Stereoselective hydroformylation: key step for the assembly of polypropionate subunits.

An anti-selective hydroformylation of 2-propylidene-substituted 1,3-dioxanes 16, 17, and 26 with excellent levels of acyclic stereocontrol has been achieved. The basis of this result was a careful substrate design making use of a syn-pentane interaction as the decisive stereochemical control element. Confirmation of this working hypothesis came from conformational analysis studies on alkenic substrate 16 employing 2D NOESY experiments in solution and MACROMODEL/MM3 calculations. This stereoselective, transition metal-catalyzed, C-C bond-forming reaction could serve as a key step for the construction of the all-anti and syn-anti stereotriad building blocks 20, 21, and 31, which should be well-suited for target-oriented polypropionate synthesis. Application of this methodology for the construction of a C5-C11 building block for the synthesis of bafilomycin A1 is described.