Francis M. Dean

The heartwood chromones of Cedrelopsis grevei

Abstract The heartwood of Cedrelopsis grevei Baill. is shown to contain the known chromones heteropeucenin, alloptaeroxylin, ptaeroglycol, and peucenin. It also contains three new ones, greveichromenol, greveiglycol, and alloptaeroxylin methyl ether, and possibly a fourth, a methyl ether of greveiglycol which, however, may be an artefact. Greveichromenol is allocated structure (VIa) on spectroscopic grounds together with a conversion into isopeucenin. Greveiglycol (VIIIa) and the methyl ether (VIIIb) are allocated these structures on spectroscopic grounds together with syntheses from alloptaeroxylin methyl ether. A long range coupling is noted between the protons of the methyl group and the proton at position 3 in derivatives of 2-methylchromone, but it seems variable in magnitude and therefore of limited diagnostic value. Comparisons of the pyrones of divers samples of the heartwoods of Cedrelopsis grevei and of Ptaeroxylon obliquum show that these are closely related species but that their constituents are unsuitable for more detailed taxonomic purposes. P. obliquum has been found to contain peucenin 7-methyl ether, overlooked in the earlier study, and not previously encountered as a natural product.

Photoelectron spectra of cyclic aromatic ethers : The question of the mills-nixon effect

Abstract UV photoelectron spectra (UPS) of the cyclic aromatic ethers (1; R = H, n = 1, 2) are compared with each other and with those of non-cyclic ethers. The spectrum of the chroman (1; R = H, n = 2) is clearly distinguishable from those of all the other ethers. The differences in the spectra have been interpreted in terms of differing conjugative effects of oxygen and of “hyperconjugative” effects of methylene with the aromatic ring. These conclusions are supported by MO calculations. The bearing of these differing conjugative effects on reactivity of cyclic aromatic ethers is discussed and the conclusion reached that the orientational preferences customarily explained by the “Mills-Nixon effect” do not depend upon variation of bond lengths or bond angles in the aromatic ring but upon cross-conjugation effects in “Wheland” transition states.

Derivatives of naphtho[2,3-c]pyran-5,10-dione ; a simple synthesis and a note of their chromogenic properties.

Abstract Appropriate N -ylides convert 2-methyl-1,4-naphthoquinone into 3-(acylmethyl) derivatives which can be cyclised to naphtho[2,3-c]pyran-5,10-diones by treatment with bromine and dehydrobromination with triethylamine; these diones give a variety of striking colours in acid media.

Leptodactylone, a yellow coumarin from Leptodactylon and Linanthus species

Abstract A new phenol in Leptodactylon and Linanthus leaf has been identified by spectral procedures as 5,7-dimethoxy-8-hydroxycoumarin. This structure has been confirmed by synthesis. Leptodactylone is unique among simple hydroxycoumarins in its yellow colour.

The use of 13C–{1H selective} nuclear Overhauser enhancement experiments in the determination of the structure of a highly crowded quinone–diazoalkane epoxide adduct

Using heteronuclear nuclear Overhauser enhancement techniques the structure and conformation have been established for a highly crowded quinone–diazoalkane epoxide adduct, (3aS*,9S*,9aR*)-3,9a-dihydro-3,3,3′,3′,9a-pentamethylspiro-[9H-benz[f] indazole-9,2′-oxiran]-4(3aH)-one, formed from 2-methylnaphthoquinone and 2-diazopropane.

Lithiation in flavones, chromones, coumarins, and benzofuran derivatives

Flavones are lithiated at position 3 by lithium di-isopropylamide in tetrahydrofuran at –78 °C and the products are stable at that temperature. Appropriate reagents replace the lithium by carboxy, ethoxycarbonyl, mercapto, methylthio, trimethylsilyl, hydroxy, and other groups, sometimes giving products not previously available.Benzofurans are preferentially lithiated at position 2 if this is free, and may not be attacked if it is blocked, but if there is an activating group (i.e., one able to co-ordinate with the lithium cation) at position 2, then lithiation occurs at position 3. In the benzofuran series ring-opening is easier and lithiation often leads directly to acetylenic phenols. Chromones can be lithiated at positions 2 and 3 depending upon the substitution pattern and whether the substituents are activating. Aurones are not easily deprotonated, and only the acetylenic phenol arising from ring opening was found in the one successful case. Coumarins tend to behave simply as esters and give amides with the lithiating reagent, but 4-methoxycoumarin is readily lithiated at position 3.It is suggested that 3-deprotonation in ethers occurs easily only when there is an ether link antiperiplanar to the proton removed, and that the lithiated species are really unstable intermediates in trans-eliminations leading to alkyne derivatives.

Spirans. Part 13. The synthesis and orientation of spirans related to Abel's ketone (naphtho[2,1-b]furan-2(1H)-spiro-1′(2′H)-naphthalen-2′one)

The aryl substituent in stereoisomers (2) and (3) of 1-phenylnaphtho[2,1-b]furan-2(1H)-spiro-1′(2′H)naphthalen-2′-one are subject to hindered rotation by an energy barrier of ca. 15 kcal mol–1. If the phenyl substituent carries an ortho substituent, however, rotation is prevented at temperatures up to 60 °C (the highest examined) : only one rotamer is obtainable (the other is too crowded) and it has the ortho-substituent cisoid with respect to the triarylmethine proton.The temperature-variable broadening of the signals from the protons of the aryl substituent serves to identify these in the 1H n.m.r, spectra. Some other resonances can be regularly identified by combinations of coupling constants, double-irradiation experiments, and shifts induced by using benzene instead of trichloromethane as solvent, but the only one of value for determining the configuration at the triarylmethine centre is that already known, i.e. the upfield shift in the resonance of the vinylic (3′) proton caused by the aryl substituent when this lies immediately below it. A less precise but more general test of configuration is afforded by the mutual shielding of the aryl substituent and ring E when these are in adjacent planes.Methods of preparation are given for several related spirans, especially those containing the spiro-1′(4′H)naphthalen-4′-one nucleus, and n.m.r. methods used to establish the configurations.

β-Deprotonation by lithium di-isopropylamide. Vinyl carbanions from oxygen heterocycles in the synthesis of carboxylic acids in the benzofuran, flavone, and coumarin series and in the regiospecific acylation of 2,6-dimethylchromone

Lithium di-isopropylamide at –70 °C can remove the α-proton from benzofuran in the absence of activating groups and the β-proton if such groups are present; in flavone and 4-methoxycoumarin β-deprotonation occurs readily and the carbanions are easily carboxylated giving acids not previously accessible, while in 2,6-dimethylchromone β-deprotonation is kinetically favoured allowing 3-acylation to be achieved separately from the conventional acylation at the 2-methyl group.

1,4-dioxa-2,3-benzofulvalene from thermolysis of 1,2-benzoquinone 2-diazide

Abstract Heated in benzene, 1,2-benzoquinone 2-diazide gives 2-hydroxybiphenyl and 1,4-dioxa-2,3-benzofulvalene ( 3 ). Heated in xylene, it gives 3 in 36% yield. Though the PMR spectrum gives no indication of it, the 13 C NMR spectrum and the dipole moment both reveal considerable dipolar character in 3 .

Revision of an enamine synthesis; the preparation and reactions of 2-morpholinoisoflav-3-ene.

Abstract The condensation of N -styrylmorpholine with salicylaldehyde does not give a product that can be oxidised to isoflavone; the product is N -morpholino-isoflav-3-ene which can be used to prepare other compounds related to isoflavan and upon oxidation gives 3-phenylcoumarin.