H. Schmid

Photochemistry of some heterocyclic systems

Whereas 2H-benztriazoles are photochemically stable, 1H-benztriazoles yield biradicals after spliting of nitrogen. These biradicals attack aromatic substrates such as anisole, toluene, fluorobenzene or benzonitrile preferentially in the o- and p-positions with formation of the corresponding o-aminobiphenyls (cf. schemes 2-5). With a deficiency of aromatic substrate, attack at the o-position is strongly favored (cf. Figures 1, 2). Thereafter the very complex photochemistry of 3,5-diaryl-2-isoxazolines will be discussed (cf. schemes 7-9). This led to the discovery of the photochemical cycloaddition between 3-phenyl-2H-azirines and aldehydes, with formation of 3-oxazolines (cf. schemes 10, 11). The nitrile methylene ylides produced photochemically from azirines react, mainly in good yield, with substrates which contain cumulative (cf. schemes 15, 16) or activated (cf. schemes 12,13) double bonds. Noteworthy, is the photochemical incorporation of carbon dioxide, leading to the little known isoazlactones (scheme 15). After a short discussion of the photochemistry of the sydnones (cf. schemes 19-23), which has been only briefly investigated so far, the photolysis of indazoles, benzisoxazoles, and anthranils in strongly acid solution will be discussed (cf. schemes 24-27). These photochemical reactions give rise to aryl azenium ions or aryl oxenium ions, which react with the solvent SH preferentially in the position para to the nitrogen or oxygen, respectively.

Addition of carboxylic acids and cyclic 1,3-diketones to 2-dimethylamino-3,3-dimethyl-1-azirine

Abstract The reaction of 2 - dimethylamino - 3,3 - dimethyl - 1 - azirine 1 with carboxylic acids 2a-e at room temperature in inert solvents generates rearranged 1:1 adducts in 65–92% yields. These adducts are N-acyl derivatives of 2-amino, -N,N dimethyl-isobutyramide 3a-e resulting from 1,2 addition of the acid followed by 1,2 ring cleavage and transfer of an acyl group. Cyclic enolizable 1,3 diketones 4a-c react similarly with 1 to yield the corresponding rearranged 1:1 adducts 5a-c, whereas acyclic diketones or ethyl acetoacetate are inert under comparable experimental conditions.

Macrocyclic spermidine and spermine alkaloids

In this short review of spermine and spermidine plant alkaloids, which are characterized by the presence of a macrocyclic Iactam ring, special consideration has been given to the alkaloids from Oncinotis species and to the spermine alkaloid, chaenorrhine.

Über die Alkaloide von Aspidosperma discolor A. DC.

From the root-bark ofAspidosperma discolor A.DC., reserpiline, isoreserpiline and isoreserpiline-ψ-indoxyl have been isolated as well as two new methoxyindole alkaloids (AD IV and AD VI), which have been partially characterised.

Über die konstitution des C-Curarins☆☆☆

Zusammenfassung Durch Abbaureaktionen und Analyse von Kernresonanz-spektren wird fur C-Curarin die Formel I abgeleitet: die Halochromiereaktionen des Alkaloids werden diskutiert.

Die Zucht vonLytta vesicatoria im Laboratorium und Nachweis der Cantharidinsynthese in Larven

Adult males ofLytta vesicatoria (Coleopt., Meloidae) synthesize cantharidin, but females do not, although the substance is present in the females too. We developed a method for rearing larvae of this parasitic beetle in the laboratory. It is shown that there exist 7 larval stages and 4 hypermetamorphic forms (triungulinus, second larva,pseudochrysalis and fourth larva). Larvae from the second to the fifth stage (second larva) synthesize cantharidin. Therefore, we conclude that the substance present in the adult female is at least in part synthesized in the larval period. Nothing is known about the biological significance of this biochemical sexual dimorphism.Adult males ofLytta vesicatoria (Coleopt., Meloidae) synthesize cantharidin, but females do not, although the substance is present in the females too. We developed a method for rearing larvae of this parasitic beetle in the laboratory. It is shown that there exist 7 larval stages and 4 hypermetamorphic forms (triungulinus, second larva,pseudochrysalis and fourth larva). Larvae from the second to the fifth stage (second larva) synthesize cantharidin. Therefore, we conclude that the substance present in the adult female is at least in part synthesized in the larval period. Nothing is known about the biological significance of this biochemical sexual dimorphism.

RECENT DEVELOPMENTS IN AROMATIC SIGMATROPIC REARRANGEMENTS AND RELATED REACTIONS

Recent developments of some aromatic pericyclic reactions are reviewed. The transition state geometry of the aromatic Claisen and Cope rearrangements is discussed. Whereas a chair-like geometry is favoured normally, the stereochemistry of the products resulting from the thermal rearrangement of methyl-substituted threo-2-(α-methylallyl)-cyclohexa-3,5-dien-l-ones indicates that a boat-like geometry is involved to an extent of 40 − 90%. Bridged biphenyl and binaphthyl allyl and propargyl ethers, which possess a ground state conformation favourable for a [3s, 3s) -rearrangement are transformed thermally, even at temperatures between 25 − 130°, into dienones and their further rearrangement products. A new 2-allyl phenol → coumaran rearrangement, as well as a one step synthesis of a twistadienone, is described. Propargyl aryl and cycloheptatrienyl ethers yield, by multistep rearrangement processes, new cyclic compounds. For example, 2,6-dimethylphenyl ether on heating, followed by treatment with acid, is transformed into the 1,2,4-trimethyl-tropyliumion in good yield. Some photochemical reactions of tricyclic ketones, resulting from the thermal rearrangement of propargyl aryl ethers, are mentioned.

On the alkaloids from Aspidosperma discolor A. DC

From the root-bark ofAspidosperma discolor A.DC., reserpiline, isoreserpiline and isoreserpiline-ψ-indoxyl have been isolated as well as two new methoxyindole alkaloids (AD IV and AD VI), which have been partially characterised.

Über die Alkaloide vonAspidosperma discolorA. DC.

From the root-bark ofAspidosperma discolor A.DC., reserpiline, isoreserpiline and isoreserpiline-ψ-indoxyl have been isolated as well as two new methoxyindole alkaloids (AD IV and AD VI), which have been partially characterised.