Reaction of allene esters with Selectfluor/TMSX (X = I, Br, Cl) and Selectfluor/NH(4)SCN: Competing oxidative/electrophilic dihalogenation and nucleophilic/conjugate addition

Reaction of benzyl and ethyl allenoates with TMSX (X = I, Br, Cl) and with NH(4)SCN were investigated in MeCN, DMF, and in imidazolium ionic liquids [BMIM][NTf(2)] and [BMIM][PF(6)] as solvent, in the presence and absence of Selectfluor. Comparative product analysis studies demonstrate that the ability of Selectflour to promote oxidative/electrophilic dihalogenation/dithiocyanation with TMSX/NH(4)SCN (as observed previously for 1-arylallenes) is diminished in allenoates, most significantly in reactions with TMSCl, and essentially disappearing in reactions with NH(4)SCN, in favor of nucleophilic/conjugate addition. The study underscores the contrasting reactivity patterns in 1-arylallenes and allenoates toward electrophilic and nucleophilic additions in halofunctionalization with TMSX/Selectfluor and thiocyanation reactions with NH(4)SCN/Selectfluor. These competing pathways are influenced by the nature of the anion, allene structure, and the choice of solvent.