Synthesis of 1-Alkenylboronic Esters via Palladium-Catalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with 1-Alkenyl Halides and Triflates

Abstract

The synthesis of 1-alkenylboronic acid pinacol esters via the palladium-catalyzed cross-coupling reaction of 1-alkenyl halides or triflates with bis(pinacolato)diboron [(Me 4 C 2 O 2 )B-B(O 2 C 2 Me 4 )] was carried out in toluene at 50 °C in the presence of potassium phenoxide (1.5 equivalents) and PdCl 2 (PPh 3 ) 2 •2PPh 3 (3 mol%).The transition metal-catalyzed cross-coupling reaction of disilanes and distannanes is an elegant method for the synthses of organosilicone 1 and -tin 2 compounds directly from organic electrophiles, but the lack of suitable boron nucleophiles has limited this protocol. We have recently demonstrated the synthesis of arylboronates from aryl halides 3 or triflates 4 , and allylboronates from allyl acetates 5 via a palladium-catalyzed cross-coupling reaction of tetra(alkoxo)diborons. Very recently, Matsuda and Murata 6 found that pinacolborane (Me 4 C 2 O 2 )BH is an excellent boron-nucleophile for the palladium-catalyzed coupling reaction in the presence of triethylamine. Thus, tetra(alkoxo)diboron and pinacolborane are two nucleophiles now available for the boron cross-coupling reaction.In this paper, we report the palladium-catalyzed coupling reaction of bis(pinacolato)diboron (1) and 1-alkenyl halides or triflates, which provides a one-step procedure for the synthesis of 1-alkenylboronic esters from vinyl electrophiles (Eq. 1) 7 .

Chemistry of Group 13 element-transition metal linkage — the platinum- and palladium-catalyzed reactions of (alkoxo)diborons

“…High reactivity of the oxo-palladium complexes for the transmetalation with organoboron compounds can be attributed to both the high reactivity of the Pd-O bond which consists of a soft acid and a hard base combination, and the high oxophilicity of the boron center. The catalytic cycles based on these observations is outlined in Scheme 21, which involves the formation of The palladium-catalyzed coupling reaction of (8b) and 1-alkenyl halides or triflates provides a one-step procedure for the synthesis of 1-alkenylboronic esters from vinyl electrophiles (Scheme 27) [52,53]. The coupling using a palladium catalyst and KOAc suffers from the formation of an inseparable mixture of several products including the Heck coupling products, the homocoupling product of haloalkenes along with the desired coupling.…”

“…The selective coupling to 1-alkenylboronats undergoes in the presence of a solid PhOK suspended in toluene. The reaction provides an alternative synthetic procedure for various vinylboronic esters, which are not available by conventional hydroboration of alkynes [52].…”

Some past achievements and future perspectives in main group chemistry

“…Diboron(4) compounds are noteworthy in this respect and have become commercially available. For example, the boron (+2) compound bis(pinacolato)diboron, in conjunction with palladium catalysts, is useful for a wide variety of transformations including the cross-coupling reactions of bis(pinacolato)diboron with haloarenes [58] or 1-alkenyl halides (triflates) [59], and the acylboration of allenes [60]. In the presence of a platinum catalyst, bis(pinacolato)diboron or bis(catecholato)diboron react with a,b-unsaturated ketones to afford the corresponding 1,4-addition products [61].…”

Regiospecific synthesis of symmetrical (1E,3E) 2,3-difluoro-1,4-diphenyl-buta-1,3-dienes via palladium-catalyzed cross-coupling of (Z) 2-bromo-2-fluoroethenylbenzenes in presence of bis(pinacolato)diboron

“…Synthesizing fluorochalcones using the same methodology meant yielding first (E)-fluoro-2-phenylvinylboronic acid. Recently, Miyaura and coworkers demonstrated that tetra(alkoxo)diborons such as bis(pinacolato)diboron are excellent boron nucleophiles which allow the palladium-catalyzed borylation of organic halides or triflates in the presence of base [21,22]. Particularly the reaction of 2-bromo-ethenylbenzene with bis(pinacolato)-diboron leads to the formation of phenylvinyl boronic acids in good yield [23].…”