Diastereoselective and Enantioselective Conjunctive Cross-Coupling Enabled by Boron Ligand Design

Abstract

Enantio- and diastereoselective conjunctive cross-coupling of β-substituted alkenylboron “ate” complexes is studied. While β substitution shifts the chemoselectivity of the catalytic reaction in favor of the Suzuki-Miyaura product, use of a boronic ester ligand derived from acenaphthoquinone allows the process to favor the conjunctive product, even with substituted substrates.

Diastereo‐ and Enantioselective 1,4‐Difunctionalization of Borylenynes by Catalytic Conjunctive Cross‐Coupling

“…With the “hac” ligand, the modest yield of 20 was due to competitive direct transmetallation, providing Suzuki–Miyaura coupling products. Inspired by a previous report, it was found that the direct transmetallation could be minimized by adding steric encumbrance near the boronate oxygen ligands that might prevent O−Pd interaction required for transmetallation. Thus, the 3,7‐dimethyl substituted “hac*” ligand provided the desired product 21 in acceptable yield and both high enantio‐ and diastereoselectivity.…”

Stereospecific 1,2‐Migrations of Boronate Complexes Induced by Electrophiles

“…[32] b-Substituted alkenyl boronic esters 67 were also successfully employed, but required alterations to the boron ligand design to prevent undesired Suzuki-Miyura-type reactivity,w hich was found to dominate with pinacol and neopentyl glycol boronic ester substrates (Scheme 13 d). [33] A more sterically demanding boronic substituent (mac), derived from acenaphthoquinone,w as required to minimize Suzuki-Miyaura coupling and direct the approach of the palladium-(II) complex to the more congested b-carbon, thus enabling access to the conjunctive cross-coupling products 68 with excellent stereoselectivities.F urthermore,t his approach was applied to b-silyl alkenyl boronate complexes 69 for the efficient construction of anti-1,2-borosilanes (Scheme 13 d). [34] Finally,u sing propargylic carbonates 72 in place of aryl triflates furnished fully substituted b-boryl allenes with high enantioselectivity (Scheme 13 e).…”

Stereospecific 1,2‐Migrations of Boronate Complexes Induced by Electrophiles

“…Extension of this approach to boronate complexes derived from α‐substituted alkenyl boronic esters 65 allowed access to highly desirable tertiary boronic esters 66 with good enantioselectivity (Scheme c) . β‐Substituted alkenyl boronic esters 67 were also successfully employed, but required alterations to the boron ligand design to prevent undesired Suzuki‐Miyura‐type reactivity, which was found to dominate with pinacol and neopentyl glycol boronic ester substrates (Scheme d) . A more sterically demanding boronic substituent (mac), derived from acenaphthoquinone, was required to minimize Suzuki–Miyaura coupling and direct the approach of the palladium(II) complex to the more congested β‐carbon, thus enabling access to the conjunctive cross‐coupling products 68 with excellent stereoselectivities.…”