Pd-catalyzed Allylic Alkylation of Pyr- roles with Allyl Alcohols Promoted by Triethylborane

Triethylborane promotes the Pd-catalyzed allylic alkylation of pyrroles with a variety of allylic alcohols to provide either C2 allylation products (α,α-, γ,γ-dimethylallyl alcohol and geraniol) or C2,C5 diallylation products (allyl alcohol, α-, β-, γ-methyl-, and α-, γ-phenylallyl alcohols) in good to excellent yields under mild conditions.(MS Word Style "04 Het-Abstract")Pyrroles is among the most important fundamental constituents of the biologically and physiologically active molecules, such as chlorophyll, porphyrin, hemoglobin and their related compounds, 1 and of electron conducting polymers with excessive π-electron systems. 2 The synthesis and reactions of pyrroles have attracted much interest for over a century.To date, however, pyrrole reactions remain a challenge for synthetic chemists because some pyrroles are extremely sensitive to acids and air. 3 Alkylation of pyrroles by the Friedel-Crafts approach, for example, frequently meets difficulties because the Brønsted acid and Lewis acid catalysts induce polyalkylation, ring opening, and polymerization reactions. 4Alkylation (at C2, 5 C3, 6 and/or N 7 ) with aliphatic halides or allyl halides has proved to be most successful under strongly basic conditions (alkaline metal hydroxides or carbonates or organomagnesium or -zinc reagents), which may be sometimes incompatible with functional groups of pyrrole substituents.Recently, we demonstrated that a Pd(0) species in the presence of Et 3 B catalytically promoted allylic alcohols to undergo the electrophilic C-allylation of active methylene compounds 8 and N-allylation of