9-Ethyl-1,4-dimethyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole and 6-bromo-9-ethyl-1,4-dimethyl-9H-carbazole.

The title carbazolyl boronic ester, C(22)H(28)BNO(2), (I), is a building block for the synthesis of new carbazole derivatives of potential utility as pharmaceutically active compounds. The crystal structure of (I) and of the title bromocarbazole compound, C(16)H(16)BrN, (II), the synthetic precursor of (I), were solved and analysed with the aim of understanding the lack of reactivity of (I) under Suzuki cross-coupling reaction conditions. In both structures, the methyl groups are coplanar with the carbazole ring system, and the ethyl group lies out of the carbazole plane. The dioxaborolane ring of boronic ester (I) adopts a half-chair conformation but lies approximately in a planar orientation with respect of the carbazole ring system, whereas the Br atom of (II) is coplanar with the carbazole plane. In (I), the carbazole-boronic ester C-B bond length is 1.5435 (14) A, which is somewhat shorter than the usual value of 1.57 A.