Enantiospecific Alkynylation of Alkylboronic Esters

Abstract

Enantioenriched secondary and tertiary alkyl pinacolboronic esters undergo enantiospecific deborylative alkynylation through a Zweifel‐type alkenylation followed by a 1,2‐elimination reaction. The process involves use of α‐lithio vinyl bromide or vinyl carbamate species, for which application to Zweifel‐type reactions has not previously been explored. The resulting functionalized 1,1‐disubstituted alkenes undergo facile base‐mediated elimination to generate terminal alkyne products in high yield and excellent levels of enantiospecificity over a wide range of pinacolboronic ester substrates. Furthermore, along with terminal alkynes, internal and silyl‐protected alkynes can be formed by simply introducing a suitable carbon‐ or silicon‐based electrophile after the base‐mediated 1,2‐elimination reaction.

Stereocontrolled Synthesis of Polypropionate Fragments based on a Building Block Assembly Strategy using Lithiation‐Borylation Methodologies

“…The boronic ester present in 3 is a versatile functional group for chemical diversification and, as a result, is a useful synthon in synthesis. This was briefly demonstrated by conducting Matteson homologation, Zweifel olefination, and alkynylation reactions (Scheme ), which all proceeded in good yields and diastereospecificity (>95 %).…”

Selective uni- and bidirectional homologation of diborylmethane

“…1 It is now clear that polyboronic esters are powerful intermediates in organic synthesis owing to the abundance of functional groups in which the C–B bonds can be transformed. 2 Many of these methods are stereospecific and regioselective transformation of polyboronic esters is feasible through the judicious manipulation of steric effects 3 and proximal functional groups. 4 Despite these advances, the types of polyboronic esters available for further functionalization remain limited.…”

Vinylidenation of Organoboronic Esters Enabled by a Pd‐Catalyzed Metallate Shift

“…1 These processes include oxidation, 2 amination, 3 cross-coupling, 4 homologation, 5 and alkynylation, among others. 6 Because of this utility, the development of new methods for constructing organoboronic esters from new classes of starting materials holds significant value. A particularly powerful transformation that applies to organoboronic esters is the halogen-promoted Zweifel-Evans-Matteson 7 reaction that results in olefination of organoboron reagents (Scheme 1, eq.…”