A cross metathesis-based synthesis of analogues of the 2-O-alkyl glycerate part of the moenomycins

Gosteli-Claisen rearrangement: substrate synthesis, simple diastereoselectivity, and kinetic studies

The results of kinetic studies on the uncatalyzed [3,3]-sigmatropic rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers are reported. Apparently first reported by Gosteli in 1972, this variation of a Claisen rearrangement enjoyed a shadowy existence for three decades until its potential for the development of a catalytic asymmetric Claisen rearrangement was discovered. Inspired by this development, we have studied substituent and solvent rate effects, and we provide evidence that a chairlike transition state is highly favorable for the uncatalyzed Gosteli-Claisen rearrangement.

Cytotoxic and Anti-HIV Principles from the Rhizomes of Begonia nantoensis

Three new compounds: begonanline (1). nantoamide (2). and methyl (S)-glycerate (3). as well as forty-four known compounds have been isolated and characterized from the rhizomes of Begonia nantoensis. The structures of these compounds were determined by spectral analyses and/or X-ray crystallography. Among them, cucurbitacin B (4). dihydrocucurbitacin B (5). cucurbitacin E (6). dihydrocucurbitacin E (7). cucurbitacin I (8). and (-)-auranamide (9). showed cytotoxicity against four human cancer cell lines. 3beta,22alpha-Dihydroxyolean-12-en-29-oic acid (10), indole-3-carboxylic acid (11), 5,7-dihydroxychromone (12), and (-)-catechin (13) demonstrated significant activity against HIV replication in H9 lymphocyte cells.

A General Model for Selectivity in Olefin Cross Metathesis

In recent years, olefin cross metathesis (CM) has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic method, CM has been limited by the lack of predictability in product selectivity and stereoselectivity. Investigations into olefin cross metathesis with several classes of olefins, including substituted and functionalized styrenes, secondary allylic alcohols, tertiary allylic alcohols, and olefins with alpha-quaternary centers, have led to a general model useful for the prediction of product selectivity and stereoselectivity in cross metathesis. As a general ranking of olefin reactivity in CM, olefins can be categorized by their relative abilities to undergo homodimerization via cross metathesis and the susceptibility of their homodimers toward secondary metathesis reactions. When an olefin of high reactivity is reacted with an olefin of lower reactivity (sterically bulky, electron-deficient, etc.), selective cross metathesis can be achieved using feedstock stoichiometries as low as 1:1. By employing a metathesis catalyst with the appropriate activity, selective cross metathesis reactions can be achieved with a wide variety of electron-rich, electron-deficient, and sterically bulky olefins. Application of this model has allowed for the prediction and development of selective cross metathesis reactions, culminating in unprecedented three-component intermolecular cross metathesis reactions.