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.     

Kinetic separation methodology for the stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters via the palladium-catalyzed carboalkoxylation of 1-bromo-1-fluoroalkenes

[reaction: see text] Methodology for the stereoselective preparation of both (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters is described. 1-Bromo-1-fluoroalkenes (E/Z approximate 1:1) can be isomerized to high E/Z ratio mixtures, which participate in palladium-catalyzed carboalkoxylation and lead to (Z)-alpha-fluoro-alpha,beta-unsaturated esters in high stereoselectivity. The same starting material can also be kinetically reduced to get an E/Z ratio of 0:100; similar carboalkoxylation reaction at 70 degrees C affords (E)-alpha-fluoro-alpha,beta-unsaturated esters stereospecifically.     

Site-specific preparation of 3-fluoro-1-substituted-naphthalenes via a novel base-catalyzed cyclization reaction from (E)-monofluoroenynes

A novel cyclization reaction for the preparation of 3-fluoro-1-substituted-naphthalenes is reported. (E)-Monofluoroenynes, which are prepared by Sonogashira coupling reaction from (Z)-1-bromo-1-fluoroalkenes, undergo cyclization to afford 3-fluoro-1-substituted-naphthalenes in good to excellent yields when treated with DABCO or DBU in refluxing N-methyl-2-pyrrolidinone (NMP). [reaction: see text]     

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]     

松毛虫性信息素(5Z,7E)-十二碳二烯醇的立体选择性合成

从简单原料乙炔出发,通过炔对丙烯醛的加成反应得到7-溴代-(4Z,6E)-庚二烯醛,再经乙二醇保护、Pd催化偶联、水解、Wittig反应和还原等步骤,立体选择性地得到松毛虫性信息素(5Z,7E)-十二碳二烯醇,其结构通过IR,NMR和MS等技术得到确认.     

Stereospecific preparation of symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes from 1-bromo-1-fluoroalkenes

A straightforward method to prepare symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes is described. High E/Z ratio 1-bromo-1-fluoroalkenes, prepared by isomerization from the E/Z ≈ 1:1 isomeric mixtures, reacted with Bu₃SnSnBu₃ and Pd(PPh₃)₄ to afford (1Z, 3Z)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in good yield. (Z)-1-Bromo-1-fluoroalkenes, which were prepared by kinetic reduction from 1-bromo-1-fluoroalkenes (E/Z ≈ 1:1), can undergo similar reaction with Bu₃SnSnBu₃ and Pd(PPh₃)₄/CuI to prepare (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes.     

Palladium-catalyzed highly regio- and stereoselective synthesis of (1E)- or (1Z)-1,2-dihalo-1,4-dienes via haloallylation of alkynyl halides

A highly efficient and selective synthesis of (1E)- or (1Z)-1,2-dihalo-1,4-dienes via Pd-catalyzed coupling of haloalkynes and allylic halides is described. The (1E)-1,2-dihalo-1,4-dienes were generated in good yields with excellent stereoselectivities (1E/1Z up to >98/2), while (1Z)-1,2-dihalo-1,4-dienes were produced in excellent yields and stereoselectivities (1Z/1E up to >98/2) by simply adding stoichiometric lithium halides.     

Reactions of lithiated (E)-3-halo-1-phenylsulfonylprop-1-enes and (Z)-1-halo-3-phenylsulfonylprop-1-enes with aldehydes

(E)-3-Chloro-1-phenylsulfonylprop-1-ene and its iodo- and bromo-analogues, (Z)-1-iodo-3-phenylsulfonylprop-1-ene and (Z)-1-bromo-3-phenylsulfonylprop-1-ene, have each been successfully converted into lithiated carbanions which react regioselectively with aromatic aldehydes to give gamma-alkylated products whose nature depends upon the halogen substituent: the chloro-sulfones yield (2Z)-1-aryl-2-chloro-4-phenylsulfonylbut-2-en-1-ols but the bromo- and iodo-derivatives behave differently, yielding (1E)-trans-4-aryl-3,4-epoxy-1-phenylsulfonylbut-1-enes. In sharp contrast, the same lithiated sulfones react with aliphatic aldehydes to give anti-configured beta-hydroxysulfones which are formed via diastereoselective alpha-alkylation reactions.     

(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.     

钯催化下(Z)-3-碘-3-三氟甲基-1-芳基烯丙醇与末端炔 烃的偶联反应

在Pd(PPh~3)~4/CuI催化下和使用1mol的NEt~3作碱和THF作溶剂,(Z)-3-碘-3-三氟甲基-1-芳基烯丙醇(1)与末端炔烃(3)反应得到正常的偶联产物5。当以NEt~3作碱和溶剂,Pd(PPh~3)~4/CuI催化1与3的交叉偶联反应生成化合物4。4为正常偶联化合物5在NEt~3存在下双键发生重排反应的产物。     

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.     

A stereoselective route to alkenyl sulfides through the palladium-catalyzed cross-coupling reaction of 9-alkyl-BBN with 1-bromo-1-phenylthioethene or (E)- and (Z)-2-bromo-1-phenylthio-1-alkenes

The reaction of 9-alkyl-9-BBNs with 1-bromo-1-phenylthioethene or (E)- and (Z)-2-bromo-1-phenylthio-1-alkenes takes place readily in the presence of Pd(PPh₃)₄ and sodium hydroxide to afford stereodefined vinylic sulfides in excellent yields.     

Planar-chiral (2E,7Z)- and (2Z,7E)-cyclonona-2,7-dien-1-yl carbamates by asymmetric,bis-allyic,alpha, alpha'-cycloalkylation--studies on their conformational stability

Enantiomerically enriched (>80 % ee) (M,1R,2Z,7E)- and (M,1R,2E,7Z)-cyclonona-2,7-dienyl carbamates have been synthesized by an intramolecular cycloalkylation of the corresponding 1-lithio-9-chloronona-2,7-dienyl carbamates. The enantioenriched precursors were generated by asymmetric deprotonation of the dienyl carbamates by means of n-BuLi/(-)-sparteine. The primarily obtained cyclononadienes, each bearing one element of planar and centre chirality, were formed by an , coupling of both allylic moieties. These are the thermodynamically less favoured epimers, which arise from those allyllithiums bearing the carbamoyloxy residue in a 1-endo position. Both (M,R)-cyclononadienes epimerize slowly (t(1/2) = 209 min and 328 min at 308 K) with inversion of the planar chirality to the corresponding, more stable (P)-epimers (ratios 3:97 and 30:70). The kinetics were measured by 1H NMR spectroscopy, the activation energies EA were found to be 26.4 and 27.5 kcal mol(-1). From quantum-chemical calculations with the B3LYP density functional, the epimerization process was shown to consist of two coupled major conformational changes with high energy barriers. The calculated values match well with the observed ones.     

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.     

A facile stereospecific synthesis of （Z）-2-sulfonyl-substituted 1,3-enynes via Sonogashira coupling of （E）-α-iodovinyl sulfones with 1-alkynes

(E)-a-Iodovinyl sulfones 1 underwent the Sonogashira coupling reactions with terminal alkynes 2 in piperidine at room temperature in the presence of 5 mol% of Pd(PPh3)4 and 10 mol% of CuI to stereospecifically afford the corresponding (Z)-2- sulfonyl-substituted 1,3-enynes 3 in high yields.     

Synthesis of 1-(4-bromo-1-naphthyl)-dihydrouracil and some of its transformations

1-(4-Bromo-1-naphthyl)dihydrouracil, which is also obtained from 1-(4-bromo-1-naphthyl)--alanine, is formed by the bromination of 1-(1-naphthyl)dihydrouracil. Hydrogenation of 1-(4-bromo-1-naphthyl)dihydrouracil with lithium aluminum hydride yields either 1-(1-naphthyl)-2-oxohexahydropyrimidine or 1-(4-bromo-1-naphthyl)-2-oxohexahydropyrimidine, depending on the solvent used. 1-(4-Bromo-1-naphthyl)-2-oxohexahydropyrimidine is formed by the bromination of 1-(1-naphthyl)-2-oxohexahydropyrimidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 524–526, April, 1971.     

Sulfur dioxide-mediated syntheses of polyfunctional alkenes and (E,Z)- and (E,E)-2,4-dien-1-ones

Efficient methods for the stereoselective synthesis of polyfunctional (E)- and (Z)-alkenes and conjugated (E,E)- and (E,Z)-dienones are presented. They rely upon one-pot, four-component processes that condense 1-oxy-1,3-dienes, silyl enol ethers, SO2, and carbon electrophiles. [structure: see text]     

Stereospecific palladium-catalyzed cross-coupling of (E)- and (Z)-alkenylsilanolates with aryl chlorides

The cross-coupling of geometrically defined (E)- and (Z)-alkenyl- and styrylsilanolates with a wide variety of aromatic and heteroaromatic chlorides has been achieved. Under catalysis by bulky, biphenyl-derived phosphines and allylpalladium chloride, the (preformed, stable) potassium salts of di-, tri- and tetrasubstituted alkenyldimethylsilanols undergo high yielding and highly stereospecific coupling to aryl chlorides in THF or dioxane. A variety of functional groups are compatible with these reaction conditions including nitro, ester, ketone, and nitrile. Both (E)- and (Z)-alkenylsilanolates coupled with nearly identical rate and efficiency.     

Synthesis of (Z)- and (E)-3,4-Dimethyl-hex-3-ene-1,6-diols

(Z)- and (E)-3,4-dimethyl-hex-3-ene-1,6-diols (1 and 2) have been synthesized in 23% and 68% yields by a three step sequence requiring only one purification at the end. The steps are a) coupling of 2-lithio-1,3-dithiane with (Z)- or (E)-1,4-dibromo-2,3-dimethyl-but-2-ene (3 or 4), b) hydrolysis of the thioketals (8 and 9) with methyl iodide in a mixture of acetonitrile, acetone and water to give the 3,4-dimethyl-hex-3-ene-1,6-diols (10 and 11) and c) reduction with diisobutylaluminum hydride to provide the (Z)- and (E)-diols.     

Chromium-mediated fluoroalkenylation reactions of 1,1-dibromo-1-fluoroalkane and 1-bromo-1-fluoroalkene derivatives

CrCl₂- and NiCl₂-mediated coupling reactions of E/Z mixture of 1-bromo-1-fluoroalkenes with aldehydes proceeded in a high stereoselectivity to give the corresponding (Z)-2-fluoroallylic alcohol derivatives. On the other hand, in the reaction of 1,1-dibromo-1-fluoroalkane with CrCl₂, (Z)-fluoroalkene derivative was formed via α-elimination reaction of the chromium carbenoid intermediate accompanying the concomitant 1,2-shift of β-hydrogen.