Transition Metal Catalyzed Cycloisomerizations of 1,n-Allenynes and -Allenenes

Advances on the transition metal catalyzed cycloisomerizations of 1,n-allenynes and 1,n-allenenes are summarized. Malacria reported the first transition metal-mediated isomerization of allenynes and Brummond proposed the formation of a rhodacyclopentene intermediate, which after β-H and reductive elimination gives the cross-conjugated triene. Hydroxylated 1,5 allenynes were explored by Malacria and Fensterbank in the context of gold and platinum catalysis. In 2008, Akita reported the gold(III)-catalyzed cycloisomerizations of 1-allenyl-1-ethynyl acetates into 4-methylene-2- cyclopentenones. Mascarenas reported the platinum and NHC-gold complexes catalyzed reaction of allenediene to give diastereoselectively 1,4-cycloheptadiene derivatives. The groups of Toste and Iwasawa independently reported respectively the gold- and platinum-catalyzed cyclization of vinylallenes.