Hydroarylations and hydroalkenylation

In the reaction of Q,/3-unsaturated ketones and esters, sometimes simple Michael-type addition (insertion and hydrogenolysis, or hydroarylation, and hydroalkenylation) of alkenes is observed[53,54]. For example, a simple addition product 56 to methyl vinyl ketone was obtained by the reaction of the heteroaromatic iodide 55[S5]. The corresponding bromide affords the usual insertion-elimination product. Saturated ketones are obtained cleanly by hydroarylation of o,/3l-unsaturated ketones with aryl halides in the presence of sodium formate, which hydrogenolyses the R—Pd—I intermediate to R— Pd—H[56]. Intramolecular hydroarylation is a useful reaction. The diiodide 57 reacts smoothly with sodium formate to give a model compound for the afla-toxin 58. (see Section 1.1.6)[57]. Use of triethylammonium formate and BU4NCI gives better results. 

C. i. Trapping with Formate Anions Hydroarylation and Hydroalkenylation Reactions... 

Several terminal and internal acetylenes have been subjected to hydroarylation and hy-droalkenylation conditions. With terminal acetylenes trisubstituted alkenes are obtained. Most of the hydroarylation and hydroalkenylation chemistry, however, has been performed with variously substituted internal acetylenes. 

Ruthenium(II) biscarboxylate complex (101) has been reported to catalyse hydroaryla-tions of unactivated alkenes RCH=CH2 with Ar-H through C-H bond activation, giving rise to ArCH2CH2R. ° The same complex is capable of promoting hydroarylations and hydroalkenylations of methylenecyclopropanes (107) with the a-pyridyl derivative (106) to produce (108). ° ... 

C.i.a. Sequential Hydroarylation (Hydroalkenylation)/Cyclization. Since the cis stereochemistry of addition pushes the substituents of the acetylenic moiety to the same side of the olefinic double bond, a cyclization reaction can follow the addition step when these substituents bear suitable nucleophilic and electrophilic centers, and the whole process resembles a valuable straightforward methodology for the preparation of cyclic compounds (Scheme 20). Cyclization can occur under hydroarylation(hydroalkenylation) conditions—either before or after the substitution of the carbon-hydrogen bond for the carbon-palladium bond—or by subjecting the isolated hydroarylation(hydroalkenylation) product to suitable reaction conditions. This strategy has been employed successfully to develop new routes to various heterocycles. 

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