Catalyst‐Free Suzuki‐Type Coupling of Allylic Bromides with Arylboronic Acids

Abstract

The coupling of arylboronic acids with electron‐rich allylic bromides is accomplished in the absence of any transition‐metal catalyst through conventional heating. The reaction is completely regioselective, affording only the α‐coupled product, and can be carried out under mild aerobic conditions in an organic solvent; the presence of a base is required.

Transition-metal-free C–C bond forming reactions of aryl, alkenyl and alkynylboronic acids and their derivatives

“…Much more recently, Scrivanti et al have reported the coupling of arylboronic acids with electron-rich allylic bromides through conventional heating in toluene in the presence of K 2 CO 3 (Scheme 15). 31 The reaction was found to be completely regioselective, affording only the α-coupled products 42, in sharp contrast to the Pd-catalyzed reaction, which gave rise to mixtures of regioisomeric alkenes. Analyses carried out by inductively coupled plasma mass spectroscopy were able to detect transition-metals only below 4.1 ppb, a concentration which seems too low to promote a metal-catalyzed reaction.…”

Stereospecific Nucleophilic Substitution with Arylboronic Acids as Nucleophiles in the Presence of a CONH Group

“…It should be noted that this proposed mechanism is different from those proposed for nonchiral and less challenging substrates. [5] Chiral a,a-diaryl acetamides are important building blocks in medicinal chemistry.C hiral mesylate 9 was coupled with 2a to form 10, ac annabinoid CB 1 receptor ligand, [14] in 91 % ee and 50 %y ield (Scheme 2a). (S)-diclofensine (15), which is an effective antidepressant, [12b] was efficiently synthesized using this method.…”

“…[2] Because of their low nucleophilicity,arylboronic acids as nucleophiles are mostly reported for addition to a p system, [3] that is,t he Petasis-borono Mannich reaction [4] (Figure 1a), while there have been afew reports on arylboronic acids for nucleophilic substitution to at etravalent sp 3 carbons. [5] No example is available on S N 2-type transformation with arylboronic acids as nucleophiles.Our previously reported stereospecific nucleophilic substitution of chiral functionalized benzylic mesylates worked well for alkenylboronic acids,b ut not for arylboronic acids (Figure 1b). [6] Taking inspiration from the a-hydroxy-group-promoted Petasis-borono Mannich reaction, [4c,d] we envisioned that an S N 2-type process with an arylboronic acid as the nucleophile could be accomplished by introducing afunctionality capable of bridging two reactants.…”

Stereospecific Nucleophilic Substitution with Arylboronic Acids as Nucleophiles in the Presence of a CONH Group

“…[1] Their applications as nucleophiles in transition-metal-free cross-couplings have been relatively overlooked. [5] No example is available on S N 2-type transformation with arylboronic acids as nucleophiles.Our previously reported stereospecific nucleophilic substitution of chiral functionalized benzylic mesylates worked well for alkenylboronic acids,b ut not for arylboronic acids (Figure 1b). [5] No example is available on S N 2-type transformation with arylboronic acids as nucleophiles.Our previously reported stereospecific nucleophilic substitution of chiral functionalized benzylic mesylates worked well for alkenylboronic acids,b ut not for arylboronic acids (Figure 1b).…”

“…The absolute configuration of 3a was determined by X-ray crystallography. [5] Chiral a,a-diaryl acetamides are important building blocks in medicinal chemistry.C hiral mesylate 9 was coupled with 2a to form 10, ac annabinoid CB 1 receptor ligand, [14] in 91 % ee and 50 %y ield (Scheme 2a). Thepresence of the thio group on the aromatic ring might facilitate the deprotonation process.T he coupling product 3y,w hich contains ad imethylamino functionality,c ould have similar properties and be prone to deprotonation and racemization.…”