Radical alkoxycarbonyl methyl

The tandem -endo/5-exo cyclization of the (alkoxycarbonyl)methyl radical (32) has indicated that 8-endo cyclization is favoured over 5-exo cyclization in this system (Scheme 24). Ab initio studies indicated that this was due to the initial radical favouring a (Z)-(32) over an ( )-(32) conformation. 

The photolysis of a-phenylselenoacetate and related compounds in the presence of an alkene and CO leads to acyl selenides via group transfer carbonylation. The mechanism of this three-component coupling reaction involves the addition of an a-(alkoxycarbonyl)methyl radical to an alkene, the trapping of the produced alkyl free radical by CO, and termination of the reaction by a phenylselenenyl group transfer from the starting material (Scheme 4-43) [73]. 

The oxidation of indoles and pyrroles by Fe(III) ions is less predictable than other chemical oxidations. 2-Methyl- and 3-methyl-indoles, respectively, yield (187) and (188), and whilst pyrroles may form pyrrole black , the rate of oxidation of pyrrole and of 1-methylpyrrole appears to be relatively slow. C-Alkyl and electron-donating substituents enhance the formation of oligimers, e.g. (189) -> (190) and (191) -> (192), and although electron-withdrawing substituents reduce the susceptibility of the pyrrole ring to oxidation, acyl- and alkoxycarbonyl-pyrroles of the type (193) are readily oxidized to the thermochromic dimer (194), which is in equilibrium with the dimer (195) via the monomeric pyrrolyl radical (72BCJ3584). 

Alkoxycarbonyl radical cyclization leads to direct formation of lactones. For example, the lactone 154 was obtained from the selenocarbonate 153 in Corey s synthesis of atractyligenin (155) [103] (Scheme 53). 5-Alkoxycarbonyl xanthates are also viable precursors for alkoxycarbonyl radicals the lactone 157 was prepared from the xanthate 156 via group transfer radical cyclization en route to methyl-enolactocin (149) [104] (Scheme 54). 

Regioselective homolytic alkoxycarbonylation of (65) with radicals derived from methyl pyruvate gave (99) in 37% yield <89JHC1751>. 

---