Oxiranylcarbinyl radical

Alkoxy (R0 ) radicals react at near diffusion controlled rates with trialkyl phosphites to give phosphoranyl radicals [ROP(OR )3] that typically undergo very fast -scission to generate alkyl radicals (R ) and phosphates [OP(OR )3]. In a mechanistic study, trimethyl phosphite, P(OMe)3, has been used as an efficient and selective trap in oxiranylcarbinyl radical systems formed from haloepoxides under thermal AIBN/n-Bu3SnH conditions at about 80 °C (Scheme 27) [64]. The formation of alkenes resulting from the capture of allyloxy radicals by P(OMe)3 fulfils a prior prediction that, under conditions close to kinetic control, products of C-0 cleavage (path a. Scheme 27), not just those of C-C cleavage (path b. Scheme 27) may result. 

A fragmentation reaction, triggered by the formation of an oxiranylcarbinyl radical resulted in the deoxygenation of a spirocyclic oxirane (Scheme 47) (95TL19). 

Ring Opening of Epoxides via Formation of Oxiranylcarbinyl Radicals... 

This cleavage will therefore be discussed first. Several substrates have proven useful for the generation of the pivotal oxiranylcarbinyl radicals. Sharpless epoxides are valuable starting materials for radical precursors [18]. After formation of the oxygen-centered radical, reactions typical for radicals are observed. With a suitably positioned double bond, cyclization occurs as shown in Scheme 10 [19]. It is interesting that the cw-disubstituted carbon-centered radical can react further to yield a bicyclo[2.2.1] system. 

Directed ring opening of bicyclic oxiranylcarbinyl radicals (Scheme 25) affords tetrahydrooxepines in 50-70% yields <92SL987>. 

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