2987-13-5Relevant academic research and scientific papers
Shorter and easier syntheses of Di-tert-butylketene and related gem-Di-tert-butyl compounds
Knorr, Rudolf,Hennig, Karsten-Olaf,Schubert, Bernhard,Boehrer, Petra
body text, p. 6651 - 6664 (2011/02/26)
The ketene tBu2C=C=O is prepared from tBu2C=O in three steps (performable as a two-stage operation) through elimination of HCl from the intermediate product tBu2CCl-CH=O. The acid tBu 2CH-CO2H, obtainable in two, three, or four preparative stages from tBu2C=O, adds slowly to the ketene to produce the anhydride (tBu2CH-CO)2O. Elemental lithium together with ClSiMe3 converts tBu2CCl-CH=O into tBu2C=CH- OSiMe3, which is a durable precursor of tBu2CH-CH=O, making this aldehyde easily and cheaply available from tBu2C=O. By exclusion of alternative mechanistic possibilities, the reduction of tBu 2CCl-CH=O by tBuMgCl is shown to involve at least one single-electron transfer, leading to the enolate tBu2C=CH-OMgCl, which can be converted into tBu2CH-CH=O (three steps from tBu2C=O) or into tBu2C=CH-OSiMe3. Hydride transfer from NaBH 4 to tBu2CCl-CH=O affords tBu2CCl-CH 2OH, the transformations of which provide an entertaining set of SN1-type reactions. Several other examples of carbenium-type behavior are encountered in this gem-tBu2 system; they are attributed to steric congestion, which also impedes bond rotations in the anhydride and in two esters. A convenient route to tBu2CH-C≡N (five steps from tBu2C=O) uses the conversion of tBu2C=CH-OSiMe3 into tBu2CH-CH=NOH. The slow thermal (Z)/(E) equilibration of tBu2CH-NH-CH=O reveals the ranking of ecliptic repulsions as H 3C 2CH. Copyright
