3.4- Diethoxycarbonyl

Zur Bildung von 3,4-Diethoxycarbonyl-furazan-2-oxid aus Oxalsaure-l-chlorid-2-ethylester-l-hydroximid284 s. Lit.285,286 ... 

Aus l-Nitro-(l,3-thiazolidin-2-yliden)-essigsaure-ethylester wird mit Acetanhydrid/Diethyl-ether-Trifluorboran unter Abspaltung dcs 1,3-Thiazoliden-Ringsystcms 3,4-Diethoxycarbonyl-furazan-2-oxiderhalten (zum Mechanismus s. Lit.)348 (zu weiteren Beispielen s. Lit.349- 354464) ... 

Furazan-2-oxide enthalten das Strukturmerkmal eines Nitrons und sind daher fur [3 + 2]-Cycloadditionen geeignet. So reagiert 3,4-Diethoxycarbonyl-furazan-2-oxid mit Olefinen unter Bildung von S-Ethoxycarbonyl S-dioxa-l-aza-bicyclopj.OJoctanen460 ... 

Nitron — F,C — en COOR) 2-Bcnzyl-3.4-diethoxycarbonyl-5-trifluoromcthyl- ElOb, 543 (Nitron + F.n-CF,)... 

Diethoxycarbonyl-1 -methy len-E17c, 2243 (Methylen-cyclopro-pan + En) E21c, 3026/3027/3031 (ROOC — CH = CH — COOR + Methylen-cyclopropan)... 

Die Cycloaddition von 2-Diazo-3-oxo-butan mit Butindisaure-dimethylester und -diethylester fuhrt zu l-Acetyl-3,4-dimethoxycarbonyl- (Schmp. 65°) bzw. l-Acetyl-3,4-diethoxycarbonyl-lH-pyrazol [Sdp. 180—181 °/l 3 Torr (1,73 kPa)]859,860 analog reagiert 2-Diazo-butanal. Mit cyclischen 2-Diazo-ketonen sind carboCyclisch kondcnsierte 1 H-Pyrazole zuganglich858-861-863. 

Acetyl-3-carboxy-4-phenyl- 649 l-Acetyl-4-chlor- 613 l-Acctyl-3,4-diethoxycarbonyl- 506 l-Acetyl-3.4-dimethoxycarbonyl- 506 3(5)-Acctyl-4,5(3)-dimethoxycarbonyl- 507 4-Acetyl-l,3-dimcthyl- 454... 

To a suspension of 1.31 g A-acetyl-D,L-alanine (10 mmol) in 10 mL acetic anhydride was added 3.2 mL diethyl acetylenedicarboxylate (20 mmol). The reaction mixture was maintained at 110°C for 2 h, cooled, and then evaporated under reduced pressure. The oily residue was dissolved in hot cyclohexane and left in the refrigerator overnight with crystal seeds. Diethyl 2,5-dimethyl pyrrole-3,4-dicarboxylate was isolated as white needles by filtration, in amount of 274 mg, in a yield of 11.4%. The filtrate was evaporated and chromatographed (dry column vacuum chromatography) using CH2CI2 and then CH2Cl2/EtOH (99 1 to 98 2) to afford 1.58 g 2-(2,5-dimethyl-3,4-diethoxycarbonyl)-pyrrolyl maleic acid diethyl ester as a yellowish oil, in a yield of 39%. 

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