Unique cascade ring-opening/cyclization reaction of azlactones and DBU or DBN: Synthesis of new pyrrolam A analogues

Multicomponent Synthesis of Diversified Chromeno[3,2-d]oxazoles

A practical and efficient synthetic procedure to novel chromeno[3,2-d]oxazoles through a one-pot sequential multistep process is presented. This procedure proceeds efficiently in propylene carbonate (PC) as a green solvent and affords a wide range of the chromenooxazole scaffolds.

Umpolung cyclization reaction of N-cinnamoylthioureas in the presence of DBU

A novel regioselective cyclization reaction of N-cinnamoylthioureas leading to six- or five-membered heterocyclic compounds was developed. N-Cinnamoylthioureas in the presence of trifluoroacetic acid (TFA) underwent the well-established intramolecular cycloaddition reaction to give 2-imino-2,3,5,6-tetrahydro-4H-1,3-thiazin-4-ones in good yields. On the other hand, the reaction with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) proceeded in an unprecedented "umpolung" cyclization fashion to afford five-membered 2-imino-1,3-thiazolidin-4-ones and/or 2-thioxoimidazolidine-4-ones. The reaction was considered to occur via a cycloadduct of DBU with the cinnamoyl moiety followed by intramolecular attack of the thiourea group.

CsF-Catalyzed Transannulation Reaction of Oxazolones: Diastereoselective Synthesis of Diversified trans- N-(6-Oxo-1,4,5,6-tetrahydropyrimidin-5-yl)benzamides with Arylidene Azlactones and Amidines

A versatile and straightforward synthetic strategy for the construction of new tetrasubstituted 1,3-diazinones is described. The procedure is based on CsF-catalyzed, microwave-assisted, ring transformation reaction of arylidene azlactones with amidines. Moreover, this technique provides diversified trans- N-(6-oxo-1,4,5,6-tetrahydropyrimidin-5-yl)benzamides with a good antimicrobial activity.