Herstellung von Methylestern durch Umesterung funktionalisierter Substrate mit Titalsäureestern als Katalysatoren

Abstract

SummaryThe low solubility of tetramethyl titanate has so far prevented the laboratory use of titanate-catalyzed transesterifications with formation of methyl esters. Two procedures are described here, which allow the application of this exceedingly mild method to the synthesis of methyl esters: one uses methyl propionate/Ti (OEt)4, the other one uses methanol/Gly-Ti, a new type of catalyst, prepared from Ti (OEt),/ ethylene glycol 2 : 1.

Quinoline Alkaloids and Other Constituents of Melicope semecarpifolia with Antiplatelet Aggregation Activity

“…The remaining compounds were all of previously known structure and comprised confusameline ( 7 ), kokusaginine ( 8 ), osthenol ( 9 ), osthole ( 10 ), syringic acid ( 11 ), ayanin ( 12 ), methyl oleate ( 13 ), evolitrine, pteleine, dictamnine, skimmianine, haplopine, platydesmine, 7- O -prenylumbelliferone, umbelliferone, anisocoumarin H, xanthyletin, and a mixture of β -sitosterol, stigmasterol, campesterol, methyl vanillate, tetracosylferulate, and 2-hydroxymethylfurfural . These compounds were identified by comparison of their spectral (UV, IR, 1 H NMR, and MS) and/or mp data with those of corresponding authentic samples or data from the literature.…”

Photochemical Synthesis of Prochiral Dialkyl 3,3-Dialkylcyclopropene-1,2-dicarboxylates with Facial Shielding Substituents and Related Substrates

“…[7] While several simple dialkyl derivatives of 8 were commercially available, the synthesis of chiral derivatives in particular remained a challenge. [9] However, the activation of the carboxylate carbon atom towards nucleophilic attack also activated the Michael system towards Eur. [8] In analogy with Charlton's results, ''protection'' of the triple bond of the relatively electron-rich dipotassium acetylenedicarboxylate (prepared in situ from the monopotassium salt 2 and KOH) by bromine, followed by the formation of the diacid dichloride 4 from the diacid 3 with PCl 5 in pentane (Scheme 2), esterification (to 5, Scheme 3) and subsequent removal of the ''protecting group'' with zinc also proved superior to other methods in our case (Scheme 4).…”

Chemoenzymatic Asymmetric Synthesis of Pregabalin Precursors via Asymmetric Bioreduction of β-Cyanoacrylate Esters Using Ene-Reductases

“…Spectroscopic data were in agreement with data for rac - 1b ; [α] 23 D +30.7 ( c 1.07, MeOH); ee >99% determined by GC analysis (G-TA, 135–165 °C temperature gradient), t R 5.09 min. For determination of absolute configuration, ( S ) -1b (0.73 g, 5.2 mmol) was converted to the methyl ester by transesterification 40 with Ti(OEt) 4 (0.5 g, 2.2 mmol) and ethylene glycol (0.07 g, 1.1 mmol) in refluxing MeOH (25 mL) for 118 h. The reaction mixture was concentrated (∼5 mL) under reduced pressure, diluted with 10 mL of 4 N aqueous HCl, and extracted with EtOAc. The organic extract was washed with water, dried over magnesium sulfate, concentrated under reduced pressure and Kugelrohr distilled to give 0.46 g (60%) of ( S )-methyl 3-cyanobutanoate as a clear liquid (97%, contaminated with ∼3% ( S ) -1b ).…”