Hydrides with electrophiles

The compatibility of sodium hydride with electrophiles means that, by adding two equivalents of base, alkylation can be encouraged to occur more than once. This dimethylated acid was required in the synthesis of a potential drug, and it was made in two steps from a nitrile. Double alkylation with two equivalents of NaH in the presence of excess methyl iodide gave the methylated nitrile which was hydrolysed to the acid. The monoalkylated product is not isolated—it goes on directly to be deprotonated and react with a second molecule of Mel. 

Ylides 2 can be prepared in situ from the sulfonium salts 1 with sodium hydride. These ylides 2 react with electrophiles, for example, acetylenes, to give the new stable ylides 3, for R1 =R2 = Me as a mixture of the cis- and trans-isomer, otherwise as the trans-isomer only. Compounds 3 are stable in refluxing tetrahydrofuran for 1 hour, but heating without solvent at 170-200r C for 3 to 5 minutes results in a 1,4-rearrangement to give thiaazulenes 4 quantitatively, with the exception of R1 = R2 = Et, where the yield is 25%.98... 

The 20e complex Fe(C6Me6)2, easily synthesized in high yield by Na/Hg reduction of the dry di-cationic precursor in THF at 20 °C [28], is also very useful for functionalization. Its reaction with electrophiles RX directly gives functional cyclohexadienyl iron cations, which saves one step with respect to the route using hydride protection/deprotection [47] Scheme V ... 

Reduction to sulphides with electrophilic hydride reagents. ... 

The hydride-methyl complex OsH(Me)(CO)2(P Pr3)2 reacts with electrophilic reagents. The reaction products depend on the nature of the reagent (Scheme 39). Whereas the reaction with iodine gives almost quantitatively the diiodide OsI2(CO)2(P,Pr3)2, the reaction with a five-fold excess of phenylacetylene does not lead to the formation of the previously mentioned bis-alkynyl complex... 

In view of the fact that early transition metal alkyls insert CO under very mild conditions (2, 5.) we chose to examine the reactions of electron-rich metal hydrides ( ) with the resultant dihapto acyl complexes. Such acyls obviously benefit from reduction of the CO bond order from three (in OO) to two. More significantly, the dihapto binding mode will significantly enhance the electrophilic character of the acyl carbon. 

Stannyllithium compounds are important as sources of nucleophilic stannyl anions, and the dialkyltin lithium hydrides, R2SnLiH, have recently come to prominence as their reaction with electrophilic alkyl halides gives hydrides, R1R2SnH, with mixed alkyl groups (see Section 3.14.18.1).397... 

The limited kinetic data for reactions of tin hydride with nitrogen-centered radicals apparently demonstrates the combined effects of the enthalpies of the reactions and polarization in the transition states for H-atom transfer. The aminyl and iminyl radicals are electron-rich, and the N-H bonds formed are relatively weak these radicals react relatively slowly with tin hydride. On the other hand, the electrophilic amidyl and aminium cation radicals form strong N-H bonds and react rapidly with the tin hydride reagents. 

Some carbyne complexes, in particular cationic ones with good Ji-accepting ligands, can react with nucleophiles to give carbene complexes [187,521]. Several reductions of carbyne complexes to carbene complexes by treatment with metal hydrides have been reported. Similarly, organolithium or other carbanionic reagents can react with electrophilic carbyne complexes to yield carbene complexes. Illustrative examples of both reactions are sketched in Figure 3.23. 

Many boron hydrides, especially the higher boranes, undergo halogenation, alkylation and other substitution reactions when treated with electrophiles. Such reactions are catalyzed by acids, yielding a variety of stable products. 

REACTION WITH ELECTROPHILES HYDRIDE ABSTRACTION AND HYDRIDE BRIDGING 145... 

Most of the applications of sulfoxides in synthesis make use of the reactions of sulfur-stabilized carbanions with electrophiles [385, 386]. Thus the methylsulfinyl methylene carbanion, conveniently generated through the interaction of sodium hydride with DMSO [387], is a powerful nucleophile. 

Borane, as a solution in tetrahydrofuran or generated in situ by the reaction of a metal hydride with boron trifluoride etherate, adds readily to alkenes to yield trialkylboranes. With a terminal alkene the reaction is highly (though not completely) regioselective and gives a primary trialkylborane, since the mode of addition results from the electrophilic character of the boron atom. 

Treatment of indole (pKa - 17) with strong bases such as butyl lithium, Grignard reagents, or metal hydrides produces the corresponding indolyl anion, which reacts with electrophiles either on nitrogen or at the C3 position. With lithium, sodium, or potassium as counterion the indolyl anion tends to react on nitrogen, as in the preparation of 7.35. However, with magnesium as the counterion the intermediate has an essentially covalent rather than ionic structure, and reaction tends to occur at the C3 position, as in the preparation of 7.36. 

The isoelectronic group of compounds represented by 30 and 31 react differently with nucleophiles. For example, the M—Si bond in 30 is cleaved by phosphines while in 31 only CO substitution occurs (80). Incorporation of phosphines into 30 has been accomplished only when attached to the metal before addition of the silicon fragment. Conversely, 31 undergoes Fe—Si bond cleavage when treated with electrophiles, such as Cl2 and PC15, whereas hydride bridged complexes 30 remain intact (79). 

Sommer and Bauman investigated the reaction of optically active a-naphthylphenylmethylsilyl hydride with trityl chloride and found that the stereochemical course was retention in benzene solution, inversion in methylene chloride, and full racemization in methylene chloride (93). The result in CH2C12 was explained as consistent with an exchange in which electrophilic attack on the silicon hydride by a triphenyl cation is of primary importance however, the counterion appears in the transition state [Eq. (16)]. Racemization of the unreacted R3SiH could arise from... 

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