Eliminate the reaction
DBU has been used in a variety of elimination reactions to enable reagent molecules to introduce unsaturated bonds, as intermediates and raw materials for organic synthesis, and just a few examples are enough to see the application of DBU in elimination reactions.
1. Alkyl halides eliminate hydrogen halides
A typical reaction is 1, 1-diiodobutane with an equal amount of DBU heated back to a brown solid, which is distilled and separated from the reaction mixture to produce the product (E) -1-iodo-1-butene with a yield of 80%. Umumnya, it is difficult for DBU to dehalogenate vinyl halides to form alkynes, but the special structure of (E) -vinyl bromide and DBU is reflow in benzene, almost quantitatively converted to the corresponding alkynes, while the (Z) -isomer cannot undergo such a reaction. There are many examples of using DBU to dehalogenate halocarbons, which is enough to show that DBU is a very effective reagent for dehalogenation of halogenated alkane.
2. N-halogenated amide eliminates hydrogen halide
Under the action of DBU, N-halogenated amide can be successfully dehalogenated and then rearranged into isocyanate, and N-chlorobenzamide can be rearranged into phenyl isocyanate under the action of DBU with a yield of more than 90%. Namun, it is difficult to obtain phenylisocyanate by replacing DBU with organic bases such as triethylamine.
Isomerization
Double bond isomerism and differential isomerism reactions are extremely useful in organic synthesis, and DBU has a good catalytic effect in these isomerism reactions.
1. Double bond isomerization reaction
The β-γ-unsaturated ester compounds can be converted into the corresponding α-β-unsaturated ester by using DBU. Under the action of DBU, the stable 2-pentenoate was formed by 60% of 3-pentenoate. Under the action of catalyst DBU, β, γ-unsaturated nitrile can also form stable α, β-unsaturated nitrile.
2. Differential isomerization reaction
The stereoisomer mixture was reacted with DBU at room temperature for 1h, and the cis-3, 4-isomer was converted into trans-3, 4-isomer with a selectivity of 96%. This provides a method for the synthesis of special configuration compounds.
Some applications of DBU
DBU is a strong alkaline reagent, but it is a weak nucleophile, easy to combine with protons and not easy to combine with carbon atoms, so the application of DBU is mainly as a strong basic reagent to transfer protons, play the role of base or catalyst. The characteristic of DBU participating in the reaction is that the amount of DBU is generally required, and the applied reactions are mainly concentrated in some reactions with proton transfer, such as elimination, isomerization, tambahan, esterifikasi, etherification, amidation, diazotization and so on.
DBU as an alkaline reagent to deα-H to produce carbanion intermediate reaction
DBU is an alkaline reagent that deprotonates active α-hydrogen compounds to form carbanion, among which Michael addition reaction is the most typical one, which has mild reaction conditions and few side reactions. In the reaction of cyclohexanone formate and methyl acrylate, DBU was used as the basic reagent to obtain the product, the yield was 96%. DBU membuat senyawa nitro dan stirena keton yang mengandung ikatan rangkap reaksi Michael, the yield was 95%. Menggabungkan 15 dan 2-siklopentenon mengalami reaksi Michael untuk menghasilkan (+) -3-asam siklopentenon asetat setelah pelepasan air. Hasil totalnya adalah 43% dan kemurnian optiknya adalah 96%. Meskipun rendemen produk yang diperoleh dengan menggunakan trifenillitium atau kalium tert-butoksi sebagai katalis hampir sama, kemurnian optiknya jauh lebih rendah, hanya 7% ~ 76%. Selain itu, dalam reaksi kondensasi Knovenagel asam malonat dan kaproaldehida, selektivitas β, Isomer tak jenuh γ adalah 94% dan hasilnya adalah 56% setelah reaksi pada 90℃ selama 10 jam dengan DBU sebagai reagen dasar.
Esterifikasi, etherification, reaksi tengahasi
DBU dapat digunakan sebagai katalis untuk pembuatan ester dan amina dari asam karboksilat dan halokarbon, serta eter, ester dan karbamat dari alkohol. Reaksi semacam ini terjadi antara asam karboksilat atau alkohol dengan alkil halida, zat pengasilasi atau reagen elektrofilik lainnya untuk mendeprotonasi, dimana reaksi esterifikasi dan midasi umumnya dapat dilakukan pada suhu kamar, dan reaksi eterifikasi umumnya dilakukan pada 60 ~ 80℃.
Reaksi sikloadisi
Dalam sintesis 2, 5-dimetil-3-fenil-2-siklopentenon, DBU digunakan sebagai katalis, dan hasilnya tercapai 70%. Dalam sintesis turunan tetrahidropirol, DBU juga digunakan sebagai katalis melalui sikloadisi untuk memperolehnya, hasilnya juga lebih dari 90%.
Diazotisasi
Baru-baru ini, telah ditemukan bahwa DBU memiliki efek katalitik yang baik dalam sintesis α-diazon dan α-diazo ester. Di bawah katalisis DBU, senyawa benzena sulfonil azida dapat diazonisasi situs aktif senyawa terkait dalam kondisi ringan dan dengan hasil tinggi.
