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Synlett 2004(15): 2746-2750  
DOI: 10.1055/s-2004-835651
LETTER
© Georg Thieme Verlag Stuttgart · New York

Site-Selective Oxidation and Metal-Induced 2-Propynylation of Pyranose Derivatives en route to Tetrodotoxins

Lidia Ozores, Fernando Cagide, Ricardo Alonso*
Departamento de Química Orgánica y Unidad asociada al C.S.I.C., Universidad de Santiago, 15782 Santiago de Compostela, Spain
Fax: +34(981)591014; e-Mail: qoraa@usc.es;
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Publication History

Received 21 July 2004
Publication Date:
08 November 2004 (online)

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Abstract

The radical-based site-selective oxidation of 2-hydroxyethyl acetals and the metal(Zn,Ti)-induced 2-propynylation of aldehydes can both be carried out successfully on highly functionalized oxygenated substrates, as demonstrated in the context of a synthetic plan for tetrodotoxin and its analogues, for which promising ­synthetic intermediates were prepared from d-mannopyranoses.

Key words

radical oxidation - acetal hydrolyses - aldehyde addition - 2-propynylation - tetrodotoxin

    References

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9

Preparation of C6-Sugar Aldehydes of Type III (Route C : 7 → 8 → IIIc). Selected Data of Allyl 2,4-Bis- O -Benzoyl-3-keto-6- O -trytil-β- d -mannopyranoside ( 8): 1H NMR (250 MHz, CDCl3, TMS): δ = 8.22-8.18 (m, 2 H, ArH), 7.87-7.84 (m, 2 H, ArH), 7.69-7.12 (m, 21 H, ArH), 6.18 (d, J = 10.4 Hz, 1 H, CH), 6.00-5.85 (m, 1 H, OCH2CHCH2), 5.47 (d, J = 1.9 Hz, 1 H, CH), 5.40-5.23 (m, 3 H, OCH2CHCH 2 + CH), 4.39-4.25 (m, 2 H, OCH 2CHCH2), 4.19-4.13 (m, 1 H, CH), 3.60 (dd, J = 10.4 Hz, J = 1.6 Hz, 1 H, CH2), 3.33 (dd, J = 10.4 Hz, J = 3.8 Hz, 1 H, CH2). 13C NMR and DEPT (63 MHz): δ = 195.2 (CO), 164.5 (2 × CO), 143.5 (Ar), 133.8 (CH), 133.3 (CH), 132.6 (CH), 130.1 (CH), 129.9 (CH), 128.8 (Ar), 128.73 (CH), 128.70 (Ar), 128.5 (CH), 128.2 (CH), 127.8 (CH), 126.9 (CH), 118.5 (OCH2CHCH2), 98.4 (CH), 86.6 (C), 76.6 (CH), 72.53 (CH), 72.47 (CH), 68.5 (CH2), 61.8 (CH2). [α]D 25 +12.0 (c 1.2, CHCl3).
Allyl 2,4-Bis- O -Benzoyl-3-benzyloximino-6- O -trytil-β- d -mannopyranoside: 1H NMR (250 MHz, CDCl3, TMS): δ = 8.16-8.12 (m, 2 H, ArH), 7.86-7.83 (m, 2 H, ArH), 7.64-7.07 (m, 26 H, ArH), 6.49 (d, J = 1.4 Hz, 1 H, CH), 6.12 (d, J = 10.2 Hz, 1 H, CH), 6.00-5.87 (m, 1 H, OCH2CHCH2), 5.36-5.21 (m, 3 H, OCH2CHCH 2 + CH), 5.03 (s, 2 H, NOCH 2Ar), 4.32-4.25 (m, 2 H, OCH 2CHCH2), 4.16-4.08 (m, 1 H, CH), 3.46 (dd, J = 10.3 Hz, J = 1.9 Hz, 1 H, CH2), 3.30 (dd, J = 10.3 Hz, J = 4.2 Hz, 1 H, CH2). 13C NMR and DEPT (63 MHz): δ = 165.1 (CO), 164.7 (CO), 146.9 (CNOBn), 143.6 (Ar), 137.3 (Ar), 133.4 (CH), 133.2 (CH), 132.9 (CH), 130.0 (CH), 129.8 (CH), 129.5 (Ar), 129.2 (Ar), 128.5 (CH), 128.1 (CH), 128.0 (CH), 127.7 (CH), 127.5 (CH), 126.8 (CH), 117.8 (OCH2CHCH2), 96.7 (CH), 86.4 (C), 76.5 (NOCH2Ar), 71.5 (CH), 68.1 (CH2), 66.1 (CH), 64.7 (CH), 62.0 (CH2). [α]D 25 -11.2 (c 1.2, CHCl3).
Allyl 2,4-Bis- O -Benzoyl-3-benzyloximino-β- d -mannopyranoside: 1H NMR (250 MHz, CDCl3, TMS): δ = 8.10-8.07 (m, 4 H, ArH), 7.66-7.26 (m, 11 H, ArH), 6.50 (d, J = 1.6 Hz, 1 H, CH), 6.05 (d, J = 10.0 Hz, 1 H, CH), 6.01-5.87 (m, 1 H, OCH2CHCH2), 5.38-5.24 (m, 2 H, OCH2CHCH 2), 5.19 (d, J = 1.3 Hz, 1 H, CH), 5.11 (s, 2 H, NOCH 2Ar), 4.36-4.07 (m, 3 H, OCH 2CHCH2 + CH), 3.93-3.80 (m, 2 H, CH2). 13C NMR and DEPT (63 MHz): δ = 165.4 (CO), 165.0 (CO), 146.6 (CNOBn), 137.2 (Ar), 133.5 (CH), 133.4 (CH), 133.0 (CH), 129.9 (CH), 129.3 (Ar), 129.0 (Ar), 128.5 (CH), 128.4 (CH), 128.2 (CH), 128.1 (CH), 127.6 (CH), 118.0 (OCH2CHCH2), 96.9 (CH), 76.6 (NOCH2Ar), 72.1 (CH), 68.3 (CH2), 65.6 (CH), 64.6 (CH), 61.6 (CH2). MS (IQ+ low resolution): m/z (%) = 532 (94) [M+ + 1], 474 (100) [M+ - OAllyl], 410 (71) [M+ - Obz]. [α]D 25 -25.1 (c 1.2, CHCl3).
1- O -Allyl-2,4-Bis- O -Benzoyl-3-deoxy-3-benzyloxyimino-6-aldehydo-β- d -arabino-hexopyranose (IIIc): 1H NMR (250 MHz, CDCl3, TMS): δ = 9.76 (d, J = 1.2 Hz, 1 H, CHO), 8.08-8.05 (m, 4 H, ArH), 7.64-7.44 (m, 6 H, ArH), 7.26-7.21 (m, 5 H, ArH), 6.46 (d, J = 1.4 Hz, 1 H, CH), 6.10 (d, J = 10.2 Hz, 1 H, CH), 5.88-6.04 (m, 1 H, OCH2CHCH2), 5.37-5.24 (m, 2 H, OCH2CHCH 2), 5.09 (s, 2 H, NOCH 2Ar), 5.06-5.02 (m, 1 H, CH), 4.55 (d, J = 11.0 Hz, 1 H, CH), 4.33-4.15 (m, 2 H, OCH 2CHCH2). 13C NMR and DEPT (63 MHz): δ = 195.7 (CHO), 170.5 (CO), 164.9 (CO), 145.2 (CNOBn), 141.8 (CH), 136.9 (Ar), 133.3 (CH), 132.6 (CH), 131.8 (CH), 129.97 (Ar), 129.95 (CH), 129.91 (Ar), 128.5 (CH), 128.4 (CH), 128.2 (CH), 128.1 (CH), 127.9 (CH), 127.7 (CH), 118.4 (OCH2CHCH2), 97.0 (CH), 76.8 (NOCH2Ar), 74.5 (CH), 68.8 (CH2), 64.9 (CH), 64.2 (CH). [α]D 25 -17.5 (c 1.2, CHCl3).

11

Radical-Based Site-Selective Oxidation of Allyl Glycoside Derivatives into Anomeric Spiroorthoesters: 2-Hydroxyethyl 2,4-Bis- O -Benzoyl-3- O -( tert -butyldimethylsilyl)-6- O -trytil-β- d -mannopyranoside ( 9): To a solution of the allyl mannopyranoside 7 [8] (369 mg, 0.47 mmol) in acetone-H2O (8:2), N-methyl morpholine oxide (54 mg, 0.52 mmol) and OsO4 (cat.), were added. After one day at r.t., the solvent was removed under reduced pressure, the residue was redissolved in EtOH-H2O (95:5). NaIO4 (113 mg, 0.52 mmol) as an aq solution (1.1 mL) and NaBH4 (20 mg, 0.52 mmol) were added. After 4 h at r.t., the reaction mixture was quenched by addition of dilute aq HCl and extracted with Et2O. Chromatographic purification (EtOAc-hexane 20:80) afforded 9 (267 mg, 72%). 1H NMR (250 MHz, CDCl3, TMS): δ = 8.18-8.14 (m, 2 H, ArH), 7.87-7.83 (m, 2 H, ArH), 7.60-7.05 (m, 21 H, ArH), 5.65 (t, J = 9.7 Hz, 1 H, CH), 5.42-5.41 (m, 1 H, CH), 5.10 (s, 1 H, CH), 4.34 (dd, J = 9.4 Hz, J = 3.4 Hz, 1 H, CH), 4.17-4.09 (m, 1 H, CH), 3.97-3.79 (m, 4 H, 2 × CH2), 3.31-3.29 (m, 2 H, CH2), 0.62 [s, 9 H, SiC(CH3)3], 0.04 (s, 3 H, SiCH3), -0.16 (s, 3 H, SiCH3). 13C NMR and DEPT (63 MHz): δ = 166.1 (CO), 164.9 (CO), 143.6 (Ar), 133.2 (ArH), 132.8 (ArH), 129.9 (ArH), 129.71 (Ar), 129.69 (Ar), 129.6 (ArH), 128.5 (ArH), 128.4 (ArH), 128.1 (ArH), 127.6 (ArH), 126.7 (ArH), 98.3 (CH), 86.7 (C), 72.7 (CH), 70.8 (CH), 70.6 (CH2), 69.7 (CH), 68.9 (CH), 62.6 (CH2), 61.9 (CH2), 25.2 [SiC(CH3)3], 17.5 [SiC(CH3)3], -4.8 (SiCH3), -5.2 (SiCH3). MS: m/z (%) = 485 (81) [M+ - CH2CH2OH - OCPh3], 243 (51) [CPh3 +], 105 (100) [Bz+]. [α]D 25 -6.9 (c 1.2, CHCl3).
Spiroorthoester 10: (Diacetoxy)iodobenzene (146 mg, 0.43 mmol) and I2 (99 mg, 0.39 mmol) were added to a solution of the 2-hydroxyethyl mannopyranoside 9 (309 mg, 0.39 mmol) in cyclohexane (30 mL, 0.01 M) under argon. After irradiating with a 100 W sunlamp for 7 h, the reaction mixture was washed with a sat. aq solution of Na2S2O3 and extracted with Et2O. Column chromatography (EtOAc-hexane 10:90) afforded 10 (145 mg, 47%). 1H NMR (250 MHz, CDCl3, TMS): δ = 8.20-8.17 (m, 2 H, ArH), 7.87-7.84 (m, 2 H, ArH), 7.60-7.06 (m, 21 H, ArH), 5.74 (t, J = 10.0 Hz, 1 H, CH), 5.57 (d, J = 3.1 Hz, 1 H, CH), 4.35 (dd, J = 9.4 Hz, J = 3.1 Hz, 1 H, CH), 4.29-3.98 (m, 5 H, 2 × CH2 + CH), 3.33-3.30 (m, 2 H, CH2), 0.64 [s, 9 H, SiC(CH 3)3], 0.09 (s, 3 H, SiCH3), -0.14 (s, 3 H, SiCH3). 13C NMR and DEPT (63 MHz): δ = 165.8 (CO), 164.8 (CO), 143.8 (Ar), 133.0 (ArH), 132.8 (ArH), 130.0 (ArH), 129.9 (Ar), 129.8 (Ar), 129.6 (ArH), 128.6 (ArH), 128.4 (ArH), 128.1 (ArH), 127.6 (ArH), 126.7 (ArH), 117.4 (OCO), 86.5 (C), 72.7 (CH), 72.5 (CH), 70.9 (CH), 69.5 (CH), 65.2 (CH2), 64.7 (CH2), 62.7 (CH2), 25.2 [SiC(CH3)3], 17.5 [SiC(CH3)3], -4.8 (SiCH3), -5.2 (SiCH3). MS (electron impact): m/z (%) = 730 (0.1) [M+ - C(CH3)3], 243 (100) [C(Ph)3 +], 165 (24), 105 (100) [Bz+]. MS (chemical ionization, CH4): m/z (%) = 545 (11) [M+ - C(Ph)3], 243 (100) [C(Ph)3 +]. [α]D 25 -19.3 (c 1.1, CHCl3).

15

CCDC 244334 contains the supplementary crystallographic data for 16a. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 (1223)336033.

16

Zn-Promoted 2-Propynylation of C6-Sugar Aldehydes: IIIc → 11:
Zn dust (80 mg, 1.21 mmol) and propargylic bromide (68 µL, 0.60 mmol) were added in two portions to aldehyde IIIc (54 mg, 0.10 mmol) in a mixture of THF and aq sat. NH4Cl (1:5, 5 mL) at r.t. After 6 h at r.t. and 2 h at 70 °C, the reaction mixture was diluted with brine and extracted with EtOAc. Chromatography afforded 11 (37 mg, 64%). 1H NMR (250 MHz, CDCl3, TMS): δ = 8.09-8.05 (m, 4 H, ArH), 7.62-7.44 (m, 6 H, ArH), 7.26-7.21 (m, 5 H, ArH), 6.45 (d, J = 12.2 Hz, 1 H, CH), 6.10-6.06 (m, 1 H, CH), 6.05-5.90 (m, 1 H, OCH2CHCH2), 5.37-5.04 (m, 5 H, OCH2CHCH 2 + NOCH 2Ar + CH), 4.39-4.31 (m, 2 H, OCH 2CHCH2), 4.14-4.09 (m, 2 H, 2 × CH), 2.62-2.60 (m, 2 H, CH2), 2.05-2.04 (m, 1 H, CH). 13C NMR + DEPT (63 MHz): δ = 165.1 (CO), 165.0 (CO), 146.9 (CN), 146.3 (CN), 137.2 (Ar), 133.6 (ArH), 133.5 (ArH), 133.3 (ArH), 133.0 (ArH), 130.1 (ArH), 130.0 (ArH), 129.0 (Ar), 128.6 (Ar), 128.4 (ArH), 128.3 (ArH), 128.28 (ArH), 128.25 (ArH), 128.11 (ArH), 127.7 (ArH), 118.11 (OCH2CHCH2), 96.9 (CH), 96.7 (CH), 80.0 (C), 76.5 (CH2), 73.0 (CH), 72.4 (CH), 71.4 (C), 70.6 (CH), 68.4 (CH2), 67.8 (CH), 66.6 (CH), 65.9 (CH), 65.6 (CH2), 64.6 (CH), 64.5 (CH), 22.7 (CH2).

17

Ti-Promoted 2-Propynylation of C6-Sugar Aldehydes: 12 → 14 → 16:
t-BuLi (1.7 M, 1.5 mL, 2.67 mmol) was added to a solution of 3-(tetrahydro-2-pyranoxyl)-1-(trimethylsilyl)propyne (13a, 0.566 g, 2.67 mmol) in THF (3 mL) at -78 °C. Stirring for 0.5 h was followed by the addition of Ti(Oi-Pr)4 (0.8 mL, 2.67 mmol), further stirring for 10 min, addition of a solution of 1,2:3,4-di-O-isopropyliden-α-d-galacto-hexodialdo-1,5-piranose (12, 355 mg, 1.37 mmol) in the same solvent and final stirring for 0.5 h at -78 °C. One hour after the reaction mixture reached r.t., aq HCl (0.1 M, 25 mL) was added. Extraction with Et2O (3 × 50 mL) and final chromatography (20% EtOAc-hexane) rendered 14 (60%) in two fractions (fraction A: R f = 0.39, 14a + 14c, 248 mg, 38% and fraction B: R f = 0.58, 14b + 14d, 143 mg, 22%), which were subsequently seperately dissolved in acetone and treated with 2,2-dimethoxypropane (2 equiv) and p-TsOH (cat.) at r.t. for 0.5 h. Addition of Et3N to reach a pH = 8 and final chromatography gave the acetonides 16a:16b:16c:16d (27:20:10:4). Compound 16a [(6 R ,7 R )-16]: 1H NMR (500 MHz, CDCl3): δ = 0.16 (s, 9 H, Si-CH3) 1.32 (s, CH3), 1.38 (s, CH3), 1.38 (s, CH3), 1.45 (s, CH3), 1.54 (s, CH3), 1.61 (s, CH3), 4.06 (dd, J 1 = 1.6 Hz, J 2 = 9.3 Hz, 1 H, CH-5), 4.18 (dd, J 1 = 4.8 Hz, J 2 = 9.3 Hz, 1 H, CH-6), 4.30 (dd, J 1 = 2.3 Hz, J 2 = 4.9 Hz, 1 H, CH-2), 4.40 (dd, J 1 = 1.7 Hz, J 2 = 7.9 Hz, 1 H, CH-4), 4.63 (dd, J 1 = 2.3 Hz, J 2 = 7.9 Hz, 1 H, CH-3), 4.85 (d, J = 4.8 Hz, 1 H, CH-7-C≡C-TMS), 5.50 (d, J = 4.8 Hz, 1 H, CH-1). 13C NMR and DEPT (75 MHz, CDCl3): δ = 0.37 (SiCH3), 25.02 (CH3), 25.41 (CH3), 26.48 (CH3), 26.69 (CH3), 27.19 (CH3), 28.06 (CH3), 67.13 (CH), 69.39 (CH), 70.89 (CH), 71.08 (CH), 71.55 (CH), 76.18 (CH), 94.13 (C), 96.37 (CH), 101.92 (C), 109.07 (C), 109.58 (C), 110.33 (C). For the X-ray data of 16a see ref. [15] ; [α]D 20 -20.1 (c 1.6, CHCl3); mp 132 °C. Compound 16b [(6 S ,7 S )-16]: 1H NMR (250 MHz, CDCl3): δ = 0.17 (s, 9 H, Si-CH3) 1.33 (s, 9 H, 2 CH3), 1.39 (s, 2 CH3), 1.46 (s, CH3), 1.58 (s, 9 H, CH3), 4.12 (dd, J 1 = 1.5 Hz, J 2 = 8.6 Hz, 1 H, CH), 4.28 (dd, J 1 = 5.3 Hz, J 2 = 8.5 Hz, 1 H, CH), 4.35 (dd, J 1 = 2.6 Hz, J 2 = 5.0 Hz, 1 H, CH), 4.44 (dd, J 1 = 1.6 Hz, J 2 = 7.9 Hz, 1 H, CH), 4.60 (dd, J 1 = 2.3 Hz, J 2 = 7.9 Hz, 1 H, CH), 4.85 (d, J = 4.8 Hz, 1 H, OCH), 5.50 (d, J = 4.8 Hz, 1 H, OCH-C≡C-TMS). 13C NMR and DEPT (63 MHz, CDCl3): δ = 0.38 (SiCH3), 25.12 (CH3), 25.48 (CH3), 26.43 (CH3), 26.63 (CH3), 26.93 (CH3), 28.25 (CH3), 67.42 (CH), 69.36 (CH), 70.64 (CH), 71.25 (CH), 71.28 (CH), 77.59 (C), 92.81 (C), 96.73 (CH), 96.82 (C), 102.81 (C), 109.27 (C), 110.18 (C), 111.49 (C). Compound 16c [(6 R ,7 S )-16]: 1H NMR (500 MHz, CDCl3): δ = 0.15 (s, 9 H, Si-CH3), 1.32 (s, CH3), 1.38 (s, CH3), 1.41 (s, CH3), 1.48 (s, CH3), 1.50 (s, CH3), 1.60 (s, CH3), 3.59 (d, J = 9.1 Hz, 1 H, CH), 4.30-4.37 (m, 3 H, CH), 4.63 (dd, J 1 = 2.3 Hz, J 2 = 7.9 Hz, 1 H, CH), 4.79 (d, J = 2.4 Hz, 1 H, OCH-C≡C-TMS), 5.51 (d, J = 4.9 Hz, 1 H, CH). 13C NMR (75 MHz, CDCl3): δ = 0.38 (SiCH3), 24.87 (CH3), 25.41 (CH3), 26.31 (CH3), 26.47 (CH3), 27.36 (CH3), 28.70 (CH3), 68.75 (CH), 69.62 (CH), 69.67 (CH), 70.93 (CH), 71.14 (CH), 80.47 (CH), 91 (C), 96.77 (CH), 105 (C), 109.19 (C), 109.99 (C), 113 (C). [α]D 20 -110.24 (c 0.26, CHCl3).