Silyl Effect on the Regioselective Synthesis of Silylated Alkylidenecyclopropanes

Nucleophilic substitution of π-3-trialkylsilyl-1,1-dimethyleneallyl palladium complexes 2a,b occurred on the carbon bearing the silyl group whatever the hard (hydride) or soft (malonate anion) nature of the nucleophiles. Conversely, when located on the cyclopropane ring, i.e., in β of the π-allyl palladium complex 12, the silyl group appeared able to overcome the ring strain effect and to direct the substitution on the three-membered ring. This effect was however reversed by the simultaneous presence of these two trialkylsilyl substituents on the π-allyl palladium complex 27. Electrophilic substitution of 1,1-dimethyleneallylsilanes 4a,b by benzaldehyde occurred regioselectively on the cyclopropane ring.

π-1,1-dimethyleneallyl palladium complexes - nucleophilic and electrophilic substitutions - (2-trialkylsilylethylidene)cyclopropanes