Side reactions palladacycles

Chloroarenes and bromoarenes undergo high yield Heck reactions in the presence of a palladacycle prepared from Pd(OAc)2 and tri(t -tolyl)phosphine (equation 20) (66), When this catalyst was us at 140 C none of the palladium deposits which are typical at this temperature with other Pd-catalysts were detected. The catalyst is also more active, allowing a lower catalyst concentration to be used. No added phosphine is necessary, so side reactions involving this ligand do not occur. 4-Chlorobenzaldehyde and /i-butyl acrylate react to give 90 % yield of coupled product (66),... 

Once palladacycle formation has occurred, a number of possibilities exist for its reaction. A side product often seen in Catellani reactions is cyclobutane (21) formation resulting from a reductive elimination of the palladacycle (Scheme 7). In fact, under optimized conditions it is possible to achieve good yields of the cyclobutane products [26], However, the focus of this section will be to examine the reaction of the palladacycle with alkyl and aryl halides. 

Enantiomerically pure 5-palladatricyclo[4.1.0.0 " ]heptanes have been prepared and been converted into enantio-merically pure complexes with helical chirality at palladium. The reaction of an excess of dimethyl 3,3-dimethyl-cyclopropene-l,2-dicarboxylate with [Pd2(dba)3]-CHCl3 gave diastereoselectively as side-product a new palladacycle 122 308 Purthermore, a highly diastereoselective synthesis of palladepanes 120 and 121 has been achieved. ... 

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