Acyl ylides

A new synthesis of acetylenes using the reaction ot tnflic anhydride with acyl ylides (equation 48) was developed recently [97] Vinyl inflates, generated in situ, are proposed to be the key intermediates... 

In the reaction scheme (formulated abo e for enamines) the primary formation of an acyl ylide 369 (the formal product of addition of the enamine sequence C=C-N to the C /C3 bond of cyclopropenone) was first suggested by Dreiding237. ... 

Intramolecular Wittig reactions are even possible between highly stabilized acyl ylides and thiolesters22 or trithiocarbonate esters23 of low carbonyl activity . 

Five- to seven-membered O-, N-, and S-heterocycles Acyl ylides with a tethered terminal ester function requisite for the construction of five- to seven-membered heterocycles are very conveniently accessible by reaction of the cumulated ylide ketenylidenetriphenylphosphorane 11 with various carboxylic esters bearing OH-, NHR-, and SH-groups in a-, -, or y-position. 

Acylylides. The reagent reacts with a free carboxylic acid to form the phosphoraiic 2, When heated, 2 i.s converted into the acyl ylide 3 with loss ol phenyl isocyanate. These... 

Pyridinium, phosphonium, arsonium and sulfonium acyl ylides all react with diphenylcyclopropenone to give 3,4-diphenyl-a-pyrones (equation 61) These reactions are assumed to be initiated by attack of the acyl oxygen on the cyclopropenone. 

Miscellaneous Reactions.- Thermolysis of 5-hydroxyphosphonium ylides (67) provides a useful route to a,p-unsaturated ketones. The ylides (67) have been prepared by the reaction of an appropriate ylide (66) with propriolactones, although the success of this method depends on the cation of the base used in the generation of (66). An alternative and more generally useful method of generating (67) from acylated ylides (68) has now been... 

Acyl ylides add to N—N double bonds of azo compounds giving rise to the formation of l-A/-sub-stituted alkylidenephosphoranes (e.g. equation 29). ° It should be mentioned that l-/V-substituted ylides, which carry only hydrogen or alkyl groups at the nitrogen, are unknown. ... 

Acyl halides, activated esters, carboxylic anhydrides and iV-acylimidazoles react with alkylidenephos-phoranes to yield acylated ylides. " - " ... 

Carboxylic acids react with phenyliminovinylidenetriphenylphosphorane (equation 106) via the intermediates (1) with formation of the alkylidenephosphoranes (2), which, on heating, rearrange in an intramolecular acyl migration to ylides (3). By heating (2) in the presence of an alcohol the acyl ylides (4) and N-phenylurethanes are formed. - The reaction sequence allows the replacement of the OH group in carboxylic acids by the ylide function. 

Acyl-ylides, e.g. (58), prepared from a)3-unsaturated acyl chlorides and ethoxy-carbonylmethylenetriphenylphosphorane, undergo Michael addition reactions with... 

The acylation of ylides has been utilized as a method for the elaboration of a simple ylide to a functionalized ylide. Transylidation of the acylated ylide gives the... 

The pyrrolizidinediones (153) can be prepared easily, but in variable yields, from the cyclic diacylamino-acids (150) by reaction with N-phenylketeniminylidenetriphenylphosphorane (151) and subsequent intramolecular Wittig reaction of the acyl ylide (152). Optical activity present in the starting amino acid derivatives is maintained through the reaction sequence. A mild, efficient, method... 

Crignard reagents read with this phosphorane to form an ad duct that is hydrolyced to an acyl ylide (2). which can be hydrolyzed to a methyl ketone (3) or allowed to react with an aldehyde to give an a. -ertone (4) (equation 0... 

Durch Einwirkung von Acylierungsmitteln und Basen auf Monoacyl-sulfonium-ylide entstehen zahlreiche Bis-acyl-Ylide (65) in meist sehr guter Ausbeute [51, 59). 

Alkylidenephosphoranes (a.La. phosphorus yUdes) of the general formula Ph3P=CR R (1) have been frequently used in key steps of heterocycle synthesis. Numerous papers and review articles [1-4] testify their versatility in the construction of rings with sizes ranging from three to well beyond 20 and with virtually any number, kind and distribution of heteroatoms. The Wittig alkenation of carbonyl groups is doubtless the most common, though not the only, reaction of P-ylides that has been employed in the cyclization of bifunctional precursors. The cycloaddition between acyl ylides (1 = H,... 

SoHman et al. reported the synthesis of 3-triphenylphosphoranylidene-chromanes 117 from Mannich bases 115 of the commercial moUusddde niclosamide and the ciunulated yhdes 2, 82 or 88 [73]. The reaction was carried out in boihng toluene and is thought to proceed by initial addition to give the acyl ylides 116, which then cycHze by the unusual expulsion of a secondary amine, i.e. by nudeophihc attack of the ylidic carbon atom at the benzyhc carbon atom. Intermediates 116 were not isolated. The moUusdddal activities of compounds 117 were found to be about tenfold lower than that of the parent niclosamide (Scheme 25). 

Absolute Configuration.— Bestmann has described a new method for the determination of the absolute configuration of carboxylic acids. When the optically active acid chloride (16) reacts with two equivalents of the racemic phosphorane (17) to give the phosphonium salt (18), partial kinetic resolution is observed. The second equivalent of now enantiomerically enriched phosphorane then reacts with the salt (18) in a process of transylidation, giving the optically active phosphonium chloride (19), which is precipitated, and the diastereoisomeric acyl ylide (20), which remains dissolved. The absolute configurations of the chlorides (19) have been proven by chemical correlation with the corresponding bromides, whose absolute configurations are known. 

Cyclic enol-acetates and a-acetoxy-ketones are converted into keto-esters by electro-oxidative ring-cleavage. Keto-esters are prepared (in good yield) by the reduction of acyl ylides (107) with aluminium amalgam (Scheme 60). ... 

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