共查询到20条相似文献,搜索用时 0 毫秒
1.
A novel rhodium-catalyzed cycloisomerization has been developed which converts various acyclic enynes to their cyclic diene isomers with endoselectivity. Both [RhCl(COD)]2/P(4-FC6H4)3 and RhCl(PPh3)3 catalyst systems are effective in promoting the C-C bond-forming cyclization of enynes to furnish carbo- and heterocycles in good to excellent yield. Deuterium labeling studies suggest that the reaction proceeds through the formation of a rhodium vinylidene followed by subsequent [2 + 2] cycloaddition with the alkene and ring-opening of the resulting rhodacyclobutane. These mechanistic studies reevaluate a previously proposed reaction pathway and lead to the discovery of a new cycloisomerization reaction that involves migration of silyl and selenyl substituents at the alkyne of enyne substrates upon cyclization. 相似文献
2.
The synthesis of pyridines from readily available α,β-unsaturated oximes and alkynes under mild conditions and low temperatures using Rh(III) catalysis has been developed. It was found that the use of sterically different ligands allows for complementary selectivities to be achieved. 相似文献
3.
Minami Y Shiraishi Y Yamada K Hiyama T 《Journal of the American Chemical Society》2012,134(14):6124-6127
Alkynyl aryl ethers react with internal alkynes through selective ortho C-H activation by a palladium(0) catalyst to give substituted 2-methylidene-2H-chromenes. The alkynoxy group acts as a directing group to promote ortho C-H functionalization. Deuterium-labeling experiments indicated that the arylpalladium hydride complex is a key intermediate via oxidative addition. Various functional groups tolerate the present transformation to give the corresponding products. 相似文献
4.
Catalytic hydrogenation of acetylenic aldehydes 1a-12a using chirally modified cationic rhodium catalysts enables highly enantioselective reductive cyclization to afford cyclic allylic alcohols 1b-12b. Using an achiral hydrogenation catalyst, the chiral racemic acetylenic aldehydes 13a-15a engage in highly syn-diastereoselective reductive cyclizations to afford cyclic allylic alcohols 13b-15b. Ozonolysis of cyclization products 7b and 9b allows access to optically enriched alpha-hydroxy ketones 7c and 9c. Reductive cyclization of enyne 7a under a deuterium atmosphere provides the monodeuterated product deuterio-7b, consistent with a catalytic mechanism involving alkyne-carbonyl oxidative coupling followed by hydrogenolytic cleavage of the resulting oxametallacycle. These hydrogen-mediated transformations represent the first examples of the enantioselective reductive cyclization of acetylenic aldehydes. 相似文献
5.
Tomohiro Shono 《Tetrahedron letters》2006,47(8):1257-1260
Titanocene alkenylidene complexes, generated by the reductive metallation of 1,1-dichloro-1-alkenes with the titanocene(II) species Cp2Ti[P(OEt)3]2, reacted with alkynes to produce conjugated dienes. 相似文献
6.
The total synthesis of the erythrina alkaloid 3-demethoxyerythratidinone has been achieved via a strategy based on combined rhodium catalysis. The catalytic tandem cyclization effected by the interplay of alkynyl and vinylidene rhodium species allows for efficient access to the A and B rings of the tetracyclic erythrinane skeleton in a single step. The synthesis also features rapid preparation of the requisite precursor for the double ring closure and thus has been completed in only 7 total steps in 41% overall yield. 相似文献
7.
Parthasarathy K Han H Prakash C Cheng CH 《Chemical communications (Cambridge, England)》2012,48(52):6580-6582
A new method for the synthesis of various isochromen-6-ones and phenanthro[1,10-bc]oxepines via a palladium-catalyzed cascade carbocyclization of 2-iodobenzyl-3-phenylpropiolates and 1-iodo-2-(2-(phenylethynyl)benzyloxy)benzenes with arynes is described. The reactions involve interesting biscarbocyclization of alkynes and benzynes and C-H bond activation. 相似文献
8.
High yield, rapid formations of alkynes from vicdibromides are possible using powered potassium hydroxide and catalytic amounts of lipophilic phase transfer catalysts. Reasons are given why molar amounts of expensive catalysts were necessary in earlier procedures. 相似文献
9.
[chemical reaction: see text]. A direct and general synthesis of alpha-branched aldehydes and their enol derivatives is described. Carbocupration of terminal alkynes and subsequent oxygenation with lithium tert-butyl peroxide generates a metallo-enolate. Trapping with various electrophiles provides alpha-branched aldehydes or stereo-defined trisubstituted enol esters or silyl ethers. The tandem carbocupration/oxygenation tolerates alkyl and silyl ethers, esters, and tertiary amines. The reaction is effective with organocopper complexes derived from primary, secondary, and tertiary Grignard reagents and from n-butyllithium. 相似文献
10.
Yanagisawa S Sudo T Noyori R Itami K 《Journal of the American Chemical Society》2006,128(36):11748-11749
A new method for the catalytic C-H arylation of heteroarenes and arenes that manifests high activity paired with reasonably broad scope was developed. Under the catalytic influence of RhCl(CO){P[OCH(CF3)2]3}2 and Ag2CO3, the direct C-H arylation of heteroarenes/arenes with aryl/heteroaryl iodides took place to afford a range of biaryls in good to excellent yields with high regioselectivity. Thiophenes, furans, pyrroles, indoles, and alkoxybenzenes are applicable in this arylation protocol. 相似文献
11.
Nickel complexes having a bulky tri(sec-alkyl)phosphine ligand catalyze hydroheteroarylation of alkynes at 35 degrees C. Selective activation of an Ar-H bond over an Ar-CN bond of N-protected 3-cyanoindoles is achieved by a proper choice of ligand and/or an N-protecting group. The catalysis is applicable to a diverse range of heteroarenes to afford cis-hydroheteroarylation products in highly chemo- and stereoselective manners. Excellent regioselectivity is observed with unsymmetrical alkynes to give the corresponding heteroaryl-substituted ethenes having a larger substituent trans to an aryl group. 相似文献
12.
13.
14.
Gronnier C Kramer S Odabachian Y Gagosz F 《Journal of the American Chemical Society》2012,134(2):828-831
In the presence of a Cu(I) catalyst and a pyridine oxide, alkynyl oxiranes and oxetanes can be converted into functionalized five- or six-membered α,β-unsaturated lactones or dihydrofuranaldehydes. This new oxidative cyclization is proposed to proceed via an unusual allenyloxypyridinium intermediate. 相似文献
15.
A one‐pot synthesis of alkynyl sulfide from terminal alkyne has been reported via lithiation of the alkyne, oxidative addition of sulfur, consecutively followed by the nucleophilic substitution of lithium alkynyl thiolate to various halides. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:105–110, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20745 相似文献
16.
Diphenyl diselenide reacts with terminal alkynes at room temperature in DMSO in the presence of catalytic amounts of copper iodide to give good to excellent yields of alkynyl phenyl selenides. The reaction occurs under neutral conditions and the solvent acts as the oxidant. Diphenyl disulfide and ditelluride undergo the analogous reaction, but require the presence of a weak inorganic base. 相似文献
17.
Masafumi UedaYuki Ikeda Aoi SatoYuta Ito Maiko KakiuchiHiroko Shono Tetsuya MiyoshiTakeaki Naito Okiko Miyata 《Tetrahedron》2011,67(25):4612-4615
A facile and practical synthesis of 3,5-disubstituted isoxazoles via a silver-catalyzed cyclization and subsequent protonation of alkynyl oxime ethers has been developed. The methodology was successfully applied to the synthesis of a biologically active isoxazolecarboxylic acid. 相似文献
18.
The first one-step conversions of ketimines I into cyclized allylamine derivatives of types II and III are reported. 相似文献
19.
A tandem cross metathesis (CM)--ring-closing metathesis (RCM) sequence to form cyclic siloxanes is reported. This new enyne metathesis platform expands the scope and utility of the regio- and stereoselective cross metathesis reaction between silylated alkynes and terminal alkenes. The initial cross metathesis was directed to occur on the alkyne by employing sterically hindered mono-, di-, and trisubstituted alkenes tethered to the alkyne via silyl ether. The regio- and stereoselectivity feature of the initial CM step in this tandem CM-RCM process is identical to that of the CM reactions of silylated alkynes and alkenes. This tandem sequence provides both synthetically useful silylated 1,3-diene building blocks and insights into the reaction mechanism of the enyne metathesis reaction. 相似文献
20.
Alkynyl selenides were prepared under very mild conditions by reacting terminal alkynes with respective diorganic diselenides in the presence of potassium t-butoxide.The advantages of this protocol include the use of readily available substrates and reagent and good yield of the products. 相似文献