Migration du groupe éthoxycarbonyle dans la transposition de Wagner-Meerwein

Ethoxycarbonyl group migration in the Wagner-Meerwein rearrangement . 13 β-Hydroxy-esters have been treated with P₂O₅ in benzene at 80°. Olefin-forming dehydration, when possible, was found to be the main reaction. When this is excluded, tertiary or benzylic hydroxy-esters react in a manner most easily explained by migration of the COOEt group, thus avoiding the formation of α-carbonyl-carbenium ions. On the other hand, in primary hydroxy-esters (incapable of direct olefin formation), phenyl and methyl groups migrate in preference to COOEt, indicating in this case a concerted reaction.     

Transpositions de doubles liaisons de terpènes bicycliques catalysées par des bases

The displacements of double bonds and dehydrogenation by basic catalysts are examined by analogy with the preceding studies on p-menthenes and p-menthadienes [1] with bicyclic terpenes: α- and β-pinenes, sabinene and 3-carene.     

Plectranthone A,B, C und D. Diterpenoide Phenanthren-1,4-dione aus Blattdrüsen einer Plectranthuus sp. (Labiatae)

Plectranthons A, B, C, and D. Diterpenoid Phenanthrene-1,4-diones from Leaf-glands a Plectranthus sp. (Labiatae) The following structures of four new 1,4-phenanthraquionones, isolated in minute amounts from the coloured leaf-glands of a Plectranthus sp. obtained from the borders of Lake Kiwu₂, Rwanda, are proposed: plectranthon A ( 1 ; 3-hydroxy-5, 7,8-trimethyl-2-(2-propenyl)phenanthrene-1, 4-dione), plectranthon B ( 2 ; 2-(2ξ-acetoxypropyl)-3-hydroxy-5,7,8-trimethylphenanthrene-1,4-dione), plextranthon C ( 3 ; 3-hydroxy- 7,8-diemethyl-2-(2-propenyl)phenanthrene-1,4-dione), and plectranthon D ( 4 ; 3-hydroxy-7,8,10-trimethyl-2-(2-propenyl)phenanthrene-1,4-dione). 2-(2ξ-Hydroxypropyl)-3,6-dihydroxy-5,7,8-trimethylphenanthrene-1,4-dione ( 11 ), a compound very similar to 1–4 , was prepared by a Wagner-Meerwein, rearrangement of coleon E (⁵). Biogenetically, the plectranthons are derived from abietanoic precursors. The compounds 1, 2 and 4 are the first natural C₂₀-phenanthrenes of diterpenoid origin.     

Catalytic activity of the VIII Group metals in the hydrogenation and isomerization of α- and β-pinenes

The kinetic regularities of the liquid-phase hydrogenation and isomerization of α- and β-pinenes over the Pd/C, Ru/C, Rh/C, Pt/C, and Ir/C catalysts were studied at temperatures ranging from 20 to 100 °C and at hydrogen pressures of 1–11 bar using n-octane as the solvent. The hydrogenation and isomerization of α- and β-pinenes occur simultaneously on the Ru/C, Rh/C, Pt/C, and Ir/C catalysts, and the reaction mixture contains the products of double bond hydrogenation, viz., cis- and trans-pinanes. The Ru, Rh, and Pd metals have a higher catalytic activity in β-pinene isomerization than Ir and Pt. Among the VIII Group metals studied, the Pd-based catalyst has the highest catalytic activity in double bond isomerization of α- and β-pinenes. The general scheme of the mechanism of hydrogenation and isomerization of α- and β-pinenes on the Pd/C catalyst was proposed.     

Selective Hydrogen Chloride Elimination from Primary Chlorides Induced by the Fluoride Anion. Anchimeric participation of the chloromethyl group in the heterolytic opening of an epoxide. Stereospecific syntheses of 5,6-bis (methylidene)-syn-2-norbornen-7-ol and 5,6-bis (methylidene)-endo-3-chloro-exo-2-norbornanol

Syntheses of the alcohols 10 and 18 , and the corresponding ketones 11 and 19 are presented. Endo-5, exo-6-bis (chloromethyl)-endo-3-chloro-exo-2-norbornanol ( 16 ) and endo-5-(bromomethyl)-exo-6-(chloromethyl)-endo-3-chloro-exo-2-norbornanol ( 17 ) were obtained by HCl- and, respectively, HBr-addition to endo-5, exo-6-bis (chloromethyl)-exo-2, 3-epoxynorbornane ( 5 ). The Wagner-Meerwein rearrangement was precluded in these reactions probably because of the formation of a relatively stable chloronium ion 15 arising from the participation of the 1,4-chlorine atom of the endo-5-chloromethyl group in the heterolytic ring opening of the epoxide 5 . The ‘naked’ fluoride anion (excess CsF in DMF or KF in DMF with 18-crown-6-ether) permitted the selective elimination of 2 equivalents of HCl from 16 and yielded the chlorohydrin-diene 18 .     

Synthése,stéréochimie,et réactivité thermique de (N-méthylidenealkylamino)-2 aziridines

1-Alkyl-2-(N-methylidenealkylamino)aziridines are obtained by the reaction of primary amines with either α-chloroacraldehyde or α-chlorocrotonaldehyde. Structural assignments are made by nmr spectroscopy. The thermal rearrangement of 1-alkyl-2-(N-methylidenealkylamino)-3-methylaziridines to pyrroles is described.     

The Reaction of Singlet Oxygen with α- and β-Pinenes

The reaction of photogenerated singlet oxygen with α- and β-pinenes has been carefully re-examined. α-Pinene almost exclusively (99.3% yield) furnishes trans-3-hydroperoxy-pin2(10)-ene. However, detectable amounts of the three other possible products are also found, viz., cis-3-hydroperoxypin-2 (10)-ene (?0.8%), and cis- and trans-2-hydroperoxypin-3 (4)-ene (?0.04%). β-Pinene gives 99.9% of 10-hydroperoxypin-2 (3)-ene and a trace (?0.01%) of norpinan-2-one. Rates of reaction and product composition are treated by modal analysis and reflect the operation of steric and stereoelectronic factors in a reactant-like transition state.     

Pyrrolothienopyrazines. IV. Synthese de derives de 1′amino-5 pyrrolo[1,2-a]thieno[2,3-e]pyrazine

5-Aminopyrrolo[1,2-a]thieno[2-3-3]pyrazine derivatives were obtained by intramolecular cyclisation of N³(1-pyrrolyl)-2-thienylurea derivaties. Synthesis of these latter compounds was achieved from 2-(1-pyrrolyl)-3-thenoylazide via a curtius rearrangement. The H nmr spectra are discussed.     

Utilisation du 13C en Spectrométrie de Masse: Etude de la Fragmentation de Disaccharides

Twenty-nine α,β-(1 → 3) and (1 → 4) or β-(1 → 6) disaccharides, in the glucose series were analysed by electron impact mass spectrometry. In addition to the known mechanism, a few ¹³C labelled compounds led us to suggest that the ion c was formed from the reducing unit B and the C-1′ of the non-reducing residue A, while A was the starting point for rearrangement and fragmentation processes.     

Reaction of 1,3-Thiazole-5(4H)-thiones with 1,2-Epoxycycloalkanes: Formation of Spirocyclic 1,3-Oxathiolanes

Treatment of solutions of 1,3-thiazole-5(4H)-thiones 1 in CH₂Cl₂ at room temperature with BF₃⋅Et₂O and 1,2-epoxycyclohexane (7-oxabicyclo[4.1.0]heptane; 2a ) or 1,2-epoxycyclopentane (6-oxabicyclo[3.1.0]hexane; 2b ) yielded mixtures of diastereoisomeric spirocyclic 1,3-oxathiolanes ( 3 / 4 and 8 / 9 , respectively). In addition, the corresponding 1,3-dithiolane 6 was formed as a minor product in the reaction of 4,4-dimethyl-2-phenyl-1,3-thiazole-5(4H)-thione ( 1a ) with 2a . The structures of the different types of products have been established by X-ray crystal-structure analysis. An ionic two-step mechanism via nucleophilic ring-opening of the complexed oxirane by the attack of the thiocarbonyl S-atom is proposed. This proposal is supported by the formation of the propellane 10 with a Wagner-Meerwein rearrangement as the key step.     

The Reaction of Patchoulol with Lead Tetraacetate,a Regiospecific Fragmentation

Patchoulol (1) forms 2,2,6,8-tetramethylbicyclo [5.3.1]undec-7-en-3-one (5) with lead tetraacetate. This ketone undergoes acid-catalyzed cyclization to 2,6,6,10-tetramethyltricyclo [5.3.1.0^1,5]undec-9-en-5-ol (10) , and is reduced to 2 stereoisomeric alcohols with lithium aluminium hydride. One of these alcohols 8 is readily dehydrated with cyclization to 2,6,6,10-tetramethyltricyclo [5.3.1.0^1,5]undec-9-ene (12) and a double bond isomer 13 , longer treatment with acid resulting in a Wagner-Meerwein rearrangement to a mixture of two 1,3,7,7-tetramethyltricyclo [6.2.1.0^2,6]-undecenes ( 19 and 20 ), isomeric with β-patchoulene ( 23 ). The other alcohol 7 with p-toluenesulfonic acid forms the cyclic ether, 1,3,7,7-tetramethyl-11-oxatricyclo-[4.4.1.1^2,8]dodecane ( 15 ).     

Poly(β-pinenes) carrying one,two, and three functional end groups. II. Syntheses and characterization

Conditions for the convenient synthesis of linear poly(β-pinenes) that carry one or two tert-chloro end groups (～Cl^t) and three-arm star poly(β-pinenes) that carry three termini have been worked out. Specifically, the polymer with one ～Cl^t end group was prepared by the H₂O/BCl₃ system, whereas those with two and three ～Cl^t termini were prepared by the use of p-dicumyl chloride and sym-tricumyl chloride/BCl₃ inifer combinations. The ～Cl^t-terminated polymers were dehydro-chlorinated to yield the corresponding olefins. The molecular weights of the products were low enough to permit infrared (IR) and quantitative ¹H-NMR investigations. Poly(β-pinene-b-tetrahydrofuran) diblock copolymers have been synthesized by inducing the polymerization of tetrahydrofuran (THF) by the Pβ? Cl^t/AgCF₃SO₃ initiating system.     

Réarrangement de thiénobenzothiépinones en thiénoisothiazolinone et benzoisothiazolinone

Under the conditions of the Schmidt reaction the thienobenzothiepinones 1 , 2 and 13 involve a rearrangement respectively in N-benzythieno[2,3-d]isothiazolin-3-one ( 5 ) and benzoisthiazolin-3-one ( 6 ). A mechanism for this rearrangement is proposed.     

Ylides du soufre dérivés de sucres Communication préliminaire

S-Methylation of 6-S-benzyl-6-deoxy-1,2-O-isopropylidene-3-O-methyl-α-D-xylo-6-thiohexofuranos-5-ulose ( 1 ) gave the expected sulfonium salt 2 which on alcaline treatment yielded the stable sulfur ylide 3 . This compound constitutes an useful synthetic intermediate in carbohydrate chemistry. On heating in 1,2-dimethoxyethane, it underwent a Stevens rearrangement which led to an extension of the carbon chain of the sugar and, reacted with Michael acceptors, it gave cyclopropanation reactions.     

Transpositions thermiques de derives d'α-pinene

Novel thermal transformations of (+)-pin-2-en-9-al 1 and (+)-9-methyl-pin-2-en-9-one 3 by [3,3] sigmatropic mechanism to allyl vinyl ethers 2 and 4 are described. The ether 4 may undergo further rearrangement in an acid-catalysed step to the (-)-2.6-dimethylbicyclo[3.3.1]non-6-en-2ones (5 and 5'). Formation of the bicyclic ketones (+)-5 and 5' of opposite absolute configuration occurs by [3,3] sigmatropic rearrangement of the trimethylsilyl enol ether of 3 and hydrolysis. The proposed mechanism is confirmed by studying the deuterated ketone d₃^?3.     

Untersuchungen über aromatische Amino-Claisen-Umlagerungen

Investigations on Aromatic Amino-Claisen Rearrangements The thermal and acid catalysed rearrangement of p-substituted N-(1′,1′-dimethylallyl)anilines (p-substituent=H (5) , CH₃ (6) , iso-C₃H₇ (7) , Cl (8) , OCH₃ (9) , CN (10) ), of N-(1′,1′-dimethylallyl)-2,6-dimethylaniline (11) , of o-substituted N-(1′-methylallyl)anilines (o-substituent=H (12) , CH₃ (13) , t-C₄H₉ (14) , of (E)- and (Z)-N-(2′-butenyl)aniline ((E)- and (Z)- 16 ), of N-(3′-methyl-2′-butenylaniline (17) and of N-allyl- (1) and N-allyl-N-methylaniline (15) was investigated (cf. Scheme 3). The thermal transformations were normally conducted in 3-methyl-2-butanol (MBO), the acid catalysed rearrangements in 2N -0,1N sulfuric acid. - Thermal rearrangements. The N-(1′,1′-dimethylallyl)anilines rearrange in MBO at 200-260° with the exception of the p-cyano compound 10 in a clean reaction to give the corresponding 2-(3′-methyl-2′-butenyl)anilines 22–26 (Table 2 and 3). The amount of splitting into the anilines is <4% ( 10 gives ? 40% splitting). The secondary kinetic deuterium isotope effect (SKIDI) of the rearrangement of 5 and its 2′,3′,3′-d₃-isomer 5 amounts to 0.89±0.09 at 260° (Table 4). This indicates that the partial formation of the new s?-bond C(2), C(3′) occurs already in the transition state, as is known from other established [3,3]-sigmatropic rearrangements. The rearrangement of the N-(1′-methylallyl)anilines 12–14 in MBO takes place at 290–310° to give (E)/(Z)-mixtures of the corresponding 2-(2′-Butenyl)anilines ((E)- and (Z)- 30,-31 , and -32 ) besides the parent anilines (5–23%). Since a dependence is observed between the (E)/(Z)-ratio and the bulkiness of the o-substituent (H: (E)- 30 /(Z)- 30 =4,9; t-C₄H₉: (E)- 32 /(Z)- 32 =35.5; cf. Table 6), it can be concluded, that the thermal amino-Claisen rearrangement occurs preferentially via a chair-like transition state (Scheme 22). Methyl substitution at C(3′) in the allyl chain hinders the thermal amino-Claisen-rearrangement almost completely, since heating of (E)-and (Z)- 16 , in MBO at 335° leads to the formation of the expected 2-(1′-methyl-allyl) aniline (33) to an extent of only 12 and 5%, respectively (Scheme 9). The main reaction (?60%) represents the splitting into aniline. This is the only observable reaction in the case of 17 . The inversion of the allyl chain in 16 - (E)- and (Z)- 30 cannot be detected - indicated that 33 is also formed in a [3, 3]-sigmatropic process. This is also true for the thermal transformation of N-allyl- (1) and N-allyl-N-methylaniline (15) into 2 and 34 , respectively, since the thermal rearrangement of 2′, 3′, 3′-d₃- 1 yields 1′, 1′, 2′-d₃- 2 exclusively (Table 8). These reaction are accompanied to an appreciable extent by homolysis of the N, C (1′) bond: compound 1 yields up to 40% of aniline and 15 even 60% of N-methylaniline ((Scheme 10 and 11). The activation parameters were determined for the thermal rearrangements of 1, 5, 12 and 15 in MBO (Table 22). All rearrangements show little solvent dependence (Table 5, 7 and 9). The observed ΔH^≠ values are in the range of 34-40 kcal/mol and the ΔS^≠ values very between -13 to -19 e.u. These values are only compatible with a cyclic six-membered transition state of little polarity. - Acid catalysed rearrangements. - The rearrangement of the N-(1′, 1′-dimethylallyl) anilines 5-10 occurs in 2N sulfuric acid already at 50-70° to give te 2-(3′-methyl-2′-butenyl)anilines 22-27 accompanied by their hydrated forms, i.e. the 2-(3′-hydroxy-3′-methylbutyl) anilines 35-40 (Tables 10 and 11). The latter are no more present when the rearrangement is conducted in 0.1 N sulfuric acid, whilst the rate of rearrangement is practically the same as in 2 N sulfuric acid (Table 12). The acid catalysed rearrangements take place with almost no splitting. The SKIDI of the rearrangement of 5 and 2′, 3′, 3′-d₃- 5 is 0.84±0.08 (2 N H₂SO₄, 67, 5°, cf. Table 13) and thus in accordance with a [3,3]-sigmatropic process which occurs in the corresponding anilinium ions. Consequently, the rearrangement of a 1:1 mixture of 2′, 3′, 3′-d₃- 5 and 3, 5-d₂- 5 in 2 N sulfuric acid at 67, 5° occurs without the formation of cross-products (Scheme 13). In the acid catalysed rearrangement of the N-1′-methylallyl) anilines 12-14 at 105-125° in 2 N sulfuric acid the corresponding (E)- and (Z)-anilines are the only products formed (Table 14 and 15). Again no splitting is observed. Furthermore, a dependence of the observed (E)/(Z) ratio and the bulkiness of the o-substituent ( H : (E)/(Z)- 30 = 6.5; t- C ₄ H ₉: (E)- 32 /(Z)- 32 = 90; cf. Table 15) indicates that also in the ammonium-Claisen rearrangement a chair-like transition state is preferentially adopted. In contrast to the thermal rearrangement the acid catalysed transformation in 2 N-O, 1 N sulfuric acid (150-170°) of (E)- and (Z)- 16 as well as of 1 and 15 , occurs very cleanly to yield the corresponding 2-allylated anilines 33, 2 and 34 (Scheme 15 and 18). The amounts of the anilines formed by splitting are <2%. During longer reaction periods hydration of the allyl chain of the products occurs, and in the case of the rearrangement of (E)- and )Z)- 16 the indoline 45 is formed (Scheme 15 and 18). All transformations occur with inversion of the allyl chain. This holds also for the rearrangement of 1 , since 3′, 3′-d₂- 1 gives only 1′, 1′-d₂- 2 (Scheme 17). The activation parameters were determined for the acid catalysed rearrangement of 1, 5, 12 and 15 in 2 N sulfuric acid (Table 22). The ΔH^≠ values of 27-30 kcal-mol and the ΔS^≠ values of +9 to -12 e.u. are in agreement with a [3, 3]-sigmatropic process in the corresponding anilinium ions. The acceleration factors (k_H+/k_Δ) calculated from the activation parameters of the acid catalysed and thermal rearrangements of the anilines are in the order of 10⁵ - 10⁷. They demonstrate that the essential driving force of the ammonium-Claisen rearrangement is the ‘delocalisation of the positive charge’ in the transition state of these rearrangements (cf. Table 23). Solvation effects in the anilinium ions, which can be influenced sterically, also seem to play a role. This is impressively demonstrated by N-(1′, 1′-dimethylallyl)-2, 6-dimethylaniline (11) : its rearrangement into 4-(1′, 1′-dimethylallyl)-2, 6-dimethylaniline (43) cannot be achieved thermally, but occurs readily at 30° in 2 N sulfuric acid. From a preparative standpoint the acid catalysed rearrangement in 2 N-0, 1 N sulfuric acid of N-allylanilines into 2-allylanilines, or if the o-positions are occupied into 4-allylanilines, is without doubt a useful synthetic method (cf. also [17]).     

Fragmentation sous impact electronique de l'acetate de tertiobutyle

The mass spectral fragmentation of tert-butylacetate has been studied by means of high resolution studies, deuterium labelling and metastable transition determinations. Besides the McLafferty rearrangement, two less classical rearrangement mechanisms of oxygen-containing ions are observed and some isotope effects are reported.     

Essential Oil and Antimicrobial Evaluation of the Pistacia eurycarpa

The compositions of microdistilled and hydrodistilled essential oils of the mastix ofPistacia eurycarpaYalt. (Anacardiaceae) were compared. The essential oils were analyzed by GC/MS:- andbeta;-pinenes were found as the major constituents. The antimicrobial activity of the hydrodistilled oil was determined due to the ethnomedical uses of the oleo-gum resin on skin diseases.     

Diénamines hétérocycliques. III. Réexamen de la réaction de la base de Fischer avec le tétracyanoéthylène

Heterocyclic dienamines III. A re-examination of the reaction of Fischer's base on tetracyanoethylene Depending on the order of addition, Fischer's base 5 (1,3,3-trimethyl-2-methylidene-indoline) reacts 1:1 with tetracyanoethylene to give either the tricyanovinylation product 6 or the spiro compound 7 . A skeletal rearrangement of a zwitterionic intermediate can explain the formation of the spiro compound. The latter undergoes a thermal isomerization yielding by ring expansion the tetrahydroquinoléine 8 . On reaction with LiAlH₄ or CH₃ONa 7 and 8 lead both to triazatetracycles. All structures are assigned on the basis of spectral data.     

Thermische Umwandlung von Penta-2, 4-dienyl-phenyläthern in 4-(Penta-2, 4-dienyl)-phenole; [5s, 5s]-sigmatropische Umlagerungen

trans-Penta-2, 4-dienyl phenyl ether (trans- 1 ), on heating at 186° in a five-fold excess of N, N-diethylaniline, gave via a [3s, 3s] rearrangement 23% of 2-(1-vinyl-allyl)-phenol ( 2 ) and via a [5s, 5s] rearrangement 37% of trans-4-(penta-2, 4-dienyl)-phenol (trans- 3 ). The dimeric residue was formed from trans- 1 by diene synthesis. By working at high dilution, the formation of dimeric products was kept to a minimum. The inversion of the migrating pentadienyl residue during the rearrangement of trans- 1 to trans- 3 was proved by rearrangement of the methyl labelled ether trans, trans- 4 to the p-dienyl-phenol 8 (93%) (accompanied by only 7% of 9 ). trans- 5 gave the p-phenol 9 quantitatively. cis-Penta-2, 4-dienyl phenyl ether (cis- 1 ) was converted to 10 on heating, by a fast [1, 5s] H-migration. The above mentioned reactions of the type trans- 1 → trans- 3 show first order kinetics and are the first examples of [5s, 5s] sigmatropic rearrangements shown to go through a ten-membered transition state. The conformation of the activated complex is discussed in the light of the stereochemistry of the migrating penta-2, 4-dienyl group.