Eliminations to Form Alkenes, Allenes and Alkynes and Related Reactions

Chemical Degradation-Inspired Total Synthesis of the Antibiotic Macrodiolide, Luminamicin

“…This side reaction likely occurred from oxidative addition of the palladium catalyst to vinyl triflate 52 , followed by rapid β-hydride elimination instead of transmetallation of the vinyl palladium species, which was possible due to its syn configuration (see 53 ). As further support for the E -geometry of the vinyl triflate, subjecting 52 to a strong base gave no reaction, suggesting that the triflate was not antiperiplanar to the vinyl proton for rapid β-elimination to occur …”

“…As further support for the E-geometry of the vinyl triflate, subjecting 52 to a strong base gave no reaction, suggesting that the triflate was not antiperiplanar to the vinyl proton for rapid β-elimination to occur. 33 To circumvent the aforementioned problem, we turned to methyl addition into the ketone of 47 (Scheme 8). Treatment of 47 with MeLi only gave recovered starting material, presumably due to competing enolization of the ketone by MeLi, which led us to investigate a variety of additives.…”

P(v) intermediate-mediated E1cB elimination for the synthesis of glycals

“…6 Therefore, the use of a carbanion-like intermediate to facilitate further conversions has been a long-standing conundrum. 7 We hypothesized that because the oxaphosphorane-anion intermediate can provide an adjacent carbanion-like center, an E1cB-type elimination 8 could be triggered by a suitably leaving group at its β-position to form a double bond. 9 We are aware that glucosylphosphonium 2a meets the structural requirements and the hydrolysis-mediated elimination could afford the corresponding glycal (Fig.…”

GaCl3-Catalyzed Ortho-Ethynylation of Phenols

“…The most common method is the nucleophilic reactions of ethynylmetals at carbonyl, halogen, or oxiranes . Stepwise transformations as exemplified by the Corey−Fuchs method or Julia coupling are also often employed . Electrophilic ethynylation of carbon nucleophiles is another attractive methodology, since organometallic species with C−M bonds in some cases can be generated directly from organic C−H bonds in the catalytic mode.…”