Versatile, high 2,4-syn dialkyl diastereoselection in the radical debromination of α-bromo-α-methyl-δ-valerolactones with tri-n-butyltin hydride and a catalytic amount of triethylborane

An interesting 2,4-syn dialkyl diastereoselection has been observed in the radical debromination of α-bromo-α-methyl-δ-valerolactones. The reaction of 4-alkyl-2-bromo-3-hydroxy-2-methyl-5-pentanolides with Bu3SnH and a catalytic amount of Et3B gave, essentially, a single diastereomer with a 2,4-syn dialkyl relationship, independent of the orientation of the hydroxy substituent at C-3.