The discovery of novel synthetic methods that allowed rapid construction of hard-to-access seven-or eight-membered carbocycles remains a formidable challenge.Various single-step annulation reactions via metal-catalyzed C-H bond activation proved to be highly attractive owing to the high atom-economy and synthetic flexibility.1 However,only very limited examples have been reported for synthesis of seven-and especially eight-membered carbocycles in this regime,and most of these systems rely on noble metal catalysis.Furthermore,construction of cyclic products has also been mostly limited to simple annulation reactions,while complexity induced by rearrangement of the skeleton has been rarely attained.2 This limitation largely results from the relatively low reactivity of metal-carbon species and/or the limited compatibility of distinct processes in the catalytic cycle.In our work,a novel Mn(I)-catalyzed ring expansion reaction is realized leading to construction of seven-and eight-membered carbocycles,which merges C-H activation with Aldol/retro-Aldol reactions.a series of seven-and eight-membered ring skeletons were constructed.