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The first examples of calcium-catalyzed aza-Piancatelli reactions between substituted 2-furylcarbinols and aniline derivatives are described. A variety of 4-aminocyclopentenones have been synthesized stereoselectively in high yields. The experimental procedure utilizes simple salts and does not require specific precautions.

The development of a stereoselective aza‐Piancatelli reaction to access 4‐aminocyclopentenones is reported. This transformation relies on the use of chiral o‐sulfinyl anilines as chiral inductors to afford the targeted products in good to excellent yields. Remarkably, the high value‐added cyclopentenones could be obtained in drs up to >95:5, depending upon the furan substitution pattern. [ABSTRACT FROM AUTHOR]

A challenging catalytic hydroarylation of highly electron deficient styrenes has been developed on the basis of efficient cooperation between a calcium(II) triflimide salt and hexafluoroisopropanol (HFIP). This method affords a large variety of diaryl alkanes, notably diaryl ethanes, in good to excellent yields, and is simple to implement and compatible with various functional groups. Furthermore, DFT calculations and deuterium labeling experiments were conducted to elucidate the function of this promoter system. Ca can: Challenging catalytic hydroarylation of highly electron‐deficient styrenes was made possible by efficient cooperation between a calcium(II) triflimide salt and hexafluoroisopropanol (HFIP). This straightforward transformation afforded a large variety of diaryl ethanes with broad functional‐group tolerance (see scheme). [ABSTRACT FROM AUTHOR]

Efficient C−C bond-forming reactions between N,O-acetals and vinylboronic acids were achieved via a calcium(II)-catalyzed formation of a N-acyliminium intermediate or a related ion. This strategy can give a rapid access to a wide variety of alkenyl-functionalized nitrogen-containing compounds in good to excellent yields under simple reaction conditions. [ABSTRACT FROM AUTHOR]

A user-friendly, calcium(II)- and copper(II)-catalyzed one-pot reaction sequence to furnish cyclopenta[ b]pyrroles with a high level of complexity is depicted. The reaction involves the following sequential transformations: (i) an aza-Piancatelli cyclization, (ii) a hydroamination/isomerization process and (iii) a subsequent Friedel-Crafts-type reaction to afford the desired compounds from readily available 2-furylcarbinols, anilines and secondary alcohols with a minimum of precautions. [ABSTRACT FROM AUTHOR]

The aim of this short review is to highlight the interest of using Ca(NTf2)2 as catalyst in C-C and C-X bond-forming reactions. The ability of this complex to activate alcohols, alkenes, ketones, and cyclopropanes towards nucleophilic additions and other chemical processes is shown though a set of selected examples, which illustrate the substrate scope and the synthetic applications offered by this 'green' calcium salt. 1 Introduction 2 Synthetic Applications 3 Conclusion. [ABSTRACT FROM AUTHOR]

An efficient synthesis of polysubstituted 2-alkenylfurans using Ca(NTf2)2/KPF6 as a catalytic mixture is described. It is based on the cycloelimination of readily available propargyl alcohols tethered to β-keto esters under dry conditions to avoid competitive Meyer-Schuster rearrangement. The furan can be further functionalized in situ by a calcium-catalyzed Friedel-Crafts-type reaction with secondary and tertiary alcohols. The title reaction allows for the high-yielding preparation of di-, tri-, and tetrasubstituted 2-alkenylfurans, which are important subunits of bioactive compounds. [ABSTRACT FROM AUTHOR]

A method to extend the scope of the aza-Piancatelli reaction between 2-furylcarbinols and anilines is depicted. We found that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) is the solvent of choice for this transformation, as it outcompetes the usual solvents in terms of rate and yield. Side reactions and other issues raised by the title reaction are prevented, thereby providing an avenue to complex molecules that were previously inaccessible. Lewis acidity studies and computations were carried out to unveil the role of HFIP. Based on these results, we propose that HFIP is, in fact, acting as a Lewis acid and that its acidity can be enhanced when combined with a calcium(II) salt. [ABSTRACT FROM AUTHOR]

The intramolecular condensation of -keto esters to give propargyl alcohols is described. The substrates have two electrophilic sites and two nucleophilic sites. The site selectivity can be fully controlled. In the presence of a calcium-based catalyst and under anhydrous conditions, O-addition products are isolated. On the other hand, traces of water or iPrOH as additive encourage calcium-catalyzed Meyer-Schuster rearrangements. The resulting enones may be further transformed into endo- Michael addition products. The regioselectivity of the attack of the enolate can be changed by using 1-[3,5-bis(trifluoromethyl) phenyl]-3-[2-(dimethylamino)cyclohexyl]thiourea (TUC) as organocatalyst, which promotes the formation of aldol-condensation products of high synthetic interest. DFT calculations rationalize the preference for the aldol condensation when TUC is used instead of the endo-Michael addition. [ABSTRACT FROM AUTHOR]

Direct alkenylation of a variety of alcohols with vinylboronic acids has been accomplished using the airstable calcium(II) complex Ca(NTf2)2 under mild conditions with short reaction times. For reluctant transformations, an ammonium salt was used as an additive to circumvent the reactivity issue. [ABSTRACT FROM AUTHOR]

A highly enantioselective, chiral, Lewis acid calcium-bis(phosphate) complex, Ca[ 3 a] n, which catalyzes the electrophilic amination of enamides with azodicarboxylate derivatives 2 to provide versatile chiral 1,2-hydrazinoimines 4 is disclosed. The reaction gives an easy entry to optically active syn-1,2-disubstituted 1,2-diamines 6 in high yields with excellent enantioselectivities, after a one-pot reduction of the intermediate 1,2-hydrazinoimines 4. The geometry and nature of the N-substituent of the enamide affect dramatically both the reactivity and the enantioselectivity. Although the calcium-bis(phosphate) complex was a uniquely effective catalyst, the exact nature of the active catalytic species remains unclear. NMR spectroscopy and MS analysis of the various calcium complexes Ca[ 3] n reveals that the catalysts exist in various oligomer forms. The present mechanistic study, which includes nonlinear effects and kinetic measurements, constitutes a first step in understanding these calcium-bis(phosphate) complex catalysts. DFT calculations were carried out to explore the mechanism and the origin of the enantioselectivity with the Ca[ 3] n catalysts. [ABSTRACT FROM AUTHOR]

Calcium catalyzed aza-Piancatelli reactions between substituted 2-furylcarbinols and aniline derivatives are described for the first time. [ABSTRACT FROM AUTHOR]

A graphical abstract of the article "Site-Selective Calcium-Catalyzed/Organocatalyzed Condensation of Propargyl Alcohols Tethered to β-Keto Esters" is presented.