18 was generated in situ by reacting commercially available 2,5-
dimethoxytetrahydrofuran 17 with 0.6 M aq HCl. Subsequent
Wadsworth–Emmons reaction10 of 18 gave an 85:15 mixture of
(RS)-12 and the corresponding diester 19, respectively, and following
chromatographic purification (RS)-12 was isolated in 38% yield
from 17 (Scheme 2).