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

Polysubstituted cyclopentane rings can be synthesized with good to high ste reocontrol by radical cyclization using tributyltin hydride and a radical i nitiator, triethylborane-O-2 in anhydrous xylene at room temperature. We ha ve demonstrated that the nature (protected or unprotected) of the hydroxy f unctions in position 2 and 4 is responsible for the stereochemical cyclizat ion outcome of acyclic 1-substituted-2,4-dihydroxylated hex-5-enyl compound s. The presence of a 2,4-diol leads to the all-syn precursor of isoprostane s while the diprotected diol affords the diastereoisomer syn-anti-syn precu rsor.