Nitrogen ylide

An interesting intermediate 30 was proposed to result from the sequential addition of pyridine to tetrachlorocyclopropene (31). Compound 30 represents an alkyl nitrogen ylide with two 1-chloroalkyl pyridinium moieties in the same molecule. Pyridines with electron-withdrawing groups and heterocycles with an electron-deficient nitrogen, for example, pyridine-3-carbaldehyde or quinoline, react with 31 to yield the corresponding mono-substituted products 32a and 32b (83JOC2629) (Scheme 8). 

Formation of N- and N,0-heterocycles from fluoro-substituted nitrogen ylides 99MI23. 

Cycloaddition of 2-nitrosopyridine 48 with nitrile oxides can give either di-A -oxides such as 49 or 3-mono-A -oxides such as 50 (93JHC287). In general, greater electron withdrawing character in the aromatic substituent appears to favor formation of the di-A -oxides. Sulfur ylides such as compound 51 are obtained from aryl isothiocyanates and l-amino-2-methylthiopyridinium iodides (84JCS(P1)1891) nitrogen ylides can be obtained from a similar reaction (86H(24)3363). 

DCCI reacts with hydrazone derivatives or with the thiourea 83 to give nitrogen ylides such as 84 and hence by protonation 3-aminotriazolopyridines (88CC506, 93JCS(P1)705). A solution of iodine in pyridine reacts with propional... 

Mechanistically the rearrangement is formulated to proceed via an intermediate radical-pair or ion-pair. In either case the initial step is the formation of a nitrogen-ylide 2 by deprotonation of the ammonium species with a strong base. The abstraction of a proton from the a-carbon is facilitated by an electron-withdrawing group Z—e.g. an ester, keto or phenyl group ... 

The ylides have been classified on the basis of the heteroalom covalently bonded to the carbanion. Accordingly, they can be differentiated into nitrogen ylide (Scheme 2), sulfur ylide Scheme 3, phosphorus ylide Scheme 4, arsenic ylide Scheme 5, antimony ylide (Scheme 6), bismuth ylide (Scheme 7) and thallium ylide (Scheme 8). 

A comparative study on ylide stability as a function of the heteroatom type was carried out by Doering et al. [3,4]. They concluded that the phosphorus and sulfur ylides are the most stable ones. The participation of three-dimensional orbitals in the covalency determines the resonance stabilization of the phosphorus and sulfur ylides [5-8]. The nitrogen ylides are less stable from this point of view. The only stabilization factor involves electrostatic interactions between the two charges localized on adjacent nitrogen and carbon atoms [9]. 

In an attempt to broaden the use of nitrogen ylides in polymerization, Saini et al. [33] tried using imidazo-lium-p-chlorophenacylide (ICPY) for the polymerization of styrene [33] and MA [34]. Unlike /3-PCPY, ICPY... 

A class of compounds in which a positively charged atom from group V or VI of the periodic table (c.g., N, O, S, P, As, Se) is bonded to a carbon atom having an unshared pair of electrons. Whereas there is only one canonical form for nitrogen ylides (R3N —CR2 ), because of pTT-dTT bonding, two canonical forms can be written for phosphorus Le., R3P=CR2 R3P —CR2 ) and sulfur ylides (R2S=CR2 R3S —CR2 ). A number of enzyme-catalyzed reactions have been reported to utilize ylide-based chemistry. For example, the ylide form of the... 

Nitrogen ylides are also known to undergo [1,2]- (Stevens) and [2,3]-rearrangements. The Stevens rearrangement occurs through a mechanism that involves homolytic cleavage... 

The corresponding nitrogen ylides can also be generated when one of the nitrogen substituents has an anion-stabilizing group on the a carbon. For example, quaternary salts... 

An internal alkylation via a nitrogen ylide has also been reported7. Thus, the bromide salt of methyl 6-[dimethyl(2-propenyl)ammonio]penicillanate gives a 75% yield of methyl 6/J-dimeth-ylamino-6oi-(2-propenyl)peniciHanate (see Table 2). 

Formation of Nitrogen Ylide from Metal Carbene Complex and Subsequent Reactions 168... 

The addition of diazomethane to cyclobutanones results in a convenient expansion to cyclopen-tanones. With few exceptions, the rearrangement of the intermediate nitrogen ylide is highly regioselcctive, only one product is generally isolated, particularly in cases where both substituted cyclobutanones and substituted diazomethanes are used. Typical examples are shown in Tabic 6 further examples can be found in refs 57, 59. 61 -63 and 65-68. 

For a review of nitrogen ylides, sec Musker Fortschr. Chem. Forsch. 1970, 14, 295-365. 

However, in a nitrogen ylide R3 —C 2 (see p. 39), where a positive nitrogen is adjacent to the negatively charged carbon, only the field effect operates. Ylides are more stable than the corresponding simple carbanions. Carbanions are stabilized by a field effect if there is any hetero atom (O, N, or S) connected to the carbanionic carbon, provided that the hetero atom bears a positive charge in at least one important canonical form,90 e g.,... 

A closely related reaction is formation of nitrogen ylides from quaternary ammonium salts (see 7-7) ... 

Zwitterionic four-membered PN2Nb heterocycles were obtained in the reaction of ij5-phosphorus-nitrogen ylides with NbCl5 according to equation (40). 496... 

Nitrogen ylide cyclization gives isoquinolines (194) as shown in Scheme 25 (87JCS(Pl)92l). 

A synthesis of a-( trifluoromcthyl)-a-amino esters 5 has been developed based on the [1,2] Stevens rearrangement of nitrogen ylides 4, obtained by the transition-metal-calalyzed decomposition of methyl 2-diazo-3,3,3-trifluoropropanoate (3) in the presence of tertiary amines.2... 

Use Figure 6-4 (Section 6-1) to explain why phosphorus and sulfur ylides are more stable than corresponding nitrogen ylides. 

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