Reaction of some chromens and naphthopyrans with bromine and chlorine. Part IV

Hepworth, John D.; Livingstone, R.

doi:10.1039/j39660002013

Cited by 16 publications

(7 citation statements)

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“…10,11 Herein, we report a general phenylboronic acid procedure for the preparation of substituted and condensed 2Hchromenes 2 by condensation of phenols 1 with unsaturated aldehydes (Scheme 1). The advantages of this method in terms of mildness of conditions and efficiency over other Lewis acid 5,6 and base 12,13,15 induced processes anticipates its broader application and is recently demonstrated in the synthesis of naturally occurring pyroxanthones from our laboratories. 14 The reaction may be extended to the preparation of condensed 2H-chromenes from naphthols (entries [13][14][15] and from phenanthrols (entry 16).…”

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confidence: 99%

Phenylboronic Acid-Mediated Synthesis of 2H-Chromenes

Chauder

Lopes

et al. 1998

Synthesis

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Phenylboronic Acid-Mediated Synthesis of 2H-Chromenes

Chauder

Lopes

et al. 1998

Synthesis

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“…An attempt was made previously to synthesise the epoxide (8) by treating the chlorohydrin (13) with sodium hydroxide in ether. 24 The expected epoxide was not formed and the product obtained was assigned the 3,4-diol structure (10) but of unspecified stereochemistry. The melting point of this substance (I 15 "C) does not correspond to the melting point of either of the pure isomers and suggests that a mixture of the two may have been formed.…”

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confidence: 99%

The synthesis of the epoxide and some other possible metabolites of precocene I

Jennings¹,

Ottridge²

1984

J. Chem. Soc., Perkin Trans. 1

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“…10 The availability of spiro[chroman-2,1'-cycloalkan]-4-ones (2 ; Y = H) from 2hydroxyacetophenone and a cycloalkanone via the enamine l1 prompted their use as sources of the chromens. Reduction with sodium borohydride proceeded without the complications encountered by others in similar reactions 1 2 3 and dehydration of the resulting spiro-substituted chroman-4-01s (4; Y = H) with anhydrous copper(r1) sulphate afforded the title compounds (1) in isolated yields of ca. 50% from the cycloalkanone.…”

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Synthesis and reactions of some spiro[2H-chromen-2,1′-cycloalkanes]

Brogden¹,

Hepworth²

1983

J. Chem. Soc., Perkin Trans. 1

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Spiro[2H-chromen-2,1 '-cyclopentane] and the analogous cyclohexane and cycloheptane compounds have been prepared from the corresponding cycloalkanones. Reactions of the chromens with halogens and some chemistry of the derived products are described. The dehalogenation of an a-bromoketone by sodium borohydride in boiling methanol is reported. 3,4-Epoxyspiro[chroman-2,l '-cycloalkanes] have been obtained and ring-opened. The effects of the size of the spiro-annelated ring are minimal.Our studies of the chemistry of 2H-l-benzopyrans or 2H-chromens have centred around the influence which substituents in the aromatic ring have on reactions of the double bond in the pyran Despite a recent indication that the chromen ring system is not necessary for antijuvenile hormone activity: interest is still maintained in the precocenes4 and recently an attempt has been made to correlate the ' ' C chemical shift of the C-3 and C-4 atoms in chromens with precocene-like activity.' Our attention is currently focused on the effects of variation in the substituents present at C-2 and some results of our investigations into the synthesis and chemistry of a series of chromens having a cycloalkane ring spiro-annelated at the 2-position (1) are now reported.Routes to chromens from aromatic precursors have been reviewed: but, in general, these are unsuitable for the synthesis of those heterocycles bearing a 2-spiro-substituent, although spiro[2H-l-benzopyranindolines], of interest because of their photochromic ' or thermochromic properties, have been obtained directly from salicylaldehyde and alkylidene-2-indolines in ethanol or dimethylformamide.10 The availability of spiro[chroman-2,1'-cycloalkan]-4-ones (2 ; Y = H) from 2-hydroxyacetophenone and a cycloalkanone via the enamine l1 prompted their use as sources of the chromens. Reduction with sodium borohydride proceeded without the complications encountered by others in similar reactions 1 2 3 and dehydration of the resulting spiro-substituted chroman-4-01s (4; Y = H) with anhydrous copper(r1) sulphate afforded the title compounds (1) in isolated yields of ca. 50% from the cycloalkanone.The singlet near 6 2.7 arising from the C-3 protons in the chromanones (Table) is shifted upfield in the chromanols and, since the two protons are no longer equivalent, the signal is more complex. Coupling with the hydroxylic proton is not observed and the multiplet overlaps with the alicyclic signals. The signal from 4-H appears as a triplet in the cyclopentane derivative (4a), but four peaks are visible in the spectra of the other two chromanols (4b, c). It thus appears that the size of the cycloalkyl ring causes small variations in the interactions between the protons at C-3 and C-4.The spiro-chromens reacted with bromine and with chlorine to give the 3,4-dihalogenospiro[chroman-2,1 '-cycloalkanes] (3) which underwent nucleophilic attack by water to yield the corresponding 3-halogenochroman-4-01s (4; Y = Br or CI). The exclusive displacement of the halogen atom at C-4 is to be expected if the reaction p...

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Reaction of some chromens and naphthopyrans with bromine and chlorine. Part IV

Cited by 16 publications

References 0 publications

Phenylboronic Acid-Mediated Synthesis of 2H-Chromenes

Phenylboronic Acid-Mediated Synthesis of 2H-Chromenes

The synthesis of the epoxide and some other possible metabolites of precocene I

Synthesis and reactions of some spiro[2H-chromen-2,1′-cycloalkanes]

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