Factors controlling the biomimetic triple cyclisation of xylulose β-keto-esters to syringolides. Part 1: Synthesis of 4′-deoxysyringolide 2

Treatment of the 4-deoxy-d-xylulose β-ketodecanoate 13c with basic alumina affords 4′-deoxysyringolide 2 14 as a single stereoisomer, indicating that the course of the biomimetic triple cyclisation of the corresponding d-xylulose ester 3b to syringolide 2 5b is not dependent upon the presence of the 4R-hydroxyl group. The diacyl butanolide 15 is formed simultaneously by a side reaction of the initial Knoevenagel condensation product of the ester 13c.