A facile stereoselective synthesis of (E)-1,2-disubstituted vinylstannanes via hydromagnesiation of alkylarylacetylenes

Hydromagnesiation of alkylarylacetylenes 1 in diethyl ether gave (E)-α-arylvinyl Grignard reagents 2, which reacted with trialkylstannyl chlorides 3 in diethyl ether to afford stereoselectively (E)-1,2-disubstituted vinylstannanes 4 in high yields.     

The stereoselective synthesis of (E)-octafluoro-1,3,5-hexatriene and (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene

(E)-(1,2-Difluoro-1,2-ethenediyl)bis[tributylstannane], 3, readily undergoes a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction with iodotrifluoroethene to yield (E)-octafluoro-1,3,5-hexatriene, 4, in high isomeric purity. (1Z,3E,5Z)-(1,2,3,4,5,6-Hexafluoro-1,3,5-hexenetriyl)bis[tributylstannane], 7, was sequentially prepared from (1Z,3E,5Z)-(1,2,3,4,5,6-hexafluoro-1,3,5-hexenetriyl)bis[triethylsilane], 5, which was prepared via a Pd(PPh₃)₄/CuI-catalyzed cross-coupling reaction of 3 with (E)-1,2-difluoro-1-iodo-2-triethylsilylethene, 6. Pd(PPh₃)₄/CuI cross-coupling of 7 with iodotrifluoroethene gave (3E,5E,7E)-dodecafluoro-1,3,5,7,9-decapentaene, 8.     

Stereoselective synthesis of (E)-α-aryltellurenylvinylsilanes via hydromagnesiation reaction of alkynylsilanes

(E)-α-Aryltellurenylvinylsilanes have been synthesized stereoselectively via the hydromagnesiation of alkynylsilanes, followed by the reaction with aryltellurenyl iodides. (E)-α-Aryltellurenylvinylsilanes can undergo the cross coupling reaction with Grignard reagents in the presence of Ni(PPh₃)₂Cl₂ catalyst to afford (Z)-1,2-disubstituted vinylsilanes in good yields.     

Novel stereoselective synthesis of 1-substituted 1,3-dien-2-yl sulfides via Stille coupling reactions of (E)-α-stannylvinyl sulfides with alkenyl iodides

(E)-α-stannylvinyl sulfides are new difunctional reagents which undergo Stille coupling reactions with alkenyl iodides to afford stereoselectively 1-substituted 1,3-dien-2-yl sulfides in good yields.     

Palladium-catalyzed stereoselective synthesis of (E)-β,γ-unsaturated amides

A facile Suzuki type cross-coupling reaction of alkenylborane with 2-bromo-N,N-dimethylacetamide in the presence of a catalytic amount of tricyclohexylphosphine as the ligand has been demonstrated to be a convenient way for the synthesis of (E)-β,γ-unsaturated amides.     

A highly efficient stereoselective synthesis of (Z)- and (E)-allyl iodides from Baylis-Hillman adducts

A highly efficient synthesis of (Z)- and (E)-allyl iodides has been accomplished by treatment of Baylis-Hillman adducts with iodine and triphenylphosphine in methylene chloride at room temperature. The method is associated with mild reaction conditions, high yields and excellent stereoselectivity.     

Stereoselective synthesis of (E)-β-arylvinyl bromides by microwave-induced reaction of anti-3-aryl-2,3-dibromopropanoic acids using an AgOAc-AcOH system

(E)-β-Arylvinyl bromides were stereoselectively prepared in high yields by microwave irradiation of the corresponding anti-3-aryl-2,3-dibromopropanoic acids in AcOH in the presence of AgOAc for 0.5-3.0 min.     

Palladium catalysed regio- and stereoselective synthesis of (E)-4-aryl-1,3-bis(trimethylsilyl)but-3-en-1-ynes

A practical and general synthetic approach to a series of 4-aryl-but-3-en-1-ynes is described. In the presence of palladium complexes a variety of aryl bromides (or iodides) undergo coupling with two equivalents of trimethylsilylacetylene with the formation of (E)-4-aryl-1,3-bis(trimethylsilyl)but-3-en-1-ynes. The protocol is simple, efficient, and affords synthesis of regio- and stereoselectively target products in good to high yields.     

A facile stereoselective synthesis of difunctionalized 1,3-dienes containing tin and halogen via hydrozirconation of (Z)-3-(tributylstannyl)alk-3-en-1-ynes

Sonogashira coupling of (E)-α-iodovinylstannanes 1 with (trimethylsilyl)acetylene gave (Z)-1-(trimethylsilyl)-3-(tributylstannyl)alk-3-en-1-ynes 2, which underwent a desilylation reaction to afford (Z)-3-(tributylstannyl)alk-3-en-1-ynes 3 in high yields. (1E,3Z)-1-Halo-3-(tributylstannyl)-substituted 1,3-dienes 5 could be synthesized stereoselectively via hydrozirconation of (Z)-3-(tributylstannyl)alk-3-en-1-ynes 3, followed by trapping with iodine or NBS.     

Preparation of enantiomerically pure (E)-β-sulfinylenones from β-ketoesters

Enantiomerically pure (E)-β-sulfinylenones are smoothly prepared from β-ketoesters in three steps with good overall yield. Since they can be the substrates of many diastereoselective reactions, they represent versatile precursors of a wide range of chiral building blocks. We propose a rationale to explain the formation of (E)-β-sulfinylenones from the corresponding δ-enol-methylethers.     

Preparation, crystal structure, and spectroscopic, chemical, and electrochemical properties of (2E,4E)-4-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1,3-butadiene compared with those of (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene

Wittig reaction of 3-[4-(dimethylamino)phenyl]propanal (5) with (3-guaiazulenylmethyl)triphenylphosphonium bromide (4) in ethanol containing NaOEt at 25 °C for 24 h under argon gives the title (2E,4E)-1,3-butadiene derivative 6E in 19% isolated yield. Spectroscopic properties, crystal structure, and electrochemical behavior of the obtained new extended π-electron system 6E, compared with those of the previously reported (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene (12), are documented. Furthermore, reaction of 6E with 1,1,2,2-tetracyanoethylene (TCNE) in benzene at 25 °C for 24 h under argon affords a new Diels-Alder adduct 8 in 59% isolated yield. Along with spectroscopic properties of the [π4+π2] cycloaddition product 8, the crystal structure, possessing a cis-3,6-substituted 1,1,2,2-tetracyano-4-cyclohexene unit, is shown. Moreover, reaction of 6E with (E)-1,2-dicyanoethylene (DCNE) under the same reaction conditions as the above gives no product; however, this reaction in p-xylene at reflux temperature (138 °C) for four days under argon affords a new Diels-Alder adduct 9 in 54% isolated yield. Although reaction of 6E with DCNE in toluene at reflux temperature (110 °C) for four days under argon provides 9 very slightly, reaction of 6E with dimethyl acetylenedicarboxylate (DMAD) in toluene at reflux temperature for two days under argon yields a new Diels-Alder adduct 10, in 58% isolated yield, which upon oxidation with MnO₂ in CH₂Cl₂ at 25 °C for 1 h gives 11, converting a (CH₃)₂N-4″ into CH₃NH-4″ group, in 37% isolated yield. The crystal structure of 11 supports the molecular structure 10 possessing a partial structure cis-3,6-substituted 1,2-dimethoxycarbonyl-1,4-cyclohexadiene. The title basic studies on the above are reported in detail.     

Transformations of (1E,3E)-1-(benzoylamino)-4-(dimethylamino)buta-1,3-diene-1,2,3-tricarboxylates into pyridine and pyrrole derivatives

New, highly functionalised (1E,3E)-1-(benzoylamino)-4-(dimethylamino)buta-1,3-diene-1,2,3-tricarboxylates proved to be useful and versatile reagents in the formation of highly substituted pyridine, N-aminopyridine, pyrrole and pyrido[3,4-c]pyridazine derivatives. The formation of the particular type heterocyclic system is dependent on the starting (1E,3E)-1-(benzoylamino)-4-(dimethylamino)buta-1,3-diene-1,2,3-tricarboxylate. By an appropriate choice of different ester groups it is possible to drive the reactions towards the formation of either pyridine or pyrrole derivatives.     

Synthesis of (Z)-tributylstannyl enynes: systematic studies of Sonogashira cross-coupling reactions between (E)-1-iodovinyl-1-tributylstannanes and terminal acetylenes using amines or tetrabutylammonium hydroxide (TBAOH) as activator

Sonogashira cross-coupling reactions involving (E)-iodo vinyl stannanes and terminal acetylenes were carried out in the presence of Pd(PPh₃)₄, CuI and several amines, affording (Z)-tributylstannyl enynes in moderate to good yields (62-91%). Utilizing the catalytic system containing Pd(PPh₃)₄ (5%), CuI (10%), and TBAOH (40% in aqueous media) as activator, better yields (72-91%) and lower reaction times were achieved.     

First stereoselective total synthesis of (6R)-6-[(4R,6R)-4,6-dihydroxy-10-phenyldec-1-enyl]-5,6-dihydro-2H-pyran-2-one

A stereoselective total synthesis of (6R)-6-[(4R,6R)-4,6-dihydroxy-10-phenyldec-1-enyl]-5,6-dihydro-2H-pyran-2-one is reported. The strategy utilizes an iterative Jacobsen hydrolytic kinetic resolution, ring opening with a chiral propargylic synthon and a preferential (Z)-Wittig olefination reaction and lactonization as the key steps.     

Synthesis of 3-(trifluoromethyl)indeno[2,1-c]pyran-1,9-diones from 4-aryl-3-carbethoxy-6-(trifluoromethyl)-2-pyrones and their reaction with sodium azide leading to new carbostyril derivatives

Treatment of ethyl 4-aryl-6-(trifluoromethyl)-2-oxo-2H-pyran-3-carboxylates, prepared from 4,4,4-trifluorobutane-1,3-diones, PCl₅ and sodium diethyl malonate, with sulfuric acid afforded the intramolecular Friedel–Crafts acylation products, 3-(trifluoromethyl)indeno[2,1-c]pyran-1,9-diones, from which 2-(trifluoromethyl)-6H-pyrano[3,4-c]quinoline-4,5-diones were obtained via the Schmidt reaction in moderate yields. The latter reacted with sodium azide to give 2-oxo-4-(5-trifluoromethyl-1,2,3-triazol-4-yl)-1,2-dihydroquinoline-3-carboxylic acids in good yields.     

Highly stereoselective synthesis of para-substituted (E)-N-styrylcarbazoles via sequential silylative coupling-Hiyama coupling reaction

A series of new para-substituted (E)-(N)-styrylcarbazoles, i.e., eight (E)-9-[2-(aryl)ethenyl]-9H-carbazoles (5-12) and 1,4-bis[(E)-2-(9H-carbazol-9-yl)vinyl]benzene (13), have been synthesized in high yield and stereoselectively by a sequential silylative coupling-Hiyama coupling reaction, i.e., coupling of commercially available 9-vinylcarbazole with vinyltriethoxysilane or divinyltetramethyldisiloxane in the presence of [RuHCl(CO)(PCy₃)₂] (I), followed by Pd (II) catalyzed cross-coupling with para-substituted iodobenzenes.The tandem procedure has facilitated the synthesis of 13. X-ray structures of the intermediate silylvinylcarbazole (4), as well as products 12 and 13 have been obtained.     

Stereoselective synthesis of hex-2-(E)-en-4-yn-1,6-dioates and E,Z-muconic acid diesters via organo-catalyzed self-coupling of propiolates

Alkyl propiolate couples with itself in the presence of catalytic DABCO under very mild conditions to provide a quantitative yield of E-hex-2-en-4-yne dioates. Hydrogenation of these enyne dioates using Lindlar catalyst provides the corresponding E,Z-diene dioate, a common structural motif found in an array of natural products.     

A novel synthesis of new 2-aryl-6-(arylamino)-1H-imidazo[1,2-b]pyrazole-7-carbonitrile derivatives

New 2-aryl-6-(arylamino)-1H-imidazo[1,2-b]pyrazole-7-carbonitriles are synthesized in good yields, via cyclocondensation of 5-amino-1-(2-oxo-2-arylethyl)-3-(arylamino)-1H-pyrazole-4-carbonitriles, which are prepared by the reaction of 5-amino-3-arylamino-1H-pyrazole-4-carbonitriles and α-bromoacetophenone derivatives in the presence of K₂CO₃ using acetone as the solvent.     

Stereoselective synthesis of (E)- and (Z)-3-hydroxy-2-methyl-1-alkenyl iodides by base-promoted ring-opening of iodomethylated epoxides

Both (E)- and (Z)-3-hydroxy-2-methyl-1-alkenyl iodides were stereoselectively synthesized from iodomethylated epoxides by treatment with sodium hexamethyldisilazane in DMF and with LDA in THF (or lithium 2,2,6,6-tetramethylpiperidide in THF), respectively.     

Facile stereoselective synthesis of (E)- and (Z)-α-substituted cinnamates: stereospecific dehydration reaction with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and copper(II) chloride

A highly stereoselective method for the synthesis of (E)- and (Z)-α-substituted cinnamates in good yield has been achieved by dehydration reaction of anti- and syn-α-substituted-β-hydroxyphenylpropiolate using EDC. This facile method has been used to synthesize various (E)- and (Z)-α-substituted cinnamates and (E)- and (Z)-α-alkylidene-γ-butyrolactones. The reaction mechanism of this highly stereospecific dehydration using EDC can be elucidated by the ω-dimethylamino group of EDC, which is believed to facilitate the deprotonation step.