Constraining of small-ring cyclic ether triads by stereodefined spiroannulation to an inositol orthoformate platform. Solution- and gas-phase alkali metal binding affinities for three- to five-membered ring structural combinations

The structural features most conducive to complexation of the alkali metal ions Li(+), Na(+), and K(+) in a series of constrained inositol orthoformate derivatives have been probed in solution, in the solid state, and in the gas phase by electrospray ionization mass spectrometry. The eight spirotricyclic polyethers differ in the size of the rings containing the potentially ligating oxygen atoms. Although the ring sizes have been limited to three to five atoms inclusively, the combinations of oxirane, oxetane, and tetrahydrofuran are rather extensive and consist of many options. The overall trend for lithium ion affinity is [5.5.5] > [ 5.5.4] > [4.4.4] > [5.5.3] > [5.4.3] > [4.4.3] > [1.1.1] > [3.3.1], an ordering that correlates with the differing polarizabilities of the oxygen atoms, ease of alignment of the nonbonded electron pairs, and the overall size of the ligand as gauged by nonbonded O......O distances.

Effect of terminal group sterics and dendron packing on chirality transfer from the central core of a dendrimer

[structure: see text] The conformational properties of intramolecularly hydrogen-bonded dendrimers constructed from (S)-1,1'-bi-2-naphthol as a chiral central core are described. Circular dichroism studies revealed that chirality transfer to the periphery occurs only when sterically demanding terminal esters are employed and when packing interactions are present.

Direct Synthesis of Previously Inaccessible Bridgehead Azabicyclics by Intramolecular Cyclization of α-Sulfonamido and α-Sulfonimido Radicals

Syntheses of the first bridgehead sultams and the only known bridgehead disulfonimide are described. Both approaches capitalize on the electrophilicity of alpha-sulfonyl radicals and their propensity to undergo intramolecular ring closure. Where double bonds are concerned, 5-exo and 6-exo pathways operate preferentially as long as structural strain is not excessive. When the reaction center is a carbon-carbon triple bond, the first cyclization gives rise to vinyl radicals that hold sufficient reactivity to capture solvent benzene. In the case of 45, this sequential reaction leads importantly to the introduction of a styrene functionality sufficiently activated to allow a second ring closure to be kinetically feasible. The solid-state structural features of 12 and 17 have been elucidated by X-ray crystallographic methods. Despite key differences from the norm in the alignment of the nitrogen lone pair relative to the adjacent sulfonyl groups, these compounds exhibit good hydrolytic stability. For 13, generation of the alpha-sulfonamide carbanion is possible and regiospecific oxidation with chromyl acetate has been achieved.