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A readily accessible conjugate‐base‐stabilized carboxylic acid (CBSCA) catalyst facilitates highly enantioselective [4+2] cycloaddition reactions of salicylaldehyde‐derived acetals and cyclic enol ethers, resulting in the formation of polycyclic chromanes with oxygenation in the 2‐ and 4‐positions. Stereochemically more complex products can be obtained from racemic enol ethers. Spirocyclic products are also accessible.

 

A readily accessible conjugate‐base‐stabilized carboxylic acid (CBSCA) catalyst facilitates highly enantioselective [4+2] cycloaddition reactions of salicylaldehyde‐derived acetals and cyclic enol ethers, resulting in the formation of polycyclic chromanes with oxygenation in the 2‐ and 4‐positions. Stereochemically more complex products can be obtained from racemic enol ethers. Spirocyclic products are also accessible.

 

Two new Ce IV /O 2− clusters, (pyH) 8 [Ce 10 O 4 (OH) 4 (O 3 PPh) 12 (NO 3 ) 12 ] (1) and [Ce 6 O 4 (OH) 4 (O 2 PPh 2 ) 4 (O 2 C t Bu) 8 ] (2), have been prepared that contain P-based ligands for the first time. They were obtained from the reaction of (NH 4 ) 2 [Ce(NO 3 ) 6 ], PhPO 3 H 2 or Ph 2 PO 2 H, and t BuCO 2 H in a 2 : 1 : 2 molar ratio in pyridine/MeOH (10 : 1 mL). Both compounds contain a {Ce 6 O 4 (OH) 4 } face-capped octahedral core, with 1 containing an additional four Ce IV on the outside to give a supertetrahedral Ce 10 topology; the {Ce 6 O 8 } unit is the smallest recognizable fragment of the fluorite structure of CeO 2 . The HO˙ radical scavenging activities of 1 and 2 were measured by UV/vis spectral monitoring of methylene blue oxidation by HO˙ radicals in the presence and absence of the Ce/O clusters, and the results compared with those for larger Ce 24 and Ce 38 molecular nanoparticles of CeO 2 prepared in previous work. 1 and 2 are both very poor HO˙ radical scavengers compared with Ce 24 and Ce 38 , a result that is consistent with reports in the literature that PO 4 3− ions inhibit the radical scavenging ability of traditional CeO 2 nanoparticles and putatively assigned to PO 4 3− binding to the surface.