CHBr₃/TiCl₄/Mg as an Unusual Nucleophilic CBr₂ Carbenoid: Effective and Chemoselective Dibromomethylenation of Aldehydes and Ketones

Abstract

We report that instead of using CBr4, CHBr3 can serve as a highly nucleophilic dibromomethylene carbenoid in chemoselective carbonyl dibromomethylenation. Successful application of the dibromomethylenation to various carbonyl compounds such as enolizable and sterically hindered ketones by using the CHBr3/Mg/TiCl4 system highlights the weakly basic nature, extraordinary reactivity, and synthetic versatility of the approach.

Preparation of Ethynylbenzene Derivatives from Substituted Benzaldehydes

“…However, we found out that triisopropyl phosphite is not, in fact, easily removed after the reaction. Although on a small scale chromatography could be used, the harsher conditions required for triisopropyl phosphite hydrolysis (conc HCl–AcOH, reflux overnight) during larger-scale applications were not compatible with our compounds, leading to decomposition. We tested a variety of alkyl phosphites in this reaction (Table ) and were fortunate to discover that trimethyl phosphite/CBr 4 in toluene, when used at the ratio of ca.…”

Microwave‐Assisted Dibromoolefination of Aromatic and Heteroaromatic Aldehydes and Ketones

“… and subsequently with some variation by Corey and Fuchs . More recently, a metal‐induced modification with CHBr 3 /TiCl 4 /Mg was used for such a transformation . It was also shown that a perchlorate phosphine salt as well as triisopropyl phosphite can replace PPh 3 in generating gem ‐dihaloolefins .…”

Design, Synthesis, and Evaluation of Probes for Spatially Resolved Imaging of Enantioselective Sulfoxide Reductases

“…The synthesis of the probes started with the commercial benzophenone 3 that was protected with a TBDMS group and then converted to dibromide 5 by reaction with bromoform, magnesium, and TiCl 4 in 65% yield. 31 It should be noted that the more traditional Corey−Fuchs approach provided only traces of product 5 after refluxing for 24 h in toluene. 32 Subsequently, palladium-catalyzed borylation afforded intermediate 6 that was used for Suzuki coupling with enantiomeric bromides.…”

“…In the case of a probe with racemic sulfoxides, the presence of a meso form would allow only partial reduction that would complicate the design and the interpretation of the data. The synthesis of the probes started with the commercial benzophenone 3 that was protected with a TBDMS group and then converted to dibromide 5 by reaction with bromoform, magnesium, and TiCl 4 in 65% yield . It should be noted that the more traditional Corey–Fuchs approach provided only traces of product 5 after refluxing for 24 h in toluene .…”