Trivalent Organostibines: Sb,N Ligands in Double N‑Arylation of Primary Amines toward Functionalized Carbazoles

A Sb,N ligand (L-Sb)
for Pd-catalyzed double N-arylation
of primary amines was developed. This trivalent ligand L-Sb, containing a 5,6,7,12-tetrahydrodibenzo[c,f][1,5]azastibocine skeleton and stable under air and moisture,
could be synthesized facilely on a gram scale from chlorostibine (1) and cyclopentylmagnesium bromide. L-Sb showed
excellent catalytic performance in Pd2(dba)3-catalyzed double N-arylation of 2,2′-dibromo-1,1′-biphenyl
(2) with primary amines (3), affording functionalized
carbazoles in good yields. This Pd2(dba)3/L-Sb-catalyzed double N-arylation, the first example of the
application of trivalent organostibines as a ligand in N-arylation,
featured the following advantages: small catalyst loading, wide functional
group tolerance, good yields, and ease of gram-scale synthesis.