Next, we investigated the use of a radical scavenger, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), in the reaction. As expected, the 1,2-N shift process was significantly suppressed, which suggests the involvement of a radicalmediated process in the reaction (eq 1, Scheme 2). In addition, a standard radical clock (cyclopropane) was subjected to the optimal reaction conditions, and none of the expected β-arylation of amino acid ester 2bc was observed. Instead, the formation of product 5 was observed by 1 H NMR via a radical cyclopropane ring-opening process (eq 2), clearly indicating that the alkyl radical formed via dehalogenation by Ni likely triggered the sequential N-shift/C-H coupling reaction. The cross-over experiments using equivalent trifluoromethyl alkene as the coupling partner unveiled that the radical reaction proceeded with good chemoselectivity and yielded the 2aa selectively in 67% yield via the C-H cyclization, whereas an alternative 1,2-N-shift/Heck-type cross-coupling manner was completely suppressed (eq 2). We performed a radical cascade reaction of α-aminoβ-bromocarboxylic acid ester (1a) in the presence of Bu3SnH/AIBN, according to Prey's reaction conditions for 1,2-imine-migration, and no desired product (2aa) was observed (run 1; eq 4). Nevertheless, the addition of B2neo2 and K2CO3 in the above reaction led to small amount of desired product 2aa in 12% yield(run 2; eq.4), these results suggest that the 1,2-N-shift could involve a different mechanism than the 1,2-imine-shift model reported in Prey's work, and the diboron agent could play a crucial role in the catalytic cycle for cascade radical N-migration/C(sp 2 )-H coupling. Besides, the addition of typical nucleophilic reagents (e.g, t-BuOH and indole) in the cyclization reaction did not produce the corresponding nucleophilic substitution products (8), which revealed a radical-mediated C-H cyclization occurring, rather than a SEAr mechanism (eq 5). The UV-vis analysis reveals that coordination of the αamino-β-bromocarboxylic acid ester (1a) with the diboron compound B2neo2 and K2CO3 could form a new EDA-complex (i.e., 1a→• Bneo) to activate α-amino acid ester 1a, as the maximum absorption wavelength appears to be redshifted obviously (Figure ). Based on the above-mentioned experimental results and previously reported mechanisms, a proposed mechanism for the cascade reaction is shown in Scheme 3. First, activation of B2neo2 by nucleophilic CH3CN and base K2CO3 produces both acetonitrile-stabilized boryl radical (CH3CN-Bneo ) and carboxylic-boronate radical anion (X-Bneo ) as super electron donors. 22a,d Coordination of tertiary amine motif of 1a with the acetonitrile-stabilized boryl radical (CH3CN-Bneo ) led to 1a-Bneo-X complex Int-I, which would be beneficial to reduce the dissociation energy of C-N bond and enables the sequential radical 1,2-N-shift. Next, the Bneo-Ni(I)-Ln species undergoes a SET oxidation process with alkyl-Br (1a), yielding radical intermediate Int-II and a Ni(II) intermediate which is then directly involved in the next catalytic cycle or reduced to Ni(I)-Ln species by carboxylic-boronate radical anion (X-Bneo ). Subsequently, a radical 1,2-N-shift in unstable Int-II takes place quickly to yield the radical intermediate Int-III, wherein the quick cycloaddition of the electrophilic α-carboxyl radical onto the distal aromatic ring to produce the intermediate Int-IV. Finally, abstraction of an aryl hydrogen atom in intermediate Int-IV by acetonitrile-stabilized boryl radical (CH3CN-Bneo ) or B2neo2 takes place, thereby leading to the desired 2aa. Besides, in the presence of radical precursors such as BrCCl3, TsCl and (PhSe)2, quenching of Int-III by these thusresulted halo/seleno radicals would occur immediately, which would suppress the above C-H cyclization and lead to these α-halogenated and selenated β-amino acid derivatives, as showed in Table . In addition, the unrestricted density functional theory (DFT) calculations, with the hybrid functional B3LYP implemented in the Gaussian 09 package, were conducted to understand the sequential radical 1,2-Nshift/C-H bond coupling process (for details, see Scheme S1 and Figure ). These preliminary results indicate that the reaction mechanism illustrated in Scheme 3 is reasonable.