Part I. The development and mechanistic study of a biomimetic decarboxylative aldol reaction. Part II. Ruthenium-catalyzed dehydrogenation of ammonia-boranes.

摘要

Part I. The development and mechanistic study of a biomimetic decarboxylative aldol reaction. A reaction has been developed in which malonic acid half thioesters (MAHTs) and malonic acid half oxyesters (MAHOs) are shown to undergo decarboxylative nucleophilic addition reactions with ketone and aldehyde electrophiles under exceptionally mild conditions. In the presence of Et3N at room temperature in THF, various nucleophile and electrophile analogues form beta3-hydroxyester and thioester products in moderate to good yields.;Part II. Ruthenium-catalyzed dehydrogenation of ammonia-boranes. The dehydrogenation of ammonia-borane (AB) and methylammonia-borane (MeAB) is shown to be catalyzed by several Ru-amido complexes. Up to one equivalent H2 (1.0 system wt %) is released from AB by as little as 0.03 mol % Ru within 5 minutes, and up to two equivalents H2 (3.0 system wt %) are released from MeAB with 0.5 mol % Ru in under 10 minutes at room temperature, the first equivalent emerging within 10 seconds. Also, a mixture of AB/MeAB yields up to 3.6 system wt % H2 within 1 hour with 0.1 mol % Ru. Several catalytic analogues were synthesized to evaluate the active species the catalytic cycle, and computational studies were performed to elucidate the mechanism of dehydrogenation of AB. Finally, it was shown that alkylamine-boranes can serve as a source of H2 in the Ru-catalyzed reduction of ketones and imines.;It is also demonstrated spectroscopically that these decarboxylative aldol reactions proceed through a post-addition, pre-decarboxylation intermediate. The formation of this intermediate is shown to be reversible using both experimental and kinetic means of analysis. The rate constants for intermediate formation and decomposition to product in various solvents have been calculated using two different models and calculation methods.