Thermal Rearrangement Products Research Articles

Analysis of root volatiles and functional characterization of a root-specific germacrene A synthase in Artemisia pallens.

The study demonstrated that Artemisia pallens roots can be a source of terpene-rich essential oil and root-specific ApTPS1 forms germacrene A contributing to major root volatiles. Davana (Artemisia pallens Bess) is a valuable aromatic herb within the Asteraceae family, highly prized for its essential oil (EO) produced in the aerial parts. However, the root volatile composition, and thegenes responsible for root volatiles have remained unexplored until now. Here, we show that A. pallens roots possess distinct oil bodies and yields ~ 0.05% of EO, which is primarily composed of sesquiterpenes β-elemene, neryl isovalerate, β-selinene, and α-selinene, and trace amounts of monoterpenes β-myrcene, D-limonene. This shows that, besides aerial parts, roots of davana can also be a source of unique EO. Moreover, we functionally characterized a terpene synthase (ApTPS1) that exhibited high in silico expression in the root transcriptome. The recombinant ApTPS1 showed the formation of β-elemene and germacrene A with E,E-farnesyl diphosphate (FPP) as a substrate. Detailed analysis of assay products revealed that β-elemene was the thermal rearrangement product of germacrene A. The functional expression of ApTPS1 in Saccharomyces cerevisiae confirmed the in vivo germacrene A synthase activity of ApTPS1. At the transcript level, ApTPS1 displayed predominant expression in roots, with significantly lower level of expression in other tissues. This expression pattern of ApTPS1 positively correlated with the tissue-specific accumulation level of germacrene A. Overall, these findings provide fundamental insights into the EO profile of davana roots, and the contribution of ApTPS1 in the formation of a major root volatile.

Isomer-Selective Threshold Photoelectron Spectra of Phenylnitrene and Its Thermal Rearrangement Products.

The photoionization of phenylnitrene was investigated by photoion mass-selected threshold photoelectron spectroscopy in the gas phase. Flash vacuum pyrolysis of phenyl azide at 480 °C produces the nitrene, which subsequently rearranges at higher temperatures affording three isomeric cyanocyclopentadienes, in contrast to low-temperature trapping experiments. Temperature control of the reactor and threshold photoelectron spectra allows for optimizing the generation of phenylnitrene or its thermal rearrangement products, as well as obtaining vibrational information for the corresponding ions. The adiabatic ionization energies (AIE) of the triplet nitrene (3A2) to the radical cation in its lowest-energy doublet (2B2) and quartet (4A1) spin states were determined to 8.29 ± 0.01 and 9.73 ± 0.01 eV, respectively. Vibrational frequencies of ring breathing modes were measured at 500 ± 80 and 484 ± 80 cm-1 for both the [Formula: see text](2B2) and [Formula: see text](4A1) cationic states, respectively. The AIE differ from the values previously reported; hence, we revise the doublet-quartet energy splitting of the phenylnitrene radical cation to 1.44 eV, in excellent agreement with composite methods and coupled cluster calculations, but considerably higher than the literature reference (1.1 eV).

Identification of a novel hedycaryol synthase gene isolated from Camellia brevistyla flowers and floral scent of Camellia cultivars.

A novel terpene synthase (Tps) gene isolated from Camellia brevistyla was identified as hedycaryol synthase, which was shown to be expressed specifically in flowers. Camellia plants are very popular because they bloom in winter when other plants seldom flower. Many ornamental cultivars of Camellia have been bred mainly in Japan, although the fragrance of their flowers has not been studied extensively. We analyzed floral scents of several Camellia cultivars by gas chromatography-mass spectrometry (GC-MS) and found that Camellia brevistyla produced various sesquiterpenes in addition to monoterpenes, whereas Camellia japonica and its cross-lines produced only monoterpenes, including linalool as the main product. From a flower of C. brevistyla, we isolated one cDNA encoding a terpene synthase (TPS) comprised of 554 amino acids, which was phylogenetically positioned to a sole gene clade. The cDNA, designated CbTps1, was expressed in mevalonate-pathway-engineered Escherichia coli, which carried the Streptomyces mevalonate-pathway gene cluster in addition to the acetoacetate-CoA ligase gene. A terpene product was purified from recombinant E. coli cultured with lithium acetoacetate, and analyzed by (1)H-nulcear magnetic resonance spectroscopy ((1)H-NMR) and GC-MS. It was shown that a sesquiterpene hedycaryol was produced, because (1)H-NMR signals of the purified product were very broad, and elemol, a thermal rearrangement product from hedycaryol, was identified by GC-MS analysis. Spectroscopic data of elemol were also determined. These results indicated that the CbTps1 gene encodes hedycaryol synthase. Expression analysis of CbTps1 showed that it was expressed specifically in flowers, and hedycaryol is likely to be one of the terpenes that attract insects for pollination of C. brevistyla. A linalool synthase gene, which was isolated from a flower of Camellia saluenensis, is also described.

Sandalwood Fragrance Biosynthesis Involves Sesquiterpene Synthases of Both the Terpene Synthase (TPS)-a and TPS-b Subfamilies, including Santalene Synthases

Sandalwood oil is one of the worlds most highly prized fragrances. To identify the genes and encoded enzymes responsible for santalene biosynthesis, we cloned and characterized three orthologous terpene synthase (TPS) genes SaSSy, SauSSy, and SspiSSy from three divergent sandalwood species; Santalum album, S. austrocaledonicum, and S. spicatum, respectively. The encoded enzymes catalyze the formation of α-, β-, epi-β-santalene, and α-exo-bergamotene from (E,E)-farnesyl diphosphate (E,E-FPP). Recombinant SaSSy was additionally tested with (Z,Z)-farnesyl diphosphate (Z,Z-FPP) and remarkably, found to produce a mixture of α-endo-bergamotene, α-santalene, (Z)-β-farnesene, epi-β-santalene, and β-santalene. Additional cDNAs that encode bisabolene/bisabolol synthases were also cloned and functionally characterized from these three species. Both the santalene synthases and the bisabolene/bisabolol synthases reside in the TPS-b phylogenetic clade, which is more commonly associated with angiosperm monoterpene synthases. An orthologous set of TPS-a synthases responsible for formation of macrocyclic and bicyclic sesquiterpenes were characterized. Strict functionality and limited sequence divergence in the santalene and bisabolene synthases are in contrast to the TPS-a synthases, suggesting these compounds have played a significant role in the evolution of the Santalum genus.

ChemInform Abstract: On the Reaction of 3-Nitro-1,2-phenylenediamine with Ethyl Acetoacetate. Condensed Dihydrodiazepinones.

Condensation of 3-nitro-1,2-phenylenediamine with ethyl acetoacetate in boiling xylene gave two isomeric 2,3-dihydro-4-methyl-9-nitro- and 2,5-dihydro-4-methyl-6-nitro-1H-1,5-benzodiazepin-2-ones, the 9-nitro derivative thermal rearrangement product N-isopropenyl-4-nitrobenzimidazolone and a non cyclic acetoacetamide derivative. At room temperature these reactants afforded 2,3-dihydro-2-ethoxycarbonyl-methyl-2-methyl-4-nitrobenzimidazole.

On the reaction of 3-nitro-1,2-phenylenediamine with ethyl acetoacetate. Condensed dihydrodiazepinones

Condensation of 3-nitro-1,2-phenylenediamine with ethyl acetoacetate in boiling xylene gave two isomeric 2,3-dihydro-4-methyl-9-nitro- and 2,5-dihydro-4-methyl-6-nitro-1H-1,5-benzodiazepin-2-ones, the 9-nitro derivative thermal rearrangement product N-isopropenyl-4-nitrobenzimidazolone and a non cyclic acetoacetamide derivative. At room temperature these reactants afforded 2,3-dihydro-2-ethoxycarbonyl-methyl-2-methyl-4-nitrobenzimidazole.

New Dichlorosilanes, Cyclotrisilanes, and Silacyclopropanes as Precursors of Intramolecularly Coordinated Silylenes

Reductive dehalogenation of pentacoordinate dichlorosilanes with magnesium is the most straightforward method to generate highly coordinated silylenes, which can be trapped effectively by a variety of substrates [Eq. (1)]. In the absence of trapping reagents either cyclotrisilanes, which are convenient thermal silylene precursors, or dimerization and rearrangement products of the intermediate silylenes are formed.

Synthesis of tetramethyldisilane-bridged bis(1-indenyl) tetracarbonyl di-iron: A novel thermal rearrangement reaction between the Si-Si and Fe-Fe bonds

The title complex (Me 2SiSiMe 2)(η 5-l-indenyl)Fe(CO)] 2(μ-CO) 2 ( 1) was prepared by the reaction of 1,2-bis(1-indenyl)tetramethyl-disilane and Fe(CO) 5 in refluxing heptane. Its thermal rearrangement product [Me 2Si(η 5-1-indenyl)Fe(CO) 2] 2 ( 2) was also obtained from the reaction. 1 in refluxing xylene can be readily converted into 2. The crystal structures of the cis isomer 1c and the trans isomer 2t were determined by X-ray diffraction.

Thermal decomposition of arylnitramines

The thermal decomposition of various substituted N-methyl-N-nitroanilines dissolved in indifferent solvents and piperidine has been investigated. Activation volumes and product analyses support evidence that the rate-determining step is the reversible homolysis of the nitramine bond. The activation volumes range from +18 to +36 ml mol–1. A non-linear Hammett relationship is attributed to an increase in secondary caged reactions, namely rearrangement and oxidation. Arylnitramines with electron-donating substituents yield greater amounts of the thermal rearrangement products than those with electrondeactivating groups at ambient pressures. Decomposition of arylnitramines with electron-donating substituents under high pressures (ca. 1.2 GPa) favours caged reactions over separative diffusion.

Quantitative Synthesis and Formation of Cyclopenta[cd]pyrene 3,4-Oxide under Simulated Atmospheric Conditions

Cyclopenta[cd]pyrene 3,4-oxide (2) has been synthesized in a one-step, quantitative reaction using dimethyldioxirane. The oxide, or its thermal rearrangement products cyclopenta[cd]-pyren-3(4H)-one and cyclopenta[cd]pyren-4(3H)-one, is formed from cyclopenta[cd]pyrene (1) under simulated environmental conditions. In one case these products are formed when 1 is adsorbed on model particulates and then exposed to the reaction products of tetramethylethylene and ozone in the gas phase.

Identification of fluorescent products produced by the thermal treatment of bisphenol‐A‐based polycarbonate

AbstractPolycarbonate is routinely subjected to heat treatment, and the thermal degradation products formed during this thermal treatment give rise to a distinct structured fluorescence spectrum. The structured fluorescence emission is observed when polycarbonate is subjected to thermal treatment in air as well as in nitrogen. A mixture of thermal rearrangement products of polycarbonate including dibenzofuran and phenyl‐2‐phenoxybenzoate are mainly responsible for the structured fluorescence emission. Most of the thermal degradation products of polycarbonate undergo photolysis, leading to the formation of photoproducts, which subsequently undergo a photoinduced bleaching process, with the noted exception of phenyl‐2‐phenoxybenzoate. The exposure of polycarbonate to high temperature for only short time periods, simulating mild industrial processing conditions, results in the formation of a relatively small amount of thermal degradation products, which, accordingly, has only a minor effect on the photodegradation of polycarbonate. © 1994 John Wiley & Sons, Inc.

Umwandlung der Cluster Fe 3 (CO) 9 (μ 3 ‐η 2 ‐N 2 Et 2 ) und Fe 3 (CO) 9 (μ 3 ‐NEt) 2 zu organischen Produkten 1)

Conversion of the Clusters Fe3(CO)9(μ3-η2-N2Et2 and Fe3(CO)9(μ3-NEt)2 into Organic Products The azoalkane-bridged cluster Fe3(CO)9(μ3-η2-N2Et2) (1) and its thermal rearrangement product Fe3(CO)9(μ3-NEt)2 (2) are converted by standard routes into derivatives with one carbene ligand C(Ph)OEt (3, 4). Degradation (thermally or oxidatively) of these compounds produces the diaziridine (5) and/or the iminoester EtN = C(Ph)OEt (6). 4 and moist p-tolyl isocyanide form the indole derivative 8. 1 adds one or two equiv. of alkynes leading to the alkyne-bridged cluster 9 or the ferrole-type clusters 10. The clusters 10, resulting from HCCPh, exist as two isomers 10a and b which can be equilibrated and separated. An alternative route to 10 c (alkyne: MeCCMe) starts from Fe2(CO)6(C4Me4) by treating it with Fe2(CO)9 and N2Et2. Photolytic or oxidative degradation of the clusters 10 produces substituted furan 13, pyrrole 14, or dihydropyridazine 15. The crystal structures of the clusters 4, 9, 10a, and 10b have been determined.

Thermal Rearrangement of Dimethylaminomethylenethiaspirononenes and thiaspirodecenes

Abstract Enamines are the thermal rearrangement products of (5R*,6R*)-6-dimethylamino-4-methylene-1-thiaspiro(4,5)-2-decene and (4,4)-2-nonene, and (5R*,6S*)-6-dimethylamino-1-methylene-2-thiaspiro(4,4)-3-nonene. The mechanism of formation of these compounds is discussed.

Studies of Tertiary Amine Oxides. Part115. Carbon - 13 nuclear magnetic resonance spectra of some N-(4-substituted phenyl) piperidine, the corresponding N-oxides, and their thermal-rearrangement product

Abstract The carbon-13 chemical shifts of seven N-(4-substituted phenyl) piperidine; the corresponding N-oxides, and their thermal rearrangement products were analyzed and assigned. The N-oxidation effect on the carbon-13 chemical shift is discussed, a correlation of N-oxidation effect with substituent constant (σp, σm, σI and σR) has been studied; dual substituent-parameter equation produce better correlation.

Surface photochemistry: 7. Synthesis on Pt(111) of surface ethyl groups and their rearrangement to ethylidyne

The vibrational spectra of photochemically produced adsorbed ethyl fragments and their thermal rearrangement products have been measured on Pt(111). Heating ethyl fragments, in the presence of adsorbed chlorine, leads to ethylidyne, but not directly; di-σ-bonded ethylene is formed as a relatively stable intermediate.

Photosensitized oxidation of furans. Part 14. Nature of intermediates in thermal rearrangement of some endo-peroxides of 2-alkoxyfurans: new rearrangement pathway of furan endo-peroxides

2-Methoxy-5-phenylfurans (1a–c) substituted at C-4 with electron-withdrawing groups, by dyesensitized photo-oxygenation in non-participating solvents, give the endo-peroxides (3a–c) which by thermal rearrangement partly yield the 3H-1, 2-dioxoles (14a–c). The latter, which are the first examples of this ring system, are thermally very unstable. Their formation can be deduced only from the products obtained by thermal rearrangement which are structurally related with the thermal rearrangement products of 3H-1, 2, 4-dioxazoles (10). The behaviour of the furans (1a–c) contrasts with that of the 2-methoxy-5-phenylfurans unsubstituted at C-4 which under the same conditions give carbonyl oxides.

Catalyzed reaction of dimethyl diazomalonate with 2-mono- and 2,5-dialkyl-(alkenyl)furans

1. The catalyzed reaction of 2-substituted furans with dimethyl diazomalonate in the presence of Rh(OAc)2 at 20°C gives the dimethyl esters of the Z-isomers of substituted 5-oxopenta-1,3-diene-1,1-dicarboxylic acids (yields up to 100%), which undergo smooth thermal rearrangement (150°C) to the E-isomers. 2,5-Disubstituted furans react to give the products of insertion of bis(methoxycarbonyl)carbene into the β-C-H bond of the furan ring, in addition to the esters of the oxodienoic acids. 2. Analogous reactions of 2-alkenylfurans with dimethyldiazomalonate afford both adducts of the carbene to the exocyclic double bond, and products of the reaction of the carbene with the furan ring (diesters of the oxotrienedicarboxylic acids). Introduction of methyl substituents into the β-position of the vinyl group in the starting 2-alkenylfuran modifies the course of the reaction to give predominantly (or exclusively) the oxotrienoate esters. 3. The reaction of 2-propenylfuran with dimethyl diazomalonate in the presence of Rh(OAc)2 to give the 3-methyl-2-(2-furyl)cyclopropane-1,1-dicarboxylate ester has been found to be fully stereoselective. 4. The structures of the oxodienedicarboxylate esters formed in the reaction of furans with dimethyldiazomalonate, and of their thermal rearrangement products, have been confirmed by x-ray diffraction analysis, in the cases of the dimethyl esters of Z-7-methyl-5-oxoocta-1,3,6-triene-1,1-dicarboxylic and E-5-oxohexa-1,3-diene-1,1-dicarboxylic acids.

Carbon-13 Nuclear Magnetic Resonance Spectra of Some N-(2,4-dinitrophenyl) Amines, The Corresponding N-Oxides, and Their Thermal Rearrangement Products

Abstract Carbotn-13 NHR assignment of eight N-(2,4- dinitrophenyl) amines was achived. She six corresponding N- Oxides and their thermal rearr-angement products were also analyzed. The N-oxidation effect on the carbon-13 chemical shift is discussed.

Molecular rearrangement of 3-substituted 4-chloro-4,5-epoxide systems in ring A of steroids

Both stereoisomers of the 3-oxo-, 3-hydroxy-, and 3-acetoxy-4-chloro-4,5-epoxy derivatives of 17β-acetoxyandrostanes have been synthesized, and their thermal rearrangement products have been identified. A synthesis of the diosphenols, 17β-acetoxy-4-hydroxyandrost-4-en-3-one and 17β-acetoxy-4-hydroxyandrosta-4,6-dien-3-one, through a novel rearrangement of the 3-hydroxy- and 3-oxo-4-chloro-4,5-epoxides, respectively, is described. In addition to the chloro ketone products from the 3-acetoxy derivatives, rearrangement and elimination products were also formed. Structural determinations are based upon one- and two-dimensional 1H and 13C n.m.r. correlations and analyses.

Copolymerization of 1‐hexene‐3,4‐dioic anhydride and its thermal rearrangement products with styrene

Copolymerization of 1‐hexene‐3,4‐dioic anhydride and its thermal rearrangement products with styrene