The synthesis of phosphaisocoumarins by Cu(I)-catalyzed intramolecular cyclization of o-ethynylphenylphosphonic acid monoesters

Cu(I)-catalyzed intramolecular cyclization of o-ethynylphenylphosphonic acid monoethyl esters was examined, and a new class of six-membered phosphorus heterocycles was formed with high regioselectivity and good yields. The present reaction is the first example of intramolecular addition of P-OH to alkynes, which provides a convenient way to synthesize novel phosphorus heterocycles having potential bioactivities.     

Domino-Knoevenagel-hetero-Diels-Alder reactions: an efficient one-step synthesis of indole-annulated thiopyranobenzopyran derivatives

Rapid one-step synthesis of hitherto unreported indole-annulated pentacyclic heterocycles containing oxygen, nitrogen, and sulfur has been described by domino-Knoevenagel-hetero-Diels-Alder reaction. The reaction sequence provides a route to the synthesis of a novel type of polyheterocycles in excellent yields with high stereoselectivity.     

Efficient one-pot synthesis of fluorinated benzimidazolines, benzothiazolines, benzoxazolines, and dihydrobenzoxazinones using gallium(III) triflate as a catalyst

One-pot synthesis of fluorinated benzimidazolines, benzothiazolines, benzoxazolines, and dihydrobenzoxazinones was easily achieved under mild conditions in high yields and purity through gallium(III) triflate mediated condensation-cyclization. Introduction of fluorine atoms favors the formation of the five-membered heterocycles over seven-membered heterocycles. [reaction: see text].     

Synthesis of phosphaisoquinolin-1-ones by Pd(II)-catalyzed cyclization of o-(1-alkynyl)phenylphosphonamide monoesters

A Pd(II)-catalyzed intramolecular cyclization of o-(1-alkynyl)phenylphosphonamide monoethyl esters was examined, and a new class of six-membered phosphorus heterocycles (phosphaisoquinolin-1-ones) were formed with high regioselectivity and good yields. The present reaction is the first example of intramolecular addition of P-NH to substituted alkynes, which provides a valuable way to synthesize novel phosphorus heterocycles with potential bioactivities.     

Synthesis of cyclic dienamide using ruthenium-catalyzed ring-closing metathesis of ene-ynamide

[reaction: see text] Ring-closing metathesis of ene-ynamide using the second-generation Grubbs' catalyst produced nitrogen-containing heterocycles, which have dienamide moieties, in high yields. Diels-Alder reaction of the cyclized product and dienophile proceeded smoothly to afford a bi- or tricyclic compound.     

Studies on the reaction of unsymmetrical trifluoromethyl 1,2-phenylenediamine with various ketones leading to novel fluorinated heterocycles

Unsymmetrical 1,2-phenylenediamine on reaction with various ketones resulted in a number of fluorinated heterocycles such as benzimidazoles, quinoxalines and spiro benzimidazoles in high yields. The role of substituents in diamine in its reaction with various ketones and on the nature of product formation has been studied in detail.     

The tert-amino effect in heterocyclic chemistry. Synthesis of spiro heterocycles

The tert-amino reaction effect was examined. A new method to synthesize spiro heterocycles is presented. It was shown that the "tert-amino effect" could be applied to the formation of spiro-fused heterocycles. The formation of spiro compounds proceeds in most cases in good yields in a one-pot reaction.     

Methylenation of N-Acylheterocycles

Various N-alkenyl heterocycles can be obtained in modest to good yields by methylenation of N-acylheterocycles with the Tebbe reagent. The reaction provides a useful method for introducing the isopropyl group on the nitrogen of aromatic heterocycles.     

Synthesis of cyclic dienamide using ruthenium-catalyzed ring-closing metathesis of ene-ynamide

Ring-closing metathesis of ene-ynamide, which has alkene and ynamide moieties in a molecule, using a second-generation ruthenium carbene complex produced nitrogen-containing heterocycles, which have a dienamide moiety, in high yields. Diels-Alder reaction of the cyclized product with dienophile proceeded smoothly to give an indole or quinoline derivative in high yield.     

Domino Michael addition-carbene rearrangement-cyclization reaction of 1-alkynyl(aryl)-lambda3-bromanes with 2-mercapto-1,3-benzazoles

Exposure of 1-alkynyl[p-(trifluoromethyl)phenyl](tetrafluoroborato)-lambda3-bromanes to 2-mercaptobenzimidazole or benzothiazole in dichloromethane at 0 degrees C under argon resulted in a domino Michael addition-carbene rearrangement-cyclization reaction to produce directly tricyclic heterocycles in high yields, whereas the reaction with 2-mercaptobenzoxazole afforded 1-alkynyl sulfides.     

Microwave-assisted efficient synthesis of spiro-fused heterocycles under solvent-free conditions

Spiro-fused heterocycles were synthesized in good to high yields by a pseudo four-component reaction of an aldehyde, urea and a cyclic β-diester or a β-diamide such as Meldrum’s acid or barbituric acid derivatives using microwave irradiation under solvent-free conditions.     

Design and synthesis of a tetracyclic pyrimidine-fused benzodiazepine library

Method development for a heterocyclic library which entails novel scaffolds of benzodiazepines fused with various heterocycles, such as pyrimidines, indolines, and tetrahydroquinolines, was accomplished. The new synthetic strategy is based on an electrophilic cyclization reaction involving an iminium intermediate formed by the corresponding aminopyrimidine with a carbonyl compound to give the desired heterocycles in high yields. Subsequent replacement of the chloro group in the resulted structures with a nucleophile, such as boronic acids, amines, alcohols and thiols, led to a library of privileged compounds with up to eight accessible diversity points.     

Trichloroacetonitrile as a Source of Positive Chlorine Ion for Trapping Huisgen's Zwitterions

The zwitterionic 1 : 1 intermediates generated by addition of N‐heterocycles to activated acetylenes are trapped by trichloroacetonitrile to afford 1,2‐ or 1,4‐disubstituted N‐heterocycles in moderate to good yields under mild reaction conditions.     

Ultrasound Assisted Nucleophilic Cyclization of Tetrafluoroterephthalonitrile: An Efficient Way to Fluorine‐Containing Heterocycles

A simple and efficient synthesis of fluorine‐containing heterocycles via S_NAr reaction of tetrafluoroterephthalonitrile with various nucleophiles assisted by ultrasound has been developed. The reaction proceeded smoothly at room temperature within 5 min to afford mono‐substituted heterocycles in moderate to good yields.     

An efficient Friedel-Crafts alkylation of nitrogen heterocycles catalyzed by antimony trichloride/montmorillonite K-10

It has been found that SbCl₃ supported on montmorillonite K-10 is an efficient and reusable catalyst for Friedel-Crafts alkylation of nitrogen heterocycles such as indoles and pyrroles with epoxides. The reaction gives the corresponding C-alkylated derivatives in good to excellent yields with a high regioselectivity.     

Four-component assembly of chiral N-B heterocycles with a natural product-like framework

The dative N-B bond was used to simply assemble heterocycles with a skeleton akin to the 5-oxofuro[2,3-b]furan motif. Twenty-five new N-B heterocycles were prepared via a highly efficient one-pot four-component reaction in yields and diastereoselectivities up to 95% and >97%, respectively. Several reaction intermediates were discovered using electrospray ionization mass spectroscopy which set the basis for the mechanism elucidation using DFT calculations.     

Catalyst-free regioselective synthesis of benzopyran-annulated thiopyrano[2,3-b]thiochromen-5-(4H)-one derivatives by domino-Knoevenagel-hetero-Diels-Alder reaction of terminal alkynes with 4-hydroxy dithiocoumarin in aqueous medium

The synthesis of novel pentacyclic benzopyran-annulated thiopyrano[2,3-b] thiochromen-5(4H)-ones has been described by domino-Knoevenagel-hetero-Diels-Alder reaction of 4-hydroxy dithiocoumarin and O-propargylated salicylaldehyde in aqueous medium and in the absence of any catalyst. The single step reaction is highly regioselective and provides polycyclic heterocycles in high yields.     

Microwave-enhanced synthesis of cyclic amidines

We present a simple and efficient microwave based protocol for the synthesis of heterocyclic amidines by PPE promoted cyclodehydration of N-aryl-N′-acylalkylenediamines. The method is general for five- to eight-membered heterocycles and affords high yields of the desired products in remarkably short reaction times.     

Intramolecular aryne-ene reaction: synthetic and mechanistic studies

Although the chemistry of arynes is well developed, some challenges still remain. The ene reaction of arynes has not gained widespread use in synthesis as a result of poor yields and selectivity. A general, high yielding and selective intramolecular aryne-ene reaction is described providing various benzofused carbo- and heterocycles. Mechanistic data is presented, and a rationale for the resulting stereochemistry is discussed.     

A copper-free,cross-coupling of terminal alkynes with hetaryl halides

Substituted ethynyl heterocycles and heteroarylbutenynes are synthesized efficiently in good yields via a copper-free, cross-coupling reaction.