Organobase catalysed one-pot exo-selective synthesis of meso-spiro[cyclohexanone-pyrandione] derivatives


An exo-selective one-pot synthesis of novel spiro[cyclohexanone-pyrandione] derivatives through two sequential organobase-catalysed 1,4-conjugate additions of pyran-2,4-dione precursors on diarylideneacetone derivatives is described. The resulting 7,11-diaryl-2-oxaspiro[5.5] undec-3-ene-1,5,9triones were obtained as a 2 : 1 mixture of exo-and endo-diastereomers and adopt a meso-form due to the bilateral symmetry existing in the scaffold. Chiral-HPLC, NMR and single-crystal X-ray diffraction (including synchrotron data) have been used to elucidate the spiro[cyclohexanone-pyrandione] structure, showing therefore the exo/endo-diastereomers obtained in a meso-form, the cis-7,11-diaryl configuration (equatorial position) and different conformational changes in the cyclohexanone skeleton both in liquid and solid states. DFT studies proved the exo-stereoselectivity of the reaction by determining the exo/cis equatorial-equatorial configuration as the most thermodynamically stable form of our spiro[cyclohexanone-pyrandione] skeleton, while the structural substitution has no effect.






Talhi, O; Abdeldjebar, H; Belmiloud, Y; Hassaine, R; Taibi, N; Valega, M; Paz, FAA; Brahimi, M; Bachari, K; Silva, AMS

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Thanks are due to FCT/MEC for the financial support for the project PT-DZ/0005, of the QOPNA research Unit (FCT UID/QUI/00062/2013) and CICECO - Aveiro Institute of Materials (POCI-01-0145-FEDER-007679 - FCT UID/CTM/50011/2013) through national funds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, and to the Portuguese NMR Network. We would like to thank the General Directorate for Scientific Research and Technological Development - DGRSDT of Algeria and Agence Thematique de Recherche en Sciences et Technologie ATRST for approving the co-financed bilateral project PT-DZ/0005. We further wish to thank CICECO for funding the purchase of the single-crystal X-ray diffractometer, and to the European Synchrotron Radiation Facility (Grenoble, France) for approving the project CH-3995 at the Swiss-Norwegian beam line BM01a.

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