Transylidation reactions

Tellurophosphoranes, obtained through a transylidation reaction between tellurenyl halides and phosphoranes, react with aldehydes to give the expected vinylic tellurides as an E Z isomeric mixture (method a). One other methodology involves the treatment of equimolar amounts of phenyl tellurenyl bromide and phosphonium salts with t-BuOK followed by an aldehyde (method b). Under these lithium-salt-free conditions, (Z)-vinylic tellurides are the main products. ... 

In an alternative methodology, the bis-tellurophosphorane IV is prepared in situ by means of a transylidation reaction between II and excess of methylene triphenyl phospho-rane (generated from the corresponding phosphoninm salt and n-BuLi) (method d). °... 

Schmidbaur and co-workers (83-90a, 92,93). In cyclic gold-ylide complexes (3), formed by a transylidation reaction (87), the two Au atoms have a parallel two-coordinate linear arrangement of ligands [Eq. (6)]. 

It has been pointed out previously that silylation of ylides leads to stabilized products and that this is only one example of the very general phenomenon of carbanion stabilization through silicon (34, 61, 72). This effect was also found for arsenic ylides (34, 73), and is the basis for the preparation of other compounds of this series. The influence of silicon is by no means solely an electronic effect. In many cases, where alkylsilyl substituents are introduced, a steric effect may well dominate, which may reduce lattice energies for salts in transylidation reactions, preventing intermolecular contacts in decomposition processes, and rendering the formation of salt adducts unfavorable. This steric effect is reduced to a minimum, but not eliminated, if simple SiH3 groups are employed (61). Even then, however, a pronounced silicon effect is found, which must be based on electronic influences (49, 60, 61). 

Whereas iodine-carbon ylides undergo the transylidation reaction normally with copper catalysis, 1,4-dipoles require acid catalysis in this way they react with several nucleophiles through their protonated form, i.e. as iodonium salts, some of which are isolable. Pyridine, nicotinamide, isoquinoline, dimethylsulphide, thiolane... 

From carbodiphosphoranes R3P=C=PR3 and dialkyl-gold(III) halides, cyclic ylide complexes containing four Au-C <7-bonds are obtained in a multiple transylidation reaction (equation 24). Related thiophosphorus ylides and sulfonium and sulfoxonium ylides are equally effective in the formation of Au-C <7-bonds, and a series of analogous gold thiophosphonium and sulfoxonium-methyhde complexes is available (equations 25-27). ... 

The latter ylide has also been made in a transylidation reaction from the corresponding bismuthonium diacetylylide and dimedone in the presence of triethylamine no reaction took place in the absence of the amine ... 

Another arsonium ylide reaction involves a notable transylidation reaction between a phosphorus and an arsenic ylide (Scheme 6). A useful arsenic ylide which provides a hydroxymethyl epoxide has been reported (equation IS) note the use of biphasic reaction conditions for ylide generation. 

Deprotonation of a phosphonium salt by an ylide is a transylidation reaction,- which is of importance especially in those cases where ylides are reacted with electrophiles (see Section 1.6.1.3), but may also be applied to isolated phosphonium salts. For an unequivocal reaction the two involved ylides must differ sufficiently with respect to their base strength (as for example in equation 14). 

If the reaction provides a salt whose acidity is greater than that of the starting phosphorane precursor (for example in the case of X = acyl), a second mole of the starting ylide reacts with the intermediate phosphonium salt in a transylidation reaction cf equation 14) giving rise to the formation of an a-substituted ylide and the conjugated salt of the original ylide. If the proton of the phosphonium salt generated in the first step is not sufficiently acidic for this proton transfer to occur, the phosphonium salt formed in the first step can be isolated and has to be deprotonated by an external base. 

Stabilized, as well as basic ylides, react with sulfenyl chlorides in a transylidation reaction to give al-kylthiomethylenephosphoranes (equation 25)." In methylenetriphenylphosphorane both a-protons may... 

The transylidation reaction of phenylselenyl bromide with two moles of alkylidenetriphenylphos-phorane yields 1-phenylselenoalkylidenetriphenylphosphoranes (equation 28). ... 

Diphenylphosphinyl chlorides and simple ylides yield 1-diphenylphosphinylalkylidenephosphoranes in a transylidation reaction the introduction of the thiophosphinyl group may be carried out analogously (equation 32). Synthesis of diethoxy- and diphenoxy-phosphinomethylenetriphenylphosphoranes may be achieved with the corresponding phosphoro chloridates (equation 33). 

The dimethylstibino group has been introduced by the reaction of lithiated ylide with chlorodimethyl-stibine (equation 35). Bis(diphenylstibino)methylenetriphenylphosphorane results from chlorodiphe-nylstibine and methylenetriphenylphosphorane in a transylidation reaction. ... 

The reaction of ylides with saturated aliphatic alkyl halides (like methyl iodide, ethyl iodide etc.) usually stops at the stage of the alkylated salt because the +/ effect of the aliphatic substituent causes the resulting salt to be a weaker acid than the conjugated salt of the original ylide (which would result in the course of a transylidation reaction). However since partial transylidation also occurs between al-kylidenephosphoranes and phosphonium salts with equal or not very different base and acid strength, mixtures may result from Ae reaction with saturated aliphatic alkyl halides. At this point it should be mentioned that the synthesis of dialkylated ylides via the salt method is also difficult since the preparation of the necessary phosphonium salt is accompanied by -elimination. The successful synthesis of dialkylated ylides may be achieved by fluoride ion induced desilylation of a-trimethylsilylphosphonium salts (see equation 18). There is no doubt about the course of ylide alkylation in cases where the inductive effect of the new substituent leads to complete transylidation (e.g. equation 54). ... 

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). ... 

Alkynyl substituted alkylidenetriphenylphosphoranes are available from the transylidation reaction of methylenetriphenylphosphorane with bromoalkynes (equation 70) or alternatively with 1,1-dibromoal-kenes in the presence of a third mole of original ylide. ... 

Iminoalkylidenetriphenylphosphoranes result from the transylidation reaction of methylenetriphe-nylphosphorane with imidoyl chlorides (equation 76), or from Michael addition of ylides to the C—43 bond of ketenimines (formed from carbodiimide and ylides in the initial step). 

Carbamoylmethylenephosphoranes can also be synthesized from methylenetriphenylphosphorane and carbamoyl chlorides in a transylidation reaction (equation 80). ... 

Phenylcyclobutenediones (26) react with stabilized ylides to give the expected Wittig products, but (26 X=Br) also gave (27), as a result of a transylidation reaction. ... 

The addition of two equivalents of an acylmethylenetriphenylphosphorane to the hydroximoyl chlorides (61) results in a transylidation reaction, leading to the forma-... 

The dinuclear dicationic complex 7 with the di-ylide [(Ph3PCH)2CO] as a bridging ligand between two silver atoms has been obtained from a transylidation reaction between the diphosphonium salt [(Ph3PCH2)2C0]C104 and the bis(yhde) complex [Ag (Ph3P)CHC(0)CH3 2]ClC>4 described above (equation 7)19. 

Ochiai and coworkers developed a new synthetic approach to various iodonium ylides 429 by the inter-molecular transylidation reactions between halonium ylides under thermal or catalytic conditions (Scheme 2.125) [566,567], The transylidations of bromonium 428 to iodonium 429 ylides proceed under thermal... 

A particularly useful reagent in these carbenoid reactions is the highly soluble and reactive iodonium ylide 780 derived from malonate methyl ester and bearing an ortfw methoxy substituent on the phenyl ring [1059]. This reagent shows higher reactivity than common phenyliodonium ylides in the Rh-catalyzed cyclopropanation, C-H insertion and transylidation reactions under homogeneous conditions. Scheme 3.307 shows representative examples of the carbenoid reactions of ylide 780 [1059]. 

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