Regioselective Arylboration of 1,3‐Butadiene

Abstract

A method for the regioselective 1,2-arylboration of 1,3-butadiene, a feedstock chemical, is reported. The reactions result in the formation of products that can be easily elaborated to other structures. The mechanistic details of this process are also discussed. Scheme 1. Copper/palladium-catalyzed arylboration of 1,3-dienes. Scheme 2. Mechanistic analysis of arylboration of butadiene.Communication Isr. J. Chem. 2020, 60, 394 -397 Scheme 4. Mechanistic analysis of arylboration of butadiene. Scheme 5. Representative functionalizations of an arylboration product.

Copper-Catalyzed Borylative Difunctionalization of π-Systems

“…The preference for the Z -isomer could be attributed to the improved stability of the organometallic complex , and has been observed in borylcupration studies . Similar borylarylation processes using butadiene were recently reported to obtain the 1,2-difunctionalized product …”

Cooperative Pd/Cu Catalysis for Alkene Arylboration: Opportunities for Divergent Reactivity

“…The arylboration of 1,3-dienes has also been extensively explored . The development of these reactions is complicated for several reasons: (1) the addition of the NHC–Cu–Bpin complex can generate η 1 -1,2-, η 1 -1,4-, or η 3 -π-allyl–Cu complexes, (2) the transmetalation can occur through either a direct or an allylic process, and (3) the reductive elimination can occur at one of the two sites.…”

“…During the development of alkenyl arene arylboration, the reactions of dienes emerged. For example, our lab reported on the arylboration of 1- and 2-substituted 1,3-dienes (Scheme E) . More recently, Liao et al developed enantioselective reactions of enynes to generate chiral allenes (Scheme F) …”

Copper-Catalyzed Functionalization of 1,3-Dienes: Hydrofunctionalization, Borofunctionalization, and Difunctionalization

“…Their initial report demonstrated such a process in the functionalization of feedstock dienes, such as butadiene (to give 94 ), isoprene (e.g., to give 92 ), and myrcene (e.g., to give 93 ) (Scheme ). In a way similar to that reported by the Procter group (Scheme ), the authors could dictate the regioselectivity of the reaction by switching the ligands. Thus, when the palladium catalyst Pd1 was used, the 4,1-product 90 was formed, whereas the 1,2-product 91 was favored when the palladium catalyst Pd2 was used.…”