Liquid-Liquid Separation of Polysiloxane-Supported Quinine Catalysts

Significance

The authors found, as a preliminary result, the heptane-selective solubility of the poly­siloxane where azo-dye-labelled 1 was used as a marker compound. The phase-selective solubility was applied to the development of the readily separable polysiloxane-supported reagents. Thus, poly­siloxane 2 reacted with quinine acetate 3 in the presence of Pt-divinyltetramethyldisiloxane complex (Karstedt’s catalyst) to give the poly­siloxane-supported quinine acetate 4. Hydrolysis of the acetate 4 afforded the polysiloxane-supported quinine 5 (eq. 1). Polysiloxane 5 was found to catalyze the Michael addition of thiophenols 6 with α,β-unsaturated carbonyl compounds 7 in a 1:1 mixed solvent of heptane and EtOH to give the Michael adducts 8 in 42-100% yield (eq. 2). Catalyst 5 was readily separated from the reaction mixture by liquid-liquid separation, and the catalyst phase was reused without significant loss of catalytic activity for five cycles.