Palladium-catalyzed cross-coupling reactions of triarylbismuthanes with terminal alkynes under aerobic conditions

[Development of Reactivity for Organobismuth (III, V) Toward Sulfur-Containing Compounds]

Organobismuth compounds have been used in various areas of science, like biology and organic synthesis, because they are normally nontoxic and exhibit unique properties. Bismuth induces metallothionein production and is known to exhibit thiophilicity. However, few reports on the reactions between bismuth and sulfur compounds exist. This article reviews studies on the reactivity of bismuth (III and V) with sulfur compounds. A simple approach for the reaction of azole-2-thiones, which contains a heterocyclic ring, with triaryl bismuthines in the presence of a copper catalyst affords the S-arylated coupling product. When a palladium catalyst is used instead of a copper catalyst, desulfinative C-C bond formation occurs. These reactions indicate that trivalent bismuth compounds can be used as novel aryl sources. Triphenylbismuth dichloride, an organobismuth (V) reagent, successfully promotes the cyclodesulfurization of thioureas within short reaction times under mild conditions. The reaction affords N-substituted benzoxazol-2-amines in excellent yields. Tafamidis, a drug used to treat transthyretin amyloidosis, can be synthesized using this reaction.

Oxidative addition of Bi-C bonds to Pt(0): reaction of Pt(PEt3)3 with cyclic organobismuth compounds

The reaction of cyclic organobismuth compounds, 12-phenyl- and 12-chloro-5,6,7,12-tetrahydrodibenz[c,f][1,5]azabismocines, with Pt(PEt3)3 was examined. Oxidative addition of the exocyclic Bi-C bond to Pt(0) selectively took place in the reaction of the 12-phenyl derivative. Oxidative addition of the exocyclic Bi-Cl bond reversibly took place and was kinetically preferred, while endocyclic Bi-C bond oxidative addition products were thermodynamically favored and became the final products in the reaction of 12-chloro derivatives. These results demonstrate the oxidative addition of a Bi-C bond to a transition metal complex for the first time.