Regie-Control of Formal [3 + 2] Cycloadditions of 5-Alkoxyoxazoles with Diethyl Oxomalonate
作者:Hiroyuki Suga、Xiaolan Shi、Toshikazu Ibata
DOI:10.1246/cl.1994.1673
日期:1994.9
Tin(IV) chloride-catalyzed formal [3 + 2] cycloadditions of 5-alkoxy-2-(p-methoxyphenyl)- or 2-phenyloxazoles with diethyloxomalonate gave 2-oxazoline-4,5,5-tricarboxylates in high regioselectivity. 4-Substituted 5-alkoxy-2-methyloxazoles showed a trend to shift the regioselectivity to offer more 3-oxazoline-2,5,5-tricarboxylates in terms of regioselectivity than 2-oxazolines.
Tin(IV) chloride-catalyzed formal [3 + 2] cycloaddition of 5-alkoxy-2-(p-methoxyphenyl)- or 2-phenyloxazoles with diethyl oxomalonate gave 4,5,5-tris(alkoxycarbonyl)-2-oxazolines in high regioselectivity. Under similar conditions, 4-substituted 5-alkoxy-2-methyloxazoles showed a trend to shift the regioselectivity in favor for 3-oxazolines rather than 2-oxazolines. Reaction of 5-alkoxy-4-ethoxycarbonyloxazoles with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone proceeded only under high pressure to give 2-oxazolines exclusively.
Do oxazoliks undergo Diels-Alder reactions with heterodienophiles?
作者:Alfred Hassner、Bilha Fischer
DOI:10.1016/s0040-4020(01)81032-2
日期:1989.1
5-Alkoxy and 2-alkoxyoxazoles were shown to react with NN, CN or CO dienophiles to form products that in most cases can be explained to result from a Diels-Alder addition, or by nucleophilic attack of the oxazole on the dienophile, followed by rearrangement. The products are triazolines, imidazolines or oxazolines respectively. Relative reactivitles were established and mechanistic pathways discussed