2- Butene-1,4-diones synthesis

Binuclear cumulenes, synthesis, 230 Bis(methylene)propenylphosphorane, synthesis with phosphaalkenes, 19 [ ( -BuSe)Fe2(CO)6h(/i4-Se)], synthesis and structure, 275, 276 Butene 1,4-diones, synthesis, 224... 

Cydopentane reagents used in synthesis are usually derived from cyclopentanone (R.A. Ellison, 1973). Classically they are made by base-catalyzed intramolecular aldol or ester condensations (see also p. 55). An important example is 2-methylcydopentane-l,3-dione. It is synthesized by intramolecular acylation of diethyl propionylsucdnate dianion followed by saponification and decarboxylation. This cyclization only worked with potassium t-butoxide in boiling xylene (R. Bucourt, 1965). Faster routes to this diketone start with succinic acid or its anhydride. A Friedel-Crafts acylation with 2-acetoxy-2-butene in nitrobenzene or with pro-pionyl chloride in nitromethane leads to acylated adducts, which are deacylated in aqueous acids (V.J. Grenda, 1967 L.E. Schick, 1969). A new promising route to substituted cyclopent-2-enones makes use of intermediate 5-nitro-l,3-diones (D. Seebach, 1977). 

Other PK variations include microwave conditions, solid-phase synthesis, and the fixation of atmospheric nitrogen as the nitrogen source (27—>28). Hexamethyldisilazane (HMDS) is also an excellent ammonia equivalent in the PK synthesis. For example, 2,5-hexanedione and HMDS on alumina gives 2,5-dimethylpyrrole in 81% yield at room temperature. Ammonium formate can be used as a nitrogen source in the PK synthesis of pyrroles from l,4-diaryl-2-butene-l,4-diones under Pd-catalyzed transfer hydrogenation conditions. 

Similar reaction conditions as those by Bose were used for a range of other applications, for example, the synthesis of heterocycles. A combination of a microwave-assisted Paal-Knorr reaction15 with a transfer hydrogenation takes place in the preparation of 2,5-di- and 1,2,5-trisubstituted pyrroles from -l,4-diaryl-2-butene-l,4-diones in a one-pot operation. Hydrogenation was achieved with ammonium formates and 10% Pd/C as catalyst in PEG-200. Yields of up to 92% were obtained within 0.5-2 min (Scheme 4.2)16. 

Rao, H.S.P. and Jothilingam, S., One-pot synthesis of pyrrole derivatives from ( )-1,4-diaryl-2-butene-1,4-diones, Tetrahedron Lett., 2001, 42, 6595-6597. 

Butene-l,4-diones and 2-butyne-l,4-diones were converted into 2,5-diaryl- and 2,3,5-triarylfurans in high yields in the presence of HCOOH and a catalytic anaount of Pd on carbon under microwave-irradiation conditions <03JOC5392>. This procedure provides a new approach to the starting material used in the Paal-Knorr furan synthesis, as unsaturated diones are reduced to saturated diones in situ by formic acid and palladium. The solid-phase synthesis of 2,3,5-trisubstituted furans from 1,4-diketones was also reported <03SL711>. 

The synthesis of an analog of (403) with a methyl group at Cjo has also been described [Z. G. Hajos, D. R. Parrish, and E. P. Oliveto, Tetrahedron Letters, 1966 6495]. By the method of constructing ring A with l,3-dichloro-2-butene, compound (403) was converted into 4,9-estra-diene 3,17 dione, the acid isomerization of which led to the methyl ether of racemic estrone [O. I. Fedorova, G. S. Grinenko, and V. I. Maksimov, Dokl. Akad. Nauk SSSR, 171 880 (1966)]. 

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