A Transition-Metal-Free Cross-Coupling Reaction of Allylic Bromides with Aryl- and Vinylboronic Acids

Abstract

A cross-coupling reaction between aryl-and vinylboronic acids and various allylic bromides proceeded without the use of a transition-metal catalyst to give the corresponding allylated products in moderate to good yields. The use of an inorganic base (KF or Cs 2 CO 3 ) and a small amount of water is crucial in obtaining good performance in the present transition-metal-free reaction.The palladium-catalyzed cross-coupling reaction of allylic halides, 1 esters, 2 and alcohols 3 with organoboronic acids provides a magnificent tool for organic synthesis. With this method, we generally rely on the use of precious transition metals, such as Pd complexes, as the catalyst. 4 In 2005, Kabalka and co-workers reported that a crosscoupling reaction of secondary allylic alcohols with alkenylboron dihalides proceeded in the absence of a transition metal, in which typically stoichiometric n-BuLi was used as a base. 5 This work suggests the possibility of a metal-free process in the cross-coupling reaction of organoboron compounds, however, to the best of our knowledge, no related studies on the transition-metal-free crosscoupling reaction of organoboron compounds with allylic halides have not been reported. 6,7 Herein, we wish to report a Suzuki-Miyaura-type crosscoupling reaction of allylic bromides with aryl-and vinylboronic acids that proceeded under metal-free conditions (Scheme 1). Concurrently with our work, Scrivanti and co-workers reported a similar metal-free cross-coupling reaction, in which they used potassium carbonate as a base. However, the reaction reported in this work has a broader scope and generality than expected from their work. 8 Scheme 1 A transition-metal-free cross-coupling reaction of allylic bromides with organoboronic acids

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

“…32 The change of CH 2 Cl 2 for CHBr 3 together with an increase in the reaction temperature to 90ºC has permitted the reaction of electron-rich arylboronic acids with arylpropargylic bromides (13-84% yields). 32…”

“…Using Cs 2 CO 3 (CH 2 Cl 2 : H 2 O 10 : 1, 60 1C, 18 h), Ryu et al have been able to extend the scope and generality of the reaction including the possibility of coupling allylic bromides with alkenylboronic acids (56-95% yields). 32 The change of CH 2 Cl 2 for CHBr 3 together with an increase in the reaction temperature to 90 1C has permitted the reaction of electron-rich arylboronic acids with arylpropargylic bromides (13-84% yields). 33…”

Transition‐Metal‐Catalyst‐Free Cross‐Coupling Reaction of Secondary Propargylic Acetates with Alkenyl‐ and Arylboronic Acids

“…In this reaction, a stoichiometric amount of n BuLi is used as a base to prepare (halovinyl)(propargyloxy)boron halides working as a key intermediate. In 2013, we reported the transition‐metal‐free cross‐coupling reaction of alkenylboronic acids and arylboronic acids with propargylic bromides in the presence of Cs 2 CO 3 as a base [Scheme (b)] , . Recently, Gandon and co‐workers found that the cross‐coupling reaction of propargylic alcohols with alkenylboronic acids proceeds efficiently by using Ca(NTf 2 ) 2 as a catalyst [Scheme (c)] .…”

Transition-Metal-Free Suzuki-Miyaura Coupling Reaction of Arylpropar­gylic Bromides with Aryl- and Alkenylboronic Acids

“…Recently, we 5 and the Scrivanti group 6 independently reported that a cross-coupling reaction between arylboronic acids and allylic bromides proceeded well without the use of a transition-metal catalyst to give the allylated products. Herein, we wish to report that a similar metal-catalyst-free reaction of arylpropargylic bromides with aryland alkenylboronic acids proceeded well to give propargylic products selectively (Scheme 1, eq.…”