Double cross-coupling reactions

The addition of diboron compounds to alkynes is an excellent method for the synthesis of c -diboryl alkenes (Scheme 2-11) [34], The reaction is catalyzed by Pt(PPh3)4 at 80 and works well not only with terminal but also with internal alkynes. The addition of the Si-B [35] or Sn-B [36] bonds to alkynes gives mixed-metal alkenylboron reagents which have potential ability for use in the stepwise double cross-coupling reaction at both metallated carbons. 

Achieving a one-pot double cross-coupling reaction on a dihaloaromatic substrate... 

Although symmetrically structured, ( )-l,2-bis(stamiyl)ethylenef can be either selectively monosubstituted or exhaustively disubstituted. The available results indicate that, like halogens, the second Sn group accelerates the Pd-catalyzed cross-coupling. Some very attractive applications of both (E)- and (Z)-l,2-bis(stannyl)ethylenes include their Pd-catalyzed double cross-coupling reactions with a,-diiodo compounds to prodnce macrocycles in the syntheses of rapamycin and dynemicin discussed in Sect, m.2.18. 

Shimizu and Hiyama [129] reported that the palladium-catalyzed double-cross-coupling reaction of 9-stannafluorenes 213 with 1,1-dihaloethylene 214 yields the dibenzofulvene 215 (Scheme 6.57a). The 9-staimafluorene 213, an equivalent of a 1,4-dimetalated reagent, is available from the corresponding 2,2 -dihalobiphenyls. The reaction was applied to the synthesis of the jt-extended fulvalene derivative 217 from 216. The former is a stable benzaimulated Chichibabin hydrocarbon possessing an open-shell diradical character (Scheme 6.57b) [130]. 

Double Cross-coupling Reaction of Dimetal Compounds... 

SCHEME 22.29 Double cross-coupling reaction of 1,2-diborylaIkenes with 2,2 -dibromobiaryls. 

Double cross-coupling reactions of 1,1-diboryl-l-alkene 148 with 2,2 -dibromobiphenyl [58] and 1,2-diborylbenzene 150 with 1,8-dibromonaphthalene 151 [59] were also possible with the aid of a palladium catalyst and a base (Scheme 22.35). 

Stannafluorenes 156 smoothly underwent double cross-coupling reaction with 1,2-dibromoarenes 157 in the presence of Pd(PtBu3)2 catalyst in THF at 60 °C to give annulated products 158 in good to excellent yields (Scheme 22.37) [61]. Thus, 156 are synthetically equivalent to 2,2 -distannylated biaryls. The products of type 158 include triphenylene derivatives and phenanthrenes fused by heteroaromatic rings such as thiophene and pyridine. The fusion mode of a thiophene ring was easily... 

SCHEME 2236 Double cross-coupling reaction of 2,2 -bis(trimethylstannyl)binaphthyl and 1,2-diiodobenzene. 

SCHEME 22.37 Double cross-coupling reaction of 9-stannafluorenes with 1,2-dibromoarenes. 

SCHEME 22.40 Copper-mediated double cross-coupling reaction of l,4-dilithio-l,3-butadienes with 1,2-diiodoarenes. 

Double cross-coupling reaction of 1,2-dihaloarenes with 9-stannafluorene takes place using a palladium catalyst and gives triphenylene cores in high yields (Scheme 3-219). In view that 2,2 -bis(trimethylstannyl)biphenyl is hard to apply to the double... 

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