Showing papers on "Enone published in 1969"

Studies in natural product chemistry

Abstract: The first section of this thesis is concerned with a biogenetic-type approach to the synthesis of the aconitine-lycoctonine group of diterpene alkaloids. The synthetic precursor, atisine, was transformed in an eleven step sequence into a keto-tosylate. This material underwent a novel, stereospecific pyrolytic rearrangement to give a key intermediate in the proposed atisane-aconane biogenesis, whose constitution and stereochemistry were confirmed by anx-ray crystallographic analysis, conducted on a heavy atom derivative. Our efforts to convert this intermediate into the desired aconitine-lycoctonine skeleton, a task which had already been accomplished in principle by other workers, met with limited success. N. M. R. studies on some acetamides, obtained in the foregoing synthesis, revealed an interesting example of restricted rotation around the bond. Variable temperature work enabled a crude barrier to rotation to be extracted. The second section of the thesis, also in the realm of diterpenes, concerns the synthesis of the cassane skeleton, in a biogenetically-patterned fashion, from isopimaric acid. The route from isopimaric acid to an important intermediate enone is described. Despite numerous attempts,we could not induce the Wagner-Meerwein rearrangement in this enone,which would have resulted in the desired cassane skeleton.

Photochemische Reaktionen. 52. Mitteilung [1]. Zur Photochemie von α,β-ungesättigten cyclischen Ketonen: Spezifische Reaktionen der n,π*- und π,π*-Triplettzustände von O-Acetyl-testosteron und 10-Methyl-Δ1,9-octalon-(2)

Abstract: The photochemistry of the conjugated cyclohexenones O-acetyl testosterone (1) and 10-methyl-Δ1,9-octalone-(2) (24) has been investigated in detail. The choice of reaction paths of both ketones depends strongly on the solvent used. In t-butanol, a photostationary equilibrium 1 ⇄ 3 is reached which is depleted solely by the parallel rearrangement 1 5 (Chart 1; for earlier results on these reactions see [2a] [6] [7]). In benzene, double bond shift 1 16 (Chart 3) occurs instead, which is due to hydrogen abstraction from a ground-state ketone by the oxygen of an excited ketone as the primary photochemical process. In toluene, the major reaction is solvent incorporation (1 17, Chart 4) through hydrogen addition to the β-carbon of the enone, accompanied by double bond shift and formation of saturated dihydroketone as the minor reactions. Contrary in part to an earlier report [19], the photochemical transformation of the bicyclic enone 24 exhibit a similar solvent dependence. The corresponding products 25–29 are summarized in Chart 5 and Table 1. Sensitization and quenching experiments established the triplet nature of the above reactions of 1 and 24. Based on STERN-VOLMER analyses of the quenching data (cf. Figures 2, 4–8, and Table 3), rearrangement, double bond reduction and toluene addition are attributed to one triplet state of the enones which is assigned tentatively as 3(π, π*) state, and the double bond shift is attributed to another triplet assigned as 3(n, π*) state (cf. Figure 9). The stereospecific rearrangement of the 1α-deuterated ketone 2 to the 4β-deuterio isomer 4 shows the reaction to proceed with retention at C-1 and inversion at C-10. The 4-substituted testosterone derivatives 33–36 (Chart 8) were found to be much less reactive in general than 1. In particular, 4-methyl ketone 33 remains essentially unchanged on irradiation in t-butanol, benzene and toluene.

Studies on the syntheses of heterocyclic compounds. Part CCCXV. Modified total synthesis of (±)-galanthamine through phenol oxidation

Abstract: Oxidation of 2-bromo-5-hydroxy-N-(4-hydroxyphenethyl)-4-methoxy-N-methylbenzamide (VIII) with ferricyanide afforded the narwedine-type enone (X) in an excellent yield (40%). Reduction of (X) with lithium aluminium hydride gave (±)-galanthamine (II) and (±)-epigalanthamine (XXI) in yields of 50 and 40% respectively. Oxidation of (II) with manganese dioxide afforded (±)-narwedine (XIX) This work also constitutes a formal synthesis of (±)-lycoramine.

Photochemische Reaktionen 49. Mitteilung [1] Spezifisch π → π*‐induzierte Keton‐Photoreaktionen: Die Doppelbindungsverschiebung von O‐Acetyl‐10α‐testosteron Protonisierung der Doppelbindung seines δ5‐Isomeren

Abstract: The α,β-unsatured ketone 10α-testosterone has been reported previously [6] to photoisomerize in t-butanol solution to the β,γ-unsaturated ketone. The irradiation had been carried out using a high-pressure mercury lamp in a quartz vessel. For structural reasons this double bond shift cannot proceed through a photoenolization mechanism involving an intramolecular hydrogen transfer from the γ-position to the enone oxygen as has been suggested to operate in several formally analogous cases of aliphatic enone isomerizations. In the present reinvestigation, O-acetyl 10α-testosterone (1) was used, employing selectively either excitation of its n π* (with wavelengths > 300 nm) or its π π* absorption band (with 253,7 nm). In t-butanol solution the doublebond shift 1 2 could be effected with π* excitation only. Experiments in deuterated solvent (t-BuOD) resulted in deuterium in corporation in both the δ5-ketone in the C(4)-position, cf.(3) and in the conjugated ketone. These results indicate that the reactions is initiated either in the, Sπ,π* state or in a high vibrational mode of the S0 or tππ*state. n π* Excitation of 1 in t-butanol gave essentially no over-all chemical change, while in benzene solution it resulted again in a double bond isomerization (1 2). In analogy to results with similar enones [28] under identical conditions the deconjugation in benzene may be the consequence of an intermolecular hydrogen abstraction of the Tn,π* excited state of the enone. Another specifically π π* induced photoreaction was observed on irradiation of the β, γ-unsaturated ketone 2 in t-BuOD with 253,7 nm. The olefinic hydrogen at C-6 of 2 was exchanged with deuterium and, to a small extent, isomerization to the conjugated ketone 1 with concomitant deuterium incorporation occurred. It is concluded that from the higher excited state of the β, γ-unsaturated ketone, but not from its Sn,π* state, an activation mode of the double bond is accessible to effect D+ addition at C-6 followed by deprotonation to 4 and to deuterated 1, respectively.

Intramolecular electrocyclic reactions. Part I. Structure of ‘bromohydroxyphorone’: 3-bromo-5-hydroxy-4,4,5,5-tetramethylcyclopent-2-enone

Abstract: αα′-Dibromophorone (3,5-dibromo-2,6-dimethylhepta-2,5-dien-4-one) as the conjugate acid undergoes intramolecular electrocyclic addition to give 3-bromo-5-hydroxy-4,4,5,5-tetramethylcyclopent-2-enone. The reactions of this substance, its bromine-free analogue and their derivatives, recorded by Ingold and Shoppee in 1928, are clarified and reinterpreted.

Properties of 4,4-dimethylcyclopent-2-enone: methylation of the enolate ion: base-catalysed and photochemical dimerisations

Abstract: (a) Methylation of the enolate ion of 4,4-dimethylcyclopent-2-enone (IV) occurs through the monocyclic valence tautomer, giving 4,4,5-trimethyl- and 4,4,5,5-tetramethyl-cyclopent-2-enone. The action of triphenylmethylsodium on (IV) is not proton abstraction, but Michael addition. A rationalisation for this is proposed. (b) Physical measurements are described which show the dimer of 4,4-dimethylcyclopent-2-enone, formed on treatment with base, to be endo-5,5,10,10-tetramethyltricyclo[5,2,1,02,6] decane-3,8-dione (X). Its mode of formation is discussed. (c) Structures for the two photodimers of 4,4-dimethylcyclopent-2-enone are assigned on the basis of physical data and by analogy with the photodimers of cyclopent-2-enone itself.

2,4,6-Tri-t-butylresorcinol and its diketo-tautomer from thermolysis of a 3-hydroxy-4-vinylcyclobut-2-enone

Abstract: The products of the thermal rearrangement of 3-hydroxy-4-(3,3-dimethyl-trans-but-1-enyl)-2,4-di-t-butylcyclobut-2-enone are 2,4,6-tri-t-butylresorcinol and its diketo-tautomer.