Metathesis: a "Change-Your-Partners" dance - chemistry Nobel Prize - 2005

On 5th October 2005, The Royal Swedish Academy of Sciences decided to award the Nobel Prize in Chemistry for 2005 jointly to Yves Chauvin, Institute of French Petroleum, France, Robert H Grubbs, California Institute of Technology, USA and Richard R Schrock, Massachusetts Institute of Technology, USA for the development of the metathesis method in organic synthesis. This increasingly important organic process allows researchers to synthesize certain kinds of complex molecules that were previously difficult and inefficient to make. Their research has opened the door to faster and more efficient methods for developing new drugs and polymers. Imagination will soon be the only limit to what molecules can be built in the laboratory!

Facile oxidation of aldehydes to carboxylic acids with chromium(V) reagents

Recently we reported a convenient method of oxidation of alcohols to carbonyl compounds using chromium(V) reagents. Although a variety of reagents are available for effecting this transformation, there are only a few reagents which have been successfully used for the oxidation of aldehydes to carboxyllc adds. Chromic acid, silver oxide and potassium permanganate are commonly employed for this purpose and reactions are performed in protic media under conditions which are not that mild. The "non-aqueous" chromium(VI) reagent, pyridinium dichromate, recently reported by Corey oxidises alcohols and aldehydes to carboxylic acids in DMF at room temperature. Although Cr(V) species is postulated as an intermediate in all oxidations with Cr(VI), no systematic oxidation studies have been reported with these reagents. This note reports the results of some fruitful investigations on aldehyde → carboxylic acid conversion involving some "non-aqueous" chromium (V) complexes 1̲, 2̲, 3̲ and 5̲ under anhydrous conditions

An efficient and highly selective method for deoximation of ketoximes

A combination of pyridinium dichromate/tert-butyl hydroperoxide (1:1) has been found to be an excellent reagent for the highly selective regeneration of ketones from ketoximes

A facile reductive cleavage of allylic and benzylic esters with low valent titanium reagents

The reductive cleavage of allylic and benaylic esters 1a-g̲ with titanium(II) reagent derived from Mg/Hg-TiCl yielded the corresponding acids 3a-g̲ and dimeric hydro 4 carbons 2a-g̲ under mild reaction conditions

Estimation in Gaussian Graphical Models Using Tractable Subgraphs: A Walk-Sum Analysis

Graphical models provide a powerful formalism for statistical signal processing. Due to their sophisticated modeling capabilities, they have found applications in a variety of fields such as computer vision, image processing, and distributed sensor networks. In this paper, we present a general class of algorithms for estimation in Gaussian graphical models with arbitrary structure. These algorithms involve a sequence of inference problems on tractable subgraphs over subsets of variables. This framework includes parallel iterations such as embedded trees, serial iterations such as block Gauss-Seidel, and hybrid versions of these iterations. We also discuss a method that uses local memory at each node to overcome temporary communication failures that may arise in distributed sensor network applications. We analyze these algorithms based on the recently developed walk-sum interpretation of Gaussian inference. We describe the walks ldquocomputedrdquo by the algorithms using walk-sum diagrams, and show that for iterations based on a very large and flexible set of sequences of subgraphs, convergence is guaranteed in walk-summable models. Consequently, we are free to choose spanning trees and subsets of variables adaptively at each iteration. This leads to efficient methods for optimizing the next iteration step to achieve maximum reduction in error. Simulation results demonstrate that these nonstationary algorithms provide a significant speedup in convergence over traditional one-tree and two-tree iterations