Green, palladium-catalyzed synthesis of benzylic H-phosphinates from hypophosphorous acid and benzylic alcohols

Benzylic alcohols cross-couple directly with concentrated H3PO2 by using Pd/xantphos (1 or 2 mol-%). Depending on the substrate, DMF at 110 degrees C or t-AmOH at reflux with a Dean-Stark trap can be used. A broad range of benzylic alcohols react successfully to give moderate to good yields of the products. The preparation of other organophosphorus compounds (phosphinic and phosphonic acids) is also demonstrated. Asymmetric reaction with (R)-1-(2-naphthyl)-ethanol provids the corresponding H-phosphinic acid in 77 % ee. The methodology provides a green, PCl3-free route to benzylic-H-phosphinic acids. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).