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We have demonstrated that the catalytic and enantioselective vinylcyclopropane‐cyclopentene rearrangement can be carried out on (vinylcyclopropyl)acetaldehydes through activation via enamine intermediates. The reaction makes use of racemic starting materials that, upon ring opening facilitated by the catalytic generation of a donor‐acceptor cyclopropane, deliver an acyclic iminium ion/dienolate intermediate in which all stereochemical information has been deleted. The final cyclization step forms the rearrangement product, showing that chirality transfer from the catalyst to the final compound is highly effective and leads to the stereocontrolled formation of a variety of structurally different cyclopentenes. [ABSTRACT FROM AUTHOR]

The ability of cyclooctatetraene oxide to undergo two sequential ring contraction events under mild conditions, using Brønsted acid catalysis, has been studied in detail. We have found that the selectivity can be controlled by the acidity of the catalyst and by the temperature, being able to obtain selectively either the cycloheptatriene carbaldehyde product, arising from a single ring‐contraction event, or phenylacetaldehyde that is formed after a second ring contraction process. A complete mechanistic picture of the reaction and a rationale behind the influence of the catalyst is provided based on both experimental and computational data. Finally, this acid‐catalyzed ring contraction has been coupled with an in situ enantioselective allylation reaction, delivering enantioenriched cycloheptatrienyl‐substituted homoallylic alcohols when it is carried out in the presence of a chiral phosphoric acid catalyst. These homoallylic alcohols have also been converted into enantioenriched oxaborinanes through copper‐catalyzed nucleophilic borylation/cyclization protocol. [ABSTRACT FROM AUTHOR]

A highly enantio‐ and diastereoselective thiourea‐catalyzed dearomatization of isoquinolines employing N‐tert‐butylhydrazones as neutral α‐azo carbanions and masked acyl anion equivalents has been developed. Experimental and computational data supports the generation of highly ordered complexes wherein the chloride behaves as a template for the catalyst, the hydrazone reagent, and the isoquinolinium cation, providing excellent stereocontrol in the formation of two contiguous stereogenic centers. The ensuing selective and high‐yielding transformations provide appealing dihydroisoquinoline derivatives. [ABSTRACT FROM AUTHOR]

The enantioselective synthesis of tropanols has been accomplished through chiral phosphoric acid catalyzed pseudotransannular ring opening of 1‐aminocyclohept‐4‐ene‐derived epoxides. The reaction proceeds together with the desymmetrization of the starting material and leads to the direct formation of the 8‐azabicyclo[3.2.1]octane scaffold with excellent stereoselectivity. The synthetic applicability of the reaction was demonstrated by the enantioselective synthesis of the two natural products (−)‐α‐tropanol and (+)‐ferruginine. [ABSTRACT FROM AUTHOR]

Abstract: Racemic cyclopropyl ketones undergo enantioselective rearrangement to deliver the corresponding dihydrofurans in the presence of a chiral phosphoric acid as the catalyst. The reaction involves activation of the donor‐acceptor cyclopropane substrate by the chiral Brønsted acid catalyst to promote the ring‐opening event, thus generating a carbocationic intermediate that subsequently undergoes cyclization. Computational studies and control experiments support this mechanistic pathway. [ABSTRACT FROM AUTHOR]

Abstract: In this work, carboxylic acids, which are typically regarded as poor nucleophiles, are demonstrated to be competent reagents to promote the ring‐opening of formylcyclopropanes after activation of the latter through iminium ion formation. Under optimized reaction conditions, a variety of γ‐acyloxy‐substituted aldehydes can be obtained in high yields and enantioselectivities through the desymmetrization of substituted meso‐formylcyclopropanes in the presence of a chiral secondary amine as catalyst. [ABSTRACT FROM AUTHOR]

The enantioselective synthesis of tetralin derivatives bearing a trifluoromethylated all-carbon quaternary stereocenter has been accomplished through a synthetic sequence comprising an organocatalytic β-functionalization of ortho-1-trifluoromethylvinyl-(hetero)aromatic conjugated aldehydes followed by the intramolecular nitrone 1,3-cycloaddition reaction (INCR). Both nitromethane and N-Cbz-hydroxylamine were employed as nucleophiles in the initial organocatalytic conjugate addition step, which provided the chiral information required for the subsequent diastereoselective INCR. Although diastereoselectivity was moderate, good yields and enantioselectivities were, in general, obtained. Interestingly, an inversion of the selectivity in the intramolecular cycloaddition step was observed when either nitromethane or N-Cbz-hydroxylamine was employed. This outcome was studied by means of theoretical calculations, which were in agreement with the experimental results. In addition, the ring opening of the isoxazolidine moiety furnished the corresponding fluorinated diamino alcohols in a very efficient manner. [ABSTRACT FROM AUTHOR]

The reaction of nitrones with enals through iminium activation can be modulated by using cooperative hydrogen-bonding catalysis to induce the participation of a nitrone ylide (C-N-C) instead of the classical C-N-O dipole. As a consequence, N-hydroxypyrrolidines are obtained, rather than the expected isoxazolidines. The reaction proceeds smoothly and high enantioselectivities are observed in all cases. By using the appropriate substrate, polysubstituted pyrrolidines incorporating quaternary stereocenters can be efficiently prepared. [ABSTRACT FROM AUTHOR]

The reaction of aromatic nitroso derivatives with enolizable carbonyl compounds (nitroso aldol reaction) to give either α-hydroxyamino or α-aminoxy carbonyl compounds is an important synthetic method. This review illustrates the recent advances in rendering the process regio- and enantioselective as well as catalytic. By employing metal and organic catalysts a range of α-amino (α-oxyamination) and α-hydroxy (α-aminoxylation) carbonyl derivatives can be generated with total regioselectivity and high levels of enantiomeric excess. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and evaluation of a new highly efficient organocatalyst, namely, (5 S)-2,2,3-trimethyl-5-thiobenzylmethyl-4-imidazolidinone hydrochloride, has been achieved. The catalyst possesses important structural features that should increase the catalytic efficiency and solubility in polar media. The application of the ionic-liquid-supported imidazolidinone catalyst in enantioselective Diels-Alder reactions was investigated. The Diels-Alder reactions of several dienes and dienophiles proceeded efficiently in the presence of the catalyst to provide the desired products in moderate to good yields and from good to excellent enantioselectivities. The conformation study confirms that in the transition state the Re face is shielded completely by the phenyl ring and an approach on the less hindered Si face is preferred. Particularly remarkable is the fact that the entire ionic liquid/HCl 0.01 M/catalyst system can be recovered and reused in up to six runs without an appreciable loss of catalytic activity. [ABSTRACT FROM AUTHOR]

We present here the results obtained in our study on organocatalytic enantioselective Michael addition reaction of acetone to different nitroolefines using (2R,3aS,7aS)-octahydroindole-2-carboxylic acid [(R,S,S)-Oic] as a new and suitable catalyst for this process. Computational calculations support the results obtained with (R,S,S)-Oic versus its diastereomeric form (S,S,S)-Oic. The final products are obtained in good yields and moderate enantioselectivities (up to 58% ee). [ABSTRACT FROM AUTHOR]

We present here the results obtained in our study on organocatalytic enantioselective Michael addition reaction of acetone to different nitroolefines using (2R,3aS,7aS)-octahydroindole-2-carboxylic acid [(R,S,S)-Oic] as a new and suitable catalyst for this process. Computational calculations support the results obtained with (R,S,S)-Oic versus its diastereomeric form (S,S,S)-Oic. The final products are obtained in good yields and moderate enantioselectivities (up to 58% ee). [ABSTRACT FROM AUTHOR]

An abstract of the article "Efficient Organocatalyst Supported on a Simple Ionic Liquid as a Recoverable System for the Asymmetric Diels-Alder Reaction in the Presence of Water" by Antonio De Nino and colleagues is presented.

Abstract: Optically active five-membered cyclic nitrones are readily obtained in a one-pot procedure via the organocatalytic Michael addition of aldehydes to nitroolefins and in situ reductive cyclization. Application of the methodology to the synthesis of tricyclic compounds through intramolecular 1,3-dipolar cycloaddition reactions (DFT calculations have also been performed) is also demonstrated. All the reactions were carried out in water as a solvent and excellent ee values (ee >99%) were obtained. [Copyright &y& Elsevier]