Facile Generation of a Strained Cyclic Vinyl Cation by Thermal Solvolysis of Cyclopent‐1‐enyl‐λ³‐bromanes

Contemporary Carbocation Chemistry: Applications in Organic Synthesis

“…Ochiai and associates have utilized a bromane hyperleaving group to generate the highly strained cyclopentenyl vinyl cation ( 37 , Scheme ) . Previous attempts to generate 37 were unsuccessful, either from the triflate ( 38 ) or the cyclopent-1-enyl(phenyl)-λ 3 -iodane ( 39 ) .…”

Cyclizations of Alkynes: Revisiting Baldwin’s Rules for Ring Closure

“…One reason for this scarcity is that endocyclic closures should lead to the formation of cyclic vinyl cations. These species are sp-hybridized and significantly destabilized by the deviation from linearity imposed by inclusion in a small ring . For example, cyclohex-1-enyl and cyclopent-1-enyl cations, with 156° and 141° valence angles at the cationic carbon, are 17 and 27 kcal/mol less stable than the linear (179°) prop-1-enyl cation .…”

Benchtop-Stable Hypervalent Bromine(III) Compounds: Versatile Strategy and Platform for Air- and Moisture-Stable λ3-Bromanes

“…In 1984, Frohn and co-workers revolutionized this field by the synthesis of difluoro-λ 3 -bromane 6 (Frohn’s reagent): the use of the substitution reaction of BrF 3 with arylsilanes 5 circumvents the unfavorable oxidation process. Importantly, Frohn’s reagent 6 serves as a pivotal platform for various λ 3 -bromanes ( 7 ; Figure C). − Furthermore, difluoro-λ 3 -bromane 6 promotes unprecedented reactions owing to the hypernucleofugality of the ArBr­(III) + group: examples include Hofmann rearrangement of sulfonamide and Baeyer–Villiger oxidation of primary aliphatic aldehydes . However, excessive reactivity and the need for strict exclusion of moisture ( 6 immediately decomposes into ArBr, HF, and O 2 via oxidation of water) have limited the utility of Frohn’s protocol …”