- Shorter and easier syntheses of Di-tert-butylketene and related gem-Di-tert-butyl compounds
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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
- Knorr, Rudolf,Hennig, Karsten-Olaf,Schubert, Bernhard,Boehrer, Petra
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p. 6651 - 6664
(2011/02/26)
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- A UNIQUE AND HIGHLY REMARKABLE BORON TRIFLUORIDE CATALYZED REARRANGEMENT OF 2,2-DI-t-BUTYLOXIRANE INTO 2,2,3,3,4,4-HEXAMETHYLTETRAHYDROFURAN
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The boron trifluoride catalyzed rearrangement of 2,2-di-t-butyloxirane, involving competitive reactions of transient carbenium ions, could be selectively directed towards either 2,2,3,3,4,4-hexamethyltetrahydrofuran or 2-t-butyl-2,3-dimethyl-3-buten-1-ol.Hydride shift to afford 2,2-di-t-butylacetaldehyde was only observed to a minor extent.
- Kimpe, Norbert De,Buyck, Laurent De,Verhe, Roland,Schamp, Niceas
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p. 3291 - 3294
(2007/10/02)
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