4-Alkoxycarbonyl-4,5-dihydro

Alternatively, the desethylcatharanthine can be obtained from the adduct 21 in the reaction of 2-(indol-2-yl)acrylate 20 and A-alkoxycarbonyl-1,2-dihydro-pyridine 8f(81CC37). 

Amino-2-alkoxycarbonyl-athyl)- 87 3-(2-Amino-2-alkoxycarbonyl-athyl)-2,3-dihydro-87... 

Of particular interest was the carbonylation of (Z)-2-en-4-yn-l-ols and (Z)-(2-en-4-ynyl)amines, which afforded furan-2-acetic [104,105] and pyrrole-2-acetic [116] esters, respectively, in good yields, through spontaneous or acid-promoted aromatization of the initially formed ( )-2-(alkoxycarbonyl)-methylene-2,5-dihydro-furans or -pyrroles (Scheme 31). 

Bei der Verseifung der 2-Alkoxycarbonyl- bzw. 2-Aminocarbonyl-Funktion decarboxyliert das zunachst entstehende 2-Carboxy-l,3-dimethyl-benzimidazolium-iodidzu 1,3-Dimethyl-benziinid-azoUum-iodid (81% Schmp. 196 -198°). Das Cyan-Derivat solvolysiert allerdings in hoi Bern Methanol zu l,3-Dimethyl-2-oxo-2,3-dihydro-benzimidazol (67%)499 ... 

Sie sind Vorstufen auch Fur stereoselektive3 Synthesen von a-Amino-/l-hydroxy-car-bonsauren2 (s. Bd. E5, S. 581). 4-Alkoxycarbonyl-5-aryl-4,5-dihydro-l,3-oxazole IV (R3 oder R4 = Aryl) ergeben bei der katalytischen Hydrierung N-Formyl-phenylalanin-ester z.B.3 ... 

Bis-p-nitrophenyl malonate (55M29) reacts with a-alkylamino-isobutyr-onitriles in xylene to give derivatives (16b) of tetramic acids with yields of 30-50% (86UP1 88UP1). The reaction of derivatized malonic acids with a-amino acid esters to 3-alkoxycarbonyl-l,5-dihydro-4-hydroxy-2-pyrrolones presents the same problems (see Section III). (See Fig. 8.)... 

X-Ray diffraction analysis of differently 2-substituted 2-alkoxycarbonyl-3,6-dihydro-277-thiopyran 1-oxides revealed that while the alkoxycarbonyl and sulfoxide units are trans disposed, they possess different conformations. Thus, for 54 X = H and CN, the oxygen and ester functions are equatorially disposed, whereas when 55 X is methyl or phenyl, the ester and sulfinyl oxygen occupy axial positions (Figure 6) <1995HAC631, 1999EJ02573>. 

Derivatives of 1,2-, 1,4-, 2,3-, and 2,5-dihydropyrazine are known, but the structures of these compounds are not easy to establish because of the tendency of dihydropyrazines to isomerize, dimerize, and oxidize. Dihydro structures are stabilized by groups such as alkoxycarbonyl and phenyl 1,4-dihydro-2,3,5,6-tetraethoxycarbonyl-pyrazine and 2,3-dihydro-5,6-diphenylpyrazine are relatively stable compounds. 

Allopurinol, 1,5-dihydro-4//-pyrazolo[3,4-d]pyrimidin-4-one (53), was first synthesized by Robins <56JA784> and by Schmidt <58HCA1052) from 5-aminopyrazole-4-carboxylic acid derivatives. Several syntheses starting from a simple acyclic intermediate have been reported. Thus, reacting ethyl alkoxymethylene cyanoacetate with hydrazine and formamide at 14(M80°C gave allopurinol in high yield. An acid catalyst lowers the temperature required for cyclization of the intermediate 4-alkoxycarbonyl-3-aminopyrazole and raises the purity and the yield of allopurinol <69BRPI 284084). 

Alkoxycarbonyl-l-formyl-5,6-dihydro- E6a, 679 [aus 1-(4-COOR- 3-furyl)- 3,4-H2 —isochinolin]... 

Diastereoseleetive Synthesis of Substituted 3,4-Dihydro-l//-2-benzopyrans via Alkoxycarbonylation... 

Intramolecular alkoxycarbonylation of secondary benzylic alcohols (e.g., 3) requires a shorter time (2 h) and a mixture of 1,3-disubstituted 3,4-dihydro-1 //-2-benzopyrans 4 is obtained in 82% yield and a 74 26 (cis/trans) diastereomeric ratio, as determined by HPLC. The stereochemistry of each isomer is determined by a comparison with known compounds84,85. 

A useful extension of the alkoxycarbonylation reaction has been devised in order to obtain 3,4-dihydro-4-hydroxy-l//-2-benzopyran-3-acetic acid lactones from 5-alkene-l,4-diols. The intramolecular cyclization of 7, carried out with palladium(II) acetate and copper(II) chloride under a carbon monoxide atmosphere, affords the m-lactone 8 in 68% yield. The configuration is assigned on the basis of H-NMR double resonance methods86. 

Amidines 9 with an appropriate ortho-carbonyl substituent, which are obtained from the respective ortho-carbonyl aniline derivatives and 0-ethyl succinimide (5-ethoxy-4,5-dihydro-3//-pyrrol-2-one), are cyclized with sodium in alcohol to quinazolin-4(3// )-ones 10a and quinazolines 10b with a 2-[(alkoxycarbonyl)ethyl] substituent at C2. The reaction can also be carried out starting from anthranilates or 2-aminophenyl ketones as a simple one-pot synthesis. ... 

Acid-catalyzed addition of aliphatic, aromatic or heteroaromatic cyanohydrins to ethyl vinyl ether, n-butyl vinyl ether or dihydro-4//-pyran provides base stable, protected cyanohydrin derivatives. Phase transfer catalyzed alkylation of aliphatic cyanohydrins with allylic bromides gave a-substituted a-allyl-oxyacetonitrile. Carbonyl compounds react wiA cyanide under phase transfer catalysis to give cyanohydrin anions, which are trapped by an acyl chloride or ethyl chloroformate to give acyl- or alkoxycarbonyl-protected cyanohydrins respectively. The reduction of the carbonyl group of an acyl cyanide by NaBH4 under phase transfer conditions followed by esterification serves as an alternative route to aldehyde-derived cyanohydrin esters. ... 

Gebauer, M., Heinisch, G., Lotsch, G. Pyridazines. XXXIX. N-Substituted 1,2-dihydro-1,2-diazines formed in homolytic alkoxycarbonylation reactions of pyridazines. Tetrahedron 1988,44, 2449-2455. 

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