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

Abstract

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 BÀ B bridge. The catalyst-free reactions are highly selective, yielding exclusively the thermodynamically disfavored bis-1,4triazoles. The reactions are enabled by the high thermal stability of the diazido-diborane [B(hpp)(N 3 )] 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.

On the Coordination Chemistry of Triazolyl‐substituted Diborane Ligands, Prepared by 1,3‐dipolar Cycloaddition Reactions between Diazido‐diboranes and Alkynes

“…In the past, we reported the synthesis of the diazido‐diborane B 2 (hpp) 2 (N 3 ) 2 ( 1 , see Scheme 1) by reaction of the ditriflato‐diborane B 2 (hpp) 2 (OTf) 2 with two equivalents of n Bu 4 N(N 3 ) [22] . We also demonstrated the possibility to use this diazido‐diborane for metal‐free 1,3‐dipolar cycloaddition reactions with alkynes [23] . Here we report on reactions with functionalized alkynes.…”

“…[22] We also demonstrated the possibility to use this diazidodiborane for metal-free 1,3-dipolar cycloaddition reactions with alkynes. [23] Here we report on reactions with functionalized alkynes. In particular, reaction with 2-ethynylpyridine gives access to a new polydentate bis(2-pyridyl-1,2,3-triazolyl)-diborane ligand, that is used to synthesize hexaboron compounds and dinuclear ring compounds with integrated diboron units.…”