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1.
A hot couple: An unprecedented rhodium(III)-catalyzed cross-dehydrogenative coupling (CDC) of various furan and thiophene derivatives leads to valuable 2,2'-bi(heteroaryl) products in good yields and selectivities. In addition, pyrroles and indoles can also be used as coupling partners, giving C3-arylated products.  相似文献   

2.
The first transition‐metal‐free, site‐specific umpolung trifluoromethylthiolation of tertiary alkyl ethers has been developed, achieving the challenging tertiary C(sp3)–SCF3 coupling under redox‐neutral conditions. The synergism of organophotocatalyst 4CzIPN and BINOL‐based phosphorothiols can site‐selectively cleave tertiary sp3 C(sp3)–O ether bonds in complex molecules initiated by a polarity‐matching hydrogen‐atom‐transfer (HAT) event. The incorporation of several competing benzylic and methine C(sp3)?H bonds in alkyl ethers has little influence on the regioselectivity. Selective difluoromethylthiolation of C?O bonds has also been achieved. This represents not only an important step forward in trifluoromethylthiolation but also a promising means for site‐selective C?O bond functionalization of unsymmetrical tertiary alkyl ethers.  相似文献   

3.
Nitrogen-containing fused heterocycles comprise many compounds that demonstrate interesting biological activities. A new synthetic approach involving Mitsunobu alkylation of imidazoles, pyrroles, and indoles followed by palladium-catalyzed cyclization has been developed providing access to fused heterocycles with a defined stereochemistry α to nitrogen. While ethyl imidazole or indole carboxylates are good substrates for Mitsunobu alkylation with optically pure secondary benzylic alcohols, the corresponding pyrroles are poor substrates presumably due to the increased pK(a) of the NH. The presence of a synthetically versatile trichloroacetyl functional group on the pyrroles significantly reduces the pK(a) and thereby facilitates Mitsunobu alkylation. Subsequent cyclization of the alkylated products mediated by palladium in the presence or absence of a ligand gave fused heterocycles in good to excellent yields.  相似文献   

4.
《Tetrahedron》2014,70(21):3447-3451
Copper(II) catalyzed cross-dehydrogenative coupling of cyclic benzylic ethers with a variety of simple carbonyl compounds mediated by Na2S2O8 is developed. The scope of carbonyl components is broad, including simple aldehydes as well as ketones. The use of Na2S2O8 as the oxidant for the CDC reaction is attractive based on economical and environmental factors.  相似文献   

5.
A practical and efficient oxidative CH cyanation of secondary benzylic ethers with TMSCN in the presence of DDQ is described for the first time. The metal-free process is well tolerated with a wide variety of electronically varied α-monosubstituted isochromans for the synthesis of isochromans bearing α-aryl α-cyano substituent patterns.  相似文献   

6.
Silicon–nitrogen bond formation is an important subfield in main group chemistry, and catalysis is an attractive route for efficient, selective formation of these bonds. Indeed, heterodehydrocoupling and N-silylation offer facile methods for the synthesis of small molecules through the coupling of primary, secondary, and tertiary silanes with N-containing substrates such as amines, carbazoles, indoles, and pyrroles. However, the reactivity of these catalytic systems is far from uniform, and critical issues are often encountered with product selectivity, conversions, substrate scope, catalyst activation, and in some instances, competing side reactions. Herein, a catalogue of catalysts and their reactivity for Si−N heterodehydrocoupling and N-silylation are reported.  相似文献   

7.
The primary alcohols 1a-e and ethers 4a-d were effectively reduced to the corresponding hydrocarbons 2 by HSiEt(3) in the presence of catalytic amounts of B(C(6)F(5))(3). To the best of our knowledge, this is the first example of catalytic use of Lewis acid in the reduction of alcohols and ethers with hydrosilanes. The secondary alkyl ethers 4j,k enabled cleavage and/or reduction under similar reaction conditions to produce either the silyl ethers 3m-n or the corresponding alcohol 5a upon subsequent deprotection with TBAF. It was found that the secondary alcohols 1g-i and tertiary alcohol 1j, as well as the tertiary alkyl ether 4l, did not react with HSiEt(3)/(B(C(6)F(5))(3) reducing reagent at all. The following relative reactivity order of substrates was found: primary > secondary > tertiary. A plausible mechanism for this nontraditional Lewis acid catalyzed reaction is proposed.  相似文献   

8.
A very efficient procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols is reported. The reactions were carried out under neat conditions with trimethylsilyl azide (TMSN(3)) and, when necessary, in the presence of a catalytic amount (20 mol %) of tetrabutylammonium bromide (TBABr) at 30 or 70 degrees C. Under catalytic conditions, the yields of the corresponding trimethylsilyl ethers were greater than 91%. This procedure also allows the selective protection of primary and secondary alcohols in the presence of tertiary ones.  相似文献   

9.
Zhao M  Wang F  Li X 《Organic letters》2012,14(6):1412-1415
Tetrasubstituted pyrroles have been synthesized via the cross-dehydrogenative coupling between enamino esters and acetone. Silver carbonate proved to be an effective oxidant, and no transition metal catalyst is necessary.  相似文献   

10.
Direct cross-dehydrogenative coupling of different inert C−H bonds is the most straightforward and environmentally benign method to construct C−C bonds. In this paper, we developed an iron-catalyzed intramolecular cross-dehydrogenative arylation (CDA) between benzylic C(sp3)H bond and aromatic C(sp2)H bond. From the readily available linear substrates, 1-arylnaphthalenes and 4-arylcoumarins can be quickly constructed with moderate to good yield (18 examples, up to 73 % yield) in one step. Both symmetrical and unsymmetrical substrates with different functional groups could tolerate this system well to form the anticipated products. A radical initiated dehydrogenative cyclization-dehydrogenation tandem process was proposed.  相似文献   

11.
A highly efficient yttrium triflate-catalyzed chemoselective S-benzylation of indolin-2-thiones using variously substituted benzyl alcohols has been developed for the synthesis of indole-based sulfides. This procedure presents a greener approach for the synthesis of S-alkylated indoles. The reaction condition is amenable to primary, secondary, and tertiary benzylic alcohols as the benzyl group donors.  相似文献   

12.
Methyl and benzyl ethers are widely utilized as protected alcohols due to their chemical stability, such as the low reactivity of the methoxy and benzyloxy groups as leaving groups under nucleophilic conditions. We have established the direct azidation of chemically stable methyl and benzyl ethers derived from secondary and tertiary benzyl alcohols. The present azidation chemoselectively proceeds at the secondary or tertiary benzylic positions of methyl benzyl ethers or unsymmetrical dibenzyl ethers and is also applicable to direct allylation, alkynylation, and cyanation reactions, as well as the azidation. The present methodologies provide not only a novel chemoselectivity but also the advantage of shortened synthetic steps, due to the direct process without the deprotection of the methyl and benzyl ethers.  相似文献   

13.
An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl(4), is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols.  相似文献   

14.
Solvent-free reaction using a high-speed ball milling technique has been first applied to cross-dehydrogenative coupling (CDC) reactions between tetrahydroisoquinolines and three types of pronucleophiles such as nitroalkanes, alkynes, and indoles. All coupling products were obtained in good yields at short reaction times (no more than 40 min). When alkynes and indoles were used as pronucleophile, the reactions can be catalyzed efficiently by recoverable copper balls without any additional metal catalyst.  相似文献   

15.
Aliphatic and aromatic epoxides react regio- and stereoselectively with indoles and pyrroles in 2,2,2-trifluoroethanol without the use of a catalyst or any other additive. While aromatic epoxides are selectively attacked at the benzylic position, aliphatic epoxides react at the less-substituted position. Chiral epoxides react with >99 % ee (ee=enantiomeric excess).  相似文献   

16.
Chiral complexes of 1,1'-bi-2-naphthol-based ligands with zirconium tert-butoxide catalyze the Friedel-Crafts alkylation of pyrroles with α-ketoesters to afford tertiary alcohols in good yields and ee up to 98%. The reaction is also of application to 4,7-dihydroindole to give C2-alkylated indoles after oxidation with p-benzoquinone.  相似文献   

17.
Treatment of alkyl halides, including tertiary alkyl bromides, with benzylic or allylic Grignard reagent in the presence of a catalytic amount of silver nitrate in ether yielded the corresponding cross-coupling products in high yields. The coupling reactions of tertiary alkyl halides provide efficient access to quaternary carbon centers.  相似文献   

18.
Zinc triflate was found to be an effective reagent for the C3-alkylation of indoles by alkyl halides in the presence of Hünig's base and tetrabutylammonium iodide. This new method for indole alkylation proceeds by a S(N)1-like pathway, and is general for allylic, benzylic, and tertiary halides.  相似文献   

19.
The direct C(sp2) C(sp3) cross‐coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp2) C(sp3) cross‐coupling showed excellent functional‐group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp2) C(sp3) bonds.  相似文献   

20.
The direct C(sp2)? C(sp3) cross‐coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp2)? C(sp3) cross‐coupling showed excellent functional‐group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp2)? C(sp3) bonds.  相似文献   

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