| pubmed-article:15357589 | pubmed:abstractText | The double ring-closing metathesis reaction of N-alkynyl-N-(1,omega)-alkadienyl acrylamides 1 using first- or second-generation Grubbs' catalyst afforded, in a highly selectively manner, the fused bicyclic quinolizidine alkaloid derivatives and their analogues bearing a 1,3-diene moiety, which may further undergo a Diels-Alder reaction with a dienophile to afford N-containing polycyclic compounds. The excellent selectivity of fused/dumbbell-mode cyclization has been realized by the higher reactivity of the electron-rich C=C bond or carbon-carbon triple bond combined with the lower reactivity of the electron-deficient C=C bond toward metallocarbenes and the thermodynamically more stable nature of fused bicyclic compounds 3 vs dumbbell-type bicyclic compounds 4. | lld:pubmed |
