Simple Nitrogen Ylides

In an attempt to demonstrate the existence of pentavalent nitrogen, Schlenk and Holtz studied the reaction of triphenylmethyl sodium with tetramethylammonium chloride (52). The highly colored material was strongly conducting in polar solvents and could be identified as a salt, the stability of which is due to the resonance stabilization of the triphenyl-methide anion. In the absence of such stabilizing substituent effects (53), as with n-butyl or another alkyllithium reagent, a metalation of the tetramethylammonium cation occurs, which leads to type I products (18)  

These species can be formulated as alkali halide complexes of the nitrogen e 

The addition compounds (I) are insoluble in diethyl ether, and the slurries obtained are quite stable. In more strongly solvating media, such as tetrahydrofuran or dimethoxyethane, the compounds are soluble but show rapid decomposition, with trimethylamine and polymethylene as the main products. These experiments indicate (9, 40) that when the lithium salt is trapped by donor solvent molecules, the free ylide quickly undergoes decomposition (40). No free trialkylammonium ylide has yet been prepared, even under very mild conditions (35). On the other hand, it has been shown, that the tetramethylammonium cation can even be metalated twice by organolithium reagents (102) to afford dimethyl-ammonium bismethylides  

As already mentioned (105), no pentavalent nitrogen compound NRg has ever been reported. In view of the present knowledge of the valence 

Alkylidene triorganophosphoranes (phosphorus ylides) are known with a large variety of substituents both at the phosphonium center and at the carbanionic function  

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The yields of carbene (and pyridinium ylide) are thus controlled by competition between simple nitrogen loss to the carbene or 1,2-H (or 1,2-C) shift linked to nitrogen loss in the excited state of the diazoalkane precursor 56 When R=i-C3H7, the a-CH bond is weak, there is much RIES upon diazoalkane photolysis, and carbene production is inefficient. When R=/-C4H9 (no a-CH bond) or R=cyclo-CjU5 (strong a-CH bond), diazoalkane photolysis gives little RIES and much carbene.56... 

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.,... 

In the case of simple ammonium ylides there is no possibility of the nitrogen atom being doubly-bonded to the ring as in (B) in pyridinium ylides there may be some contribution from CB) since the negative charge could also be sited on the 4-position of the pyridinium ring, viz. 

Muthusamy found that with the simple cyclohexyl keto-ylide derived from 189 (Ri = H) and an electron-withdrawing group protecting the indole nitrogen, that the indole would add in a regioreversed fashion producing the other possible... 

Ylides based upon sulfur are the most generally useful in these cyclopropane-forming reactions.133 Early work in this area was done with the simple dimethyloxysulfonium methylide (9) derived from dimethyl sulfoxide. The even simpler dimethylsulfonium methylide (10) was studied at the same time as a reagent primarily for the conversion of carbonyl compounds into epoxides.134 Somewhat later, other types of sulfur ylides were developed, among which the nitrogen-substituted derivatives such as (11) are... 

The tandem reaction of carbenoids with simple imines to form azomethine ylides which then undergo 1,3-dipolar cycloaddition with various dipolarophiles was first reported in 1972.81 Treatment of phenyldiazomethane with copper bronze in the presence of excess N-benzylidenemethylamine resulted in the isolation of imidazoline 170. Formation of this product was rationalized by carbenoid addition onto the imine nitrogen to give azomethine ylide 169 which then underwent a 1,3-dipolar cycloaddition with another molecule of imine to produce the observed product. Bartnik and Mloston subsequently extended this observation by using other dipolarophiles.82 For example, catalytic decomposition of phenyldiazomethane and A-benzylidenemethylamine in the presence of dimethyl maleate or benzaldehyde gave pyrrolidine 171... 

Arsinimines 35 are the nitrogen analogues of arsonium ylides. They appear to be more resistant to hydrolysis than are ylides, for even the simple non-stabilized example (35,... 

Carbenes can also be trapped by thioamides as in the reactions of the carbenes obtained by irradiation of564. The possibility is that a sulphur ylide is formed in this system and the subsequent intramolecular reaction with the amide nitrogen affords the final products 565. Even in simple systems an ylide can be formed, as in the reaction of singlet methylene with acetone. ... 

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