Highly substituted 4H-pyrans can be smoothly synthesized from readily available 2-(1-alkynyl)-2-alkene-1-ones by DBU- or n-Bu3P catalyzed hetero-[4+2] cycloaddition reactions, in which 2-(1-alkynyl)-2-alkene-1-ones act as both heterodiene and heterodinenophile.
在
DBU- 或 n-Bu3P 催化的杂-[4+2]环加成反应中,2-(1-炔基)-2-烯-1-酮既是杂二烯,又是杂二亲烯,可以从容易获得的 2-(1-炔基)-2-烯-1-酮顺利合成高取代的 4H-pyrans 。