Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• -position of the aromatic ring could contribute to the stabilization of TS1, in which the Ar–C3–C2–P dihedral angle is close to 0°, by considering the mesomeric form TS2. The observed dependence of the diastereoselectivity on the σ+ Hammett constant of the para substituents further supported the proposed

Revisiting ring-degenerate rearrangements of 1-substituted-4-imino-1,2,3-triazoles

• James T. Fletcher,
• Matthew D. Hanson,
• Joseph A. Christensen and
• Eric M. Villa

Beilstein J. Org. Chem. 2018, 14, 2098–2105, doi:10.3762/bjoc.14.184

• ortho positions (Table 3, entries 1–4) and reaction rates increased with increasing electron-donating character of para substituents (Table 3, entries 5–7). Reaction rates also increased as the size (and corresponding polarizability) of aromatic amines increased (Table 3, entries 8–10). Similar steric

Polysubstituted ferrocenes as tunable redox mediators

• Sven D. Waniek,
• Jan Klett,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2018, 14, 1004–1015, doi:10.3762/bjoc.14.86

• characteristic relationship is supported by correlating the electrochemical data with the Hammett substituent constants [37][39][74][75]. Typically, the E1/2 data of substituted ferrocenes correlate linearly with the sum ∑σp of the Hammett values σp of para-substituents [37][39][74]. For esters 1–4, the

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• were subjected to the reaction with 2a (Scheme 2). Pivalophenone N–H imines bearing a series of para-substituents all participated in the alkenylation reaction to afford the desired products 3ba–ga in good yields. The reaction of m-methyl-substituted imine took place preferentially at the less hindered

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• conformer A, conformer B should be favored. Assisted by the chloride, this species is deprotonated forming the condensation product 4h with an (E)-configured double bond. Obviously, this formal dehydration is possible only in the presence of electron-donating para-substituents in the benzaldehyde. In order

Azirinium ylides from α-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

• Nikolai V. Rostovskii,
• Mikhail S. Novikov,
• Alexander F. Khlebnikov,
• Galina L. Starova and
• Margarita S. Avdontseva

Beilstein J. Org. Chem. 2015, 11, 302–312, doi:10.3762/bjoc.11.35

• depends on the electronic effects of the para substituents in the aryl group of 3-aryl-2H-azirine 1. The [3.2.1] adduct is preferably formed from azirines 1e,f with electron-donating substituents (Table 1, entries 7 and 8), while 3-(4-nitrophenyl)-2H-azirine (1g) provides the [4.3.1] adduct only (Table 1

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• unexpectedly pronounced meta activation of substituted aryl phosphates. A strong ‘meta effect’ resulting in enhanced reaction efficiency by electron withdrawing, meta substituents is contrary to their ground state effects on solvolysis reactions which, instead, display enhanced reactivity for para substituents

A convenient enantioselective decarboxylative aldol reaction to access chiral α-hydroxy esters using β-keto acids

• Zhiqiang Duan,
• Jianlin Han,
• Ping Qian,
• Zirui Zhang,
• Yi Wang and
• Yi Pan

Beilstein J. Org. Chem. 2014, 10, 969–974, doi:10.3762/bjoc.10.95

• groups (Scheme 1, 3b–e). The ortho substituted phenyl α-keto ester gave a lower ee (41%) than those with para substituents (49–84% ee, 3b–e). Aliphatic α-keto esters provided the corresponding aldol products with moderate enantioselectivity (56–77% ee, 3g–i). Also, different β-keto acids 1a–d with

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• , and water or alcohols 38. The scope of the reaction was thoroughly investigated. Thus, methyl aryl diazoacetates and N-aryl aldimines, with electronically diverse metha or para-substituents on the aryl moieties, as well as ethyl 2-diazobutanoate gave good results, only nitro and ortho-substituted aryl

Gold(I)-catalysed one-pot synthesis of chromans using allylic alcohols and phenols

• Eloi Coutant,
• Paul C. Young,
• Graeme Barker and
• Ai-Lan Lee

Beilstein J. Org. Chem. 2013, 9, 1797–1806, doi:10.3762/bjoc.9.209

• shorter reaction times, the Friedel–Crafts allylation intermediates are usually observed. The reaction works with ortho-, meta- and para-substituents as well as electron donating and withdrawing substituents on the phenol, and hydroquinones (Table 2). A variety of allylic alcohol substrates work well

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• , therefore different para-substituents must be introduced through the starting phenol in order to obtain derivatives with different groups at the upper rim. A number of other para-substituted bis(hydroxymethyl)phenols were therefore also cyclized in the presence of methanesulfonic acid (MsOH) or para

Bromine–lithium exchange: An efficient tool in the modular construction of biaryl ligands

• Laurence Bonnafoux,
• Frédéric R. Leroux and
• Françoise Colobert

Beilstein J. Org. Chem. 2011, 7, 1278–1287, doi:10.3762/bjoc.7.148

• of aryllithiums mirrors the effects of ortho, meta, and para substituents to the extent of 36%, 30%, and 25%, respectively [73]. These results explain the difference in regioselectivity of the bromine–lithium exchange, between a bromine atom residing on a phenyl ring that bears a "stabilizing

Electronic differentiation competes with transition state sensitivity in palladium- catalyzed allylic substitutions

• Dominik A. Lange and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2007, 3, No. 36, doi:10.1186/1860-5397-3-36

• -coordination sites are tuned electronically with para-substituents to reveal energetic and geometrical effects on cis- vs. trans- additions of nucleophiles to the Pd-η3-allylic intermediates (Scheme 1). Results and Discussion Electron donating or withdrawing groups (i. e. X, Y = HNMe, H, NO2) in para-positions