Facile and convenient synthesis of B‐amino‐9‐borabicyclo[3.3.1]nonanes. Aminoboration of lsocyanates

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Abstract
The reaction of 9‐borabicyclo[3.3.1]nonane (9‐BBN) with aliphatic and aromatic primary and secondary amines in tetrahydrofuran (THF) at 65°C proceeds rapidly and quantitatively with evolution of hydrogen and the formation of the corresponding B‐amino‐9‐borabicyclo[3.3.1] nonane (B‐amino‐9‐BBN). Simple evaporation of THF from the reaction mixture gives the B‐amino‐9‐BBN derivatives in high yield and purity. These B‐amino‐9‐BBN derivatives are reactive towards alkyl and aryl isocyanates. Consequently, the aminoboration of various isocyanates has been studied using B‐phenylamino‐9‐BBN. Thus, two equivalents of isocyanates react with one equivalent of B‐phenylamino‐9‐BBN to afford, following the hydrolysis of the intermediate with ethanolamine, N, N'‐disubstituted‐N ‐(phenylamido)‐ureas in excellent yields. A plausible mechanism for this aminoboration reaction of isocyanates is also presented.