Stereoselective Allyl Enol Carbonates for the Synthesis of Chiral Aldehydes Bearing All Carbon Quaternary Stereocenters via the Decarboxylative Asymmetric Allylic Alkylation (DAAA)

Abstract

A stereoselective synthesis of carbonates derived from 3-hydroxy-2-aryl acrylates was devised that can form the Zor E-stereoisomer in very high Z/E ratios (50:1 and 1:99, respectively). The stereochemical outcome depends on the choice of base, addition of TMEDA and reaction temperature. The Zand E-stereoisomers have different reactivities towards the DAAA reaction, with the E-stereoisomer displaying both greater reactivity and enantiodifferentiation with chiral ligands. The DAAA of E-stereoisomer analogues takes place in excellent yields ranging from 96-99% and enantioselectivities ranging from 42-78% ee.

The Catalytic Asymmetric Allylic Alkylation of Acyclic Enolates for the Construction of Quaternary and Tetrasubstituted Stereogenic Centres

“…Subsequently, the same group carried out the analogous decarboxylative reaction of geometrically pure E ‐allyl enol carbonates ( E )‐ 70 (B, Scheme 14). [25] The authors found that, in comparison to the aforementioned AAA reaction of enols ( Z )‐ 68 , there was a significant reduction in the enantioselectivity of alkylation in the decarboxylative process, giving 69 a , 69 b and 69 c with 58 %, 61 % and 61 % ee, respectively. In addition, they expanded on their work by exploring E ‐allyl enol ethers ( E )‐ 71 as substrates, made stereoselectively by O ‐allylation of 68 with allyl bromide [26] .…”