The Hiyama–Denmark coupling is an organosilicon-mediated, transition-metal-catalyzed cross-coupling reaction and an important extension of the classical Hiyama coupling. In this reaction, organosilanols or silanolates typically serve as the organic group donors and, under catalysis by palladium or other transition metals, undergo coupling with electrophiles such as organic halides to achieve efficient construction of carbon–carbon (C–C) bonds.

Unlike the classical Hiyama coupling, which generally relies on fluoride ion activation of the organosilicon reagent, the Hiyama–Denmark coupling can activate silanols through a base to form reactive silanolates, thereby promoting the transmetalation process and providing another important strategy for the activation of organosilicon reagents. This reaction expands the application of organosilicon reagents in modern organic synthesis and offers a more flexible synthetic method for the selective construction of carbon–carbon bonds in complex molecules. One of its key advantages is that it generally does not require the use of fluoride as an activator, which helps improve compatibility with certain fluoride-sensitive functional groups and silyl protecting groups, and provides a new synthetic tool for the synthesis of complex natural products, the construction of drug molecules, and the preparation of functional organic materials.

Reagents: Basic activators (e.g., KOSiMe₃, NaOH, KOH), palladium catalyst
Reactants: Organosilanols or organosilanolates, organic halides
Products: Compounds with new C–C bonds
Reaction type: Cross-coupling reaction

Experimental Tips

1. The reaction is applicable to a wide range of alkenyl, alkynyl, aryl, and heteroaryl dimethylsilanols. Among these, alkenylsilanols generally exhibit higher reactivity and can undergo efficient coupling under mild conditions; the transmetalation of arylsilanols is relatively slower and typically requires stronger base activation conditions or higher reaction temperatures.

2. The choice of base depends primarily on the structure of the organosilanol and its deprotonation characteristics:
   • Alkenyl/alkynyl dimethylsilanols: The mild base KOSiMe₃ is typically employed, generating the reactive silanolate in situ through reversible deprotonation.
   • Aryl dimethylsilanols: Cs₂CO₃·xH₂O and similar bases are typically used to promote silanolate formation; some substrates require heating in toluene to approximately 90 °C.
   • Electron-rich heteroarylsilanols: For substrates prone to side reactions such as protodesilylation, NaH or NaHMDS can be used for rapid, irreversible deprotonation to pre-form the corresponding metal silanolate.

3. Common solvents include DME (1,2-dimethoxyethane), THF, toluene, and dioxane. Alkenylsilanols can typically react in DME at room temperature, whereas arylsilanols often require heating in toluene or dioxane. The specific temperature should be optimized according to substrate reactivity, catalyst system, and reaction selectivity.

4. Commonly used palladium catalysts include Pd(dba)₂, Pd₂(dba)₃, and [allylPdCl]₂, with the phosphine ligand selected according to the substrate type. For alkenylsilanols, the reaction generally exhibits good stereospecificity, with the original alkene configuration well retained.

5. Attention should be paid to the influence of water content on reaction activity and side reactions, avoiding undesired processes such as desilylation and homocoupling of the halide.

Reaction Mechanism

References

Denmark, S. E.; Baird, J. D. Palladium-Catalyzed Cross-Coupling Reactions of Silanolates: A Paradigm Shift in Silicon-Based Cross-Coupling Reactions. Chemistry, 2006, 12 (19), 4954-4963.

Key References

Bidirectional Hiyama–Denmark Cross-Coupling Reactions of Bissilyldeca-1,3,5,7,9-pentaenes for the Synthesis of Symmetrical and Non-Symmetrical Carotenoids. Chem. Eur. J. 2019, 25(63), 14399–14407.

Hiyama Cross-Coupling Reaction in the Stereospecific Synthesis of Retinoids. Org. Lett. 2009, 11(45), 141-144.

Related Reactions

Suzuki Cross-Coupling

Hiyama Coupling

Related Products

Reactants

• Dimethylphenylsilanol  Cas：5272-18-4  Cat.No：D5571
• Iodobenzene, 97.5%  Cas：591-50-4  Cat.No：267597
• Bromobenzene, 99%  Cas：108-86-1  Cat.No：274969
• 4-Iodoanisole, 98%  Cas：696-62-8  Cat.No：557266

Base and Activating Reagent(s)

• Potassium Trimethylsilanolate  Cas：10519-96-7  Cat.No：SY024672
• Cesium carbonate, 99.9%, for synthesis  Cas：534-17-8  Cat.No：904086
• Cesium hydroxide monohydrate, 99%   Cas：35103-79-8  Cat.No：956413
• Sodium hydride, for synthesis, 60%, dispersion in mineral oil   Cas：7646-69-7  Cat.No：961241

Palladium Catalyst(s)

• Bis(dibenzylideneacetone)palladium, 98%, for synthesis   Cas：32005-36-0  Cat.No：958772
• Tris(dibenzylideneacetone)dipalladium(0), 20% Pd   Cas：51364-51-3  Cat.No：960139
• Allylpalladium(II) chloride dimer, 98%   Cas：12012-95-2  Cat.No：982398
• Palladium(II) acetate, 47.5% Pd   Cas：3375-31-3  Cat.No：234582
• Tetrakis(triphenylphosphine)palladium, 98%, Pd ≥9%   Cas：14221-01-3  Cat.No：970483

Ligand(s)

• Triphenylphosphine, 98.5%, for synthesis   Cas：603-35-0  Cat.No：563925
• 1,4-Bis(diphenylphosphino)butane, 98%, for synthesis   Cas：7688-25-7  Cat.No：574746
• 1,1'-Bis(diphenylphosphino)ferrocene, 98%, for synthesis   Cas：12150-46-8  Cat.No：460490