Cis-substituted 1,3-dienes undergo Pt-catalyzed enantioselective 1,2-diboration with bis(pinacolato)diboron in the presence of chiral TADDOL-phosphonite ligands. These intermediates can be used to synthesize enantioenriched homoallylic alcohols through a diastereoselective allylboration reaction with aldehyde electrophiles. Interestingly, when 1,4-dicarbonyl electrophiles are employed, an iterative double allylation occurs; the product of this tandem diboration/double allylation method is a cyclic diol with four contiguous stereocenters. This reaction is compatible with both aliphatic and aromatic 1,4-dialdehydes, and proceeds in high yield and good diastereoselectivity. When sterically or electronically differentiated 1,4-dicarbonyl compounds are employed, a regioselective reaction occurs. Pumilaside B aglycone, a tricyclic sesquiterpene natural product, was synthesized for the first time via the 1,2-diene diboration/double allylation method using 4-oxopentanal as the dicarbonyl electrophile. The double allylation strategy installs four of the six stereocenters and nearly the entire carbon framework of the natural product.

Asymmetric double allylation of 1,4-dicarbonyl compounds with enantioenriched allyl bis(boronate) esters

245th National Meeting (2013)

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