Synthetic Studies toward Jatrophane Diterpenes from Euphorbia characias. Enantioselective Synthesis of (−)-15-O-Acetyl-3-O-propionyl-17-norcharaciol

Helmboldt, Hannes; Hiersemann, Martin

doi:10.1021/jo802581g

Cited by 38 publications

(39 citation statements)

References 103 publications

(65 reference statements)

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“…Comparatively, the uncatalyzed carbonyl-ene processes usually require much higher temperatures. [36] Surprisingly, the cyclization temperature may be even lower in more substituted pyranose frameworks; for example, permethylated diketone 1 was transformed into 2 by irradiation at 0 8C for 12 h in 55 % yield. In contrast, the dideoxy photoenol 51 is stable at room temperature and requires 60 8C for complete cyclization.…”

Section: A-c-propynyl Glycosidementioning

confidence: 99%

Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of α‐Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives

Álvarez-Dorta

León

Kennedy

et al. 2013

Chemistry A European J

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The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish type II photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enolexo)-exo-trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 °C).

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Section: A-c-propynyl Glycosidementioning

confidence: 99%

Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of α‐Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives

Álvarez-Dorta

León

Kennedy

et al. 2013

Chemistry A European J

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“…Plant latex has been extensively studied but relatively little is known on the biochemical features of latex from plants belonging to the large genus Euphorbia , although several authors are working to fill this gap 20–26…”

Section: Introductionmentioning

confidence: 99%

Extraction and characterization of a natural rubber from Euphorbia characias latex

et al. 2012

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A natural rubber was identified and characterized for the first time in the latex of the perennial Mediterranean shrub Euphorbia characias. Four different methods, i.e., acetone, acetic acid, trichloroacetic acid, and Triton® X-100, followed by successive treatments with cyclohexane/ethanol, were employed to extract the natural rubber. The rubber content was shown to be 14% (w/v) of the E. characias latex, a low content compared with that of Hevea brasiliensis (30-35%) but a similar content to other rubber producing plants. E. characias rubber showed a molecular weight of 93,000 with a M(w) /M(n) of 2.9. (1) H NMR, (13) C NMR, and FTIR analysis revealed the characteristic of the cis-1,4-polyisoprene typical of natural rubber. These results provided novel insight into latex components and will ultimately benefit the broader understanding of E. characias latex composition.

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“…For Julia-Kocień ski olefination, see: Blakemore et al (1998). For the use of unsaturated -keto esters in intramolecular carbonyl-ene reactions in natural product synthesis, see: Helmboldt & Hiersemann (2009); Helmboldt et al (2006); Schnabel & Hiersemann (2009); Schnabel et al (2011) The title compound was synthesized using a reduction of ethyl 2-(trimethylsilyl)acetate (Gerlach, 1977) followed by a Mitsunobu reaction and a subsequent Mo-(VI)-catalyzed oxidation of the thioether (Schultz et al, 1963). Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis CCD; data reduction: CrysAlis CCD; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009).…”

Section: Related Literaturementioning

confidence: 99%

1-Phenyl-5-{[2-(trimethylsilyl)ethyl]sulfonyl}-1H-tetrazole

et al. 2011

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The title compound, C12H18N4O2SSi, was synthesized to be employed in a Julia–Kocieński olefination. In the molecule, the dihedral angle between the phenyl ring and the tetrazole ring is 41.50 (5)°. The significantly longer Si—C(methylene) bond [1.8786 (13) Å] and the shortened adjacent C—C bond [1.5172 (18) Å], as well as the significant deviation of the corresponding Si—C—C angle [114.16 (9)°] from the ideal tetrahedral angle, can be attributed to the β-effect of silicon. In the crystal, molecules are held together by van der Waals interactions.

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Synthetic Studies toward Jatrophane Diterpenes from Euphorbia characias. Enantioselective Synthesis of (−)-15-O-Acetyl-3-O-propionyl-17-norcharaciol

Cited by 38 publications

References 103 publications

Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of α‐Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives

Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of α‐Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives

Extraction and characterization of a natural rubber from Euphorbia characias latex

1-Phenyl-5-{[2-(trimethylsilyl)ethyl]sulfonyl}-1H-tetrazole

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