Supported Reagents

ChemFiles Vol. 2, No. 6
Functionalized SILICA GELS for Organic Synthesis

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Supported Reagents

Bases and Acid Scavengers / Coupling Reagents / Oxidizing Reagents
Phosphines / Diols and Epoxides



Bases and Acid Scavengers

36,425-8 3-Amino-functionalized silica gel 10g; 50g; 250g
Loading ca. 1.0 mmol N/g
This functionalized silica gel has been used for the separation and solid-phase extraction (SPE) of sugars18, as well as for the separation of steroids19, cholesterol, and triglycerides20. It has also been used in size-exclusion chromatography of cationic polymers21, as a scavenger to remove excess acid chlorides22 and as a catalyst in Knoevenagel reactions23,24.

53,804-3 3-(Dimethylamino)propyl-functionalized silica gel 5g; 25g; 100g
Loading ca. 1.6 mmol N/g
This dimethylamine immobilized on silica gel can be used as a base catalyst in Michael27 or Knoevenagel reactions28. It can also be used as a catalyst for alkane oxidation29. It is a strong supported tertiary amine that can be used to scavenge acids.

56,986-0 3-(1,3,4,6,7,8,-Hexahydro-2H-pyrimido-[1,2-a]
pyrimidino)propyl-functionalized silica gel
5g; 25g; 100g
Loading ca. 2.4 mmol N/g
This grafted hindered strong base has been used as a basic catalyst in Michael reactions, Knoevenagel condensations, Robinson annulations and nucleophilic epoxidations30,31.

53,795-0 3-(1-Imidazol-1-yl)propyl- functionalized silica gel 5g; 25g; 100g
Loading ca. 2.2 mmol N/g
This gel has been used for anchoring ruthenium complexes used in catalytic cyclization reactions32,33 and as a chromatographic packing for the separation of metal chelates34.

 56,979-8 3-(1-Morpholino)propyl-functionalized silica gel 5g; 25g; 100g
Loading ca. 1.1 mmol N/g
This grafted morpholine silica gel is commonly used as an acid sponge. It is used in the same manner as morpholine functionalized polymers35,36.

55,260-7 3-(1-Piperazino)propyl-functionalized silica gel 5g; 25g; 100g

Loading ca. 1.9 mmol N/g
This silica-bound piperazine is a useful deblocking and scavenging agent for Fmoc37 and for the Bsmoc38 amino protecting group. According to the results of one study, silica-bound piperazine is superior to polystyrene-based reagents. It has also been used to immobilize metal carbonyl complexes39, for the synthesis of 2-aminobutadienes, as a traceless linker in cross-coupling strategy starting with diazonium ions and as a solid phase Knoevenagel catalyst.

56,984-4 3-(1-Piperidino)propyl-functionalized silica gel 5g; 25g; 100g
Loading ca. 1.1 mmol N/g
Used as an immobilized catalyst for Knoevenagel condensation40,41, and for selective monoglyceride synthesis42,43,44. May also be used as a tertiary-bound amine for scavenging acids, thereby avoiding salt elimination problems.

56,985-2 3-(4,4'-Trimethylenedipiperidino)propyl- functionalized silica gel 25g; 100g
Loading ca. 2.0 mmol N/g
Used as a deblocking-scavenging agent for Fmoc amino-protecting42. It is a better deblocking agent than the piperazino gel, but less efficient for scavenging dibenzofulvene. Can be used in conjunction with the piperazino gel for enhanced performance. May also be used as an electrophile scavenger or a silica-bound base.

53,798-5 2-(2-Pyridyl)ethyl-functionalized silica gel 5g; 25g; 100g
Loading ca. 1.3 mmol/g
This gel can be used as a tertiary amine for acid removal. It can also be used to anchor Cu2+ ions, which can then be used as a catalyst for hydroquinone oxidation45.

55,288-7 3-(Trimethylammonium)propyl- functionalized silica gel-carbonate 5g; 25g; 100g
Loading ca. 0.7 mmol/g
Can be used as a general base to scavenge acids.



Coupling Reagents
 56,988-7 3-(1-Cyclohexylcarbodiimido)propyl- functionalized silica gel 5g; 25g
Loading ca. 2.0 mmol N/g
Coupling reagent for peptide synthesis.


Oxidizing Reagents

56,989-5 Potassium permanganate,
15-20 wt. % on silica gel (phosphate buffered)
25g; 100g
This solid-supported oxidant is used for converting aldehydes to carboxylic acids46 and alcohols to aldehydes47.

 56,980-1 Pyridinium chlorochromate, ca. 20 wt. % on silica gel 25g; 100g
Used for the general oxidation of alcohols to carbonyl compounds, selective oxidation of allylic and benzylic alcohols, organometallic oxidation, oxidative transpositions, oxidative cleavages, allylic and benzylic oxidation, and oxidative cyclizations48,49,50,51. Using PCC immobilized on silica gel provides anhydrous conditions that may otherwise promote side reactions and reduce yields. It greatly facili-
tates removal of polymeric reduced chromium by-products, and is compatible with acid-sensitive protecting groups52,53. When used in conjunction with ultrasound, kinetics are increased and the amount of oxidant required to complete the reaction is decreased42,54,55.

 56,982-8 Pyridinium dichromate, ca. 20 wt. % on silica gel 25g; 100g
Used as an alternative to PCC in nucleoside and carbohydrate oxidation, particularly for fragile molecules56. Can also be used in conjunction with tert-butyl hydroperoxide for a variety of oxidative transformations57. PDC-on-silica is a very convenient and effective reagent for oxidizing allylic and benzylic alcohols, as well as saturated primary and secondary alcohols and it is compatible with acid-sensitive groups, such as cyclopropane ring, or a ketal function58.

 57,634-4 TEMPO on silica gel 5g; 25g; 100g
catalyst in the Anelli oxidation of alcohols.



53,801-9 2-(Diphenylphosphino)ethyl- functionalized silica gel 5g; 25g; 100g
Loading ca. 0.7 mmol/g
Used for NiCl2 and CoCl2 complexation59, chromatographic phase preparation, hydro-formylation of 1-heptene with silica-anchored rhodium thiolate complexes60, cross-coupling reactions of organic halides with organotin and organomagnesium reagents with silica-supported palladium61, and for carbonickel complex immobilization62. Can also be used with a supported rhodium(I) catalyst for olefin catalytic reduction, with dinuclear rhodium(I) complexes for hydro-formylation reactions, with palladium(0) for cross-coupling organoboron compounds, and with organic halides or organic triflates.


Diols and Epoxides

55,274-7 2-(3,4-Cyclohexyldiol)propyl- functionalized silica gel 5g; 25g; 100g
Loading ca. 0.8 mmol/g
Scavenging or protection of ketones and aldehydes used in chromatography and as a solid support.

53,796-9 3-(Glycidoxy)propyl-functionalized silica gel 5g; 25g; 100g
Loading ca. 1.0 mmol/g
Used for immobilizing organic molecules when extracting heavy metals bearing hydroxy63, amine64, thiol65, and thiocarboxylic acid66 functionalities. Also used to develop chemically bonded stationary phases for chiral ligand exchange67 and reversed phase liquid chromatography68.

55,273-9 2-(3,4-Epoxycyclohexyl)propyl- functionalized silica gel 5g; 25g; 100g
Loading ca. 0.8 mmol/g
Serves the same purpose as the glycidoxy gel, but the epoxide ring is more reactive.