An Unexpected α-Oxidation of Cyclic Ketones with 1,4-Benzoquinone by Enol Catalysis.

The first direct and asymmetric α-aryloxylation of cyclic ketones via enol catalysis has been achieved using quinones as the reaction partners. Catalytic amounts of a phosphoric acid promote the exclusive formation of α,α-disubstituted ketones from the corresponding α-substituted ketones in good yields and enantioselectivities (up to 96.5:3.5 er). Preliminary mechanistic experiments suggest that this reaction proceeds via a proton-coupled electron transfer (PCET) followed by radical recombination.

Dynamic kinetic resolution of homoallylic alcohols: application to the synthesis of enantiomerically pure 5,6-dihydropyran-2-ones and δ-lactones.

Dynamic kinetic resolution of various homoallylic alcohols with the use of Candida antarctica lipase B and ruthenium catalyst 2 afforded homoallylic acetates in high yields and with high enantioselectivity. These enantiopure acetates were further transformed into homoallylic acrylates after hydrolysis of the ester function and subsequent DMAP-catalyzed esterification with acryloyl chloride. After ring-closing metathesis 5,6-dihydropyran-2-ones were obtained in good yields. Selective hydrogenation of the carboncarbon double bond afforded the corresponding δ-lactones without loss of chiral information.

Cobalt-catalyzed C-H bond functionalizations with aryl and alkyl chlorides.

Inexpensive cobalt catalysts derived from N-heterocylic carbenes (NHC) allowed efficient catalytic C-H bond arylations on heteroaryl-substituted arenes with widely available aryl chlorides, which set the stage for the preparation of sterically hindered tri-ortho-substituted biaryls. Likewise, challenging direct alkylations with ß-hydrogen-containing primary and even secondary alkyl chlorides proceeded on pyridyl- and pyrimidyl-substituted arenes and heteroarenes. The cobalt-catalyzed C-H bond functionalizations occurred efficiently at ambient reaction temperature with excellent levels of site-selectivities and ample scope. Mechanistic studies highlighted that electron-deficient aryl chlorides reacted preferentially, while the arenes kinetic C-H bond acidity was found to largely govern their reactivity.