Boronic acids organo

Besides lithium, zinc and tin derivatives (see Scheme 13), other types of organo-metallic reagents have been used as nucleophiles in related processes (Scheme 17). Yoon described a 3CR, resembling a Petasis process, in which isoquinolines or quinolines are reacted with activating agents and boronic acids to yield the expected a-arylated dihydroazines 111 [108]. 

Synthetically attractive arylation and alkenylation of a-bromoalkenyl phosphonates (471) with organo-boranes and -borates have been performed. Arylation was successful with the aryl boronic acids and a palladium catalyst, while alkenylation proceeded best with alkenyl borates, and a nickel catalyst (Figure 87). ... 

A/ "-Hexamethylguanidiniuin chloride (542 Scheme 100) is readily reduced by means of NaH in the presence of sodium alkoxyaluminates, boronic acid esters or aluminum alkoxides J Organo-metallic derivatives such as phenyllithium, 2-thienyllithium or 2-furanyllithium or sodium acetylides add to the guanidinium salt to give the corresponding orthoamides. From tetrakis(dimethylamino)methane and phenylacetylene l-phenyltris(dimethylamino)-l-propyne (543 equation 242) was prepared. ... 

Because the initial oxidative addition of Pd(0) is faster with the aryl bromide than the vinyl bromide, the vinyl groups can be selectively coupled to give 78, by using one equivalent of organo-stannane or boronic acid. Coupling with a second equivalent of organo-... 

Boronates (i.e. boronic acids and esters) are usually prepared by one of two methods reaction of organo-lithiums or Grignard reagents with a trialkyl borate, usually tri-Ao-propyl borate, or palladium-catalysed boronation. 

Several methods are available for the synthesis of boronic acids and their esters (see also refs. 1-8, 5.3.2.4). Trialkoxyboranes react with polar organometallics. Organo-magnesium halides and organolithiums are most often used. 

Organo derivatives of boroxine are much more stable than boroxine or its halo derivatives. They are formally anydrides of boronic acids, and most are prepared nearly quantitatively by dehydration of the corresponding acid ... 

The attractiveness of organo-9-BBN derivatives as coupling partners is largely due to their accessibility via the hydroboration of alkenes and alkynes on the other hand, they suffer from the drawbacks of not being easily manipulated in air or commercially available. In contrast, boronic acids are air-stable, and a large number and variety are commercially available. Consequently, the development of methods for cross-coupling alkyl electrophiles with boronic acids is undoubtedly an important objective. 

The most important palladium-catalyzed processes include Heck vinylation of halides and sulfonates and various cross-coupling reactions in which a nucleophilic intermediate (stannane, organo-zinc halide or boronic acid) is coupled with an electrophile (halide or sulfonate). These coupling reactions are usually restricted to arylation and vinylation because of the tendency of alkylpalladium species to undergo elimination. The pyrrole and indole rings can participate in cross-coupling as either the nucleophilic or electrophilic component. 

Darses and co-workers have published a series of papers on the synthesis of stereo-defined trisubstituted alkenes by the coupling of readily available unreactive MBH adducts with either organoboronic acids or potassium tri-fluoro(organo)borates in the presence of a rhodium complex via a reaction pathway involving a 1,4-addition/p-hydroxy elimination mechanism. Compared with the aforementioned Pd-catalyzed cross-coupling reaction, this reaction does not need the activation of the hydroxyl group with acetate or carbonate therefore it is more desirable, particularly in terms of atom economy. For the MBH adducts derived from methyl acrylates, the initial reported catalyst, [ Rh-(cod)Cl 2], was active at 50 °C for boronic acids and at 70 °C... 

Additionally, the protocol proved not only applicable to aryl-substituted organo-metallics, but also enabled the use of an alkenyl boronic acid. Further, aldimine 11 was regioselectively arylated with this catalytic system, yielding-after subsequent hydrolysis-aldehyde 12 (Scheme 9.6) [17]. 

Other Applications. DBBS has been used for the synthesis of boronic acid-based calix[6]arene) (acts as a singlechain surfactant at the air-water interface), 14-vertex carborane, and 14-vertex metallocarborane, 14- and 15-vertex ruthenacarboranes, and organo-tricyanoborates as tectons. ... 

A highly regio- and stereoselective palladium(O) catalyzed addition of organo-boronic acids to 1,2-allenylphosphonates (134) in the presence of acetic acid forming tri- and tetrasubstituted l( )-alkenylphosphonates (135) has been reported (Scheme 47). ... 

Scheme 4.32 Addition of organo-boronic acids to aldehydes catalyzed by Rh(acac)(CO)2/dppf.

Three-component Petasis reactions among salicylaldehydes, amines, and organo-boronic acids have been catalysed with a chiral thiourea BINOL catalyst to prepare alkylaminophenols with yields and ee values of up to 92% and 95%, respectively. Formation of amino esters Et02CCH(Ar)NR2 by Petasis combination of Et02CH0, R2NH, and ArB(OH)2, catalysed by Cu(I), is believed to involve transmetallation from boron to copper from which Ar is delivered intramolecularly to the iminium group of the coordinated intermediate. ... 

Scheme 3.47 Copper-catalyzed cross-coupling of organo-thiolimides with boronic acids.

Since the publication of the seminal paper of Miyaura et al. [31, 32] in 1979, some issues concerning the mechanistic details of the transmetalation step in the Suzuki-Miyaura reaction have appeared. For example, the role of the base was not clear and several proposals were made [67]. In order to cast light on this issue, many experimental studies were carried out [31, 32, 68, 69]. Particularly, two main pathways consisting on the base attacking hrst either the palladium complex or the organo-boronic acid were proposed to account for the effect of the base in this step (Fig. 3.6). 

Catalysts. The choice of the proper catalyst for an esterification reaction is dependent on several factors (43—46). The most common catalysts used are strong mineral acids such as sulfuric and hydrochloric acids. Lewis acids such as boron trifluoride, tin and zinc salts, aluminum haHdes, and organo—titanates have been used. Cation-exchange resins and zeoHtes are often employed also. 

The second well-known and much-used carbon-carbon bond forming reaction is a [4 + 2]-cycloaddition, the Diels Alder reaction. Very many chiral Lewis acid catalysts have been used to promote this reaction and a pot-pourri of organo-aluminium, -boron and -copper catalysts are described, in brief, below. 

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