N-heterocyclic carbene catalyzed domino cyclization of propargylic alcohols and benzoyl isocyanates.

N-Hetereocyclic carbenes (NHCs) were found to be efficient catalysts for the cyclization of propargylic alcohols and isocyanates. Domino cyclization reactions were carried out using isopropyl-substituted imidazolium salt as a precatalyst, and a wide range of substituted oxazolidinones were obtained in high yields.

Synthesis, structural revision, and antioxidant activities of antimutagenic homoisoflavonoids from Hoffmanosseggia intricata.

Intricatinol and intricatin, the two homoisoflavonoids isolated from Hoffmanosseggia intricata, and two analogs have been synthesized from pyrogallol in three steps. The spectral data of synthetic intricatinol are in good agreement with those of natural metabolite, but the spectral data of intricatin are not corroborative with those of the natural product. The structure of intricatin has been thus revised to 8-methoxybonducellin, a compound isolated from Caesalpinia pulcherrima.

Two new homoisoflavonoids from Caesalpinia pulcherrima.

Two new homoisoflavonoids, (E)-7-methoxy-3-(4'-methoxybenzylidene)chroman-4-one (1) and (E)-7-hydroxy-3-(3',4',5'-trimethoxybenzylidene)chroman-4-one (5), along with three known homoisoflavonoids (Z)-7-hydroxy-3-(4'-methoxybenzylidene)chroman-4-one (isobon ducellin) (2), (E)-7-hydroxy-3-(4'-methoxybenzylidene)chroman-4-one (bonducellin) (3) and (E)-7-hydroxy-3-(2',4'-dimethoxybenzylidene)chroman-4-one (4) were isolated from the whole plant of Caesalpinia pulcherrima. The structures of these new compounds were elucidated by electron impact mass spectrometry (EI-MS) and 1D and 2D-NMR spectral studies. Antimicrobial activity of the new compounds was evaluated.

Two new 5-deoxyflavonoids from Calliandra inermis.

Two new 5-deoxyflavonoids, 7,2',3',4'-tetramethoxyflavone (1) and 7,2',3',4'-tetramethoxyflavanone (2) together with a known flavone 7,4'-dimethoxy-3'-hydroxyflavone (3) were isolated from the whole plant of Calliandra inermis. The structures of these new compounds were elucidated by high resolution electron impact mass spectrometry (HR-EI-MS) and 1D and 2D-NMR spectral studies including 1H-1H correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and nuclear Overhauser enhancement spectroscopy (NOESY).