Showing papers on "Enone published in 1973"

A Rapid Route to Hex-1-enopyran-3-uloses

Abstract: Whereas the pseudo-axial 3-hydroxyl group of allal derivatives is known to be inert to manganese dioxide oxidation, the equatorial counterpart in glucal derivatives is shown to be readily oxidized. Thus glucal is converted to the 6-O-triphenylmethyl ether or 6-O-benzoyl ester to promote solubility in chloroform, and the derivatives are oxidized in that solvent in 12 h or less.Acetonation of glucal is readily accomplished in 45 min using 2,2-dimethoxypropane and p-toluenesulfonic acid in dimethylformamide; the product may be oxidized directly either with manganese dioxide or dipyridine chromium oxide. Thus it is possible to obtain 1–3-g quantities of the crystalline acetonated enone from triacetyl glucal (via deacetylation, acetonation, and oxidation) in 3–4 h.If the acetonation medium stands for 2 h methyl 2,3-dideoxy-4,6-O-isopropylidene-α-D-erythro-hex-2-enopyranoside is obtained. The mechanism of its formation in the reaction medium is discussed.

The photoaddition of nucleophiles to uracil

Abstract: — Quantum yields for 254 nm ultraviolet photoaddition of the nucleophiles hydrazine, HCN, HSO3-, methyl amine, and BH4- to uracil have been measured; the quantum yields for hydrazine, HCN, and HSO3- additions are pH-dependent. The nucleophiles sulfide, azide, chloride, bromide, iodide, nitrite and thiocyanate failed to photo–add under similar conditions. These reactions are interpreted as 1,4-additions to the conjugated enone system of the anti-aromatic compound, uracil; as suggested by S. Y. Wang (Wang and Nnadi, 1968). The nuclear magnetic resonance (NMR) spectrum of the photohydrate of uracil-5-d-showed that the proton was added to the 5-position in a stereochemically random manner. The photoaddition of HSO3- takes place at much lower concentrations than required for the thermal addition of this anion and is also stereochemically random.

Constituents of the higher fungi. Part XII. Identification of involutin as (–)-cis-5-(3,4-dihydroxyphenyl)-3,4-dihydroxy-2-(4-hydroxyphenyl)-cyclopent-2-enone and synthesis of (±)-cis-involutin trimethyl ether from isoxerocomic acid derivatives

Abstract: Xerocomic and isoxerocomic acids have been synthesised and converted into the corresponding 2,5-diaryl-4-methoxycyclopent-4-ene-1,3-diones. Reduction of the dione from isoxerocomic acid has given racemic involutin trimethyl ether (IV); this identifies involutin as (III). Isoxerocomic acid is readily oxidised to xerocomorubin; this is compared with the naturally occurring variegatorubin.

α‐Chlor‐nitrone VI: Ag+‐induzierte Reaktion mit Acetylen‐derivaten. Eine neue Bildungsweise von α,β‐ungesättigten Carbonylsystemen Über synthetische Methoden, 10. (vorläufige) Mitteilung

Abstract: α-Chloro-aldonitrones provide a novel synthetic pathway from acetylenes to αβ-unsaturated enone systems.

Zur Photochemie von Δ1,9‐10‐Methyl‐2‐octalon

Abstract: Some aspects of the photochemistry of Δ1,9-10-methyl-2-octalone (1) were reinvestigated. In view of the hitherto neglected substantial thermal reversibility of the photolytic double bond shift under previous conditions of analysis (1) the solvent-dependent selectivity in product formation in C6H6 and t-BuOH was confirmed, (2) the essentially exclusive double bond shift and its intermolecular nature in C6F6 were established, (3) the quantum yields of the major products in these three solvents were measured, and (4) the dependence of triplet quenching data on temperature, enone concentration and conversion was shown in C6F6 for the double bond shift. In conclusion, the previously published experimental basis for the postulate of two differentially reactive triplet states of 1 is insufficient, although the postulate itself is not necessarily disproved.

Photochemical Reactions of Enamino Ketones

Abstract: Photochemical reactions of N-aryl enamino ketones including one enone system and one divinylamine system in the molecule were examined. Photochemical behaviours of N-aryl enamino ketones differed for the tertiary and secondary amines involved. While 5,5-dimethyl-3-(N-methylanilino)cyclohex-2-en-1-one gave an oxidative cyclization product, 3-anilino-5,5-dimethyl-cyclohex-2-en-1-one gave two major products and a minor one. One of the major products was characterized as 3,3-dimethyl-5-hydroxy-3,4-dihydro-1-benzazocines by their elemental analyses and spectroscopic properties. The compounds showed 6π system pseudo aromaticity in their NMR spectra. The temperature-dependent NMR signals for gem-dimethyl protons were due to the flapping of the 8-membered ring. The reduction product with diborane was identified as 1,2,3,4,5,6-hexahydro-1-benzazocine by comparison with an authentic sample. The other major product was a ketene adduct and the minor product, a lactone.

Investigation of singlet‐triplet transitions by phosphorescence excitation spectroscopy. X A simple α, β‐unsaturated ketone

Abstract: X‐ray diffraction techniques and Patterson methods have been used to determine the crystal structure of the simple conjugated enone, ketone I. The crystals studied belong to space group P1 with a = 9.365(6), b = 6.578(4), c = 8.321(5), α = 101.70(3), β = 101.55(3), and γ = 101.37(3). Least squares refinement of 836 counter‐collected, unique reflections having | F |2>2.5σ(| F |2) led to a final value of the conventional R1 factor (based on F) of 5.8%. The structure consists of rather loosely packed, strain free bicyclic molecules, in which the enone chromophore is planar. Phosphorescence excitation spectroscopy was used to obtain the polarized singlet‐singlet and singlet‐triplet absorption spectra of oriented crystals. The important results are: (i) The ordering of excited states in this molecule is 1(n, π*)>3(n, π*)>3(π, π*). (ii) Polarization measurements and Franck‐Condon considerations indicate that the difference in geometry between the 3(π, π*) state and the gound state is small. (iii) The 1(n, π*) s...

Specifically π→π* Induced Photoreactions of α,β‐Unsaturated Ketones: Hydrogen Abstraction by the α‐carbon. (Preliminary Communication)

Abstract: Irradiations at 254 nm of the α,β-unsaturated γ-dimethoxy-methyl ketone 7 in iso-octane and t-butyl alcohol afforded in a specifically ππ*induced process and in high chemical yield the epimeric products 9 and 10. These products were not formed on nπ* excitation of 7 at > 340 nm, but triplet energy transfer to 1,3-cyclohexadiene could be observed. Photolyses of the hexadeuterio analog 7-d6 at 254 nm led to the fully deuteriated products (cf.9-d6) in both solvents, with stereospecific incorporation of a deuterium atom in position C(1α). The structures of 9 and 10 were determined by an X-ray diffraction analysis of 9 and chemical correlations of the two products. The structural constraints in 7 demand a hitherto unprecedented direct transfer of a methoxyl hydrogen to the α-carbon of the excited enone and formation of intermediate 8.

The pimarane → cassane rearrangement. Synthesis of a potential intermediate from isopimaric acid

Abstract: The unstable cisoid enone diester dimethyl 7-oxoisopimar-8(14)ene-16,18-dioate (27), a potential intermediate for the pimarane → cassane rearrangement, has been synthesised regiospecifically from isopimara-7,15-dien-18-oic acid (isopimaric acid)(11)via the keto-lactone 18-methoxycarbonyl-7-oxo-18-norisopimaran-16,8α-olactone (25). Several unsuccessful attempts to induce the rearrangement with derivatives of the enone (27) are described.