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

Abstract

Allylboron reagents are popular in synthesis owing to their versatility and the predictable stereochemical outcomes of their reactions with carbonyl compounds. Herein, we describe the synthesis of (Z,Z)-hexadienyl bis-boronate 1, a configurationally stable, crystalline, and easy to handle compound, which represents a class of bis-allylic boron reagents with heretofore untapped synthetic potential. In combination with a chiral phosphoric acid catalyst, the reagent can be employed for the enantioselective allyl transfer reaction to a variety of one-pot transformations, enabling swift access to functionalized 1,n-diols. The in situ conversion of the reagent into the corresponding bis-borinic ester allows for the direct and diastereoselective two-fold allyl transfer to aldehydes. This affords C - or C -symmetric stereotetrads containing a 1,4-diol moiety for natural product synthesis. The usefulness of our method was demonstrated with a short synthesis of the lignan (±)-neo-olivil.

An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

“…As a particular case of an allylboration reaction, in 2018 Trauner and co-workers described the ( R )- BPA2 catalysed reaction of aldehydes 86 using diboronates 422 (Scheme 124). 333 The reaction can be applied to a variety of aromatic, aliphatic and α,β-unsaturated aldehydes 86 that, after oxidative workup, yields 1,5-diols 423 in good yield, diastereo- and enantioselectivity (67–91%, 12 : 1 to 15 : 1 dr, 72–98% ee).…”

Synthesis of α-Borylmethyl-(E)-allylborons via Cu-Catalyzed Diboration of 1-Substituted Allenols and Their Application in Stereoselective Aldehyde Allylation

“…Subsequently, we investigated the feasibility of ( Z )- and ( E )-stereoselective allylations using 1-alkyl- or 1-aryl-substituted ( E )-allyldiborons. Trauner and co-workers described the phosphoric acid catalyzed enantioselective monoallylation of aldehydes using bisallylborons (class I ) to provide chiral ( Z )-4-vinyl-3-penten-1,5-diols . Chen and co-workers applied these catalytic conditions to the synthesis of chiral ( Z )-4-methyl-3-penten-1,5-diols via allylation of aldehydes using a class IV diboron reagent (Scheme d) .…”

“…Based on Hall’s category of bimetallic double-allylation reagents, we suggested the revised four classes of allyldiborons (Scheme a) . In contrast to classes I and II , which are direct bisallylborons, , classes III and IV have one allyl- and one pro-allylboron moiety (vinylboron for class III and homoallylboron for class IV ). Extensive investigations on class I , II , and III reagents have been successfully conducted by several research groups. , On the other hand, class IV is less common and has only been studied recently.…”

Copper-Catalyzed Highly Enantioselective 1,4-Protoboration of Terminal 1,3-Dienes

“…Due to the utility of allylic boron reagents in organic synthesis, chemists are increasingly attentive to their preparations. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Usually, basic main-group organometallics, such as organolithium or Grignard reagent, are necessary for traditional methods to make allylboranes. [19][20][21][22][23][24][25] The disadvantage of these strategies is their incompatibility with electrophilic functional groups.…”