Iterative assembly line synthesis of polypropionates with full stereocontrol.

The polypropionate motif is ubiquitous, being characteristic of the most important family of natural products for human health, the polyketides. Numerous strategies have been devised to construct these molecules with high stereocontrol, but certain stereoisomers remain challenging to prepare. We now describe the development of an iterative assembly line strategy for the construction of polypropionates. An assembly line strategy for the synthesis of deoxypolypropionates has already been described. However, the introduction of carbinol units required the development of new building blocks and new reaction conditions. This has been achieved by the use of enantioenriched lithiated α-chlorosilanes [1-((2'-lithiochloromethyldimethylsilyl)-methyl)-2-(methoxymethyl)-pyrrolidine], thus enabling the programmed synthesis of polypropionates in a fully stereocontrolled manner, including the stereochemically challenging anti-anti isomers. The versatility of the approach is exemplified in its extension to the synthesis of 1,3-related polyols. The methodology now allows access to a much wider family of polyketide natural products with stereochemistry being dialled in at will.