Radical cyclization of highly functionalized precursors: stereocontrol of ring closure of acyclic 1-substituted-2,4-dihydroxylated hex-5-enyl radicals

Abstract

Polysubstituted cyclopentane rings can be synthesized with good to high stereocontrol by radical cyclization using tributyltin hydride and a radical initiator, triethylborane–O2 in anhydrous xylene at room temperature. We have demonstrated that the nature (protected or unprotected) of the hydroxy functions in position 2 and 4 is responsible for the stereochemical cyclization outcome of acyclic 1-substituted-2,4-dihydroxylated hex-5-enyl compounds. The presence of a 2,4-diol leads to the all-syn precursor of isoprostanes while the diprotected diol affords the diastereoisomer syn-anti-syn precursor.