Scheme 10.
Reagents and conditions: a) Dess–Martin reagent, CH2Cl2; b) but‐3‐en‐1‐ylmagnesium bromide, THF; c) trimethylsilyl trifluoromethanesulfonate (TBSOTf), diisopropylethylamine (DIPEA), CH2Cl2; d) Grubbs II (10 mol %), CH2Cl2, heating to reflux; e) HCl, EtOH, Et2O.