Generation ovf 5- and 6-membered ring radicals by deoxygenation of alkoxy radicals with triphenylphosphine

Abstract

A new approach, using triphenylphosphine as a deoxygenation reagent, for the formation of five- and six-membered ring radicals from acyclic precursors has been studied. Our approach is based on the assumption that trialkylphosphine would trap the cyclic alkoxy radical before it could undergo b-fragmentation to afford the open chain radical intermediate. Alkyl and vinyl radicals attacked aldehydes easily and deoxygenation with triphenylphosphine occured successfully in good yields. Radical cyclization of iodoaldehyde in the presence of electron deficient alkenes with tributyltin hydride proceeded, yielding alkylated cyclic compounds. This demonstrated the formation of two carbon-carbon bonds in succession at the same carbon. Next, we applied this approach in tandem radical cyclization reactions to afford bicyclic compounds.