1,8-Diazabicyclo[5.4.0]undec-7-ene CAS 6674-22-2 DBU

DBU has been applied to a variety of elimination reactions to introduce unsaturated bonds into reagent molecules, as intermediates and raw materials for organic synthesis, just to name a few examples is enough to see the application of DBU in elimination reactions.

1. Haloalkanes eliminate hydrogen halide
   A typical reaction is that 1,1-diiodobutane is heated to reflux with an equivalent amount of DBU until a brown solid appears, and the product (E)-1-iodo-1-butene is obtained by distillation and separation from the reaction mixture. The yield is is 80%. Usually DBU is difficult to dehydrohalogenate vinyl halides to alkynes, but the special structure (E)-vinyl bromide and DBU are refluxed in benzene, almost quantitatively converted to the corresponding alkynes, while (Z)-form isomerization The body does not have such a reaction. The use of DBU for the dehydrohalogenation of halocarbons is numerous enough to demonstrate that DBU is a very efficient haloalkane dehydrohalogenation reagent.
2. N-halogenated amides to eliminate hydrogen halide
   Under the action of DBU, N-halogenated amides can successfully remove hydrogen halide, and then rearrange into isocyanates. Under the action of DBU, N-chlorobenzamides can be rearranged to obtain benzene isocyanates with a yield of more than 90%. However, it is difficult to obtain benzene isocyanate by replacing DBU with an organic base such as triethylamine.

Double bond isomerization and epimerization reactions are extremely useful in organic synthesis, and DBU has a good catalytic effect in such isomerization reactions.

1. Double bond isomerization reaction
   Using DBU, β,γ-unsaturated esters can be converted into corresponding α,β-unsaturated esters. Under the action of DBU, 60% of 3-pentenoate is isomerized into stable 2-pentenoate; under the action of catalyst DBU, β,γ-unsaturated nitrile can also be isomerized into stable α,β-unsaturated Nitrile.
2. Epimerization reaction
   The mixture of stereoisomers was reacted with DBU for 1 h at room temperature, and its cis-3,4-isomer was converted to trans-3,4-isomer with a selectivity of 96%. This provides a way to synthesize compounds of special configurations.

DBU is an alkaline reagent that deprotonates active α-hydrogen compounds to form carbanions, among which Michael addition reaction is the most typical, with mild reaction conditions and few side reactions. In the reaction of cyclohexanone formate and methyl acrylate, DBU was used as an alkaline reagent to obtain the product with a yield of 96%:

DBU makes Michael reaction between nitro compound and styryl ketone containing double bond, and the yield is 95%; compound 15 undergoes Michael reaction with 2-cyclopentenone, and generates (+)-3-cyclopentenone after hydrolysis and decarboxylation Acetic acid with a total yield of 43% and an optical purity of 96%. The yield of the product obtained by using triphenyllithium or potassium tert-butoxide as a catalyst is close, but the optical purity is much lower, only 7% to 76%. In addition, in the Knovenagel condensation reaction between malonic acid and hexanal, DBU was used as a basic reagent, and the reaction was carried out at 90 °C for 10 h to obtain β, γ-unsaturated isomers with a selectivity of 94% and a yield of 56%. %.

DBU can be used as a catalyst for the preparation of esters and amine compounds from carboxylic acids, halogenated hydrocarbons, and the preparation of ethers, esters and carbamates from alcohols. This type of reaction is formed by deprotonation of carboxylic acid or alcohol with alkyl halide, acylating agent or other electrophilic reagents, wherein esterification and amidation reactions are generally carried out at room temperature, while etherification reactions are generally carried out at 60 ℃. at ~80°C.

When synthesizing 2,5-dimethyl-3-phenyl-2-cyclopentenone, using DBU as a catalyst, the yield reached 70%. In the synthesis of tetrahydropyrrole derivatives, it is also obtained by cycloaddition using DBU as a catalyst, and the yield is also over 90%.

Recently, it was found that DBU has a good catalytic effect in the synthesis of α-diazoketones and α-diazoesters. Under the catalysis of DBU, benzenesulfonyl azide compounds carry out diazotization reaction on the active sites of related compounds under mild conditions and high yields.