Scalable Synthesis of Enantiopure Bis-3,4-diazaphospholane Ligands for Asymmetric Catalysis.

An optimized route to enantiopure tetra-carboxylic acid and tetra-carboxamide bis(diazaphospholane) ligands that obviates chromatographic purification is presented. This synthesis, which is demonstrated on 15 and 100 g scales, features a scalable classical resolution of tetra-carboxylic acid enantiomers with recycling of the resolving agent. When paired with a rhodium metal center, these bis(diazaphospholane) ligands are highly active and selective in asymmetric hydroformylation applications.

KetoABNO/NOx Cocatalytic Aerobic Oxidation of Aldehydes to Carboxylic Acids and Access to α-Chiral Carboxylic Acids via Sequential Asymmetric Hydroformylation/Oxidation.

A method for aerobic oxidation of aldehydes to carboxylic acids has been developed using organic nitroxyl and NOx cocatalysts. KetoABNO (9-azabicyclo[3.3.1]nonan-3-one N-oxyl) and NaNO2 were identified as the optimal nitroxyl and NOx sources, respectively. The mildness of the reaction conditions enables sequential asymmetric hydroformylation of alkenes/aerobic aldehyde oxidation to access α-chiral carboxylic acids without racemization. The scope, utility, and limitations of the oxidation method are further evaluated with a series of achiral aldehydes bearing diverse functional groups.

Asymmetric hydroformylation of Z-enamides and enol esters with rhodium-bisdiazaphos catalysts.

Asymmetric hydroformylation (AHF) of Z-enamides and Z-enol esters provides chiral, alpha-functionalized aldehydes with high selectivity and atom economy. Rh-bisdiazaphospholane catalysts enable hydroformylation of these challenging disubstituted substrates under mild reaction conditions and low catalyst loadings. The synthesis of a protected analog of l-DOPA demonstrates the utility of AHF for enantioselective, atom-efficient synthesis of peptide precursors.

Four novel spirooxazacamphorsultam derivatives.

The chiral compounds (6aS,9S,10aR)-11,11-dimethyl-5,5-dioxo-2,3,8,9-tetrahydro-6H-6a,9-methanooxazaolo[2,3-i][2,1]benzisothiazol-10(7H)-one, C(12)H(17)NO(4)S, (1), (7aS,10S,11aR)-12,12-dimethyl-6,6-dioxo-3,4,9,10-tetrahydro-7H-7a,10-methano-2H-1,3-oxazino[2,3-i][2,1]benzisothiazol-11(8H)-one, C(13)H(19)NO(4)S, (2), (6aS,9S,10R,10aR)-11,11-dimethyl-5,5-dioxo-2,3,7,8,9,10-hexahydro-6H-6a,9-methanooxazolo[2,3-i][2,1]benzisothiazol-10-ol, C(12)H(19)NO(4)S, (3), and (7aS,10S,11R,11aR)-12,12-dimethyl-6,6-dioxo-3,4,8,9,10,11-hexahydro-7H-7a-methano-2H-[1,3]oxazino[2,3-i][2,1]benzisothiazol-11-ol, C(13)H(21)NO(4)S, (4), consist of a camphor core with a five-membered spirosultaoxazolidine or six-membered spirosultaoxazine, as both their keto and hydroxy derivatives. In each structure, the molecules are linked via hydrogen bonding to the sulfonyl O atoms, forming chains in the unit-cell b-axis direction. The chains interconnect via weak C-H...O interactions. The keto compounds have very similar packing but represent the highest melting [507-508 K for (1)] and lowest melting [457-458 K for (2)] solids.