Synthesis of (-)-6,7-Dideoxysqualestatin H5 by Carbonyl Ylide Cycloaddition-Rearrangement and Cross-electrophile Coupling

An asymmetric synthesis of (-)-6,7-dideoxysqualestatin H5 is reported. Key features of the synthesis include the following: (1) highly diastereoselective n-alkylation of a tartrate acetonide enolate and subsequent oxidation-hydrolysis to provide an asymmetric entry to a β-hydroxy-α-ketoester motif; (2) facilitation of Rh(II)-catalyzed cyclic carbonyl ylide formation-cycloaddition by co-generation of keto and diazo functionality through ozonolysis of an unsaturated hydrazone; and (3) stereoretentive Ni-catalyzed Csp³-Csp² cross-electrophile coupling between tricarboxylate core and unsaturated side chain to complete the natural product.