2- Butene-1,4-diones

Another variation of the Paal-Knorr eondensation involves starting with a derivative 0 2-butene-1,4-dione and performing a reduetion prior to the eyelization reaetion. For exampk Rao has reeently reported that trisubstituted furans 84 ean be produeed in high yield upo treatment of diones 83 with formic acid, catalytic sulfuric acid, catalytic palladium on carbor... 

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. 

Oxidation of 1,4-disubstituted 2-butene-1,4-dione dioximes with lead tetraacetate or phenyliodoso bis(trifluoroacetate) leads to mixtures containing 3,6-disubstituted dihy-droisoxazolo[5,4-c ]isoxazoles and 3,6-disubstituted pyridazine 1,2-dioxides (equation 78)... 

Photolysis of [(Z)-2-(acyloxy)ethenyl]carbene complexes (= 4-acyloxy-1-chroma-l,3-dienes) (CO)sCr=C(OEt)-CH=C(OCOR1)R (Z)-169 (R = C6H5, t-Bu, c-Pr R1 = C6H5, c-Pr, c-C7H7CH2, f-Bu, Me2C=CH) with UV light of >300 nm affords 2-butene 1,4-diones R CO —C(OEt)=CH — COR (E)-170 (60-68%) by a novel metal-mediated acyl migration. Compounds (Z)-171 and furans 172 are formed as minor products (Scheme 72).4g... 

Double bond cleavge. A surprising oxidative cleavage of l,2,3,4-tetraaryl-2-butene-1,4-diones to afford benzils in good yields (instead of forming the furans) occurs when they are irradiated by microwaves in formic acid and a catalytic amount of cone. H2SO4. 

Microwave-mediated transformations of 2-butene-1,4-diones 33 and 2-bu-tyne-l,4-diones 34 to furan derivatives 35 have been studied [40]. Several di-and triaryl furan derivatives have been prepared in high yields from but-2-ene-... 

Cyclization of unsaturated iminoxyl radicals has been proposed to rationalize the products resulting from the reaction of 2-butene-1,4-dione dioximes (BDD) with oxidizing agents such as lead tetraacetate (Scheme 48A). As yields of dihydroisoxazoloisoxazoles (CyS) of up to 60% may be obtained (R = Ph), this would be a remarkable reaction since it would involve the generally much disfavored Cy5/Cy4 cyclization. But it must be noted that the (Cy 5) radical is stabilized, particularly when R = Ph. Examples of oxidative cyclization of oximes of a -ethylenic ketones to dihydroisoxazoles have been reported in the steroid series and could involve an analogous mechanism. ... 

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