Coupling arylboronic acids with alkynes

Fukutani T, Hirano K, Satoh T, Miura M (2009) Synthesis of highly substituted naphthalene and anthracene derivatives by rhodium-catalyzed oxidative coupling of arylboronic acids with alkynes. Org Lett 11 5198-5201. doi 10.1021/ol9021172... 

Coupling of Arylboronic Acids with Alkynes. The oxidative coupling of arylboronic acids with internal alkynes effectively proceeded under [Cp RhCl2]2-Cu(OAc)2 catalytic system in a 1 2 manner via C-H bond activation to produce the corresponding product (eq 24) It is noted that the electron-deficient phenyl-boronic acids were less reactive in the present reaction. 

Zou, G. Zhu, J. Tang, J. Cross-coupling of arylboronic acids with terminal alkynes in air. Tetrahedron Lett. 2003, 44, 8709-8711. 

The transmetallation with organoboron reagent precedes the carbometallative addition of the arylrhodium intermediates 394 to the unsaturated substrate, and the intermediate alkenylrhodium species 395 then undergo hydrolysis to close the catalytic cycle with regeneration of the catalytically active species 393 and formation of the observed enamide products. An intermolecular carborhodation event was proposed to occur in a three-component coupling of arylboronic acids with disubstituted alkynes in the presence of methyl acrylate (Scheme 10.135) [113]. 

A variation of this aryl-alkyne coupling reaction reacted methylthioalkynes (R—C=C—SMe) with arylboronic acids and a palladium catalyst to give the aryl alkyne (R—C=C—Ar). 1-TrialkyIsilylalkynes (R3Si—C=C—R ) were coupled... 

Cationic palladium-catalyzed addition of arylboronic acids to nitriles for the formation of benzo[h]furans was reported <06OL5987>, an example of which is illustrated in the following scheme. The palladium-catalyzed cross coupling of alkynes with appropriately substituted aryl iodides for the synthesis of substituted dibenzofurans in moderate to excellent yields was also achieved <06JOC5341>. The benzo[fc]furan core of heliannuls G and H were constructed by a palladium-catalyzed Ji-allyl cyclization reaction <06TL7353>. The palladium-catalyzed oxidative activation of arylcyclopropanes was applied to the synthesis of 2-substituted benzo[Z>]furans <06OL5829>. 

Under the reaction conditions, phenylacetylene was found to be a much more reactive coupling partner than arylboronic acids in the analogous Suzuki-Miyaura coupling, as in addition to the desired product (38), alkynylation and further addition reactions occurred with a variety of transient palladium(II) species (Scheme 27). Despite these undesired side reactions, Catellani was able to fine-tune the reaction conditions to form predominantly product 38 or 39. The formation of the desired product 38 (and suppression of product 39) is promoted by acceleration of norbomene carbopalladation by KOAc [47] and by using an excess of alkyl halide affording several structurally similar unsymmetrical alkyne products in good yields (Scheme 28). 

Halopyridines or pyridinyl triflates take part in palladium-catalysed reactions -Heck, carbonylation, and coupling reactions, for example with alkynes, or in Suzuki reactions with arylboronic acids,and cyclopropylboronic acids. 

Work on mechanistic details is in progress, but the present transformation may result from a catalytic cycle that involves the transmetalation between the hydroxo-rhodium(I) 4 and arylboronic acid to give the arylrhodium(I) species 5, and the insertion of enone to the Ar-Rh bond. The hydrolysis of the rhodium(I) enolate with water reproduces the hydroxorhodium species, as shown in Figure 1. The arylrhodium(I) complexes are unstable such as to preclude isolation in pure form, but they have been reasonably speculated to be the key intermediates carrying out various coupling reactions with organic halides and the addition to alkenes and alkynes. 

Recently, Zhou and Larock [57] have also used a domino Mizoroki-Heck/Suzuki process in their syntheses of several tamoxifen analogues. They described a three-component coupling reaction of readily available aryl iodides, internal alkynes and arylboronic acids to give the expected tetrasubstituted olefins in good yields. For instance, the treatment of a mixture of iodobenzene, alkyne 92 and phenylboronic acid with catalytic amounts of PdCl2(PhCN)2 gave 93 in 90% yield. In this process, substituted aryliodides and... 

In 2006, the group of Artok showed that 5-aryl-2(5H)-furanones could be prepared in moderate to good yields by a rhodium-catalyzed carbonylative arylation of internal alkynes with aryl boronic acids (Scheme 1.9a) [22]. a,P-Unsaturated ketones (chal-cone derivatives) were formed as the major product when some TFA (trifluoroacetic acid) was added under the same reaction conditions [23a]. By varying the catalytic system, indanones could be produced as the main product [23b]. The chemical behavior of terminal alkynes is different, and either a,P-unsaturated ketones or furans starting from propargylic alcohols can be achieved (Scheme 1.9b) [24, 25]. In the case of vinyl ketones, 1,4-diketones were obtained by rhodium-catalyzed coupling of arylboronic acids in the presence of 20-40 bar of CO [26]. In 2007, Chatani demonstrated that indenones could be accessed by a carbonylative rhodium-catalyzed cyclization of alkynes with 2-bromophenylboronic adds (Scheme 1.9c) [27]. Here, the key intermediate is a vinylrhodium(I) spedes that is formed by transmetaUation of RhCl with 2-bromophenylboronic acid followed by insertion of... 

Reddy and collaborators reported a new one-pot, three-component procedure toward the synthesis of novel 4-phenyl-2-[3-(alkynyl/alkenyl/aryl) phenyl] pyrimidine libraries starting with the Michael addition of enaminone 64 with 3-bromobenzimidamide hydrochloride (65) (Scheme 28) (13S75). This was followed by a cyclization, an isomerization, a dehydration, and a subsequent Sonogashira reaction with terminal alkynes or a Suzuki reaction with arylboronic acids or a Heck coupling reaction with alkenes. 

Yu et al. combined the Suzuki coupling with an alkyne insertion in aryl iodides and developed an efficient route to seven-membered rings with a stereodefined exocyclic double bond [43] (Scheme 6.25). Various aryl iodides and arylboronic acids bearing electron-donating or electron-withdrawing groups could be introduced efficiently to the palladium-promoted catalytic system. 

In 2003, Zhu and Zhang reported a palladium-catalyzed cyclization/arylation cascade reactions of enynes with arylboronic acids leading to cyclic products with a stereodefined exocyclic double bond [44] (Scheme 6.26). Several types of enynes can be anployed carbon, oxygen, and nitrogen tethers [Y=C(COjMe)j, O, Ts], and alkyl- and arylalkynes are well tolerated. The author proposed a plausible mechanism, probably involving a Jt-allylpalladium complex which is formed from the aUyUc halide, followed by insertion of the alkynes and Suzuki coupling reactions. 

Details on oxidation and reduction reactions mediated by [(NHC)Pd] complexes can be found in Chapters 12 and 13, respectively. Further reports of interest disclosed include diboration of alkenes catalysed by a pincer complex, deuteration of C-H bonds with an N,0-functionalised NHC complex, and an intriguing Suzuki-type reaction of [FeI(Cp)(CO)2] with arylboronic acids. A number of useful C-heteroatom coupling reactions have also been reported recently, including alkene hydrophosphination and alkyne silylation. ... 

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