Asymmetric Syntheses of Pectenotoxins-4 and -8, Part II: Synthesis of the C20–C30 and C31–C40 Subunits and Fragment Assembly

The total syntheses of the marine macrolides pectenotoxins-4 and -8 have been realized. The pectenotoxins are a new class of marine macrolides that exhibit a high level of biological activity. Key fragment couplings include a Felkin-selective Grignard addition reaction (green), a metalated dimethylhydrazone alkylation (red), and a late-stage olefination reaction with a β-alkoxy sulfone (blue). The utility of the N-phenylamide as a carboxy surrogate and the use of the base labile tert-butoxydiphenylsilyl ether is also described.