Bistriazoles Connected Through a B−B Bridge, Synthesized by Highly Selective Dipolar Cycloaddition Reactions of a Diazido‐diborane(4)

In this work we report the first cycloaddition reactions between a diazido diborane(4) and terminal alkynes, providing unique access to bis‐1,2,3‐triazoles connected by a B−B bridge. The catalyst‐free reactions are highly selective, yielding exclusively the thermodynamically disfavored bis‐1,4‐triazoles. The reactions are enabled by the high thermal stability of the diazido‐diborane [B(hpp)(N3)]2 (hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐α]pyrimidinate). Due to the tetra‐coordinate boron atoms in this reagent, the reactions are tolerant with respect to the introduction of Lewis‐basic groups at the alkyne. The scope and limitations of the new reactions are discussed. An exceptionally thermally stable diazido diborane was applied in dipolar cycloaddition reactions with terminal alkynes. The products are the first bistriazoles connected by a B−B bond. The reactions are highly regioselective, leading exclusively to the 1,4‐triazoles, and tolerate the presence of Lewis‐basic groups and additional alkynyl groups at the alkyne.