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 (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 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 (Z)-selective hydrosilylation of terminal alkynes catalyzed by a diphosphinidenecyclobutene-coordinated ruthenium complex: application to the synthesis of (Z,Z)-bis(2-bromoethenyl)arenes

[reaction: see text] Complex 1 bearing a diphosphinidenecyclobutene ligand (DPCB-OMe) catalyzes highly stereoselective hydrosilylation of diethynylarenes with HSiMe2Ph to afford (Z,Z)-bis(2-silylethenyl)arenes. Treatment of the hydrosilylation products with N-bromosuccinimide causes bromodesilylation in a stereospecific manner, giving (Z,Z)-bis(2-bromoethenyl)arenes in high geometrical purity (>98%).     

Studies on Pd(II)-catalyzed synthesis of (Z)-alpha-haloalkylidene-beta-lactones from cyclocarbonylation of 2-alkynols and the subsequent coupling reactions

[reaction: see text] A good regio- and stereoselectivity was observed for the PdCl2-catalyzed cyclocarbonylation of 2-alkynols with CuCl2 affording (Z)-alpha-chloroalkylidene-beta-lactones. The highly optically active (Z)-alpha-chloroalkylidene-beta-lactones could be easily prepared from the readily available optically active propargylic alcohols. The Pd(II)-catalyzed cyclocarbonylation of 2-alkynols with CuBr2 was also studied. Although the yields of (Z)-alpha-bromoalkylidene-beta-lactones were low, due to the relatively higher activity of the C-Br bond, the coupling reactions of (Z)-alpha-bromoalkylidene-beta-lactones were quite smooth to afford the corresponding products in high yields. A rationale for this reaction is discussed.     

A new halopropargylation of alkynes promoted by boron trihalides. highly stereo- and regioselective syntheses of substituted (Z)-1-halo-1,4-enyne derivatives

[reaction: see text] A new halopropargylation of alkynes promoted by boron trihalides has been developed. Reactions of (Z)-2-halo-1-vinylboron dihalides (generated in situ via reaction of alkynes with boron trihalides) with lithium propargyloxides in CH(2)Cl(2) at room temperature produce the corresponding (Z)-1-halo-1,4-enynes in modest to good yields.     

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 the N-((1E)-alkenyl)-(2Z,4Z)-heptadienamide side chain of salicylihalamide A and apicularens A and B

[reaction: see text] The unstable N-((1E)-alkenyl)-(2Z,4Z)-heptadienamide side chain of salicylihalamide A (1) and apicularens A and B (3 and 4) has been prepared in one pot by the addition of (1Z,3Z)-hexadienylcuprate, prepared in situ from EtLi, CuBr.SMe2, and acetylene, to a (1 E)-alkenyl isocyanate.     

Diastereoselective allylations of allyl-propargyl hybrid cations: synthesis of conjugated 1,5-dien-7-yne frameworks bearing C(4)-stereogenic centers

[reaction: see text] Chiral C(4)-substituted (E)- or (Z)-1-alkynyl-1-trimethylsilyloxy-2-butene systems provide anti-(Z) or syn-(Z) conjugated dienyne, with a very high level of stereocontrol, on treatment with BF(3).OEt(2) in CH(2)Cl(2) at -50 degrees C in the presence of allyltrimethylsilane. The Cieplak conformation for (E)-substrates and neighboring-group participation for (Z)-substrates are considered to be responsible for the stereochemical consequences.     

Reaction Pathways upon Interaction of Allenic Phosphonates with Selenyl Chlorides

Abstract

Studies were performed on the reaction between alkyl- and arylselenyl chlorides with esters of allenic phosphonic acids, variously substituted at their terminal C-atom. With the esters of the C-3 diasubstituted acids the reaction is highly regioselective and only oxaphosphol heterocyclization occurs to 2,5-dihydro-1,2-oxaphosphols 21-e. With the esters of the propadiene phosphonic acid the reaction is regio- and (Z)-stereoselective: only the 2,3-adducts 3a-b are formed, where the (Z)-isomer and the allenic phosphonates 4a-b are prevalent, as a result of 1,3-sigmatropic isomerization of 3a-b. With the esters of the C-3 monosubstituted acids, complex reaction mixtures are formed. From them were isolated: (E)- and (Z)-isomers of 2,5-dihydro-1,2-oxaphosphols 2f-j; (E)-and (Z)-isomers of the 2,3-adducts 3c-h; (E)-and (Z)-isomers of 4c-f; and (E)-and (Z)-isomers of the 1,2-adducts 5a-d. The reaction partially loses its regioselectivity, but the (Z)-stereoselectivity is preserved:     

A novel method for the construction of (z,e)- or (z,z)-conjugated alkadienyl carboxylates

[reaction: see text] The stereocontrolled dehydrobromination of 1,2-dibromoethyl carboxylates giving (Z)-2-bromovinyl carboxylates could readily be approached by using DBU and a catalytic amount of hydroquinone as a base at -78 degrees C. The first investigation on the Suzuki-type cross-coupling of (Z)-2-bromovinyl carboxylates as electrophiles with stereodefined alkenylboronic acids provides a novel method for the construction of (Z,E)- or (Z,Z)-conjugated alkadienyl carboxylate moieties, which are often present in a range of natural products.     

Palladium-catalyzed ring expansion reaction of (Z)-1-(1,3-butadienyl)cyclobutanols with aryl iodides. stereospecific synthesis of (Z)-2-(3-aryl-1-propenyl)cyclopentanones

[reaction: see text] A novel type of cascade ring expansion process has been developed by the palladium-catalyzed reaction of (Z)-1-(1,3-butadienyl)cyclobutanols with aryl iodides. The reaction proceeds in a stereospecific manner to produce (Z)-2-(3-aryl-1-propenyl)cyclopentanones. It has also been found that regioselective alpha-arylation of alkenyl cyclopentanones proceeds to afford the alpha-arylated cyclopentanones.     

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]     

柱撑阴离子粘土的合成、表征及催化性能研I．ZnAl─SiW_（11）及ZnAl—SiW_（11）Z的合成

采用水热合成及离子交换方法将缺位及单取代型Ｋｅｇｇｉｎ结构钨硅杂多含氧酸根ＳｉＷ（１１）及ＳｉＷ（１１）Ｏ（３９）Ｚ（Ｈ２Ｏ）（６－）嵌入Ｚｎ─Ａｌ型阴离子粘土层间，得到了大层间距的新型层往状微孔材料ＺｎＡｌ─ＳｉＷ（１１）及ＺｎＡｌ—ＳｉＷ（１１）Ｚ（Ｚ＝Ｃｏ（２＋）、Ｎｉ（２十）和Ｃｕ（２＋）），ＸＲＤ与ＩＲ测试结果表明，它们只有９．７　的通道高度．     

第五、六族元素的有机化合物在有机合成中应用的研究 XXXIII: 氰基亚甲基三苯基膦、胂与2-全氟炔酸甲酯的反应以及3-全氟烷基-4-氰基-3-丁烯酸甲酯的立体选择性合成

氰基亚甲基三苯基胂(1)与2-全氟炔酸甲酯(2)反应,生成加合产物2-三苯胂基-3-全氟烷基-4-氰基丁烯-3-酸甲酯(3)通过3的水解,立体选择性地合成了3-全氟烷基-4-氰基-3-丁烯酸甲酸甲酯[5(Z),6(E)],Z:E约为95:5.氰基亚甲基三苯基膦(7)与2亦可反应,生成加合产物2-三苯基膦叉-3-全氟烷基-4-氰基丁烯-3-酸甲酯的顺式和反式异构体(8)和(9).总产率在90%左右.8与9的比例受反应介质极性的影响,若溶剂极性增大,则有利于8的生成.     

A new reaction of aryl aldehydes with aryl acetylenes in the presence of boron trihalides

[reaction: see text]. The reactions of aryl aldehydes with 2 equiv of arylacetylenes in the presence of boron trichloride yield (E,Z)-1,3,5-triaryl-1,5-dichloro-1,4-pentadienes. Reactions carried out in the presence of boron tribromide generate the corresponding (Z,Z)-1,3,5-triaryl-1,5-dibromo-1,4-pentadienes.     

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]     

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.     

Stereochemical inversion in the vinylic substitution of boronic esters to give iodonium salts: participation of the internal oxy group

[reaction: see text] Alkenylboronic esters having an acyloxy, alkoxy, or methoxycarbonyl group were employed for the reaction with (diacetoxyiodo)benzene in the presence of BF(3).OEt(2) to provide the alkenyliodonium tetrafluoroborates with inversion of configuration: (E)- and (Z)-boronates give (Z)- and (E)-iodonium salts, respectively. This selectivity can be reversed by the addition of ether to the dichloromethane solution. The stereoselectivity can be explained by participation of the neighboring oxy group.     

Ethyl (benzothiazol-2-ylsulfonyl)acetate: a new reagent for the stereoselective synthesis of alpha,beta-unsaturated esters from aldehydes

The title reagent engaged in the modified Julia olefination with aldehydes under mild reaction conditions (DBU, CH(2)Cl(2), rt or -78 degrees C) to yield alpha,beta-unsaturated esters; aryl aldehydes and aliphatic aldehydes possessing significant chain branching elements gave trans alkene products with high stereoselectivity (E : Z up to >98 : 2), while straight chain aliphatic aldehydes gave cis products preferentially (Z : E up to 92 : 8).