Ylide anions

NitrilesCyanomethylenetriphenylphosphorane (1) can be deprotonated with sodium bis(trimethylsilyl)amide to give sodium cyanotriphenylphosphoran-ylidenemethanide (2). This ylide anion can be alkylated to give a wide variety of... 

The ylide anion (48) reacts with a variety of electrophiles at the terminal carbanion site to form /S-keto-ylides, e.g. (49). 53>64 The reaction between the ylide derived from cyclobutyltriphenylphosphonium bromide and cyclobutanone gave a reasonable yield of bicyclobutylidene (50).68... 

The synthesis of alkenes through the Wittig reaction has generated an impressive understanding of the chemistry of organophosphorus compounds. The generated car-banions stabilized by a phosphoryl moiety can be considered as ylide anions, and the... 

These molecules can be further deprotonated to give the ylide anions, Me2P(CH2)2 and Ph2P(CH2)2, which can serve as bridging ligands, as in (10-XXXI) and (10-XXXII). 

At the same time, the synthesis of mononuclear silver ylide complexes were achieved, Schmidbaur and his colleagues discovered that the ylide anions produced dinuclear species, Ag2[(CH2)2PMe2]. The remarkably stable methyl compound melts at 153-155°C and can be sublimed at 150°C and 0.1 atm. Mass spectral and H and P H NMR studies demonstrated the ring structure of the compound, although no structural analysis could be performed due to the photosensitivity of the compound. The synthesis of the dinuclear silver(I) ylide complex (6) is described in Inorganic Syntheses, and although colorless crystals are obtained, no X-ray stracture was possible due to sample decomposition in the X-ray beam. 

In contrast to earlier reports the product of the reaction of bromoacetone with diphenyltrimethylsilylphosphine is now shown to be the salt (7).10 This salt is readily converted (Scheme 1) into the corresponding ylide (8) which on treatment with butyllithium gives an ylide-anion shown to... 

Ylide-anions continue to be used in synthesis. Treatment of the trifluoromethylketo-stabilized ylide (31) with butyllithium leads to formation of the ylide-anion (32) via nucleophilic addition of the alkyllithium to the carbonyl group.27 The ylide-anion (32) reacts readily with aldehydes... 

Reactions of ylide anions with electrophiles lead directly to substituted ylides. 

Ylides with ambident character, like 1-formyl- or 1-acyl-methylenephosphoranes, may be attacked by alkylating reagents (the same is true for acylation) at the a-carbon or at the O atom. - Bromomethyl acetate C-alkylates acylmethylenetriphenylphosphoranes in a transylidation reaction (equation 55). Recently cyanomethylenetriphenylphosphorane has been successfully alkylated via its ylide anion, the substituted cyano ylides being accessible more readily in greater variety than previously (equation 56). ... 

Besides protons a series of heteroligands in the a-position of phosphonium ylides can also be substituted, giving rise to the formation of new alkylidenephosphoranes. Halogen atoms have been substituted by carbon groups (with lithium organyls or acyl chlorides) or another halogen. Reaction of a-lithiated ylides (see equation 35) or ylide anions with electrophiles may be considered as substitution of an alkali metal substituent at the ylide carbon atom. 

Another route to substituted ylides via ylide anions involves charge-directed addition of a wide range of carbon nucleophiles to 7,8-unsaturated acylphosphoranes yielding intermediate anions which further react with electrophiles, mostly alkyl halides (equation 94).>6i,i84,i92... 

McKenna, E. G., Walker, B. J. The mechanism and stereochemistry of Wittig reactions of phosphonium ylide-anions. Phosphorus, Sulfur Silicon Relat. Elem. 1990, 49-50, 445-448. 

The above-mentioned features of ylides, together with the ability to form ylide anions, and their ease of synthesis make them exciting and versatile ligands for transition metal chemistry [8]. Ylides have outstanding potential with respect to fhe formation of transition metal-carbon bonds, because a major reaction path for fhe decomposition of such moieties, i.e. j5-H ehmination, is blocked by the phospho-nium group, a significant difference in comparison wifh simple alkyl complexes [Eqs. (2) and (3) Fig. 1.1]. 

Phosphorus-based olefinations continue to be the most widely used methods for the synthesis of alkenes. An understanding of most facets of the mechanism of the Wittig reaction seems to have been achieved and this has been summarised in a substantive review. Some of the principles established in these mechanistic studies can be applied to phosphorus-based olefinations other than the Wittig reaction. However, substantive mechanistic studies of phosphine oxide-based and phosphonate-based oiefinations are urgently required. A combination of the variety of phosphorus-based methods and the improved understanding of their mechanisms now aliows a substantiai degree of controi of both reactivity and stereochemistry in olefin synthesis. However, studies are required of the applications of established structure-reactivity relationships in ylides and of the various carbon and nitrogen ylide-anions recently reported. 

An improved electrochemical procedure for the synthesis of alkoxyphos-phonium salts has been reported. Salts bearing a wide range of unusual counterions have been prepared, including phenoxide, polyhalide, halogeno-metallate, di-O-alkyl dithiophosphate, herbicidal phosphonate, and ylide-anions. ... 

Iminophosphoranes (96) react with primary isocyanates (97) or isothiocyanates (98) to give the betaines (99), while similar reaction with / opropyl or tertiarybutyl isocyanate gives the corresponding carbodiimides (100).52 The reactions of 1,3-ylide-anions (101) with phenylisocyanate and with dicyclohexacarbodiimide have been investigated.53 Both reactions follow a similar path to provide the adducts (102) which are themselves ylide-anions. Due to their substantial nucleophilicity, compounds (102) react with ketones as well as aldehydes to give a,p-unsaturated anilines (103) and amidines (104) with good (E)-stereoselectivity. 

Reaction of 2-thienyllithium with the fluorinated phosphoranes (579) gave the ylide anion (580) which after protonation and elimination of PhjPO afforded the product (581) in which the -isomer was predominant. However, methylation of ( 0) with methyl iodide gave the O-methyl derivative (582) this on hydrolysis gave mainly Z-(581) (Scheme 127) <94JCS(P1)1473>. 

NaHMDS has been shown to be the necessary base for the generation of the ylide anion of sodium cyanotriphenylphospho-ranylidenemethanide, which may be alkylated with various electrophiles and in turn used as an ylide to react with carbonyl compounds. NaHMDS was used as the base of choice in a Homer-Emmons-Wadsworth-based synthesis of terminal conjugated enynes. ... 

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