Deltic acid

Dehmlow, E. V. Tetrahedron Lett. 1972, 1271. This reaction principle was adapted for the synthesis of deltic acid (dihydroxycyclopropenone) from bis(trimethylsilyl)squarate Egger-ding, D., West, R., J. Amer. Chem. Soc. 97, 207 (1975). 

The calculated 13C NMR chemical shift of the carbonyl carbon of monoproton-ated benzaldehyde131,132 for the. E-form 102 (205.5 ppm) and that for the Z-form 103 (207.4ppm) agree well with the experimental shifts of 203.5 and 205.9 ppm, respectively. Protonation of a-substituted cinnamic acids such as 104 was studied by 13C NMR spectroscopy and IGLO-HF calculations.133 Protonated deltic acid (105) and related compounds,134,135 as well as protonated urea 106 (X = O)136 and thiourea 106 (X = S)137 have been investigated by 13C NMR spectroscopy and quantum chemical calculations.138... 

The trihydroxyyclopropenium ion (175) shows a single absorption in its C NMR spectrum, 128.7, which can be ascribed to the monoprotonated deltic acid from the DFT/IGLO calculations. Interestingly, the cation does not form the diprotonated species (176) even in Magic Acid (//q = -22). 

Deltic acid Squaric acid Croconic acid Rhodizonic acid Tropolone... 

Carbon-13 NMR spectra of the H2C On series, such as deltic, squaric, croconic and rhodizonic acids, obtained in anhydrous solvents [304] display carbonyl shifts similar to those reported for quinones (Table 4.33). Considerable shielding of the carbonyl carbon of deltic acid diethyl ester is not only attributed to the three-membered ring but also to an electron releasing effect of the ethoxy groups. 

The structure of 2,3-dihydroxycyclopropen-l-one, deltic acid (184), which has been determined by XD at 135 K, reflects significant contributions from cyclopropenylium or dipolar resonance forms286. The difference between formally double bonds and single... 

The most dramatic synthetic achievement with cyclobutenediones is the synthesis of deltic acid derivatives. As illustrated below, photolysis43 of diethyl squarate (16 d) yielded, among other products, diethyl debate (21). The bis-trimethylsilyl ester (16 e) of squaric acid similarly furnished a deltate ester which was successfully hydrolysed to deltic acid itself (22), the lowest member of the series of oxocarbon acids48). 

Figure 4 Syntheses of squaric acid and deltic acid...

The method by which cyclopropenones were first prepared namely the addition of dichloro (or dibromo) carbene to an alkyne and subsequent hydrolysis of the adduct continues to be a good source of cyclopropenones despite the generally low yields involved. In particular, it has provided a convenient synthesis of deltic acid (70) in 13-35% overall yield from di-t-butoxyacetylene (equation 29). The dicyclopropyl... 

Deprotonation of 76a can be effected and imine 73a, the first aza-analogue of deltic acid (70), is obtained in 72 % yield. Compound 73a is stable for long periods at - 30°C but at ambient temperatures decomposition is complete in a period of days. In this way a range of resonance-stabilized cyclopropenones, cyclopropenethiones and cyclopropenimines can be conveniently prepared as illustrated by compounds 77-80 over page ". ... 

The unstable imine 73a is the first aza analogue of deltic acid A single carbon resonance ( 115.0) for C(1)C(2)C(3) indicates rapid prototropic shift between the three nitrogen atoms. The debate dianion equivalent is available from the zwitterion 80. ... 

Treatment of 2,3-di-ier/-butoxycyclopropenone with trifluoroacetic acid at 6 "C produced 2,3-dihydroxycyclopropenone (deltic acid, 4) in quantitative yield. This compound was also obtained by treatment of 2,3-bis(trimethylsiloxy)cyclopropenone with butanal at — 78 C in 98% yield. 

The trianilinocyclopropcnylium salt, prepared from tetrachlorocyclopropene and A-trimethyl-silylaniline, was dehydrochlorinated with sodium hexamethyldisilazanidc at — 78 C in tetrahydrofuran to yield 2,3-dianilino-A-phenylcyclopropenimine (3), a nitrogen analog of deltic acid, in 72% yield. 

Deltic acid (242a) has been prepared via the photochemical decarbonylation of the squaric acid derivative (243) in hexane solution using a Vycor filter to... 

Reactions. The triple bond of 1 is neither hydrogenated nor hydrated under usual conditions. It does react with dichlorocarbene, however the adduct was used in a synthesis of deltic acid (2). The reagent was also used for a synthesis of squaric acid (5). When heated in benzene, 1 is converted into r-butoxyketene (a), which reacts with 1 to form 3. Oxidation followed by hydrolysis gives 5. 

Diethoxycyclopropenone, which is formally the diethyl ester of deltic acid has been prepared similarly by irradiation of diethoxy-cyclohutenedione [150]. It is very hygroscopic and is partially stable to cold alkali or acid but resinifies quickly when heated with 10% hydrochloric acid. 

Dihydroxycyclopropenone or "deltic acid" has been prepared from squaric acid (dihydroxycyclobutenedione) [145] ... 

Deltic acid is stable to atmospheric oxygen and water but appears to decompose in aqueous ethanol of pH i ... 

The bis-(p-hydroxyaryl)quinocyclopropenes are converted into dianions when treated with base [170]. These anions have also been prepared directly from tris(p-hydroxy)cyclopropenium salts and have been isolated as yellow powders [171]. They are in effect vinyl-ogues of the dianion of deltic acid. 

The acid dissociation constants of deltic acid (2,3-dihydroxycyclopropenone) ipK 2.57, pXj 6.03 at 25 °C) indicate that it is a much weaker acid than its higher homologues cf. squaric acid pXj 0.54, pX2 3.48). The thermodynamic pX values... 

Photolysis of squaric acid (108a) in 1 8H20 CH3CN solution gives ketene 109a, and on further photolysis deltic acid is formed (110, Eqn... 

Despite several earlier attempts from related substrates, the synthesis of deltic acid proceeds quantitatively from (162), and the compound exhibits moderate thermal... 

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