a
Fluoro & Agro Chemicals Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India
c
AcSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India Email: krishnu@iict.res.in
› Author AffiliationsWe are grateful to SERB-DST, New Delhi, for financial support (Grant no. EEQ/20l6/000066). We gratefully acknowledge the help received from the Centre for NMR & Structural Chemistry and Analytical Chemistry & Mass Spectrometry, CSIR –IICT.
The title compounds were synthesized from 5,5-dimethylcyclohexane-1,3-dione, benzaldehyde, and malononitrile promoted by molecular iodine in basic medium via 2-amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile, by a novel protocol. The protocol involves a novel rearrangement in which the 4H-chromene fragment dissociates to a cyclopropane moiety and rearranges to the five-membered compound 6,6-dimethyl-4-oxo-2-phenyl-4,5,6,7-tetrahydrobenzofuran-3,3(2H)-dicarbonitrile. Simple reaction conditions, excellent yields, and high compatibility are the advantages of this protocol.
4b
Gottlieb OR,
Yoshida M.
In
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Rowe JW.
Springer; Berlin: 1989
14a For leading references to the asymmetric synthesis of tetrahydrofurans, see:
Hou X.-L,
Yang Z,
Yeung K.-S,
Wong HN. C.
Prog. Heterocycl. Chem. 2005; 17: 142
28 CCDC 1824517 contains the supplementary crystallographic data for compound 2c. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.
292-(Het)aryl-6,6-Dimethyl-4-oxo-2-phenyl-4,5,6,7-tetrahydrobenzofuran-3,3(2H)-dicarbonitriles (2a–r); General Procedure
A round-bottomed flask equipped with a reflux condenser and stopper was charged with the appropriate nitrile 1 (1.02 mmol), I2 (1.02 mmol), Et3N (2.04 mmol), and DCE (20 mL), and the mixture was refluxed with stirring for 2 h. When the reaction was complete (TLC), the homogeneous reaction mass was concentrated under reduced pressure and the residue was transferred to a separatory funnel, washed with H2O (3 × 20 mL), and extracted with EtOAc (20 mL). The organic layer was dried (Na2SO4) and concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, 20–40% EtOAc–hexane).
6,6-Dimethyl-4-oxo-2-phenyl-4,5,6,7-tetrahydro-1-benzofuran-3,3(2H)-dicarbonitrile (2a)
Colorless solid; yield: 0.232 g (80%); mp 142–144°C. IR (KBr): 2952, 2238, 1655, 1412, 1120, 1059, 985, 850, 776 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.55–7.46 (m, 3 H), 7.45–7.41 (m, 2 H), 6.14 (s, 1 H), 2.64–2.50 (m, 2 H), 2.46–2.31 (m, 2 H), 1.19–1.15 (s, 6 H). 13C NMR (100 MHz, CDCl3): δ = 190.4, 179.2, 131.4, 130.9, 129.3, 125.9, 112.8, 110.2, 108.2, 92.4, 50.4, 42.5, 37.8, 34.3, 28.8, 27.9. ESI-MS: m/z = 293 [M + H]+. HRMS (ESI): m/z [M + H]+ calcd for C18H17N2O2: 293.1300; found: 293.1284.
