To determine the absolute configuration of the propargylic ether products, ether 4an was deprotected using BF3OEt2 to give alcohol 18 in 87% yield (Scheme 5B). Compound 18 was reacted with p-nitrobenzoyl chloride to give compound 19, which allow us to determine the absolute configuration via X-rays analysis. Deprotection of the TIPS group was performed on compound 11b by treatment with AgF, giving terminal alkyne 20 in 82% yield , albeit with a lower dr.