Cyclopropenone, reaction with

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. 

Trichloromethyl lithium (generated from BrCCl3 and CH3Li at —100 °C) adds to dialkyl acetylenes and to monoalkyl acetylenes23, thus monoalkyl cyclopropenones became accessible which could not be obtained from terminal acetylenes by reaction with the above carbene sources. The 3,3-dihaIogeno-A1,2-cycIopropenes formed as primary products in the dihalocarbene reactions are usually not isolated, but are hydrolyzed directly to cyclopropenones. 

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. 

The reaction with hydroxide ion is frequently used as proof for the chemical structure of cyclopropenones and has been examined in some detail with respect to the factors governing ring-cleavage. Thus, methyl cyclopropenone23 and aqueous NaOH react to yield a mixture of methacrylic and crotonic acids in a ratio of 3 1 as expected from the relative stabilities of the two possible intermediate carbanions (type 317) ... 

Similiarly, cyclopropenone reacts with Grignard s compounds via conjugate addition, which is followed by an ene -reaction of intermediate 341 with a second cyclopropenone moiety (342) leading to 2-substituted resorcinols20... 

Finally, a reaction should be mentioned in which a nucleophile gives support to another reacting species without appearing in the final product. Diphenyl cyclopropenone interacts with 2,6-dimethyl phenyl isocyanide only in the presence of tri-phenylphosphine with expansion of the three-ring to the imine 344 of cyclobutene-dione-1,2229,230 Addition of the isocyanide is preceded by formation of the ketene phosphorane 343, which can be isolated in pure formss 231 it is decomposed by methanol to triphenyl phosphine and the ester 52. 

In contrast, methyl cyclopropenone is reported283) to react with the Pt-olefin complex 455 at low temperature with replacement of the olefin ligand. In the resulting complex 456 the cyclopropenone interacts with the central atom via the C /C2 double bond according to spectroscopic evidence284). At elevated temperatures a metal insertion to the C1<2)/C3 bond occurs giving rise to 457. Pt complexes of a similiar type were obtained from dimethyl and diphenyl cyclopropenone on reaction with 455 and their structures were established by X-ray analysis285). 

The reaction with optically active hydrazones provided an access to optically active ketones. The butylzinc aza-enolate generated from the hydrazone 449 (derived from 4-heptanone and (,S )-1 -amino-2-(methoxymethyl)pyrrolidine (SAMP)) reacted with the cyclopropenone ketal 78 and led to 450 after hydrolysis. The reaction proceeded with 100% of 1,2-diastereoselectivity at the newly formed carbon—carbon bond (mutual diastereo-selection) and 78% of substrate-induced diastereoselectivity (with respect to the chiral induction from the SAMP hydrazone). The latter level of diastereoselection was improved to 87% by the use of the ZnCl enolate derived from 449, at the expense of a slight decrease in yield. Finally, the resulting cyclopropanone ketal 450 could be transformed to the polyfunctional open-chain dicarbonyl compound 451 by removal of the hydrazone moiety and oxymercuration of the three-membered ring (equation 192). 

Eschenmoser s pyrone 38 on treatment with cyclopropenone ketal 39 in refluxing benzene afforded lactone 40 (73%). Lactone 40 on hydrolysis with acetic acid at 100°C afforded, after deprotection and decarboxylation, tropone 37 (70%). Introduction of the tropolonic hydroxyl group was achieved with hydrazine hydrate in ethanol, to give a mixture of deacetyl-colchiceinamides 41 (53%) and 42 (37%), followed by reaction with ethano-lic potassium hydroxide, which afforded tropolones 43 and 44, respectively. Tropolone 43 was converted to 44 which, therefore, became the major reaction product. Methylation of 44 gave a mixture of enol ether 18 and 45 which were separated by chromatography. 

The addition of dihalocarbenes to alkynes is again a rather inefficient process and usually leads, to the isolation of the cyclopropenone rather than the 3,3-dichlorocyclo-propene. In a rather unusual example, however, 2-butyne is reported to be converted to (67). This product is apparently derived by addition of dichlorocarbene to the corresponding methylenecyclopropene, derived in turn by elimination of HC1 from the primary adduct (68). The cyclopropene (67) does not appear to ring open to a vinylcarbene, but can be trapped in Diels-Alder reactions with cyclopentadiene 60). A related addition of dichlorocarbene to ethyl 2-butynoate also leads to a low yield of the 3,3-dichlorocyclopropene, which may be hydrolysed to the cyclopropenone 6l). 

Reactions of cyclopropenone ketal with terminal alkenes afford 1,4-divinyl ketone ketals in good yields (Eq. 51) [88]. 

CycloadditionJ Reaction of cyclopropenone ketals with alkenes bearing only one electron-withdrawing group results in unstable cyclopropane ketene ketals, which are not isolated, but rather are converted into m-disubstituted cyclopropanes by acid hydrolysis. 

Although the triaminocyclopropenium ion is stable to water, even hot water, unlike the trichloro and triphenyl derivatives, this ion readily reacts with the hydroxide ion at room temperature to afford diamino-cyclopropenone (77) as the major product and an acrylamide derivative (75) as the minor product i ) (Eq. 10). On the other hand, the reaction with sodium sulfide yields diaminocyclopropenethione (79) and di-... 

Table 21 Reaction of Cyclopropenone Ketal With Electron Deficient Alkenes O...

The cyclization in Step B is an improvement of Butler s procedure for the synthesis of which employs less convenient reagents, KNH and l-bromo-3-chloroacetone acetal. Beside the acetals derived from neopentyl glycol, those derived from ethanol, 1,3-propanediol and 2,4-pentanediol have been synthesized by the present method. The second part of Step B involves the formation and the electrophilic trapping of cyclopropenyl anion 2, which is the key element of the present preparations. Step B provides a simple route to substituted cyclopropenones, but the reaction is limited to alkylation with alkyl halides. The use of lithiated and zincated cyclopropenone acetal, on the other hand, is more general and permits the reaction with a variety of electrophiles alkyl, aryl and vinyl halides, Me3SiCl, Bu3SnCl, aldehydes, ketones, and epoxides. Repetition of the lithiation/alkylation sequence provides disubstituted cyclopropenone acetals. 

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). 

The nucleophilicities of cyclopropenone acetals", bromoketene acetals and an oxaphosphorane derivative, 26, are high enough to enable reaction with some Michael acceptors. Thus, cyclopropaneacetic esters (e.g. equation 88), cyclopropanecarboxylic esters, and 1-acetyl-1-methylcyclopropanes have been generated, respectively, from these precursors. 

This discovery represented an important advance in the synthesis of cyclopropenyl ions, since 18 can serve as a point of departure in the synthesis of a large variety of new cyclopropenyl salts by reaction with nucleophiles. This is discussed in the subsequent section of this chapter. The conversion of cyclopropenones to cyclopropenyl salts is similarly reserved for a later section. 

Substituted cyclopropenones such as the diphenyl derivative undergo cycloaddition reactions with activated dienes either by [4 + 2] or [4 + 3] modes. For example, N-1,3-butadienyl-N,N-diethylamine adds to diphenylcyclopropenone via the normal [4 + 2]... 

Lown and Matsumoto studied the reactions of a variety of heteroaromatic nitrogen compounds with diphenylcyclopropenone (39) and diphenylcy-clopropenethione (40). Quinazoline with the cyclopropenone 39 gave the pyrrolo[l,2-c]quinazoline 41, but reaction with thione 40 resulted in 42, a product in which one molecule of the solvent methanol was also incorporated. 

Dehydrobrommation. In a procedure for the preparation of tri-r-butylcyclo-propenyl fluoroborate (4), Ciabattoni et al. prepared dineopentylketone (1) by the Grignard synthesis formulated, converted it to the a,a -dibromide (2), and effected double dehydrobromination by treatment of this intermediate with potassium t-butoxide. The resulting cyclopropenone (3) was then brought into reaction with a solution of commercial t-butyllithium in pentane. The mixture was quenched with water, and the pentane layer was washed, dried, and evaporated on a rotary evaporator. The resulting pale-yellow oil is taken up in ether and treated at 0° under rapid magnetic... 

The first approach has been realized in various ways. The second one only works with the aid of transition metal catalysts, whereas the third one has been realized so far only in the thermal reaction of cyclopropenone acetals with electron-deficient alkenes 81). 

The carbocupration of cyclopropenes has been especially investigated with cyclopropenone ketals as reactants. The cuprio cyclopropanes formed can serve as a synthon for the cyclo-propanone enolate. " Achiral ketals with an unsubstituted cyclopropene double bond 15 undergo instantaneous reaction with lithium dimethylcuprate at — 78 C to give the methyl derivative 17 (R = Me) in 96% yield after quenching with methanol. Similar reactions, with a deuterium oxide or iodomethane quench, indicate that the carbocupration takes place in a cis fashion. 

The thermal reaction of cyclopropenone acetals with carbonyl compounds for 12 hours at 80"C, or reactions catalyzed by acid at 25 C, gave furan derivatives 5 (or and 7... 

---