Non stability

With "non-stabilized" ylides the Wittig Reaction gives predominantly Z-olefins. Seebach et al... 

Table 17. Reactions of Non-Stabilized Phosphorus Ylides 2 PhjP C with CHCIFi [46]...

The (Horner-)Wadsworth-Emmons reaction generally is superior to the Wittig reaction, and has found application in many cases for the synthesis of a ,/3-unsaturated esters, a ,/3-unsaturated ketones and other conjugated systems. Yields are often better then with the original Wittig procedure. However the Wadsworth-Emmons method is not suitable for the preparation of alkenes with simple, non-stabilizing alkyl substituents. 

Electrophile trapping of simple metalated epoxides (i. e., those not possessing an anion-stabilizing group) is possible. Treatment of epoxystannane 217 with n-BuLi (1 equiv.) in the presence of TMEDA gave epoxy alcohol 218 in 77% yield after trapping with acetone (Scheme 5.51) [76], In the absence of TMEDA, the non-stabilized epoxides underwent dimerization to give mixtures of enediols. 

Addition Reactions of Metal Enolates of Non-stabilized Esters, Amides, and Ketones to Epoxides... 

In spite of their intrinsic synthetic potential, addition reactions of metal enolates of non-stabilized esters, amides, and ketones to epoxides are not widely used in the synthesis of complex molecules. Following the seminal work of Danishefsky [64], who introduced the use of Et2AlCl as an efficient catalyst for the reaction, Taylor obtained valuable spiro lactones through the addition reaction of the lithium eno-late of tert-butyl acetate to spiro-epoxides, upon treatment of the corresponding y-... 

Thus unsubstituted (R=H) and substituted (R = alkyl) non-stabilized diyiides 1 react with phenylisocyanate and dicyclohexylcarbodiimide (R NCX), leading to the formation of new monoylide type intermediates. These last ones react in situ with carbonyl compounds through a Wittig type reaction leading respectively to a,)8-unsaturated amides 2 and amidines 3, with a high E stereoselectivity, the double bond being di- or tri-substituted [48,49]. By a similar reactional pathway, diyiides also react with carbonic acid derivatives, with the synthesis as final products of -a,/l-unsaturated esters 4 and acids 5 [50]. 

Pandey, G., Bagul, T.D., Sahoo, A.K. (1998) [3 -E 2] Cycloaddition of Non stabilized Azomethine Ylides. 7. Stereoselective Synthesis of Epibatidine and Analognes. Journal of Organic Chemistry, 63, 760-768. 

The same method of analysis of emitted particles was applied to elucidate the origin of non-stability of piezoquartz resonators with silver electrodes [35]. 

On well characterised non-stabilized PP samples [48] having molar mass within 45-180 kg/mol with differing tacticity and crystallinity, we can see that the increasing molar mass leads to an increase of induction time and reduction of the maximum chemiluminescence intensity (Figure 14). The polymer with higher average molar mass appears to be more stable than that with lower molar mass. This may be ascribed to the effect of increased concentration of more reactive terminal groups, which promote initiation of thermal oxidation. 

Figure 18 Chemiluminescence during oxidation of a non-stabilized polypropylene film and a stabilized film containing 0.1% (w/w) of the phenolic antioxidant Irganox 1010 at 140°C, in an oxygen atmosphere.

Photolysis of 5 in a non-stabilizing hydrocarbon solvent gives lower yields of 8 and only traces of (r/5-H3CC5H4)MnH(CO)2SiH(f-Bu)2 15 [19], which underlines a strong solvent influence. 

Synthetic work commenced with evaluation of an azomethine ylide dipole for the proposed intramolecular dipolar cycloaddition. A number of methods exist for the preparation of azomethine ylides, including, inter alia, transformations based on fluoride-mediated desilylation of a-silyliminium species, electrocyclic ring opening of aziridines, and tautomerization of a-amino acid ester imines [37]. In particular, the fluoride-mediated desilylation of a-silyliminium species, first reported by Vedejs in 1979 [38], is among the most widely used methods for the generation of non-stabilized azomethine ylides (Scheme 1.6). 

Bis-ylides (Scheme 31) may function as four-electron donors and become geminally diaurated. The donor capacity of ylides is generally higher than that of most other ligands, and even powerful donors like tertiary phosphines can thus be readily replaced by non-stabilized ylides. Ylides may therefore be used as auxiliary ligands which are retained, while other components of the coordination sphere are subject to substitution. 

The Generation and Reactions of Non-stabilized a-Aminocarbanions <1998T2647> - includes significant amount of benzotriazole chemistry ... 

The precision of the latter method when applied in the distilled water runs was found to be significantly better than the conventional method. This could be attributed to the non-stability of the glass electrode, which is corrected for by the proposed algorithm. 

Pheromones.—A careful examination of the factors which affect the ratio of the cis-cis- and mww-c/.y-alkenes formed from the reaction of thealdehyde (69) with a non-stabilized ylide has been described.70 Methods were specifically developed to give the... 

Calculations on two Wittig reactants, alkylidenetriphenylphosphorane (a non-stabilized ylid) and its benzylidene analogue (a semi-stabilized one), have been used to identify the origin of the product selectivities for the two classes. A planar transition state gives a trani-oxaphosphetane intermediate, while a puckered one leads to cis-. These two transition states were favoured by the semi- and un-stabilized reactants, respectively. 

The generation and reactions of non-stabilized a-aminocarbanions has been reviewed and developed further in the case of bis(a-aminocarbanions) which can be trapped by... 

It has been suggested that the preferential formation of ( )-alkene on Wittig reaction of amide-substituted phenyl 3-pyridyl ketones with non-stabilized phosphorus ylides which contain a carboxyl terminus is a consequence of either hydrogen bonding or salt... 

Non-stabilized a, p y, 5-unsaturated azomethine ylides (158), generated by the decarboxylation method from 3,3-diarylpropenals (156) and secondary amino acids (157), have been found to undergo [1,7]-electrocyclization followed by a [1,5]-hydrogen shift, to yield 2,3-dihydro-17/-2-benzazepines (159). 

In sharp contrast to the olefmation reaction employing stabilized telluronium ylides, semi-and non-stabilized ylides react with carbonyl compounds to give epoxides (like non-stabilized sulphonium and selenonium ylides). 

This was the first-described, non-stabilized ylide, obtained by treatment of the corresponding telluronium tetrafluoroborate with hthium 2,2,6,6-tetramethylpiperidide (LiTMP). Epoxides are obtained by reaction with both aldehydes and ketones. ... 

The imidoylation of non-stabilized radicals (R=/-prop, t-Bu), also takes place, but the reaction is slow and requires a longer reaction time, the efficiency being increased by the addition of a radical initiator [l,l-azobis(cyclohexane-l-carbonitrile)]. 

The bis-ylide ligands [R2P(CH2)2] can easily be prepared by treatment of the phosphonium salts [R2PMe2] (R = Me, Ph) with strong deprotonating reagents such as lithium derivatives, NaNH2, or non stabilized ylides R3P=CH2. However, Au Ag, and Cu complexes (99) were prepared by reaction of ClMPMe3 (M = Ag, Au) or CuCl with excess of R3P=CH2 [202, 203] (Scheme 30). 

Certain substances which are susceptible to spontaneous polymerization or decomposition are generally placed on the market in a stabilized form. It is in this form that they are listed in Annex I to the Commission Directive 98/98/EC. However, such substances are sometimes sold in a nonstabilized form. In this case, the manufacturer or any person who places such a substance on the market must state on the label the name of the substance followed by the words non-stabilized . 

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