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A novel synthesis of pyrrolidine-2-carbaldehydes or tetrahydropyridine-2-carbaldehydes from the cascade reactions of N-arylpiperidines or N-arylazepanes is presented. Mechanistically, the formation of the title compounds involves an unprecedented oxidative ring contraction of inactivated cyclic amines via Cu(OAc)2/KI/O2-promoted oxidative cleavage and reformation of the C–N bond. Interestingly, when PhI(OAc)2 was used in place of KI, 1,1-diacetates of the corresponding aldehydes were directly obtained with good efficiency. To the best of our knowledge, this is the first example of regioselective C(sp3)–H bond functionalization and C(sp3)–N bond activation of saturated cyclic amines using copper salt and oxygen. [ABSTRACT FROM AUTHOR]

A sequential one-pot two-step tandem reaction for efficient synthesis of polysubstituted cyclopropanes has been developed. The three-component reaction of α-halogenated methylene compounds, aromatic aldehydes, and acetonitrile derivatives produced first the intermediates pyridinium salts and electron-deficient olefins, followed by cyclopropanation of pyridinium ylide with electron-deficient olefins in situ to afford polysubstituted cyclopropanes. Target compounds were obtained in high yields and were diastereomerically pure after recrystallization. [ABSTRACT FROM AUTHOR]

An efficient synthetic procedure for the preparation of fused 2,3-dihydrofuran derivatives was developed with the assistance of pyridinium ylide. A sequential one-pot, two-step tandem reaction starting from pyridine, aromatic aldehyde, dimedone, or 4-hydroxycoumarin and α-phenacyl bromide or p-nitro- benzyl bromide with triethylamine as catalyst proceeded smoothly in acetonitrile. ¹H NMR spectroscopy and single-crystal analysis demonstrated that the obtained 2,3-dihydrofurans are trans isomers. [ABSTRACT FROM AUTHOR]

Polysubstituted pyrido[1,2-α]benzimidazole derivatives are efficiently produced in moderate yields in a novel one-pot, four-component reaction from pyridine or 3-picoline, chloroacetonitrile, malononitrile, and aromatic aldehyde in refluxing acetonitrile. The mechanism of this novel reaction was believed involving the formation of polysubstituted benzenes with subsequent substitution and annulation reaction of pyridine. All pyrido[1,2-α]benzimidazoles, polysubstituted benzenes, polysubstituted indoles, and some key reaction intermediates are characterized by 1H and 13C NMR, MS, IR spectra, and elemental analysis as well as X-ray crystallography. [ABSTRACT FROM AUTHOR]

A feasible nucleophilic trifluoromethylating protocol has been developed using trifluoroacetaldehyde hydrate as an atom-economical trifluoromethyl source. The reaction was found to be applicable to the nucleophilic trifluoromethylation of a broad spectrum of carbonyl compounds with satisfactory yields in general. DFT calculations have been performed to provide mechanistic insight into the present and related reactions employing 2,2,2-trifluoro-1-methoxyethanol and hexafluoroacetone hydrate. [ABSTRACT FROM AUTHOR]