The generation and trapping of enantiopure bromonium ions

Braddock, D. Christopher; Hermitage, Stephen A.; Kwok, Lilian; Pouwer, Rebecca H.; Redmond, Joanna M.; White, Andrew J. P.

doi:10.1039/b816914d

Cited by 37 publications

(35 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, rate and stereochemical findings from multiple prior studies require the alternative concerted scenario. 5a,7b,9a,b,14 …”

Section: Resultsmentioning

confidence: 99%

“…Proposed in 1937 by Kimball, 24 and further developed by Fahey, 9a,b Olah, 9c–e and Brown, 9f it has remained the usual scheme due to its conceptual simplicity, structural appeal, and, importantly, its reinforcement by the extensive and elegant work probing stabilized halonium ions. The conditions, however, under which those bridged onium ions are generated and probed are quite different from those used in synthetically relevant additions, so the derived mechanistic insights cannot be generalized with confidence.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Nucleophile-Assisted Alkene Activation: Olefins Alone Are Often Incompetent

et al. 2016

View full text Add to dashboard Cite

Emerging work on organocatalytic enantioselective halocyclizations naturally draws on conditions where both new bonds must be formed under delicate control, the reaction regime where the concerted nature of the AdE3 mechanism is of greatest importance. Without assistance, many simple alkene substrates react slowly or not at all with conventional halenium donors under synthetically relevant reaction conditions. As demonstrated earlier by Shilov, Cambie, Williams, Fahey, and others, alkenes can undergo a concerted AdE3-type reaction via nucleophile participation, which sets the configuration of the newly created stereocenters at both ends in one step. Herein, we explore the modulation of alkene reactivity and halocyclization rates by nucleophile proximity and basicity, through detailed analyses of starting material spectroscopy, addition stereopreferences, isotope effects, and nucleophile–alkene interactions, all obtained in a context directly relevant to synthesis reaction conditions. The findings build on the prior work by highlighting the reactivity spectrum of halocyclizations from stepwise to concerted, and suggest strategies for design of new reactions. Alkene reactivity is seen to span the range from the often overgeneralized “sophomore textbook” image of stepwise electrophilic attack on the alkene and subsequent nucleophilic bond formation, to the nucleophile-assisted alkene activation (NAAA) cases where electron donation from the nucleophilic addition partner activates the alkene for electrophilic attack. By highlighting the factors that control reactivity across this range, this study suggests opportunities to explain and control stereo-, regio-, and organocatalytic chemistry in this important class of alkene additions.

show abstract

“…However, rate and stereochemical findings from multiple prior studies require the alternative concerted scenario. 5a,7b,9a,b,14 …”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Nucleophile-Assisted Alkene Activation: Olefins Alone Are Often Incompetent

et al. 2016

View full text Add to dashboard Cite

show abstract

“…Additionally, recent studies, most notably by the Denmark laboratory, bode well for the invention of new catalytic enantioselective methods. Denmark and co-workers, [35] building on the careful mechanistic work of Brown and co-workers, [36] have shown that enantiopure bromonium ions [37] may undergo degenerate halogen-exchange reactions with olefins, [36a] racemizing the halonium ions at rates competitive with nucleophilic capture. As unreacted alkene is present until the end of a catalytic reaction, the relative rates of racemization and nucleophilic capture must be overcome to achieve a successful catalytic enantioselective bromination.…”

Section: Asymmetric Halogenation Of Olefinsmentioning

confidence: 99%

Current Methods for Asymmetric Halogenation of Olefins

Castellanos

Fletcher

2011

Chemistry A European J

271

View full text Add to dashboard Cite

show abstract

“…Braddock et al showed that enantiopure haliranium ions can be prepared and subsequently trapped, [14] but it is often assumed that under halocyclization conditions haliranium ions might racemize by means of alkene-to-alkene transfer. Braddock et al showed that enantiopure haliranium ions can be prepared and subsequently trapped, [14] but it is often assumed that under halocyclization conditions haliranium ions might racemize by means of alkene-to-alkene transfer.…”

Section: Introductionmentioning

confidence: 99%