Bromide compounds halide hydrogenolysis

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. 

Boron substituents in the [l,3,2]diazaborolo[l,5- ]pyridine derivative 109 were studied. This compound was obtained via reduction of its precursor 108 with sodium amalgam (Scheme 27). The bromide attached to the boron atom was further displaced with various halide, hydride, sulfur, and carbon nucleophiles <2001JCD378>. [l,2,5]thiadiazolo[2,3- ]pyridine derivative 110 was deprotected (R = Cbz to R=H) by classical hydrogenolysis <2002AGE3866>. 

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