Synthesis of 4-[(E)-1-Alkenyl]-2-hydroxybutanolides and (Z)-4-Alkylidene-2-butenolides through Cycloadditions Using a Phosphorus-Functionalized Nitrile Oxide
Horner–Emmons Olefination of 4-Hydroxy-2-oxoalkylphosphonates and Related Compounds: Applications to the Syntheses of (±)-Gingerol, (±)-Yashabushiketol, and (±)-Dihydroyashabushiketol
作者:Otohiko Tsuge、Shuji Kanemasa、Norihiko Nakagawa、Hiroyuki Suga
DOI:10.1246/bcsj.60.4091
日期:1987.11
Horner–Emmons olefination of 4-hydroxy-2-oxoalkylphosphonates, readily available by hydrogenation of 5-substituted 3-phosphinylmethyl-2-isoxazolines, gives mainly E-isomers of 1-hydroxy-4-alken-3-ones bearing a variety of substituents at the 1-position. Use of the combination of triethylamine (or DBU)+lithium bromide as a weak base on the O-unprotected phosphonates is favored. Similar olefinations on the isoxazolines, 2-oxo-3-alkenylphosphonates, and 4-alkoxy-2-oxoalkylphosphonates have been also examined. Their synthetic applications to (±)-Gingerol, (±)-Yashabushiketol, and (±)-Dihydroyashabushiketol are described.
An Efficient Synthesis of 4-Oxo-2,5-hexadienoates via Δ<sup>2</sup>-Isoxazoline Intermediates
作者:Pier Giovanni Baraldi、Rita Bazzanini、Angelica Bigoni、Stefano Manfredini、Daniele Simoni、Giampiero Spalluto
DOI:10.1055/s-1993-26023
日期:——
An efficient method for the preparation of 4-oxo-2,5-hexadienoates starting from 3,5-disubstituted Î2-isoxazolines is described. The N-O bond cleavage of the isoxazoline ring, promoted by molybdenum hexacarbonyl, afforded the β-hydroxy ketone intermediates 9a-d which were smoothly dehydrated to the expected 4-oxo-2,5-hexadienoates 10a-d in about 40% yield starting from 6a,b.
Synthesis of 4-[(<i>E</i>)-1-Alkenyl]-2-hydroxybutanolides and (<i>Z</i>)-4-Alkylidene-2-butenolides through Cycloadditions Using a Phosphorus-Functionalized Nitrile Oxide
A sequence of cycloadditions of (diethoxyphosphinyl)acetonitrile oxide with α,β-unsaturated esters, the Raney Ni reduction of the resulting cycloadducts, the Horner–Emmons olefination, and the carbonyl reduction with sodium borohydride leads to 5-[(E)-1-alkenyl]-3-hydroxy-4,5-dihydro-2(3H)-furanones which can be converted into (Z)-5-alkylidene-2(5H)-furanones in two steps.