DBU

Description

DBU is a bicyclic amidine base. It is non-nucleophilic, sterically hindered, tertiary amine base in organic chemistry. It is reported to be superior to amine catalyst in Baylis-Hillman reaction.It promotes the methylation reaction of phenols, indoles and benzimidazoles with dimethyl carbonate under mild conditions.

Chemical Properties

Colorless to yellow liquid

Occurrence

Although all commercially available DBU is produced synthetically, it may also be isolated from the sea sponge Niphates digitalis.The biosynthesis of DBU has been proposed to begin with 1,6-hexanedial and 1,3-diaminopropane. 

Uses

DBU may be used:

2. as catalyst for carboxylic acid esterification with dimethyl carbonate
4. in the synthesis of duocarmycin and CC-1065 analogs
6. as catalyst in aza-Michael addition and Knovenegal condensation reaction
8. as base for dehalogenation of halogenated Diels-Alder adducts and the resulting activated 2,4-dienones were subjected to regio- and stereo-directed Michael additions, using Yamamoto′s reagent (CH3Cu · BF3)
10. in a new synthesis of the ABCD ring system of Camptothecin
12. DBU may be used as an catalyst for the dissolution and activation of cellulose by a reversible reaction of its hydroxyl groups with carbon dioxide. This dissolved cellulose system can be derivatized to form cellulose mixed esters.
14. Used in a new synthesis of the ABCD ring system of Camptothecin.

Uses

DBU is used in organic synthesis as a catalyst, a complexing ligand, and a non-nucleophilic base. It is used as a protecting agent for the synthesis of cephalosporin and as a catalyst for polyurethane.

General Description

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Flammability and Explosibility

Non flammable

Synthesis

The synthesis of DBU is as follows:As a base, sodium hydroxide was used at a concentration of 25% by weight and 2.3 times molar equivalent. A stirrer was placed in a 100 mL screw tube, and 11.5 g (50 mmol) of DBU hydrochloride, 8.5 g of toluene and 18.5 g (116 mmol) of 25% sodium hydroxide aqueous solution were charged at room temperature. It was placed on a magnetic stirrer and mixed for 1 hour with stirring. The mixture was separated with a 100 mL separatory funnel to obtain 18.8 g of the upper layer containing DBU and 18.4 g of the lower layer of the aqueous layer. The upper layer portion was analyzed by gas chromatography and contained 31.9% by weight of DBU, and the yield was 6.0 g (39.4 mmol) in a yield of 78.8%.

Purification Methods

Fractionally distil DBU under vacuum. Also purify it by chromatography on Kieselgel and eluting with CHCl3/EtOH/25% aqueous NH3 (15:5:2) and checking by IR and MS. [Oediger et al. Chem Ber 99 2012 1962, Angew Chem, Int Ed Engl 6 76 1967, Guggisberg et al. Helv Chim Acta 61 1057 1978, Beilstein 23/5 V 271.]

Toxics Screening Level

The Initial Threshold Screening Level (ITSL) for 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) is 25 μg/m3 with an annual averaging time.