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Synlett 2007(12): 1851-1856  
DOI: 10.1055/s-2007-984523
LETTER
© Georg Thieme Verlag Stuttgart · New York

Stereocontrolled Photocyclization of 1,2-Diketones Applied to Carbohydrate Models: A New Entry to C-Ketosides

Antonio J. Herrera*, María Rondón, Ernesto Suárez*
Instituto de Productos Naturales y Agrobiología del C.S.I.C, Carretera de La Esperanza 3, 38206 La Laguna, Tenerife, Spain
Fax: +34(922)260135; e-Mail: esuarez@ipna.csic.es; e-Mail: ajherrera@ipna.csic.es;
Further Information

Publication History

Received 16 March 2007
Publication Date:
25 June 2007 (online)

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Abstract

Photolysis of 1-glycosyl-2,3-butanedione derivatives ­using visible light is a mild and selective procedure for the synthesis of chiral 1-hydroxy-1-methyl-5-oxaspiro[3.5]nonan-2-one carbohydrate derivatives. The results strongly suggest that stereocontrol of the cyclization is dependent on conformational and stereoelectronic factors which can be modulated efficiently by using photosensitizers in some cases. Further oxidative opening of the 1-hydroxy-1-methyl-2-cyclobutanone moiety affords new C-ketoside derivatives. This two-step process could be considered to be a ­stereocontrolled 1,3-transfer of an acetyl group.

Key words

photochemistry - spiro compounds - memory effect - ­diastereoselectivity - glycosides

10

The numbering system used throughout the text is based on 1-methyl-2,3-alkanedione and corresponds to that depicted in structures of Table [1] and Schemes 1-3.

12

Conformation of substrates 1-4 were determined by 1H NMR spectroscopic analysis.

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A 450 W ACE-Hanovia medium-pressure mercury lamp in an immersion well with 4.8 mm Pyrex walls.

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Conditions: 1,2-diketone (40 mM), pyrene, naphthalene or benzophenone (0.5 M), CHCl3, UV lamp (10 cm).

19

General Procedure for the Photocyclization of 1,2-Diketones
The corresponding 1,2-diketone placed in a Pyrex vessel with or without the indicated solvent (approx. 0.05 M) was irradiated with sunlight or a UV lamp, placed at 10 cm distance from the flask, until the reaction turned colorless. If it proceeded, the mixture was concentrated in vacuo. Column or Chromatotron® chromatography of the residue (hexanes-EtOAc mixtures) afforded the cyclic compounds.
General Procedure for the Photocyclization of 1,2-Diketones with Photosensitizers
The corresponding 1,2-diketone (0.038 mmol) and photosensitizer (benzophenone or pyrene; 0.5 mmol) was dissolved in CDCl3 (1 mL) and placed in a NMR tube. The reaction mixture was irradiated with an UV lamp, placed at 10 cm distance from the flask, until complete conversion and the solvent was removed under vacuum. The reaction was monitored by 1H NMR. Chromatotron® chromatography of the residue with hexanes to remove the photosensitizer followed by elution with hexanes-EtOAc mixtures afforded the cyclic compounds.
Data of some representative compounds are included; only the major compound from the mixtures is shown.
Compound 5a (2R,5R): colorless oil; [α]D +23.8 (c 0.3). 1H NMR (400 MHz, CDCl3): δ = 1.38 (3 H, s), 2.36 (1 H, d, J = 17.3 Hz), 2.91 (1 H, d, J = 17.3 Hz), 3.50 (1 H, dd, J = 3.7, 9.8 Hz), 3.53 (3 H, s), 3.76 (1 H, d, J = 9.8 Hz), 3.99 (1 H, br s), 4.34 (1 H, t, J = 9.8 Hz), 4.57 (1 H, d, J = 3.9 Hz), 4.66 (1 H, d, J = 11.9 Hz), 4.67 (1 H, d, J = 10.9 Hz), 4.75 (1 H, d, J = 10.9 Hz), 4.82 (1 H, d, J = 10.6 Hz), 4.83 (1 H, d, J = 12.0 Hz), 4.98 (1 H, d, J = 11.1 Hz), 7.15 (2 H, dd, J = 2.0, 7.6 Hz), 7.28-7.38 (13 H, m). 13C NMR (100 MHz, CDCl3): δ = 19.6 (CH3), 50.6 (CH2), 59.7 (CH3), 74.0 (CH2), 76.0 (CH2), 76.7 (CH2), 77.8 (C), 78.2 (CH), 80.8 (CH), 83.3 (CH), 90.5 (C), 101.2 (CH), 128.2-129.3 (15 × CH), 136.5 (C), 138.5 (C), 138.7 (C), 208.2 (C). MS (EI): m/z (rel. int.) = 518 (<1) [M+], 427 (<1), 412 (<1), 395 (<1), 91 (100). HRMS: m/z calcd for C31H34O7: 518.2305; found: 518.2322. Anal. Calcd for C31H34O7: C, 71.80; H, 6.61. Found: C, 71.90; H, 6.59.
Compound 6a (2R,5R): colorless oil; [α]D +1.4 (c 1.0). 1H NMR (400 MHz, CDCl3): δ = 1.51 (3 H, s), 2.42 (1 H, d, J = 17.5 Hz), 3.03 (1 H, d, J = 17.5 Hz), 3.43 (1 H, dd, J = 8.1, 9.1 Hz), 3.61 (3 H, s), 3.86 (1 H, d, J = 9.5 Hz), 4.00 (1 H, br s), 4.15 (1 H, t, J = 9.4 Hz), 4.62 (1 H, d, J = 7.7 Hz), 4.68 (1 H, d, J = 10.9 Hz), 4.72 (1 H, d, J = 11.4 Hz), 4.75 (1 H, d, J = 11.7 Hz), 4.82 (1 H, d, J = 11.1 Hz), 4.93 (1 H, d, J = 11.1 Hz), 4.96 (1 H, d, J = 10.9 Hz), 7.15 (2 H, dd, J = 1.9, 7.1 Hz), 7.28-7.36 (13 H, m). 13C NMR (100 MHz, CDCl3): δ = 17.7 (CH3), 50.1 (CH2), 57.7 (CH3), 75.1 (CH2), 75.6 (C), 76.1 (CH2), 76.5 (CH2), 81.6 (CH), 82.2 (CH), 82.8 (CH), 90.5 (C), 102.8 (CH), 128.1-129.2 (15 × CH), 136.5 (C), 138.6 (C), 138.7 (C), 206.6 (C). MS (EI): m/z (rel. int.) = 518 (<1) [M+], 476 (1.1), 427 (<1), 395 (1), 91 (100). HRMS: m/z calcd for C31H34O7: 518.2305; found: 518.2319.
Compound 7d (2S,5S) [data taken from a (4:1) mixture of 7d-c]: colorless oil. 1H NMR (400 MHz, CDCl3): δ = 0.08 (3 H, s), 0.09 (3 H, s), 0.10 (3 H, s), 0.11 (6 H, s), 0.12 (3 H, s), 0.88 (18 H, s), 0.92 (9 H, s), 1.29 (3 H, d, J = 6.4 Hz), 1.34 (3 H, s), 2.75 (1 H, d, J = 17.5 Hz), 3.00 (1 H, d, J = 17.5 Hz), 3.42 (1 H, dq, J = 5.4, 6.4 Hz), 3.57 (1 H, dd, J = 2.0, 5.4 Hz), 3.76 (1 H, t, J = 2.0 Hz), 4.38 (1 H, d, J = 2.3 Hz), 4.71 (1 H, s, OH). 13C NMR (100 MHz, CDCl3): δ = -5.2 (CH3), -4.6 (CH3), -4.3 (CH3), -4.2 (CH3), -3.9 (CH3), -3.8 (CH3), 17.8 (C), 17.9 (C), 18.0 (C), 18.9 (CH3), 20.6 (CH3), 25.6 (3 × CH3), 25.8 (6 × CH3), 51.4 (CH2), 73.5 (CH), 75.7 (C), 76.1 (CH), 76.3 (CH), 77.4 (CH), 90.5 (C), 210.1 (C). MS (EI): m/z (rel. int.) = 574 (5) [M+], 529 (17), 517 (22), 73 (100). HRMS: m/z calcd for C28H58O6Si3: 574.3541; found: 574.3534.
Compound 8b (2S,5R) [data taken from a (3:1) mixture of 8b-c]: colorless oil. 1H NMR (400 MHz, CDCl3): δ = 1.37 (3 H, s), 2.62 (1 H, d, J = 17.5 Hz), 3.31 (1 H, d, J = 17.5 Hz), 3.50 (1 H, m), 3.55 (1 H, m), 3.60 (1 H, t, J = 8.8 Hz), 3.70 (1 H, d, J = 8.6 Hz), 3.61-3.79 (2 H, m), 4.44 (1 H, d, J = 11.7 Hz), 4.46 (1 H, d, J = 11.8 Hz), 4.53 (1 H, d, J = 10.8 Hz), 4.58 (1 H, d, J = 10.8 Hz), 4.71 (1 H, d, J = 10.8 Hz), 3.74 (1 H, d, J = 10.8 Hz), 4.85 (1 H, d, J = 10.8 Hz), 5.04 (1 H, d, J = 11.4 Hz), 7.09-7.28 (20 H, m). 13C NMR (100 MHz, CDCl3): δ = 16.6 (CH3), 44.7 (CH2), 68.3 (CH2), 73.3 (CH2), 73.7 (CH2), 74.1 (CH2), 75.1 (CH2), 75.5 (CH), 76.2 (CH), 76.9 (C), 77.7 (CH), 86.4 (CH), 89.5 (C), 127.0-128.5 (20 × CH), 137.5 (C), 137.7 (C), 137.8 (C), 138.0 (C), 208.4 (C). MS (EI): m/z (rel. int.) = 608 (<1) [M+] , 580 (1), 566 (<1), 517 (<1), 457 (1), 91 (100). HRMS: m/z calcd for C38H40O7: 608.2777; found: 608.2770.
Compound 10: colorless oil; [α]D -81.2 (c 0.16). 1H NMR (400 MHz, CD3OD + D2O): δ = 1.32 (3 H, d, J = 6.1 Hz), 2.28 (3 H, s), 3.01 (1 H, d, J = 15.4 Hz), 3.07 (1 H, d, J = 15.4 Hz), 3.43 (1 H, dd, J = 8.0, 10.3 Hz), 3.58 (1 H, dq, J = 10.4, 6.0 Hz), 3.66 (3 H, s), 3.67 (1 H, dd, J = 3.2, 5.0 Hz), 3.86 (1 H, d, J = 3.28 Hz). 13C NMR (100 MHz, CD3OD): δ = 19.1 (CH3), 28.5 (CH3), 38.2 (CH2), 52.6 (CH3), 72.9 (CH), 73.2 (CH), 74.2 (CH), 75.3 (CH), 86.6 (C), 171.7 (C), 213.9 (C). MS (EI): m/z (rel int.) = 263 (<1) [M+ + H], 245 (<1), 231 (8), 201 (8). HRMS: m/z calcd for C11H19O7: 263.1131; found: 263.1143. Anal. Calcd for C11H18O7: C, 50.38; H, 6.92. Found: C, 50.28; H, 7.11.
Compound 13 (4R) [data taken from a (5:1) mixture]: white solid. 1H NMR (400 MHz, CDCl3): δ = 1.25 (3 H, s), 1.45 (3 H, s), 2.38 (3 H, s), 2.87 (1 H, d, J = 15.9 Hz), 3.36 (1 H, d, J = 16.1 Hz), 3.63 (3 H, s), 4.42 (1 H, d, J = 11.7 Hz), 4.65 (1 H, d, J = 5.8 Hz), 4.67 (1 H, d, J = 11.4 Hz), 4.75 (1 H, d, J = 5.8 Hz), 5.33 (1 H, s), 7.27-7.37 (5 H, m). 13C NMR (100 MHz, CDCl3): δ = 23.9 (CH3), 25.7 (CH3), 27.9 (CH3), 41.9 (CH2), 51.7 (CH3), 69.8 (CH2), 85.2 (CH), 85.6 (CH), 92.4 (C), 108.2 (CH), 112.9 (C), 127.6-128.5 (5 × CH), 136.9 (C), 170.0 (C), 208.9 (C). MS (EI): m/z (rel. int.) = 349 (1) [M+ - CH3], 321 (8), 91 (100). HRMS: m/z calcd for C18H21O7: 349.1287; found: 349.1278. Anal. Calcd for C19H24O7: C, 62.63; H, 6.64. Found: C, 62.88; H, 6.63.