Cyclobutenediones rearrangement

Quinone synthesis. Two laboratories12 have found that the adducts formed by addition of an aryl-, alkynyl-, or heteroaryllithium to a cyclobutenedione rearrange when heated (138-160°) to hydroquinones, which are usually isolated as the quinone after air or chemical oxidation. The rearrangement involves an interme-... 

Alkylidenecyclopentene-l,4-diones (cf. 12, 130).2 The cobaltacyclopente-nedione (2) formed on reaction of a cyclobutenedione with 1, when complexed with dimethylglyoxime, reacts with 1-alkynes to form 5-alkylidenecyclopentene-1,4-diones (3). The reaction involves an alkyne-vinylidene rearrangement. Ben-zoquinones are usually formed in minor amounts. 

Two one-pot syntheses of highly substituted pyran-2-ones have been published. One involves the reaction between t-BuNC, dialkyl acetylenedicarboxylates and bromomalonates <99JCR368>. In the other, cyclobutenediones are treated with 0-silylated cyanohydrins to yield a 4-acylcyclobutenone by a 1,4-silyl migration and cyanide displacement which rearranges to the pyranone (Scheme 18) <99JOC2145>. 

It has been reported that compound 16 with alkali rearranges to phenyl-1,2-cyclobutenedione, 3 (Section 26-2E). This reaction appears to be the first reported reverse benzil-benzilic acid rearrangement (Section 26-4E). Explain how and why this process occurs. 

Cyclobutenones. Cyclobutenones and cyclobutenediones undergo photochemical rearrangement to unsaturated acids in a manner analogous to that of 6,6-disubstituted-2,4-cyclohexadienones. Irradiation of Formula 133 in ether saturated with water gives Formula 134 (49). In... 

The ethoxycarbocation intermediate (363) produced by the action of acid on the cyclobutenedione monoacetal (362) has been found to react with bis(trimethylsilyl)-acetylene to afford a 2-methylenecyclopent-4-ene-l,3-dione derivative (365). The authors426 proposed that the rearrangement results from an unprecedented cationic 1,2-silyl migration on the alkynylsilane, subsequent ring expansion via a vinyl cation intermediate (364), and re-closure by intramolecular addition of an acyl cation to a silylallene in a 5-exo-trig mode (see Scheme 90). 

Stannylquinones.1 The quinone synthesis based on addition of alkynyllithiums to substituted cyclobutenediones (13, 209-210, 284) can provide stannylquinones. Thus thermolysis of the alkynylcyclobutenol 1 with Bu3SnOCH3 results in rearrangement to the stannylquinone 2. As expected, these stannylquinones undergo palladium-catalyzed cross-coupling with organic halides (Stille reaction, 14, 35), particularly with allylic halides. 

Cyclobutenediones. A general route to these diones involves the regiospecific cycloaddition of dichloroketene to the phenylthio enol ether (1) of a ketone. The adduct (2) on treatment with triethylamine eliminates (J MsSCI and rearranges to 3. Peracid oxidation of 3 results directly in a cyclobutenedione (4). 

The electrocyclic reaction in which unsaturated substituents participate at C-2 of cyclobutenedione provides a somewhat different cyclization mode. The thermal rearrangements of 2-dienylcyclobutenones 88 and 3-(o-vinylphenyl)-cyclobutenediones 92 imderwent well-precedented 47r-67r electrocycUc reactions, but within the diene moiety to phenolic intermediates 90 and 94. These were allowed to react intramolecularly to give benzofurans 91 and naphthofu-... 

Gnrski, A. and Liebeskind, L. S. 1993. A new process for the regiocontrolled synthesis of sub-stitnted catechols and other 1,2-dioxygenated aromatics Conjugate addition of vinyl-copper, aryl-copper, and heteroarylcopper reagents to cyclobutenediones followed by thermal rearrangement. J. Am. Chem. Soc. 115 6101-6108. 

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