Arylboronic acids alkenes

Rhodium-catalyzed Heck-type coupling of boronic acids with activated alkenes was carried out in an aqueous emulsion.82 The couplings between arylboronic acids and activated alkenes catalyzed by a water-soluble tm-butyl amphosrhodium complex were found to progress at room temperature to generate Heck-type products with high yields and excellent selectivity. It was necessary to add two equivalents of the... 

Another example involves dioxygen-promoted regioselective oxidative Heck aryla-tions of electron-rich alkenes with arylboronic acids (Scheme 4.12c). For this, two types of microwave reactors have been used. In a single-mode instrument (1 mmol run 25 mL vessel), the Heck arylation was performed by first pre-pressurizing the... 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

Very recently, Murakami has published an Rh(i)-catalyzed cyclization of 1,6-enynes triggered by addition of arylboronic acids (Scheme 74).281 Initial carborhodation of the alkyne moiety is followed by insertion into the alkene moiety. /3-Alkoxy elimination provides the final product 289 in good yield and regenerates the catalyst species. 

In the Suzuki reaction, an aryl iodide or synthetic equivalent thereof is coupled with an arylboronic acid or a borane, again using palladium(O) as the catalyst. This reaction is usually used to prepare biaryls, and few examples have been reported of the solid-phase synthesis of alkenes by means of a Suzuki coupling (Table 5.8). 

The Pd-catalysed three-component coupling of readily available aryl iodides (53), internal alkynes (54), and arylboronic acids (55) has been developed as a one-step, regio- and stereo-selective route to tetrasubstituted alkenes (56) in good to excellent yields, although electron-poor aryl iodides and dialkylalkynes normally afford only low yields under standard reaction conditions. The right combination of substrates and reaction conditions has been shown to be important for attaining high yields. The presence of water substantially increased the yields of the desired tetrasubstituted... 

Arylboronic acids added to alkynes975-977 and activated alkenes such as norbornene978-981 or 2-vinylpyridines982 in the presence of a rhodium(i) catalyst. Addition of arylboronic acids to allenes was reported to be catalyzed by Pd(PPh3)4 in the presence of AcOH.983... 

The addition of arylboronic acids to oxabicyclic alkenes yielded ring-opening products via insertion-elimination process.979,980 Chiral DPPF-P(/-Bu)2 was identified as the ligand giving the best reactivity and enantioselectivity (Equation (221)). 

The boronate esters used for Suzuki reactions can be synthesized from commercially available alkyl-, vinyl-, and arylboronic acids. Alkyl and vinyl boronate esters are also synthesized by the hydroboration of double and triple bonds, similar to the hydrobora-tion of alkenes and alkynes in Chapters 8 and 9. Note that the boron atom generally adds to the less substituted end of a double or triple bond. Also, the B and H add to the same side of a triple bond (syn addition) to give a trans alkenylboronate ester. 

Certain pyrones react with active hydrogen compounds in a quite different way they display their alkenic character by participating in Michael reactions, thus coumarin itself gives 316 with malonate anion, and coumarins 317 react with arylboronic acids catalyzed by rhodium giving 318 in greater than 99% ee <2005OL2285>. 

Aryl diazonium salts can be used coupled with alkenes in a Heck-Uke reaction (12-15)7 Other reactive aryl species also couple with aryldiazonium salts in the presence of a palladium catalyst7 A Suzuki type coupling (13-9) has also been reported using arylboronic acids, aryldiazonium salts and a palladium catalyst/ ... 

Arylboronic acids (p. 905) add to alkynes to give the substituted alkene using a rhodium catalyst. Allenes react with phenylboronic acid and an aryl iodide, in the presence of a palladium catalyst, to give a substituted alkene. 2-Bromo-1,6-dienes react with phenylboronic acid with a palladium catalyst to give a cyclopentane with an exocyclic double bond and a benzyl substituent. ... 

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. 

Table 1 Applications of Catalysts on Soluble Supports. Isolated yields of products from Heck and Suzuki couplings using various iodoarenes and various alkene and arylboronic acid substrates under thermomorphic conditions with the SCS-Pd(II) catalyst 115 ...

Hydroboration of alkenes and alkynes is an established preparative method of alkyl- and alkenylboranes. Arylboranes, arylboronic acids and their esters (boronates) are prepared from aryllithium or Grignard reagents. 

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