Chemoselective synthesis of multiple epoxy-bridged tetrahydropyranone ring systems

Bis- as well as tris-tetrahydropyranone ring systems were obtained via multiple tandem cyclization-1,3-dipolar cycloaddition reactions of α-diazo ketones with ketone as well as aldehyde functional groups in a chemoselective manner.     

“On water” cascade synthesis of benzopyranopyrazoles and their macrocycles

Reported herein is an intramolecular 1,3-dipolar cycloaddition strategy for rapid entry into benzopyranopyrazoles (BPP) on water medium as “open flask chemistry” approach. The in situ generation of diazo functionality in two-step sequence from the appropriate alkylated salicylaldehydes undergoes smooth [3?+?2]-cycloaddition with unactivated alkynes/alkenes furnishing benzopyranopyrazoles in good yield. This methodology was also extended for the synthesis of pyrazole incorporated macrocycles. This cascade protocol involving water medium provides an atom-economical and environment friendly approach.     

Catalytic enantioselective intermolecular cycloaddition of diazodiketoester-derived carbonyl ylides with indoles using chiral dirhodium(II) carboxylates

The first example of enantioselective intermolecular cycloaddition of carbonyl ylides with indoles is described. The cycloaddition of five- and six-membered carbonyl ylides derived from diazodiketoesters with N-methylindoles under catalysis by dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], Rh(2)(S-TCPTTL)(4), gave cycloadducts in high yields and with high levels of enantioselectivity (up to 99% ee) as well as excellent exo diastereoselectivity.     

Probing interatomic potentials by ion translational energy spectrometry: A new crossed molecular beams apparatus

This report presents details of the development of a new crossed molecular beams apparatus designed and fabricated to carry out high sensitivity ion translational energy spectrometric investigations of the potential energy surfaces of small molecular species. The translational energy spectrometer is used to carry out experimental studies of ion-neutral reactions resulting in charge stripping of CS⁺ radicals and dissociation of metastable CO²⁺ dications. These results are interpreted in the light of high-levelab initia molecular orbital calculations of the pertinent molecular potential energy functions. New results for the double ionisation energy of CS and the kinetic energy released upon dissociation of specific electronic states of CO²⁺ are presented.     

A Random Walk with Collapsing Bonds and Its Scaling Limit

Abstract

We introduce a new self-interacting random walk on the integers in a dynamic random environment and show that it converges to a pure diffusion in the scaling limit. We also find a lower bound on the diffusion coefficient in some special cases. With minor changes the same argument can be used to prove the scaling limit of the corresponding walk in ? ^d .     

Optimal extraction,sequential fractionation and structural characterization of soda lignin

Research on Chemical Intermediates - In this research, soda lignin was extracted from Bambusa bambos using a soda pulping process, and interaction effects of pulping variables were statistically...     

Highly regio- and chemoselective ring opening of oxa-bridged piperidinones toward functionalized furanones and piperidines

Lewis acid mediated competitive ring-opening reactions of N-tosyl-substituted oxa-bridged piperidinone ring systems are demonstrated. A majority of the Lewis acids furnished the regio- and chemoselective reductive ring opening at the C(1)-N bond, whereas TiCl(4) furnished at the C(1)-O bond in the presence of triethylsilane, affording functionalized furanones and dihydroxypiperidines, respectively. [reaction: see text]     

Anomalous reaction of Rh2(OAc)4-generated transient carbonyl ylides: chemoselective synthesis of epoxy-bridged tetrahydropyranone, oxepanone, oxocinone, and oxoninone ring systems

A series of symmetrical and unsymmetrical alpha,beta-unsaturated ketones such as arylmethylidenecycloalkanones (16, 19), bis(arylmethylidene)cycloalkanones (21, 23, 27), bisdiphenylnonatetraenones (30), and bis(phenylpropenylidene)cycloalkanones (33, 38, 42) were synthesized and subjected to the rhodium(II)-catalyzed tandem cyclization-cycloaddition reactions with various alpha-diazo ketones. These reactions afforded spiro epoxy-bridged tetrahydropyranone, spiro epoxy-bridged oxepanone (41, 43), epoxyoxocin-4(5H)-one (35, 37), and epoxyoxonin-5(6H)-one (40) frameworks starting from relatively simple precursors. The regio- and stereochemistry and solid-state architecture arrangements of several products were characterized by single-crystal X-ray structure analysis. The cycloaddition of carbonyl ylides with the compounds having both C=O and C=C groups was found to be chemo- and regioselective. Interestingly, an unusual ring enlargement of cycloadducts 34, 36, and 41 derived from C=O group addition was observed, affording epoxyoxocin-4(5H)-one and epoxyoxonin-5(6H)-one frameworks. Examples for the tandem cyclization-cycloaddition-ring enlargement reaction were also described. The rhodium(II)-generated carbonyl ylides behaved anomalously, furnishing the cycloadducts as a result of the cycloaddition of carbonyl ylides to C=O group despite the presence of C=C groups.