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2,3-Dioxo-2,3-dihydrofurans, 2. - Versatile Synthesis of 2,3-Dioxo-2,3-dihydrofurans and Alkylidenebutenolides. - Crystal and Molecular Structure of 5-(4-Chlorophenyl)-4-methoxycarbonyl-2,3-dioxo-2,3-dihydrofuran
Saalfrank, Rolf W.,Lutz, Thomas,Hoerner, Bernd,Guendel, Juergen,Peters, Karl,Schnering, Hans Georg von
, p. 2289 - 2295 (2007/10/02)
Reaction of the 1,3-dicarbonyl compounds 5a-f, containing at least one α-hydrogen atom in R1 and/or R2, with oxalyl halides 2 in the presence of magnesium chloride yields regio- and on the whole stereospecifically the previously unknown (Z)-alkylidenebutenolides 7a-f.Similarly, the 4-alkoxycarbonyl-5-aryl-2,3-dioxo-2,3-dihydrofurans 6g-p are obtained (X-ray structure of 6i) starting from 3-aryl-3-oxo-propanoates 5g-p.Correspondingly, malondiamides 8a, b, e, f react with oxalyl chloride (2a) to give the 2,3-dioxo-2,3-dihydrofurans 9a, b and 11a, b.Having mono(alkyl/aryl)amino substituents in position 5, compounds 11a, b spontaneously tautomerize to give imino enols 12a, b.Hydrochlorides 10a, b are formed on treatment of malondiamides 8c, d with oxalyl chloride (2a).In the case of the β-oxocarboxamides 13/14 the substituents at the amide nitrogen atom control the regiochemistry.Starting from 13 (R2 = Ph) and oxalyl chloride (2a), 4-acetyl-5-diphenylamino-2,3-dioxo-2,3-dihydrofuran (15) is formed regiospecifically, whereas under the same conditions 13/14 (R2 = CH2Ph) afford 4-dibenzylcarbamoyl-5-methyl/phenyl-2,3-dioxo-2,3-dihydrofurans 16/17.Furanone 16 spontaneously enolizes to give 4-dibenzylcarbamoyl-3-hydroxy-5-methylene-2(5H)-furanone (18).Similarly, the N-monosubstituted β-oxocarboxamides 19a, b readily react regiospecifically with oxalyl chloride (2a) to give via the 2,3-dioxo-2,3-dihydrofurans 20a, b the imino enols 21a, b.Key Words: 2,3-Dihydrofuran-2,3-diones / Alkylidenebutenolides
