Efficient Approach to Fluvirucins B₂−B₅, Sch 38518, and Sch 39185. First Synthesis of their Aglycon, via CM and RCM Reactions

A route to fluvirucinins B(2-5) (the common aglycon of fluvirucins B(2)-B(5), Sch 38518, and Sch 39185) is reported for the first time. A ring-closing metathesis (RCM) generated the C6-C7 double bond, which by catalytic hydrogenation (in toluene) gave the desired epimer with a 9:1 diastereoselection. Azide 8a and carboxylic acid 5 came from ethyl-branched fragments C9-C13 (CHO at C9) and C1-C5 via an asymmetric allylation of the former and a cross metathesis (CM) followed by a ketone methylenation (with 20 mol % of DMF as a sacrificial additive) of the latter.