Radical cyclisation route to furanolignans: short and stereoselective synthesis of (±)-dihydrosesamin and (±)-lariciresinol
The furanolignans, (±)-dihydrosesamin 3a and (±)-lariciresinol 4 have been synthesised by a very short and stereoselective route in good overall yield using a radical cyclisation as the key step. The radical precursor 2, prepared from the easily accessible cinammyl alcohol 1, on radical cyclisation in the presence of Bu3SnH and a catalytic amount of AIBN, furnished 3 along with a second isomer in a ratio of 7:1. The product 3a was identical with natural dihydrosesamin. The lariciresinol dibenzyl ether 3b, on controlled catalytic hydrogenation, afforded (±)-lariciresinol 4 in excellent yield.