Tungstate-catalysed oxidation of tetrahydroquinolines with hydrogen peroxide: a novel method for synthesis of cyclic hydroxamic acids

Murahashi, Shun‐Ichi; Oda, Tetsuya; Sugahara, Toshiaki; Masui, Yoshiyuki

doi:10.1039/c39870001471

Cited by 19 publications

(1 citation statement)

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“…Oxidation of secondary amines to the corresponding N-oxides with peroxy acids derived from Group VI transition metals (W, Mo) (which are prepared in situ from metal salts and hydrogen peroxide) is widely used in organic synthesis [1][2][3][4][5][6]. Accessibility of initial amines, simple experimental procedure, mild reaction conditions, high yields, and wide synthetic potential of the resulting nitrones ensured fast propagation of this method into the chemistry of heterocyclic compounds [7][8][9][10][11][12].…”

Section: Short Communicationsmentioning

confidence: 99%

Reaction of Allyl Phenylcarbamate with 5-Methyl-4,5-dihydro-3H-2-benzazepine-3-spirocyclohexane N-Oxide

2005

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SHORT COMMUNICATIONSOxidation of secondary amines to the corresponding N-oxides with peroxy acids derived from Group VI transition metals (W, Mo) (which are prepared in situ from metal salts and hydrogen peroxide) is widely used in organic synthesis [1][2][3][4][5][6]. Accessibility of initial amines, simple experimental procedure, mild reaction conditions, high yields, and wide synthetic potential of the resulting nitrones ensured fast propagation of this method into the chemistry of heterocyclic compounds [7][8][9][10][11][12].In the present communication we report the results of our study on the reaction of allyl phenylcarbamate (I) with 5-methyl-4,5-dihydro-3H-2-benzazepine-3-spirocyclohexane N-oxide (II). The latter was prepared in turn by intramolecular cyclization of 1-allyl-1-benzylaminocyclohexane in concentrated sulfuric acid at 70-80°C, followed by oxidation with hydrogen peroxide in aqueous acetone in the presence of 0.05 mol % of sodium tungstate at room temperature [13]. 1,3-Dipolar cycloaddition of compounds I and II was effected by heating equimolar amounts of the reactants in boiling toluene for 5 h. Study of the product structure by IR and 1 H NMR spectroscopy showed that the reaction occurred in a regio-and stereoselective fashion with formation of 7-methyl-2-(phenylcarbamoyloxymethyl)-1,2,5,6,7,11b-hexahydrobenzo[c]-isoxazolo[2,3-a]azepine-5-spirocyclohexane as a mixture of two diastereoisomers IIIa and IIIb. The IR spectra of IIIa and IIIb lack absorption bands typical of the N-oxide moiety in initial compound II (1230, 928, 1647 cm -1 ; stretching vibrations of the N→O and C=N bonds, respectively [13]), but bands belonging to stretching vibrations of the NH and carbamate carbonyl groups appeared at 3340 at 1720 cm -1 , respectively.Compounds IIIa and IIIb are likely to be formed via exo-transition state as a result of approach of the carbamate I molecule to the trans or cis position with respect to the 5-methyl group in II. The regioselectivity is controlled by the lowest unoccupied molecular N Me

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