2-Ene-l,5-diones

An 80% yield of tetraphenylfuran is obtained by treatment of benzoyl chloride with active titanium generated by lithium aluminum hydride reduction of titanium trichloride (Scheme 84e) (8UOC2407). The reaction nroceeds via benzil and tetraphenylbut-2-ene-l,4-dione, both of which are minor products of the reaction. 

Photochemical cycloaddition of cyclohex-2-ene-l,4-dione (31) and acenaphthylene (32) in dichloromethane gives the iM-,un//,c -adduct 33 in 15% yield, in addition to large amounts of acenaphthylene dimers, which are insoluble and precipitate during the photolysis.100... 

Among the more recent examples of furan synthesis is the cyclization of the unsaturated 1,4-diketone (9) in acetic anhydride to afford 3-acetoxy-2,4,5-triphenylfuran (10). Treatment of l,2,3,4-tetrapheny but-2-ene-l,4-dione (PhCOCPh==CPhCOPh) with triethyl phosphite yields 2,3,4,5-tetraphenylfuran (79JOC494). 1,2-Diaroylethylenes have been converted to 2,5-diarylfurans with tin(II) chloride and hydrochloric acid (62ZOB1195). 

Treatment of l,2,3,4-tetraphenylbut-2-ene-l,4-dione with triethyl phosphite yields tetraphenylfuran (79JOC494), 2,5-Dimethylfuran has been prepared in high yield (94%) by distillation of hexane-2,4-dione from an acidic ion exchange resin. Alkylfurans are important as synthons for 1,4-diketones (73S209). 

Dichlorooctafluorocyclohexene (20) under similar conditions gives cyclohex-2-enone 21 and cyclohex-2-ene-l,4-dione 22.146... 

Most of the chemical properties of fused aziridines described in the literature are concerned with cycloaddition reactions. For example, it was shown in one of the first works [93] that refluxing azirenoimidazole 72 with different compounds containing multiple C-C bonds in / interaction with diethyl acetylene dicarboxylate 116, diethyl fumarate 118 or 1,4-diarylbut-2-ene-l,4-diones 120 gives rise to the cycloadducts 117,119 and 121, respectively... 

There are several exceptions in the literature. One of them is a reaction of 3-amino-1,2,4-triazole 147 with l,4-diphenylbut-2-ene-l,4-dione (dibenzoylethy-lene) 170 [169] the first stage—alkylation of the amine with oc,(3-unsaturated ketone—is carried out with participation of all possible endocyclic reaction centers of the aminoazole (Scheme 3.51). 

Rawal and Thadani [160] have taken advantage of alkynes as excellent insertion partners in Pd(II)-catalyzed allylations. Interestingly, the Pd(II) species present in the medium after alkyne insertion into allyl chlorides or bromides can serve for a sequential Wacker-Tsuji oxidation upon introduction of CuCl, oxygen, and water to the reaction medium to give y-halo /-fy-cnones 220 in good yields (Scheme 91). If phenylacetylene is used as an alkyne l-phenyl-pent-2-ene-l,4-dione can be isolated in 77% yield as the result of a subsequent oxidative hydration of the y-halo P,y-enone 220. 

Acetoxy)ethenylcarbene complexes of chromium underwent photochemically induced acyl migration to give ( )-but-2-ene-l,4-diones as the major product. ... 

C2-Symmetric chiral 1,4-diols can be prepared by the oxazaborolidine-cata-lyzed reduction of 2-ene-l,4-diones and 2-yne-l,4-diones [93]. From ferrocenyl diketones, the corresponding C2-symmetrical chiral diols were prepared in high ees (>98% ee) [94]. Enantiopure (>99% ee) (S, S)-l,2-diarylethanediols were also synthesized by borane reduction of diaryl 1,2-diones using 4a [95]. 

Intramolecular cyclization of bis-a-diazoketones. The decomposition of 1,7-bisdiazoheptane-2,6-dione (1) with this copper chelate in boiling benzene under high dilution conditions affords cyc ohept-2-ene-l,4-dione (2) in 32% yield.1 A lower yield (20%) is obtained if copper bronze is used as catalyst. 

The method has been used to synthesize 4-hydroxytropone (y-tropolone). Thus catalytic decomposition of 1,7-bis(diazo)-4-chloroheptane-2,6-dione (3) leads to 6-chlorocyclohept-2-ene-l, 4-dione (4) loss of HC1 on treatment with weak bases affords 4-hydroxytropone (5). 

Selective reduction of 2-ene-l,4-diones and 2-ene-l-ones. This metal hydride is excellent for reduction of 1,4-enediones to the corresponding unsaturated alcohols... 

D.88) 2-Cyclohexene- 1,4-dione, 2,6,6-trimethyl-, 2,6,6-trimethylcyclohex-2-ene-l,4-dione, 3,5,5-trimethyl-2-cyclohexene-1,4-dione, 4-oxoisophorone [1125-21-9]... 

Alkoxy-2,5-diphenylfurans and 2,3,5-triphenylfuran can be oxidatively cleaved with DDQ in CH2CI2 or CH2CI2/DMSO to give cfr-2-aIkoxy (or 2-phenyl)-but-2-ene-l,4-diones eq (48). With 2-methyl-5-pentylfuran, the fraws-enedione was obtained, but the reaction was unsuccessful with 2,5-diphenylfuran, 2-methoxyfuran, and some other furans. 

The rearrangement of 3,5,5-trimethylcyclohex-2-ene-l,4-dione to trimethylhy-droquinone, an intermediate in vitamin E synthesis, can be accomplished over HY-zeolite in the presence of hydrogen (Hoelderich et al., 1988). 

A catalyst prepared as a suspension by warming diloroplatinic acid and an organosilicon hydride such as triethylsilane in 95 /o-ethanol is remarkably stable on storage and in many cases more active than Adams catalyst Diisobutyl aluminum hydride has been found to be an excellent reagent for the selective reduction of 2-en-l-ones and 2-ene-l,4-diones to the corresponding alcohols . Nickel boride catalysts have been recommended for the hydrogenation of strained carbon-... 

This reaction has been modified by the cyclization of 2-ene-l,4-diones or 2-yne-l,4-diones under microwave irradiation in PEG-200 in the presence of formic acid and palladium on carbon. ... 

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