Enantioselective Synthesis and Cross‐Coupling of Tertiary Propargylic Boronic Esters Using Lithiation–Borylation of Propargylic Carbamates

Abstract

Chiral tertiary boronic esters have been shown to be useful intermediates in organic synthesis, as they can undergo a variety of functional group transformations, for example, conversion to alcohols, amines, quaternary centers, or aryldialkylmethines with high stereospecificity. [1] Recently, such intermediates have become available in high ee through two distinct methods: 1) borylation of Michael acceptors [2] or allylic electrophiles, [3] and 2) lithiation-borylation of secondary benzylic carbamates (Scheme 1), [4] which can deliver exceptionally high enantioselectivities over a broad range of substrates (> 99.1 e.r.).

Stereospecific Couplings of Secondary and Tertiary Boronic Esters

“…[62] The desired starting materials were synthesized by lithiationborylation of propargylic carbamates (Scheme 19). Only tertbutyl-functionalized propargylic substrates could be used because of the inherent configurational instability of alternative propargylic lithiated carbamates.…”

Transition Metal‐Free ipso‐Functionalization of Arylboronic Acids and Derivatives

“…[4] Later, Aggarwal and others contributed many remarkable studies into the conversion of chiral alkylboranes. [5] Complementary to the aforementioned transformations of alkylboranes, considerable progress has been made recently in transition-metal-free transformations of arylboronic acids for the construction of C-C, C-N, C-O and many other C-X bonds. These efforts will be summarized herein and organized on the basis of the type of bonds being formed.…”

Synthesis of Chiral Tertiary Boronic Esters by Oxime‐Directed Catalytic Asymmetric Hydroboration

“…[15] Aggarwal has very elegantly exploited enantioselective lithiation followed by the addition of a boronic ester and subsequent rearrangement to prepare chiral tertiary boronic esters bearing benzyl, allyl, propargyl, and most recently all alkyl substituents. [16] Tertiary boronic esters can also be constructed by deborylative alkylation of geminal bis(boronates) as reported by Kingsbury [17] and Morken. [18] …”