Supramolecular approaches to mediate chemical reactivity

• Pablo Ballester,
• Qi-Qiang Wang and
• Carmine Gaeta

Beilstein J. Org. Chem. 2022, 18, 1463–1465, doi:10.3762/bjoc.18.152

• capsule can catalyze the cyclization of (S)-citronellal forming isopulegol. In this study it was exploited the ability of the resorcinarene capsule to work as a Brønsted acid catalyst, and its aptitude to stabilize cationic intermediates and transition states inside the cavity. Velmurugan, Hu and co

Inductive heating and flow chemistry – a perfect synergy of emerging enabling technologies

• Conrad Kuhwald,
• Sibel Türkhan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2022, 18, 688–706, doi:10.3762/bjoc.18.70

• temperature control can be ensured, e.g., by IR pyrometers. 2.2 Application of trickle bed reactor systems for isopulegol production Berenguer-Murcia et al. [25] developed a near isothermal micro trickle bed reactor operated by radiofrequency (RF; 300 kHz) heating of nickel ferrite particles (110 µm

• particle size of 110 µm. Conventionally heated trickle bed reactors using externally located heating devices suffer from uneven temperature distribution in the reactor bed and the formation of hot spots that can lead to rapid deactivation of the catalyst. The authors selected the synthesis of isopulegol (2

• ) from citronellal (1) as test reaction (Scheme 1). Thus, citronellal (1) was cyclized to isopulegol in the heating zone. This was achieved at 80 °C in 1,4-dioxane using a Zeolite-encapsulated magnetic nickel ferrite nanoparticles (NiFe2O4@TiO2@ZSM-5) catalyst, an aluminosilicate zeolite, which gave best

A resorcin[4]arene hexameric capsule as a supramolecular catalyst in elimination and isomerization reactions

• Tommaso Lorenzetto,
• Fabrizio Fabris and
• Alessandro Scarso

Beilstein J. Org. Chem. 2022, 18, 337–349, doi:10.3762/bjoc.18.38

• series of reactions like the carbonyl–ene cyclization of (S)-citronellal preferentially to isopulegol, the water elimination from 1,1-diphenylethanol, the isomerization of α-pinene and β-pinene preferentially to limonene and minor amounts of camphene. The role of the supramolecular catalyst consists in

• the vinylic hydrogen atoms of the isopulegol obtained in higher amount with respect to neoisopulegol (Figure 1 and Table 1, entry 1). In order to achieve larger substrate conversion, the reaction was repeated for 72 h at 60 °C observing almost complete substrate conversion and high isopulegol to

• and 4). The reaction promoted by acetic acid (4) as purely Brønsted acid led to comparable conversion of the substrate with respect to the use of 16, albeit with much similar product distribution between isopulegol and neoisopulegol, even extending the reaction time up to 72 h at 60 °C (Table 1

Solvent-free synthesis of novel para-menthane-3,8-diol ester derivatives from citronellal using a polymer-supported scandium triflate catalyst

• Lubabalo Mafu,
• Ben Zeelie and
• Paul Watts

Beilstein J. Org. Chem. 2016, 12, 2046–2054, doi:10.3762/bjoc.12.193

• -diol (3) [1][2]. These chemical derivatives have a wide range of uses in pharmaceuticals, cosmetics, toothpastes, insect repellents, cleaning agents and other products [3]. The synthesis of menthol involves the acid-catalysed cyclisation of 1 to form isopulegol 4 as a stable intermediate. The latter is

A practical way to synthesize chiral fluoro-containing polyhydro-2H-chromenes from monoterpenoids

• Oksana S. Mikhalchenko,
• Dina V. Korchagina,
• Konstantin P. Volcho and
• Nariman F. Salakhutdinov

Beilstein J. Org. Chem. 2016, 12, 648–653, doi:10.3762/bjoc.12.64

• -fluorohexahydro-2H-chromenes under the developed conditions, the reaction occurs with inversion of configuration. Keywords: chirality; fluorine; halo-Prins reaction; isopulegol; monoterpene; Introduction Recently, we have found that a reaction between para-mentha-6,8-dien-2,3-diol (1) and aromatic aldehydes in

• acts both as a catalyst and as a fluorine source. At the same time, as a rule, reactions in the presence of BF3·Et2O involved relatively simple homoallylic alcohols, such as but-3-en-1-ol (3) and its analogues, as substrates (Scheme 2). If more complex substrates, such as isopulegol (4) or geraniol (5

• epimeric ratio would be consistent with a stereoselective aspect to the conversion. Further experimentation is therefore needed to elucidate the precise mechanistic details of this reaction. Isopulegol (4), like diol 1, has a hydroxy group and an isopropenyl group at the 1- and 2-positions; these two

Stereoselective synthesis of hernandulcin, peroxylippidulcine A, lippidulcines A, B and C and taste evaluation

• Marco G. Rigamonti and
• Francesco G. Gatti

Beilstein J. Org. Chem. 2015, 11, 2117–2124, doi:10.3762/bjoc.11.228

• synthesis of the latter on a multigram scale. Few years ago we have reported a new stereospecific synthesis of (+)-hernandulcin [9] starting from the very cheap commercially available (+)-isopulegol. Mori [10][11] and Cheon [12][13] reported some syntheses of 1. They epoxidized the side-chain olefinic

• double bonds of (+)-limonene or (−)-isopulegol with m-chloroperbenzoic acid (MCPBA) to introduce the stereogenic center at the C(2’) position. Unfortunately both methods were only modestly stereoselective and resulted in mixtures of the respective epoxides. These results implied a not simple column

• the synthesis optimisation of the key intermediate 4 that can be prepared starting from (−)-isopulegol by two different approaches: i) oxidation of the hydroxy group to give (S)-isopulegone, which in turn is reduced stereospecifically into the desired cis diastereoisomer; or ii) by inversion of C(1

A concise enantioselective synthesis of the guaiane sesquiterpene (−)-oxyphyllol

• Martin Zahel and
• Peter Metz

Beilstein J. Org. Chem. 2013, 9, 2028–2032, doi:10.3762/bjoc.9.239

• from (−)-isopulegol [5]. Remarkably, its cinnamate [(−)-9-deoxyenglerin A] displayed a cytotoxic activity in the μM range against several cancer cell lines [5]. Herein we report a concise enantioselective access to (−)-oxyphyllol (1) in a few preparatively simple operations. Results and Discussion

• Recently, we developed an efficient access to the anticancer guaiane (−)-englerin A (5) starting from (−)-photocitral A (6), which in turn can be prepared in only 2 steps from commercially available (−)-isopulegol through dual catalysis [6]. Due to the structural similarity of the hydroazulene core in