Largely Entangled Diamondoid Framework with High-Density Urea and Divergent Metal Nodes for Selective Scavenging of CO2 and Molecular Dimension-Mediated Size-Exclusive H-Bond Donor Catalysis

Pore environment modulation with high-density polarizing groups in metal-organic frameworks (MOFs) can effectively accomplish selective and multicyclic carbon dioxide (CO₂) adsorption, whereas the incorporation of task-specific organic sites inside these porous vessels promise to evade self-quenching, solubility, and recyclability issues in hydrogen-bond donating (HBD) catalysis. However, concurrent amalgamation of both these attributes over a single platform is rare but extremely demanding in view of sustainable applications. We designed a robust diamondoid framework CSMCRI-17 (CSMCRI = Central Salt and Marine Chemicals Research Institute) from the mixed-ligand assembly of azo group-containing dicarboxylate ligand, urea-functionalized pyridyl linker, and Zn(II) nodes with specific divergent coordination. Seven-fold interpenetration to the microporous structure largely augments N-rich functionality that facilitates high CO₂ uptake in the activated form (17a) with good CO₂ selectivity over N₂ and CH₄ that outperform many reported materials. The framework displays very strong CO₂ affinity and no reduction in adsorption capacity over multiple uptake-release cycles. Benefitting from the pore-wall decoration with urea functionality from the pillaring strut, 17a further demonstrates hydrogen-bond-mediated Friedel-Crafts alkylation of indole with β-nitrostyrene under mild conditions, with multicyclic usability and excellent reactivity toward wide ranges of substituted nucleophiles and electrophiles. Interestingly, interpenetration-generated optimum-sized pores induce poor conversion to sterically encumbered substrate via molecular dimension-mediated size selectivity that is alternatively ascribed from additional control experiments and support the occurrence of HBD reaction within the MOF cavity. The catalytic path is detailed in light of the change of emission intensity of the framework by the electrophile as well as the judicious choice of the substrate, which authenticates the prime role of urea moiety-governed two-point hydrogen bonding.

Urea derivative organocatalyzed enantioselective Friedel-Crafts alkylation of α-naphthols with isatins

An organocatalytic enantioselective Friedel-Crafts alkylation of α-naphthols with isatin derivatives was catalyzed by Takemoto-type urea catalyst to give optical active 3-(naphthalen-2-yl)-3-hydroxy-2-oxindoles in 75%-92% yields with up to 95% enantiomeric excess (ee) value. The catalyst type and the substrate scope were broadened in this methodology.

Diastereoselective 1,6-Addition of α-Phosphonyloxy Enolates to para-Quinone Methides

The addition of α-ketoamide to p-quinone methide initiated by dialkylphosphite in the presence of organic base 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) is explored. Coupling of dialkylphosphites to α-ketoamides in the presence of a base follows [1,2]-phospha-Brook rearrangement, generating corresponding α-phosphonyloxy enolates that are subsequently seized by p-quinone methides (p-QMs). The two-step one-pot 1,6-conjugate addition provides effective access to a series of isatin-incorporated phosphate-bearing 1,6-adducts having two vicinal tertiary carbons with up to 90% yield and >20:1 dr.

Urea-engineering mediated hydrogen-bond donating Friedel−Crafts alkylation of indoles and nitroalkenes in dual-functionalized and microporous metal-organic framework with high recyclability and pore-fitting-induced size-selectivity

As an effective alternative to Lewis acid activation, hydrogen-bond donating (HBD) organo-catalysis denotes a powerful construction tool to important classes of carbon–carbon bonds, wherein metal-organic frameworks (MOFs) alleviate issues like...

Enantioselective Friedel-Crafts reaction of hydroxyarenes with nitroenynes to access chiral heterocycles via sequential catalysis

Naphthols, hydroxyindoles and an activated phenol are reacted with differently substituted (E)-nitrobut-1-en-3-ynes using the commercially available Rawal's chiral squaramide. The corresponding β-nitroalkynes were obtained with good yields and excellent enantioselectivities. Moreover, dihydronaphthofurans can be accessed via silver catalysed cyclization in a tandem one-pot procedure, with high preservation of the optical purity.

Catalytic dehydrogenative aromatization of cyclohexanones and cyclohexenones

Prompted by the scant attention paid by published literature reviews to the comprehensive catalytic dehydrogenative aromatization of cyclohexa(e)nones, this review describes recent methods developed to-date involving transition-metal-catalyzed oxidative aromatization and metal-free strategies for the transformation of cyclohexa(e)nones to substituted phenols.

Tryptophan/copper-catalyzed aromatization reaction of chiral cyclohexanones to phenols

By merging organocatalysis with copper catalysis, a highly efficient stereospecific approach for the synthesis of chiral phenols from cyclohexanones has been developed for the first time. The aromatization reaction proceeds through the in situ formation of enone intermediates and further subsequent bromination/dehydrobromination reactions. And a series of functionalized phenol derivatives are obtained in good yields (up to 89%) and good to excellent enantioselectivities (up to 99% ee).

A highly enantioselective Friedel–Crafts reaction of 3,5-dimethoxylphenol with nitroolefins mediated by a bifunctional quinine derived thiourea catalyst

A useful and highly enantioselective Friedel–Crafts reaction of 3,5-dimethoxylphenol with nitroolefins catalyzed by a bifunctional quinine derived thiourea catalyst was developed.

Turning on catalysis: incorporation of a hydrogen-bond-donating squaramide moiety into a Zr metal-organic framework

Herein, we demonstrate that the incorporation of an acidic hydrogen-bond-donating squaramide moiety into a porous UiO-67 metal-organic framework (MOF) derivative leads to dramatic acceleration of the biorelevant Friedel-Crafts reaction between indole and β-nitrostyrene. In comparison, it is shown that free squaramide derivatives, not incorporated into MOF architectures, have no catalytic activity. Additionally, using the UiO-67 template, we were able to perform a direct comparison of catalytic activity with that of the less acidic urea-based analogue. This is the first demonstration of the functionalization of a heterogeneous framework with an acidic squaramide derivative.

Catalyst-controlled regio- and stereoselective synthesis of diverse 12H-6,12-methanodibenzo[d,g][1,3]dioxocines

Regio- and stereoselective synthesis of 12H-6,12-methanodibenzo[d,g][1,3]dioxocines has been accomplished by the EDDA and PTSA-catalyzed cascade reactions of resorcinols and 2-hydroxychalcones.

Dynamic asymmetric organocatalysis: cooperative effects of weak interactions and conformational flexibility in asymmetric organocatalysts

This review describes recent advances by our research group in the design and applications of conformationally flexible guanidine/bisthiourea organocatalysts to facilitate unique bond-forming processes, including retro-free, enantiodivergent, entropy-controlled, and cycle-specific organocatalysis. Special emphasis is placed on the key requirements to attain high selectivity and on functional switching by exploiting the structural flexibility of our organocatalysts.