Silyl Effect on the Regioselective Synthesis of Silylated Alkylidenecyclopropanes
作者:Pia Menningen、Christian Harcken、Björn Stecker、Stefanie Körbe、Armin de Meijere、Maria Rodrigues Lopes、Jean Ollivier、Jacques Salaün
DOI:10.1055/s-1999-2882
日期:——
Nucleophilic substitution of Ï-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 Ï-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 Ï-allyl palladium complex 27. Electrophilic substitution of 1,1-dimethyleneallylsilanes 4a,b by benzaldehyde occurred regioselectively on the cyclopropane ring.
Ï-3-三烷基硅烷基-1,1-二甲基烯丙基钯络合物 2a,b的亲核取代发生在带有硅基的碳上,无论亲核物的性质是硬(氢化物)还是软(丙二酸根阴离子)。相反,当位于环丙烷环上时,即在Ï-烯丙基钯络合物 12 的δ²中,硅基似乎能够克服环应变效应,并将取代作用引向三元环。然而,在Ï-烯丙基钯络合物 27 上同时存在这两个三烷基硅取代基时,这种效应被逆转了。苯甲醛对 1,1-二甲基烯丙基硅烷 4a,b的亲电取代作用在环丙烷环上有选择性地发生。