Cyclobutane-1,2-diones

Cyclobutane-1,2-dione, bromine used in formation of, 4 303 Cyclobutane derivatives, 75 489 Cyclobutene adducts, 75 489... 

Bromine has been used to form cyclobutane-1,2-dione [33689-28-0], C4H402, when other methods failed (35,36). 

Cychbutane-1,2-dione. Attempts to prepare cyclobutane-1,2-dione by oxidation of the readily accessible 3-hydroxycyclobutanone have all failed. Heine now has prepared tbe dione by bromination of 1,2-bistrimethyIsiloxycyclobutene-i (I). 

CYCLOBUTANE-1,2-DIONE Bromine. CYCLOBUTANEDIONES Chlorotiifluo-roethylenc. 

Acyloin-type cyclization of dimethyl 2,3-di-tert-butylbutanedioate by sodium in refluxing toluene gave the 3,4-di-/erf-butyl-2-hydroxycyclobutanone (1) in 90% yield.Oxidation with dimethyl sulfoxide and acetic anhydride - gave 3,4-di-tm-butylcyclobutane-l,2-dione (2, 55%). Irradiation of this a,/1-diketone gave 2,3-di-terf-butylcyclopropanone (3) and a polymeric product. (For the base- or acid-induced ring contraction of cyclobutane-1,2-diones, see Section 4.1.2.2.7.). 

Ring contraction of a cyclobutane-1,2-dione was first postulated in order to account for the formation of an a-oxo acid 2 from 2-phenylcyclobutane-1,2-dione (1). ... 

The parent compound cyclobutane-1,2-dione itself was proposed as an intermediate in the acid- or base-catalyzed ring contraction of l,2-dichlorocyclobutyl-l,2-diylcarbonate (5), adduct of dichlorovinylene carbonate with ethene under photolysis, which on dissolution in cold dilute potassium hydroxide and subsequent acidification or on dissolution in hydrochloric acid, gave the 1-hydroxycyclopropanecarboxylic acid (6) as a single product. (For other examples of such a reaction, see ref 70.)... 

Cyclobutane-l,2-dione has been isolated from the bromination of 1,2-bis(trimethyl-siloxy)cyclobutene, prepared by sodium induced acyloin cyclization of butanedioate in the presence of chlorotrimethylsilane . The acyloin cyclization of 1,4-, 1,5- and 1,6-diesters to give four-, five- and six-membered rings and the cyclization of )9-chloro esters to three-membered rings in the presence of chlorotrimethylsilane, which usually requires highly dispersed sodium, has been recently simplified by the use of sonochemical activation. The ring contraction of cyclobutane-1,2-diones to 1-hydroxyeyclopropanecarboxylic acid (7) and derivatives may be catalyzed by aqueous acid or base, by methoxide anion, amines or hydrazines and even takes place, though more slowly, in pure water or ethanol. ... 

For the photochemical ring contraction of cyclobutane-1,2-diones with carbon monoxide elimination, see Section 4.1.1. 

One-pot bromination of 1,2-bis(trimethylsiloxy)cyclobutenes and subsequent hydrolysis without isolating the intermediate cyclobutane-1,2-diones provided a convenient and ready route to 1-hydroxycyclopropanecarboxylic acids 8 (R = H). 

In the same way, from dimethyl (5)-2-methylbutanedioate (>95% ee) was obtained the methyl (15,25)-l-hydroxy-2-methylcyclopropanecarboxylate, via the (5)-3-methyl-cyclobutane-1,2-dione. ... 

The syntheses of the metal-benzenethiolate complexes are accomplished by a ligand substitution reaction between the appropriate O-ethyl dithiocarbonate complexes and potassium benzenethiolate, KSPh. In the original report on the syntheses of the [M(SPh)4]2 complexes,1 the bis(3,4-dimercapto-cyclobutane-1,2-dione) [dithiosquaric acid] metal complexes were used in the ligand substitution reactions. The rather involved synthesis of the dithiosquarate ligand,2 using expensive starting materials, prompted us to develop new synthetic procedures which utilize the readily available, inexpensive O-ethyl dithiocarbonate complexes.3... 

Oxidative cleavage of l,2-bis(trimethylsilyloxy)cyclobutene with Br2, to give cyclobutane-1,2-dione. 

Conjugate addition, 34-5, 51-2, 53, 132, 133 Conjugate hydroxymethylation, 59-60 Copper(ii) bromide, 54 Copper(i) chloride, 120 Copper(ii) chloride, 120 Copper(i) cyanide, 7, 52, 53 Copper(i) iodide, 54 Corey s internal quench, 104 Cyanohydrin trimethylsilyl ether, 137 Cycloaddition, 34, 112 Cyclobutane-1,2-dione, 135 Cyclohept-2-dione, 135 Cyclohex-2-enone, 52,123 Cyclohexa-1,3-diene, 26 Cyclohexane carboxaldehyde, 22-3,69 73,78... 

DFT has been used to calculate pathways for the addition of hydroxide to cyclobutane-1,2-dione and to its hydrate, " and addition of hydroxide ion to the carbonyl group of formyl heterocyclics has been studied by ab initio methods. ... 

In connection with work on very strained fused thiophens, compound (42) has been obtained through a Wittig reaction between cyclobutane-1,2-dione (43) and the bis-ylide (44). From the cis-form of the diacetylenic thiiran (45), the long-elusive thienocyclobutadiene (46) has been obtained by flow pyrolysis at 250 °C. Compound (46) decomposes immediately on attempted chromatography or exposure to air. In benzene solution at room temperature it dimerizes to (47). 

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