Ketones cyclopropenyl

Metallation of alkynylcyclopropanes at the acetylenic end is accomplished either by deprotonation or via metal-halide exchange reaction with strong bases. Metallation of ethynylcyclopropane may be affected by KOH in DMF, ethereal EtMgBr or preferably BuLi in THF (equation 151)231. All three metal acetyl ides react with methyl ketones to give the corresponding alcohols. However, the instability of cyclopropyl ketones towards bases, especially at the reaction conditions required by KOH (20 °C, 6h), and the sensitivity of cyclopropenyl double bonds in cyclopropenyl ketone derivatives towards addition reactions of alkylmagnesium compounds, make the alkyllithium (-78 °C, instant reaction) superior to the other reagents. 

Tsuchiya, T., Arai, H. and Igeta, H. (1973) Photochemistry - IX. Formation of cyclopropenyl ketones and furans from pyridazine N-oxides by irradiation. Tetrahedron, 29 (18), 2747-2751. 

Dewar thiophene (9.113A) and, from this, Dewar pyrrole derivatives have been isolated [246]. In contrast, photolysis of furan derivatives only promoted cyclopropenyl ketone rearrangements [271] (Figure 9.113). 

When 3-cyclopropenyl ketones (230), formed by irradiation of pyridazine N-oxides (229), were heated with n-butylamine under reflux for 1 h or stirred at room temperature for 3-4 h a mixture of pyrroles was formed in 80% yield (equation 151). ... 

No Dewar furan has been isolated or observed spectrometrically. Van Tamelen, who first isolated Dewar benzene substituted with f-butyl groups, examined the photolysis of di- and tri-t-butylfurans to compare results with those for the benzene. In the photoreaction of 2,5-di-r-butylfuran, three isomers were isolated (Eq. 2), including a cyclopropenyl ketone but not a Dewar furan.3... 

Perfiuorotetramethylfuran, though it has four trifluoromethyl groups to stabilize valence-bond isomers, gave only a cyclopropenyl ketone (Eq. 4).5... 

Since many furans are not particularly sensitive to light they often form as products of photochemical reactions. A high pressure mercury arc can be used to eject nitrogen from pyridazine Ai-oxides and form cyclopropenyl ketones and their furan isomers.29 High yields of 2-acetylfuran can be achieved by irradiating the pyrilium ion in Scheme 5 (i.e., the requisite pyrone dissolved in sulfuric acid) although the conditions, mainly the acidity, have to be carefully controlled.30 Surprisingly, the intermediate cyclopen-tenone diol can be isolated with 50% sulfuric acid it is converted to the furan in a separate step. 

The formation of (39) was further confirmed by its cycloadditions with furan and pyrrole to give the corresponding Diels-Alder adducts. When heated, (39) suffers valence isomerization, yielding the cyclopropenyl ketone (41), presumably via the vinylcarbene (40) (Scheme 4). 

An early example of the isolation of a cyclopropenyl ketone analog, obtained by photoisomerization of a 3-aryl-5-phenyl-l,2-oxazole, was reported by Ullman and his coworker (103) 103). 

After the isolation of a Dewar benzene substituted by tert-butyl groups, van Tamelen tried to isolate a Dewar furan stabilized by terr-butyl groups. However, the photolysis of di- or tri-fe/7-butylfuran did not give any Dewar compound but only cyclopropenyl ketones and its ring-opened products I04>. The reaction of di-fert-butylfuran is described by the following equation (104). 

Another attempt to synthesize a Dewar furan by the photolysis of tetrakis(tri-fluoromethyl)furan was made since the photolysis of tetrakis(trifluoromethyl)thio-phene gives a stable Dewar compound (see Eq. 109). However, even this furan only yields the corresponding cyclopropenyl ketone 105) ... 

The photolysis of 2-methylfuran in the presence of a primary amine gives a 1,3-disubstituted pyrrole. This photolysis is assumed to proceed via a cyclopropenyl ketone, which reacts with the amine to form an imine. This imine rearranges to the pyrrole derivative (106)106). Couture and his coworker also found that the photo-... 

Depending on the formed intermediates, the photoreactions of five-membered heteroaromatic compounds may be classified into two types, these involving formation of cyclopropenyl ketones and Dewar intermediates. However, there are some reactions where both types of intermediates participate. Kojima and his coworker showed that both isomers should be taken into account in the photoreaction of an 1,3-oxazole compound (116)ll6). 

The thermal back reaction to the tricyclic compound has attracted our attention. The application of this reaction to a cyclopropenyl ketone imine system gives a similar isomer of a diazepin compound (165)181). This is the first synthesis of a valence-bond isomer of a nitrogen-containing heterocyclic compound having a bicyclobutane part. 

Two other approaches to the furan derivative 67 have been described (a) from perfluoro-2-butyne and involving the novel cyclopropenyl ketone derivative 74154 and (b) by ozonolysis of hexakistrifluoromethylbenzvalene (75), followed by treatment of the ozonide (76) with triphenylphosphine and... 

In some cases NaNH2 is described as an isomerisating reagent by deprotonation of dienes or alkynes (refs. 40, 41). Cyclopropenyl ketones or vinyl cyclopropyl ketones treated by NaNH2 in HMPA or DMSO (ref. 42) lead to the cis- and trans-cyclopropyl ketones (Fig. 7). 

Some pyridazine N-oxides, when irradiated in methanol with a high-pressure mercury lamp, gave a mixture of the deoxygenated product and 4-hydroxymethylpyridazine, accompanied in some cases by 3-acylpyr-azoles.590 By contrast, irradiation in the presence of primary amines gives the N-sbustituted pyrroles 304 and 305 in a ratio of about 1 2. It could be shown that isolatable cyclopropenyl ketones (303) are initially formed.594 595... 

Diazo transfer to cyclopropenyl ketone (73) is accomplished with diphenylphosphoro ester azide (DPPA). The conversion of tricyclic ketone 75 to the a-formyl derivative followed by the reaction with tosyl azide yields the diazoketone 76 via deformylation.28... 

Perfluorotetramethylcyclobutadiene oxide (43) rearranges with a half-life of about 20 min at 95°C." As a Dewar furan, it might have been expected to aromatize to perfluorotetramethylfuran (44). That process is orbital topology forbidden," however, and instead 43 is transformed cleanly into cyclopropenyl ketone 45, apparently... 

Cyclopropenyl ketones also undergo isomerization to produce furan derivatives (Eq. 11) [26]. It has been proposed that the initial chloropalladation on their unsymmetrically substituted double bond occurs regioselectively to give one of the possible CP-Pd intermediates predominantly, which undergoes p-carbon elimination and several subsequent reactions to yield the major products. 

Later, Padwa reported a regioselective Rh(II)-catalyzed room temperature cycloisomerization of trisubstituted cyclopropenyl ketones to give 2,3,4-trisubstituted... 

The Diels-Alder reaction of cyclopropenyl ketones with cyclic dienes and 2,3-dimethylbutadiene yielded substituted tricyclo[3.2.2.0 " ]non-6-ones in high yields (90%). The inter- and intra-molecular Diels-Alder reactions of 2-halocycloalkenones with dienes formed [4,2,0]octenones. The 2-bromocycloalkenones are highly reactive and endo-sdective. ... 

Tetrakis(trifluoromethyl)furan 137 was reported to be inert in a reaction with common dienophiles and stable to irradiation, unlike the most other furans [139, 149], However, later it was shown that 137 rearranged into cyclopropenyl ketone 220 under irradiation with high pressure Hg-lamp. Similarly, furan 141 was transformed into acyl fluoride 247 [105],... 

The solvolytic ring-contraction of the cyclobutene (116) is an interesting reaction which produces the cyclopropenyl ketone in high yield. ° Diethoxy-cyclopropenone (117) is the low-yield product (10%) of photolysis of diethoxy-cyclobutenedione in ether (after a difficult isolation procedure) and quite different products were obtained when the photolysis was done in other... 

Rhodium-catalyzed carbonylation of cyclopropenyl esters and cyclopropenyl ketones to a-pyrones and of vinylcyclopropenes to phenols... 

Rhodium-Catalyzed Carbonylation of Cyclopropenyl Esters and Cyclopropenyl Ketones to a-Pyrones and of Vinylcyclopropenes to Phenols... 

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