Gold-Catalyzed Nucleophilic Cyclization of Functionalized Allenes: A Powerful Access to Carbo- and Heterocycles

Studies conducted in the field of gold-catalyzed cyclization reactions of allenes by attack of carbon or heteroatom nucleophiles are compiled. The cycloisomerization of .α- or β-hydroxyallenes can also be carried out in water with tetrachlorogold acid as catalyst and this system was utilized for the first example of a tandem lipase/gold-catalyzed transformation. An alternative catalytic system reported by Toste and coworkers that takes advantage of a chiral counterion, which was introduced into the catalyst by a silver salt. In 2004, Morita and Krause reported the first intramolecular endo-selective hydroamination of allenes. In an another study allenic hydrazones were found to undergo a gold(I)-catalyzed cycloisomerization to substituted pyrroles. Morita and Krause reported the gold-catalyzed cycloisomerization of α-thioallenes to the corresponding 2,5-dihydrothiophenes.