Cyclopropenones preparation

Cyclopropenone prepared in this way is quite pure and suitable for most chemical purposes. It can he repurified by crystallization from 3 volumes of ethyl ether at — 60° using a cooled filtering apparatus. The residual ethyl ether is then removed by evaporation at 1-2 mm. and 0° very pure cyclopropenone is obtained in 60-70% recovery from the above distilled material. 

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... 

Dimethyleneketene acetals 546 are easily available by a thermolytic rearrangement of methylenecyclopropanone ketals 544, in turn prepared from the corresponding cyclopropenone ketals [146a]. The thermolysis is a two-step process, involving the reversible formation of a dipolar TMM intermediate 545 [146b], followed by the irreversible production of stable 546 at higher temperature (Scheme 75) [145],... 

The origin of cyclopropenone chemistry goes back to the successful preparation of stable derivatives of the cyclopropenium cation <5 3), the first member of a series of Huckel-aromatic monocyclic carbo-cations possessing a delocalized system of (4n + 2)-7r-electrons. This experimental confirmation of LCAO-MO theory stimulated efforts to prepare other species formally related to cyclopropenium cation by a simple resonance description of electron distribution, namely cyclopropenone 7 and methylene cyclopropene (triafulvene) 8 ... 

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). 

The preparation of unsubstituted cyclopropenone (7)27,28 was achieved by reducing the readily available tetrachlorocyclopropene (2/)29 with tris(n-butyl)-stannane this produced 3,3-dichloro-AI,2-cyclopropene (22), whose carefully controlled hydrolysis gave rise to a 41—46% yield of pure cyclopropenone, which was stable under an inert gas atmosphere at temperatures below its melting point of -21 °C. 

A further convenient preparation of 7 was found30 to be the hydrolysis of cyclopropenone dimethyl ketal (22)31 ... 

Finally, the alkylation could be extended to vinyl halogen compounds38 and in this way, bis(trichlorovinyl)cyclopropenone 30) was prepared from cation 24 and trichloroethylene. A recently reported variation of the West procedure40) makes use of the difluoro chloro cyclopropenium cation 33. 

This procedure is the method of choice for the preparative chemist, since it not only provides the advantage of generally good yields (40—60%), but also can be carried out on a large scale. The modified Favorski reaction of dibromoketones offers a remarkably wide scope of application and has made possible the preparation of a large number of dialkyl-, diaryl-, and monoaryl cyclopropenones (see Table 1). Interestingly, the bicyclic cyclopropenones 5943) and 4041 have become accessible by use of the dibromoketone method. 

The theoretically interesting phenyl hydroxy cyclopropenone (57) was prepared by Famums1, s2 according to the general principle of cyclopropene ring closure developed by Closss3) from 53 via the vinyl carbene 54 and phenyl trichloro cyclopropene (55). 

Table 1. Preparation of some cyclopropenones and comparison of methods applied1)...

Triafulvenes derived from cyclic 0-dicarbonyl systems like 84/85ia 861S and S779 are conveniently prepared from cation 75 by the DIPEA method and in some cases (5780,81), 8862 8983 ) from diphenyl cyclopropenone by condensation in acetic anhydride. 

An elegant method for the preparation of some cyclopropenone imines reported by Krebs118 is the (1 + 2) cycloaddition of isonitriles (as divalent carbon species) to activated triple bond of ynamines and certain cycloalkynes, e.g. ... 

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). 

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 ... 

The first example of enantioselective allylzincation of an alkene was also reported for the cyclopropenone ketal 78 as substrate. The chiral allylzinc complex 135 was prepared from the corresponding bis-oxazoline derived from (,V)-valine by deprotonation with n-BuLi and transmetallation with allylzinc bromide. This reagent reacted with 78 and afforded the allylated product 136 with high optical purity ( = 99%) (equation 66)101. 

Cyclopropenone has been prepared by a route that illustrates the value of the acetal grouping in protecting ketone groups (Section 16-8) ... 

Three-membered ring systems have also provided examples of aromatic and antiaromatic behavior. Despite the very substantial angle strain, Breslow and his collaborators have succeeded in preparing a number of cyclopropenyl cations (51).30 Cyclopropenone (52) has been isolated and is stable in pure form below... 

PREPARATION AND THREE-CARBON + TWO-CARBON CYCLOADDITION OF A CYCLOPROPENONE KETAL CYCLOPROPENONE 1,3-PR0PANEDI0L KETAL... 

The classic labeling studies of Loftfield 49a> have demonstrated that cyclopropanones are intermediates in the Favorskii reaction 49b) — the base-induced rearrangement of a-haloketones (Scheme 8). The related reaction of a,a -dibromoketones has, in fact, become a convenient preparative route for cyclopropenones, e.g., 48 ->- 49 via 50.50>... 

Recently, the bicyclic cyclopropanones 78 and 79 were prepared in high yield by the Diels-Alder addition of cyclopropenone to the diphenyl-isobenzofuran 80 and the dimethylanthracene 57.62>... 

Although this review does not in general cover cyclopropenones, it is important to note the elegant preparation of cyclopropenone dimethylacetal by reaction of 2,3-dichloropropene with N-bromosuccinimide in methanol to produce (4), followed by treatment with potassium amide in liquid ammonia 14) ... 

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]. 

The most general methods for preparing seven- or eight-membered rings from enamines are by ring expansion of the cyclobutene, cyclobutanone or chlorocyclopro-pane adducts formed by cycloaddition of acetylene carboxylates, ketenes or chlor-ocarbenes, respectively, to enamines of cyclopentanone or cyclohexanone. These are two-carbon or one-carbon ring expansions. Three-carbon ring expansions can also be carried out by cycloaddition of activated cyclopropenes or cyclopropenones. 

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 procedures described herein illustrate the preparation of a substituted cyclopropenone acetal and an alkylidene cyclopropanone acetal.The latter compound has been used to generate a dipolar trimethylenemethane (TMM) species that undergoes [3+2] cycloaddition with electron-deficient 2p-electron C=C and C=X compounds. ... 

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... 

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... 

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