Keteni mines

Diazo(trimethylsilyl)methyl lithium (3) was found to be the reagent of choice for the synthesis of azoles from heterocumulenes (Scheme 8.43). The reaction is typically carried out in ether at 0-20 °C. Thus, alkyl- (or aryl-)substituted keteni-mines are transformed into 1,2,3-triazoles 188 (246), while C-acceptor-substituted ketenimines yield either 4-aminopyrazoles 189 or 1,2,3-triazoles, depending on the substituents (247). Isocyanates are converted into 5-hydroxy-1,2,3-triazoles 190 (248). Reaction of 3 with isothiocyanates are strongly solvent dependent. 

N,iV-Disulfonyl ynamides react with salicylaldehydes through a keteni-mine intermediate in the presence of triethylamine giving access to 3-substituted iminosulfonylcoumarins (140BC3986). Biscoumarins fused at the pyrone ring arise from the indium(III) trifluoromethanesulfonate-catalyzed reaction of methyl coumarin-3-carboxylate with phenols, in good yields (14JOC8723). A library of 3,3 -biscoumarin-based protein kinase inhibitors is achieved from the condensation of 2 -hydroxyacetophenones... 

The failure of all but 2-methyl- or 2-benzyl-dihydro-l, 3-oxazine anions to alkylate has been turned to ingenious advantage. Meyers has reported that the above two anions are stable at the generation temperature, —78 °C, but, on warming to room temperature, they rapidly rearrange to the keteni-mines (140) higher alkyl dihydro-oxazine anions form the ketenimine spontaneously at —78°C. Thus, dihydro-oxazine anions can function as nucleophiles or electrophiles, depending on the temperature employed. This has been used for the assembly of ketones with a-quaternary carbon atoms of varied structure, but specifically alkylated in one of two available sites (Scheme 64). 

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