Cyclopropenones synthesis

The first synthesis of a cyclopropenone was reported in 1959 by Breslowls who achieved the preparation of diphenyl cyclopropenone (11) by reacting phenyl ketene dimethylacetal with benzal chloride/K-tert.-butoxide. The phenyl chloro carbene primarily generated adds to the electron-rich ketene acetal double bond to form the chlorocyclopropanone ketal 9, which undergoes 0-elimination of HC1 to diphenyl cyclopropenone ketal 10. Final hydrolysis yields 11 as a well-defined compound which is stable up to the melting point (120—121 °C). 

Independently Volpin17 synthesized diphenyl cyclopropenone from diphenyl-acetylene and dibromo carbene (CHBr3/K-tert.-butoxide). This reaction principle of (2 + 1) cycloaddition of dihalocarbenes or appropriate carbene sources ( caibenoids ) to acetylenic triple bonds followed by hydrolysis was developed to a general synthesis... 

In 1963 Breslow published a synthesis of cyclopropenones, which approached formation of the three-ring without the use of divalent carbon species41-45, a, a -Dibromo ketones 36, in general readily available from ketones R-CH2—CO—CH2—R, are de-... 

Their synthesis is possible from (a) condensation of arylmalononitriles and cyclopropenones in acetic anhydride, or (b) thermolysis of A1,2-cyclopropene-3-ethers 114 (adducts of cation 117 and arylmalononitrile anion), as exemplified by 115/116 ... 

The synthesis of cyclopropenone imines 3 has been accomplished by several methods. Thus aromatic amines, e.g. p-nitraniline, can be reacted either with diphenyl cyclopropenone in HCl/ethanol or with the ethoxy cation 75 forming the immonium cation 150, which is deprotonated by tertiary bases to the N-(p-nitro-phenyl)-imine /5/llsl ... 

Alkylation of cyclopropenones — effected by means of trialkyloxonium tetra-fluoroborates42,119) — leads to the easily hydrolyzable O-alkyl cyclopropenium cations 295, which are potential sources for triafulvene synthesis ... 

CYCLOPROPANECARBOXYLIC ACID, cis-2-PHENYL-, 50, 94 Cyclopropane derivatives, synthesis, 52, 22, 33, 132 Cyclopropenes, 50, 30 Cyclopropenone, di-tert-buty1-,... 

In this approach to pyranone synthesis, it is thought that the carbanionic site in the betaine attacks the cyclopropenone in a Michael fashion. Subsequent opening of the three-membered ring may lead directly to the pyranone (route a) or the heterocyclic system may form via the ketene (route b Scheme 98). 

SCS-MP2 and the new perturbative B2-PLYP density functional methods provide accurate reaction barriers and outperform MP2 and B3-LYP methods when applied to the 1,3-dipolar cycloaddition reactions of ethylene and acetylene.39 Phosphepine has been shown to catalyse the asymmetric 3 + 2-cycloaddition of allenes with a variety of enones (e.g. chalcones) to produce highly functionalized cyclopentenes with good enantiomeric excess.40 The AuPPh3SbF6 complex catalysed the intramolecular 3 + 2- cycloaddition of unactivated arenyne- (or enyne)-yne functionalities under ambient conditions.41 A review of the use of Rh(I)-catalysed 3 + 2-cycloadditions of diaryl-and arylalkyl-cyclopropenones and aryl-, heteroaryl-, and dialkyl-substituted alkynes to synthesise cyclopentadienones for use in the synthesis of natural products, polymers, dendrimers, and antigen-presenting scaffolds has been presented.42... 

In several synthetic studies, cyclopropane derivatives were used as synthones or building elements for ring enlargement steps, e.g. reaction of enamines with cyclopropenone [65], synthesis of 2,3-dihydro-l,4-diazepine by thermal isomerization of 1,2-diamino-cyclopropanes [32] [66], and preparation of 3-amino-fulvenes from methylencyclopropenes with alkynamines [67]. 

General Synthesis of Substituted Cyclopropenones and Their Acetals 2-Ethyl-2-cyclopropen-1-one Acetal and 2-(1-Hydroxyhexyl)-2-cyclopropen-1 -one. 

For the first time, the synthesis of 2-methyl-4,6-dialkyl-l,2,3-triazin-5-ones 3 from the corresponding cyclopropenones 1 via triazines 2, using Nakamura s method, has been achieved <03H477>. 

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. 

The substituted cyclopropenone acetal synthesized in Step B can be readily hydrolyzed to the corresponding cyclopropenone. This synthetic sequence provides the best and most versatile current synthetic route to substituted cyclopropenones. The deficiencies of conventional procedures are precisely the synthesis of cyclopropenones with aliphatic substituents and functional groups, for which the present method has proven to be particularly useful. ... 

Cyclopropenones show considerable biological activity, " and have recently been employed as a key structural unit for a novel inhibitor of a cysteine protease. The utility of cyclopropenone acetals has recently been recognized for vinylcarbene formation, " asymmetric synthesis, and other processes. Cycloaddition reactions of cyclopropenone acetals and congeners have also proven to be useful for chiral functionalization of buckminsterfiillerenes. 

Whilst the potential for synthesis of cyclopropene under volcanic conditions on primeval earth is recognized , the extent to which the ring system occurs in nature is known for only four classes of compounds, one of which involves cyclopropenone derivatives. Plants of the order Malvales contain varying amounts of the biologically active and homologous cyclopropene fatty acids sterculic acid (2) and malvalic acid (3). The... 

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... 

The use of perhalocyclopropenes, and particularly tetrachlorocyclopropene , in the preparation of cyclopropenones and their derivatives is important. Deem has reported a convenient, high yielding (71 %) synthesis of diphenylcyclopropenone and this, and the following reactions, proceed by way of an ionization-cation capture sequence which works... 

Annelation of a three-carbon unit derived from cyclopropenone acetals across the sp carbon atoms of electron-deficient olefins has provided a simple new cyclopentenone synthesis Thus, a 1 1 mixture of the a,j5-unsaturated ketone 275 and acetal 276 affords... 

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