N, C-Dianions as intermediate

Hydroxycarboxylie acid amides from ketones N,C-Dianions as intermediates Inverse neutralization... 

Another route to thioaldehyde and thioketone complexes uses the tungstate [W(CO)5SH] as the precursor. When [W(CO)5SH] was treated with ketones in the presence of trifluoroacetic acid, thioketone complexes [W(CO)5 S = C(R1)R2 ] were formed. Analogously, thiobenzaldehyde complexes were obtained from [W(CO)sSH]- and benzaldehydes bearing electron-releasing para substituents. Benzaldehyde, benzaldehydes with electron-withdrawing substituents, and aliphatic aldehydes did not react. Presumably, the binuclear dianion [p,-S W(CO)5 2]2 is an intermediate in the reaction, as on acidification of a mixture of [ju,-S W(CO)5 2]2 and p-N, A -dimethylaminobenzaldehyde the thioaldehyde complex [W(CO)5 S = C(C6H4NMe2-p)H ] is formed.143... 

The nucleophilicity of the aromatic system can alternatively be increased by using organometallic aromatic compounds, which also solves the problem of regioselectivity. This method was applied by Sulikowski et al., who reacted a variety of sugar lactones with aryl lithiums to afford intermediate lactols which were subsequently reduced to the C-glycosides by cyanoboro hydride [137]. For example, selective orfho-bromination of monobenzylated napthalene diol 174 affords the bromide 175 which is converted into the dianion with three equivalents of n-BuLi. Treatment with the benzylated lactone 176 afforded lactol 177 (Scheme 45, the D-dideoxygluconolactone 176 was erroneously drawn as the... 

Preparative Methods. As discussed above, one of the simplest methods of preparation of 3-acetoxy-2-trimethylsilyhnethyl-1-propene (1) is the direct silylation of the C,0-dianion derived from methallyl alcohol, followed by 0-desilylation and subsequent acetylation (eq 1 However, because of laboratory safety concerns (use of large quantities of 10 M n-BuLi) one might choose another more user-friendly route such as the copper-mediated conversion of 2-chloromethylallyl chloride to 2-chloro-methylallyl trichlorosilane (5), followed by methylation and nucleophilic displacement of the chloride by an acetate (eq 18). Moreover, the intermediate 3-chloro-2-trimethylsilylmethyl-l-propene (6) is also a useful reagent in organic synthesis and in many aspects has similar reactivity to 1. Alternatives to 1 include the carbonate derivatives 7. 

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