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1 -L 2IH RPdL X + R CH=CH ____ I R―Pd―)t

2 2 I LL Rh H R1 L =C / +L NC C / + H― Pd―X Ri" N11 LL J H―Pd ―x _____ PdL + New applications of palladium in organic syntheses

693 This reaction becomes catalytic in palladium if RX is added along with a base to remove HX from the final equilibrium. The base must be present or the reaction ceases after one or two cycles of the catalyst. We have generally empolyed triethyl― or tri―n―butylamine as the base although secondary amines may also be used in cases where they do not cause side reactions. Triarylphosphines are preferred over trialkylphosphines, triphenyl phosphite, or bisdiphenylphosphinoethane when a phosphine is used. We have now carried out a large number of these reactions and can make the following generalizations. 1. The organic group of the RX always adds exclusively or predominantly to the least substituted carbon of the double bond. If a functional group is attached directly to the double bond, the R group generally adds to the other carbon if steric factors are similar. 2. The reaction is stereospecific with 1,2―disubstituted alkenes, proceeding by a cis addition―cis elimination sequence. If there is a choice of hydrogens for elimination, the most stable products are preferred and the most hydridic hydrogen tends to be lost. 3. Generally, organic bromides do not undergo the reaction well unless the catalyst is a triarylphosphine or secondary amine complex. Organic iodides do not require the phosphine or secondary amine. Organic chlorides usually do not undergo the reaction under the usual conditions (