Alcohol Etherification via Alkoxy Radicals Generated by Visible-Light Photoredox Catalysis.

A mechanistically divergent method is described that, employing a commercially available hypervalent iodine(III) reagent, generates alkoxy radicals from 1°, 2°, and 3° alcohols and allows their use in the functionalization of C(sp3)-H and C(sp2)-H bonds. This visible-light photoredox catalysis produces alkyl ethers via 1,5/6-hydrogen atom transfer or aryl ethers via 1,5-addition. This mild methodology provides a practical strategy for the synthesis of acetals, orthoesters, tetrahydrofurans, and chromanes.

Palladium-Catalyzed Benzylic Arylation of Pyridylmethyl Silyl Ethers: One-Pot Synthesis of Aryl(pyridyl)methanols.

An efficient palladium-catalyzed direct arylation of pyridylmethyl silyl ethers with aryl bromides is described. A Pd(OAc)2/NIXANTPHOS-based catalyst provides aryl(pyridyl)methyl alcohol derivatives in good to excellent yields (33 examples, 57-100% yield). This protocol is compatible with different silyl ether protecting groups, affording either the protected or the free alcohols in an effective one-pot process. The scalability of the reaction is demonstrated.

Synthesis of oxaspiranic compounds through [3 + 2] annulation of cyclopropenones and donor­acceptor cyclopropanes.

The Sc(OTf)3-catalyzed [3 + 2]-annulation reaction between cyclopropenones and donor­acceptor cyclopropanes is described. The process leads directly to the formation of 4-oxaspiro[2.4]hept-1-ene derivatives in good to excellent reaction yields. Density functional theory calculations suggest that the [3 + 2]-annulation pathway is strongly preferred over the possible [3 + 3]-process.

The photochemical reaction of vinylaziridines and vinylazetidines with chromium(0) and molybdenum(0) (Fischer) carbene complexes.

The [5+2] and [6+2] cycloaddition reactions of vinylaziridines and vinylazetidines with ketenes generated photochemically from chromium(0) and molybdenum(0) Fischer carbene complexes have been investigated. These processes constitute a straightforward and efficient route to azepanones and azocinones, respectively. The peculiar electronic properties of the metalated ketenes allow for the introduction of electron-rich substituents in the final cycloadducts, a difficult task using conventional organic chemistry procedures. The versatility of the process is demonstrated by using Cr(0) Fischer bis(carbene) complexes as metalated bis(ketene) precursors. These species produce tethered bis(azepanone)s in a single step under mild reaction conditions. Density functional theory calculations point to a stepwise reaction pathway through the initial nucleophilic attack of the nitrogen atom of the aziridine on the metalated ketene, followed by ring closure of the zwitterionic intermediate formed.

Regio- and diastereoselective stepwise [8 + 3]-Cycloaddition reaction between tropone derivatives and donor-acceptor cyclopropanes.

A novel SnCl4-catalyzed [8 + 3]-cycloaddition reaction between tropone derivatives and donor-acceptor aminocyclopropanes is described. The process leads to the formation of amino-substituted tetrahydrocyclohepta[b]pyrans with complete regio- and diastereoselectivity. Density functional theory calculations suggest that the cycloaddition occurs stepwise through an aromatic zwitterionic intermediate.

Regioselective and stepwise [8 + 2] cycloaddition reaction between alkynyl-Fischer carbene complexes and tropothione.

The formal [8 + 2] cycloaddition reaction between alkynyl Fischer carbene complexes and tropothione leads to the regioselective formation of novel 3aH-cyclohepta[b]thiophene carbene complexes. Computational DFT calculations indicate that the process proceeds stepwise via antiaromatic zwitterionic intermediates.