Temhedron Lenem. Vo1.32. No.27, pi 32653268. 1991 P&ted in Great Britain oo40-4039191 $3.00 + .oo Pergamon Press plc zyxwvutsrqpo Radical Addition to Vinylphosphine Oxides: 1,243tereoinduction of Phosphorus Stereogenic Centre Albert0 Brandi,* Stefano Cicchi, Andrea Goti Dipahrento di Uairnica orgcudca and Centro dei Composti Etemciciic~ C.N.R., UdversitJ di I+enze, vi0 G. Capponi 9, I-50121 Firerue, Italy K. Michal Pietrusiewicz* Polish Academy of Sciences, Centre of ~Uokador and Macmmokctdar Slttdies, Sienkiewicm 112, 90-362 Lodz, Polatkd Key wordr: radical addition; vinylphosphme oxides; phosphorus stcrcogcnic ccntrc; asymmetric induction; phosphincs. Ahtmct: Carbon centered radicals derived from reactions of halides 3-5 with BuSnH in the prcscncc of AIBN have becntrappcd bydiphenylvinyiphosphineoxide2 giving the addition product&gin high yields. Free radical addition to 2 employing the Barton methodology gave lower yields. The USC of chiral (raccmic) vinylphosphinc oxides allowed a stereosclectivc radical addition with a diastercomcric ratio as high as 91 for mesityhncthylvinylphosphinc oxide 1. Vinylphosphine oxides show a growing interest as useful precursors for the synthesis of new phosphine ligands for transition metal catalyzed reactions. A strong impulse to their broader utilization was especially given by the availability of enantiomerically pure vinylphosphine oxides.’ A large number of nucleophiles has been added across the double bond of vinylphosphine oxides, including carbon,‘- nitrogen,‘c2 oxygen,‘& phosphorus,lbXc” and sulft#’ nucleophiles. Recently, vinylphosphine oxides have also been shown to be excellent dipolarophiles in 1,fdipolar cycloaddition of nitrones.6 Chiral vinylphosphine oxides were able to induce a diastereofacial selection in the cycloaddition to a cyclic nitrone with a selectivity as high as 9:l in the case of mesitylmethylvinylphosphine oxide 1.7 We now report on the novel intermolecular and stereoselective radical addition to vinylphosphine oxides.8 Reactions of alkyl halides 3-5 with diphenylvinylphosphine oxide 2 in presence of tributyltin hydride’ and catalytic AIBN gave excellent yields of addition products 6-8 (Scheme l).” Three equivalents of the halide and slow addition of Bu3SnH to the refluxing solution by mean of a syringe pump were required to get consumption of the phosphine oxide 2.” 3265