Diverse Natural Products from Dichlorocyclobutanones: An Evolutionary Tale.

11-Nor PGE2 was prepared in our laboratory several years ago and used to obtain the corresponding ring-expanded γ-butyrolactam, γ-butyrolactone, and cyclopentanone derivatives. The conversion of a cyclobutanone into a cyclopentanone had relatively little precedent and merited further study. It was soon found that the presence of a single chlorine adjacent to the carbonyl not only greatly accelerated the reaction with ethereal diazomethane, but also substantially enhanced its regioselectivity; not surprisingly, a second chlorine further increased both.

The Pauson-Khand mechanism revisited: origin of CO in the final product.

The mechanism of the Pauson-Khand reaction has been studied by mass spectrometry and it has been found, through ion-molecule reaction with (13) CO, that the carbon monoxide incorporated into the product cyclopentenone is one that has been retained within the complex. Theoretical and kinetic calculations support this finding, which provides a complementary explanation for the effect of Pauson-Khand promoters.

The ACPE supervisory education process: an historical perspective.

As the number of Clinical Pastoral Education students increases, supervisors in the Association for Clinical Pastoral Education (ACPE) are in short supply due to retirements. We explore factors associated with this supply problem, reporting here four results from our survey of active and retired supervisors. We identify the ages of the current supervisory pool, the ages at which supervisors were certified and the length of time spent in the supervisory education program across the decades.

Asymmetric approach to hyacinthacines B1 and B2.

Naturally occurring hyacinthacines B1 and B2 have been prepared from a common, easily available, advanced intermediate. The approach features several highly stereoselective transformations: inter alia, a dichloroketene-enol ether [2 + 2] cycloaddition, a Bruylants alkylation, and an amino-nitrile alkylation-reduction.

A Diels-Alder-based total synthesis of (-)-kainic acid.

An efficient synthesis of (-)-kainic acid, through a high-pressure-promoted Diels-Alder cycloaddition of a vinylogous malonate derived from 4-hydroxyproline, is described. The bicyclic adduct could be converted into the natural product with complete stereocontrol.

Asymmetric synthesis of cyclobutanones: synthesis of cyclobut-G.

A simple, efficient, and stereoselective approach has been developed for obtaining chiral cis- and trans-disubstituted cyclobutanones from readily available alkyl- and functionalized alkyl-substituted enol ethers. The usefulness of these cyclobutanones is illustrated by an enantioselective synthesis of cyclobut-G (Lobucavir).

Little boy black and blue.

Tooth decay is common in US children, especially for children in low-income families. More than half of second-grade children have cavities. Therefore, root canal procedures are becoming more common in children.

Asymmetric synthesis of functionalized, monocyclic chlorocyclobutenes.

The selective synthesis of a variety of stereopure monocyclic chlorocyclobutenes is described. These derivatives could be coupled with Grignard reagents; two dienes from coupling with vinylmagnesium bromide reacted smoothly with maleic anhydride to yield illudol-related [4 + 2] cycloadducts.

Asymmetric synthesis of (+)-castanospermine through enol ether metathesis-hydroboration/oxidation.

An asymmetric synthesis of (+)-castanospermine is presented in which enol ether metathesis-hydroboration/oxidation is used for stereoselective installation of the trans-trans hydroxyl groups on the piperidine ring of the alkaloid.

Characterization of wheatgrass-derived barley yellow dwarf virus resistance in a wheat alien chromosome substitution line.

ABSTRACT Wheatgrass (Thinopyrum intermedium) possesses a high level of resistance to barley yellow dwarf virus (BYDV) subgroup I and subgroup II strains. A wheat line (P29), in which the 7D chromosome has been substituted with a group 7 chromosome from T. intermedium, was examined for the level of resistance to two subgroup I and two subgroup II BYDV strains.

Ynol ethers from dichloroenol ethers: mechanistic elucidation through 35Cl labeling.

The mechanism of ynol ether formation from dichloroenol ethers, a decades-old transformation, has been studied by experimental and theoretical techniques to determine the relative importance of the Fritsch-Buttenberg-Wichell rearrangement (alpha-elimination) and beta-elimination in the evolution of the intermediate carbenoid.

Approach to the hyacinthacines: first non-chiral pool synthesis of (+)-hyacinthacine A1.

The first non-chiral pool total synthesis of (+)-hyacinthacine A(1) is described. This synthesis is based on an effective [2 + 2] cycloaddition of dichloroketene to a Stericol-based enol ether, a diastereoselective dihydroxylation, and an efficient Tamao-Fleming oxidation.

Synthesis and bioevaluation of 22-hydroxyacuminatine analogs.

A series of 22-hydroxyacuminatine analogs was prepared by using different Friedländer condensations. Several of the new compounds were tested for antiproliferative activity on cancer cell lines and for topoisomerase I inhibitory activity.

Expedient approach to chiral cyclobutanones: asymmetric synthesis of cyclobut-G.

An efficient one-pot asymmetric synthesis of cyclobutanones from chiral enol ethers is described. The approach is illustrated with alkyl- and functionalized alkyl-substituted enol ethers (nine examples). A new enantioselective synthesis of cyclobut-G (Lobucavir) could thus be achieved.

Terminal olefins from aldehydes through enol triflate reduction.

The transformation of aldehydes into terminal olefins through reduction of the corresponding enol triflates is described. The method is effective with both linear and alpha-branched aldehydes.

1-(2,4,6-triisopropylphenyl)ethylamine: a new chiral auxiliary for the asymmetric synthesis of gamma-amino acid derivatives.

The title compound has proven to be an excellent chiral auxiliary for nitrones in SmI2-mediated reductive coupling with alpha,beta-unsaturated esters. A variety of such nitrones, prepared from aldehydes and enantiopure N-hydroxy-1-(2,4,6-triisopropylphenyl)ethylamine, afforded gamma-N-hydroxyamino esters in high yields and diastereomeric purity. These adducts, readily available as either enantiomer, could be transformed into gamma-N-acetoxyamino esters, N-Boc-gamma-amino esters, and gamma-lactams.

High dispersal in a frog species suggests that it is vulnerable to habitat fragmentation.

Global losses of amphibian populations are a major conservation concern and their causes have generated substantial debate. Habitat fragmentation is considered one important cause of amphibian decline. However, if fragmentation is to be invoked as a mechanism of amphibian decline, it must first be established that dispersal is prevalent among contiguous amphibian populations using formal movement estimators.

High-pressure Diels-Alder approach to natural kainic acid.

The first Diels-Alder based synthesis of (-)-kainic acid is described. Danishefsky's diene and a vinylogous malonate derived from 4-hydroxyproline combine under high pressure to afford a key bicyclic intermediate with virtually no loss of enantiopurity. This adduct can be converted into the natural product with complete stereocontrol.

Novel, efficient total synthesis of natural 20(S)-camptothecin.

Enantiopure 20(S)-camptothecin has been prepared from a known hydroxypyridone through a novel approach that involves a Claisen rearrangement, an asymmetric nucleophilic ethylation, a Heck coupling and a Friedländer condensation as the key transformations.

Asymmetric [2 + 2] cycloaddition: total synthesis of (-)-swainsonine and (+)-6-epicastanospermine.

[reaction: see text] An asymmetric total synthesis of (-)-swainsonine and (+)-6-epicastanospermine is described from a common intermediate, which is obtained through diastereoselective [2 + 2] cycloaddition of dichloroketene to a chiral enol ether.

Concise synthesis of 22-hydroxyacuminatine, cytotoxic camptothecinoid from Camptotheca acuminata, by pyridone benzannulation.

A short, efficient synthesis of 22-hydroxyacuminatine, starting from a readily accessible hydroxy pyridone, is presented; key steps include a Heck coupling with methyl pentadienoate, a flash vacuum pyrolytic cyclization, and a Friedländer condensation.

Stereocontrolled synthesis of (-)-kainic acid from trans-4-hydroxy-L-proline.

[reaction: see text] A highly stereoselective synthesis of (-)-kainic acid has been achieved in 14 steps and >7% overall yield starting from inexpensive trans-4-hydroxy-L-proline. The key steps are diastereoselective enolate alkylation and cuprate substitution reactions.

Reaction of nitrones with silyl ketene acetals: a DFT study.

Theoretical calculations at the DFT level indicate that the reaction of a nitrone with a silyl ketene acetal proceeds, contrary to previous suggestions, through a classical 1,3-dipolar cycloaddition, followed by a silyl group transfer step to give the open-chain product. Introduction of a diffuse basis set is necessary to describe properly nitrones. The influence of a Lewis acid has been studied.

The electrophysiology of atrioventricular nodal reentry tachycardia following the Mustard or Senning procedure and its radiofrequency ablation.

We describe the electrophysiological studies undertaken in four patients with atrioventricular nodal reentry tachycardia in the setting of concordant atrioventricular and discordant ventriculo-arterial connections (transposition). Radiofrequency ablation was attempted in three, all with success. Clear evidence of dual antegrade pathways through the atrioventricular node was present in only one of the four, but other characteristics of discrete fast and slow pathways into the atrioventricular node were present in all.