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The present personalized account summarizes various cyclization reactions, including multicomponent and domino processes, which are directed towards the synthesis of complex heterocyclic products. Domino Knoevenagel/hetero‐Diels‐Alder reactions provide a synthesis of annulated quinol‐2‐ones. The combination of Knoevenagel reactions with [3+2] cycloadditions of nitrogen ylides afford complex spiroheteriocyclic products. Domino Knoevenagel/enamine cyclization reactions result in the formation of condensed purine analogues. Formal [3+3] cyclizations of pyridinium salts allow for a rapid assembly of bridged heterocyclic systems and include the employment of thioxindoles and cyclohexane‐1,3‐diones as dinucleophilic building blocks. The formal [3+3] cyclization of thioxindoles with fluoroaroyl chlorides, such as 2‐fluorobenzoyl chlorides and 2‐chloropyridine‐3‐carboxylic chloride, give rise to the synthesis of condensed benzothiophenes. The cyclization of heterocyclic enamines with diimines and triazines afford various purine analogues by domino [4+2]/retro [4+2] reactions. The formal [3+3] cyclization of 2,4,6‐tris(trifluoromethyl)‐1,3,5‐triazine with 1,3‐bis(silyloxy)‐1,3‐butadienes afford, depending on the conditions, 2,6‐bis(trifluoromethy)pyrid‐4‐ones or triazaadamantanone derivatives. Heating of 2‐ethynylpyridines with electron‐rich dienes afforded 2‐(2‐methoxyphenyl)pyridines by a domino [4+2]/retro [4+2] process. The reaction of 2‐ethynylpyridines with enones afforded indolizines by a formal [3+3] cyclization. The reaction of trifluoromethyl‐substituted 1,3‐diketones with lithiated alkynes afforded 3‐hydroxy‐pent‐4‐yn‐1‐ones. Formal [5+1] cyclization of the latter with urea afforded trifluoromethyl‐substituted pyridines. The Pd catalyzed formal [3+2] cyclizations of 2,3‐dihalopyridines with imines afforded a series of regioisomeric 4‐ and 7‐azaindoles. [ABSTRACT FROM AUTHOR]

Cyclizations, epoxides, regioselectivity, silyl enol ethers, epihalohydrins, dianions They possess three electrophilic centers and can undergo nucleophilic substitution reactions at the halide or ring-opening reactions at the epoxide moiety. In 2000, on the basis of the known cyclization of 1,3-dicarbonyl dianions with epoxides, [18] my student Tobias -Eckardt developed a related cyclization of epoxides with 1,3-bis(silyloxy)-1,3-butadienes. Keywords: cyclizations; dianions; epoxides; regioselectivity; silyl enol ethers; epihalohydrins EN cyclizations dianions epoxides regioselectivity silyl enol ethers epihalohydrins 1953 1960 8 10/09/23 20231024 NES 231024 Graph 1 Introduction Epichlorohydrin is a bulk chemical (800,000 t/a) that is used technically for the synthesis of epoxy resins and other polymers. [Extracted from the article]

Cyclopropanes, cyclizations, dianions, regioselectivity, silyl enol ethers We studied cyclizations of free dianions with dielectrophiles, [6] cyclizations of dianions and other dinucleophiles with oxalic acid-bis(imidoyl)dichlorides, [7] cyclizations of oxime and hydrazine dianions, [8] and cyclizations of 1,3-dicarbonyl dianions with 1,2-dielectrophiles to give 2-(alkylidene)tetrahydrofurans. Keywords: cyclopropanes; cyclizations; dianions; regioselectivity; silyl enol ethers EN cyclopropanes cyclizations dianions regioselectivity silyl enol ethers 1765 1776 12 08/29/23 20230915 NES 230915 Graph 1 Introduction From 1998-2001, I carried out my habilitation, the first period of independent research in Germany, at the University of Göttingen under the mentorship of Prof. Armin de Meijere. Based on work of T. H. Chan and co-workers, we studied cyclizations of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with silyl enol ethers to give salicylates, such as B C b . [Extracted from the article]

The present personalized account highlights reactions of the dianion of 1,1-diphenylacetone and its applications. From a study directed towards the regioselectivity of such reactions a new allene synthesis via allene dianions was found by serendipity. In addition, reactions of allene dianions with various electrophiles have been studied. 1 Introduction 2 Cyclizations of the Dianion of 1,1-Diphenylacetone 2.1 Reaction with Bis(cyclopentadienyl)zirconium Dichloride 2.1 Reactions with Dichlorosilanes 2.1 Reactions with Difluorosilanes 2.1 Reactions with Ketones and Dielectrophiles 3 Regioselectivity of Dianion Reactions 4 Allene Dianions from Silyl Enol Ethers 5 Scope of the Reactions of Allene Dianions 6 Reactions of Allene Dianions with Ketones 7 Reactions of Allene Dianions with Nitriles 8 Conclusions [ABSTRACT FROM AUTHOR]

Spirocyclic diindenothiophenes were prepared by cyclization of tosylhydrazones, readily available from ketones, with 3,4-dibromo-2,5-bis(2-bromphenyl)thiophene. For bicyclic ketones, the bis-spirocycles were formed with very good diastereoselectivity. [ABSTRACT FROM AUTHOR]

The synthesis of 1,3-selenazoles and related compounds, including 2,4,5-trisubstituted, 2,4-disubstituted, 4,5-disubstituted, 4-substituted 1,3-selenazoles, and parent unsubstituted 1,3-selenazole, is highlighted. Emphasis is also given on 2-benzoyl-1,3-selenazoles which can be functionalized by Knoevenagel reactions or by rearrangements via their corresponding oximes. Syntheses of bis-, tris-, and tetrakis(1,3-selenazoles) are discussed as well. 1,3,4-6 H -Selenadiazines are available from selenosemicarbazides and can undergo ring-contraction or deselenation reactions. Most syntheses rely on the application of selenocarboxylic amides, selenourea and related building blocks which are conveniently available by reaction of the corresponding oxygen analogues with P4 Se10. 1 Introduction 2 Selenocarboxylic Amides 3 2,4,5-Tri- and 2,4-Disubstituted 1,3-Selenazoles 4 Bis(1,3-selenazoles) 5 2-Amino-1,3-selenazoles 6 2-Unsubstituted 1,3-Selenazoles 7 1,3,4-Selenadiazines 8 Conclusions [ABSTRACT FROM AUTHOR]

A variety of thieno[3,2‐f]isoquinolines were prepared by combination of Pd catalysed cross‐coupling reactions with Brønsted acid mediated cycloisomerisations. The reactions tolerate various functional groups and proceed with high selectivity. In addition, benzothieno[3,2‐f]isoquinolines were prepared which represent a new heterocyclic core structure. The optical properties of selected compounds were studied by experimental and theoretical methods. Emission solvatochromism, characteristic of intramolecular charge transfer was observed for one of the compounds with a push‐pull structure. [ABSTRACT FROM AUTHOR]

Two efficient and practical approaches are reported for the synthesis of β- and δ-carbolines from 3,4-dibromopyridine. The synthesis is based on site-selective Cu-catalyzed double C–N coupling reactions and subsequent annulations by twofold Pd-catalyzed C–N coupling with amines. [ABSTRACT FROM AUTHOR]

An efficient Lewis acid mediated domino Knoevenagel/hetero Diels–Alder (DKHDA) reaction of pyrazolone derivatives with N -acrylated anthranilic aldehydes was developed, which afforded functionalized tetracyclic tetrahydropyrazolo[4',3':5,6]pyrano[3,4- c ]quinolones. The products were formed in good yields and with excellent regio- and stereoselectivity in favor of the cis-configured isomer. [ABSTRACT FROM AUTHOR]

Hitherto unknown thiadiazolo[2′,3′:2,3]imidazo[4,5- b ]indoles were synthesized for the first time by base-mediated cyclocondensation, bromination, and subsequent cyclization by two-fold Buchwald–Hartwig reactions. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed one-pot reaction for the synthesis of benzo[b]carbazolediones is described which proceeds by amination of 2,3-dibromonaphthoquinone, Suzuki cross-coupling with (2-bromophenyl) boronic acid, and subsequent intramolecular C-N Buchwald- Hartwig cyclization with amines. [ABSTRACT FROM AUTHOR]

The formal [3+3]cyclization of 3-arylthio-1-silyloxy-1,3-butadienes with 2-aryldiazenyl-3-silyloxy-2-en-1-ones afforded a variety of 2-arylthio-5-aryldiazenylbenzoates. [ABSTRACT FROM PUBLISHER]

Dibenzothiophenes and carbazoles were prepared by tetrafold Heck reactions of tetrabromothiophene and N-methyltetrabromopyrrole and subsequent 6π-electrocyclization and dehydrogenation. A number of reactions could be successfully carried out as domino reactions in only one synthetic step. [ABSTRACT FROM AUTHOR]

1,1-Bis(trimethylsilyloxy)ketene acetals represent useful synthetic building blocks that can be regarded as masked carboxylic acid dianions. In recent years, a number of cyclization reactions of 1,1-bis(trimethylsilyloxy)ketene acetals have been reported that provide a convenient synthesis of various pharmacologically relevant heterocyclic products. [ABSTRACT FROM AUTHOR]

Functionalized 2-hydroxy-5-arylselanyl-benzoates were prepared by formal [3+3] cyclizations of 1,3-bis(silyloxy)-1,3-butadienes with 2-arylselanyl-3-silyloxy-alk-2-en-1-ones. GRAPHICAL ABSTRACT [image omitted] [ABSTRACT FROM AUTHOR]

The [4+2] cycloaddition of 1-ethoxy-2-fluoro-1,3-bis(trimethylsilyloxy)-1,3-diene with dimethyl acetylenedicarboxylate (DMAD) afforded dimethyl 4-fluoro-3,5-dihydroxyphthalate. Site-selective Suzuki-Miyaura reactions of its bis(triflate) provide a convenient approach to 3,5-diaryl-4-fluorophthalates. [ABSTRACT FROM AUTHOR]

The first 3-(3-pyrazolyl)indole-N-glycosides were prepared starting from indole-N-glycosides by conversion with 4-ethoxy-1,1,1-trifluorobut-3-en-2-one and following cyclization with hydrazine. The cytotoxic activity of the products against human keratinocytes (HaCaT) was studied. [ABSTRACT FROM AUTHOR]

5-Thioxo-4,6,8,9,10,11-hexahydro-benzo[b]thiopheno[2,3-d]-1,2,4-triazolo[1,5-c]pyrimidines and related compounds were prepared based on cyclizations of 2-isothiocyanato-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene with aminoketones and carboxylic hydrazides. [ABSTRACT FROM AUTHOR]

A variety of functionalized benzonitriles were regioselectively prepared by formal [3+3] cyclocondensation of 1,3-bis(silyloxy)buta-1,3-dienes with 3-ethoxy- and 3-silyloxy-2-cyano-2-en-1-ones. [ABSTRACT FROM AUTHOR]

6-Arylsalicylates were regioselectively prepared by formal [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with 1-aryl-3-ethoxyprop-2-en-1-ones which are available by Heck reaction of benzoyl chlorides with ethylvinyl ether. In this context, the first [3+3] cyclizations of brominated substrates are reported. [ABSTRACT FROM AUTHOR]

Abstract: Chlorinated phenols, benzophenones, and butenolides are prepared by various one-pot cyclization reactions of the first 4-chloro-1,3-bis(trimethylsilyloxy)-1,3-butadiene. [Copyright &y& Elsevier]

Unknown functionalized 1-aminopyrroles and 1-amino-4,5,6,7-tetrahydroindoles were prepared under mild conditions and with excellent yields by one-pot ‘conjugate addition/cyclization’ reactions of 1,3-bis(silyl enol ethers) with 1,2-diaza-1,3-butadienes. [ABSTRACT FROM AUTHOR]

4-(Silyloxy)benzopyrylium triflates can be readily generated in situ by reaction of chromones with trialkylsilyl-tri�fluoromethanesulfonate. Domino reactions of silyl enol ethers with benzopyrylium triflates - derived from chromones, 3-cyanochromones and 3-formylchromones - allow an efficient synthesis of a variety of carba- and heterocycles. [ABSTRACT FROM AUTHOR]

The one-pot cyclization of 2-isothiocyanatobenzonitrile (ITCB) with carbon nucleophiles afforded 4-alkylidene-3,4-dihydroquinazoline- 2(1H)thiones with very good E diastereoselectivity. [ABSTRACT FROM AUTHOR]

4-Alkyl- and 4-(ω-chloroalkyl)-1,3-bis(trimethylsilyl­oxy)buta-1,3-dienes were prepared from ethyl acetoacetate in three steps. Their cyclization with oxalyl chloride allowed an efficient synthesis of 4-alkyl- and 4-(ω-chloroalkyl)-5-alkylidenebuten­olides. [ABSTRACT FROM AUTHOR]

Abstract: A number of pulvinic acid natural products were prepared based on Suzuki cross coupling reactions of α-hydroxy-γ-alkylidenebutenolides which are readily available by cyclization of 1,3-bis-silyl enol ethers with oxalyl chloride. The formal total synthesis of pulvinic acid, atromentic acid, gomphidic acid and of 4-hydroxypulvinic acid, 4′-hydroxypulvinic acid and iso-gomphidic acid are reported. In addition, total syntheses of pinastric acid, xerocomic acid and variegatic acid were accomplished. [Copyright &y& Elsevier]

A variety of 5-chlorosalicylates were prepared by regio�selective one-pot cyclizations of 1,3-bis(trimethylsilyloxy)buta-1,3-dienes with novel 2-chloro-3-ethoxy-2-alken-1-ones. [ABSTRACT FROM AUTHOR]

Highly functionalized arylphosphonates were prepared by TiCl4-mediated cyclocondensation of 3-ethoxy-2-phosphonyl�alk-2-en-1-ones with 1,3-bis(trimethylsilyloxy)buta-1,3-dienes. [ABSTRACT FROM AUTHOR]

A variety of 2-arylthio-4-methoxybenzoates are regio�selectively prepared by the first formal [3+3] cyclocondensations of 3-arylthio-1-trimethylsilyloxybuta-1,3-dienes with 3-oxo-ortho�esters. [ABSTRACT FROM AUTHOR]

A variety of 4-methoxysalicylates and related polyketide-type phenols are regioselectively prepared by the first formal [3+3]-cyclocondensations of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-oxoorthoesters. [ABSTRACT FROM AUTHOR]

2-(Arylthio)benzoates were regioselectively prepared by the first catalytic [3+3] cyclizations of 3-(arylthio)-1-(trimethylsilyloxy)-1,3-butadienes with 1,1,3,3-tetramethoxypropane. [ABSTRACT FROM AUTHOR]

The [3+3] cyclocondensation of 1,3-bis(silyl enol ethers) with 1,1-bis(methylthio)-1-en-3-ones results in the regioselective formation of 3-(methylthio)phenols. The products represent useful synthetic building blocks, which are not readily available by other methods. [ABSTRACT FROM AUTHOR]

Abstract: Functionalized arenes were prepared by chelation-controlled ‘[3+3] cyclization/homo-Michael’ reactions of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with benzyloxy- or methoxy-substituted 1,1-diacylcyclopropanes. [Copyright &y& Elsevier]

The formal [3+3] cyclocondensation of 1,3-bis(trimethylsilyloxy)buta-1,3-dienes with 1,1-bis(methoxy)trifluoromethyl-1-en-3-ones afforded functionalized 3-methoxy-5-(trifluoromethyl)phenols with very good regioselectivity. [ABSTRACT FROM AUTHOR]

Functionalized resorcins are regioselectively prepared by cyclization of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3,3-dimethoxypentanoyl chloride. The regioselectivity is controlled by the type of Lewis acid employed. [ABSTRACT FROM AUTHOR]

Abstract: Functionalized diaryl-diazenes (azo-dyes) were regioselectively prepared by formal [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with 2-aryldiazenyl-3-silyloxy-2-en-1-ones. [Copyright &y& Elsevier]

Functionalized 7,8-benzo-4-hydroxy-1,9-diazabicyclo[3.3.1]non-3-enes were prepared by one-pot cyclization of 1,3-bis(silyl enol ethers) with quinazolines. [ABSTRACT FROM AUTHOR]

Abstract: Functionalized diaryl ethers were prepared by [3+3] cyclization of 3-aryloxy-1-siloxy-1,3-butadienes with 3-(silyloxy)alk-2-en-1-ones. [Copyright &y& Elsevier]

The first 1-hydroxyspiro[2.5]cyclooct-4-en-3-ones were prepared by cyclization of free and masked 1,3-dicarbonyl dianions with 1,1-diacetylcyclopropane. 1-Hydroxyspiro[2.5]cyclooct-4-en-3-ones represent precursors of unstable spiro[5.2]cycloocta-4,7-dien-6-ones and reactions with a number of nucleophiles were studied. The reactions are enhanced by dynamic spiro-activation. [Copyright &y& Elsevier]

Functionalized benzophenones were prepared by domino ‘Michael-retro-Michael-aldol’ reactions of 1,3-bis-silyl enol ethers with 3-formylchromones. [Copyright &y& Elsevier]

Benzopyrano[2,3-b]pyridines were efficiently prepared by condensation of 1,3-bis-silyl enol ethers with 3-cyanobenzopyrylium triflates and subsequent domino ‘retro-Michael–lactonization–aldol’ reactions. [Copyright &y& Elsevier]

Abstract: 5-(2-Aryl-2-haloethyl)salicylates are efficiently prepared by the first domino ‘[3+3] cyclization/ring-cleavage’ reactions of 1,3-bis(silyloxy)-1,3-butadienes with 3-acetyl-5-aryl-4,5-dihydrofurans. [Copyright &y& Elsevier]

Abstract: Highly functionalized ferrocenyl-substituted phenols were prepared by cyclization of masked or free dianions with 1,3-dielectrophilic 1-η5-ferrocenyl-3,3-bis(methylthio)prop-2-en-1-ones. While the cyclizations of 1,3-bis(silyloxy)-1,3-butadienes (masked dianions) proceed by initial 1,2-addition, the reactions of free 1,3-dicarbonyl dianions proceed by initial 1,4-addition. Therefore, both regioisomeric ferrocenylphenols are available from one and the same electrophile dependent on the type of nucleophile and reaction conditions employed. The reactions reported represent the first examples of the application of formal [3 + 3] cyclizations to the synthesis of organometallic compounds. [Copyright &y& Elsevier]