Neutral ylide

Neutral ylide, isocyanide and carbene pentafluorophenyl gold] 111) complexes with the general formulae trans-[Au]C6F5)X2]CH2PR3)[ ]PR3 = PPh3, PPh2Me, PPhMe2),... 

Ph)jP, is a good nucleophile in S(j2 reactions, and yields of the resultant alkyl-tfiphenylphosphonium. salt are hi. The hydrt en on the carbon next to the positively charged phosphorus is weakly acidic and cem be removed by a base such as butyllithium (BuLi) to generate the neutral ylide. For example ... 

In our opinion, heterofullerenes with divalent heteroatoms, like O and S, are potentially interesting compounds because they could possibly exist as neutral ylide structures with > C-0+< and > C-S+< bonds, respectively. Alternative structures for C59O and C59S are less ionic truncated quasi-fullerene structures bearing a carbonyl or thiocarbonyl moiety, as shown in Fig. 35. 

The reaction of [Au(CgFg)2CK2(PPh2)2]C10 with NaH provided the neutral ylide complex [Au(CgFg)2(Ph2PCHPPh2)l (18) (18)... 

Ylide (Section 17 12) A neutral molecule in which two oppo sitely charged atoms each with an octet of electrons are di rectly bonded to each other The compound... 

N-Alkylations, especially of oxo-di- and tetra-hydro derivatives, e.g. (28)->(29), have been carried out readily using a variety of reagents such as (usual) alkyl halide/alkali, alkyl sulfate/alkali, alkyl halide, tosylate or sulfate/NaH, trialkyloxonium fluoroborate and other Meerwein-type reagents, alcohols/DCCI, diazoalkanes, alkyl carbonates, oxalates or malon-ates, oxosulfonium ylides, DMF dimethyl acetal, and triethyl orthoformate/AcjO. Also used have been alkyl halide/lithium diisopropylamide and in one case benzyl chloride on the thallium derivative. In neutral conditions 8-alkylation is observed and preparation of some 8-nucleosides has also been reported (78JOC828, 77JOC997, 72JOC3975, 72JOC3980). 

To understand the mechanism of the Wittig reaction, we need to exanine the structure and properties of ylides. Ylides are neutral molecules that have two oppositely... 

In the Wittig reaction, a phosphorus ylide, R2C—P(C6H03, also called a phosphoreme and sometimes written in the resonance form R2C=P(C6H5)3, adds to an aldehyde or ketone to yield a dipolar intermediate called a betaine. (An ylide—pronounced ill-id—is a neutral, dipolar compound with adjacent plus and minus charges. A betaine—pronounced bay-ta-een—is a neutral, dipolar compound with nonadjacent charges.)... 

Ylide (Section 19.11) A neutral dipolar molecule with adjacent positive and negative charges. The phosphoranes used in Wittig reactions are ylides. 

Iminocarbene complexes of chromium and tungsten are useful isolable synthetic equivalents to nitrile ylides having the advantage that the range of 1,3-dipo-larophiles is not limited to electron-acceptor substrates and can be extended to electronically neutral as well as to electron-rich systems [56] (Scheme 18). 

The bis-phosphonium salt 56 in presence of Pd(OAc)2 leads to the formation of the neutral bis-ylide 57 which reacts with TICIO4 to give the dinuclear cationic complex 58 (Scheme 22) [89,90]. The bis-ylide part, which has potentially two carbons and one oxygen donor atoms, acts as a C,C-chelating ligand through its two soft ylidic carbons. 

Thiols like pyridine-2-thiol yield (carbene)gold thiolates, and onium salts give cationic (carbene)gold ylide complexes, isolated and characterized as the perchlorates.170 The reaction of dithiocatechol with (cyclohexylisocya-nide)gold chloride affords a carbene complex [(CyNC)AuC(NHCy)2]+Cl-, which co-crystallizes with a neutral tetranuclear complex [(CyNCAu)2Au2(S2C6H4)2].224... 

Solid supports such as silica gel and alumina have also been used in the generation of 1,3-dipoles to obtain heterocyclic compounds. However, changes in regios-electivity were not observed under microwave irradiation conditions. The regioselec-tivity can be modified by changing the polarity of the solid support [90], De la Hoz reported the reaction of pyridinium dicyanomethylidene ylide (130) with ethyl phenyl-propiolate (73), and found that the selectivity changes from 88 12 to 98 2 when the support is changed from celite, to neutral bentonite (Scheme 9.39). 

An acid- and base-sensitive siloxycarboxylic acid was treated with AW -carbonyldi-imidazole and the resulting imidazolide (51) transformed into the desired ylide using one equivalent of salt-free methylenetriphenylphosphorane in benzene, rather than two equivalents as usually recommended. Coupling, under neutral conditions, with two equivalents of aldehyde (52) gave a mixture of diastereomeric epoxythiolates (Scheme 15).68... 

The most unusual bond in this system is the N-Cl bond. The nucleophilic substitution step must involve cleavage of this bond. No base is present, but S is an excellent nucleophile, even in its neutral form, so the first step probably entails formation of an S9-N2 bond. Now we have to make the C4-C10 bond and make the S9-N2 bond. Deprotonation of C4 gives an ylide, which as discussed in problem 4.15 is likely to undergo a [2,3] sigmatropic rearrangement. Tautomerization to rearomatize then gives the product. 

Yates, B.F. Bouma, W.J. Radom, L. Detection of the Prototype Phosphonium (CH2PH3), Sulfonium (CH2SH2), and Chloronium (CH2CIH) Ylides by Neutralization-Reionization Mass Spectrometry a Theoretical Prediction. J. Am. Chem. Soc. 1984,106, 5805-5808. 

Class A. Neutral -Carbon Ligands Ylides and Carbodiphosphoranes... 

Although, in principle, the chemistry here reported should be centered on the late transition metals, sometimes we will jump the frontier between late and middle or early transition metal since this line could be more or less diffuse and could change as a function of the history. At least seven different coordination modes have been identified (I-VII, Scheme 3) as the main bonding modes. In modes I and II the ylide behaves as neutral and monodentate, bonded exclusively through the Ca atom (kC mode) this is the case for simple ylides and carbodipho-sphoranes. Mode 111 covers the variants of a metallated ylide, that is, a situation in which the metal replaces a substituent of the ylide and transforms it into an anionic ligand. 

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