Halogenated Sesquiterpenes from the Marine Red Alga Laurencia saitoi (Rhodomelaceae)

Four new halogenated sesquiterpenes, 10‐bromo‐3‐chloro‐2,7‐epoxychamigr‐9‐en‐8α‐ol ( 1 ), 2,10β‐dibromochamigra‐2,7‐dien‐9α‐ol ( 2 ), (9S)‐2‐bromo‐3‐chloro‐6,9‐epoxybisabola‐7(14),10‐diene ( 3 ), and (9R)‐2‐bromo‐3‐chloro‐6,9‐epoxybisabola‐7(14),10‐diene ( 4 ), were characterized from the marine red alga Laurencia saitoi. In addition, two known halosesquiterpenes, 2,10‐dibromo‐3‐chlorochamigr‐7‐en‐9α‐ol ( 5 ) and isolaurenisol ( 6 ), were also isolated and identified. Their structures were established on the basis of extensive analysis of spectroscopic data.     

An Unexpected Double Diels–Alder Reaction of (E)‐2‐Bromo‐4‐aryl‐1,3‐pentadiene Involving [1,5]‐Hydrogen Migration and HBr Elimination: Synthesis of Bicyclo[2.2.2]octene Derivatives

An unexpected double Diels–Alder (DDA) reaction of (E)‐2‐bromo‐4‐aryl‐1,3‐pentadiene was developed and resulted in a series of “butterfly‐like” bicyclo[2.2.2]octene derivatives in moderate to good yields without the need for a metal catalyst. The proposed mechanism involves a [1,5]‐sigmatropic hydrogen migration and HBr elimination. Through this decisive [1,5]‐hydrogen shift step, the electronic properties and steric hindrance of the conjugated diene substrate are completely altered and the DDA reaction of this potential diene synthon is successfully achieved.     

Sesquiterpenes and Other Metabolites from the Marine Red Alga Laurencia composita (Rhodomelaceae)

Two new halogenated sesquiterpenes, (8β)‐10‐bromo‐3‐chloro‐2,7‐epoxychamigr‐9‐en‐8‐ol ( 1 ) and 2‐bromo‐3‐chlorobisabola‐7(14),11‐diene‐6,10‐diol ( 3 ), and one new phytol‐derived diterpene, 2,3‐epoxyphytyl acetate ( 4 ), along with cis‐ and trans‐1‐methylcyclohexane‐1,4‐diol ( 5 and 6 ) which were isolated from a natural source for the first time but have been previously synthesized, were isolated from the marine red alga Laurencia composita and characterized. In addition, a known sesquiterpene, pacifenediol ( 2 ), and the known furanone derivative 7 were also identified. Their structures were established by NMR and mass spectroscopic methods.     

Towards the synthesis of osteoclast inhibitor SB-242784

Osteoclast inhibitor SB-242784 (1) was prepared from pivotal indol intermediate 4. A ‘Stille’ cross coupling of organotin 2c with bromo acrylate 11 afforded diene 12 which was also obtained via a reduction-isomerization process of enyne 16. Bromoamide 3 was prepared from the corresponding acid 7 which was readily obtained from bromopyruvic acid.     

Facile Synthesis and Palladium‐Catalyzed Cross‐Coupling Reactions of 2,3‐Bis(pinacolatoboryl)‐1,3‐butadiene

Treatment of 1,1‐bis(pinacolatoboryl)ethene with an excess of 1‐bromo‐1‐lithioethene gave 2,3‐bis(pinacolatoboryl)‐1,3‐butadiene in high yield. Palladium‐catalyzed cross‐coupling of the resulting diborylbutadiene with aryl iodides took place smoothly in the presence of a catalytic amount of Pd(OAc)₂/PPh₃ and aqueous KOH to give 2,3‐diaryl‐1,3‐butadienes in good yields. The coupling reaction with commercially available 4‐acetoxyphenylmethyl chloride under the same conditions followed by hydrolysis of the acetyl groups gave anolignan B in a one‐pot manner. A variety of [3]‐ to [6]dendralenes were synthesized by palladium‐catalyzed coupling of the diene or 1,1‐bis(pinacolato)borylethene with alkenyl or dienyl halides, respectively, in good yields.     

Studies on α‐Bromination of Ketone in Hydrindane Ring System

The present paper describes the results of various attempts to synthesize 5‐bromo‐6‐ketone ( 11 ). When standard procedures for the α‐bromination were tried, a mixture of 5‐bromo‐6‐ketone ( 11 ) and 7‐bromo‐6‐ketone ( 12 ) was obtained. However, when bromination was carried out under buffered conditions, the desired 5‐bromo‐6‐ketone ( 11 ) could be obtained in a good yield.     

Reactions of the 1-halo-7-(2-hydroxyethoxy)cycloheptenes and the 3-halo-4-(2-hydroxyethoxy)bicyclo[3.2.1]oct-2-enes with potassium t-butoxide

Reactions of 1 - bromo - 7 - (2 - hydroxyethoxy)cycloheptene 2 and its chloro analogue 3 with potassium t-butoxide in dimethyl sulphoxide or tetrahydrofuran gave cycloheptatriene and cis - 8,11 - dioxabicyclo[5.4.0]undec - 2 - ene 18 as the major products together with small amounts of the trans-isomer 17,8,11-dioxabicyclo[5.4.0]undec - 1(7) - ene 14, 8,11 - dioxabicyclo[5.4.0] - undec - 1 - ene 19, cyclohept - 2 - enone ethylene ketal 15, cyclohept - 3 - enone ethylene ketal 16, and 1- and 2 - t - butoxycyclohepta - 1,3 - diene 20. Similar reactions of 3 - bromo - and 3 - chloro - 4 - (2 - hydroxyethoxy)bicyclo[3.2.1]oct - 2 - ene 4 and 5 gave 4,7 - dioxatricyclo[7.2.1.0^3,8]dodeca - 2 - ene 26 as the major product together with small amounts of 3,6 - dioxatricyclo[7.2.1.0^2,7]dodeca - 2(7) - ene 27 and bicyclo[3.2.1]oct - 3 - ene - 2 - one ethylene ketal 28. Mechanisms for these transformations are discussed.     

Novel Synthesis and Antimicrobial Activity of 3‐Substituted 5‐bromo‐7‐methyl‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazoles

4‐Methyl acetanilide ( 1 ) on treatment with bromine in acetic acid, followed by hydrolysis with dilute HCl/NaOH solution, yielded 2‐bromo‐4‐methyl aniline ( 2 ), which on treatment with sodium thiocyanate in acetic acid afforded 2‐amino‐4‐bromo‐6‐methyl benzothiazole ( 3 ). Compound 3 in ethylene glycol was heated at 150°C with 80% hydrazine hydrate to get 4‐bromo‐2‐hydrazino‐6‐methyl benzothiazole ( 4 ). This hydrazino compound 4 on heating with formic acid for 3 h yielded 4‐bromo‐2‐hydrazinoformyl‐6‐methyl benzothiazole ( 5 ). Same compound 4 when heated independently with formic acid for 6 h/urea for 3 h/carbon disulfide in alkali afforded 5‐bromo‐7‐methyl ( 6 )/5‐bromo‐3‐hydroxy‐7‐methyl ( 7 )/5‐bromo‐3‐mercapto‐7‐methyl ( 8 )‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazoles, respectively. Compound 4 on heating with acetic acid/acetic anhydride gave acetyl benzothiazolyl derivative 9 , which on cyclization with orthophosphoric acid yielded 5‐bromo‐3,7‐dimethyl‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazole ( 10 ). All these newly synthesized compounds were screened for antimicrobial activity against Escherichia coli (Gram ?ve), Bacillus subtilis (Gram +ve), Erwinia carotovora, and Xanthomonas citri using ampicillin, streptomycin, and penicillin as a standard for comparison.     

4-溴-5-甲基靛红的Baeyer-Villiger氧化反应

Baeyer-Viliger反应是由酮制备酯的重要方法^[1].氧化剂通常有两类:(1)有机过酸;(2)过硫酸钾/硫酸(Caro酸).由于靛红结构特殊,我们分别以单过邻苯二甲酸^[2]和过硫酸钾/硫酸^[3]为氧化剂氧化4-溴-5-甲基靛红(1).     

溴代丙二醛的合成

采用加入自由基引发剂过氧二苯甲酰和适当加热的方法合成了2－溴－1,1,3,3－四乙氧基丙烷,后者经水解进而合成了溴代丙二醛,收率达60％。     

The proton magnetic resonance spectra of some disubstituted acetophenones

An accurate measurement of the chemical shifts and the coupling constants of some disubstituted acetophenones has been made. The acetophenones studied contained nitro, bromo or amino groups substituted in either the 3,4 or 2,5 positions. For compounds with no substituent adjacent to the acetyl group, the chemical shifts and the coupling constants estimated by the simple additivity of the substituent increments were found to be in reasonable agreement with the experimental values. The two nitro, bromo derivatives substituted in positions 2 and 5 probably prefer the conformer in which the proton H-6 is adjacent to the acetyl methyl group whilst the 3,4-disubstituted bromo, nitro and bromo, amino derivatives prefer the conformer in which the H-6 proton is adjacent to the carbonyl group.     

Anharmonic thermochemistry of cyclopentadiene derivatives

This paper focuses on the thermochemistry of some derivatives of cyclopenta‐1,3‐diene, namely, 5‐methylcyclopenta‐1,3‐diene, 5‐ethylcyclopenta‐1,3‐diene, 5‐formylcyclopenta‐1,3‐diene, 5‐methylcyclopenta‐1,3‐diene‐1‐yl radical, 5‐ethylcyclopenta‐1,3‐diene‐1‐yl radical, 5‐carbonylcyclopenta‐1,3‐diene radical, 1‐formylcyclopenta‐2,4‐diene‐1‐yl radical, 5‐methylenecyclopenta‐1,3‐diene radical, 5‐ethylidenecyclopenta‐1,3‐diene radical, and 3,6‐dimethylenecyclohexa‐1,4‐diene. Several different chemistries of these compounds are of interest in combustion modeling. Here, we present gas‐phase thermochemical properties for the above cited species, which are, except for 3,6‐dimethylenecyclohexa‐1,4‐diene, previously unknown. These were obtained from corrected (using bond additivity corrections) high‐level ab initio quantum chemistry calculations validated with well‐known compounds including cyclopentane, cyclopentene, cyclopenta‐1,3‐diene, and cyclopentadienyl radical. Heat capacities and entropies have been corrected for anharmonic molecular motions, in particular for internal rotations. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 453–463, 2003     

Regioselective Synthesis of Para‐Bromo Aromatic Compounds

Reaction of substituted benzene rings with N‐bromophthalimide, under neutral conditions, gave the corresponding bromo derivatives with a preference for the formation of the para bromo isomer over the ortho isomer. The simple work‐up procedure minimizes loss of product and the yields are good.     

Synthesis of silyl aziridines and alpha-amino acylsilanes with silyldibromomethyllithium

The reaction of silyldibromomethyllithium with aromatic imines provides alpha-amino acylsilanes via a bromo aziridine intermediate upon quenching the reaction with water. Alternatively, treatment of the bromo aziridine intermediate with various Grignard reagents or lithium aluminum hydride permits the nucleophilic displacement of the halogen to furnish substituted silyl aziridines.     

Synthesis, characterization, and reactivity of ruthenium diene/diamine complexes including catalytic hydrogenation of ketones

Thermal reactions between [RuCl2(diene)]n (diene = 2,5-norbornadiene, nbd; 1,5-cyclooctadiene, cod) with an excess of N,N,N',N'-tetramethylethylene diamine (tmeda) afforded derivatives [RuCl2(diene)(tmeda)] (diene = nbd, 1; cod, 2) as a mixture of cis and trans isomers. When thermolysis was performed under H2 mixtures of hydride species [RuCl(H)(diene)(tmeda)] (diene = nbd, 3; cod, 4) and the bis-tmeda adduct trans-[RuCl2(tmeda)2] (5) were obtained in different ratios depending upon the reaction conditions and reaction times. Heating polymeric Ru(II) precursors in toluene in the presence of a 5-fold excess of the bulkier N,N,N',N'-tetraethylethylene diamine (teeda) resulted in a rare diamine dealkylation process with formation of trans-[RuCl2(nbd)(Et2NCH2CH2NHEt)] (6) and trans-[RuCl2(cod)(EtHNCH2CH2NHEt)] (7) in high yields. The presence of N-H functionalities in the coordinated diamine ligands of 6 and 7 was unambiguously established by single-crystal X-ray diffraction studies. The dealkylation process of the teeda ligand seems to proceed intramolecularly as shown by solution NMR studies performed with the soluble Ru(II) precursors trans-[RuCl2(amine)2(diene)] (diene = nbd, amine = morpholine, 9; diene = cod, amine = Et2NH, 10). The above complexes [RuCl2(diene)(diamine)] have been tested as precatalysts in the hydrogenation of ketones both for transfer as well as direct hydrogenation, the latter route being the most effective.     

Bromination of deactivated aromatics: a simple and efficient method

Highly deactivated aromatic compounds were smoothly monobrominated by treatment with N-bromosuccinimide (NBS) in concentrated H2SO4 medium affording the corresponding bromo derivatives in good yields. Mild reaction conditions and simple workup provides a practical and commercially viable route for the synthesis of bromo compounds of deactivated aromatics.     

A cobalt complex of a microbial arene oxidation product

ABSTRACT: We report the first synthesis of a cobalt Cp diene complex wherein the diene is derived by microbial dearomatising dihydroxylation of an aromatic ring. The complex has been characterised crystallographically and its structure is compared to that of an uncomplexed diene precursor.     

Nucleophilic Solvent Participation in the Solvolysis of Tertiary Bromoalkanes

The solvolysis of 2‐bromo‐2‐methylpropane ( 1B ), 2‐bromo‐2‐methylbutane ( 2B ), 2‐bromo‐2, 3‐di‐methylbutane ( 3B ), 2‐bromo‐2, 3, 3‐trimethylbutane ( 4B ), 3‐bromo‐3‐methylpentane ( 5B ), 3‐bromo‐2, 3‐dimethylpentane ( 6B ), 3‐bromo‐2, 2, 3‐trimethylpentane ( 7B ), 3‐bromo‐3‐ethylpentane ( 8B ), 3‐bromo‐3‐ethyl‐2‐methylpentane ( 9B ) and 2‐bromo‐2, 4, 4‐trimethylpentane ( 11B ) in 15 to 21 solvents was studied, and correlation analyses by using the single‐ and dual‐parameter Grunwald‐Winstein equations (Eqns 1 and 2) were examined. Substrates 7B, 9B and 11B showed excellent linear relationship (R ≥ 0.997) in the logk ‐ Y_Br plots and indicated limiting S_N1 mechanism for the solvolysis. On the other hand, bromides 1B‐6B and 8B gave linear correlations (R = 0.987–0.996) with the dual‐parameter (Y_Br and N_OTs) equation (2) only, which indicated the presence of significant nucleophilic solvent participation. Normal trends of reactivity due to the relief of B‐strain could be found in the poorly nucleophilic trifluoroethanol. Similar to the corresponding chlorides, the overwhelming influence of nucleophilic solvent assistance results in the observed inverse order of reactivity: k( 2B ) > k( 3B ), k( 5B ) > k( 6B ) and k( 8B ) > k( 9B ).     

A new diene, 2-methoxy-1,3-pentadiene-5-ol. Synthesis and intramolecular diels-alder reactions

Reactions of the diene 1-benzyloxy-2-methoxy-1,3-pentadiene-5-ol in intramolecular Diels-Alder reactions using maleic anhydride or fumaric acid ethyl ester is described. The new reactive diene is prepared starting from 3-methoxypyridine. The structure of the diene was elucidated by a NOE nmr experiment.     

Selective Preparation of 4-(Bromo or Iodo)-2,5-dimethoxybenzonitrile and 2-(Bromo or Iodo)-3,6-dimethoxybenzonitrile from 2,5-Dimethoxybenzaldehyde

By use of appropriate reactions and sequence of steps, 2,5-dimethoxybenzaldehyde can be converted either to 4-(bromo or iodo)-2,5-dimethoxybenzonitrile or 2-(bromo or iodo)-3,6-dimethoxybenzonitrile.