... Tetrahedron Letters. Volume 42, Issue 15, 9 April 2001, Pages 2817–2820. ... The standard procedure 16 involving the following steps of (i) Cl 3 C 6 H 2 COCl, Et 3 N, THF; (ii) filtration; (iii) slow addition to DMAP in toluene, produced the 14-oxo lactone 13 in 35–42% yield, while ...