[reaction: see text] A sequential acylation-intramolecular cyclopropanation reaction takes place upon treatment of a series of tetraalkylammonium acylchromates with beta,gamma-unsaturated acyl chlorides at -10 degrees C. The reaction leads to 2-oxabicyclo[3.1.0]hexan-3-ones with exo selectivity in good yields. The diastereoselectivity of the reaction allows the preparation of cis-divinyl cyclopropanes, which evolve via Cope sigmatropic reaction toward cycloheptadiene derivatives. Furthermore, the aromatic Cope rearrangement of a series of cis-aryl vinyl cyclopropanes prepared by means of this methodology has been studied.

A cholic acid-based bis-primary amine is capable of promoting the insertion of CO2 into epoxides with the cooperative aid of an iodide anion. This framework is transformed in situ into a bis-carbamic acid. The latter is the active catalytic species, operating through H-bonding interactions. Our system works with complete atom economy, under solvent-free, metal-free, and mild conditions. Also, it can be recycled.

A novel tripodal carbamate-based steroidal architecture works as an efficient catalyst on the Michael-type addition reaction between dimethyl malonate and nitrostyrene. Its action mode has been disclosed by quantum chemical calculations. It comprises the preorganization and confinement of the reagents within the active chiral cavity of the steroid, which are held together by means of cooperative Hbond contacts. Organocatalysis consists in the acceleration of chemical reactions employing small organic frameworks typically assembled from C, H, O, N, S and P atoms. [1] Some privileged structures have been widely used for building up asymmetric organocatalysts: derivatives of 1,2-diamines, 1, BINOL, 2, proline or other natural amino acids, 3, and cinchona alkaloids, 4 (Figure 1). Alternative chiral scaffolds are extensively sought after. Herein we describe the ability of a steroidal platform, based on cholic acid, 5, to work as an enantioselective organocatalyst that makes use of cooperative weak H-bonding interactions.

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Inspired by natural molecular recognition processes, many research efforts have been routed in recent years towards the design of new host-guest molecular systems based on non-covalent interactions. Within this field, 2-aminopyridines (2APs) have been widely studied due to their tunable spectroscopic response in presence of carboxylic acids. Herein, we present and analyze a novel family of 2AP core compounds based on 2phosphorylamidopyridine (2PAP). Linear response timedependent density functional theory (TD-DFT) has been used to characterize and model several spectroscopic properties of 2PAP. Our results, validated through experiments, show that TD-DFT can provide a reliable description of the electronic excited states of these aromatic systems. In addition, we have also studied the amino-imino tautomerization of 2AP and 2PAP under the light of TD-DFT tools. We show that the presence of a carboxylic acid has a catalytic effect on the tautomerization reaction, which otherwise does not occur spontaneously at room temperature. These results suggest that this low-cost computational approach can be applied to more complex organic systems derived from 2-aminopyridine, paving the way for the development of potentially useful sensing materials and organic species for molecular recognition.

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Various additives, typically based on molecules featuring H‐bond donor motifs, have been essayed towards improving the catalytic properties of proline. However, their mode of action is not clear yet. By employing in situ 1H and 19F NMR DOSY experiments, the role of a tetrafluoroborate guanidinium salt in a novel proline‐catalyzed cross‐aldol reaction between α,α‐dichloroacetone and aromatic aldehydes has been fully disclosed.