Control of regioselectivity and stereoselectivity in (4 + 3) cycloadditions of chiral oxyallyls with unsymmetrically disubstituted furans.

The regioselectivities and stereoselectivities of ZnCl2-catalyzed (4 + 3) cycloadditions between chiral oxazolidinone-substituted oxyallyls and unsymmetrical disubstituted furans have been determined. The substitution pattern on the furan is found to provide a valuable tool for controlling the stereochemistry (endo-I or endo-II) of the 7-membered cycloadduct. While cycloadditions with monosubstituted furans usually favor endo-I products, from addition of the furan to the more crowded face of the oxyallyl, cycloadditions with 2,3- and 2,5-disubstituted furans instead favor the endo-II stereochemistry.

Stereoselectivities and regioselectivities of (4 + 3) cycloadditions between allenamide-derived chiral oxazolidinone-stabilized oxyallyls and furans: experiment and theory.

A systematic investigation of the regioselectivities and stereoselectivities of (4 + 3) cycloadditions between unsymmetrical furans and a chiral oxazolidinone-substituted oxyallyl is presented. Cycloadditions were performed using an oxyallyl containing a (R)-4-phenyl-2-oxazolidinone auxiliary (2(Ph)), under either thermal or ZnCl(2)-catalyzed conditions. Reactions of 2(Ph) with 2-substituted furans gave syn cycloadducts selectively, while cycloadditions with 3-substituted furans gave selectively anti cycloadducts.

Stereoselectivity in Oxyallyl-Furan 4+3 Cycloadditions: Control of Intermediate Conformations and Dispersive Stabilisation with Evans' Oxazolidinones.

Chiral oxazolidinones were previously thought to control cycloaddition stereoselectivity by steric crowding of one face of the substrate. We have discovered that in 4+3 cycloaddition reactions of oxallyls, the stereoinduction is caused instead by stabilising CH-π interactions that lead to reaction at the more crowded face of the oxazolidinone. Density functional theory calculations on the 4+3 cycloadditions of oxazolidinone-substituted oxyallyls with furans establish unexpected transition state conformations and a new explanation of selectivity.

Regioselectivities of (4 + 3) cycloadditions between furans and oxazolidinone-substituted oxyallyls.

The (4 + 3) cycloadditions of oxazolidinone-substituted oxyallyls and unsymmetrically substituted furans lead to syn regioselectivity when the furan has a 2-Me or 2-COOR substituent, while anti regioselectivity is obtained with a 3-Me or 3-COOR group. DFT calculations are performed to explain the selectivities. The reactivities and regioselectivities are consistent with the ambiphilic reactivity of amino-oxyallyls with furans.

A Stereoselective Intramolecular Cyclopropanation via a De Novo Class of Push-Pull Carbenes Derived from DMDO-Epoxidations of Chiral Ynamides.

This work describes the first examples of diastereoselective intramolecular cyclopropanations of a de novo class of push-pull carbenes derived from DMDO-epoxidations of chiral ynamides. This reaction sequence essentially constitutes a tandem epoxidation-cyclopropanation that effectively gives arise to a series of structurally unique amido-cyclopropanes. A plausible mechanistic model is proposed revealing insights into this novel cyclopropanation process.

Highly stereoselective [4 + 3] cycloadditions of nitrogen-stabilized oxyallyl cations with pyrroles: an approach to parvineostemonine.

[structure: see text]. A highly stereoselective [4 + 3] cycloaddition of N-substituted pyrroles with allenamide-derived nitrogen-stabilized chiral oxyallyl cations is described here. This method provides an approach for constructing tropinone alkaloids.

De novo chiral amino alcohols in catalyzing asymmetric additions to aryl aldehydes.

[reaction: see text] A de novo structural class of chiral amino alcohol catalysts has been identified through a synergistic effort combining novel architectures from [4 + 3] cycloadditions and quantum mechanical interaction field predictions that closely match subsequent experimental measurements.

Copper-catalyzed stereospecific N-allenylations of amides. Syntheses of optically enriched chiral allenamides.

[reaction: see text] Syntheses of chiral allenamides via a stereospecific amidation of optically enriched allenyl iodides using catalytic copper(I) salt and N,N'-dimethylethylene-diamine are described here.

Syntheses of 2,5-disubstituted dihydrofurans from gamma-substituted chiral allenamides.

[reaction: see text] Details of a synthesis of dihydrofurans using gamma-substituted chiral allenamides are described here. Some transformations of these dihydrofurans are also examined including a highly stereoselective dihydroxylation and a rare account of a Lewis acid-mediated removal of an N-acyl substituent at the anomeric carbon of a tetrahydrofuran ring system. These studies provide further support for the synthetic utility of allenamides.