Methanide substitution

The effect of the counterion on the diastereomer ratio was investigated in detail for the Peterson condensation3 of phenyl(trimethylsilyl)methanide with benzaldehyde2 or substituted cyclohexanones4 and was found to be remarkably low. The variation of the solvent and the temperature has an influence of similar magnitude. 

The formation of the (SiN)2 ring can be explained by a nucleophilic 1,3-rearrangement of a methanide ion at silicon. The cyclic ylide is formed because the two nitrogen atoms are identically substituted and a silyl group migration would be without energy profit in such a molecule. 

Rhodium(II) acetate was found to be much more superior to copper catalysts in catalyzing reactions between thiophenes and diazoesters or diazoketones 246 K The outcome of the reaction depends on the particular diazo compound 246> With /-butyl diazoacetate, high-yield cydopropanation takes place, yielding 6-eco-substituted thiabicyclohexene 262. Dimethyl or diethyl diazomalonate, upon Rh2(OAc)4-catalysis at room temperature, furnish stable thiophenium bis(alkoxycarbonyl)methanides 263, but exclusively the corresponding carbene dimer upon heating. In contrast, only 2-thienylmalonate (36 %) and carbene dimer were obtained upon heating the reactants for 8 days in the presence of Cul P(OEt)3. The Rh(II)-promoted ylide formation... 

In the reactions with phosphonio-a-methoxycarbonyl-alkanides, the products of type 261 derived from 1,3-cycloaddition can rearrange to the tautomeric lif-pyrazolo-triazole (87MI2). The reaction of 3-diazopyra-zoles and 3-diazoindazole with acyl-substituted phosphonium ylides led to pyrazolo-triazine and indazolo-triazine derivatives 266 instead of the expected triazole compounds (8IJHC675). In this case, the ylides, which can exist as phosphonium enolates, possess nucleophilic and electrophilic centers in a /8-relationship, giving [7 + 2] or [11 -I- 2]cycloaddition reactions. With dimethylsulfonio-a-aroyl-methanides, very complex, temperature-dependent mixtures were obtained, in some cases with sulfur retention (87MI3). 

As depicted in Figure 34, the NNCM anion is planar within experimental error (E < (Cl) = 359.9°) like most of the known NO, NO2 and CN substituted methanide anions (except from trinitromethanide, in which the balance between resonance stabilization... 

Carbanions of the type [HjCR ], [HCR R ] and [CR R R ] (R = NO and R R = CN, NO, NO2) can be considered to be resonance-stabilized, nonlinear pseudohalides. All experimentally known resonance-stabilized methanides are reported to be planar or nearly planar (Table 1). While the parent ion, the methanide anion HsC, adopts a pyramidal structure [Afipianar-pyramidai = 9.8 kJmol rf(CH) = 1.099 A, <(HCH) = 109.7° cf. rf(CH) = 1.093 A, <(HCH) = 109.6°] due to the lack of delocalization (no resonance for the p-AO-type lone pair possible) , substitution of one H atom by NO results in a planar anion since the empty jr -orbitals of the NO group are perfectly suitable to delocalize the carbon lone pair. Further substitution of the second H atom again results in planar anions, and the same holds for the third substitution in case of R = CN. In case of R = NO and NO2, the third substitution leads either to a propeller-type structure with only a small distortion from planarity or one NO2 group is twisted by 90°, nevertheless leaving the central carbon in an almost trigonal planar environment . ... 

In summary, as shown by different theoretical approaches (charge transfer, resonance energies and NLMO delocalization) resonance effects occur in all three classes of methanides. However, the magnitude of such effects strongly differs depending on the degree of substitution. 

In contrast to most of the high energy-density alkali and silver (NO- and NO2-substituted) methanides, the ionic liquids of these methanides with a bulky organic cation are neither heat nor shock sensitive, and hence can be prepared and stored in large scale. Nevertheless, this type of methanide-based ionic liquids can also be considered energetic ionic liquids since the thermodynamically unstable methanide anion is only kinetically... 

Elimination of methyl chloride returns the oxidation state to +2 and the coordination number to 4 with a net substitution of chloride for methanide. 

The structure of the hybrid lithium methanide complex 12 was reported by So.23 Complex 12 is similar to 3, 6, 9, and 11, except an extra molecule of solvent is coordinated to the lithium centre (in this case THF), presumably due to the diminished steric demands of a thio group compared to a substituted imino group. 

Extending the theme of cyclopentadienyl-substituted methanides, complexes 51, 54, and 56 were used to prepare the mono-pentamethyl-cyclo-pentadienyl complexes 62, 63, and 64 in which the metal-methanide bond was maintained.39 Complexes 62-64 were tested for their activity in the polymerisation of e-caprolactone and they exhibited low activities. However, treatment of 62-64 with one equivalent of iso-propyl alcohol resulted... 

Cavell also reported alkyl derivatives. Tetrabenzyl zirconium was found to react separately with one molar equivalent of two parent methanes to afford complexes 135 and 136 in excellent yields.66 The 13C NMR chemical shifts of the methandiide centres in 135 (Ad = adamantyl) and 136 of 82.8 and 84.4 ppm are clearly different from the dichloride congeners and reflect the substitution of the chlorides by alkyls. The corresponding hafnium dialkyl 137 was also prepared from 133 and neopentyl lithium and the methanide resonance for this complex appeared at 71.6 ppm in its 13C NMR spectrum.63 Noteably, these alkyls displayed far greater stability than their homoleptic tetraalkyl cousins. 

Recent examples of this type of methylene transfer are the cyclopropanation of several a, -unsaturated esters 1 with dimethyloxosulfonium methanide to afford the cyclopropanated products 2 which were used for the synthesis of cyclopropanated barbiturates. Aryl-substituted spirocyclopropanobarbiturates 4 were obtained by the reaction of 2 with urea (3). ... 

Cyclopropanation of a,jS-unsaturated AT-methoxy-AT-methylamides 5 with dimethyloxo-sulfonium methanide afforded the cyclopropanecarboxamides 6 in yields far superior to those obtained with the corresponding a,/J-unsaturated ketones. In almost all cases, the trans-isomer was exclusively obtained in analogy to the cyclopropanation of the corresponding unsaturated ketones. The oxygen atom of the methoxy group on the A -methoxy-A -methyl-amide 5 was found to facilitate the reaction. The substituted amides 6 can be converted to ketones (methylmagnesium bromide), aldehydes (diisobutylaluminum hydride) and carboxylic acids (potassium rerf-butoxide/water). It is noteworthy that cyclopropanecarbaldehydes and -carboxylic acids, which are not directly accessible from the corresponding a,)8-unsaturated systems under standard cyclopropanation reactions, can be obtained indirectly by this method. 

Reaction of dimethyloxosulfonio- and triphenylphosphonio-substituted (3-oxocyclohex-l-enyl)methanides with 2,3-diphenylcyclopropenone gave 8-hydroxy-6,7-diphenyl-3,4-dihydro-naphthalen-l(2//)-ones 6. ... 

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