## 3 Oxylabogenation of Hydrocarbons
### Alkenes as Substrates  
Styrene derivatives have proven to be excellent oxylabogenation substrates. In 2020, [PERSON] and co-workers developed a FeX\({}_{3}\)-catalysed oxylabogenation mediated by KX in methyl _tert_-butyl ether (MTBE) (Scheme 51) [136]. Fourteen \(\alpha\)-bromo and fourteen \(\alpha\)-chloroketones were isolated in moderate to good yields. Electron-poor, -rich and sterically hindered substrates were efficiently functionalised by the developed procedure. However, the protocol failed in the oxylabogenation of \(p\)-OH substituted alkenes, attributed to the use of TsOH. The reaction proceeds via a radical mechanism, where the Br radical is trapped by the styrene derivative. This radical intermediate is then captured by O\({}_{2}\) and FeBr\({}_{2}\), affording a peroxide intermediate which upon water elimination yielded the corresponding halogenated ketone. Additionally, the oxylabogenation presents a substrate specific character, as the oxylchorination yields were significantly lower than the oxybromination relatives. Another metal-catalysed oxybromination of olefins was established using a molybdenum-(VI)-based complex (Scheme 52) [137]. 2-Bromo-1-phenylethylanone was obtained in 73% yield upon addition of 0.2 mol% of a cis-dioxomolybdenum(VI) complex to a mixture of H2O2, KBr, HClO4 and styrene. The bromohydrin and epoxide were isolated as important side products (in 15 and 11%, respectively), highlighting the moderate catalyst selectivity. [PERSON] and co-workers reported the oxybromination of 11 styrene derivatives upon the addition of KBr (2 equiv. ), K2S2O8 (2.5 equiv.) in H2O (Scheme 53) [138]. After stirring for 12 h at 60 \({}^{\circ}\)C, the corresponding aryl bromokotones were isolated in low to excellent yields (24-90%). The method tolerated substrates bearing electron-donating (e.g., Me, \(t\)-Bu) or -withdrawing (e.g., F, Cl, Br) substituents on the aromatic ring. A significant decrease in hydration efficiency (i.e., 24%) was observed for the OMe-substituted styrene derivative. Furthermore, this route was not compatible with heteroaromatic substrates. Despite its shortcomings, the developed procedure did benefit from readily available starting materials and a safe halogen source. The mechanism involves the initial K2S2O8-mediated oxidation of Br\({}^{-}\) to Br\({}_{2}\), which leads to the formation of HOBr in the presence of water. Addition of HOBr onto the alkene affords the bromohydrin intermediate. Upon oxidation of the latter, the corresponding bromokotone is obtained. In 2019, the authors slightly altered their oxyhalogenation procedure [139]. A KI- and TBHP-based system transformed styrene into the corresponding \(\alpha\)-iodoketone in 97% yield. [PERSON] and [PERSON] independently established an aqueous H2O2-based oxyhalogen method [140; 141]. Both authors reported the use of HBr as a bromination agent, which generated the corresponding \(\alpha\)-bromoketone and the bromohydrin (Table 2). [PERSON] and co-workers demonstrated that using NBS instead of HBr considerably shifted the selectivity towards the \(\alpha\)-haloketone. Despite enhanced selectivity, the hydrin intermediate was still observed in 19% yield. Furthermore, the reported substrate scope consisted of only styrene. The \(\alpha\)-haloketone selectivity appeared to be less problematic in the [PERSON] route (Table 2), and a broader scope was established; eight aromatic \(\alpha\)-bromoketones were isolated in low to excellent yields (20-94%). Although electron-donating aromatic substituents (e.g., Me, \(t\)-Bu) were well tolerated, electron-withdrawing substituents (e.g., Cl, Br, NO2) were not. Moreover, the presence of steric bulk close to the alkene centre appeared to have a detrimental effect on the system's efficiency. [PERSON] and [PERSON] discussed the use of HOBr in the oxybromination of alkenes (Scheme 54) [142]. Their procedure involved the addition of two equivalents of HOBr to various olefins in 1,4-dioxane. Several \(\alpha\)-bromoketones were obtained in moderate to excellent yields (40-87%).