Ketenes with phosphoranes

The interaction of dibenzoyldiazine with (triphenylphosphoranylidene)ketene furnished a novel cyclic adduct with phosphorane function (Scheme 97). ... 

The acylation of Wittig reagents provides the most convenient means for the preparation of allenes substituted with various electron-withdrawing substituents. The preparation of o-allenic esters has been accomplished by the reaction of resonance-stabilized phosphoranes with isolable ketenes and ketene itself and with acid chlorides in the presence of a second equivalent of the phosphorane. The disadvantages of the first method are the necessity of preparing the ketene and the fact that the highly reactive mono-substituted ketenes evidently cannot be used. The second method fails when the a-carbon... 

The submitters have shown that these reactions proceed by dehydro-chlorination of the acid chloride to the ketene, which is then trapped by reaction with the phosphorane. The resulting betaine decomposes to the allenic ester via an oxaphosphetane. In contrast, the reaction of acid chlorides with 2 equivalents of phosphoranes involves initial acylation of the phosphorane followed by proton elimination from the phosphonium salt. ... 

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. 

Ring opening of diphenylthiiren 1,1-dioxide5 8 and diphenylcyclopropenone6 occurs on reaction with tertiary phosphines to form the betaines (69) and the keten phosphoranes (70), respectively. Tertiary phosphines react with the thione (71) to form mainly the betaine (72).60... 

The (aziridin-l-ylimino)phosphoranes (57) react with ketens to give nitrile derivatives, presumably from an intermediate ketenimine by breaking the N—N bond and migration of the aziridinyl group.60 They also react with acyl halides and... 

A novel heterocyclic system has been achieved from methyl 3-aminopyra-zine-2-carboxylate and several aroyl chlorides, leading to 3-aroylamino derivatives the latter are cyclized with dibromotriphenylphosphorane to 2-arylpyrazino[2,3-rf][3,l]oxazin-4-one (94S405). Furthermore, vinylimino-phosphoranes and diphenylketene react (Scheme 87) to give nonisolable vinylketenimines (233) which afford, with a second equivalent of ketene in a [4 + 2]-cycloaddition, 1,3-oxazinones (234) [89JCS(P1)2140]. 

Additional supporting evidence for the mechanism includes the formation of pyrylium salts when arylacetyl chlorides, which yield ketenes by loss of HC1, react with the phosphorane (63CR(257)926). It is also known that diphenylketene reacts in a similar manner to give a pyran, whilst aryl isocyanates yield pyran-4-one derivatives. 

Further reports have appeared on the reaction of trivalent phosphorus compounds with acetylene dicarboxylates. In the first, alkyl diphenylphosphinites (e.g.57) are shown to react with dialkylacetylene dicarboxylates (e.g.58) in the presence of carbon dioxide to form 1,2-oxaphosphol-3-enes (e.g.59) which in the presence of excess phosphinite decompose via (60) to give di-ylids (e.g.61). On the other hand, the phosphoranes (62) from phosphonites and phosphites react with a further phosphorus component to give the ylids (63) which are readily converted by treatment with alcohol into phosphonates (65) apparently via ketene intermediates (64) as evidenced by and isotopic tracer studies. ... 

Addition of an electrophile to the lone pair of oxo-, thioxo- and imino-vinylidenephosphoranes transforms the nucleophilic system into the dipolar ir -ir system of a ketene. The resulting phosphonium salt becomes a true dipolar ketene which, as such, reacts in a known manner (equation 101). Whenever the anion Nu is a stronger nucleophile than the original cumulated ylide, the new alkylidene-phosphorane will be formed, in which compound ElNu has added to the parent vinylidenephosphorane. If the starting phosphacumulene ylide is a stronger nucleophile than Nu , the intermediate salt always reacts with a second molecule of unreacted ylide in a [2 + 2] cycloaddition to give 1,3-cyclobutanedione derivatives. 

Mixed substituted orthoesters, e.g. (383 equation 180), can be obtained by addition of alcohols to ketene 0,0-acetals. With the aid of phosphoranes containing a ketene O,(7-acetal structure, various orthoesters, e.g. (384) and (385) (Scheme 70) were prepared. " Cyclic orthoesters (386)-(390) (Scheme 71) are formed in cycloaddition reactions of ketene 0,0-acetals with aldehydes, ketones, 7.848 gj.yj cyanides, oxiranes, a-keto esters, o-diketones or ketones (with irradiation), a,3-unsaturated aldehydes and ketones (under pressure or catalyzed by ZnCh), diazoaceto-phenone, 7 diazoacetone and azodicarboxylate. ... 

The formation of acrylonitriles from the reaction of dihalogenomethylene-phosphoranes with aroyl cyanides has now been extended to include the use of aliphatic acyl cyanides, although the conditions need to be closely defined. Perfluoroisocyanates with diphenylmethylenetriphenylphosphorane give the expected keten-imines (28) or their rearrangement products (29). Formylation of both reactive and stable ylides has been achieved using the mixed anhydride of formic and acetic acids. ... 

An ingenious synthesis, albeit in low yield, of 1-oxo-1,2,3,4-tetrahydro-9-hydroxyanthracene has been achieved from a phosphoran and a ketene formed as an intermediate. The phosphoran with homophthalic anhydride (3.3mols.) and trimethylsilane (3mols.) upon themolysis in toluene at 150°C for 40 hours in a sealed tube gave the product in 23% yield (ref.24). 

The diazo-ketone (43) forms the j -lactone (44) and 2-methylhexan-3,5-dione on refluxing in benzene, presumably through alkyl migration and cyclization of resulting hydroxyketen. Malonyl anhydrides (46) and ketens are formed from the deoxygenation of malonyl peroxides with triphenyl-phosphine, possibly via an intermediate phosphorane (45). 

The phosphonium salt (280) is formed on treatment of ethoxycarbonylmethylene-triphenylphosphorane with phenyl-lithium and methyl iodide. The keten (281), formed by elimination of ethanol from the phosphorane, is suggested as a likely intermediate. 

A facile synthesis of allenic esters (187) is by reaction between acid chlorides (185) and phosphoranes (186) derived from a-halo-esters. Yields are 10— 70% presumably ketens are intermediates. Cyclic /3-keto-esters can serve as precursors to cyclic allenic esters by sequential conversion to the 2-pyrazolin-5-one derivatives, using hydrazine and oxidation with thallium trinitrate (Scheme 26) overall yields are around 50%. ... 

Nucleophilic attack of triphenylphosphine on diphenylcyclopropenone gives a phosphorane keten (278X which reacts with other nucleophiles to give cinnamic acid derivatives. ... 

The allyl staimane 2 was prepared fi om the acid chloride 5. Exposure of 5 to Et,N generated the ketene, that was homologated with the phosphorane 6 to give the aUene ester 7. Cu-mediated conjugate addition of the stannyhnethyl anion 8 then delivered 2. 

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