Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• -substituted iodides as radical precursors and the triethylborane/TBC system as a radical initiator, the authors obtained anti-Markovnikov hydroalkylation products 92 under mild reaction conditions (room temperature and under air atmosphere). Terminal and non-terminal alkenes were successfully functionalized

Amine–borane complex-initiated SF₅Cl radical addition on alkenes and alkynes

• Audrey Gilbert,
• Pauline Langowski,
• Marine Delgado,
• Laurent Chabaud,
• Mathieu Pucheault and
• Jean-François Paquin

Beilstein J. Org. Chem. 2020, 16, 3069–3077, doi:10.3762/bjoc.16.256

• temperatures, which requires the use of air-free techniques in the laboratory. Et3B in the pure form has limited commercial availability and is known to spontaneously react with oxygen to produce a green flame [36]. To avoid the pyrophoric properties of triethylborane, this reagent is mostly sold in low

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• cage escape of the Selectfluor® radical cation to participate in this mechanism, in contrast to cyclic ketones. Under light-free conditions initiated by triethylborane (BEt3), they observed an identical monofluorination selectivity, which suggested the same intermediate (Selectfluor® radical cation) in

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• purification of the desired products. A combination of triethylborane (Et3B) and molecular oxygen can also initiate the reaction at lower temperature (e.g., room temperature), while the employment of Et3B is hampered due to its pyrophoric nature under aerobic conditions as well as undesired Et3B-mediated

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

• SF5X (X = Cl, Br, SF5) across π-bonds. The unconventional conditions usually required were overcome by Dolbier’s elegant triethylborane initiation [21]. Recently, the radical arylation of a SF5-substituted alkene was realized in order to gain access to SF5-containing dihydrobenzofurans and indolines

NMR reaction monitoring in flow synthesis

• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2017, 13, 285–300, doi:10.3762/bjoc.13.31

• . [45], who developed a micro-channelled cell for synthesis and monitoring (MICCS) (Figure 8) and this was integrated into a 500 MHz NMR instrument. The system was used to elucidate the mechanism of the radical addition to an oxime ether with triethylborane (Scheme 1). The use of the NMR micro flow cell

• (a) 9 s and (b) 3 min. Stoichiometry: benzyl alcohol/DIPEA/acetyl chloride 1:1:1.2. Reproduced with permission from reference [44]. Copyright 2009 The American Chemical Society. a) Design of MICCS and b) schematic diagram of MICCS–NMR [45]. CH2Cl2 solutions of oxime ether and triethylborane were

Et₃B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

• Ahlem Abidi,
• Yosra Oueslati and
• Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2402–2409, doi:10.3762/bjoc.12.234

• ; Morita–Baylis–Hillman; palladium; triethylborane; Introduction In nucleophilic allylic substitutions, π-allylpalladium complexes are useful intermediates for the construction of carbon–carbon and carbon–heteroatom bonds in organic synthesis [1]. Usually, palladium species are used as catalysts in the

• to catalyze these reactions by coordination with the hydroxy moiety, thereby increasing its leaving group ability [23][24][25][26][27][28]. Recently, Tamaru and co-workers have intensively investigated the use of triethylborane as an additive with either Pd(PPh3)4 or Pd(OAc)2 as catalysts for the

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• the allylation procedure with the simplest vinyl epoxide to furnish derivative 148. It is interesting to note that the carbon–carbon bond formation takes place in ketoester xanthate 146 on the carbon bearing the least acidic hydrogens. Triethylborane, through its autoxidation, serves to initiate the

Synthesis of compounds related to the anti-migraine drug eletriptan hydrobromide

• Suri Babu Madasu,
• Nagaji Ambabhai Vekariya,
• M. N. V. D. Hari Kiran,
• Badarinadh Gupta,
• Aminul Islam,
• Paul S. Douglas and
• Korupolu Raghu Babu

Beilstein J. Org. Chem. 2012, 8, 1400–1405, doi:10.3762/bjoc.8.162

• formed at 1.0–1.5% during hydrogenation due to hydrolytic cleavage. This impurity is reduced down to 0.25–0.50% during isolation and in further stages. Impurity 5 was prepared by alkylation of N-acetyl bromoindolyl pyrrolidine 10 with triethylborane [15][16][17] in the presence of a catalytic amount of

Discovery of practical production processes for arylsulfur pentafluorides and their higher homologues, bis- and tris(sulfur pentafluorides): Beginning of a new era of “super-trifluoromethyl” arene chemistry and its industry

• Teruo Umemoto,
• Lloyd M. Garrick and
• Norimichi Saito

Beilstein J. Org. Chem. 2012, 8, 461–471, doi:10.3762/bjoc.8.53

• , phenylsulfur pentafluoride was prepared by reaction of 1,4-bis(acetoxy)-2-cyclohexene with SF5Br under 250 W sunlamp irradiation, followed by dehydrobromination and then aromatization reactions [36]. A triethylborane-catalyzed reaction of 4,5-dichloro-1-cyclohexene with SF5Cl followed by dehydrochlorination

Amines as key building blocks in Pd-assisted multicomponent processes

• Didier Bouyssi,
• Nuno Monteiro and
• Geneviève Balme

Beilstein J. Org. Chem. 2011, 7, 1387–1406, doi:10.3762/bjoc.7.163

• species with a boronic acid or triethylborane, followed by a reductive elimination, afforded the indenamine core in good to excellent yields. However, this Pd-catalyzed cyclization was only effective for aldehydes since ketones did not participate in the process (Scheme 6). Tsukamato extended this

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• efficient C3-selective allylation [82]. Employing free allyl alcohols and a combination of 5 mol% of Pd(PPh3)4 and 30 mol% triethylborane as catalyst, the desired 3-allylated indoles were isolated in excellent yields (Scheme 29). Electron withdrawing as well as electron donating groups were well tolerated

• the indole moiety, this method led to a convenient stereoselective synthesis of a highly substituted pyrroloindole framework 74 (Scheme 30); however, equimolar amounts of triethylborane were necessary. An improved FC allylation of indoles with allyl alcohols was developed recently by Breit et al

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

Part 3. Triethylborane- air: a suitable initiator for intermolecular radical additions of S-2-oxoalkyl- thionocarbonates (S-xanthates) to olefins

• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 47, doi:10.1186/1860-5397-3-47

• triethylborane-air combination proves to be an efficient radical initiator that allows intermolecular radical additions of S-2-oxoalkyl-thionocarbonates (S-xanthates) to olefins. Depending on both the structures of the xanthate and the olefin, the addition process can be achieved at room temperature or slightly

• higher. Background Alkylboranes, mainly triethylborane, have become more and more popular as radical initiators because of their ability to generate alkyl radicals by reaction with dioxygen (or air) even at very low temperature (–78°C). [1][2][3][4] To the best of our knowledge, only one attempt to use

• additions of various S-alkylxanthates to vinyl epoxides and related derivatives using an excess of triethylborane (2 equiv vs xanthate) at room temperature. The mechanism is different from that reported in this note as the radical chain is maintained by the ring opening of the oxirane that produces an

Part 2. Mechanistic aspects of the reduction of S-alkyl- thionocarbonates in the presence of triethylborane and air

• Florent Allais,
• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 46, doi:10.1186/1860-5397-3-46

• Materials, 3B, Quang Trung, Hanoi, Vietnam 10.1186/1860-5397-3-46 Abstract Experiments conducted with deuterated compounds demonstrated that during the reduction of S-alkylxanthates with triethylborane, the hydrogen atom transferred has several competing origins. Hydrogen abstraction from water (or an

• Supporting Information File 1]. When xanthate 1a was reacted with perdeuterated triethylborane (5 equiv), an 8.3% incorporation of deuterium was observed in the resulting reduced compounds 1b + 1c (Table 3, entry 1). This result is perfectly reproducible as shown by comparison of entries 1 and 2. When the

• presence of deuterated triethylborane. Therefore, one must assume that the deuterium transfer occurs directly from Et3B-d15 to the transient carbon radical formed by fragmentation of the xanthate function in compound 1a. Interestingly, the deuterium abstraction occurs not only from the methylene group as