Total synthesis of grayanane natural products

• Nicolas Fay,
• Rémi Blieck,
• Cyrille Kouklovsky and
• Aurélien de la Torre

Beilstein J. Org. Chem. 2022, 18, 1707–1719, doi:10.3762/bjoc.18.181

• -membered ring closure through a SmI2-promoted pinacol coupling. This reaction had been previously described by the same group and proved to be highly effective [23]. For rings A, C and D, other SmI2-promoted steps were employed, giving respectively the cyclopentane A ring moiety and the bicyclo[3.2.1

• suitable starting material for the SmI2-promoted pinacol coupling, directed by the free hydroxy group, affording a complete selectivity in the formation of the 7-membered ring B. The synthesis of grayanotoxin III was then achieved by acetylation of the secondary alcohols, oxidative cleavage of the MOM

Electrochemical formal homocoupling of sec-alcohols

• Kosuke Yamamoto,
• Kazuhisa Arita,
• Masashi Shiota,
• Masami Kuriyama and
• Osamu Onomura

Beilstein J. Org. Chem. 2022, 18, 1062–1069, doi:10.3762/bjoc.18.108

• Kosuke Yamamoto Kazuhisa Arita Masashi Shiota Masami Kuriyama Osamu Onomura Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan 10.3762/bjoc.18.108 Abstract Electrochemical pinacol coupling of carbonyl compounds in an undivided cell with a

• electrolysis; Introduction Carbon–carbon bond formation is one of the most fundamental and important reactions in synthetic organic chemistry. Reductive coupling of carbonyl compounds known as pinacol coupling would be a powerful method to construct vic-1,2-diol scaffolds through C–C bond formation [1][2

• ]. Such scaffolds are widely utilized as versatile building blocks in the synthesis of biologically active compounds [3][4][5][6][7], chiral auxiliaries [8][9], and chiral ligands [10][11][12][13]. Traditional pinacol coupling reactions are performed with a stoichiometric or even excess amount of low

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• biradical intermediate may lead to all four conformations. Photolysis products of benzaldehyde (8) in different solvents. a) In benzene or ethanol. b) In hex-1-yne. N-tert-Butylbenzamide formation proceeds via a benzoyl radical. Photochemical pinacol coupling. Photochemical ATRA catalyzed by 4-anisaldehyde

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• % isolated yield. In 2019, Collins and co-workers reported the synthesis of a new bifunctional copper photocatalyst for the reductive pinacol coupling of ketones and aldehydes (Scheme 33) [50]. This new catalyst was designed to activate the ketones or aldehydes due to an acidic proton present on the

• avoided the presence of a Brønsted acid in the reaction media. As such, Collins and co-workers developed the catalyst [Cu(I)(pypzs)(BINAP)]BF4 where the ligand (5-(4-fluorosulfonyl)amino-3-(2pyridyl)pyrazole)) (pypzs) had an acidic proton prone to activate the carbonyl group during the pinacol coupling

• lactone synthesis using a copper-photocatalyzed PCET reaction. Photocatalytic Pinacol coupling reaction catalyzed by [Cu(I)(pypzs)(BINAP)]BF4. The ligands of the copper complex are omitted for clarity. Azide photosensitization using a Cu-based photocatalyst. Funding This work was partially supported by

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• conversion to the diastereomer by oxidation and reduction. Conformational analysis of some of the resulting diols obtained under McMurry conditions was complicated by the presence of several conformers of similar energy. The pinacol coupling appears to start at the ketone, as indicated by the selective

• carbinols afforded novel allene systems. Our study may be of help towards the total synthesis of solenopodin or klysimplexin derivatives. Keywords: conformational analysis; low valent titanium; marine natural products; pinacol coupling; ten-membered rings; Introduction Eunicellane-type diterpenoids share

• have also been obtained (TiCl4/Zn [12][13][14][15][16][17] or TiCl3/Zn-Cu [18][19][20]), often as mixture of diastereomers. The use of samarium diiodide to achieve the pinacol coupling was not advised, since we had observed that intially formed ketyl radicals would add to the alkyne moiety [11], even

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Solvent-free sonochemistry: Sonochemical organic synthesis in the absence of a liquid medium

• Deborah E. Crawford

Beilstein J. Org. Chem. 2017, 13, 1850–1856, doi:10.3762/bjoc.13.179

• a decrease of their reaction times from >10 hours to 1–2 hours. Also, in some cases sonication greatly improved the yield, for example in a Vilsmeier–Haack reaction [21]; in addition selectivity can also be improved as demonstrated in a Pinacol coupling whereby a meso-isomer was the dominant product

Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route

• Felicia D’Andrea,
• Giorgio Catelani,
• Lorenzo Guazzelli and
• Venerando Pistarà

Beilstein J. Org. Chem. 2016, 12, 2343–2350, doi:10.3762/bjoc.12.227

• -promoted [28][29][30] pinacol coupling of dialdehyde derivatives). A strategy related to the latter approach relies on a base-promoted aldol condensation of aldohexos-5-uloses followed by reduction of the carbonyl group, as reported in the retrosynthetic Scheme 1. This method again uses sugars as starting

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• followed by deoxygenation which finally gave the paracyclophane 108 (85%, Scheme 15). Pinacol coupling: Kanomata and co-workers [123] have reported the synthesis of the cyclophane 112 by using pinacol coupling [124] mediated by SmI2. A double Sonogashira reaction of 1,4-diiodobenzene (109) with 4-pentyn-1

• -ol (110) generates the diyne product in quantitative yield. Next, the in situ prepared diyne was subjected to hydrogenation followed by oxidation with PCC which gave the dialdehyde 111 (85%). The pinacol coupling of the dialdehyde 111 in the presence of Sm2+ and HMPA generated the cyclophane 112 in a

Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

• Axel G. Griesbeck and
• Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

• coupling is the dominant process for semiconductor catalysis and ketone reduction dominates the Ti(OiPr)4/methanol or isopropanol systems. Application of dilution effects on the TiO2 catalysis leads to an increase in hydroxymethylation at the expense of the pinacol coupling. Keywords: alkylation; carbonyl

• -catalyzed photohydroxymethylation of ketones by methanol were investigated in order to evaluate the most active photocatalyst system. Dialkoxytitanium dichlorides are the most efficient species for chemoselective hydroxymethylation of acetophenone as well as other aromatic and aliphatic ketones. Pinacol