2D covalent organic frameworks (COFs) with flexible urea linkages have been synthesized by condensation of 1,3,5-triformylphloroglucinol (TFP) with 1,4-phenylenediurea (BDU) or 1,1′-(3,3′-dimethyl-[1,1′biphenyl]-4,4′-diyl)diurea (DMBDU). The resulting COF-117 and COF-118 undergo reversible structural dynamics within their layers, in response to inclusion and removal of guest molecules, emanating from urea CN bond rotation and interlayer hydrogen-bonding interactions. These compounds are the first urea-linked COFs, serving to expand the scope of reticular chemistry.

Ester-linked, crystalline, porous, covalent organic frameworks (COFs) have been synthesized and structurally characterized. Transesterification reactions between di-topic 2-pyridinyl aromatic carboxylates and tri-or tetra-topic phenols gave the corresponding ester-linked COFs. They crystallize as 2D structures in kgm (COF-119) and hcb (COF-120, 121, 122) topologies with surface areas of up to 2,092 m 2 /g. Notably, crystalline COF-122 comprises edges spanning over 10 phenylene units; an aspect had only been achieved in metal-organic frameworks. This work expands the scope of reticular chemistry to include for the first time crystalline ester-linked COFs, related to common polyesters.

Two catalysts, an amine HCl salt and a bisthiourea, work in concert to enable the generation of oxocarbenium ions under mild conditions. The amine catalyst generates an iminium ion of sufficient electrophilicity to enable 1,2-attack by an alcohol. Catalyst turnover is achieved by amine elimination with concomitant formation of an oxocarbenium intermediate. The bisthiourea catalyst accelerates all of the steps of the reaction and controls the stereoselectivity via anion binding/ion pair formation. This new concept was applied to direct catalytic enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes.

Pyrrolidine and related amines undergo asymmetric A(3) reactions in the presence of copper iodide and an easily accessible cocatalyst possessing both a carboxylic acid and a thiourea moiety. Propargylamines are obtained with up to 96% ee, and catalyst loadings can be as low as 1 mol %. Pyrrolidine-derived propargylamines, in the absence of directing groups, can be transformed to the corresponding allenes without loss of enantiopurity.

Reductive condensations of alcohols with aldehydes/ketones to generate ethers are catalyzed by a readily accessible thiourea organocatalyst that operates in combination with HCl. 1,1,3,3-tetramethyldisiloxane serves as a convenient reducing reagent. This strategy is applicable to challenging substrate combinations and exhibits functional group tolerance. Competing reductive homocoupling of the carbonyl component is suppressed.

SummaryCopper(II) acetate/acetic acid/O2 and potassium iodide/tert-butylhydroperoxide systems are shown to affect the selective oxidation of ring-fused aminals to dihydroquinazolines and quinazolinones, respectively. These methods enable the facile preparation of a number of quinazoline alkaloid natural products and their analogues.

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Acyclic ketone-derived oxocarbenium ions are involved as intermediates in numerous reactions that provide valuable products,h owever,t hey have thus far eluded efforts aimed at asymmetric catalysis.W er eport that ar eadily accessible chiral carboxylic acid catalyst exerts control over asymmetric cyclizations of acyclic ketone-derived trisubstituted oxocarbenium ions,t herebyp roviding access to highly enantioenriched dihydropyran products containing atetrasubstituted stereogenic center.T he high acidity of the carboxylic acid catalyst, whiche xceeds that of the well-known chiral phosphoric acid catalyst TRIP,i sl argely derived from stabilization of the carboxylate conjugate base through intramolecular anion-binding to athiourea site.