Ligand-controlled Regioselective Cu-Catalyzed Trifluoromethylation to Generate Trifluoromethylallenes

“Cu–CF3” species have been used historically for a broad spectrum of nucleophilic trifluoromethylation reactions. Although recent advancements have employed ligands to stabilize and harness the reactivity of this key organometallic intermediate, the ability of a ligand to differentiate a regiochemical outcome of a Cu–CF3-mediated or -catalyzed reaction has not been previously reported. Herein, we report the first example of a Cu-catalyzed trifluoromethylation reaction in which a ligand controls the regiochemical outcome. More specifically, we demonstrate the ability of bipyridyl-derived ligands to control the regioselectivity of the Cu-catalyzed nucleophilic trifluoromethylation reactions of propargyl electrophiles to generate trifluoromethylallenes. This method provides a variety of di-, tri- and tetra-substituted trifluoromethylallenes, which can be further modified to generate complex fluorinated substructures

Computational insight concerning catalytic decision points of the transition metal catalyzed [2 + 2 + 1] cyclocarbonylation reaction of allenes

Rhodium- and molybdenum-catalyzed allenic [2 + 2 + 1] cycloaddition reactions give 4-alkylidene and α-alkylidene cylopentenones, respectively. The selective reaction of one double bond of the allene over another is controlled by the transition metal and not the substrate structure. Calculations were performed to explain this unique control element using the B3LYP functional as implemented in Gaussian 03. The 6-31G(d) basis set was applied to all elements except rhodium, which is described with the LANL2 effective core potential and the LANL2DZ basis set. The product-determining step for both reaction pathways is oxidative addition of the metal to the alkynyl allene to form the corresponding metallocycles B and B'. The calculations strongly suggest that geometric constraints imposed by the metal in the transition state are the key controlling factor of the double-bond selectivity. The transition state structure of rhodium-catalyzed oxidative addition has a distorted square planar geometry that affords a lower transition state energy when coordinated to the distal double bond of the allene. In turn, the distorted trigonal bipyramidal geometry of molybdenum in the transition state structure imposes conformational constraints upon binding to the distal double bond on the allene and thus leads to the energetically preferred complexation and reaction with the proximal double bond. © 2006 American Chemical Society

Sacred waters of the Mongols: Protecting natural and cultural diversity in the Lake Baikal region.

Using freshwater springs (Rashaan in Mongolian, Arshan in Buryat language) as multi-faceted models of cultural and natural diversity, this study broadly questions how biophysical, cultural and social interactions at different spatial and temporal scales can be reconciled into integrated heritage protection strategies in the Lake Baikal region of Mongolia and the Russian Republic of Buryatia. The location, general geochemistry, and physical parameters of over 90 mineral springs are correlated with ethnographic data about their ecological, medicinal, and spiritual benefits as understood and experienced by local people. Specific springs and their associated ecological and cultural values are described in six distinct natural zones. The context of regional resource development, protected area management, and institutional changes are integrated with spring data to assess the relative physical risks, ecological values, and cultural significance of sampled springs and an additional 269 regional spring sites. Strategies for addressing these local spring protection priorities are outlined and evaluated, including two international conventions (World Heritage Convention and Ramsar Convention on Wetlands of International Significance) and two national programs (The Baikal Plan and the Mongolian National Service for Protected Areas and Ecotourism). As part of a growing body of case studies documenting indigenous knowledge and cultural concerns related to natural resource protection and transformation in postsocialist societies, this study concludes that multiple perspectives and integrated knowledge are required to effectively support efforts to keep cultural and natural resources locally viable yet regionally significant.Ph.D.Cultural anthropologyEnvironmental scienceHealth and Environmental SciencesInternational lawSocial SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124636/2/3150167.pd

Heterocyclic α-alkylidene cyclopentenones obtained via a Pauson-Khand reaction of amino acid derived allenynes. A scope and limitation study directed toward the preparation of a tricyclic pyrrole library

(Chemical Equation Presented) The synthesis of a novel class of tricyclic pyrroles has been accomplished by using a Pauson-Khand/Stetter/Paal-Knorr reaction sequence. Full details of the Pauson-Khand reaction of amino acid tethered allenynes 4a-e and 9a-d are disclosed. The study of this reaction led to the discovery of an unprecedented substituent effect on the diastereoselectivity of the Mo(CO)6 mediated allenic Pauson-Khand reaction. It was found that amino acid tethered allenynes with aromatic side chains afford α-alkylidene cyclopentenones with the opposite diastereoselectivity compared to those with aliphatic side chains. This effect has been attributed to complexation of the metal mediator to the aromatic ring in the substrate. Furthermore, an isomerization of one of the diastereomers of the α-alkylidene cyclopentenones was encountered, leading to eventual decomposition. The stable diastereomers were found to react well in the Stetter reaction leading to 1,4-diketones that were converted to pyrroles. The observation that the first generation of 2-alkyl-substituted pyrroles was unstable led to a second generation of 2-carboxamide pyrroles with sufficient stability for biological tests which are in progress. © 2005 American Chemical Society