Ylide compounds chemical behavior

The chemical behavior of heteroatom-substituted vinylcarbene complexes is similar to that of a,(3-unsaturated carbonyl compounds (Figure 2.17) [206]. It is possible to perform Michael additions [217,230], 1,4-addition of cuprates [151], additions of nucleophilic radicals [231], 1,3-dipolar cycloadditions [232,233], inter-[234-241] or intramolecular [220,242] Diels-Alder reactions, as well as Simmons-Smith- [243], sulfur ylide- [244] or diazomethane-mediated [151] cyclopropanati-ons of the vinylcarbene C-C double bond. The treatment of arylcarbene complexes with organolithium reagents ean lead via conjugate addition to substituted 1,4-cyclohexadien-6-ylidene complexes [245]. 

The dipolar structure 1 describes the chemical behavior of thiocarbonyl ylides best, although other mesomeric forms have been used for the representation of the electronic structure of these dipoles. The parent compound, thioformaldehyde (5)-methylide (1), was studied by means of spectroscopic and theoretical methods (2-5), which showed that the molecule possesses a bent allyl-type structure (6). According to theoretical calculations, structures lA and IB have the largest contribution (31.5% each) in the representation of the electronic structure, whereas 1C, which reflects the 1,3-dipolar character, has only a 4.2% contribution (5). 

Arsonium ylides were discovered near the turn of the century, but their reactions with carbonyl compounds did not become elucidated until the 1960s. In a broad sense, arsonium ylides are midway in chemical behavior between ylides of phosphorus and those of sulfur. Stabilized arsonium ylides react with carbonyl compounds to afford alkenes, whereas the unstabilized analogs give rise to epoxides. More subtly, the nature of the substituents on either the ylide arsenic or carbon atom can alter the course of the reaction the choice of solvent can exert a similar effect. ... 

Gold(I) ylides are oxidized in 0.1 M [Bu4N]BF4/THFat low potentials of +0.11 and + 0.23 V vs. Ag/AgCl (quasi-reversible). The dinuclear amidinate oxidizes under the same conditions at + 1.24 V vs. Ag/AgCl (reversible). These large differences in chemical character of the dinuclear gold(I) complexes appear to explain the widely different behavior of these compounds and especially toward the reaction with mercury cyanide. 

Calculation of the electronic distribution of 6- and 7-phenyl derivatives of (15) showed that there is only a very slight difference between the two compounds, which cannot account for the essentially different biological behavior of the two compounds <89MI 816-01 >. Quantum chemical studies have also been reported on an ylide derivative of (37) (i.e. (106)), and the frontier orbital energies have been calculated by an ab initio (STO-3G) method <87JCS(Pl)253i>. 

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