Stereoselective synthesis of (Z)-2-fluoro-1-alkenyl(phenyl)iodonium tetrafluoroborates

[reaction: see text] (Z)-2-Fluoro-1-alkenyl(phenyl)iodonium salts were stereoselectively prepared by the reaction of alkynyl(phenyl)iodonium salts with aqueous HF in good yields. The method is applicable to the synthesis of fluoroalkenyliodonium salts having functional groups such as ketone, ester, and chloride. (Z)-2-Fluoro-1-alkene, (Z)-2-fluoro-2-alkenoate, and (Z)-beta-fluoroenyne could be stereoselectively prepared from the fluoroalkenyliodonium salt.     

Stereoselective generation of (E)- and (Z)-2-fluoroalkylidene-type carbenoids from (2-fluoro-1-alkenyl)iodonium salts and their application for stereoselective synthesis of fluoroalkenes

Alkylidene-type carbenoids, generated from (Z)- or (E)-(2-fluoro-1-alkenyl)iodonium salts by treatment with LDA, reacted with trialkylboranes to give (E)- or (Z)-(fluoroalkenyl)boranes stereoselectively. The resulting (fluoroalkenyl)borane can be used for the selective synthesis of (E)- or (Z)-fluoroalkenes, (E)- or (Z)-fluoroiodoalkenes, and alpha-fluoroketones. [reaction: see text]     

Titanocene(II)-promoted stereoselective alkenylation utilizing (Z)-alkenyl sulfones

The stereoselective alkenylation of unsaturated compounds by means of a (Z)-alkenyl sulfone-titanocene(II) system is described. Treatment of alkynes and (Z)-alkenyl methyl sulfones with the titanocene(II) reagent Cp2Ti[P(OEt)3]2 produced conjugated dienes. This alkenylation system is also applicable to polar C=O bonds; the simple mixing of carbonyl compounds, (Z)-alkenyl methyl sulfones, and the titanocene(II) reagent formed allylic alcohols. The advantages of alkenylation are that it requires no prepreparation of the alkenylmetal reagent and that it proceeds with complete stereoselectivity.     

Pd(OAc)2-catalyzed cyclization of 2,3-allenoic acids in the presence of terminal alpha,beta-unsaturated alkynones: a one-pot highly stereoselective synthesis of 4-(3'-oxo-1'(E)-alkenyl)-2(5H)-furanones

The Pd(OAc) 2-catalyzed cyclization reaction of 2,3-allenoic acids in the presence of terminal alpha,beta-unsaturated alkynones afforded an E/ Z mixture of 4-(3'-oxo-1'-alkenyl)-2(5 H)-furanones. A subsequent complete isomerization of the Z-isomer to E-isomer was observed in DMSO at 90 degrees C, which led to a highly stereoselective synthesis of 4-(3'-oxo-1'( E)-alkenyl)-2(5 H)-furanones. A possible mechanism is proposed.     

Highly stereoselective iodolactonization of 4,5-allenoic acids--an efficient synthesis of 5-(1'-iodo-1'(Z)-alkenyl)-4,5-dihydro-2(3H)-furanones

In this paper, it is reported that the efficient iodolactonization of 4,5-allenoic acid with I2 in cyclohexane in the presence or absence of K2CO3 afforded 5-(1'-iodo-1'(Z)-alkenyl)-4,5-dihydro-2(3H)-furanones highly stereoselectively. However, the reaction of axially optically active 4,5-allenoic acids (R)-(-)-5 a and (R)-(-)-5 b with I2 afforded the corresponding products with a serious loss of chirality. This problem was solved by conducting the iodolactonization with N-iodosuccinimide in CH2Cl2 in the presence of Cs2CO3; however, the Z/E selectivity is somewhat lower. The pure optically active Z products were prepared by subsequent kinetic resolution with Sonogashira coupling. The reaction of the substrates with a substituent at the 3-position of the starting 4,5-allenoic acids afforded the trans-4,5-disubstituted gamma-butyrolactones as the only products. The reaction of the 4,5-allenoic acids (S)-(+)-1 l, (R)-(-)-1 l, and (S)-(+)-1 m with a center chirality at the 3-position afforded the trans products with very high enantiopurity and up to 98:2 Z/E selectivity regardless of the axial chirality of the allene moiety.     

Stereospecific preparation of (Z)- and (E)-2,3-difluoro-3-stannylacrylic ester synthons and a new, efficient stereospecific route to (Z)- and (E)-2,3-difluoroacrylic esters

[reaction: see text] The (Z)-2,3-difluoro-3-stannylacrylic ester is readily prepared from (Z)-1,2-difluorovinyltriethylsilane via stereospecific stannyl/silyl exchange with KF/(Bu3Sn)2O or Bu3SnCl in DMF at 70 degrees C. The corresponding (E)-2,3-difluoro-3-stannylacrylate is prepared by stereospecific carbonylation of (E)-1,2-difluorovinyl iodide followed by low temperature/in situ stannylation of the resultant (Z)-2,3-difluoroacrylic ester. With Cu(I) iodide and Pd(PPh3)4 catalysis, the (Z)- and (E)-stannylacrylate esters readily couple with aryl iodides and vinyl bromides, as well as 2-iodothiophene, at room temperature to stereospecifically produce the respective (E)- and (Z)-2,3-difluoro-3-aryl substituted acrylic esters or conjugated dienes in high yields.     

Synthesis of Z and E-(2',5'-dimethoxyphenyl)-methylene-butyrolactones

Pseudotaxlactone was isolated by Zhang1 from Taxaceae plant pseudotaxus chienii(Cheng) Cheng. It's structure was tentatively assigned as 5-(4-hydroxy-3,5- 20%(Z,9), 4%(E,8).The intermediate 7 was synthesized using 2,5-dimethoxy-phenyl acetic acid as astarting material. However, cyclization reaction gave Z-(2,5-dimethoxy-phenyl)methylene-butyrolactone 9 (20%) and E-(2,5-dimethoxy-phenyl)-methylelactone 8 (4%), instead of the desired counterpart with endocyclic unsaturation. Thereaction of t…     

Diastereoselection in the reactions of thioallylic anions with benzaldehyde

Reactions of the anions of (Z)-2-alkenyl N,N-dimethyldithiocarbamates with benzaldehyde gave the $\text{erythro}$ isomers of 4-hydroxy-4-phenyl-(E)-1-alkenyl N,N-dimethyldithiocarbamates stereoselectively and those of the anions of (E)-2-alkenyl N,N-dimethyldithiocarbamates afforded the $\text{threo}$ isomers predominantly.     

(E)- and (Z)-1-benzenesulfonyl-4-trimethylsilyl-2-butenes as (E)-1-(1,3-butadienyl) synthons

(E)- and (Z)-1-benzenesulfonyl-4-trimethylsilyl-2-butenes (E/Z=9), prepared from 4-trimethylsilyl-1-buten-3-ol, $\text{n}$-butyllithium and benzenesulfenyl chloride and oxidation of the intermediate (E)- and (Z)-1-benzenesulfinyl-4-trimethylsilyl-2-butenes with hydrogen peroxide, react with $\text{n}$-butyllithium and then primary halides to give 4-benzenesulfonyl-1-trimethylsilyl-2-alkenes which are rapidly 1,4-debenzenesulfonyltrimethylsilated to (E)-1,3-alkadienes by tetra-$\text{n}$-butylammonium fluoride at O°C.     

Stereoselective synthesis of enantiomerically pure 1-(E)-alkenylsulfoximines

Optically active (E)-N-tosyl-S-(1-alkenyl)-S-phenylsulfoximines 4 are synthesized stereoselectively in a one pot sequence from readily available 1 via C-silylation, metallation and reaction of the corresponding lithiosulfoximine 3 with various carbonyl compounds. The El-MS spectra of the so prepared alkenylsulfoximines 4 show unexpected fragmentations, pointing to a new, unusual S-O-migration of the 1-alkenyl moiety.     

Stereoselective Suzuki-Miyaura cross-coupling reactions of potassium alkenyltrifluoroborates with alkenyl bromides

[reaction: see text] The stereoselective synthesis of conjugated dienes using air-stable potassium alkenyltrifluoroborates as coupling partners is described. The palladium-catalyzed cross-coupling reaction of potassium (E)- and (Z)-alkenyltrifluoroborates with either (E)- or (Z)-alkenyl bromides proceeds readily with moderate to excellent yields to give the corresponding (E,E)-, (E,Z)-, (Z,E)-, or (Z,Z)-conjugated dienes stereospecifically. The cross-coupling can generally be effected using 5 mol % of Pd(OAc)2, 10 mol % of PPh3, and 3 equiv of Cs2CO3 in THF-H2O (10:1). A variety of functional groups are tolerated in both coupling partners.     

Synthesis of 2,4-disubstituted thiazoles from (Z)-(2-acetoxyvinyl)phenyl-lambda3-iodanes: nucleophilic substitution of alpha-lambda3-iodanyl ketones with thioureas and thioamides

In the presence of triethylamine, (Z)-(2-acetoxy-1-alkenyl)phenyl-lambda(3)-iodanes react with thioureas or thioamides in MeOH to give 2,4-disubstituted thiazoles directly in good yields. The reaction probably involves generation of highly reactive alpha-lambda(3)-iodanyl ketones through ester exchange of the beta-acetoxy group with liberation of methyl acetate, followed by nucleophilic substitutions with thioureas or thioamides.     

Stereoselective preparation of (E)- and (Z)-alpha-fluorostilbenes via palladium-catalyzed cross-coupling reaction of high E/Z ratio and (Z)-1-bromo-1-fluoroalkenes

A highly stereoselective method to prepare both (E)- and (Z)-alpha-fluorostilbenes is described. 1-Bromo-1-fluoroalkenes (E/Z approximately 1:1), a readily available starting material, isomerizes to high E/Z ratios by storage at -20 degrees C or by photolysis at 254 nm. Stille coupling between these high E/Z 1-bromo-1-fluoroalkenes and aryl stannanes gave (Z)-alpha-fluorostilbenes in high stereoselectivity. (Z)-1-Bromo-1-fluoroalkenes, which were kinetically separated from 1-bromo-1-fluoroalkenes (E/Z approximately 1:1), can participate in Suzuki coupling reactions to give (E)-alpha-fluorostilbenes stereoselectively.     

A new route to the synthesis of (E)- and (Z)-2-alkene-4-ynoates and nitriles from vic-iiodo-(E)-alkenes catalyzed by Pd(0) nanoparticles in water

An efficient procedure for the stereoselective synthesis of (E)- and (Z)-2-alkene-4-ynoates and -nitriles by a simple reaction of vic-diiodo-(E)-alkenes with acrylic esters and nitriles catalyzed by in situ prepared Pd(0) nanoparticles in water has been developed. Addition of acrylic esters leads to (E)-isomers exclusively, whereas (Z)-isomers are obtained in high stereoselectivity from reactions of acrylonitrile. The aqueous slurry of Pd nanoparticles is recycled. A probable mechanism has been suggested.     

Thiazolo[4,5-d]pyrimidines. Part I. synthesis and anti-human cytomegalovirus (HCMV) activity in vitro of certain alkyl derivatives

Alkyl derivatives of the thiazolo[4,5-d]pyrimidine congeners of guanine and uracil were prepared and assessed for in vitro activity against human cytomegalovirus (HCMV). The finding that the 3-pentyl 1b and 3-hexyl 1c derivatives of 5-aminothiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione (1e) had potent in vitro anti-HCMV activity prompted a broader study of alkyl derivatives in this ring system. A series of 3-alkyl derivatives of 1e , viz. 1f-w , were prepared by direct alkylation of the sodium salt of 1e and by subsequent modifications, 2a-d. For comparison with 1c , 5-amino-2-hexylaminothiazolo[4,5-d]pyrimidin-7(6H)-one (4) was prepared and studied. The 3-(2-alkenyl) derivatives of 1e were found to be the more active antiviral agents with the Z isomer of 5-amino-3-(2-penten-1-yl)thiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione (1f) having the better therapeutic index. Analogous 4-(2-alkenyl) derivatives of 2-aminothiazolo[4,5-d]pyrimidine-5,7(4H,6H)-dione 6a and 6b were also prepared but were found to have poor therapeutic indices. Single crystal X-ray diffraction analysis was used to unequivocally establish the structure of 1f.     

(Z)-3-丁烯基-4-羟基苯酞的合成

（Ｚ）－３－丁烯基－４－羟基苯酞的合成李绍白,王志伟,方小平,李裕林（兰州大学应用有机化学国家重点实验室,兰州,７３００００）关键词（Ｚ）－３－丁烯基－４－羟基苯酞,苯酞,３－丙基－５－羟基异香豆素,异香豆素,合成（Ｚ）－３－丁烯基－４－羟基苯酞（１...     

Gas-phase reactions of NO3 and N2O5 with (Z)-hex-4-en-1-ol, (Z)-hex-3-en-1-ol ('leaf alcohol'), (E)-hex-3-en-1-ol, (Z)-hex-2-en-1-ol and (E)-hex-2-en-1-ol

The night-time atmospheric chemistry of the biogenic volatile organic compounds (Z)-hex-4-en-1-ol, (Z)-hex-3-en-1-ol ('leaf alcohol'), (E)-hex-3-en-1-ol, (Z)-hex-2-en-1-ol and (E)-hex-2-en-1-ol, has been studied at room temperature. Rate coefficients for reactions of the nitrate radical (NO(3)) with these stress-induced plant emissions were measured using the discharge-flow technique. We employed off-axis continuous-wave cavity-enhanced absorption spectroscopy (CEAS) for the detection of NO(3), which enabled us to work in excess of the hexenol compounds over NO(3). The rate coefficients determined were (2.93 +/- 0.58) x 10(-13) cm(3) molecule(-1) s(-1), (2.67 +/- 0.42) x 10(-13) cm(3) molecule(-1) s(-1), (4.43 +/- 0.91) x 10(-13) cm(3) molecule(-1) s(-1), (1.56 +/- 0.24) x 10(-13) cm(3) molecule(-1) s(-1), and (1.30 +/- 0.24) x 10(-13) cm(3) molecule(-1) s(-1) for (Z)-hex-4-en-1-ol, (Z)-hex-3-en-1-ol, (E)-hex-3-en-1-ol, (Z)-hex-2-en-1-ol and (E)-hex-2-en-1-ol. The rate coefficient for the reaction of NO(3) with (Z)-hex-3-en-1-ol agrees with the single published determination of the rate coefficient using a relative method. The other rate coefficients have not been measured before and are compared to estimated values. Relative-rate studies were also performed, but required modification of the standard technique because N(2)O(5) (used as the source of NO(3)) itself reacts with the hexenols. We used varying excesses of NO(2) to determine simultaneously rate coefficients for reactions of NO(3) and N(2)O(5) with (E)-hex-3-en-1-ol of (5.2 +/- 1.8) x 10(-13) cm(3) molecule(-1) s(-1) and (3.1 +/- 2.3) x 10(-18) cm(3) molecule(-1) s(-1). Our new determinations suggest atmospheric lifetimes with respect to NO(3)-initiated oxidation of roughly 1-4 h for the hexenols, comparable with lifetimes estimated for the atmospheric degradation by OH and shorter lifetimes than for attack by O(3). Recent measurements of [N(2)O(5)] suggest that the gas-phase reactions of N(2)O(5) with unsaturated alcohols will not be of importance under usual atmospheric conditions, but they certainly can be in laboratory systems when determining rate coefficients.     

Highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides from 1-bromo-1-fluoroalkenes via palladium-catalyzed carbonylation reactions

The highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides is described. 1-Bromo-1-fluoroalkenes (E/Z approximately 1:1), which are readily available starting materials, have been found to isomerize to high E/Z ratios after storage at -20 degrees C for 1 week or by photolysis at 254 nm. Since the (E)-isomers have been found to react faster than the corresponding (Z)-isomers at room temperature in Pd(0)-catalyzed reactions, the palladium-catalyzed carboalkoxylation of high E/Z 1-bromo-1-fluoroalkenes lead to a high Z/E (Z/E >/= 98:2) ratio of the alpha-fluoro-alpha,beta-unsaturated esters. When 1-bromo-1-fluoroalkenes (E/Z approximately 1:1) were reacted with HCOOH/NBu(3)/Pd(II)/DMF, the (E)-isomer was selectively reduced, and the remaining (Z)-1-bromo-1-fluoroalkenes were recovered in essentially pure isomeric form. The resulting mixture of (Z)-1-bromo-1-fluoroalkenes and the reduced products underwent similar palladium-catalyzed carboalkoxylation reactions at 70 degrees C, and the (E)-alpha-fluoro-alpha,beta-unsaturated esters were stereospecifically obtained. This methodology was also successfully applied for the stereospecific synthesis of (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides: the palladium-catalyzed carboamidation reaction of high E/Z and (Z)-1-bromo-1-fluoroalkenes lead to pure (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides, respectively.     

Lewis acid catalyzed intramolecular Diels-Alder reactions of acyclic (Z)-substituted 1,3-dienes

Lewis acid catalyzed intramolecular Diels-Alder reactions of trienes (E,E,Z)-1a-d, (E,E,Z)-4a-d, and (E,Z,Z)-7a,b are described. Trienes containing enal or enone dienophiles cyclize in excellent yield under mild conditions using substoichiometric amounts of MeAlCl(2), in most cases with high levels of diastereoselectivity. The thermal IMDA reactions of 1a, 4a, and 7a require forcing conditions and proceed in low yield with reversed stereoselectivity in the cases of 1a and 4a.     

Synthese der (1Z,3E) und (1Z,3Z)-isomeren des wisanins

The (1Z,3E)- and (1Z,3Z)-isomers of wisanine were synthesized and characterized by their spectroscopic data.