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A novel synthesis of optically active α-arylamino ketones through an organocatalytic enantioselective Amadori-Heyns rearrangement is described.

This concept review describes the recent achievements on the Heyns rearrangement appeared in literature over the last decade and aims to provide the reader with a general overview of the fundamental synthetic advances in this research area. [ABSTRACT FROM AUTHOR]

A general strategy for the synthesis of 2-substituted cyclobutanone sulfides via a tandem Brønsted acid-catalyzed nucleophile addition/ring contraction/C3-C4 ring expansion reaction sequence has been exploited. The procedure led to a wide panel of four-membered cyclic ketones in good to excellent yields and with broad substrate scope. Mechanistic aspects and kinetic parameters were investigated by quantum chemical DFT calculations, allowing us to rationalize the different reactivity of 2-aryl- and 2-alkyl-substituted 2-hydroxycyclobutanones towards thiol nucleophiles in reactions mediated by sulfonic acids. NMR and in situ Raman techniques were employed to better understand the reaction kinetics and parameters that affect the desired outcome. [ABSTRACT FROM AUTHOR]

A synthetically useful Z‐selective cascade formal thiyl radical addition, 1,3‐double bond isomerization, oxygen trapping reaction, can be promoted by Eosin B under visible light, leading to the construction of 2‐aryl‐ and alkylthio enone derivatives in good yields. An accurate study on the reactivity of different thiols and the screening of the reaction conditions, allowed us to extend this reaction to a large number of substrates, showing a good functional groups tolerance while highlighting the limitations of this procedure. Background experiments and mechanistic studies were also. performed to rationalize this cascade process. The usefulness of this methodology was finally demonstrated via the transformation of a series of α‐sulfanyl‐enone adducts through selected oxidation reactions, stereoselective synthesis of cyclopropyl ketones, indanones, and pyrazole compounds. [ABSTRACT FROM AUTHOR]

We have developed one‐step protocols for the preparation of a large selection of α‐aminocyclopropyl ketones or benzo[d]imidazoles, by reacting 2‐substituted‐2‐hydroxycyclobutanones with aryl amines or o‐phenylenediamines, respectively. In most case the reactions proceed at room temperature and are catalyst‐free. The formation of benzo[d]imidazoles is rationalized in terms of an unusual ring‐closure/ring‐fission process followed by aromatization. [ABSTRACT FROM AUTHOR]

The stereoselective solvent-free organocatalyzed aldol reaction of 2-hydroxycyclobutanone with a selection of aromatic aldehydes has been investigated. Using L-threonine (20 mol%), deracemized aldol adducts featuring a chiral quaternary center were obtained in yields up to 72%, with syn selectivity up to 85:15 and ee up to 84%. The title compound has markedly superior reactivity to other a-hydroxy ketones. [ABSTRACT FROM AUTHOR]

L-Tryptophan has been shown to catalyse the enantioselective aldol reaction between 2-hydroxycyclobutanone and an aromatic aldehyde in DMF solution. The reaction is completely regioselective and gives the 2,2-disubstituted cyclobutanone in up to 80% yield. The major adduct is obtained with ee values up to 67%, and has an anti relative configuration which contrasts with the selectivity of organocatalysed aldol reactions conducted on acyclic hydroxyacetone substrates. [ABSTRACT FROM AUTHOR]

An organocatalyzed enantioselective desymmetrization reaction for converting 3-substituted cyclobutanones into 4-substituted 5-hydroxy-γ-lactams is presented. This involves a ring-expanding O-nitroso aldol-cyclization domino sequence. This synthetic protocol provides access to five-membered ring systems in good yields with the generation of two new stereogenic centers. [ABSTRACT FROM AUTHOR]

Abstract: α-Phenoxy- and phenylthio-ketones have been explored as donors and acceptors in organocatalytic aldol reactions. Our studies have revealed effective methodologies for accessing structurally varied and enantiomerically enriched secondary and tertiary phenylthio- and phenoxy-aldols, expanding the scope and potential synthetic utility of organocatalytic direct aldol reactions. [Copyright &y& Elsevier]

The titanium-mediated cyclopropanation of an easily prepared chiral a-siloxylactone leads efficiently to an enantiomerically pure cyclopropanol derivative. The trimethylsilyl trifluoro�methane sulfonate induced pinacol rearrangement allows high level of chirality transfer into a cyclobutanone, which is a useful intermediate in the total synthesis of (+)-grandisol. [ABSTRACT FROM AUTHOR]

A novel metal-free proline-catalyzed protocol is presented for the sulfanylation of cyclic and acyclic ketones by using diphenylsulfides. [ABSTRACT FROM AUTHOR]

Title compounds [(III), (V), and (VIII)] are synthesized in good yields and good enantioselectivities. [ABSTRACT FROM AUTHOR]

Abstract: Herein we report a study on the enantioselective organocatalyzed cross-aldol reaction of 1-benzothiophene and thiophenecarbaldehydes with different ketones. The reactions were conducted at 0°C or room temperature to afford the corresponding adducts in high yields and good to excellent ee using different organocatalysts. Interestingly, using (S)-pyrrolidine tetrazole and acetoxyacetone an inversion of the aldol regiochemistry was observed. [Copyright &y& Elsevier]