Cyclopropenones reduction

Cyclopropenone was flrst synthesized " by the hydrolysis of an equilibrating mixture of 3,3-dichlorocyclopropene and 1,3-dichloro-cyclopropene (prepared by reduction of tetrachlorocyclopropene with tributyltin hydride). This procedure has been adapted - to prepare... 

The [3S+1C] cycloaddition reaction with Fischer carbene complexes is a very unusual reaction pathway. In fact, only one example has been reported. This process involves the insertion of alkyl-derived chromium carbene complexes into the carbon-carbon a-bond of diphenylcyclopropenone to generate cyclobutenone derivatives [41] (Scheme 13). The mechanism of this transformation involves a CO dissociation followed by oxidative addition into the cyclopropenone carbon-carbon a-bond, affording a metalacyclopentenone derivative which undergoes reductive elimination to produce the final cyclobutenone derivatives. 

The 4-hydroxy aryl substituted cyclopropenone 251 was found by West193 to exhibit a remarkable cycle of decarbonylation and oxidation-reduction reactions ... 

Dimerization of cyclopropenones has also been found to occur under reductive conditions. Tetraphenyl resorcinol is formed in addition to a small amount of tetra-phenyl p-benzoquinone on treatment of diphenyl cyclopropenone with aluminum amalgam200 its formation can be rationalized via dimerization of the cyclopropenone ketyl 266 and subsequent aromatization, possibly according to a prismane mechanism. 

An analogy at least formally valid can be seen in the reductive conversion of cyclopropenone to hydroquinone occuringwith l%Na-amalgam201. ... 

Ethyl phenyl cyclopropenone (14) on reduction with NaBH4 gave rise to prod ucts 289-291, which can be ascribed to a common cyclopropanone intermediate 288 ring-opened by further reduction or attack of solvent209 ... 

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 ... 

Direct reduction of chloro cation 292 in non-aqueous media to diphenylcyclopro-pene 293 is possible by means of dimethylamine borane211. The chloro cation 292 is easily prepared from the dichlorocyclopropene 154 and Lewis acids like AICI3 or SbCls11S. The reductive dimerization of cyclopropenones has already been mentioned (p. 58). 

An analogy with reductive dimerization of diphenyl cyclopropenone (p. 58) was found on polarography of l,2-diphenyl-4,4-dicyano triafulvene (64)289. In a one-electron reduction step the cyclopropenyl radical anion 469 is likely to be generated and dimerized to the dianion of tetraphenyl-l,4-dicyanomethyl benzene (470) the dianion 471 could be successively oxidized via the anion radical 472 to the 1,4-quinodimethane derivative 473. 

The elusive radical cation of pyridine (140) has been obtained by irradiation of pyridine in CFCb at 4 K (79MI20403) and g values and hyperfine coupling constants have been measured for the parent molecule and deuterated derivatives. This species is of cr-type, the odd electron spending most of its time in the N sp2 lone pair orbital. Radical cations and anions of pyridinium bis(alkoxycarbonyl)methylides have been produced in the former case (78CC817) as a cyclopropenone complex, and in the latter by reduction of pyridinium bis(methoxycarbonyl)methylide with sodium (79JMR(35)l7l). The coupling constants in the ESR spectrum of both the radical cation and the anion agree to some extent with simple Huckel MO calculations. 

Cyclopropenone (I). Breslow and Oda" have effected the preparation and isolation of pure recrystallized cyclopropenone (I, m.p. —29 to —28 ) by reduction of tetra-chlorocyclopropenc in paraffin oil with tri-n-butyltin hydride under argon. A mixture... 

Unsubstituted cyclopropenone was prepared by hydrolysis of the di- and trichloro-cyclopropenes obtained from the reduction of tetrachlorocyclopropene " . Treatment of the trichlorides 37 and 38 with SbCls affords the hexachloroantimonate salt of... 

Reductive dimerization was observed when 27 was treated with aluminum amal-gam ° . This reaction probably proceeds via the cyclopropenone ketyl 53 (equation 44). A prismane intermediate has been suggested. 

Although catalytic reduction of cyclopropenones can be effected readily, the course of the reaction is sensitive to the catalyst used. Thus, Pt/Hj gives acyclic ketones resulting... 

Cyclopropenone (3) has been prepared for the first time by reduction of tetra-chlorocyclopropene (1) with 2 equivalents of tri-n-butyltin hydride 11 careful hydroly-... 

Reduotion. Catalytic reduction of cyclopropenone commonly leads to reduction of both the double bond and the three-membered ring with formation of a dialkyl ketone ... 

Examples are provided by the catalytic reduction of diphenyl- [26], di-n-propyl- [88], di-t-butyl- [111] andn-pentyl- [100] cyclopropenones. However, when palladium replaced platinum as catalyst, the product from di-n-propylcyclopropenone was instead 2-propylhex-2-enal [88]. 

Reduction back to the cyclopropenone is only possible if carried out immediately otherwise carbon monoxide is lost spontaneously from this product. Compounds (XII) have been prepared, by a condensation reaction followed by oxidation, from the corresponding bis(p-hydroxyaryl)cyclopropenone, and are brilliantly coloured dichroic solids, blue or violet in solution but reflecting metallic gold or red [169],... 

Reduction. Cyclopropenone is catalytically reduced in methanolic solution, using platinum as catalyst, to give acetone as main product together with a small amount of 1-hydroxy-l-methoxycyclopropane both products presumably arise through the intermediacy of... 

Diphenylcyclopropene may be made either by dehydrochlorination of l chloro-1,2-diphenyl cyclopropane,or by reduction of the chlorodiphenyl-cyclopropenium ion with trimethylamine-borane in the presence of DMF. Although derivatives of cyclopropenone have been isolable as pure compounds for a number of years, the parent compound has been known only in solution until recently. It has now been purified and shown to have an unusually high b.p. (30 C, 0.45 Torr). It is stable only below its m.p. (—29 to —28°C) and polymerizes at room temperature. 

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