Functionalized carbosilane dendritic species as soluble supports in organic synthesis

A new methodology, which is compatible with the use of reactive organometal lic reagents, has been developed for;the use of carbosilane dendrimers as s oluble supports in organic synthesis. Hydroxy-functionalized dendritic carb osilanes Si[CH2CH2CH2SiMe2(C6H4CH(R)OH)](4) (G0-OH, R = H or (S)-Me) and Si [CH2CH2CH2Si[CH2CH2CH2SiMe2(C2H4CH(R)OH])(3)](4) (G(1)-OH, R = H or (S)-Me) were prepared and subsequently converted into the:esters Si[CH2CH2CH2SiMe2 (C2H4CH(R)O C(O)CH2Ph)](4) (R = H or (S)-Me) and Si[CH2CH2CH2Si[CH2CH2CH2Si Me2(C6H4CH(R)OC(O)CH2C6H4R')](3)](4) (R = H and R' = H or R = (S)-Me and RI = H or R = H and R' = Br). As an example the latter compound was functiona lized under Suzuki conditions. The functionalized carboxylic acid,was obtai ned in high yield after cleavage from the dendritic support. Moreover, the ester functionalized dendrimers were converted to the corresponding zinc en olates followed by a condensation reaction with an imine to a beta-lactam i n excellent yield and purity. Furthermore, it was demonstrated that a small combinatorial library of beta-lactams could be prepared starting from a ca rbosilane dendrimer- functionalized with different ester moieties. These re sults show that carbosilane dendrimers can be applied as soluble substrate carriers for the generation of low molecular weight organic molecules. In c ombination with nanofiltration techniques, separation and recycling of the dendrimers can be realized.