promoted aryl migration in a cyclic N,O-acetal system. However, their method did not afford an aryl migration product bearing the stereochemically defined silicon center. See: Huang P.-Q. Liu L.-X. Wei B.-G. Ruan Y.-P. Org. Lett.  2003,  5:  1927 
• Related examples of phenyl migration from silicon to carbon have been reported. For 1,4- or 1,5-phenyl or vinyl migration promoted by Lewis acids, see:
• 6a Archibald SC. Fleming I. Tetrahedron Lett.  1993,  34:  2387 
• 6b Hioki H. Izawa T. Yoshizuka M. Kunitake R. Ito S. Tetrahedron Lett.  1995,  36:  2289 
• For 1,2-phenyl migration promoted by fluoride ion, see:
• 6c Morihata K. Horiuchi Y. Taniguchi M. Oshima K. Utimoto K. Tetrahedron Lett.  1995,  36:  5555 
• A few synthetic methods for enantioenriched silanol have been reported. For resolution or separation of racemic or diastereomeric silanols, see:
• 11a Tacke R. Linoh H. Ernst L. Moser U. Mutschler E. Sarge S. Cammenga HK. Lambrecht G. Chem. Ber.  1987,  120:  1229 
• 11b Yamamoto K. Kawanami Y. Miyazawa M. J. Chem. Soc., Chem. Commun.  1993,  436 
• 11c Feibush B. Woolley CL. Mani V. Anal. Chem.  1993,  65:  1130 
• 11d Mori A. Toriyama F. Kajiro H. Hirabayashi K. Nishihara Y. Hiyama T. Chem. Lett.  1999,  549 
• 11e Yamamura Y. Toriyama F. Kondo T. Mori A. Tetrahedron: Asymmetry  2002,  13:  13 
• For stereospecific oxidation of enantioenriched silanes or halosilanes, see:
• 11f Cavicchioli M. Montanari V. Resnati G. Tetrahedron Lett.  1994,  35:  6329 
• 11g Adam W. Mitchell CM. Saha-Möller CR. Weichold O. J. Am. Chem. Soc.  1999,  121:  2097 ; and references therein
• 12 All spectral data of 7 matched with those reported in the following literature: Angle SR. Neitzel ML. J. Org. Chem.  1999,  64:  8754 
• 15 All spectral data of 12 matched those reported in the following literature: Schmidt B. J. Org. Chem.  2004,  69:  7672 
• Methyl acetal 13 was prepared from d-xylose in five steps: (1) acetone, cat. H₂SO₄, (2) 0.2% aq HCl, 97% (two steps), (3) NaH, BnBr, 87%, (4) cat. H₂SO₄, MeOH, 96%, and (5) TBDPSCl, imidazole, 72%.
• 16a Levene PA. Raymond AL. J. Biol. Chem.  1933,  102:  317 
• 16c Baker BR. Schaub RE. J. Am. Chem. Soc.  1955,  77:  5900 
• 16d Martin OR. Rao SP. El-Shenawy HA. Kurz KG. Cutler AB.
  J. Org. Chem.  1988,  53:  3287 
• 18 We have already demonstrated that enantioenriched silanol bearing allyloxy group can be converted into a chiral allylsilane, which is a more useful and versatile chiral building block. See: Nakazaki A. Nakai T. Tomooka K. Angew. Chem., Int. Ed.  2006,  45:  2235 

7

General Procedure of the 1,4-Aryl Migration
The 4-Å MS (580 mg) was placed in a two-necked flask and was flame dried under reduced pressure. After the contents in the flask had cooled down, the flask was purged with argon. Cyclic hemiacetal 1a (96 mg, 0.28 mmol) and benzyl alcohol (58 µL, 0.56 mmol) in dry CH₂Cl₂ (9.5 mL) were added to the flask at 0 ˚C. The resulting mixture was stirred at that temperature for 30 min. Flame-dried montmorillonite K10 (482 mg) was added to the suspension. The resulting mixture was stirred at that temperature for 12 h, filtrated through a pad of Celite, and concentrated. Purification by column chromatography (silica gel, hexane-Et₂O, 12:1) afforded 86 mg (71%) of aryl migration product 2 with 90% dr.

8

All new compounds were fully characterized by ^¹H NMR, ^¹³C NMR, and IR spectroscopy. Data for selected compounds follow.
Compound 2 (90% dr at Si by ^¹H NMR analysis): ^¹H NMR (300 MHz, CDCl₃): δ = 7.53-7.21 (m, 13.2 H), 7.13-7.09 (m, 1.8 H), 4.85 (d, J = 3.6 Hz, 0.1 H), 4.82 (d, J = 3.3 Hz, 0.9 H), 4.77 (d, J = 13.2 Hz, 1 H), 4.69 (d, J = 13.2 Hz, 1 H), 4.61 (br dd, J = 3.3, 6.0 Hz, 1 H), 4.36 (q, J = 7.8 Hz, 0.9 H), 4.31 (q, J = 8.1 Hz, 0.1 H), 4.05 (dt, J = 4.8, 7.8 Hz, 0.9 H), 4.03-3.97 (m, 0.1 H), 2.29-2.14 (m, 2 H), 0.88 (s, 8.1 H), 0.81 (s, 0.9 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 140.84, 138.17, 135.42, 130.95, 129.95, 129.84, 128.35, 128.27, 128.19, 127.87, 127.80, 127.60, 127.54, 127.43, 127.04, 126.94, 125.66, 88.56, 85.42, 74.82, 74.59, 66.99, 66.84, 64.79, 64.50, 36.76, 36.58, 26.10, 26.00, 19.00, 18.70. IR (neat): 3068, 3032, 2934, 2862, 1951, 1895, 1810, 1723, 1669, 1605, 1593, 1495, 1475, 1456, 1431, 1064 cm^-¹. Anal. Calcd for C₂₇H₃₂O₃Si: C, 74.96; H, 7.46. Found: C, 74.91; H, 7.20.
Compound 3a (>95% dr by ^¹H NMR analysis): [α]_D ^²4 +130.3 (c 1.40, CHCl₃). ^¹H NMR (300 MHz, CDCl₃):
δ = 7.43-7.27 (m, 5 H), 4.90 (d, J = 3.6 Hz, 1 H), 4.41 (br s, 1 H), 4.27 (q, J = 8.7 Hz, 1 H), 4.03 (dt, J = 4.2, 8.7 Hz, 1 H), 2.28 (ddt, J = 13.2, 4.2, 8.7 Hz, 1 H), 2.15 (dddd, J = 13.2, 8.7, 4.2, 1.5 Hz, 1 H), 1.19 (s, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 136.97, 128.66, 127.99, 126.80, 85.14, 73.72, 67.07, 34.93. IR (neat): 3392, 3066, 3032, 2928, 2884, 1957, 1895, 1820, 1493, 1454, 1125, 1083, 1060, 1029, 739, 700 cm^-¹. ESI-HRMS: m/z calcd for C₁₀H₁₂O₂Na: 187.0729; found: 187.0734.
Compound 6 (93% dr at Si by ^¹H NMR analysis): ^¹H NMR (300 MHz, CDCl₃): δ = 7.51-7.47 (m, 0.2 H), 7.43-7.27 (m, 10.8 H), 7.20-7.14 (m, 2 H), 6.96-6.92 (m, 2 H), 5.10 (d, J = 4.8 Hz, 0.07 H), 5.04 (d, J = 4.2 Hz, 0.93 H), 4.90 (d, J = 13.2 Hz, 0.93 H), 4.84 (d, J = 13.2 Hz, 0.93 H), 4.64 (d, J = 13.5 Hz, 0.07 H), 4.56 (d, J = 13.5 Hz, 0.07 H), 4.37 (d, J = 4.8 Hz, 0.07 H), 4.18 (d, J = 4.8 Hz, 0.93 H), 3.98 (d, J = 7.8 Hz, 0.93 H), 3.91 (d, J = 7.8 Hz, 0.07 H), 3.62 (d, J = 7.8 Hz, 0.93 H), 3.56 (d, J = 7.8 Hz, 0.07 H), 1.23 (s, 2.79 H), 1.15 (s, 2.79 H), 1.02 (s, 0.42 H), 0.86 (s, 8.37 H), 0.75 (s, 0.63 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 140.77, 138.54, 135.42, 131.11, 129.69, 129.08, 128.36, 127.90, 127.64, 127.51, 127.07, 125.86, 85.66, 81.97, 79.11, 65.39, 44.94, 26.52, 26.05, 21.02, 19.11. IR (neat): 3068, 3032, 2966, 2862, 1949, 1870, 1810, 1740, 1607, 1593, 1473, 1456, 1065, 733, 698 cm^-¹. ESI-HRMS: m/z calcd for C₂₉H₃₆O₃NaSi: 483.2331; found: 483.2310.
Compound 7 (>95% dr by ^¹H NMR analysis): ^¹H NMR (300 MHz, CDCl₃): δ = 7.42-7.27 (m, 5 H), 5.30 (d, J = 3.6 Hz, 1 H), 3.96 (d, J = 7.5 Hz, 1 H), 3.80 (br t, J = 3.0 Hz, 1 H), 3.72 (d, J = 7.5 Hz, 1 H), 1.21 (s, 3 H), 1.15 (s, 3 H), 1.07 (br s, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 137.80, 128.69, 127.88, 126.73, 84.48, 80.61, 79.01, 44.21, 25.82, 19.41. IR (neat): 3342, 2960, 1950, 1900, 1830, 1466, 1309, 1096, 1038, 739, 700 cm^-¹. Anal. Calcd for C₁₂H₁₆O₂: C, 74.97; H, 8.39. Found: C, 74.86; H, 8.16.
Compound 11 (90% dr at Si by ^¹H NMR analysis): ^¹H NMR (300 MHz, CDCl₃): δ = 7.63-7.61 (m, 0.3 H), 7.48-7.13 (m, 10.7 H), 7.17 (t, J = 7.5 Hz, 2 H), 6.99 (t, J = 7.5 Hz, 2 H), 4.76 (d, J = 13.5 Hz, 1 H), 4.65 (d, J = 13.5 Hz, 1 H), 4.43 (s, 1 H), 4.27-4.22 (m, 1 H), 4.09 (s, 1 H), 3.90-3.80 (m, 0.1 H), 3.66 (dt, J = 2.6, 12.6 Hz, 0.9 H), 2.42-2.00 (m, 2 H), 1.84-1.73 (m, 1 H), 1.40 (br d, J = 13.5 Hz, 1 H), 0.95 (s, 8.1 H), 0.83 (s, 0.9 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 141.02, 140.79, 135.89, 135.47, 135.39, 131.20, 129.59, 128.28, 128.17, 127.99, 127.88, 127.62, 127.51, 127.41, 127.28, 127.17, 126.93, 126.78, 126.73, 125.63, 82.58, 69.80, 69.55, 68.87, 68.77, 64.63, 31.34, 26.37, 26.31, 20.26, 19.04. IR (neat): 2930, 2856, 1961, 1898, 1808, 1453, 1115, 1098, 1071, 1026 cm^-¹. ESI-HRMS: m/z calcd for C₂₈H₃₄O₃NaSi: 469.2169; found: 469.2159.
Compound 12 (>95% dr by ^¹H NMR analysis): ^¹H NMR (300 MHz, CDCl₃): δ = 7.38-7.25 (m, 5 H), 4.50 (d, J = 1.2 Hz, 1 H), 4.18 (ddt, J = 11.1, 4.5, 1.8 Hz, 1 H), 3.94-3.91 (m, 1 H), 3.65 (ddd, J = 12.3, 11.1, 2.4 Hz, 1 H), 2.17-2.02 (m, 2 H), 1.92-1.78 (m, 1 H), 1.72 (d, J = 5.4 Hz, 1 H), 1.48-1.42 (m, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 139.64, 128.49, 127.52, 125.81, 81.18, 68.96, 68.01, 30.25, 19.92. IR (neat): 3454, 2947, 2849, 1958, 1887, 1813, 1451, 1267, 1216, 1091, 1057, 1003, 725, 699 cm^-¹.
Compound 13 (63% dr by ^¹H NMR analysis): ^¹H NMR (300 MHz, CDCl₃): δ = 7.76-7.65 (m, 4.14 H), 7.50-7.21 (m, 14.6 H), 7.11-7.07 (m, 1.26 H), 4.86 (s, 0.63 H), 4.63-4.58 (m, 0.37 H), 4.62 (d, J = 12.0 Hz, 0.63 H), 4.59 (d, J = 11.7 Hz, 0.37 H), 4.57 (d, J = 11.7 Hz, 0.37 H), 4.54 (d, J = 12.0 Hz, 0.63 H), 4.51 (d, J = 11.7 Hz, 0.37 H), 4.46 (d, J = 11.7 Hz, 0.37 H), 4.39 (dt, J = 6.3, 3.9 Hz, 0.37 H), 4.35-4.27 (m, 1.63 H), 4.20 (d, J = 12.3 Hz, 0.63 H), 4.18 (d, J = 3.9 Hz, 0.37 H), 3.95 (d, J = 12.3 Hz, 0.63 H), 3.82 (br dd, J = 5.1, 1.2 Hz, 0.63 H), 3.74 (dd, J = 10.2, 5.1 Hz, 0.63 H), 3.70 (dd, J = 10.2, 6.9 Hz, 0.63 H), 3.66 (dd, J = 10.5, 3.9 Hz, 0.37 H), 3.51 (dd, J = 10.5, 6.3 Hz, 0.37 H), 3.24 (s, 1.11 H), 3.23 (s, 1.89 H), 1.12 (s, 3.33 H), 1.09 (s, 5.67 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 138.38, 138.25, 138.28, 138.07, 136.08, 135.90, 134.87, 133.80, 133.40, 133.22, 133.15, 130.08, 129.85, 129.79, 128.38, 128.32, 128.24, 127.91, 127.83, 127.70, 127.62, 127.56, 127.49, 127.44, 110.49, 101.59, 83.54, 83.46, 81.02, 79.96, 78.01, 75.55, 73.54, 73.48, 73.27, 71.49, 69.90, 69.68, 26.98, 26.95, 19.22. IR (neat): 3072, 3034, 2934, 2862, 1963, 1891, 1827, 1473, 1456, 1429, 1112, 1060, 822, 739, 700 cm^-¹. Anal. Calcd for C₃₆H₄₂O₅Si: C, 74.19; H, 7.26. Found: C, 74.38; H, 7.36.
Compound 14 (81% dr at Si by ^¹H NMR analysis): ^¹H NMR (300 MHz, CDCl₃): δ = 7.56 (d, J = 1.5 Hz, 0.19 H), 7.54 (d, J = 1.5 Hz, 0.19 H), 7.47-7.12 (m, 18 H), 6.98 (d, J = 1.5 Hz, 0.81 H), 6.95 (d, J = 1.5 Hz, 0.81 H), 5.22 (d, J = 3.0 Hz, 0.19 H), 5.20 (d, J = 3.0 Hz, 0.81 H), 4.76 (dt, J = 3.6, 6.0 Hz, 1 H), 4.70 (d, J = 12.0 Hz, 0.81 H), 4.68 (d, J = 12.0 Hz, 0.19 H), 4.57 (d, J = 12.0 Hz, 0.81 H), 4.56 (d, J = 12.0 Hz, 0.81 H), 4.55 (d, J = 12.0 Hz, 0.19 H), 4.45 (d, J = 12.0 Hz, 0.81 H), 4.42 (dd, J = 3.3, 0.9 Hz, 0.19 H), 4.36 (dd, J = 2.7, 1.2 Hz, 0.81 H), 4.33 (d, J = 12.0 Hz, 0.19 H), 4.21 (d, J = 12.0 Hz, 0.19 H), 4.18 (dd, J = 3.6, 1.2 Hz, 0.81 H), 4.05 (dd, J = 3.6, 1.2 Hz, 0.19 H), 3.85 (dd, J = 9.9, 6.0 Hz, 0.81 H), 3.81 (dd, J = 9.9, 6.0 Hz, 0.81 H), 3.78 (d, J = 6.0 Hz, 0.38 H), 3.47 (s, 2.43 H), 3.07 (s, 0.57 H), 0.79 (s, 7.29 H), 0.77 (s, 1.71 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 138.38, 138.04, 137.54, 135.37, 130.55, 130.13, 129.90, 128.43, 128.15, 128.07, 127.98, 127.93, 127.78, 127.62, 127.57, 127.48, 127.35, 85.32, 85.09, 83.44, 80.04, 79.75, 77.17, 73.69, 72.31, 69.08, 51.96, 26.21, 25.97, 18.62. IR (neat): 3068, 3032, 2934, 2862, 1953, 1890, 1810, 1087 cm^-¹. Anal. Calcd for C₃₆H₄₂O₅Si: C, 74.19; H, 7.26. Found: C, 74.09; H, 7.09.
Compound 15 (>95% dr by ^¹H NMR analysis): [α]_D ^²4 -63.2 (c 1.07, CHCl₃). ^¹H NMR (300 MHz, CDCl₃): δ = 7.40-7.28 (m, 15 H), 5.33 (d, J = 3.3 Hz, 1 H), 4.72 (d, J = 12.0 Hz, 1 H), 4.69 (d, J = 12.3 Hz, 1 H), 4.67 (ddd, J = 6.6, 5.7, 4.2 Hz, 1 H), 4.65 (d, J = 12.0 Hz, 1 H), 4,57 (d, J = 12.3 Hz, 1 H), 4.27 (br s, 1 H), 4.17 (br dd, J = 4.2, 1.2 Hz, 1 H), 3.84 (dd, J = 9.9, 5.7 Hz, 1 H), 3.80 (dd, J = 9.9, 6.6 Hz, 1 H), 1.27 (br s, 1 H). ^¹³C NMR (75 MHz, CDCl₃): δ = 138.41, 138.05, 136.36, 128.74, 128.53, 128.43, 128.14, 127.86, 127.64, 127.57, 126.83, 84.19, 83.01, 80.21, 76.45, 73.56, 72.70, 68.88. IR (neat): 3432, 3066, 3032, 2924, 2870, 1955, 1883, 1814, 1497, 1456, 1083, 737, 698 cm^-¹. ESI-HRMS: m/z calcd for C₂₅H₂₆O₄Na: 413.1723; found: 413.1707.

9

Benzyl acetal 1b was prepared from cyclic hemiacetal 1a and benzyl alcohol in the presence of a catalytic amount of PPTS.

10

The stereochemistry and ee of benzyloxysilanol (S)-4 was established by chiral HPLC analysis [CHIRALCEL OD column, hexane-i-PrOH = 150:1, flow rate = 0.6 mL/min, detection 254 nm light; t _R = 36.5 (major isomer), 41.9 min (minor isomer)].

13

A similar reaction of hemiketal 8a provided the correspond-
ing phenyl migration product 9 in 93% dr, albeit in low yield. The stereochemistry of 9 was assumed on the basis of the reaction mechanism (Scheme  [7] ).

14

Due to their ease of preparation, we chose acetals 10 and 13 as substrates, rather than the corresponding hemiacetals.

17

The starting material 13 was not consumed after 2 d at r.t.