Catalytic radical acetylation of adamantanes with biacetyl by a cobalt salt under atmospheric dioxygen

Photoacetylation of Diamondoids: Selectivities and Mechanism

“…In contrast, the differences in the barriers for hydrogen abstraction with the triplet diacetyl diradical (TS3 and TS4), as well as with the peroxoacetyl radical (TS5 and TS6), are large enough (∆∆H 298 ‡ = 2.4 and 2.1 kcal mol -1 , respectively) to correspond to the high experimentally observed selectivities for the photoacetylation of adamantane. It is conceivable that the selectivity decrease previously observed in the photoacetylation of adamantane in the presence of oxygen [36] is not due to the suggested participation of peroxoacetyl radical but rather due to formation of other oxygen-centered radicals as found in the aerobic oxidations of adamantane. [21] We assume that both triplet diacetyl and the peroxoacetyl radical could be responsible for the high positional selectivities in the photoacetylation of adamantane in the presence of oxygen.…”

“…[34,35] Thermal metal-catalyzed adamantane C-H substitutions with diacetyl are also well documented but occur only in the presence of oxygen and with substantially lower selectivities. [36] Under these conditions, the peroxoacetyl radical MeC(O)OO · rather than the acetyl radical or diacetyl diradical were assumed to participate in the activation step. [36] Currently, the regiospecificity for the tertiary C-H positional selectivities of the adamantane cage with diacetyl upon irradiation is difficult to explain within a traditional free-radical mechanism.…”

“…[36] Under these conditions, the peroxoacetyl radical MeC(O)OO · rather than the acetyl radical or diacetyl diradical were assumed to participate in the activation step. [36] Currently, the regiospecificity for the tertiary C-H positional selectivities of the adamantane cage with diacetyl upon irradiation is difficult to explain within a traditional free-radical mechanism. The high apical selectivities for the photoacetylations of higher diamondoids require careful scrutiny.…”

Cobalt-Catalyzed Markovnikov-Selective Radical Hydroacylation of Unactivated Alkenes with Acylphosphonates

“…Biacetyl has been reported as a radical acceptor, but its efficiency and generality are both far from satisfactory. 81,82 Acylphosphonates, 83−85 acylgermanes, 86 and thio-and selenoesters 87 have been tested as radical acylating agents by the groups of Kim, Curran, and Zard. However, only intramolecular acylation reactions have been achieved, while analogous intermolecular acylation has proved unsuccessful.…”

“…To our surprise, the long search for radical acylating reagents other than the above-mentioned unstable acyl-Ni II species remains unsolved and a challenging task. Biacetyl has been reported as a radical acceptor, but its efficiency and generality are both far from satisfactory. , Acylphosphonates, − acylgermanes, and thio- and seleno-esters have been tested as radical acylating agents by the groups of Kim, Curran, and Zard. However, only intramolecular acylation reactions have been achieved, while analogous intermolecular acylation has proved unsuccessful. ,, As an alternative, sulfonyl oxime ethers have been used as surrogates for an indirect radical acylation approach, which requires acid hydrolysis in the last step. , It is therefore highly desirable to develop stable, highly reactive, and preferably nonmetallic reagents for direct, intermolecular radical acylation.…”