作者:Peter Wipf、Thomas H. Graham
DOI:10.1021/jo034813s
日期:2003.11.1
5-dihydroxy-1-alkynes, as well as, more decisively, on the type of O-protective group. Oxygen substitution at the propargylic carbon slows the rate of alkyne insertion and allows for dihydrofuran formation through exo-cyclization. In contrast, the use of bulky silyl ethers or carbon substituents leads to dihydropyrans through endo-cyclization. Substrates bearing leaving groups such as esters, phenols, or thiophenols
光活化的W(CO)(6)/ DABCO / THF系统已用于炔烃正式内环化成吡喃环。我们发现,闭环的区域选择性取决于3,5-二羟基-1-炔烃的相对构型,并且更决定性地取决于O-保护基团的类型。炔丙基碳上的氧取代减慢了炔烃的插入速度,并允许通过外环化形成二氢呋喃。相反,使用大体积的甲硅烷基醚或碳取代基会通过内环化作用生成二氢吡喃。在炔丙基位点带有离去基团如酯,酚或硫酚的底物被消除,因此代表了对环异构化方法的限制。炔丙基乙烯基醚将重新排列以生成二醛而不是缩醛。1,