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.     

Palladium-catalyzed stereoconvergent formylation of (E/Z)-β-bromo-β-fluorostyrenes: straightforward access to (Z)-α-fluorocinnamic aldehydes and (Z)-β-fluorocinnamic alcohols

We report here the stereoconvergent formylation of (E/Z)-β-bromo-β-fluorostyrene mixtures with carbon monoxide and sodium formate catalyzed by palladium. Optimization of reaction conditions leads to the corresponding pure (Z)-α-fluorocinnamaldehydes in good yields. The reaction was extended to styrenes bearing electro-attracting or electro-donating groups. The obtained α-fluoroaldehydes were smoothly reduced to the corresponding (Z)-β-fluorocinnamic alcohol by NaBH(4). The reaction could be performed on functionalized substrates as demonstrated by the access to the glucoside of β-fluoroconiferyl alcohol, (Z)-β-fluoroconiferin, a strong inhibitor of lignin polymerization.     

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.     

Highly stereospecific, palladium-catalyzed cross-coupling of alkenylsilanols

[reaction: see text] Alkenylsilanols bearing methyl ((E)-1 and (Z)-1) or isopropyl ((E)-2 and (Z)-2)) substituents are converted to disubstituted alkenes by a palladium(0)-catalyzed cross-coupling reaction with aryl or vinyl iodides in the presence of tetrabutylammonium fluoride or hydroxide. Yields and stereoselectivities are generally high, and the reaction is compatible with a wide range of functional groups.     

Synthesis of novel star-like hyperbranched polymers with poly(amido amine) core and poly(l-lysine) shell

Hyperbranched poly(amido amine)s containing vinyl and hydroxyl groups were successfully synthesized via Michael addition polymerization of triacrylamide (TT) and 3-amino-1,2-propanediol (APD) with equal molar ratio in feed. ¹H, ¹³C and HSQC NMR techniques were used to clarify the structure of hyperbranched polymers and polymerization mechanism. The Michael addition reaction of hyperbranched poly(1TT-1APD)s with primary amine-terminated poly(ε-benzyloxycarbonyl-l-lysine)s [PLys(Z)] yielded a star-like hyperbranched polymers with poly(1TT-1APD) core and Plys(Z) shell. The Z groups in PLys(Z) were removed under acidolysis, and thus star-like hyperbranched polymers with hydroxyl groups inside and primary amine groups outside were obtained successfully.     

The Hammett relationship and reactions in the excited electronic state: hemithioindigo Z/E-photoisomerization

The photochemical reaction dynamics of a set of photochromic compounds based on thioindigo and stilbene molecular parts (hemithioindigos, HTI) are presented. Photochemical Z/E isomerization around the central double bond occurs with time constants of 216 ps (Z --> E) and 10 ps (E --> Z) for a 5-methyl-hemithioindigo. Chemical substitution on the stilbene moiety causes unusually strong changes in the reaction rate. Electron-donating substituents in the position para to the central double bond (e.g., para-methoxy) strongly accelerate the reaction, while the reaction is drastically slowed by electron-withdrawing groups in this position (e.g., para-nitrile). We correlate the experimental data of seven HTI-compounds in a quantitative manner using the Hammett equation and present a qualitative explanation for the application of ground-state Hammett constants to describe the photoisomerization reaction.     

硫代四配位磷化物与邻氨基酚反应

在三乙胺存在下,多种硫代磷酰二氯与邻氨基酚反应,经磷硫双键断开并以σ键与磷相连的基团被置换下来等过程,最终生成双环五配位磷化物.苯基硫代环膦酸酯与邻氨基酚反应分别生成螺环五配位磷化物.苯氧基或烷氧基硫代环磷酸酯与邻氨基酚反应,除磷硫键断裂以及苯氧基、烷氧基被置换外,还发生邻亚氨基苯氧基与邻苯二氧基进行相互交换反应.这些反应机理依据磷原子的电负性,氢质子的活泼性以及P-X键的稳定性进行了讨论.     

Dipole interaction-controlled stereoselectivity in aldol reaction of alpha-CF3 enolate with fluoral

The stereoselectivity of a reaction is generally determined by minimizing steric repulsion. However, the aldol reaction of alpha-CF(3)-ketone (Z)-enolate with fluoral anomalously gave an anti-aldol through a sterically demanding transition state, because of the strong dipole interaction of the two CF(3) groups. We have thus disclosed a paradigm shift from steric to electronic control of reaction stereoselectivity. [reaction: see text]     

Synthesis of (Z)-4-hydroxytamoxifen and (Z)-2-[4-[1-(p-hydroxyphenyl)-2-phenyl]-1butenyl]phenoxyacetic acid

The synthesis of (Z)-4-hydroxytamoxifen and (Z)-2-[4-[1-(p-hydroxyphenyl)-2-phenyl]-1-butenyl]phenoxyacetic acid was accomplished using a McMurry reaction as the key step. The perfluorotolyl derivatives of the McMurry products enabled the separation of the minor undesirable geometrical isomer. The methodology proceeds without E,Z isomerization, employs a very mild final debenzylation step compatible with a large array of functional groups, and can be applied to the generation of a variety of 4-hydroxytamoxifen analogues.     

Anionic cycloaromatization of 1-aryl-3-hexen-1,5-diynes initiated by methoxide addition: synthesis of phenanthridinones,benzo[c]phenanthridinones,and biaryls

Treatment of 2-((Z)-6-substituted-3-hexene-1,5-diynyl)benzonitriles with sodium methoxide in refluxing methanol in the presence of a polar aprotic solvent, such as DMSO, HMPA, THF, or 18-crown-6, gave phenanthridinones in 21-77% yields. In these cases, addition of 10% DMSO into the reaction mixture gave the highest yield. On the other hand, methanolysis of 2-(2-(2-alkynylphenyl)ethynyl)benzonitriles under the same reaction conditions gave benzo[c]phenanthridinones in 31-57% yields. Methanolysis of (Z)-1-aryl-3-hexen-1,5-diynes in the presence of 2 equiv of tetrabutylammonium iodide gave biaryls in 14-64% yields. It is found that the reactions with aryl groups bearing electron-withdrawing groups proceeded at greater rates and gave better yields.     

共轭三烯及Galbanolenes的立体选择性合成

通过修饰改造的Ramberg-Backlund反应,(E,E)-,(E,Z)-,(Z,Z)-二烯丙基砜(6)在CBr~2F~2存在下,用KOH/Al~2O~3处理,选择性地生成(E,E,E)-,(E,E,Z)-,(Z,E,Z)-1,3,5-己三烯(7),反应的立体选择性依赖于溶剂和温度,通常在0℃时用CH~2Cl~2作溶剂可达到良好的(E)-选择性,有些时候在-78℃以下,以V(t-BuOH):V(CBr~2F~2)=1:1作为混合溶剂时(E)-选择性更好,该新方法被用于天然产物Galbanolenes(7m)和(7n)的合成中。     

Stereoselective Synthesis of 1,3-Enynylstannanes via Palladium Catalyzed Cross-Coupling Reactions of （Z）-α-Bromovinylstannanes

Based on the different reactivity of stannyl and bromo groups, (Z)-α-bromovinylstannanes can undergo the cross-coupling reaction with alkynyl Grignard reagents in the presence of tetrakis(triphenylphosphine)palladium(0) catalyst in THF at room temperature to afford stereoselectively 1,3-enynylstannanes in good yields.     

Analysis of melt copolymers

Melt copolymer chains are the main (most abundant) reaction product obtained when heating a blend of two (or more) condensation polymers (such as polyester + polycarbonate or polyester + polyamide or polyester + polyester) in which exchange reactions occur. In fact, during the melt-mixing reaction, an AB copolymer is formed and, as a consequence, the sample is a complex mixture made of three components or simply "parts", referred to as Z1, Z2 and Z3, where Z1 and Z2 are the parts for unreacted homopolymers (A and B), whereas Z3 is the part for the copolymer. In this paper, it is shown that matrix-assisted laser desorption/ionization mass spectrometry (and mass spectrometry in general) can be used to monitor the yield of the reactive blending reaction, YR, by measuring the amount of unreacted homopolymer (Z1 and Z2). In order to allow for comparisons, the paper also discusses conventional methods for measuring Z1 and Z2, such as liquid chromatography and nuclear magnetic resonance.     

Synthesis of

A series of 1,1'-dicinnamoylferrocenes were converted to the corresponding [3]ferrocenophane diols (4a-e) in a stereoselective manner by using samarium diiodide to effect the intramolecular coupling reaction, aldol reaction, and reduction in one-pot operation. The major reaction pathway might be derived from a samarium chelated transition state (I(A)()) having the moieties of s-cis enone and (Z)-enolate. A solid-state structure of such [3]ferrocenophane diol product showed that the cyclopentadienyl groups were in an eclipsed orientation and slightly tilted.     

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.     

Silver technology for stabilization of simple (Z)-enethiols: stereoselective synthesis and reaction of silver (Z)-enethiolates

Reported here for the first time are the stereoselective synthesis and reaction of simple silver (Z)-enethiolates, which serve as stabilized (Z)-enethiol storage. In contrast to labile enethiols, silver (Z)-enethiolates are stable even in solutions, and their isolation and purification are very simple. The method for synthesis of silver (Z)-enethiolates involves an unusual vinylic SN2 reaction of (E)-vinyl-lambda3-iodanes with thiobenzamides yielding the inverted (Z)-S-vinylthioimidonium salts, followed by their regioselective C-S bond cleavage with silver acetate. Alkylation, arylation, and Michael addition of silver (Z)-enethiolates yielding (Z)-vinyl sulfides were dramatically accelerated by the addition of Bu4NI (LiI), which probably generates reactive ammonium (Z)-enethiolates with an increased nucleophilicity.     

Subtle stereochemical and electronic effects in iridium-catalyzed isomerization of C-allyl glycosides

[reaction: see text] Stereoselective isomerization of C-allyl glycosides into (E)-C-vinyl glycosides or (Z)-exo-glycals was carried out in the presence of the cationic iridium(I) catalyst [(Ph(2)MeP)(2)Ir(cod)PF(6)]. The products of the isomerization were affected by the relative 1,2-stereochemical relationships and by the nature of the protecting groups. These effects are discussed along with a plausible reaction mechanism.     

Novel approach to multifunctionalized homoallylic alcohols via regioselective ring opening of aryl oxiranes with 3-iodo allenoates

[reaction: see text] 3-Iodo allenoates were generated in situ and utilized, for the first time, in the ring opening of oxiranes in a regioselective fashion. This simple one-pot three-component reaction protocol provides easy access to highly functionalized homoallylic alcohols in good yields and moderate to very good (Z/E) selectivity. The two functional groups (ester and halogen) can be further subjected to many synthetic transformations.     

Synthesis and structures of 15- and 18-membered unsaturated selenacrown ethers and their complexation with silver trifluoroacetate

The reaction of Na(2)Se with cis-dichloroethene yielded (Z,Z,Z,Z,Z)-1,4,7,10,13-pentaselenacyclopentadeca-2,5,8,11,14-pentaene (15-US-5) and (Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16-hexaselenacyclooctadeca-2,5,8,11,14,17-hexaene (18-US-6). X-ray crystallographic analysis of 15-US-5 and 18-US-6 revealed an all-cis geometry around the carbon-carbon double bonds, with all of the selenium atoms located on one side of the respective ring planes. 15-US-5 and 18-US-6 were also found to be oxidized more easily than the corresponding sulfur analogues. The complexation of 15-US-5 and 18-US-6 with silver trifluoroacetate afforded Ag(I)(15-US-5)(CF(3)COO) and Ag(I)(5)(18-US-6)(3)(CF(3)COO)(5), respectively. [reaction: see text]     

Crystalline-state Z,E-photoisomerization of a series of (Z,E,Z)-1,6-diphenylhexa-1,3,5-triene 4,4'-dicarboxylic acid dialkyl esters. Chain length effects on the crystal structure and photoreactivity

[reaction: see text] Crystalline-state Z,E-photoisomerization of a series of (Z,E,Z)-1,6-diphenylhexa-1,3,5-triene 4,4'-dicarboxylic acid dialkyl (R) esters [(Z,E,Z)-1a, R = Me; (Z,E,Z)-1b, R = Et; (Z,E,Z)-1c, R = n-Pr; (Z,E,Z)-1d, R = n-Bu] was investigated. All Z,E,Z isomers underwent one-way isomerization to the corresponding E,E,E isomers. The reaction efficiency was strongly enhanced as the length of the alkyl chain increased. Single-crystal X-ray analyses of (Z,E,Z)-1a-d showed that the alkyl chain part of the crystals became larger as the chain length increased. The conformational flexibility of the alkyl chains made the large change in the triene geometry in the lattice possible, leading to the enhancement of the photoreactivity in the crystalline state.