Carbonylonium ions: the onium ions of the carbonyl group

• Daniel Blanco-Ania and
• Floris P. J. T. Rutjes

Beilstein J. Org. Chem. 2018, 14, 2568–2571, doi:10.3762/bjoc.14.233

• aldehyde- and ketone-based intermediates, respectively. Keywords: carboxonium ion; glycosylium ion; oxacarbenium ion; oxocarbenium ion; oxycarbenium ion; Introduction There is much confusion in the literature over the name of the intermediates R1C(=O+R3)R2 (R1, R2, R3 = H or organyl [1], 1; Figure 1). In

• term “carboxonium ion” to describe intermediates 1. The issue with this term is that it is used for many different oxonium ions independently of their structure, mainly intermediates with a variable number of oxygen atoms bound to the central carbon atom. This name is used to describe protonated

• formed from protonation of carboxylic acids and esters are different than the ones from aldehydes and ketones and therefore should not have the same name. We recommend applying “carboxonium ion” only to intermediates whose carbon atom presents the same oxidation state as carboxylic acids, that is

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• . This suggests charge–charge repulsive effects in this system. When camphor (44) is reacted with HF-SbF5, three products are isolated (Scheme 10) [22]. A mechanism is proposed for conversion of ketone 45 to enone 47. Initially, the carboxonium ion 45a is formed by protonation of the carbonyl oxygen. A

• relatively strong base site, the ketone is completely protonated in the superacid to give the carboxonium ion 68. In the protolysis steps, there is a strong preference to generate the second cationic charge at a site distant from the carboxonium center. Protolysis of the methyl group C–H σ-bonds (i.e., 69

• closer proximity. Consequently, the carboxonium ion has two interesting effects in this superelectrophilic chemistry. It directs protolysis to the most distant site(s) and it “protects” the alkyl chain from cleavage in the superacid. A series of ozone-based oxidation-rearrangements have been reported by