Functional Polymers from (Vinyl)polystyrene. Recyclable Polymer-Supported Organosilicon Protecting Groups for Solid-Phase Synthesis

Abstract

Dicobalt octacarbonyl catalyzed the hydrosilylation of residual vinyl groups on insoluble porous beads of divinylbenzene-rich copolymer, exclusively with β orientation, by either dialkylhalosilanes or alkyldihalosilanes. The resulting silyl halide functionalities, now bound to a cross-linked polystyrene matrix through stable dimethylene spacers, could then be used to protect and immobilize hydroxyl-containing free molecules for their further modification in the course of solid-phase synthesis. The reaction proved selective for primary hydroxyls in the presence of secondary, and secondary over tertiary. Together with product free alcohols, later cleavage of these silyl ethers with aqueous acid or base also released the corresponding silanol groups, while HF, under particularly mild and selective conditions, left silyl fluorides that themselves could then be very conveniently regenerated by BCl3/CH2Cl2 back to the polymer-supported silyl chlorides. For a variety of possible applications, these solid-phase protecting groups offer control, yield, recovery, and reusability, as well as other possible advantages involving site-site isolation of functional groups within the cross-linked polystyrene matrix.