Preparation of Enolate–Homoenolate Species as (Z)‐γ‐Siloxyallylmetal Equivalents: Sequential 1,4‐Addition of Bis(iodozincio)methane to 1,4‐Dicarbonylbutenes and Cyclopropanation

Abstract

In einem Schritt werden die Enolat‐Homoenolat‐Äquivalente 1 durch die Titelreaktion erzeugt. Durch Ringöffnung in Gegenwart einer Lewis‐Säure entstehen (Z)‐γ‐Siloxyallylzinkreagentien 2, die an Tosylimine addieren und mit hoher Diastereoselektivität vic‐Aminoalkohole liefern. Vermutliche Ursache der Selektivität ist eine durch Koordination des Metallzentrums fixierte Konformation.

Zinc-Mediated Hydroxyallylation of Aldehydes with Cyclopropanols: Direct Access to Vicinal anti-sec,tert-Diols via Enolized Homoenolate

“…The reaction is promoted using the combination of Et2Zn and 2,2'-bipyridine (bpy) at room temperature, engaging a variety of 1-substituted cyclopropanols and bicyclic cyclopropanols as well as aromatic and aliphatic aldehydes. The present reaction features the action of enolized homoenolate, [8][9][10][11] formed through Et2Zn-mediated ring-opening of cyclopropanol and subsequent enolization of the resulting homoenolate, as a stereodefined α-oxyallylzinc nucleophile toward the aldehyde. The complementary antiselectivity of the reaction was ascribed to a bicyclic chairlike transition state of allylation, where the aldehyde substituent prefers to occupy the pseudoaxial position.…”