Stereo‐ and Enantioselective Synthesis of Propionate‐Derived Trisubstituted Alkene Motifs

We report a new method for constructing propionate‐derived trisubstituted alkene motifs in a stereoselective manner. 1‐Substituted 1,1‐di(pinacolatoboryl)‐( E )‐alk‐2‐enes are generated in situ from 1‐substituted 1,1‐di(pinacolatoboryl)alk‐3‐enes through ruthenium(II)‐catalyzed double‐bond transposition. These species undergo a chiral phosphoric acid catalyzed allylation reaction of aldehydes to produce the E isomers of anti ‐homoallylic alcohols. On the other hand, the corresponding Z isomers of anti ‐homoallylic alcohols are obtained when a dimeric palladium(I) complex is employed as the catalyst for this double‐bond transposition. Thus, both E and Z isomers can be synthesized from the same starting materials. A B−C(sp 2 ) bond remaining with the allylation product undergoes the Suzuki–Miyaura cross‐coupling reaction to furnish a propionate‐derived trisubstituted alkene motif in a stereo‐defined form. The present method to construct the motifs with ( E )‐ and ( Z )‐alkenes are successfully applied to the syntheses of (+)‐isotrichostatic acid, (−)‐isotrichostatin RK, and (+)‐trichostatic acid, respectively.