Organobismuth compounds

In a manner similar to phosphoms, arsenic, and antimony, the bismuth atom can be either tri- or pentacovalent. However, organobismuth compounds are less stable thermally than the corresponding phosphoms, arsenic, or antimony compounds, and there are fewer types of organobismuth compounds. For example, with R MX, R3MX2, R2MX3, and RMX, where M is a Group 15 (VA) element and X is a halogen, only the first two types have been prepared where M = Bi, but all four types are known where M = P, As, or Sb. 

The chemistry of organobismuth compounds has been described in several pubHcations (28—31). The use of organobismuth compounds, as well as organoantimony ones, in organic synthesis has been exhaustively reviewed (32). 

The secondary bismuthides discussed herein are useful for preparing several types of organobismuth compounds, eg, tertiary bismuthines and dibismuthines. 

Bismuth compounds were once employed for the treatment of amoebic dysentery, certain skin diseases, and several spirochetal diseases besides syphilis, but these substances are now seldom considered the dmgs of choice. Various insoluble preparations of bismuth, especially the subcarbonate, subnitrate, subgaHate, subcitrate, and subsahcylate, are stiU employed for the treatment of ulcers and other gastrointestinal disorders, even though use for these purposes is often supported largely by tradition. With a few possible exceptions, it is now difficult to justify the presence of bismuth compounds in a modem therapeutic armamentarium. A review of the biological activity of organobismuth compounds has been pubHshed (179). 

Transition-Metal Catalyzed C-C Bond Formation Using Organobismuth Compounds... 

Keywords Carbon-carbon bond formation Cross-coupling reaction Organobismuth compounds Transition-metal catalysis... 

Organobismuth compounds would have high potential as reagents for transition-metal catalyzed carbon-carbon bond forming reactions, because bismuth-carbon bonds are weak and can be easily cleaved by transition metals. The mean bond... 

There are several review articles that include descriptions of transition metal-catalyzed carbon-carbon bond formation of organobismuth compounds [5-10]. During the last decade, considerable development has been achieved in this area. However, there is no comprehensive review of this topic. Therefore, this review intends to comprehensively summarize transition-metal catalyzed carbon-carbon bond formation using organobismuth compounds. 

Heck-type arylation reactions of organobismuth compounds were first reported by Asano et al. in 1973 [11]. This article described the stoichiometric reaction of styrene, Ph3E (E = group 15 elements) and Pd(OAc)2 (Scheme 2). Ph3Bi afforded frans-stilbene only in 7% yield. The major product was biphenyl, which was... 

Scheme 5 Heck-type phenylation reaction with organobismuth compounds...

It is well established that metallic copper or copper salts efficiently catalyze N- and O-arylation reaction using pentavalent and trivalent organobismuth compounds [5-9, 24]. The C-arylation reaction of phenols and active methylene compounds using pentavalent organobismuth compounds are usually mediated by a base. However, in some cases, copper catalysts mediate C-arylation using pentavalent organobismuth compounds. 

Phenylation of terminal alkynes took place with Ph3BiF2 in the presence of Cu(I) chloride (Scheme 10) [26], Trimethylsilyl alkynes similarly worked as terminal alkynes. Other pentavalent organobismuth compounds such as Ph3BiC03 and Ph3BiCl2 were much less efficient than Ph3BiF2. Biphenyl was also formed as a by-product. It was proposed that the products were formed through reductive elimination of the intermediate Ph3Bi(C=CR1)2. 

Hypervalent organobismuth compounds 1 bearing a 2,6-pyridinedialkoxide ligand [43] were used for the cross-coupling reaction with aryl triflates (Scheme 28) [44], Phenylation using phenylbismuth compounds smoothly proceeded for the reactive... 

Organobismuth compound 1" was also used for the cross-coupling reaction with alkenyl triflates. CC Et-substituted cyclopentenyl triflate afforded the coupling product quantitatively, while the sterically hindered triflate gave the product in poor yield (Scheme 39) [44], Azabismocine 2 reacted with activated alkenyl chlorides to give the coupling products in moderate to good yields (Scheme 40) [54],... 

Transmetalation between the organopalladium(II) intermediate and organobismuth compounds to form diorganopalladium(II) intermediate [step... 

Fig. 2 Plausible mechanism for the cross-coupling reaction of organobismuth compounds with organic halides and triflates...

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