The carbocyclization of non-conjugated dienes mediated by organometallicsi sa ni mportant reaction for the synthesis of a variety of carbocyclic derivatives, but the directa nnulation of dienes with an inert CÀHbond of asubstrate has remained unexplored to date. We herein report as eries of novel rare-earth dialkyl complexes bearing ap hosphinoamide anion and demonstrate that the combination of am ono(phosphinoamido)-ligated scandium dialkyl complex with B(C 6 F 5 ) 3 resultsi na ne xcellent catalyst for the cis-selective cyclization of 1,5-dienes with the ortho-C(sp 2 )ÀHb ond of pyridines to afford an ew family of pyridyl-functionalized 1,3-disubstituted cyclopentane derivatives containing monocyclic,bicyclic, spirocyclic, and heterocyclic skeletons in moderatet oexcellent yields with high diastereoselectivities (cis/trans up to 99:1).The cyclization of non-conjugated dienes prompted by organometallics has emergeda sap owerful methodt oc onvert simple, readilya ccessible substrates into more complex cyclic skeletons that exist widely in natural products and bioactive molecules. [1][2][3] In principle, the cyclization of dienesw ith the CÀHb onds of organic compounds is the most straightforward and atom-efficient route for the construction of C-substituted carbocyclic molecules. However,t he CÀH-activation-mediated annulation of dienes hasn ot been reported previously,d espite extensive studies on diene cyclizationc ombined with various transformationss uch as silylation, boration, hydrogenation, hydrogermylation, and carbometalation. [1b,c, 4-8] This is probably owing to the lack of as uitable catalyst that shows high activity not only for the CÀHa ctivation of an organic compound but also for the cyclization of ad iene.Some of us recently showed that cationic half-sandwich rare-earth alkyls served as efficient catalysts for the CÀHa ddition of heteroatom-containing aromatic compounds such as pyridines,a nisoles,a nd N,N-dimethylanilines to aw ider ange of C=Cb onds such as those in 1-alkenes, styrenes,a nd allenes; [9, 10] these catalysts were also found to be efficient for the cyclopolymerizationo f1 ,5-and 1,6-dienes. [11] We therefore envisioned that ac atalytic protocol based on the integration of theset wo processes might be feasible for the direct cyclization of dienes with the CÀHb onds of arenes mediated by an appropriate rare-earth complex. In these studies, we became interested in the analogous rare-earth complexes bearing noncyclopentadienyl (Cp) ligands such as phosphinoamides. [12,13] The h 2 -N-P coordinationm ode of ap hosphinoamide ligand could partly resemble the h 5 -bonding fashion of aC pl igand, but the catalytic potential of ac ationic phosphinoamido-ligated rare-earth alkyl species has remained unexplored to date. Herein, we reportt he first mono(phosphinoamido)-ligated rare-earth dialkyl complexesa nd their application in catalytic pyridine CÀHa ddition/diene cyclization reactions. We found that ac ationic alkyl scandium species bearing mono(phosphinoamide) ligands generated from ne...
