SOMOphilic alkyne vs radical-polar crossover approaches: The full story of the azido-alkynylation of alkenes

• Julien Borrel and
• Jerome Waser

Beilstein J. Org. Chem. 2024, 20, 701–713, doi:10.3762/bjoc.20.64

• diasteroisomer was determined to be trans. Diyne 4l could be accessed in 44% yield from the exclusive 1,2-functionalization of the corresponding ene-yne. Crude NMR of the reaction did not show the presence of an allene product which could have been formed by a 1,4-functionalization. Enol ether could also be

Palladium-catalyzed three-component radical-polar crossover carboamination of 1,3-dienes or allenes with diazo esters and amines

• Geng-Xin Liu,
• Xiao-Ting Jie,
• Ge-Jun Niu,
• Li-Sheng Yang,
• Xing-Lin Li,
• Jian Luo and
• Wen-Hao Hu

Beilstein J. Org. Chem. 2024, 20, 661–671, doi:10.3762/bjoc.20.59

• alkylpalladium radical with the release of dinitrogen. The radical intermediate selectively adds to the double bond of a 1,3-diene or allene, followed by the allylpalladium radical-polar crossover path and selective allylic substitution with the amine substrate, thereby leading to a single unsaturated γ- or ε

• modification of pharmaceutical scaffolds. Naturally, we were eager to acquire detailed mechanistic insights into this protocol. To validate the radical nature of this transformation, both model reactions of 1,3-diene 2a and allene 5a were terminated completely with 2.5 equiv 2,2,6,6-tetramethylpiperidinyloxyl

• subsequent attack of amine 3 at the latter stage would afford the unsaturated ε-AA derivative 4 and regenerates the Pd(0)Ln to close the catalytic cycle. Different from the reactive site of 1,3-diene, the hybrid alkylPd radical I selectively adds to the central position of the allenyl group of allene 5a

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• Since the seminal 1998 report by Teles et al. on the gold(I)-catalyzed addition of alcohols to alkynes [1], a multitude of gold-catalyzed reactions have been reported. Great successes in mechanistic analysis and synthetic methods have been achieved for allene and alkyne activation, while the activation

• competing Brønsted acid catalysis in gold-catalyzed alkene functionalization remains a consideration [2], and while it is assumed that alkene activations follow the same prototypical mechanisms as allene and alkyne activations, that is (1) π-activation with nucleophilic attack followed by (2

• intermediates (expected from allene/alkyne addition) are more reactive than the C(sp3)-alkylgold intermediates expected from alkene addition [29]. Another study demonstrated the inefficiency of protodeauration in the presence of (albeit more basic) alkylamines [30]. These studies cast doubt on protodeauration

(E,Z)-1,1,1,4,4,4-Hexafluorobut-2-enes: hydrofluoroolefins halogenation/dehydrohalogenation cascade to reach new fluorinated allene

• Nataliia V. Kirij,
• Andrey A. Filatov,
• Yurii L. Yagupolskii,
• Sheng Peng and
• Lee Sprague

Beilstein J. Org. Chem. 2024, 20, 452–459, doi:10.3762/bjoc.20.40

• -1,1,1,4,4,4-hexafluorobut-2-enes have been investigated. A simple, one-pot procedure for the preparation of a new allene (1,1,4,4,4-pentafluorobuta-1,2-diene) and some of its transformations is presented. Keywords: allenes; dehydrohalogenation; halogenation; 1,1,1,4,4,4-hexafluorobut-2-enes; isomerization

• 11 had an allene structure. It was also important to note that the reaction proceeded more selectively in ether, which significantly reduced the amount of byproducts. Pure final alcohol 10 was isolated by column chromatography on SiO2 in 46% yield and 1H, 19F and 13C NMR spectra were in full

• aldehyde 9, elimination of MgBrF results in the formation of allene 11. To confirm our hypothesis, we studied the reaction of haloolefins 3 and 7 with iPrMgCl and BuLi. Thus, olefin 3a in Et2O reacted with iPrMgCl solution in THF at −80 °C to form Grignard reagent 12 and by heating the reaction mixture to

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• congestion. In previous studies, chiral induction in TCBD structures was accomplished by introducing chiral allene (51) [124][125] or binaphthyl (52 and 53) [126][127] moieties, as shown in Figure 1. These molecules exhibited Cotton effects related to ICT absorptions, and chiral induction in TCBD moieties

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• sulfide molecules 137 (Scheme 58) [90]. The Lewis basicity nature of PhSePh as a catalyst and the presence of Lewis acid TMSOTf improved the chemical yields. It is interesting to note that the reaction carried out at a lower temperature because of the high reactivity of allene 136. When the reaction was

Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

Pyridine C(sp²)–H bond functionalization under transition-metal and rare earth metal catalysis

• Haritha Sindhe,
• Malladi Mounika Reddy,
• Karthikeyan Rajkumar,
• Akshay Kamble,
• Amardeep Singh,
• Anand Kumar and
• Satyasheel Sharma

Beilstein J. Org. Chem. 2023, 19, 820–863, doi:10.3762/bjoc.19.62

• optimized conditions in hand, diverse 2-arylated pyridines were screened resulting in the corresponding products 74 in good yields. Allene, a cumulated diene and an important building block in organic synthesis has versatile biological properties and is also an important subunit in various natural products

• ). The half-sandwich scandium complex 76 along with the tetrakis(pentafluorophenyl)borate and pyridine forms a cationic Sc-pyridyl complex 78, which after addition of allene 75, forms a transient pentacyclic intermediate 80 via intermediate 79. Next, another molecule of pyridine adds to intermediate 80

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• would afford the [2 + 2] adduct. Hydroruthenation of the allene produces 103 which can either undergo reductive elimination to afford the cyclopropanated bicyclic alkene or undergo a [2 + 2] cycloreversion to generate the Ru–carbene 104. The Ru–carbene 104 can rearrange to 100 through a 1,3-migration of

Group 13 exchange and transborylation in catalysis

• Dominic R. Willcox and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2023, 19, 325–348, doi:10.3762/bjoc.19.28

• of allenes, using various boronates as the terminal reductant (Scheme 5) [68]. Experimental and computational studies suggested the reaction proceeded by hydroboration of the allene 14 by bis(pentafluorophenyl)borane to give an allylborane 15, which underwent allylation of a second equivalent of the

• allene 14, giving a boryl diene 16. A Cope rearrangement of the boryl diene 16 followed by transborylation gave the dienyl boronic ester 18 and regenerated the catalyst (Scheme 5). Chang reported the alkoxide-promoted hydroboration of N-heteroarenes with HBpin, the first explicit example of a B‒N/B‒H

• isotopic labelling and proposed to proceed by hydroboration of the allene 62 by the borane catalyst (H-B-9-BBN or 10-phenyl-9-borabicyclo[3.3.2]decane [Ph-BBD]) followed by rapid isomerisation from the (Z)-63 to (E)-allylborane 64 which underwent allylation of the ketone 65 to give an allylic borinic ester

Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

• allowed the functionalization for each natural product. Their general method consisted in using an intramolecular Pauson–Khand reaction catalyzed by a rhodium complex from an allene-yne substrate to build the eight-membered ring, which was quite challenging. Starting from commercial (R)-limonene (51), Li

• and co-workers synthesized allene-yne intermediate 182 (Scheme 36) in 7 steps, with a 16% overall yield. To access the allene moiety 182, they first tried addition of propadienyllithium to aldehyde 180, but they obtained a complex mixture of allenic alcohol and homopropargylic alcohol. Then, they were

• internal position of the allene (51%). In the same conditions, an excellent yield (86%) was obtained for the synthesis of a precursor of schindilactone

Enantioselective total synthesis of putative dihydrorosefuran, a monoterpene with an unique 2,5-dihydrofuran structure

• Irene Torres-García,
• Josefa L. López-Martínez,
• Rocío López-Domene,
• Manuel Muñoz-Dorado,
• Ignacio Rodríguez-García and
• Miriam Álvarez-Corral

Beilstein J. Org. Chem. 2022, 18, 1264–1269, doi:10.3762/bjoc.18.132

• of the hydroxy group to the terminal double bond of the allene in compound 3. Another key step is the Ti(III)-mediated straightforward synthesis of this α-hydroxyallene, which could be achieved through a regioselective Barbier-type coupling of a propargylic halide (1-bromo-2-butyne) with the aldehyde

• some contamination of the product with lactone 5 can arise at low pH values, which goes in detriment of the yield. The 2,5-dihydrofuran ring in target compound 1 was obtained through a Ag(I)-mediated intramolecular addition of the hydroxy to the allene group, a process that transformed allene 3 into

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• -yl)methanols 87 as electrophile and 2-naphthols 88 or phenols 90 as nucleophile (Scheme 29) [45]. The (3-alkynylindol-2-yl)methanol 87 is expected to convert to the allene-iminium intermediate I-24 by accepting a proton from CPA 14. Then, the CPA anion activates the nucleophilic addition between 2

• -naphthol (88) and allene-iminium intermediate I-24 to form axially chiral I-25, followed by rearomatization of the naphthol ring of I-25 and isomerization to I-26. Thereafter, CPA forms two hydrogen bonds with the two OH groups of I-26 to generate a carbocation and facilitates an intramolecular

• regio- and stereoselective γ-addition reaction of isoxazol-5(4H)-ones 103 to β,γ-alkynyl-α-imino esters 102 for the synthesis of axially chiral tetrasubstituted α-amino allenoates 104 containing an adjacent quaternary carbon stereocenter and an axially chiral tetrasubstituted allene scaffold [104

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• ‘path b' was followed. Cyclization involving allenes (>C=C=C<) Apart from alkenes/alkynes, there are also examples where cyclization takes place involving allene functionalities. Some of the examples are discussed below. Balasubramanian et al. reported the cyclization of aryl allenic ethers 113 on

• ]. Devan et al. had developed similar types of Hg(TFA)2-mediated cyclizations of allene 116 at low temperature followed by reduction with alkaline NaBH4 to form cyclized product 117 in moderate yield [88]. The reaction was believed to proceed through Hg(II) ion-promoted electrophilic cyclization (Scheme 35

• treatment with Hg(OTf)2. Hg(TFA)2-mediated cyclization of allene. Hg(II)-catalyzed intramolecular trans-etherification reaction of 2-hydroxy-1-(γ-methoxyallyl)tetrahydropyran derivatives. a) Cyclization of alkene derivatives by catalytic Hg(OTf)2 salts and b) mechanism of cyclization. a) Synthesis of 1,4

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• the allene intermediate D. Finally, an intramolecular 6π-electrocyclization and tautomerism results in the desired products 143a. The authors proposed a mechanism for azepinoindoles (Scheme 59) [128] wherein acid-catalyzed protonation of arylglyoxal monohydrate followed by dehydration and addition of

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• methylenecyclopropanes are of interest as Michael acceptors and as substrates for thermal rearrangements. As they are not readily available by difluorocarbene addition to allene derivatives, Taguchi et al. developed an alternative route to these compounds by selenoxide elimination (Scheme 30) [75]. Later, this approach

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• TMS group of 126 was found to be extremely challenging. The commonly used conditions provided the allene as a major product instead of the desired product. Ultimately, the mono-desilylated product 127 was obtained in 85% yield by using sodium sulfide in a mixture of THF and water. Next, the zirconium

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• of a triple bond, which has ultimately led to the total synthesis of several natural compounds [2][8]. The gold-catalyzed rearrangement of suitably substituted propargylic esters in particular provides a platform for cascade processes that involve a cationic or an allene intermediate generated in the

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• trimethylenemethane diyl [3 + 2] cycloaddition of 40 led to the formation of angular fused triquinane 41 in 98% yield. The authors suggested that an intramolecular cycloaddition of the diazo group and allene 38 produces tetrahydrocyclopentapyrazole 39. Extrusion of nitrogen from the newly formed 39 produces diyl 40

• -workers proposed that the catalytic mechanism involves a reaction between phosphine catalyst A and allene 82 to give B and/or C (Scheme 5B). Catalytic [3 + 2] cycloaddition of B and/or C and alkene D gives the cyclic intermediates E and F in an equilibrium state through a 1,2-proton transfer. The loss of

• isoindigos to give an enantioenriched annulation adduct bearing vicinal quaternary stereocenters [46] (Scheme 7A). Both symmetric and unsymmetric isoindigos can undergo enantioselective [3 + 2] annulation with an allene and produced a chiral adduct with high yield and high ee value. When unsymmetric

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• -deficient alkenes 190 to synthesise cyclobutanes 191 (Scheme 28c) [83]. Recently, Bach et al. also employed this methodology for the intramolecular [2 + 2] cycloaddition of quinolones 192 containing either a pendant alkene or allene to obtain cyclobutanes 193 (Scheme 28d) [84]. Recently, ent-185 was applied

• by Bach to the deracemisation of allenes rac-194 (Scheme 29) [85]. The proposed mechanism proceeds through configurationally isomeric hydrogen bonding complexes 195 and 195’, with subsequent photoexcitation of the thioxanthone chromophore leading to racemisation of the allene through a triplet state

• intermediate 196. In 195 there is additional steric repulsion between the large R group and the thioxanthone that is not present in 195’, which results in a smaller association constant and a larger calculated separation between the allene and the chromophore in 195 (r = 510 pm) relative to 195’ (r = 363 pm

A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

• Olusesan K. Koleoso,
• Matthew Turner,
• Felix Plasser and
• Marc C. Kimber

Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165

• radical adds to the central carbon of the allene giving a conjugated N-acyliminium that undergoes nucleophilic addition by arylamines and alcohols. Keywords: allenamide; allene; intermolecular; N-acyliminium; photoredox; Introduction Allenamides (Scheme 1, 1) and their congeners have attracted

• considerable attention over the past 15 years due to their characteristic reactivity profiles [1][2][3][4]. The reactivity that an allenamide can display is distinct from a traditional allene due to the presence of an amide unit attached at the α-carbon. This substituent can donate electron density into the

• allene, principally onto the central β-carbon, that can be harnessed in subsequent chemical transformations leading to regiochemical confidence in the resulting products (Scheme 1). Importantly, this unique reactivity has underpinned allenamide chemistry and led to the development of a number of

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

• Zhen Cao,
• Aline Lacoudre,
• Cybille Rossy and
• Brigitte Bibal

Beilstein J. Org. Chem. 2019, 15, 2465–2472, doi:10.3762/bjoc.15.239

• catalysis has proved its effectiveness for numerous transformations involving unsaturated bond activation (allene, alkyne, alkene) [11][12][13][14][15][16][17], radical-based reactions [18][19][20] and several applications in asymmetric reactions [21][22]. This successful chemistry was usually conducted in

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• such phosphorylallenes under the action of Brønsted or Lewis acids. Apart from that, the reaction of dichlorophosphorylallenes with arenes and AlCl3 led to products of hydroarylation of the allene system, phosphoryl-substituted alkenes and/or indanes. This is the first example of a Lewis acid-promoted

• –H (Table 1). These species are formed by protonation of the central carbon atom of the allene system that gives the corresponding allyl cations, which undergo cyclization onto the oxygen of the P=O group. These ions have similar NMR data: the signal of the new proton H4 is located in the range 6.30

• at room temperature for a long time, they are not transformed into other species under the superacidic conditions. Unlike the others, allene 1g undergoes consequent transformations in TfOH at room temperature (see Scheme 1 and Figure 2). First, when dissolved in the acid, allene 1g forms

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• conjugate addition of benzamide nitrogen onto the 2-ynamide generates the final cyclization product 24 through allene intermediate 28. Taking into account that the reaction does not take place with internal alkynes, the authors conclude that a terminal alkyne is necessary for the formation of the first

An anomalous addition of chlorosulfonyl isocyanate to a carbonyl group: the synthesis of ((3aS,7aR,E)-2-ethyl-3-oxo-2,3,3a,4,7,7a-hexahydro-1H-isoindol-1-ylidene)sulfamoyl chloride

• Aytekin Köse,
• Aslı Ünal,
• Ertan Şahin,
• Uğur Bozkaya and
• Yunus Kara

Beilstein J. Org. Chem. 2019, 15, 931–936, doi:10.3762/bjoc.15.89

• ], chlorosulfonyl isocyanate (CSI, 1) continues to be the most reactive isocyanate to date. CSI is relatively more reactive than alkylsulfonyl isocyanate in olefin additions [2]. Its highly reactive nature is due to the polarization of the allene double bond by the highly electronegative chlorosulfonyl group. CSI