Arylborone formation

Drivers for Performing Arylboron Formation in Micro Reactors... 

Beneficial Micro Reactor Properties for Arylboron Formation... 

Arylboron Formation Investigated in Micro Reactors Organic synthesis 40 [OS 40] Formation of phenyl esters of boronic add... 

Carbonnelle, A.-C., Zhu, J. A Novel Synthesis of Biaryl-Containing Macrocycles by a Domino Miyaura Arylboronate Formation Intramolecular Suzuki Reaction. Org. Lett. 2000, 2, 3477-3480. 

Yamamoto and co-workers reported abase- and ligand-free palladium (II) catalysed method, in methanol at room temperature and under air [49], While the conversion of arylboronic acids bearing an electro-donating group was very efficient, the presence of an electro-withdrawing substituent led to lower conversions. To solve this problem and also prevent the fast formation of palladium black, Yamamoto and co-workers described a new approach where the reaction was catalysed by NHC-bearing complexes 21 and 22 in the presence of an oxidant (Fig. 7.4) [50]. The best results were obtained when complex 21b was used in methanol at room temperature, in the presence of a small excess of p-benzoquinone. 

In a reaction similar to the (>-alkoxide elimination reactions seen with zir-conocenes, catalytic Rh(OH)(cod)2 and 2 eq. of arylboronic acids gave cyclic products 165 from enynes 166 (Scheme 35) [100]. In this reaction, transmet-allation of Rh - OR with B - Ph gave Rh - Ph species 167, which inserted into the alkyne, cyclized to 168, and finally underwent [>-alkoxidc elimination to provide Rh-OCH3. This reaction is limited to the formation of five-membered rings, but it can also undergo cascade type reactions of enediynes to give multicyclic products [100]. 

For the domino transition metal-catalyzed synthesis of macrocycles, conditions must be found for two distinct cross-coupling reactions, of which one is inter- and the other intramolecular. For this purpose, Zhu s group [115] has developed a process of a Miyura arylboronic ester formation followed by an intramolecular Suzuki reaction to give model compounds of the biphenomycin structure 6/1-232 containing an endo-aryl-aryl bond. 

Cationic palladium-catalyzed addition of arylboronic acids to nitriles for the formation... 

Vinyl- or arylboronic acids also react with allenes, affording 1,3-dienes or styrene derivatives, respectively.89 This palladium-catalyzed addition proceeds with good regioselectivity and high stereoselectivity in favor of the formation of (ft)-trisubstituted isomer. 

Rhodium(i) complexes are excellent catalysts for the 1,4-addition of aryl- or 1-alkenylboron, -silicon, and -tin compounds to a,/3-unsaturated carbonyl compounds. In contrast, there are few reports on the palladium(n) complex-catalyzed 1,4-addition to enones126,126a for the easy formation of C-bound enolate, which will result in /3-hydride elimination product of Heck reaction. Previously, Cacchi et al. described the palladium(n)-catalyzed Michael addition of ArHgCl or SnAr4 to enones in acidic water.127 Recently, Miyaura and co-workers reported the 1,4-addition of arylboronic acids and boroxines to a,/3-unsaturated carbonyl compounds. A cationic palladium(n) complex [Pd(dppe)(PhCN)2](SbF6)2 was found to be an excellent catalyst for this reaction (dppe = l,2-bis(diphenyl-phosphine)ethane Scheme 42).128... 

Simiraly, alkynones undergo arylative cyclization with arylboronic acids in the presence of a rhodium catalyst (Equation (49)).400 When acetylenic /3-keto esters are employed as shown in Equation (50), arylative cyclization (formation of cyclobutanols) and subsequent, facile acid-catalyzed bond cleavage take place to give <5-keto esters.401 Ring expansions of cyclic [3-keto esters are also possible according to this reaction. 

Acetylenic esters react with arylboron reagents in the presence of rhodium diphosphine catalyst to give cyclic ketones.409 Equation (61) shows an example which may involve ortfe-metallation and ketone formation. A catalytic, enantioselective reaction was also achieved (Equation (62)). These processes presumably involve unprecedented addition of organorhodium species to the ester carbonyl group. 

The carbonylative cross-coupling reactions of haloazines are usually run under an ambient to moderate carbon monoxide pressure. Arylboronic acids or tetraarylborates are usually the reagent of choice due to their robustness and availability. The coupling of 2-iodopyridine and phenylboronic acid under ambient CO pressure, for example, led to the formation of 2-benzoylpyridine in good yield (7.66.),87... 

Reactions between a representative range of alkyl- and aryl-amines and of aliphatic and aromatic acids showed that the direct formation of amides from primary amines and carboxylic acids without catalyst occurs under relatively low-temperature conditions (Scheme 1). The best result obtained was a 60% yield of N-bcnzyl-4-phenylbutan-amide from benzylamine and 4-phenylbutanoic acid. For all these reactions, an anhydride intermediate was proposed. Boric and boronic acid-based catalysts improved the reaction, especially for the less reactive aromatic acids, and initial results indicated that bifunctional catalysts showed even greater potential. Again, anhydride intermediates were proposed, in these cases mixed anhydrides of carboxylic acids and arylboronic acids, e.g. (I).1... 

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