Enantioselective diboration of unsaturated hydrocarbons with bis(pinacolato)diboron is an efficient means for functionalizing readily accessible olefinic compounds. Recently, we demonstrated that cis-substituted 1,3-dienes undergo Pt-catalyzed enantioselective 1,2-diboration with B2(pin)2 in the presence of chiral TADDOL-phosphonite ligands. The allyl bis(boronate) ester generated is a versatile reagent. Under oxidation conditions, the corresponding 1,2-diol is generated. Conversely, allylboration occurs upon the addition of an aldehyde to synthesize propionate-like homoallylic alcohols after oxidation. When a 1,4-dicarbonyl electrophile is used, an iterative inter/intramolecular allylation occurs. This double allylation strategy has been used to synthesize highly substituted enantioenriched carbocycles with four contiguous stereocenters in high yield and good diastereoselectivity. Pumilaside B agylone, a tricyclic sesquiterpene natural product, was synthesized using the tandem diene diboration/double allylation strategy. By diversifying the electrophilic partners, we hope to develop a general strategy for carbocycle synthesis.

Enantioenriched allyl bis(boronate) esters: Versatile reagents in organic synthesis

245th National Meeting (2013)

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