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

• at C3) could stabilize the pentadienyl cationic intermediate 6, and thus relenting the 4π-electrocyclization, causing either the degradation of the starting material or the formation of unwanted side products. In fact, preliminary experimental results with 5 pointed in this direction, and we decided

• species to the alkyne 5, as in I (Figure 2). The first step TS1 has a low activation energy (ΔG‡ = 12.2 kcal⋅mol−1) to form the unstable cyclic intermediate II. This short-lived species rapidly reopens through TS2 (ΔΔG‡ = 8.1 kcal⋅mol−1) to give the pentadienyl cation III, which presents a high stability

Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

• Gabrielle R. Hammersley,
• Meghan F. Nichol,
• Helena C. Steffens,
• Jose M. Delgado,
• Gesine K. Veits and
• Javier Read de Alaniz

Beilstein J. Org. Chem. 2019, 15, 1569–1574, doi:10.3762/bjoc.15.160

• a trans relationship between the C4 and C5 substituents [13][14][15]. It is believed that the 4π conrotatory electrocyclization step that converts the pentadienyl cation 5 into the corresponding cyclopentenone adduct 6 is responsible for controlling the relative diastereoselectivity in this cascade

Decarboxylative and dehydrative coupling of dienoic acids and pentadienyl alcohols to form 1,3,6,8-tetraenes

• Ghina’a I. Abu Deiab,
• Mohammed H. Al-Huniti,
• I. F. Dempsey Hyatt,
• Emma E. Nagy,
• Kristen E. Gettys,
• Sommayah S. Sayed,
• Christine M. Joliat,
• Paige E. Daniel,
• Rupa M. Vummalaneni,
• Andrew T. Morehead Jr,
• Andrew L. Sargent and
• Mitchell P. Croatt

Beilstein J. Org. Chem. 2017, 13, 384–392, doi:10.3762/bjoc.13.41

• at Greensboro, Greensboro, NC 27402, USA Department of Chemistry, East Carolina University, Greenville, NC 27858, USA 10.3762/bjoc.13.41 Abstract Dienoic acids and pentadienyl alcohols are coupled in a decarboxylative and dehydrative manner at ambient temperature using Pd(0) catalysis to generate

• this reaction, substitutions at every unique position of both coupling partners was examined and two potential mechanisms are presented. Keywords: decarboxylation; diene; dienoate; palladium; pentadienyl; tetraene; Introduction The construction of sp2–sp3 carbon–carbon bonds remains a difficult and

• ], nitro [26][27], or alkyne [21][28][29][30][31][32], Scheme 1), or use an aryl carboxylate [33][34] which typically requires the assistance of silver or copper(I) salts for the decarboxylative step. It is rare to use a pentadienyl electrophile [35], or to have a diene or simple alkene adjacent to the

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

• Thibault E. Schmid,
• Sammy Drissi-Amraoui,
• Christophe Crévisy,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 2418–2434, doi:10.3762/bjoc.11.263

• compound to an extended Michael acceptor was reported independently as early as 1972, by the Näf [4] and Corey [5] groups, who studied the reactivity of pentadienyl methyl ester (1, Figure 2). In both cases, the 1,6-conjugate addition of a stoichiometric amount of a Gilman reagent proceeded in a selective

Streptopyridines, volatile pyridine alkaloids produced by Streptomyces sp. FORM5

• Ulrike Groenhagen,
• Michael Maczka,
• Jeroen S. Dickschat and
• Stefan Schulz

Beilstein J. Org. Chem. 2014, 10, 1421–1432, doi:10.3762/bjoc.10.146

• derivatives streptazones B1 (1), B2 (2), C (3), the 4-pyridone derivative streptazone D (4) with a pentadienyl side chain, and streptazolin (5) (Figure 1) [8]. Streptazolin is produced by several streptomycetes [8][9][10][11][12], and is formed biosynthetically by a polyketide mechanism [13]. The respective

• the extract revealed that a small peak (7) eluted slightly earlier than compound 8. The mass spectrum of compound 7 matched that of 2-pentylpyridine, present in public databases [14]. From these data we concluded that the unknown compound 12 might be a 2-(pentadienyl)pyridine with conjugated side

• -pyridinecarbaldehyde (19) a mixture of four diastereoisomers of 2-(1,3-pentadienyl)pyridine was formed (Figure 4), all showing similar mass spectra. These four diastereomers proved to be identical to the natural compounds 9 to 12 by comparison of mass spectra and GC retention. The major compound, 2-((1E,3E)-penta-1,3

On the control of secondary carbanion structure utilising ligand effects during directed metallation

• Andrew E. H. Wheatley,
• Jonathan Clayden,
• Ian H. Hillier,
• Alison Campbell Smith,
• Mark A. Vincent,
• Laurence J. Taylor and
• Joanna Haywood

Beilstein J. Org. Chem. 2012, 8, 50–60, doi:10.3762/bjoc.8.5

• azaenolate contribution to anion stability (C7–C1 1.493(3) Å). Moreover, though the analysis of charge delocalisation has recently been undertaken for benzylic tertiary carbanions, revealing a pentadienyl bonding pattern with alternating short and long bonds noted between the deprotonated (α-C) and the

• exhibiting pentadienyl character) is not replicated in 6-Lil·PMDTA. Instead, combined with the planarity of the ring system observed here, bond lengths in 6-Lil·PMDTA suggest the retention of aromaticity. Consistent with this, a torsion of only 6.1(3)° between directing and deprotonated groups (C(=O)–C–C–C

• -methylphenyldiphenylphosphinimine [63] demonstrated a short aryl-(α-C) distance (of 1.376(6) Å in both cases [20][63]) in tandem with a pentadienyl bonding pattern and significant perturbation of the aryl system. Uniquely, the secondary carbanion in 6-Lil·PMDTA shows both a short aryl–(α-C) distance and the significant retention

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• onto the gold-activated alkyne, and ring closure of the resulting pentadienyl cation species (XVIII) to give the final tricyclic adducts in good yields. Although PtCl2 is the most efficient catalyst for these intramolecular cycloadditions, the reaction of substrate 25 can also be performed with 5 mol

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• other mammal and vegetal alkaloids. The Naruta–Maruyama group exploited this reaction for the synthesis of a leucoaziridinomitosane based on the retrosynthesis shown in Scheme 12 [57][58]. The synthesis began with a Claisen rearrangement of the pentadienyl aryl ether 47 under Lewis acidic conditions

• (Scheme 13). After protection of the resulting phenol with a MOM group, the regioselective introduction of an alkoxymethyl group at the C9 position, the most crowded location on the pentadienyl moiety of compound 50, was the next obstacle. The best results were obtained by forming the pentadienyl anion

• with butyllithium followed by quenching with benzyloxymethyl chloride. The desired compound was obtained in 55% yield while the other regioisomers were isolated in a combined 22% yield. The more direct approach using the alkoxymethyl substituted pentadienyl aryl ether 49 failed to give the Claisen