Pyrroles alkenylations, palladium acetate

There are reports of an increasing number of palladium-assisted reactions, in some of which the palladium has a catalytic function. Thus furan and thiophene undergo facile palladium-assisted alkenylation giving 2-substituted products. Benzo[6 Jfuran and TV- acetyl-indole yield cyclization products, dibenzofurans and carbazoles respectively, in addition to alkenylated products (8UOC851). The arylation of pyrroles can be effected by treatment with palladium acetate and an arene (Scheme 86) (81CC254). 

In 2006, Gaunt and co-workers described a regioselective alkenylation of pyrroles under mild aerobic oxidative conditions. A catalytic amount of palladium acetate was able to selectively functionalize tert-butojycarbamate (BOC)-protected pyrrole at the C2-position while a C3-selectivity was achieved with triisopropylsilyl (TIPS)-protected pyrroles (Scheme 9.4). The aerobic conditions worked well for reactive alkenes such as acrylate derivatives, nevertheless the use of peroxide ( BuOOBz) appeared necessary in order to achieve good yields with more challenging substrates [i.e., methyl vinyl sul-fone). Interestingly, intermolecular alkenylation of pyrrole can also be effected with complete selectivity and good yields. 

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