Boron compounds arylation

Dimethylsulfoxide Acyl and aryl halides, boron compounds, bromomethane, nitrogen dioxide, magnesium perchlorate, periodic acid, silver difluoride, sodium hydride, sulfur trioxide... 

ArSnRs, and with arylmercury compounds. Aryl triflates react with arylbo-ronic acids ArB(OH)2, or with organoboranes, in the presence of a palladium catalyst, to give the arene in what is called Suzuki couplingCyclopropyl groups can be attached to aromatic rings by this reaction. Even hindered boronic acids give good yields of the coupled product. 

High ee values have also been obtained with organometallics," including organotitanium compounds (methyl, aryl, allylic) in which an optically active ligand is coordinated to the titanium," allylic boron compounds, and organozinc compounds. 

Cross-coupling reactions 5-alkenylboron boron compounds, 9, 208 with alkenylpalladium(II) complexes, 8, 280 5-alkylboron boron, 9, 206 in alkyne C-H activations, 10, 157 5-alkynylboron compounds, 9, 212 5-allylboron compounds, 9, 212 allystannanes, 3, 840 for aryl and alkenyl ethers via copper catalysts, 10, 650 via palladium catalysts, 10, 654 5-arylboron boron compounds, 9, 208 with bis(alkoxide)titanium alkyne complexes, 4, 276 carbonyls and imines, 11, 66 in catalytic C-F activation, 1, 737, 1, 748 for C-C bond formation Cadiot-Chodkiewicz reaction, 11, 19 Hiyama reaction, 11, 23 Kumada-Tamao-Corriu reaction, 11, 20 via Migita-Kosugi-Stille reaction, 11, 12 Negishi coupling, 11, 27 overview, 11, 1-37 via Suzuki-Miyaura reaction, 11, 2 terminal alkyne reactions, 11, 15 for C-H activation, 10, 116-117 for C-N bonds via amination, 10, 706 diborons, 9, 167... 

Aryl boron compounds, Ar,B(OH)3 (n = 1-3), bearing electron-withdrawing aromatic groups such as triarylboranes,... 

So far wc have used only protic acids to help oxygen atoms to leave, Lewis acids work well too, and the cleavage of aryl alkyl ethers with BBr3 is a good example. Trivalent boron compounds have an empty p orbital so they are very electrophilic and prefer to attack oxygen. The resulting oxonium ion can be attacked by Br in an S 2 reaction. 

The removal of all methyl ethers in 22 is performed by using the Lewis acid BBrs. This trivalent boron compound is very electrophilic and attacks the oxygen atom in aryl methyl ether 40 to give intermediate 41. Then, the resulting oxonium ion 42 is attacked by Br in an Sn2 reaction providing the free phenol 44 after aqueous workup. 

The synthesis of alkyl-, aryl-, and 1-alkenylboronic acids or their esters from Grignard or lithium reagents and trialkylborates is a classical and efficient method for making relatively simple boron compounds in large quantities (Scheme 2-6) [25]. The stereocontrolled synthesis of alkenylboronic acids and esters involves the reaction of a (Z)- or ( )-2-buten-2-ylmagnesium bromide with trimethyl borate [26]. 

Aryl and alkyl boron compounds have received significant research attention as building blocks in organic synthesis. One of the most straightforward methods for making such compounds is the reaction of a boronic acid ester with a Grignard reagent. However, the reaction... 

There are many other ways of making boronic acids and you are referred to Suzuki s review37 for a full discussion. A Suzuki coupling would occur if one of these boron compounds 236 was combined with an aryl or vinyl halide or triflate in the presence of Pd(0) and an oxy-anion. 

The dotted arrows on the transmetallation step 243 show only what joins to what and are not intended as a serious mechanism. Indeed a better mechanism might involve addition of RO to the boron atom before transmetallation. This process can be used to couple aryl to aryl, vinyl to vinyl, and aryl to vinyl (either way round ). As boron compounds are much less toxic than tin compounds, the Suzuki coupling is often preferred industrially. Because each partner in the coupling reaction is marked in a different way - one with a boron atom and one with a halide - we can be sure that we shall get cross coupling reactions only. 

Probably the best modem method for introduction of OF by electrophilic aromatic substitution is lithiation, reaction with a boronate ester, and oxidation.4 These are the same boron compounds that are used in Suzuki coupling (chapter 18) and are made the same way. In this example, selective mono-lithiation by Br/Li exchange on available tribromoanisole 39 (easily prepared by bromination of anisole or phenol) occurs ortho to the MeO group and reaction of aryl-lithium 39 with trimethyl borate gives the boronic ester 40. Peroxyacids such as peracetic acid are usually used for the final oxidation. 

Figure 5.1. Chiral boron compounds for asymmetric allyl addition to achiral primary, secondary, and tertiary alkyl, vinyl, and aryl aldehydes, and their typical enantioselectivities (a-e at -78°, g-j at -100°). (a) [17] (b) [18] (c) [19] (d) [19] (e) [20] (f-h) [21-24] (i-j) [25].

---