Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• -indanones and their heteroatom analogues 138–142 which may be further converted into biologically active compounds (Figure 4) [72]. Products 138–142 were obtained by electrocyclization of the substrates substituted by electron-withdrawing groups, such as CO2Me, P(O)(OEt)2, CN or NO2. This reaction was

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• case of similar thiocarbonyl S-isopropanides, the intermediate zwitterions, formed in the course of the attempted [3 + 2]-cycloaddition with electron-deficient ethenes, undergo 1,3-electrocyclization yielding mixtures of stereoisomeric cyclopropanes in addition to the expected 5-membered thiolanes

• pathway via a diradical intermediate leading to the formation of the unusual macrocyclic dimer 9 by computational methods. First calculations were made for phenyl selenophen-2-yl thiocarbonyl S-methanide (8A), which can undergo a 1,3-dipolar electrocyclization (1,3-ring closure) to form the thiirane 3a

• course of the dimerization of a reactive diaryl thiocarbonyl S-methanides. Potential 1,3-dipolar electrocyclization of thiocabonyl S-methanide 8A. Computed enthalpies (free energies in parentheses) at 298 K at the SMD(tetrahydrofuran)/M06-2X/6-311+G(2df,p)//M06-2X/6-31G(d) level of theory. Stepwise

Rapid regio- and multi-coupling reactivity of 2,3-dibromobenzofurans with atom-economic triarylbismuths under palladium catalysis

• Maddali L. N. Rao,
• Jalindar B. Talode and
• Venneti N. Murty

Beilstein J. Org. Chem. 2016, 12, 2065–2076, doi:10.3762/bjoc.12.195

• the synthesis of 2,3-dialkenylbenzofurans and functionalized dibenzofurans with domino “twofold Heck/6π-electrocyclization” of 2,3-di- and 2,3,5-tribromobenzofuran substrates [34]. In this regard, the cross-coupling studies of triarylbismuth reagents in regioselective studies with functionalized

Synthesis of 2,1-benzisoxazole-3(1H)-ones by base-mediated photochemical N–O bond-forming cyclization of 2-azidobenzoic acids

• Daria Yu. Dzhons and
• Andrei V. Budruev

Beilstein J. Org. Chem. 2016, 12, 874–881, doi:10.3762/bjoc.12.86

• -benzisoxazolones; 1,5-electrocyclization; nitrenes; photochemical cyclization; Introduction Substituted 2,1-benzisoxazoles display diverse biological activity [1][2][3][4][5][6] (Figure 1) and are widely used as starting materials for the synthesis of important heterocyclic pharmacophores, such as acridines [7][8

• through a 1,5-electrocyclization reaction [56][57]. Nonreacted singlet nitrenes A may undergo intersystem crossing (ISC) into the less reactive triplet state (Scheme 1, intermediate D). Although a multiplicity change is a spin-forbidden transition, it can be partially allowed in some cases. According to

• . Finally, the electron pair of the carboxylic group (Scheme 2, intermediate A) was joined by 1,5-electrocyclization to the electron-deficient singlet nitrene A with formation of 2-anion (see Scheme 2), which was neutralized by water (path I). Thus, the first path of cyclization of 1 was realized. Meanwhile

Diradical reaction mechanisms in [3 + 2]-cycloadditions of hetaryl thioketones with alkyl- or trimethylsilyl-substituted diazomethanes

• Grzegorz Mlostoń,
• Paulina Pipiak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2016, 12, 716–724, doi:10.3762/bjoc.12.71

• . Only after warming up above −45/40 °C compounds 2 are expected to decompose yielding the reactive thiocarbonyl ylide 3. Under these conditions, the latter intermediates can undergo either 1,3-dipolar electrocyclization to give thiiranes 8 or dimerization leading to 1,4-dithianes 4 [20][26]. This

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

• Laura A. Bryant,
• Rossana Fanelli and
• Alexander J. A. Cobb

Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46

• set up a 4π-electrocyclization, generating second intermediate 27. Elimination of the tertiary amine then gives γ-methylene cyclopentenone 28. 1,2-Addition reactions Henry reaction The use of cupreine and cupreidine derivatives in the addition of nitroalkanes to carbonyl compounds was first

Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study

• Mateo Alajarin,
• Marta Marin-Luna,
• Pilar Sanchez-Andrada and
• Angel Vidal

Beilstein J. Org. Chem. 2016, 12, 260–270, doi:10.3762/bjoc.12.28

• into the isomeric spirotricycle 12a. The computed energy barriers for these processes are relatively small, 13.9 and 17.0 kcal·mol−1 respectively. Again the differences in the extent of the electronic conjugation in these electrocyclization transition states can give account of the relative stabilities

• geometry of transition structures TS1-A, TS1-B, and TS1-C computed at the B3LYP/6-31+G** theoretical level. Distances in Ångstroms, bond angles in degrees. Lewis acid-catalyzed [1,4]-H transfer/1,5-electrocyclization tandem processes of benzylidenemalonates 1 leading to indan-1-ones 2. Preparation of benz

Copper-mediated synthesis of N-alkenyl-α,β-unsaturated nitrones and their conversion to tri- and tetrasubstituted pyridines

• Dimitra Kontokosta,
• Daniel S. Mueller,
• Dong-Liang Mo,
• Wiktoria H. Pace,
• Rachel A. Simpson and
• Laura L. Anderson

Beilstein J. Org. Chem. 2015, 11, 2097–2104, doi:10.3762/bjoc.11.226

• modularity of the Chan–Lam coupling process, and proceeds through a pathway that is distinct from the Liebeskind copper-catalyzed C–N bond coupling and electrocyclization (Scheme 2). Results and Discussion A Chan–Lam coupling between chalcone oxime 6a and cyclohexenylboronic acid (7a) was initially tested

• enamine to the ketone. This pathway may explain the solvent dependence that was observed for the transformation (Scheme 3). The lack of any observation of dihydropyridine N-oxide intermediate 17ae suggests that the reaction is not proceeding through an electrocyclization and elimination process. A second

On the strong difference in reactivity of acyclic and cyclic diazodiketones with thioketones: experimental results and quantum-chemical interpretation

• Andrey S. Mereshchenko,
• Alexey V. Ivanov,
• Viktor I. Baranovskii,
• Grzegorz Mloston,
• Ludmila L. Rodina and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2015, 11, 504–513, doi:10.3762/bjoc.11.57

• =S ylides bearing at least one acyl group is identified as the 1,5-electrocyclization into 1,3-oxathioles. However, in the case of diazomalonates, the dominating process is 1,3-cyclization into thiiranes followed by their spontaneous desulfurization yielding the corresponding alkenes. Finally

• bond (step 1), followed by decomposition of thiadiazoline 6 formed (step 2) and competitive electrocyclization of the intermediate thiocarbonyl ylide 7 either into 1,3-oxathiole 3 or thiirane 4 (step 3) (Scheme 2). According to the latest molecular orbital (MO) theory, reactions of diazodicarbonyl

• diazodiketones 1e,f. Transformations of thiocarbonyl ylides 7 and 7' In order to evaluate the correlation between the structure of thiocarbonyl ylides 7, 7' and the direction of their electrocyclizations (1,5- or 1,3-dipolar electrocyclization), the relative energies of the stationary points on the potential

Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

• Ivana Šagud,
• Simona Božić,
• Željko Marinić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230

• )oxazole small quantities of electrocyclization product, 4-(1,2-dihydronaphthalen-2-yl)oxazole, are isolated and spectroscopically characterized. Keywords: bicyclo[3.2.1]octane; intramolecular photocycloaddition; oxazole; styryl; vinyl; Introduction The bicyclo[3.2.1]octane skeleton is the basic

• electrocyclization of the benzodivinyl moiety to intermediate C followed by 1,5-H shift and rearomatization of the benzene ring. Analogue electrocyclization was not detected in phenyl or furyl-substituted o-divinylbenzenes but instead stilbene-like 6π electrocyclization and formation of 1-vinylphenanthrene [42] or 6

Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

• Alexander F. Khlebnikov,
• Mikhail S. Novikov,
• Yelizaveta G. Gorbunova,
• Ekaterina E. Galenko,
• Kirill I. Mikhailov,
• Viktoriia V. Pakalnis and
• Margarita S. Avdontceva

Beilstein J. Org. Chem. 2014, 10, 1896–1905, doi:10.3762/bjoc.10.197

• -electrocyclization to give oxazine E (Scheme 1). At the same time, the third mechanism of the reaction, involving a one-step formation of 1-oxa-5-azahexa-1,3,5-triene D, cannot be excluded. The reaction of a carbenoid with isoxazoles is the only known one-step intermolecular reaction which can in principle produce

• synthetic approach to derivatives of 2H-1,3-oxazines via a Rh2(OAc)4-catalyzed reaction of diazo esters with 2-acyl-2H-azirines F. This reaction involves the intermediate formation of azirinium ylides G, their transformation into 1-oxa-5-azahexa-1,3,5-triene D, and finally the 6π-electrocyclization of the

Aza-Diels–Alder reaction between N-aryl-1-oxo-1H-isoindolium ions and tert-enamides: Steric effects on reaction outcome

• Amitabh Jha,
• Ting-Yi Chou,
• Zainab ALJaroudi,
• Bobby D. Ellis and
• T. Stanley Cameron

Beilstein J. Org. Chem. 2014, 10, 848–857, doi:10.3762/bjoc.10.81

• reported reaction conditions for imino [4 + 2] Diels–Alder reactions [13][14] were employed here for the electrocyclization of N-acyliminium ions from N-aryl-3-hydroxyisoindolinones and tert-enamide analogues namely N-vinylpyrrolidone and N-vinylcaprolactam as the electron-rich dienophiles. Sixteen

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• rearrangement in great detail. Electrocycloreversion of initialy formed nitrene 321 leads to intermediate 322, which can undergo electrocyclization to give the required trans-vinylisocyanatocyclopropane 323, which underwent the desired rearrangement to give tricycle 324. The group of Boeckman pioneered the

Less reactive dipoles of diazodicarbonyl compounds in reaction with cycloaliphatic thioketones – First evidence for the 1,3-oxathiole–thiocarbonyl ylide interconversion

• Valerij A. Nikolaev,
• Alexey V. Ivanov,
• Ludmila L. Rodina and
• Grzegorz Mlostoń

Beilstein J. Org. Chem. 2013, 9, 2751–2761, doi:10.3762/bjoc.9.309

• react at room temperature with cycloaliphatic thioketones, e.g. 2,2,4,4-tetramethyl-3-thioxocyclobutanе-1-one and adamantanethione, via a cascade process in which the key step is a 1,5-electrocyclization of the intermediate thiocarbonyl ylide leading to tetrasubstituted spirocyclic 1,3-oxathioles. The

• most reactive diazodicarbonyl compound was diazoacetylacetone. In the case of dimethyl diazomalonate competitive 1,3-electrocyclization yielded the corresponding thiirane at elevated temperature, which after spontaneous desulfurization produced a tetrasubstituted alkene. To explain the observed

• -oxathiole to alkene were performed at the DFT PBE1PBE/6-31G(d) level. Keywords: 1,3-dipolar electrocyclization; 1,5-dipolar electrocyclization; 1,3-oxathioles; thiocarbonyl ylides; thiiranes; thioketones; Introduction Aryl- and alkylsubstituted thioketones exhibit high 1,3-dipolar reactivity towards

Flexible synthesis of anthracycline aglycone mimics via domino carbopalladation reactions

• Markus Leibeling and
• Daniel B. Werz

Beilstein J. Org. Chem. 2013, 9, 2194–2201, doi:10.3762/bjoc.9.258

• -electrocyclization [39] or a direct CH-activation to the respective anthracycline precursor 13. The design of the dialkyne provides a simultaneous formation of the linear ring system. All four cycles were annulated in a single step, in which the B and C-ring were formed as a consequence of the reaction cascade

The chemistry of isoindole natural products

• Klaus Speck and
• Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

• ozonolysis and acid-promoted cyclization afforded (+)-41 and (−)-41 in an overall yield of 60% and 46%, respectively. For the synthesis of staurosporinone (30) and its 3,4-dimethoxybenzyl (DMB)-protected derivative 45, a ruthenium-catalyzed C–H insertion/electrocyclization cascade using 2,2’-bisindole 44 and

Cyclization of substitued 2-(2-fluorophenylazo)azines to azino[1,2-c]benzo[d][1,2,4]triazinium derivatives

• Aleksandra Jankowiak,
• Emilia Obijalska and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2013, 9, 1873–1880, doi:10.3762/bjoc.9.219

• unsaturated bridge in the cyclization step and points towards a 6π-electrocyclization rather than to a simple nucleophilic aromatic displacement mechanism. Among the triazinium salts prepared in this work is the hydroxymethyl derivative 1e, which, in principle, can be incorporated into more complex molecular

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

• Rajendra K. Jangid,
• Nidhi Sogani,
• Neelima Gupta,
• Raj K. Bansal,
• Moritz von Hopffgarten and
• Gernot Frenking

Beilstein J. Org. Chem. 2013, 9, 392–400, doi:10.3762/bjoc.9.40

• theoretically as well as experimentally [16]. In this context, we found that 1,3-bis(alkoxycarbonyl)-2-phosphaindolizines (1a, Z = CO2R1) prepared through 1,5-electrocyclization of in situ generated bis(pyridinium ylidyl)phosphenium chlorides [17] lead to successful DA reaction [18][19], but 3-alkoxycarbonyl-2

Polar reactions of acyclic conjugated bisallenes

• Reiner Stamm and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

• − in this case) the (E)-diastereomer 55 results; likewise 53 furnishes the (Z)-isomer 56. From these considerations we would expect 55 to be the dominant product. If 50 loses a proton the butadienylallene 51 results, which by reprotonation at its allene carbon atom, followed by electrocyclization is

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• bisallenes. After the first isolation of 2 it was quickly demonstrated that on heating (either in solution or in the gas phase) it cyclizes to 3,4-bismethylenecyclobutene (130) in quantitative yield (Scheme 34) [6]. Up to the present day this electrocyclization remains the most thoroughly investigated

• [108][109], Pasto [29][115][116], Skattebøl [117] and others [118]. As shown in Scheme 35, the electrocyclization occurs in a strictly conrotatory manner and the stereoselectivity of the process depends on the steric size of the terminal substituents. For example, bisallene 131 has two distinct

• display anomalies in their bond lengths (Csp2–Csp2 bonds as long as 1.540 Å) [120]. For another route to benzocyclobutenes see Section 2.4, Scheme 71. A most interesting electrocyclization/dimerization process has been discovered by McGlinchey and co-workers for the disilylated hydrocarbon 86 (Scheme 37

Synthesis of a novel chemotype via sequential metal-catalyzed cycloisomerizations

• Bo Leng,
• Stephanie Chichetti,
• Shun Su,
• Aaron B. Beeler and
• John A. Porco Jr.

Beilstein J. Org. Chem. 2012, 8, 1338–1343, doi:10.3762/bjoc.8.153

• with the Pt-activated alkyne, the resulting metal-“ate” intermediate 28 may undergo preferential elimination and proto-demetallation to afford 1,5-diene 29. A second elimination results in the ring-opened triene 30. Subsequent 6π-electrocyclization affords alcohol 31, which aromatizes through loss of

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

• Rick C. White,
• Benny E. Arney Jr. and
• Heiko Ihmels

Beilstein J. Org. Chem. 2012, 8, 1208–1212, doi:10.3762/bjoc.8.134

•  3). The cis-stilbene (10) is subsequently transformed into phenanthrene (11) by photoinduced electrocyclization [22] as shown in Scheme 4. Conclusion We have demonstrated that the performance of photoreactions of cyclic sulfites under relatively mild reaction conditions enables the detection of

On the bromination of the dihydroazulene/vinylheptafulvene photo-/thermoswitch

• Virginia Mazzanti,
• Martina Cacciarini,
• Søren L. Broman,
• Christian R. Parker,
• Magnus Schau-Magnussen,
• Andrew D. Bond and
• Mogens B. Nielsen

Beilstein J. Org. Chem. 2012, 8, 958–966, doi:10.3762/bjoc.8.108

• ; photoswitch; vinylheptafulvene; Introduction 1,8a-Dihydroazulene-1,1-dicarbonitrile (DHA, 1) is a yellow photochromic compound, which undergoes a light-induced 10-electron retro-electrocyclization to a red-colored vinylheptafulvene (VHF) (Scheme 1) [1][2][3]. The VHF compound is formed as the s-cis conformer

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

• Farhan R. Bou-Hamdan,
• François Lévesque,
• Alexander G. O'Brien and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2011, 7, 1124–1129, doi:10.3762/bjoc.7.129

• increased concomitant formation of the byproduct 10. Lactam 10 was obtained upon re-exposure of purified 9a to the reaction conditions and is believed to result from photochemical disrotatory electrocyclization of the 3H-azepinone diene moiety [51][52][53][54] (Scheme 3). Instead of making a direct

A practical two-step procedure for the preparation of enantiopure pyridines: Multicomponent reactions of alkoxyallenes, nitriles and carboxylic acids followed by a cyclocondensation reaction

• Christian Eidamshaus,
• Roopender Kumar,
• Mrinal K. Bera and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2011, 7, 962–975, doi:10.3762/bjoc.7.108

• , we reported a new synthesis of pyridines based on the trimethylsilyl trifluoromethanesulfonate (TMSOTf) induced cyclocondensation reaction of β-ketoenamides [29][30][31][32][33][34]. This cyclocondensation step can be rationalized as a 6π-electrocyclization of the disilylated intermediate 5 to