Photochemisches Verhalten von 1- und 2-alkylierten 1,2-Dihydronaphtalinen

Irradiation of 1-alkyl-substituted 1,2-dihydronaphthalenes ( 10, 11, 12 ) with a lowpressure mercury lamp yields by ring opening ω-vinyl-o-quinodimethanes, which undergo [1, 7] H-shifts to give 1,2-divinyl-benzenes ( 8, 18, 23 ; cf. schemes 2, 3 and 4). In a further photoreaction of the divinylbenzenes, benzobicyclo [3.1.0]hex-2-enes ( 17, 19, 22 ) are formed. 2-Alkyl-substituted 1,2-dihydronaphthalenes ( 13, 14, 15, 16 ) are transformed by irradiation into ω-vinyl-o-quinodimethanes, which show [1, 7] H-shifts to yield in this case 2-(buta-1′, 3′-dienyl)-toluenes ( 9, 25, 26, 27 ; cf. schemes 6 and 7). The irradiation of 1-methyl- ( 10 ) and 1-ethyl-1, 2-dihydronaphthalene ( 11 ) with a high-pressure mercury lamp produces, besides the products of irradiation using the lowpressure lamp, 2-ethyl-allenylbenzene ( 24 ), and (from 11 ) 4-exo-ethyl-benzobicyclo[3.1.0]hex-2-ene (exo- 20 ) and 2-propyl-allenylbenzene ( 21 ), respectively (cf. scheme 5). Obviously, these products arise from a photreaction of the primarily formed ω-vinyl-o-quinodimethanes a .     

Aromatische [1,5s]-sigmatropische H-Verschiebungen in Arylallenen

1-Mesityl allene ( 1 ), 1-mesityl-3-methyl allene ( 2 ) and 1-mesityl-3,3-dimethyl allene ( 3 ) rearrange thermally at 150–190° in decane via [1,5s]sigmatropic H-shifts to yield the o-quinodimethanes 4 , which cyclise to give the 1,2-dihydronaphthalenes 5 and 6 and/or undergo [1,7 a]sigmatropic H-shifts to give 1-mesityl-(Z)-buta-1, 3-dienes (Z)- 7 and (Z)- 8 , respectively (Schemes 1,3,4 and 5) in almost quantitative yields. The activation parameters of these isomerisations are given in Table 1. 1-Mesityl-1-methyl allene ( 9 ) isomerises at 190° to give 4,5,7-trimethyl-1,2-dihydronaphthalene ( 17 ) in 50% yield (Scheme 6). 2′-Isopropylphenyl allene ( 10 ) in decane rearranges at 170° to 1-(Z)-propenyl-2-isopropenyl-benzene ((Z)- 19 , Scheme 7). Deuterium labelling experiments show that the rate determining step is an aromatic [1,5s]sigmatropic hydrogen shift from an sp³- to an sp-hybridised carbon atom. The primary kinetic isotopic effect (k_H/k_D) is 3.45, while the secondary βisotopic effect is 1.20 (Scheme 7 and Table 2).     

Photochemie von 1,1-Dimethyl-4-phenyl- und 1-Methyl-1-phenyl-1,2-dihydronaphthalin; Nachweis einer photochemischen,sigmatropischen [1,7]H-Verschiebung. 41. Mitteilung über Photoreaktionen

Photochemistry of 1,1-dimethyl-4-phenyl-and 1-Methyl-1-phenyl-1,2-dihydronaphthalene; evidence for a photochemical, sigmatropic [1,7]H-shift. Irradiation of 1,1-dimethyl-4-phenyl-1,2-dihydronaphthalene ( 11 ) and 1-methyl-1-phenyl-1,2-dihydronaphthalene ( 8 ) in pentane were investigated at ?112° to ?118°, using a mercury high pressure lamp. The [1,5]-hydrogen-shift products 13 and 17 , respectively, the [1,7]-hydrogen-shift products 15 and 10 , respectively and the photochemical Diels-Alder products 14 and 18 , respectively, were obtained, presumably via the ω-vinyl-o-quinodimethane intermediates 12 and 9 (Schema 3). Irradiation of the 1,2-dihydronaphthalene 11 at ?181° to ?183° in a 2,2-dimethylbutane/pentane matrix, gave rise to an UV.-maximum at 402 nm which is assigned to the o-quinodimethane derivative 12 . After warming the solution around ?130° or to room temperature, a product mixture was obtained, which mainly consist of the [1,7]-hydrogen-shift product 15 accompanied by the [1,5]-hydrogen-shift products 13 and 16 and the photochemical Diels-Alder product 14 (Table 1). When the o-quinodimethane intermediate 12 was irradiated with 406 nm-light, the longwavelength absorption completely disappeared. This solution, after warmingup, yielded mainly the [1,5]-hydrogen-shift products 13 and 16 together with the bicyclic compound 14 and surprisingly a small amount of the [1,7]-hydrogen-shift product 15 (Table 1). Similar experiments were carried out with the 1,2-dihydronaphthalene 8 . The results clearly indicate that irradiation of the o-quinodimethane 9 at ?180° to ?185° with 406 nm-light caused [1,5]- and [1,7]-hydrogen shifts in a ratio of approximately 1:1 (Table 2). From the experiments described above it follows, that the phenyl-substituted α-methyl-ω-vinyl-o-quinodimethanes 12 and 9 undergo upon irradiation with light of λ > 400 nm, besides photochemical Diels-Alder reactions, also [1,5]- and [1,7]- hydrogen shifts. It is remarkable that the thermal [1,7]-hydrogen-shifts of the o-quinodimethanes 12 and 9 occur readily around ?130°, whilst a temperature of ?70° is needed to promote [1,7]-hydrogen-shifts in the non-phenylated o-quinodimethanes of the type 2 (Schema 1). The phenyl group in ω- or α-position may enter into conjugation with the π-system in the helcal transition state of the [1,7]-hydrogen shift, but not in the reactants 12 and 9 .     

Thermische Cyclodehydratisierung von Salicylalkoholen; eine einfache Synthese von 4-substituierten 2H-Chromenen

Heating of 1-(o-hydroxyaryl)-2-propen-1-ols ( 9–13 ; see scheme 1) in diglyme solution at 147° leads to a 1,4-elimination of water to yield ω-vinyl-o-quinomethides ( b ; see scheme 2) as intermediates which cyclise rapidly to form 2H-chromenes ( 17–21 ). 1-(o-Hydroxyphenyl)-5-hexen-1-ol ( 14 ) on heating at 147° is transformed into o-(1,5-hexadienyl)-phenol ( 23 ). This phenol rearranges at higher temperature (270°) in N,N-diethylaniline to yield a mixture of 2,4-propanochromane ( 25 ) and cis- and trans-3,4-propanochromane (cis- and trans- 26 ). The kinetically controlled ratio of these compounds is 2,8:1:2,9. The formation of 25 and 26 can be explained by an intramolecular Diels-Alder reaction (see scheme 3).     

Thermisches Verhalten von 1,2-Dipropenylbenzolen

1-cis, 2-cis-Dipropenylbenzene (cis, cis- 1 ) isomerises thermally at 215–235° with 1st order kinetics to give trans, cis- 1 and vice versa. At equilibrium 89% trans, cis- and 11% cis, cis- 1 are present. It is shown by thermal rearrangement of cis, cis-2′, 2″-d₂- 1 that the isomerisation is attributable to aromatic [1, 7a]-sigmatropic H-shifts. trans, trans- 1 rearranges thermally at 225–245° to yield 2, 3-dimethyl-1, 2-dihydronaphthalene ( 2 ). The formation of 2 can be visualized by disrotatory ring closure followed by an aromatic [1, 5s]-sigmatropic H-shift. 2 is also formed when, cis, cis- or trans, cis- 1 are heated for 153 h at 225°. Besides 2 a small amount (3%) of 1-ethyl-1, 2-dihydronaphthalene ( 5 ) is formed. The rearrangement of trans, trans- 1 and trans, trans-2′, 2″-d₂- 1 shows a secondary isotope effect k_H/k_D = 0,90.     

Die thermische Umlagerung von 2-(Buta-1′,3′-dienyl)-phenolen in 2-Alkyl-2H-chromene; Beispiele für aromatische [1,7a]- und [1,5s]sigmatropische Wasserstoffverschiebungen

2-(1′-cis,3′-cis-)- and 2-(1′-cis,3′-trans-Penta-1′,3′-dienyl)-phenol (cis, cis- 4 and cis, trans- 4 , cf. scheme 1) rearrange thermally at 85–110° via [1,7 a] hydrogen shifts to yield the o-quinomethide 2 (R ? CH₃) which rapidly cyclises to give 2-ethyl-2H-chromene ( 7 ). The trans formation of cis, cis- and cis, trans- 4 into 7 is accompanied by a thermal cis, trans isomerisation of the 3′ double bond in 4. The isomerisation indicates that [1,7 a] hydrogen shifts in 2 compete with the electrocyclic ring closure of 2 . The isomeric phenols, trans, trans- and trans, cis- 4 , are stable at 85–110° but at 190° rearrange also to form 7 . This rearrangement is induced by a thermal cis, trans isomerisation of the 1′ double bond which occurs via [1, 5s] hydrogen shifts. Deuterium labelling experiments show that the chromene 7 is in equilibrium with the o-quinomethide 2 (R ? CH₃), at 210°. Thus, when 2-benzyl-2H-chromene ( 9 ) or 2-(1′-trans,3′-trans,-4′-phenyl-buta1′,3′-dienyl)-phenol (trans, trans- 6 ) is heated in diglyme solution at >200°, an equilibrium mixture of both compounds (～ 55% 9 and 45% 6 ) is obtained.     

A Variable-Pressure 2D 1H-NMR Study of the Mechanism of Trimethyl Phosphate Intermolecular Exchange and cis/trains-Isomerisation of Tetrachlorobis(trimethyl phosphate)zirconium(IV)

In chloroform, [ZrCl₄·2(MeO)₃PO] exists in both cis- and trans-isomeric forms. Three reactions can be envisaged in the presence of excess (MeO)₃PO = L: (1) cis-[ZrCl₄·2L] + *L?cis-[ZrCl₄·L*L]+ L; (2) trans-[ZrCl₄·2L] + *L ? trans-[ZrCl₄·L*L] + L; (3) cis-[ZrCl₄·2L]? trans-[ZrCl₄·2L]. To distinguish between these possible reaction pathways, we have used 2D ₁H-NMR spectroscopy. For the first time, variable-pressure 2D exchange spectra were used for mechanistic assignments. cis/trans-Isomerisation was found to be the fastest reaction (in CHCl₃/CDCl₃), with a small acceleration at higher pressure: it is concluded to be an intramolecular process with a slightly contracted six-coordinate transition state. The intermolecular (MeO)₃PO exchange on the cis- and trans-isomer are second-order processes and are strongly accelerated by increased pressure: I_a mechanisms are suggested without ruling out limiting A mechanisms.     

Thermisches Verhalten von o-Dipropenylbenzol,Beispiel einer aromatischen [1,7]-sigmatropischen H-Verschiebung. Vorläufige Mitteilung

cis, cis-, cis, trans- and trans, trans-o-Dipropenylbenzene (cis, cis-, cis, trans- and trans, trans- 1 ) were prepared. At 225° cis, cis- 1 isomerises to give cis, trans- 1 and vice versa. The isomerisation follows 1. order kinetics. At equilibrium 89% cis, trans- and 11% cis, cis- 1 are present. It is shown by deuterium labelling that the isomerisation is due to aromatic [1, 7 a] sigmatropic H-shifts. trans, trans- 1 rearranges at 225° to yield 2, 3-dimethyl-1, 2-dihydronaphthalene ( 3 ). This can be visualized by disrotatory ring closure of trans, trans- 1 followed by an aromatic [1, 5 s] H-shift. When cis, cis- or cis, trans- 1 are heated for 153 hrs at 225° a small amount (3%) of 1-ethyl-1,2-dihydronaphthalene ( 5 ) is formed.     

Thermisches Verhalten von Cyclopropa[c]chromenen

The Cyclopropa[c]chromenes 14 , trans-and cis- 15 , trans-and cis- 16 and 17 rearrange on heating > 200° in N, N-diethylaniline to give 2-alkyl-2H-chromenes 7, 8, 21, 22. The rate determining step of this rearrangement is the ‘homoelectrocyclic’ ring opening of the cyclopro-pa[c]chromenes to give ω-allyl-quinomethanes of type 4. These intermediates show fast [1,5s] and [1,7a] H-shifts, followed by electrocyclic ring closure. Deuterium labelling experiments are in agreement with this mechanism. The remarkable dependence of the rates of rearrangement with respect to the stereochemistry of the cyclopropa[c]chromenes (cf. table 2) suggests that in the first step only one of the two possible disrotatory modes of ring opening is involved.     

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.     

Stereochemical Analysis of an Aromatic Triplet Di-π-methane Rearrangement

It is shown that (−)-(S)-N,N-dimethyl-2-(1′-methylallyl)aniline ((−)-(S)- 4 ), on direct irradiation in MeCN at 20°, undergoes in its lowest-lying triplet state an aromatic di-π-methane (ADPM) rearrangement to yield (−)-(1′R,2′R)- and (+)-(1′R,2′S)-N,N-dimethyl-2-(2-methylcyclopropyl)aniline ((−)-trans- and (+)-cis- 7 ) in an initial trans/cis ratio of 4.71 ± 0.14 and in optical yields of 28.8 ± 5.2% and 15 ± 5%, respectively. The ADPM rearrangement of (−)-(S)- 4 to the trans- and cis-configurated products occurs with a preponderance of the path leading to retention of configuration at the pivot atom (C(1′) in the reactant and C(2′) in the products) for (−)-trans- 7 and to inversion of configuration for (+)-cis- 7 , respectively. The results can be rationalized by assuming reaction paths which involve the occurrence of discrete 1,4- and 1,3-diradicals (cf. Schemes 10, 12, and 13). A general analysis of such ADPM rearrangements which allows the classification of these photochemical reactions in terms of borderline cases is presented (Scheme 14). It is found that the optical yields in these ‘step-by-step’ rearrangements are determined by the first step, i.e. by the disrotatory bond formation between C(2) of the aromatic moiety and C(2′) of the allylic side chain leading to the generation of the 1,4-diradicals. Moderation of the optical yields can occur in the ring closure of the 1,3-diradicals to the final products, which may take place with different trans/cis-ratios for the individual 1,3-diradicals. Compounds (−)-trans- 7 as well as (+)-cis- 7 easily undergo the well-known photochemical trans/cis-isomerization. It mainly leads to racemization. However, a small part of the molecules shows trans/cis-isomerization with inversion of configuration at C(1′), which is best explained by a photochemical cleavage of the C(1′)–C(3′) bond.     

Criteria for the Efficiency,Stability, and Capacity of Abiotic Photochemical Solar Energy Storage Systems

The utilization of simple photochemical reactions for the storage of solar energy in the form of chemical energy in energy-rich products has often been considered in the further development and improvement of e. g. simple thermosolar techniques. The hitherto proposed criteria for the qualification of an abiotic photochemical system are, however, mostly of a qualitative nature, so a mutal comparison of the systems is not precise enough. In this article it is shown how a useful correlation on the basis of time-independent experimental data can be achieved and how, from the viewpoint of photochemistry, a comparative classification of known reactions is possible. The following reactions are compared: the [2 + 2]-photocycloadditions of norbornadiene, dimethyl 2,3-norbornadienedicarboxylate, and dicyclopentadienone, the photoisomerization of trans- to cis-diacetylindigo, the photodissociation of nitrosyl chloride as well as a photocatalytic redox reaction. The quantity of material required and storage efficiency are by far the most favorable in the case of trans-diacetylindigo. The main disadvantage of the latter however, is that the energy-rich cis-from rapidly reverts to the stable trans-form at elevated temperatures.     

Three-component one-pot synthesis of fused uracils – pyrano[2,3-d]‐pyrimidine-2,4-diones

5-Arylidene-N,N-dimethylbarbituric acids undergo smooth hetero-Diels-Alder reactions with enol ethers to afford cis and trans diastereoisomers of 7-alkoxy-5-aryl-2H-pyrano[2,3-d]pyrimidine-2,4-diones in excellent yields (84–95%). Cycloadducts with cis-configuration were the major products. Three-component one-pot reactions of N,N-dimethylbarbituric acid, aromatic and heteroaromatic aldehydes, and enol ethers in the presence of piperidine gave uracils also in very good yields (87–95%). The structure of the cycloadducts is discussed in terms of configuration and preferred conformation. Correspondence: Aleksandra Pałasz, Department of Organic Chemistry, Jagiellonian University, Kraków, Poland.     

1,2,3-benzotriazines. II. Reactions of benzimidazo[1,2-c][1,2,3]benzotriazines and naphth[1′,2′(2′,1′):4,5]imidazo[1,2-c][1,2,3]benzotriazine

A number of methyl- and halogeno-substituted benzimidazo[1,2-c][1,2,3]benzotriazines were subjected to a series of hydrolytic cleavages in acid media. The reactions of these compounds with dilute sulfuric acid yielded 2-(o-hydroxyphenyl)benzimidazoles. Concentrated hydrochloric acid produced a mixture of 2-(o-chlorophenyl)- and 2-(o-hydroxyphenyl)benzimidazoles. Hydrogen chloride in ethanol caused the formation of 2- phenylbenzimidazoles contaminated with small amounts of 2 - (o-chlorophenyl)benzimidazoles. The benzimidazo[1,2-c][1,2,3]benzotriazines underwent the Sandmeyer reaction to form 2-(o-chlorophenyl)- and 2-(o-bromophenyl)benzimidazoles in excellent yields. These reactions illustrated the behavior of these 1,2,3-triazines as internal diazonium compounds. Naphth[1′,2′(2′,1′):4,5]imidazo[1,2-c][1,2,3]benzotriazine behaved similarly. Bromination of some benzimidazo[1, 2 - c][1,2,3]benzotriazines in aqueous medium yielded bromine-substituted [1,2-c][1,2,3]benzotriazines.     

Transition metal complexes with bidentate ligand 2, 11-Bis (diphenylphosphinomethyl)benzo[c]phenanthrene (1). X. Preparation and spectroscopic properties of cis-[PtCl2 (1)] trans- and cis-[PtH (PPh3) (1)] [BF4] and crystal and molecular structure of cis-[PtCl2 (1)] · CHCl3

It is shown that ligand 1 , designed to span trans-positions, under appropriate conditions also gives cis-mononuclear complexes of platinum (II). The structure of cis-[PtCl₂ (1) ] (2) has been determined by single-crystal X-ray diffraction. The major distortion from square planar coordination is the P-Pt-P angle of 104.8°. Values of valence angles within the bidentate ligand indicate that this part of the molecule is very strained. Two phenyl groups, one on each phosphorus, lie almost parallel to each other separated by ca. 3.2–3.3 Å. The ¹H-NMR. data for this compound show that the π-phenyl interactions observed in the solid state occur also in solution. The preparation and NMR.-spectroscopic properties of trans- and cis-[PtH(PPh₃) (1) ] [BF₄] are reported.     

Hetero-Diels-Alder reaction of propenenitriles with enol ethers: a convenient approach to functionalized 3,4-dihydro-2H-pyrans

The hetero-Diels-Alder reaction of 3-(N-acetyl-N-benzylamino)-2-formylprop-2-enenitrile with enol ethers yielded cis/trans diastereoisomers of 2-alkoxy-4-amino-3,4-dihydro-2H-pyran-5-carbonitriles in moderate yields. Acidic hydrolysis of cis-diastereoisomer in concentrated sulfuric acid gave 2-oxo-1,2-dihydropyrydine-3-carbaldehyde. The reaction of 2-benzoyl-3-heteroaromaticprop-2-enenitriles with enol ethers afforded diastereoisomeric cis/trans cycloadducts in good yields. The structure of the products is discussed in terms of configuration and preferred conformation.     

Synthesis, 1H- and 13C-NMR spectra,crystal structure and ring openings of 1-methyl-6,9-epoxy-9-aryl-5,6,9,10-tetrahydro-1H-imidazo [3,2-e] [2H-1,5] oxazocinium methanesulfonate

The methanesulfonic acid catalyzed reaction of 1-(4-chloro- and 2,4-dichlorophenyl)-2-(1-methyl-2-imida-zolyl)ethanones 1a and 1b with glycerol produced cis- and trans-{2-haloaryl-2-[(1-methyl-2-imidazolyl)methyl]-4-hydroxymethyl}-1,3-dioxolanes 2a and 2b with a 2:1 cis/trans ratio. Besides these five-membered ketals, the reaction of 1a with glycerol afforded a small amount of trans-{2-(4-chlorophenyl)-2-[(1-methyl-2-imidazolyl)methyl]-5-hydroxy}-1,3-dioxane ( 3a , 7%). The reaction of methanesulfonyl chloride with cis-1 formed the corresponding methanesulfonates, cis- 4 , which rapidly cyclized to the title compounds 5 . Base-catalyzed ring opening of 5 furnished 1-methyl-5,6-dihydro-6-hydroxymethyl-8-(4-chloro- and 2,4-dichlorophenyl)-1H-imidazo[3,2-d][1,4]oxazepinium methanesulfonates 7 . Acid-catalyzed hydrolyses of 5 or 7 provided 1-methyl-2-[(4-chloro- and 2,4-dichloro)phenacyl]-3-[(2,3-dihydroxy)-1-propyl]imidazolium salts 12 . Structure proofs were based on extensive ¹H and ¹³C chemical shifts and coupling constants and structures of 3a and 5a were confirmed by single crystal X-ray crystallography.     

The interaction of cis and trans-1-cyclohexyl-2-phenyl-3-benzoylaziridine with lithium N-Methylanilide

A reaction pathway for the rearrangement-dehydrogenation of cis-1-cyclohexyl-2-phenyl-3-benzoylaziridine into 2-cyclohexylamino-3-phenylindenone can now be suggested. Furthermore, a competing degradation pathway involving C? C bond scission accounts for the major product in these reactions and leads to ω-cyclohexylaminoacetophenone and benzaldehyde. Observed also is the fact that trans-1-cyclohexyl-2-phenyl-3-benzoylaziridine fails to undergo the rearrangement-dehydrogenation reaction.     

Diels-Alder Reactions of 6,9-Dipropyl-1, 4-Dioxaspiro[4.5]Deca-6, 8-Diene-2, 10-Dione with Substituted Alkenes. An Entry to Bicyclo[2.2.2]Oct-5-Ene-2, 3-Diones and 1, 3-Cyclohexadienes

The cycloadditions of the title compound, 1, a masked 3, 6-dipropyl-o-benzoquinone to various disubstituted (diethyl maleate, diethyl fumarate, trans- and cis-stilbene, and cycloheptene) and monosubstituted alkenes (methyl acrylate, methyl vinyl ketone, styrene, ethyl vinyl ether, and 1-hexene) have been studied; the yields of the Diels-Alder adducts, 2, are generally high (> 75%) except for stilbenes. These adducts are effectively transformed into the corresponding bicyclo[2.2.2]oct-5-ene-2, 3-diones, 3, whose stereochemistries are determined from the ring current effect of the respective quinoxalines, 4, on the chemical shifts of the vinyl and the methine protons and/or the lanthanide (Eu(fod)₃) induced shift on the pertinent protons of 3. It is interesting to note that the quinoxaline ring current makes the vinyl protons down-field shifted by 0.15–0.27 ppm whereas the methine protons (R³=H) syn to the quinoxaline moiety up-field shifted by 0.18–0.39 ppm as compared to the chemical shifts of the corresponding protons in 3. The transformations of α-diketones 3 into the corresponding 1, 3-cyclohexadienes, 5, by irradition with a Hanovia medium pressure lamp through a uranium glass filter are almost quantitative. The present study provides facile and effective methods for the preparation of bicyclo[2.2.2]oct-5-ene-2, 3-diones and 1, 3-cyclohexadienes from catechols via masked o-benzoquinones.     

Synthesis of Potential Inhibitors of Ethylene Biosynthesis: The diastereoisomers of 1-amino-2-bromocyclopropanecarboxylic acid

The preparation of the diastereoisomers of 1-amino-2-bromocyclopropanecarboxylic acid is described using the methyl (1RS, 5SR)-2-oxo-3-oxabicyclo[3.1.0]hexane-1-carboxylate 5 as starting material. The key step is the oxidation of 9 with subsequent radical introduction of bromine according to the Barton procedure. The 2-bromo-cyclopropanecarboxylates cis- 11 and trans- 11 were obtained as diastereoisomer mixture in a ratio of 3:1. They were converted into cis- and trans-esters 12 and the acids 13 .