Cationic Platinum-Complex-Catalyzed Skeletal Reorganization of Enynes

研究了乙炔端有甲基的1,6-炔在2mol %的阳离子铂配合物存在下，在CHCl_3中室温反应20 h后的骨架重组。这个反应产生的环化产物在乙烯基的末端有一个甲基。该反应涉及双键和三键碳碳键的裂解，这被^<13>C-和^ 2h标记实验证实。GC-MS和NMR均未观察到有序重排产物。考察了各种催化剂在该反应中的作用。一系列阳离子铂（和钯在某些情况下）配合物与双齿二膦配体如dppe， dppp和dppb配合物表现出良好的催化活性，以约75%的收率提供罕见的重排产物。dppp和dppb优先得到Z异构体。与PPh_3单齿配体配合物的催化活性较弱。中性二氯铂配合物PtCl_2（dppp）和PtCl_2(PPh_3)_2和阳离子钯配合物[Pd(dppp)(PhCN)_2](BF_4)_2和[Pd(PPh_3)_2(PhCN)_2](BF_4)_2在相同的反应条件下都没有表现出催化活性。在四氢呋喃、丙酮、乙腈和硝基甲烷等溶剂中均未发生反应，CHCl_3和CH_2Cl_2是适宜的溶剂。根据这些实验结果，提出了全烯丙基和环丙基碳基阳离子重排的反应途径。

The skeletal reorganization of 1,6-enyne having a methyl group on the acetylene terminus was examined in CHCl_3 at room temperature for 20 h in the presence of 2 mol% of cationic platinum complexes. This reaction afforded the cyclized product having a methyl group on the terminal of the vinyl group. This reaction involves the cleavage of both the double and triple carbon-carbon bonds, which was confirmed by ^<13>C- and ^2H-labeling experiments. No ordinal rearranged product was observed by either GC-MS or NMR analysis. The effect of the various catalysts in this reaction has been examined. A series of cationic platinum (and palladium in certain cases) complexes coordinated with bidentate diphosphine ligands such as dppe, dppp, and dppb exhibited good catalytic activities, affording the unusual rearrangement product in approximately 75% yield. The Z isomer was obtained preferentially in the case of dppp and dppb. The complex coordinated with the monodentate ligand of PPh_3 exhibited only minor catalytic activity. Neither neutral dichloroplatinum complexes such as PtCl_2(dppp) and PtCl_2(PPh_3)_2 nor cationic palladium complexes such as [Pd(dppp)(PhCN)_2](BF_4)_2 and [Pd(PPh_3)_2(PhCN)_2](BF_4)_2 exhibited catalytic activity under the same reaction conditions. CHCl_3 and CH_2Cl_2 were suitable solvents for this cyclization, and no reaction occurred in other solvents such as THF, acetone, acetonitrile, and nitromethane. Reaction pathways involving the rearragement of homoallyl and cyclopropylcarbinyl cations were proposed based on these experimental results.