Cross-coupling Reaction of Diborons

In the synthesis of 1-alkenyIboronic acids or esters from the corresponding magnesium or lithium reagents, it is often difficult to retain the stereochemistry of start- 

PdCl2(PPh3)2/2PPh3 PdCl2(PPh3)2/2PPh3 Pd(dba)a/2AsPh3 

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The traditional synthesis of organoboron compounds from organic halides is based on the reaction of trialkyl borates with Grignard or lithium reagents. However, the cross-coupling reaction of diboron solves the difficulties associated with the use of Mg/Li compounds. The cross-coupling reaction of diborons... 

Scheme2.1 Organoboron compounds via cross-coupling reactions of diborons.

The cross-coupling reaction of diborons—particular with bis(pinacolato)diboron (see also Figure 5-17)—with organic halides (iodides,bromides, and chlorides... 

Diborons and HBpin have been found to act as the boron nucleophiles in the presence of a base for the palladium-catalyzed cross-coupling reaction of organic electrophiles. Both reactions provide a simple and direct method for the borylation of organic halides and triflates. 

Very recently, arylboronic esters have been directly obtained from aiyl halides via the cross-coupling reaction of (tetraalkoxy)diboron (Scheme 2-7) [28]. The reaction tolerates various functional groups such as ester, nitrile, nitro, and acyl groups. 

Ishiyama, T., Itoh, Y., Kitano, T., Miyaura, N. Synthesis of arylboronates via the palladium(0)-catalyzed cross-coupling reaction of tetra(alkoxo)diborons with aryl trifiates. Tetrahedron Lett. 1997, 38, 3447-3450. 

Ishiyama, T., Ishida, K., Miyaura, N. Synthesis of pinacol arylboronates via cross-coupling reaction of bis(pinacolato)diboron with chloroarenes catalyzed by palladium(0)-tricyclohexylphosphine complexes. Tetrahedron 2001, 57, 9813-9816. 

The Pd-catalyzed cross-coupling reaction of the pinacol ester of diboronic acid with aryl halides and triflates gives a direct procedure for various functionalized arylboronic esters (Table 6), which are useful for highly efficient and selective carbon-carbon bond formation by Pd catalysts (Sect. III.2.2). The combination of PdCl2(dppf) with KOAc (and dppf) is effective in the carbon-boron bond formation. KOAc is essential not only to accelerate the reaction but also to prevent the formation of biaryl by-products. 

The Pd-catalyzed cross-coupling reactions of metal nucleophiles with carbon electrophiles are of considerable value for the regio- and stereocontrolled synthesis of functionalized organometalhc compounds, in particular, silanes, stannanes, and boranes, which are important reagents for Pd-catalyzed carbon-carbon cross-coupling as shown in Sects. in.2.2-in.2.4. Symmetrical bimetallic compounds such as disilanes, distannanes, and diborons are usually used as metal nucleophiles. The present metallation is applicable to aryl, benzyl, vinyl, acyl, and aUyl (Sect. V.2.3.3) electrophiles. 

Ishiyama T, Itoh Y, Kitano T, Miyaura N (1997) Synthesis of Arylboronates via the Palladium(0)-Catalyzed Cross-Coupling Reaction of Tetra(alkoxo)diborons with Aryl Inflates. Tetrahedron Lett 38 3447... 

Takagi J, Takahashi K, Ishiyama T, Miyaura N (2002) Palladium-Catalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with 1-Alkenyl Halides orTriflates Convenient Synthesis of Unsymmetrical 1,3-Dienes via the Borylation-Coupling Sequence. J Am Chem Soc 124 8001... 

The palladiuin-catalyzed cross-coupling reaction of tetra(alkoxo)di-borons provides a method for direct boiylation of aryl iodides, bromides, or triflates (Eq. 13). Because bis(pinacolato)diboron is... 

Ready availability of arylboronic esters from aryl halides or triflates (Eqs. 13 and 14) now offers a one-pot, two-step procedure for synthesizing unsymmetrical biaryls. The cross-coupling reaction of bis(pinaco-lato)diboron with triflate in dioxane is followed by a subsequent coupling with another triflate in the presence of K3PO4 to furnish an unsymmetrical biaryl from two triflates (Eq. 63). The synthesis from two different... 

It is also possible to synthesize chiral PPPs as Scherf et al. reported [72]. They are composed of chiral cyclophane subunits, made by a Suzuki-type aryl aryl cross-coupling reaction of the corresponding diboronic acid and dibromo derivatives. The monomers containing cyclic -O-C10H20-O- loops were separated into the pure enantiomers and used to generate the corresponding stereoregular iso- and syndiotactic PPP-derivatives (Scheme 26). The isotactic derivative possesses a chirality of its main chain. 

The Pd-catalyzed cross-coupling reaction of the pinacol ester of diboronic acid with aryl halides and triflates gives a direct procedure for various functionalized arylboronic esters (Table which are useful for highly efficient and selective carbon-carbon bond... 

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