Bistriazoles Connected Through a B-B Bridge, Synthesized by Highly Selective Dipolar Cycloaddition Reactions of a
Daniel Vogler1, Maximilian Schöner1, Elisabeth Kaifer1
1Anorganisch-Chemisches Institut, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany.
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 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.
Related Concept Videos
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Hydroboration-Oxidation of Alkenes
Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Halogenation of Alkenes
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.


