Copper-Catalyzed Asymmetric Oxidation of Sulfides

Copper-catalyzed asymmetric sulfoxidation of aryl benzyl and aryl alkyl sulfides, using aqueous hydrogen peroxide as the oxidant, has been investigated. A relationship between the steric effects of the sulfide substituents and the enantioselectivity of the oxidation has been observed, with up to 93% ee for 2-naphthylmethyl phenyl sulfoxide, in modest yield in this instance (up to 30%). The influence of variation of solvent and ligand structure was examined, and the optimized conditions were then used to oxidize a number of aryl alkyl and aryl benzyl sulfides, producing sulfoxides in excellent yields in most cases (up to 92%), and good enantiopurities in certain cases (up to 84% ee)

Asymmetric Synthesis of <i>cis</i>-7-Methoxycalamenene via the Intramolecular Buchner Reaction of an α-Diazoketone

The asymmetric synthesis of <i>cis</i>-7-methoxycalamenene <b>1</b> has been accomplished using the intramolecular Buchner reaction of α-diazoketone <b>7</b> as the key step in the synthetic route. Upon reduction of the equilibrating azulenone structure <b>8</b>, the resulting azulenol <b>9</b> rearranges to dihydronaphthalene <b>10</b> containing the 6,6-membered bicyclic ring system characteristic of <b>1</b>, by means of an acid-catalyzed aromatization process. Transformation of <b>10</b> to <b>1</b> is accomplished through a three-step reaction sequence

Desymmetrization by asymmetric copper-catalyzed intramolecular C–H insertion reactions of α-diazo-β-oxosulfone

Effective desymmetrization in copper-catalyzed intramolecular C–H insertion reactions of α-diazo-β-oxosulfones in the formation of fused thiopyran dioxides is described for the first time. The use of a copper–bis(oxazoline)–NaBARF catalyst complex system leads to formation of the major thiopyran dioxide stereoisomer with up to 98:2 dr and up to 98% ee. The effect of varying the bis(oxazoline) ligand, copper salt, and site of C–H insertion on both diastereo- and enantioselectivities of these intramolecular C–H insertion reactions has been investigated. Similarly, desymmetrization in the formation of a fused cyclopentanone proceeds with up to 64% ee. These results represent the highest enantioselectivity reported to date in a copper-mediated desymmetrization through C–H insertion