Copper(I)-mediated and microwave-assisted C(aryl)-O(carboxylic) coupling: synthesis of benzopyranones and isolamellarin alkaloids

A simple and highly effective C-O(carboxylic) coupling reaction catalyzed by copper(I) salts has been developed to synthesize benzopyranones. The reaction of various 2-halobiarylcarboxylic acids was examined using microwave irradiation. A new class of pyrroloisoquinoline alkaloid, isolamellarin, was synthesized based on the annulation of dihydroisoquinoline with aryl pyruvates under basic condition and Cu-mediated/MW-assisted C-O(carboxylic) lactonization.     

A Diepoxide Belonging to the Rare C1 Point Group

2,6- and 2,7-Dimethylanthracenes were reduced seriatim with lithium in liquid ammonia and lithium in methylamine to their 1,4,5,8,9,10-hexahydro derivatives. Two-fold epoxidation of these tetraenes provided the cis and trans diepoxides resulting from electrophilic attack at the inner double bonds. Trans diepoxide 1 has the very unusual characteristic of lacking a σ plane of symmetry but possessing an inversion center. As a consequence, the ¹H NMR spectrum of C₁-symmetric 1 is simplified relative to those of its isomers 5, 9, and 10.     

Low-pressure collisional narrowing in CO2

We report the observation of collisional narrowing of the Q branch of the Raman spectrum for the (000) → (100) transition in CO₂ at very low pressures. The minimum linewidth is reached at ≈250 Torr. An estimate for the difference in rotational constants of the (100) state and the ground state is obtained. The narrowing of the linewidth and the changes in line-shape are interpreted in terms of velocity changing collisions and rotationally inelastic collisions between the CO₂ molecules.     

Pectenotoxin-2 synthetic studies. 1. Alkoxide precoordination to [Rh(NBD)(DIPHOS-4)]BF(4) allows directed hydrogenation of a 2,3-dihydrofuran-3-ol without competing furan production

[reaction: see text] The alkoxide-directed hydrogenation shown is reported as a key step in a concise synthesis of a fully functionalized precursor to the C29-C40 F/G sector of pectenotoxin-2.     

The photoelectron spectra of tricyclo[3.3.0.02,6]Octene and tricyclo[3.3.0.02,6]Octane

The photoelectron spectra of tricyclo[3.3.0.0^2,6]octene (1) and tricyclo[3.3.0.0^2,6]octane (2) have been recorded. The first bands in these spectra are correlated with orbitals which are linear combinations of the Walsh orbitals and of the olefinic π-orbital. This assignment is based on a zero differential overlap molecular orbital model as well as on the results of extended Hückel calculations. The resonance integral <π|H|W > for 1 is found to be ?1.34 eV.     

A vinyl sulfone-mediated diels-alder approach to the fully regiocontrolled elaboration of 4,5-disubstituted 2- and 3-cyclohexenones

Reported here is a scheme which enables one to prepare independently 4,5-disubstituted 2- or 3-cyclohexenones where the nature of the pendant sidechains can be widely varied.