Absolute rate constants and Arrhenius parameters for hydrogen abstractions (from carbon) by the t-butoxyl radical ((t) BuO.) are reported for several hydrocarbons and tertiary amines in solution. Combined with data already in the literature, an analysis of all the available data reveals that most hydrogen abstractions (from carbon) by (t) BuO. are entropy controlled (i.e., TdeltaS > deltaH, in solution at room temperature). For substrates with C-H bond dissociation energies (BDEs) > 92 kcal/mol, the activation energy for hydrogen abstraction decreases with decreasing BDE in accord with the Evans-Polanyi equation, with alpha approximately 0.3. For substrates with C-H BDEs in the range from 79 to 92 kcal/mol, the activation energy does not vary significantly with C-H BDE. The implications of these results in the context of the use of (t) BuO. as a chemical model for reactive oxygen-centered radicals is discussed.

Atom transfer radical polymerization (ATRP) and the copper-catalyzed azide-alkyne cycloaddition (CuAAC) were utilized for the synthesis of photodegradable polymeric materials by two complementary schemes. Linear azido-telechelic macromonomers possessing a photocleavable functionality at the center were synthesized by ATRP and subsequent end-group modification. These macromonomers were cross-linked with a tetrafunctional alkyne by CuAAC to form insoluble materials which degraded upon exposure to UV light of 350 nm to yield soluble star polymer products of defined molecular weight. Complementary to this approach, four-armed star polymers possessing photocleavable arms and terminal azides were prepared by a novel one-pot CuAAC/ATRP reaction followed by end-group modification. These star polymers were cross-linked with a linear, bifunctional alkyne to yield insoluble materials which, upon exposure to UV light, degraded to yield linear polymers of defined molecular weight.

Gold(III) activation of unprotected propargyl glycosyl donors has been shown to be effective for the synthesis of saccharides. Terminal propargyl glycosides of glucose, galactose, and mannose required heating at reflux in acetonitrile with 5% AuCl(3) for reaction with various primary alcohol acceptors, the latter used in 10-fold molar excess relative to donor. Donors containing the 2-butynyl group were more reactive, giving good yields of glycoside products at lower temperatures. Secondary alcohols could also be used but with diminished efficiency. The propargylic family of donors is especially convenient because they can be easily prepared on large scale by Fischer glycosylation and stored indefinitely before chemoselective activation by the catalyst.

The in situ preparation and trapping of chlorine azide provided a versatile one-pot method for the azidochlorination of alkenes. Gaseous ClN3 generated from sodium azide, hypochlorite, and acetic acid can be explosive if isolation is attempted. Instead, we generated the reagent in biphasic media in the presence of olefinic compounds dissolved in the organic layer or evenly emulsified throughout the solution in the absence of organic solvent. Under these conditions, ClN3 is created slowly and trapped immediately at the aqueous-organic interface. The resulting safe and reliable procedure provided 1,2-azidochloride derivatives of a variety of substrates, with evidence for both polar and radical mechanisms. Minor impurities characterized in the product mixtures indicated the presence of alternative reaction pathways deriving primarily from radical intermediates.