DBU

DBU

DBU-Mediated Diastereoselective Aldol-Type Cyanomethylation of Isatins.[Pubmed:28357854]

J Org Chem. 2017 Apr 21;82(8):4489-4496.

An efficient, metal-free approach to 3-substituted 3-hydroxyoxindole by DBU-mediated highly diastereoselective addition of aryl acetonitrile to N-protected isatin under mild conditions has been developed. The reaction proceeds smoothly to produce respective cyanomethylated adducts in good yield and excellent diastereoselectivity. Further transformation of the cyanide group allowed the synthesis of an advance intermediate of corresponding (+/-) CPC analogue. The mechanistic insight toward the aldol-type cyanomethylation of N-tritylisatin with benzyl cyanide was obtained by DFT calculations.

A DBU-catalyzed Michael-Pinner-isomerization cascade reaction of 3-hydroxyoxindoles with isatylidene malononitriles: access to highly functionalized bispirooxindoles containing a fully substituted dihydrofuran motif.[Pubmed:28067385]

Org Biomol Chem. 2017 Jan 25;15(4):984-990.

The first DBU-catalyzed Michael/Pinner/isomerization cascade reaction of 3-hydrooxindoles with isatylidene malononitriles was developed, and the corresponding highly functionalized bispirooxindoles containing a fully substituted dihydrofuran motif were obtained in up to 92% yields. This protocol also provides an efficient method for the synthesis of an alpha-cyano-gamma-butyrolactone bispirooxindole. In addition, a one-pot three-component cascade reaction was conducted. Also, the asymmetric version of the cascade reaction was achieved.

Azomethine-isocyanide [3+2] cycloaddition to imidazoles promoted by silver and DBU.[Pubmed:28317960]

Chem Commun (Camb). 2017 Mar 30;53(27):3858-3861.

A new silver-promoted [3+2] cycloaddition of azomethine ylides with isocyanides has been described. The methodology provides an efficient and modular approach to 1,2,4-trisubstituted imidazoles of vital bioactive molecules and atypical antipsychotics analogues.

Mechanistic insights on DBU catalyzed beta-amination of nbs to chalcone driving by water: Multiple roles of water.[Pubmed:28114731]

J Comput Chem. 2017 Mar 15;38(7):438-445.

DFT calculations were conducted to pursue deeper understandings on the mechanism and the explicit role of trace water in the DBU-catalyzed beta-amination of NBS to chalcone. Being different from previously proposed by Liang et al., a cooperative participation of both DBU and water is noticed in the preferred mechanism. The preferential mechanistic scenario assisted by water undergoes three major steps: the formation of succinimide and HBrO, concerted nucleophilic addition and H-shift, and keto-enol tautomerization. Moreover, we found that DBU-HBrO is unnecessary in the third step and three-water-cluster assisted keto-enol tautomerization is the most advantageous case. It is further noted that the catalytic position of the third water molecule and the proton shift orientation to some extent affect step 3 via O...HO and OH...pi interactions, which is confirmed by AIM analysis. The computational results suggest that water molecules play pivotal roles as reactant, catalyst, and stabilizer to promote the reaction of chalcone and NBS. The origin of the more stable transition state structure in the rate-determining step of DBU-water catalyzed mechanism is ascribed to noncovalent interactions, halogen bond, and electrostatic interactions than DBU only ones. (c) 2017 Wiley Periodicals, Inc.