1.4- dicarbonyl compounds, from succinic

Methoxy- and 2-acetoxy-furans are available from 2,5-dimethoxy- and 2,5-diacetoxy-2,5-dihydro-furans (18.1.1.4) via acid-catalysed elimination. They undergo Diels-Alder cycloadditions the adducts can be further transformed into benzenoid compounds by acid-catalysed opening. 3,4-Dihydroxyfuran is undetectable in tautomeric equilibria between mono-enol and dicarbonyl forms the dimethyl ether behaves as a normal furan, undergoing easy a-electrophilic substitution, mono- or dilithiation at the a-position(s), and Diels-Alder cycloadditions. 2,5-Bis(trimethylsilyloxy)furan is synthesised from succinic anhydride it too undergoes Diels-Alder additions readily. Both furan-2- and -3-thiols can be obtained by reaction of lithiated furans with sulfur in each case the predominant tautomer is the thiol form. ... 

Formation of pyridazine ring by reaction of 1,4-dicarbonyl compounds of the type 987 was reported first in 1960, when characterization of 5,5,5-trifluorolevulinic acid (991) and its lactone 992 was performed (Scheme 211) [602]. Upon their reaction with 2,4-dinitrophenyl hydrazine (2,4-DNPG) in ethanol, a product 993 was obtained instead of 2,4-dinitrophenyl hydrazones. The starting compound 991 was obtained by hydrolysis of a Claisen adduct 990, prepared from ethyl trifluoro-acetate and diethyl succinate 989. 

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