Cyclopropenone carbonyl

Cycloadditions of aziridines to diphenylcyclopropenone lead to 4-oxazolines (36) (70CJC89). A mechanism involving initial addition to the cyclopropenone carbonyl group followed by ring opening and recyclization was suggested. 

Selective reduction of the cyclopropenone carbonyl group to a CH2 group has been described for diphenyl cyclopropenone utilizing its protonation product 294 or the diphenyl chloro cyclopropenium cation 292, which yielded 1,2-diphenyl-A1,2-cyclopropene (293) on treatment with trimethylamine borane210 ... 

Y (as confirmed by results with triafulvenes (see p. 101)). With phosphonium ylides 2-pyrone formation competes with Wittig olefination of the cyclopropenone carbonyl group. 

Bernhardsson and coworkers have recently used CASPT2 calculations (electron-correlation correction to the CAS wave function) to model carbonyl oxides in solution. Solvation effects in acetonitrile solvent also suggest that the zwitterionic form would be favored with an elongation of the 0—0 bond length and a decrease in the C—O bond. Ab initio calculations have been recently reported for monofluorocarbonyl oxide , diflu-orocarbonyl oxide , methylcarbonyl oxide and cyclopropenone carbonyl oxide. In the recent literature the idea that carbonyl oxide can be an important source of OH radicals has also been presented. ... 

Diphenylcyclopropene thione (156) was prepared11S-12°) from 3,3-dichloro-1,2-diphenyl cyclopropene (154) by reaction with thioacetic acid, since transformation of the carbonyl function of diphenyl cyclopropenone with P4S10121 was complicated by ring expansion to the trithione 155122 In a useful recent thioketone synthesis123) 156 was obtained directly from diphenyl cyclopropenone in a quantitative yield by simultaneous treatment with HC1 and H2S. 

Since the dipole moments of cyclopropenones are enlarged with respect to simple ketones and compare to other polar systems, e.g. trimethylamine oxide in Table 4, there seems to be evidence for considerable charge separation in the carbonyl group, which was expressed in terms of a cyclopropenium oxide contribution to the ground state. 

The carbonyl distances in diphenyl cyclopropenone and cyclopropenone (1.225/1.212 A) are larger than in cyclopropanone and indicate enhanced singlebond character. The same is true for the C=S bond in the thione 156 (1.63 A) compared to the C=S distance in thioketones (1.56 A1S7 ). 

Electrophilic attack on cyclopropenones takes place at carbonyl oxygen, as indicated by the formation of hydroxy cyclopropenium cations on protonation (see p. 28). Hydrogen-bonded complexation between the carbonyl oxygen of diphenyl cyclopropenone and the O-H hydrogen in water212 and substituted acetic acids213 is reported to give rise to well-defined 1 1-adducts (296). 

Tetracyano ethylene oxide, however, which represents a potential 1,3-dipole of the carbonyl ylide type, reacts with diphenyl cyclopropenone to give a cycloadduct of probable structure 415/417263, which may arise from insertion into the cyclopropenone C1(2)/C3 bond. 

Recent investigations confirmed earlier findings on diphenyl cyclopropenone277 278 ruling out the intermediacy of cyclopropenones in the catalytic carbonylation of alkynes ... 

Thus asymmetric diaryl cyclopropenones were converted to the isomeric acrylic acids 318/319 by aqueous Ni(C0)4 in a similar proportion to that obtained from the corresponding acetylenes by carbonylation with the same catalyst279, whilst in non-aqueous media carbonyls like Ni(C0)4, Co2(CO)8, or Fe3(CO)12 effected de-carbonylation278, 280) probably via metal-complexed intermediates, e.g. 

A large number of stable planar, tetrahedral, or octahedral complexes of lb, lib, and Vlllb elements (Cu2+, Zn2+, Co2+, Ni2+, Ru2+, Rh2+, Pd2+, Pt2+, Pt4+) using cyclopropenones (preferentially the diphenyl compound) as ligands has been evaluated mainly by Bird281. Their preparation may start either with metal salts or with carbonyls, as the octahedral Co(II) complex [Co(Dcp)6]2+ may exemplify ... 

In all these complexes the cyclopropenone ligand was shown to interact with the central transition element by means of the carbonyl function from spectroscopic criteria, its donor capacity was compared to pyridine-N-oxide282). 

Berson and colleagues119 re-examined the Diels-Alder reaction between 1,3-diphenyli-sobenzofuran and cyclopropenone. They selectively obtained the exo adduct, as was confirmed by X-ray analysis. Ab initio calculations indicated a kinetic preference for the exo isomer due to stabilizing interactions between the ether oxygen and the carbonyl carbon in the exo transition state120. 

On heating with cyclopropenone 113 (Scheme 28), 59 gives equal amounts of two products 114 arises from a Diels-AIder reaction, and 115 from direct attack of the pyrazole nitrogen at the carbonyl group.77... 

Cyclopropenone undergoes many interesting reactions — one example is Diels-Alder addition, the product of which in methanol solution is a hemiketal. That the hemiketal is favored for the adduct, but not for cyclopropenone, indicates that the double bond of cyclopropenone has a considerable effect on the reactivity of the carbonyl group. 

Cyclopropenones and carbon monoxide react in the presence of Ru3(CO)12 to form tetrasubstituted pyranopyr-andiones 655 in high yield (Equation 266) <2002JA6824>. Unsymmetrical tetrasubstituted pyranopyrandiones 656 can be accessed by the cross-carbonylation of cyclopropenones and internal alkynes in the presence of a ruthenium catalyst (Equation 267) <2002JA6824>. 

Cyclopropanone is a highly reactive ketone, presumably because of the extra angle strain introduced into the three-membered ring by the, vp2-hybridized carbonyl carbon. Cyclopropenone is much less reactive even though it has more angle strain. Offer an explanation for this experimental observation. 

The reaction was extended to the cross-carbonylation of cyclopropenones and internal alkynes, leading to unsymmetrically substituted pyranopyrandiones (Eq. 18) [33]. 

Cyclobutenediones 148 possessing an alkoxy substituent reacted with norbornene 40 in quite a different way, in which CO molecule was extmded from the dione substrates (Scheme 4.52) [103]. In the presence of catalytic amounts of Ru3(CO)i2 and PEt3, 148 and 40 was heated at 160 °C under 3 atm CO to regioselectively afford cyclobutenones 149. Such a novel reconstructive cycloaddition was further extended to the carbonylative dimerization of a cyclopropenone 150 resulting in the formation of a pyranopyrandione 151 in high yields [104], These novel transformations of... 

Cyclopropenones react with CO in the presence of Ru3(CO)i2/NEt3 to give pyrano-pyrandiones. This reaction involves C-C bond cleavage and a successive reconstructive carbonylation reaction (Eq. 11.45). 

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