Asymmetric Bisvinylogous Aldolation of Aldehydes via 2-Oxonia-Cope Rearrangement Enabling Total Stereochemical Control

Abstract

Highly stereoselective 2-oxonia-Cope rearrangement reactions between newly designed bisvinylogous aldolation synthons and aldehydes, which can provide ε-hydroxy-α,β,γ,δ-unsaturated esters with excellent enantioselectivities, as well as with unprecedented E- and Z-selectivities without regioselectivity issues, are described.

A Versatile Bis‐Allylboron Reagent for the Stereoselective Synthesis of Chiral Diols

“…The preferential reactivity of the allylic alcohol group can be exploited to form to form a γ‐substituted lactone (see Supporting Information for details). Furthermore, these compounds can be seen as vinylogous aldol products bearing an extra vinyl group, the synthetic utility of which has just begun to emerge …”

“…NaOH, H 2 O 2 ,08 8CtoRT; g) chloroiodomethane, n-BuLi, THF, À78 8 8Ct oRTthen aq. [31] Thesingle addition of 1 to an aldehyde led to intermediate 3 (Scheme 3), the attenuated reactivity of which towards as econd allyl transfer presumably results from the higher steric congestion of the unreacted allyl boronate.T his compound represents an important branching point for diversification. Ac atalyst loading of 10 %w as necessary to effect full conversion, likely because of an on-productive catalyst interaction with the second boron center in 1.T he optimized reaction conditions were applied to av ariety of aldehydes.…”

“…Furthermore,t hese compounds can be seen as vinylogous aldol products bearing an extra vinyl group,t he synthetic utility of which has just begun to emerge. [31] Thesingle addition of 1 to an aldehyde led to intermediate 3 (Scheme 3), the attenuated reactivity of which towards as econd allyl transfer presumably results from the higher steric congestion of the unreacted allyl boronate.T his compound represents an important branching point for diversification. First, the boric acid ester in 3 was cleaved in presence of the pendant allyl pinacol boronate forming 4.…”

Stereoselective Construction of (E,Z)‐1,3‐Dienes and Its Application in Natural Product Synthesis

“…Starting from stereodefined αvinylogous aldol products 19 and 20, Han described the stereoselective access to both E,Z-and Z,Ebisvinylogous aldol products 21 and 22 through an oxonia-Cope rearrangement (Scheme 6). [20] Scheme 3. Cyclobutene ring-opening strategies.…”

Ein vielseitiges Bisallylbor‐Reagenz für die stereoselektive Synthese von chiralen Diolen

“…Furthermore, these compounds can be seen as vinylogous aldol products bearing an extra vinyl group, the synthetic utility of which has just begun to emerge. [31] The single addition of 1 to an aldehyde led to intermediate 3 (Scheme 3), the attenuated reactivity of which towards a second allyl transfer presumably results from the higher steric congestion of the unreacted allyl boronate. This compound represents an important branching point for diversification.…”