3,3-Bis(4-bromobenzyl)pent-4-en-1-ol-d4 is labelled 3,3-Bis(4-bromobenzyl)pent-4-en-1-ol (B485935) which is used to prepare opper-catalyzed intramolecular carboetherification/C-H functionalization of aryl-containing alkenols to form fused and bridged tetrahydrofurans.