Reaction of allene esters with Selectfluor/TMSX (X = I, Br, Cl) and Selectfluor/NH₄SCN: Competing oxidative/electrophilic dihalogenation and nucleophilic/conjugate addition

Abstract

SummaryReaction of benzyl and ethyl allenoates with TMSX (X = I, Br, Cl) and with NH4SCN were investigated in MeCN, DMF, and in imidazolium ionic liquids [BMIM][NTf2] and [BMIM][PF6] 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/NH4SCN (as observed previously for 1-arylallenes) is diminished in allenoates, most significantly in reactions with TMSCl, and essentially disappearing in reactions with NH4SCN, 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 NH4SCN/Selectfluor. These competing pathways are influenced by the nature of the anion, allene structure, and the choice of solvent.

An Efficient Selectfluor-Mediated Oxidative Thio- and Selenocyanation of Diversely Substituted Indoles and Carbazoles

“…In connection with previous studies from our laboratory on the use of Selectfluor as a versatile mediator for generation of incipient electrophiles through oxidation [55,56], we report here a mild and efficient Selectfluor-mediated direct thio-and selenocyanation of C-H bonds (Scheme 1), focusing mainly on diversely substituted indoles 3 and carbazoles 6. Sequential introduction of SCN and SeCN and synthesis of thio-and selenotetrazoles on a carbazole motif are also demonstrated, in preliminary studies using this chemistry.…”

Metal-Free Transfer Hydroiodination of C–C Multiple Bonds

“…We report here the gram-scale synthesis of a HI surrogate similar to the generic structure IV and its application to the Brønsted-acid-initiated transfer hydroiodination of alkynes, alkenes, and allenes ( V → VII for X = I, Scheme , bottom right).…”