Hirao, Bulletin of the Chemical Society of Japan, 1926, vol. 1, p. 76,79
作者:Hirao
DOI:——
日期:——
Synthesis of Substituted Pyridines via Regiocontrolled [4 + 2] Cycloadditions of Oximinosulfonates
作者:Adam R. Renslo、Rick L. Danheiser
DOI:10.1021/jo981014e
日期:1998.10.1
Diels-Alder cycloadditions of oximinosulfonate 8 with a variety of 1,3-dienes proceed with regiochemistry opposite to that observed with conventional imino dienophiles, providing expeditious synthetic routes to substituted pyridines, tetrahydropyridines, and pyrrolines. The oximinosulfonate 8 is prepared in one convenient synthetic operation from Meldrum's acid and reacts with conjugated dienes at -78 degrees C in the presence of 2 equiv of dimethylaluminum chloride to afford [4 + 2] cycloadducts in good to excellent yield. Exposure of these cycloadducts to the action of NaOMe and N-chlorosuccinimide in methanol-THF at room temperature then produces substituted pyridines. The utility of this new two-step annulation protocol is demonstrated in total syntheses of the pyridine alkaloids fusaric acid and (S)-(+)-fusarinolic acid. Heating the [4 + 2] cycloadducts derived from 8 in a mixture of acetonitrile and pH 7 phosphate buffer induces an unusual Stieglitz-type rearrangement leading to the formation of interesting spirobicyclic pyrrolines.
The ternary semiconducting compound Cu2GeSe3 is of considerable interest, because it has a low melting point (MP approximate to 770 degrees C) which makes this materials a potential candidate for acousto-optical applications. In this work, measurements of the Hall coefficient R-H and the transverse magnetoresistance (Delta(Q/Q)) of p-type Cu2GeSe3 were realized. The measurements were carried out at temperatures of 100 to 250 K in magnetic fields from 0 to 1.6 T. This compound exhibits a metallic impurity conduction at temperatures above 150 K and present a thermally activated transport mechanism at low temperatures. In this semiconductor, magnetoresistance of both positive and negative signs was observed.