Methylseleno acetal

The presence of a group able to delocalize the charge from the caibanionic center favors the synthesis of the carbanion whatever the method used, whereas substitution of the carbanionic center by alkyl groups disfavors it. Thus, whereas methyl phenyl and dimethyl selenide cannot be metallated wiA LDA at -78 °C or 0 C, phenylseleno and methylseleno acetates and propionates lead, on reaction with the same base at -78 °C, to the corresponding organometallics (Scheme 10). - ... 

Reaction of estrone enol acetate with phenylselenenyl or methylselenenyl bromide in the presence of potassium carbonate affords 16a-(phenylseleno)- or 16a-(methylseleno)estrone derivatives l17. 

The n-BuLi cleavage of the axial C-Se bond of bis(phenylseleno)acetals, derived from 4-ferf-butylcyclohexanone, always occurs under kinetic control at -78°C [14]. In the case of a mixed acetal, having respectively the phenylseleno and methylseleno groups in axial and equatorial positions, the cleavage of the equatorial C-SeMe bond was predominantly observed. The resulting stabilized carbanion rearranges almost instantaneously leading to the a-phenylselanyl-cyclohexyllithium with the C-Li bond in the axial position [14] (Scheme 14). 

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