Highly Selective Allylborations of Aldehydes Using α,α‐Disubstituted Allylic Pinacol Boronic Esters

Abstract

α,α-Disubstituted allylic pinacol boronic esters undergo highly selective allylborations of aldehydes to give tetrasubstituted homoallylic alcohols with exceptional levels of anti-Z-selectivity (>20:1). The scope of the reaction includes both acyclic and cyclic allylic boronic esters which leads to acyclic and exocyclic tetrasubstituted homoallylic alcohols. The use of β-borylated allylic boronic esters gave fully substituted alkenes bearing a boronic ester which underwent further cross-coupling enabling a highly modular and stereoselective approach to the synthesis of diaryl tetrasubstituted alkenes. Computational analysis revealed the origin of the remarkable selectivity observed.

Organocatalytic Synthesis of α-Trifluoromethyl Allylboronic Acids by Enantioselective 1,2-Borotropic Migration

“…The first methods for asymmetric homologation of organoboron compounds were reported by the Matteson group. 4 , 5 Aggarwal and co-workers 6 applied a useful lithiation–borylation method ( Figure 1 b) for the synthesis of chiral allyl-Bpin species, 7 including an example of an α-trifluoromethyl allylboronate derivative. 8 This method is based on stoichiometric formation of chiral lithium carbenoid intermediates, and therefore, it is not suitable for the direct synthesis of allylboronic acids.…”

Synthesis and Utility of Dihydropyridine Boronic Esters

“…Therefore we next explored their synthetic utility For example, addition of the allyl boronate to benzaldehyde generated the desired homoallylic alcohol 52 with good yield and diastereoselectivity (Scheme 3a). [17] Hydrogenation of this alcohol gave the trisubstituted piperidine 53 while oxidation provided the disubstituted pyridine 54 , in which the benzoyl group migrated from N to O. In this way the (pin)B moiety was used to functionalize both C2 and C4 of the pyridine ring – a distinguishing characteristic of the current method relative to Suzuki couplings and related reactions.…”