Mechanistic pathways for halogen dance reactions in bromo-thiophenes: a cascade-like pattern

Ever since the halogen dance reaction was discovered by Bunnet et al, synthetic chemists have utilized the transformation in many desirable ways to build substituted heterocyclic target molecules of all kind. Using DFT-Cam-B3LYP/ land2dz computations and focused on Hannes Frohlich et al. Halogen Dance (HD) reactions of bromothiophenes, a new bromo-bridged Transition State (TS) is proposed. This bromo-bridged TS was then used to put forth eight possible isomerization as well as eight possible disproportionation paths. These mechanistic pathways were then carefully inspected based on TS's energy and protonation/deprotonation steps to find the most suitable pathways. Collectively these mechanistic pathways joined like a jigsaw puzzle to give, for the first-time, a fully comprehensive cascade-like pattern for base-catalyzed halogen dance in its entirety. The present work may well shed light on a dynamic domino mechanism which dominates the realm of nonaqueous strongly basic medium, organic chemistry, reactions.

Graphic abstract

C-Br reactivity and σ-holes in bromothiophenes are shown to be the major mechanistic driving force in their base catalyzed Halogen dance reactions.