Effect of steric bulk on the absolute reactivity of allene oxides.
Alpha-alkyl substituted fluorenylidene allene oxides were generated photochemically from appropriately substituted fluorenol derivatives in 2,2,2-trifluoroethanol (TFE) in order to assess the affect of steric bulk on the absolute reactivity of the allene oxides. The absolute reactivities of the allene oxides were measured using nanosecond laser flash photolysis, and were found to change little in TFE upon going from alpha-methyl to alpha-butyl to alpha-t-butyl. However, all three alpha-alkyl substituted allene oxides were considerably more reactive than the alpha-hydrogen derivative, indicating that steric bulk did not result in a decrease in reactivity as is typically found in other allene oxides. The contrary reactivity of the fluorenylidene allene oxides is explained by examining in detail the reactions of these allene oxides, determined from product studies.
Stereoselective synthesis of vinylsilanes from alkynylsilanes via hydromagnesiation. Application to a synthesis of 7(E)-dodecenyl acetate and dihydrojasmone
Abstract Hydromagnesiation of 1-trimethylsilyl-1-alkynes with isobutylmagnesium bromide in the presence of a catalytic amount of Cp 2 TiCl 2 followed by treatment of the resulting vinyl Grignard reagents with alkyl iodides and copper iodide affords (Z)-1,2-dialkylvinylsilanes in excellent yields. The utility of the reaction sequence is illustrated by a simple synthesis of 7(E)-dodecenyl acetate and dihydrojasmone.
trans-Di-tert-butylcyclopropanone. Preparation, properties, resolution, and reaction with nucleophiles
Aus Brom-neopentylketon (I) erhalt man mit definierten Mengen an tert.-Butylat das trans-1,2-Di-tert.-butyl-cyclopropanon (II), das mit weiterem tert.-Butylat zum Ester (III) gespalten wird.