Density　functional　theory　calculations　have　revealed　the　mechanism　and　origins　of　the　reactivity　and　regioselectivity　of　the　Cp∗Ir(iii)/Cp∗Rh(iii)-catalyzed　allylic　C-H　amidation　of　alkenes　and　dioxazolones.　Generally,　the　catalytic　cycle　consists　of　alkene　coordination,　C(sp3)-H　activation,　dioxazolone　oxidative　addition,　reductive　elimination　and　proto-demetallation　to　give　the　final　amidation　product.　The　C-H　activation　is　found　to　be　the　rate-determining　step,　and　it　controls　the　reactivity　of　the　reaction.　For　the　Cp∗Ir(iii)-catalyzed　system,　the　C-H　activation　undergoes　an　Ir(iii)-assisted　proton　transfer　process　with　a　low　energy　barrier,　elucidating　its　high　reactivity.　In　contrast,　the　C-H　activation　step　is　more　like　a　direct　deprotonation　in　the　Cp∗Rh(iii)-catalyzed　system,　which　is　responsible　for　its　higher　barrier　and　lower　reactivity.　The　branched-selectivity　arises　from　the　electronic　effect　of　the　alkyl　group　on　the　charge　distribution　over　the　allylic　moiety.　Herein,　iridium(v)　polarizes　the　allylic　group　greater　than　that　of　the　rhodium(v)　system,　which　accounts　for　its　good　regioselectivity.　The　mechanistic　insights　will　be　useful　for　the　further　development　of　transition　metal-catalyzed　selective　C-H　amination　reactions.　©　The　Royal　Society　of　Chemistry.