ALKYL PYRIDINESULFONATES AND ALLYLIC PYRIDINECARBOXYLATES, NEW BOOSTERS FOR THE SUBSTITUTION AT SECONDARY CARBONS

摘要

Substitution at allylic secondary carbons using the pyridinecarboxylate (picolinoxy, PyCO2, or Pic) leaving group is described in the first part of this review (Sections 2-4). Alkyl as well as less reactive alkenyl, heteroaryl, and aryl copper reagents are suitable for the substitution, giving anti S(N)2' products highly regio- and stereoselectively. In Section 2, finding and synthetic application of the allylic substitution giving tertiary carbon centers are presented. Extension of the substitution for the construction of quaternary carbon centers is described in Section 3 with its synthetic application. Section 4 deals with the construction of quatemary carbon centers on cyclohexane rings by the allylic substitution of cyclohexylidene picolinates. The stereochemistry is created by equatorial attack to the chair conformer with high diastereselectivity. The stereochemical prediction facilitated synthesis designs of biologically active compounds. The second part of the review (Section 5) presents recent advances in metal-catalyzed substitutions at secondary alkyl carbons, giving enantiomerically enriched products. Our findings of the pyridinesulfonyloxy leaving group and an associated copper catalyst are included. Substitutions with cuprates are mentioned briefly for reactivity discussion with the copper-catalyzed substitution.