Recent developments in the engineered biosynthesis of fungal meroterpenoids

• Zhiyang Quan and
• Takayoshi Awakawa

Beilstein J. Org. Chem. 2024, 20, 578–588, doi:10.3762/bjoc.20.50

• Aspergillus nidulans, within the same phylogenetic clade. Expression of this enzyme in place of Trt1 resulted in the formation of the 6-6-6-6-membered ring protoaustinoid A (8) (Figure 2) [9]. In addition, the expression of the cyclase AdrI (38% identity with Trt1) from Penicillium chrysogenum produced the 6

• approach led to the discovery of new CYCs, InsA7 (32% identity with Trt1) and InsB2 (40% identity with Trt1) from Aspergillus insuetus [13]. These enzymes catalyze the formation of the terpenoid skeleton from 6, adopting chair–boat and chair–chair conformations to create two distinct 6-6-6-6-membered ring

Synthesis of π-conjugated polycyclic compounds by late-stage extrusion of chalcogen fragments

• Aissam Okba,
• Pablo Simón Marqués,
• Kyohei Matsuo,
• Naoki Aratani,
• Hiroko Yamada,
• Gwénaël Rapenne and
• Claire Kammerer

Beilstein J. Org. Chem. 2024, 20, 287–305, doi:10.3762/bjoc.20.30

• afford 1,2-dithiin 42. At room temperature, the latter then spontaneously evolved via a S-extrusion to yield the desired carborane-fused thiophene 43. The same method was further employed to prepare other analogues incorporating a group-16 heteroatom. The strategy involving 6-membered ring contraction by

• milder conditions in 55% yield. For increased synthetic utility, the latter could be converted in a straightforward manner into the corresponding thiophene under Pummerer conditions. A 6-membered ring contraction through SO-extrusion was also introduced as key step in a molecular “surgical” method

• [65]. Synthesis of dinaphthooxepine bisimide 33 and conversion into PBI 6f by O-extrusion triggered by electron injection [66]. Top: Early example of 6-membered ring contraction with concomitant S-extrusion leading to dinaphthothiophene [69]. Bottom: Photoactivated S-extrusion occurring in natural

Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity

• Swagat K. Mohapatra,
• Khaled Al Kurdi,
• Samik Jhulki,
• Georgii Bogdanov,
• John Bacsa,
• Maxwell Conte,
• Tatiana V. Timofeeva,
• Seth R. Marder and
• Stephen Barlow

Beilstein J. Org. Chem. 2023, 19, 1651–1663, doi:10.3762/bjoc.19.121

• counterparts, while there has also been limited effort on examining the effects of substituents on the benzimidazole 6-membered ring in either class of reductant [16][24]. Furthermore, there has been little work on Y = 2-thienyl 1H derivatives. Here, we report two new dimers (1g2 and 1h2) and three new hydride

Photoredox catalysis enabling decarboxylative radical cyclization of γ,γ-dimethylallyltryptophan (DMAT) derivatives: formal synthesis of 6,7-secoagroclavine

• Alessio Regni,
• Francesca Bartoccini and
• Giovanni Piersanti

Beilstein J. Org. Chem. 2023, 19, 918–927, doi:10.3762/bjoc.19.70

• the importance of steric effects [99]. Indeed, while the addition of the nucleophilic α-amino radical to the α-styrenyl position affords the 6-membered ring (kinetic product via intramolecular 6-exo-trig ring closure) [100] the resulting radical is unstabilized, the 7-membered ring (obtained via

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• . In the case of activated alkenes, the species will undergo a 7-exo-trig cyclization. On the other hand, it is energetically more favorable for the maleimide species to sequentially undergo a 1,4-HAT, 1,4-HAT, 1,6-HAT and intramolecular cyclization to form the 6-membered ring. Further, by applying

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• that a specific geometry of the tethered alkene is required, as no 6-membered ring formation was observed. Interestingly, Cárdenas’ precursor 35 [30] led, after a cascade of reactions, to the formation of compound 36. Computational as well as experimental studies suggested that the ligand and

Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• 2: 1.1 kJ/mol for the 6-membered ring and 2.2 kJ/mol for the 5-membered ring; conformer 3: 20 kJ/mol for the 6-membered ring and 19 kJ/mol for the 5-membered ring). Thus, conformer 2 was slightly higher in energy than conformer 1 and should be populated at room temperature. However, we did not carry

Inherent atomic mobility changes in carbocation intermediates during the sesterterpene cyclization cascade

• Hajime Sato,
• Takaaki Mitsuhashi,
• Mami Yamazaki,
• Ikuro Abe and
• Masanobu Uchiyama

Beilstein J. Org. Chem. 2019, 15, 1890–1897, doi:10.3762/bjoc.15.184

• 5/6/8/5 tetracyclic intermediate. This, in turn, is transformed to a 4/6-membered ring in quiannulatene biosynthesis, whereas 5/5 ring formation proceeds in sesterfisherol biosynthesis (Scheme 1, Scheme 2, and Scheme 3). Based on our DFT calculations, this regioselectivity is determined by the

Anomeric sugar boronic acid analogues as potential agents for boron neutron capture therapy

• Daniela Imperio,
• Erika Del Grosso,
• Silvia Fallarini,
• Grazia Lombardi and
• Luigi Panza

Beilstein J. Org. Chem. 2019, 15, 1355–1359, doi:10.3762/bjoc.15.135

• around the boron atom. Compound 8 shows two isochronal protons at C-2 with a J2,3 = 4.9 Hz, and superposition of protons H-3 and H-5 not allowing to hypothesize a clear picture of the 6-membered ring conformation. Concerning compound 10, the molecule is rigid around the benzylidene ring, while a

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• high yields, irrespective of the nature of the substituents (Scheme 28) [68]. The scope of the reaction has been extended to 6-membered ring cyclic diaryl-λ3-iodanes 64. The acridines 65, hence, have been obtained with similar yields. The group of Shimizu has reported the formation of dibenzothiophenes

Fluorocyclisation via I(I)/I(III) catalysis: a concise route to fluorinated oxazolines

• Felix Scheidt,
• Christian Thiehoff,
• Gülay Yilmaz,
• Stephanie Meyer,
• Constantin G. Daniliuc,
• Gerald Kehr and
• Ryan Gilmour

Beilstein J. Org. Chem. 2018, 14, 1021–1027, doi:10.3762/bjoc.14.88

• explored (to generate 2k and 2l, respectively). Unsurprisingly, whilst the 6-membered ring formed in 42% yield, cyclisation to form the analogous 7-membered ring failed. It was, however, possible to generate heterocyclic species such as the 9-fluorenonyl-substituted oxazoline 2m (48%) and the furan 2n (59

Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz–Fritsch–Bobbitt reaction with non-activated and moderately-activated systems

• Marco Mottinelli,
• Mathew P. Leese and
• Barry V. L. Potter

Beilstein J. Org. Chem. 2017, 13, 1871–1878, doi:10.3762/bjoc.13.182

• noticed a strong preference for the 6-membered ring formation over the 5-membered ring, and the latter formed only in a greatly activated system. Conversely, no preference between 6- and 7-membered ring formation was observed. In addition, a 4-MeO-THIQ side product may be identified and its formation

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

• to a mixture of 1,2-dihydroisoquinolines 236 and substituted 1-indanone derivatives 237 via alkoxy group migration in 16 and 57% yields, respectively (Scheme 66) [95]. 2 Construction of the 6-membered ring The titles of subsections in this chapter contain names of the 1-indanone precursors which

• 76% yield. The former 271 was obtained from the trienone 270/270’ which underwent ring closure to give the 6-membered ring [105] (Scheme 76). 2.2 From alkynes DBU and CpRu(PPh3)2Cl dual catalysts enabled a one-pot annulation of aldehyde 273 and cyclopentanone (274) to give the 1-indanone derivative

cis-Diastereoselective synthesis of chroman-fused tetralins as B-ring-modified analogues of brazilin

• Dimpee Gogoi,
• Runjun Devi,
• Pallab Pahari,
• Bipul Sarma and
• Sajal Kumar Das

Beilstein J. Org. Chem. 2016, 12, 2816–2822, doi:10.3762/bjoc.12.280

• ) between the 4-aryl group and H atom at the C-3 position of 4-arylchroman-3-ols (thus giving rise to trans-4-arylchroman-3-ols) [22][23]. But it was not obvious how the planned IFCEA cyclization onto the pre-existing 6-membered ring, in case of stepwise-epoxide ring opening, would influence the product

A new paradigm for designing ring construction strategies for green organic synthesis: implications for the discovery of multicomponent reactions to build molecules containing a single ring

• John Andraos

Beilstein J. Org. Chem. 2016, 12, 2420–2442, doi:10.3762/bjoc.12.236

• integer partitioning exercise. For example, for a generalized 6-membered ring we find that there are only three possible 3-partitions; namely, [4 + 1 + 1], [3 + 2 + 1], and [2 + 2 + 2]. If we choose a pyridine ring as a target we permute each of these partitions to determine all possible unique [4 + 1 + 1

• consist algebraically of the same kinds of fragment elements; namely, two 2s and two 1s. The fourth entry in Figure 3 shows the visual distinction between partitioning a 6-membered ring via [2 + 2 + 1 + 1] and [2 + 1 + 2 + 1] cycloadditions. Similarly, [3 + 2 + 1 + 1] and [3 + 1 + 2 + 1] partitions for a

• 7-membered ring are distinguishable; and for an 8-membered ring [4 + 2 + 1 + 1] and [4 + 1 + 2 + 1] are distinguishable as are [3 + 2 + 2 + 1] and [3 + 2 + 1 + 2], and [3 + 3 + 1 + 1] and [3 + 1 + 3 + 1]. where r is the ring size. Case studies Cyclohexanone Cyclohexanone is a 6-membered ring

Bridgehead vicinal diallylation of norbornene derivatives and extension to propellane derivatives via ring-closing metathesis

• Sambasivarao Kotha and
• Rama Gunta

Beilstein J. Org. Chem. 2016, 12, 1877–1883, doi:10.3762/bjoc.12.177

• exo configuration. Thus, in the final compound 1a the newly formed 6-membered ring during RCM is supposed to be in the exo configuration. To our surprise, single-crystal X-ray analysis of 1a revealed that the 6-membered ring (C28–C30–C31–C32–C33–C27) formed via RCM is in endo configuration as depicted

Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

• Takashi Nishikata,
• Alexander R. Abela,
• Shenlin Huang and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2016, 12, 1040–1064, doi:10.3762/bjoc.12.99

• the product from their 5-membered isoxazoline-containing palladacycle [160][168][225]. Although BQ is sometimes used as a ligand for palladium to accelerate reductive elimination [103][226][227][228][229][230], its presence was not necessary in our stoichiometric reaction of a cationic 6-membered ring

The synthesis of functionalized bridged polycycles via C–H bond insertion

• Jiun-Le Shih,
• Po-An Chen and
• Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

• carbenes and nitrenes generated from sulfonate esters prefer 6-membered ring formation (i.e., 1,6-insertion) opened the door for easy access to 1,3-functionalized products via C–H insertion [64][65]. The sulfonate can be a useful functional group for subsequent transformations, also. If used in the

• ]decane 82, which would require the formation of a new 6-membered ring instead of a 5-membered ring, though the latter is typically preferred in intramolecular reactions [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]. Nevertheless, 82 was produced as the

A comprehensive study of olefin metathesis catalyzed by Ru-based catalysts

• Albert Poater and
• Luigi Cavallo

Beilstein J. Org. Chem. 2015, 11, 1767–1780, doi:10.3762/bjoc.11.192

• on the cis/trans preference for 12, whereas for 11 trans coordination of C2H4 is not favored. This is easily explained by considering that the 5-membered ring formed through chelation of the cresol group to Ru makes a trans O–Ru–O disposition geometrically difficult, whereas the 6-membered ring

Structure and conformational analysis of spiroketals from 6-O-methyl-9(E)-hydroxyiminoerythronolide A

• Ana Čikoš,
• Irena Ćaleta,
• Dinko Žiher,
• Mark B. Vine,
• Ivaylo J. Elenkov,
• Marko Dukši,
• Dubravka Gembarovski,
• Marina Ilijaš,
• Snježana Dragojević,
• Ivica Malnar and
• Sulejman Alihodžić

Beilstein J. Org. Chem. 2015, 11, 1447–1457, doi:10.3762/bjoc.11.157

• ]. Only one enantiomer at 8-C was isolated, showing retention of stereochemistry. This would support the hypothesis that the difference in energies of the 6-membered ring anomers relative to a 5-membered ring is sufficient to drive the conversion of 3 to 4. Conclusion In this paper we have presented the

Hydrogenation of unactivated enamines to tertiary amines: rhodium complexes of fluorinated phosphines give marked improvements in catalytic activity

• Sergey Tin,
• Tamara Fanjul and
• Matthew L. Clarke

Beilstein J. Org. Chem. 2015, 11, 622–627, doi:10.3762/bjoc.11.70

• to the fact that there is a ring strain due to the double bond in a 6-membered ring, which is released after the double bond is hydrogenated. 1a does not get hydrogenated with the catalysts studied. It is likely that this is due to the substrate binding to the catalyst via the pyridine nitrogen and

Further exploration of the heterocyclic diversity accessible from the allylation chemistry of indigo

• Alireza Shakoori,
• John B. Bremner,
• Mohammed K. Abdel-Hamid,
• Anthony C. Willis,
• Rachada Haritakun and
• Paul A. Keller

Beilstein J. Org. Chem. 2015, 11, 481–492, doi:10.3762/bjoc.11.54

• -one heterocycles 17 and 18, which arise from the addition of two allyl units with one cyclising to form a 6-membered ring and the other to form a 7-membered ring [4]. These yields are now excellent for the production of these reasonably complex heterocycles, around 70% for 17 and 18. Notably, the

The Shono-type electroorganic oxidation of unfunctionalised amides. Carbon–carbon bond formation via electrogenerated N-acyliminium ions

• Alan M. Jones and
• Craig E. Banks

Beilstein J. Org. Chem. 2014, 10, 3056–3072, doi:10.3762/bjoc.10.323

• ]. The scope of the anodic methoxylation has so far been limited to either acyclic or 4–6-membered ring sizes, the use of electrosynthetic approaches can also be applied to larger 7-membered ring systems, albeit less frequently [65][66]. β-Lactams (4-membered rings) undergo anodic oxidation of the carbon

Theoretical studies on the intramolecular cyclization of 2,4,6-t-Bu₃C₆H₂P=C: and effects of conjugation between the P=C and aromatic moieties

• Masaaki Yoshifuji and
• Shigekazu Ito

Beilstein J. Org. Chem. 2014, 10, 1032–1036, doi:10.3762/bjoc.10.103

• 2 to 1 were determined as 95.0 kcal/mol and 91.5 kcal/mol, respectively. Whereas the P1–C1 distance is typical for phosphaalkenes [21], dihedral angle of the P=C and almost planar benzene ring is close to co-planar due to the fused 6-membered ring [τ(C1–P1–C3–C4] = 22.9°, τ(C1–P1–C3–C9) = 160.1

Site-selective covalent functionalization at interior carbon atoms and on the rim of circumtrindene, a C₃₆H₁₂ open geodesic polyarene

• Hee Yeon Cho,
• Ronald B. M. Ansems and
• Lawrence T. Scott

Beilstein J. Org. Chem. 2014, 10, 956–968, doi:10.3762/bjoc.10.94

• surpasses that in fullerene C60 (POAV angle = 11.6°, Figure 4). Moreover, the X-ray structure of circumtrindene (6) reveals that the carbon–carbon bonds around the 6-membered ring at the top of the dome are not equivalent. The bond lengths vary depending on their location (Figure 5), as is also observed in

• fullerenes [53]. The carbon–carbon bond shared by two six-membered rings (so-called 6:6-bonds: 1.379 Å) are shorter than those shared by a 5-membered ring and a 6-membered ring (5:6-bonds: 1.430 Å). That is, the carbon–carbon bonds of the hexagonal ring in the center of circumtrindene are not the same as