1,721,163 research outputs found
Reazioni di Ciclopropanazione di Carbeni Tipo Fischer con Alchilossazoline e Ossirani Litati
No full text
Fast and Slow Racemization of Chiral Lithiated Sulphurated Aryloxiranes: The Influence of TMEDA and the Solvent
No full textRecent Developments in the Lithiation Reactions of Oxygen Heterocycles
No full textThis survey describes how the chemistry of lithiated oxygen heterocycles has been fruitfully exploited, particularly over the last 10 years, for the preparation of more (stereodefined) functionalized derivatives and products derived from them. Also, how they have contributed to natural product synthesis and molecules of relevant pharmaceutical interest. The genesis of the reactive lithiated intermediates (especially alpha- and ortho-lithiated (hetero)arylepoxides, -oxetanes and -tetrahydrofurans) requires a careful choice of the experimental conditions in terms of solvents and temperature in order them to be successfully intercepted by electrophiles. The study of the aggregation and solvation of certain chiral functionalized lithiated oxygen heterocycles has provided further hints about the factors affecting their configurational stability and their carbanionic/carbene-like character, and the way the latter can be finely tuned to facilitate the desired reactivity for synthetic purposes
Synthetic applications of polar organometallic and alkali-metal reagents under air and moisture
Full text linkRecently, there has been an upsurge interest in developing chemoselective and fast processes when working with polar organometallic of s-block and d-block elements and alkali-metal reagents under air and moisture, and also in protic bio-based solvents like Deep Eutectic Solvents or water. A discussion is offered to highlight cutting-edge stoichiometric and catalytic synthetic applications in this evolving field, with an accent over the literature published in the last couple of years
“The Great Beauty” of organolithium chemistry: a land still worth exploring
No full textThis Frontier highlights and analyses, from the authors’ perspective, the impact on organic synthesis of some recent contributions from the organolithium field, also discussing the opportunities that are on the horizon
A Chemo-Enzymatic Approach to the Synthesis of Optically Active 2,4-Disubstituted Aryloxetanes
No full textFunctionalized oxetanes are useful building blocks in the preparative chemistry as well as in synthesis of drugs, materials, agrochemicals [1]. In this communication we report the preliminary results of the first chemo-enzymatic synthesis of optically active 2,4-disubstituted oxetanes, prepared by cyclization of optically active 1,3-diols [2], in turn obtained by steroselective reduction of the corresponding 1,3-diketones with yeasts.
The stereoselective reduction of symmetrical and nonsymmetrical substituted 1,3-diketones was investigated in the presence of some conventional and non-conventional yeast strains (Saccharomyces cerevisiae, Kluyveromyces marxianus, Baker’s yeast, etc.). Optically active aldols were obtained with high stereopreference by baker’s yeast, and then diastereoselectively converted in the corresponding diols (dr> 95%) which were then cyclized into the corresponding 2,4-disubstituted oxetanes in good yields, with high diastereoisomeric ratio (dr) and enantiomeri excess up to 80 %
Deep eutectic solvents and their applications as green solvents
Full text linkSeveral examples illustrate the effectiveness of using Deep Eutectic Solvents (DESs) as environmentally responsible reaction media in polar organometallic chemistry, and in metal- and bio-catalysed processes in place of conventional, often hazardous volatile organic compounds (VOCs). Aside from the standpoint of “greenness”, applications of DESs in the above fields also reveal novel aspects of reactivity of practical significance, which are worthy of an in-depth mechanistic understanding: (a) metal-mediated organic transformations can be run in DESs competitively with protonolysis, often at room temperature and under air; (b) metal-catalysed reactions proceed efficiently and under milder conditions in DESs than in VOCs, with the catalyst and DES being easily and successfully recycled; (c) biocatalysts often exhibit higher stability, selectivity and performances in DES mixtures than in aqueous solutions, and a somewhat intriguing stereoselectivit
- …
