Cobalt(I)-mediated cycloisomerization of enynes: mechanistic insights

[CpCo(CO)2] catalyzes the cycloisomerization of 1,n-enynes to afford selectively five- and six-membered ring systems in high yields. The factors governing the cyclization have been explored and we have discovered that the reaction associates two different, but complementary, reactivities of the cobalt(I) complexes. By a judicious choice of the substitution of the enyne, it was also possible to isolate a cyclobutene that arises from a cobaltcyclopentene