Palladium-Catalyzed Cross-Coupling of 2-Aryl-1,3-Dithianes

Palladium-catalyzed cross-coupling of aryl bromides with 2-aryl-1,3-dithianes is described. This methodology takes advantage of the relatively acidic benzylic proton of the dithiane, allowing it to act as a competent, polarity-reversed transmetalation reagent. This unique approach affords the ability to employ an orthogonal deprotection strategy, and practical routes to both diaryl ketones and diarylmethanes are illustrated. Cross-coupling of a range of aryl dithianes with aryl bromides, including scope and current limitations, is presented

A non-traditional approach to synthesizing aryl vinyl sulfides is described. 2,2-diphenyl-1,3-oxathiolane slowly liberates vinyl sulfide anion under basic conditions. Using a Pd/Xantphos catalyst system to activate a wide range of aryl bromides, this transient sulfide species can be effectively trapped and fed into a traditional Pd0/PdII catalytic cycle. Scope and limitations of the methodology are presented along with significant discussion of a competitive C–S bond activation by this catalyst system.

A non-traditional approach to synthesizing aryl vinyl sulfides is described. 2,2-diphenyl-1,3-oxathiolane slowly liberates vinyl sulfide anion under basic conditions. Using a Pd/Xantphos catalyst system to activate a wide range of aryl bromides, this transient sulfide species can be effectively trapped and fed into a traditional Pd0/PdII catalytic cycle. Scope and limitations of the methodology are presented along with significant discussion of a competitive C–S bond activation by this catalyst system

Population, Land Use and Deforestation in the Pan Amazon Basin: a Comparison of Brazil, Bolivia, Colombia, Ecuador, Perú and Venezuela

This paper discusses the linkages between population change, land use, and deforestation in the Amazon regions of Brazil, Bolivia, Colombia, Ecuador, Perú, and Venezuela. We begin with a brief discussion of theories of population–environment linkages, and then focus on the case of deforestation in the PanAmazon. The core of the paper reviews available data on deforestation, population growth, migration and land use in order to see how well land cover change reflects demographic and agricultural change. The data indicate that population dynamics and net migration exhibit to deforestation in some states of the basin but not others. We then discuss other explanatory factors for deforestation, and find a close correspondence between land use and deforestation, which suggests that land use is loosely tied to demographic dynamics and mediates the influence of population on deforestation. We also consider national political economic contexts of Amazon change in the six countries, and find contrasting contexts, which also helps to explain the limited demographic-deforestation correspondence. The paper closes by noting general conclusions based on the data, topics in need of further research and recent policy proposals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42720/1/10668_2003_Article_6977.pd

Expanding the scope and utility of the scientific microwave apparatus in organic synthesis: Reaction monitoring, scale-up and new methodology development

The work contained within this dissertation covers three broad areas in the continued development of the scientific microwave apparatus. A brief introduction of pertinent fundamental microwave background and theory is presented in Chapter 1, and a short background of microwave-assisted organic synthesis is described, including areas of recent growth, its widespread use, and contains a discussion of the range of equipment available to the organic chemist. ^ Three fundamental research areas are discussed. First, the interface of a Raman spectrometer with a commercially available scientific microwave apparatus is discussed in detail. The apparatus was used both qualitatively as a reaction-monitoring tool and as a quantitative tool for rapid kinetic studies. Second, the scale-up of microwave mediated organic reactions is discussed. Within the pharmaceutical industry, a great number of synthetic protocol are developed utilizing the scientific microwave. The scope and limitations of utilizing microwave heating, especially in batch reactors, is thoroughly examined and presented within this work. Finally, the development of novel synthetic methodologies utilizing microwave heating is presented.

Synthesis of Disubstituted Dithioethers: <i>tert</i>-Butoxide Promoted Elimination/Ring Opening of 1,3-Dithianes Followed by Palladium-Catalyzed C–S Bond Formation

We report the tandem base-promoted elimination/ring-opening of 2-benzyl-1,3-dithianes with subsequent cross coupling of the pendent thiol with a range of aryl bromides. A simple Pd­(OAc)₂/Xantphos catalyst system affects this new reaction and is compatible with a wide range of functional groups, including heteroaromatic coupling partners. The transformation proceeds in good to excellent yields (69–99%) and exhibits strong stereoselectivity, forming the <i>E-</i>alkene as the major diastereomer. This new methodology provides access to nonsymmetric propylene styryl/aryl dithioethers, a previously undisclosed motif

Pd-Catalyzed Aldehyde to Ester Conversion: A Hydrogen Transfer Approach

Aliphatic and aromatic aldehydes are successfully converted into their corresponding esters using Pd(OAc)₂ and XPhos. This approach utilizes a hydrogen transfer protocol: concomitant reduction of acetone to isopropanol provides an inexpensive and sustainable approach that mitigates the need for other oxidants

Palladium-Catalyzed Cross-Coupling of 2‑Aryl-1,3-dithianes

Palladium-catalyzed cross-coupling of aryl bromides with 2-aryl-1,3-dithianes is described. This methodology takes advantage of the relatively acidic benzylic proton of the dithiane, allowing it to act as a competent, polarity-reversed transmetalation reagent. This unique approach affords the ability to employ an orthogonal deprotection strategy, and practical routes to both diaryl ketones and diarylmethanes are illustrated. Cross-coupling of a range of aryl dithianes with aryl bromides, including scope and current limitations, is presented

Scale-Up of Microwave-Promoted Reactions to the Multigram Level Using a Sealed-Vessel Microwave Apparatus

A range of synthetic transformations have been scaled up successfully using a sealed-vessel multimode microwave unit. These include metal-catalyzed couplings, synthesis of heterocycles, reactions under an atmosphere of reactive gas and two-step one-pot procedures. Also, observations have been made along the way that are of use to chemists addressing scale-up of microwave-promoted reactions