Synthesis of Elongated Esters from Alkenes

Abstract

Ac onvenient method for synthesizing elongated aliphatic esters from alkenes is reported. An (alkoxycarbonyl)methyl radical species is generated upon visible-light irradiation of an ester-stabilized phosphorus ylide in the presence of ap hotoredox catalyst. This radical species adds onto the carbon-carbon double bond of an alkene to produce an elongated aliphatic ester.

Metal-free visible light photoredox enables generation of carbyne equivalents via phosphonium ylide C–H activation

“…1d). To the best of our knowledge, there is only one recent example of a reaction between ester-stabilized ylides and olefin under photoredox conditions, as reported by Miura and Murakami 42. It was proposed that the formation of an alkyl radical from the phosphonium salt using an iridium photocatalyst is the key step in the mechanistic pathway.…”

Photoinduced 1,2-Hydro(cyanomethylation) of Alkenes with a Cyanomethylphosphonium Ylide

“…We recently reported that an ester-stabilized phosphonium ylide 2 can act as a precursor to an (alkoxycarbonyl)methyl radical species 3 when irradiated with visible light in the presence of an iridium catalyst, a thiol, and ascorbic acid. 4 The radical species, substituted by an electron-withdrawing alkoxycarbonyl group, adds across the C=C double bond of an alkene to generate an elongated alkyl radical. Subsequently, the thiol delivers a hydrogen atom to the radical, 5 producing an elongated aliphatic ester.…”

“…The former act as the precursor of a cyanomethyl radical species [7][8][9][10] that, due to the electron-withdrawing nature of the cyano group, is sufficiently electrophilic to attach to a C=C double bond of an alkene, as in the case of an (alkoxycarbonyl)methyl radical. 3,4,6 The appended alkyl radical species is not as electrophilic as the original cyanomethyl radical, and can therefore abstract a hydrogen atom from a sulfanyl group 5 to form an elongated aliphatic nitrile.…”

“…The formation of the product 3a can be reasonably explained by assuming the radical mechanism depicted in Scheme 2, which is similar to that proposed in the case of ester-stabilized phosphonium ylides. 4 First, an acid/base…”

Visible light photoredox mediated C-C bond formation under metal-free condition

“…To the best of our knowledge, there is only one recent example of the reaction between ester-stabilized ylides and olefin under photoredox condition, reported by Miura and Murakami. 42 It was proposed that the formation of alkyl radical from the phosphonium salt using Iridium photocatalyst is the key step in the mechanistic pathway.…”